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Essay On The Volcano – 10 Lines, Short & Long Essay For Kids

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Key Points To Remember When Writing An Essay On The Volcano For Lower Primary Classes

10 lines on the volcano for kids, a paragraph on the volcano for children, short essay on volcano in 200 words for kids, long essay on volcano for children, interesting facts about volcanoes for children, what will your child learn from this essay.

A volcano is a mountain formed through an opening on the Earth’s surface and pushes out lava and rock fragments through that. It is a conical mass that grows large and is found in different sizes. Volcanoes in Hawaiian islands are more than 4000 meters above sea level, and sometimes the total height of a volcano may exceed 9000 meters, depending on the region it is found. Here you will know and learn how to write an essay on a volcano for classes 1, 2 & 3 kids. We will cover writing tips for your essay on a volcano in English and some fun facts about volcanoes in general.

Volcanoes are formed as a result of natural phenomena on the Earth’s surface. There are several types of volcanoes, and each may emit multiple gases. Below are some key points to remember when writing an essay on a volcano:

  • Start with an introduction about how volcanoes are formed. How they impact the Earth, what they produce, and things to watch out for.
  • Discuss the different types of volcanoes and talk about the differences between them.
  • Cover the consequences when volcanoes erupt and the extent of the damage on Earth.
  • Write a conclusion paragraph for your essay and summarise it. 

When writing a few lines on a volcano, it’s crucial to state interesting facts that children will remember. Below are 10 lines on volcanoes for an essay for classes 1 & 2 kids.

  • Some volcanoes erupt in explosions, and then some release magma quietly.
  • Lava is hot and molten red in colour and cools down to become black in colour. 
  • Hot gases trapped inside the Earth are released when a volcano erupts.
  • A circle of volcanoes is referred to as the ‘Ring of Fire.’
  • Volcano formations are known as seismic activities.
  • Active volcanoes are spread all across the earth. 
  • Volcanoes can remain inactive for thousands of years and suddenly erupt.
  • Most volcanic eruptions occur underwater and result from plates diverging from the margins.
  • Volcanic hazards happen in the form of ashes, lava flows, ballistics, etc.
  • Volcanic regions have turned into tourist attractions such as the ones in Hawaii.

Volcanoes can be spotted at the meeting points of tectonic plates. Like this, there are tons of interesting facts your kids can learn about volcanoes. Here is a short paragraph on a volcano for children:

A volcano can be defined as an opening in a planet through which lava, gases, and molten rock come out. Earthquake activity around a volcano can give plenty of insight into when it will erupt. The liquid inside a volcano is called magma (lava), which can harden. The Roman word for the volcano is ‘vulcan,’ which means God of Fire. Earth is not the only planet in the solar system with volcanoes; there is one on Mars called the Olympus Mons. There are mainly three types of volcanoes: active, dormant, and extinct. Some eruptions are explosive, and some happen as slow-flowing lava.

Small changes occur in volcanoes, determining if the magma is rising or not flowing enough. One of the common ways to forecast eruptions is by analysing the summit and slopes of these formations. Below is a short essay for classes 1, 2, & 3:

As a student, I have always been curious about volcanoes, and I recently studied a lot about them. Do you know? Krakatoa is a volcano that made an enormous sound when it exploded. Maleo birds seek refuge in the soil found near volcanoes, and they also bury their eggs in these lands as it keeps the eggs warm. Lava salt is a popular condiment used for cooking and extracted from volcanic rocks. And it is famous for its health benefits and is considered superior to other forms of rock or sea salts. Changes in natural gas composition in volcanoes can predict how explosive an eruption can be. A volcano is labelled active if it constantly generates seismic activity and releases magma, and it is considered dormant if it has not exploded for a long time. Gas bubbles can form inside volcanoes and blow up to 1000 times their original size!

Volcanic eruptions can happen through small cracks on the Earth’s surface, fissures, and new landforms. Poisonous gases and debris get mixed with the lava released during these explosions. Here is a long essay for class 3 kids on volcanoes:

Lava can come in different forms, and this is what makes volcanoes unique. Volcanic eruptions can be dangerous and may lead to loss of life, damaging the environment. Lava ejected from a volcano can be fluid, viscous, and may take up different shapes. 

When pressure builds up below the Earth’s crust due to natural gases accumulating, that’s when a volcanic explosion happens. Lava and rocks are shot out from the surface to make room on the seafloor. Volcanic eruptions can lead to landslides, ash formations, and lava flows, called natural disasters. Active volcanoes frequently erupt, while the dormant ones are unpredictable. Thousands of years can pass until dormant volcanoes erupt, making their eruption unpredictable. Extinct volcanoes are those that have never erupted in history.

The Earth is not the only planet in the solar system with volcanoes. Many volcanoes exist on several other planets, such as Mars, Venus, etc. Venus is the one planet with the most volcanoes in our solar system. Extremely high temperatures and pressure cause rocks in the volcano to melt and become liquid. This is referred to as magma, and when magma reaches the Earth’s surface, it gets called lava. On Earth, seafloors and common mountains were born from volcanic eruptions in the past.

What Is A Volcano And How Is It Formed?

A volcano is an opening on the Earth’s crust from where molten lava, rocks, and natural gases come out. It is formed when tectonic plates shift or when the ocean plate sinks. Volcano shapes are formed when molten rock, ash, and lava are released from the Earth’s surface and solidify.

Types Of Volcanoes

Given below various types of volcanoes –

1. Shield Volcano

It has gentle sliding slopes and ejects basaltic lava. These are created by the low-viscosity lava eruption that can reach a great distance from a vent.

2. Composite Volcano (Strato)

A composite volcano can stand thousands of meters tall and feature mudflow and pyroclastic deposits.

3. Caldera Volcano

When a volcano explodes and collapses, a large depression is formed, which is called the Caldera.

4. Cinder Cone Volcano

It’s a steep conical hill formed from hardened lava, tephra, and ash deposits.

Causes Of Volcano Eruptions

Following are the most common causes of volcano eruptions:

1. Shifting Of Tectonic Plates

When tectonic plates slide below one another, water is trapped, and pressure builds up by squeezing the plates. This produces enough heat, and gases rise in the chambers, leading to an explosion from underwater to the surface.

2. Environmental Conditions

Sometimes drastic changes in natural environments can lead to volcanoes becoming active again.

3. Natural Phenomena

We all understand that the Earth’s mantle is very hot. So, the rock present in it melts due to high temperature. This thin lava travels to the crust as it can float easily. As the area’s density is compromised, the magma gets to the surface and explodes.

How Does Volcano Affect Human Life?

Active volcanoes threaten human life since they often erupt and affect the environment. It forces people to migrate far away as the amount of heat and poisonous gases it emits cannot be tolerated by humans.

Here are some interesting facts:

  • The lava is extremely hot!
  • The liquid inside a volcano is known as magma. The liquid outside is called it is lava.
  • The largest volcano in the solar system is found on Mars.
  • Mauna Loa in Hawaii is the largest volcano on Earth.
  • Volcanoes are found where tectonic plates meet and move.

Your child will learn a lot about how Earth works and why volcanoes are classified as natural disasters, what are their types and how they are formed.

Now that you know enough about volcanoes, you can start writing the essay. For more information on volcanoes, be sure to read and explore more.

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Essays About Volcanoes: Top 5 Examples and 10 Prompts

Do you need to write essays about volcanoes but don’t know where to start? Check out our top essay examples and prompts to help you write a high-quality essay.

Considered the planet’s geologic architects, volcanoes are responsible for more than 80% of the Earth’s surface . The mountains, craters, and fertile soil from these eruptions give way to the very foundation of life itself, making it possible for humans to survive and thrive.  

Aside from the numerous ocean floor volcanoes, there are 161 active volcanoes in the US . However, these beautiful and unique landforms can instantly turn into a nightmare, like Mt. Tambora in Indonesia, which killed 92,000 people in 1815 .

Various writings are critical to understanding these openings in the Earth’s crust, especially for students studying volcanoes. It can be tricky to write this topic and will require a lot of research to ensure all the information gathered is accurate. 

To help you, read on to see our top essay examples and writing prompts to help you begin writing.

Top 5 Essay Examples

1. short essay on volcanoes by prasad nanda , 2. types of volcanoes by reena a , 3. shield volcano, one of the volcano types by anonymous on gradesfixer.com, 4. benefits and problems caused by volcanoes by anonymous on newyorkessays.com, 5. volcanoes paper by vanessa strickland, 1. volcanoes and their classifications, 2. a dormant volcano’s eruption, 3. volcanic eruptions in the movies, 4. the supervolcano: what is it, 5. the word’s ring of fire, 6. what is a lahar, 7. why does a volcano erupt, 8. my experience with volcanic eruptions, 9. effects of volcanic eruptions, 10. what to do during volcanic disasters.

“The name, “volcano” originates from the name Vulcan, a god of fire in Roman mythology.”

Nanda briefly defines volcanoes, stating they help release hot pressure that builds up deep within the planet. Then, he discusses each volcano classification, including lava and magma’s roles during a volcanic eruption. Besides interesting facts about volcanoes (like the Ojos del Salado as the world’s tallest volcano), Nanda talks about volcanic eruptions’ havoc. However, he also lays down their benefits, such as cooled magma turning to rich soil for crop cultivation.

“The size, style, and frequency of eruptions can differ greatly but all these elements are correlated to the shape of a volcano.”

In this essay, Reena identifies the three main types of volcanoes and compares them by shape, eruption style, and magma type and temperature. A shield volcano is a broad, flat domelike volcano with basaltic magma and gentle eruptions. The strato or composite volcano is the most violent because its explosive eruption results in a lava flow, pyroclastic flows, and lahar. Reena shares that a caldera volcano is rare and has sticky and cool lava, but it’s the most dangerous type. To make it easier for the readers to understand her essay, she adds figures describing the process of volcanic eruptions.

“All in all, shield volcanoes are the nicest of the three but don’t be fooled, it can still do damage.”

As the essay’s title suggests, the author focuses on the most prominent type of volcano with shallow slopes – the shield volcano. Countries like Iceland, New Zealand, and the US have this type of volcano, but it’s usually in the oceans, like the Mauna Loa in the Hawaiian Islands. Also, apart from its shape and magma type, a shield volcano has regular but calmer eruptions until water enters its vents.

“Volcanic eruptions bring both positive and negative impacts to man.”

The essay delves into the different conditions of volcanic eruptions, including their effects on a country and its people. Besides destroying crops, animals, and lives, they damage the economy and environment. However, these misfortunes also leave behind treasures, such as fertile soil from ash, minerals like copper, gold, and silver from magma, and clean and unlimited geothermal energy. After these incidents, a place’s historic eruptions also boost its tourism.

“Beautiful and powerful, awe-inspiring and deadly, they are spectacular reminders of the dynamic forces that shape our planet.”

Strickland’s essay centers on volcanic formations, types, and studies, specifically Krakatoa’s eruption in 1883. She explains that when two plates hit each other, the Earth melts rocks into magma and gases, forming a volcano. Strickland also mentions the pros and cons of living near a volcanic island. For example, even though a tsunami is possible, these islands are rich in marine life, giving fishermen a good living.

Are you looking for more topics like this? Check out our round-up of essay topics about nature .

10 Writing Prompts For Essays About Volcanoes

Do you need more inspiration for your essay? See our best essay prompts about volcanoes below:

Identify and discuss the three classifications of volcanoes according to how often they erupt: active, dormant or inactive, and extinct. Find the similarities and differences of each variety and give examples. At the end of your essay, tell your readers which volcano is the most dangerous and why.

Volcanoes that have not erupted for a very long time are considered inactive or dormant, but they can erupt anytime in the future. For this essay, look for an inactive volcano that suddenly woke up after years of sleeping. Then, find the cause of its sudden eruption and add the extent of its damage. To make your piece more interesting, include an interview with people living near dormant volcanoes and share their thoughts on the possibility of them exploding anytime.

Essays About Volcanoes: Volcanic eruptions in the movies

Choose an on-screen depiction of how volcanoes work, like the documentary “ Krakatoa: Volcano of Destruction .” Next, briefly summarize the movie, then comment on how realistic the film’s effects, scenes, and dialogues are. Finally, conclude your essay by debating the characters’ decisions to save themselves.

The Volcanic Explosivity Index (VEI) criteria interpret danger based on intensity and magnitude. Explain how this scale recognizes a supervolcano. Talk about the world’s supervolcanoes, which are active, dormant, and extinct. Add the latest report on a supervolcano’s eruption and its destruction.

Identify the 15 countries in the Circum-Pacific belt and explore each territory’s risks to being a part of The Ring of Fire. Explain why it’s called The Ring of Fire and write its importance. You can also discuss the most dangerous volcano within the ring.

If talking about volcanoes as a whole seems too generic, focus on one aspect of it. Lahar is a mixture of water, pyroclastic materials, and rocky debris that rapidly flows down from the slopes of a volcano. First, briefly define a lahar in your essay and focus on how it forms. Then, consider its dangers to living things. You should also add lahar warning signs and the best way to escape it.

Use this prompt to learn and write the entire process of a volcanic eruption. Find out the equipment or operations professionals use to detect magma’s movement inside a volcano to signal that it’s about to blow up. Make your essay informative, and use data from reliable sources and documentaries to ensure you only present correct details.

If you don’t have any personal experience with volcanic eruptions, you can interview someone who does. To ensure you can collect all the critical points you need, create a questionnaire beforehand. Take care to ask about their feelings and thoughts on the situation.

Write about the common effects of volcanic eruptions at the beginning of your essay. Next, focus on discussing its psychological effects on the victims, such as those who have lost loved ones, livelihoods, and properties.

Help your readers prepare for disasters in an informative essay. List what should be done before, during, and after a volcanic eruption. Include relevant tips such as being observant to know where possible emergency shelters are. You can also add any assistance offered by the government to support the victims.Here’s a great tip: Proper grammar is critical for your essays. Grammarly is one of our top grammar checkers. Find out why in this  Grammarly review .

essay on volcano in short

Maria Caballero is a freelance writer who has been writing since high school. She believes that to be a writer doesn't only refer to excellent syntax and semantics but also knowing how to weave words together to communicate to any reader effectively.

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A volcano is an opening in a planet or moon’s crust through which molten rock and gases trapped under the surface erupt, often forming a hill or mountain.

Volcanic eruption

Volcanic eruptions can create colorful and dramatic displays, such as this eruption of this volcano in the Virunga Moutains of the Democratic Republic of the Congo.

Photograph by Chris Johns

Volcanic eruptions can create colorful and dramatic displays, such as this eruption of this volcano in the Virunga Moutains of the Democratic Republic of the Congo.

A volcano is an opening in a planet or moon’s crust through which molten rock, hot gases, and other materials erupt . Volcanoes often form a hill or mountain as layers of rock and ash build up from repeated eruptions .

Volcanoes are classified as active, dormant, or extinct. Active volcanoes have a recent history of eruptions ; they are likely to erupt again. Dormant volcanoes have not erupted for a very long time but may erupt at a future time. Extinct volcanoes are not expected to erupt in the future.

Inside an active volcano is a chamber in which molten rock, called magma , collects. Pressure builds up inside the magma chamber, causing the magma to move through channels in the rock and escape onto the planet’s surface. Once it flows onto the surface the magma is known as lava .

Some volcanic eruptions are explosive, while others occur as a slow lava flow. Eruptions can occur through a main opening at the top of the volcano or through vents that form on the sides. The rate and intensity of eruptions, as well as the composition of the magma, determine the shape of the volcano.

Volcanoes are found on both land and the ocean floor. When volcanoes erupt on the ocean floor, they often create underwater mountains and mountain ranges as the released lava cools and hardens. Volcanoes on the ocean floor become islands when the mountains become so large they rise above the surface of the ocean.

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Essay on volcanoes | geology.

essay on volcano in short


After reading this article you will learn about:- 1. Introduction to Volcanoes 2. Volcano Formation 3. Volcanic Landforms 4. Major Gases Emitted by Volcanoes 5. Lightning and Whirlwinds 6. Features Produced by the Escape of Gases from Volcanic Lavas 7. Volcanic Products 8. Source of the Explosive Energy 9. Classification of Pyroclastics 10. Lahars-Mudflows on Active and Inactive Cones and Other Details.

Essay Contents:

  • Essay on the Volcanoes and Atmospheric Pollution

Essay # 1. Introduction to Volcanoes :

A volcano is a cone shaped hill or mountain which is built-up around an opening in the earth’s surface through which hot gases, rock fragments and lavas are ejected.

Due to the accumulation of the solid fragments around the conduit a conical mass is built which increases in size to become a large volcanic mountain. The conical mass so built-up is called a volcano. However the term volcano is taken to include not only the central vent in the earth but also the mountain or hill built around it.

Volcanoes are in varying sizes, varying from small conical hills to loftiest mountains on the earth’s surface. The volcanoes of the Hawaiian Islands are nearly 4300 metres above sea level since they are built over the floor of the Pacific ocean which at the site is 4300 to 5500 metres deep, the total height of the volcano may be about 9000 m or more.

The very high peaks in the Andes, in the Cascade Range of the Western United States, Mt. Baker, Mt. Adams, Mt. Hood etc. are all volcanoes which have now become extinct. Over 8000 independent eruptions have been identified from earth’s volcanoes. There are many inaccessible regions and ocean floors where volcanoes have occurred undocumented or unnoticed.

The eruption of a volcano is generally preceded by earthquakes and by loud rumblings like thunder which may continue on a very high scale during the eruption. The loud rumblings are due to explosive movement of gases and molten rock which are held under very high pressure. Before eruption of a volcano fissures are likely to be opened, nearby lakes likely to be drained and hot springs may appear at places.

The eruptive activity of volcanoes is mostly named after the well-known volcanoes, which are known for particular type of behaviour, like Strambolian, Vulcanian, Vesuvian, Hawaiian types of eruption. Volcanoes may erupt in one distinct way or may erupt in many ways, but, the reality is, these eruptions provide a magical view inside the earth’s molten interior.

The nature of a volcanic eruption is determined largely by the type of materials ejected from the vent of the volcano. Volcanic eruptions may be effusive (fluid lavas) or dangerous and explosive with blasts of rock, gas, ash and other pyroclasts.

Some volcanoes erupt for just a few minutes while some volcanoes spew their products for a decade or more. Between these two main types viz. effusive and explosive eruptions, there are many subdivisions like, eruption of gases mixed with gritty pulverised rock forming tall dark ash clouds seen for many kilometres, flank fissure eruptions with lava oozing from long horizontal cracks on the side of a volcano.

There is also the ground hugging lethally hot avalanches of volcanic debris called pyroclastic flows. When magma rises, it may encounter groundwater causing enormous phreatic, i.e., steam eruptions. Eruptions may also release suffocating gases into the atmosphere. Eruptions may produce tsunamis and floods and may trigger earthquakes. They may unleash ravaging rockslides and mudflows.

Volcanoes which have had no eruptions during historic times, but may still show fairly fresh signs of activity and have been active in geologically recent times are said to be dormant. There are also volcanoes which were formerly active but are of declining activity a few of which may be emitting only steam and other gases.

Geysers are hot springs from which water is expelled vigorously at intervals and are characteristics of regions of declining volcanic activity. Geysers are situated in Iceland, the Yellowstone park in USA and in New Zealand.

In contrast to the explosive type of volcanoes, there exist eruptions of great lava flows quietly pouring out of fissures developed on the earth’s surface. These eruptions are not accompanied by explosive outbursts. These are fissure eruptions.

Ex: Deccan Trap formations in India. The lavas in these cases are mostly readily mobile and flow over low slopes. The individual flows are seldom over a few meters in thickness; the average thickness may be less than 15 meters. If the fissure eruptions have taken place in valleys however, the thickness may be much greater.

A noteworthy type of volcano is part of the world encircling mid-ocean ridge (MOR) visible in Iceland. The MOR is really a single, extremely long, active, linear volcano, connecting all spreading plate boundaries through all oceans. Along its length small, separate volcanoes occur. The MOR exudes low-silica, highly fluid basalt producing the entire ocean floor and constituting the largest single structure on the face of the earth.

Essay # 2. Location of Volcanoes:

Volcanoes are widely distributed over the earth, but they are more abundant in certain belts. One such belt encircles the Pacific ocean and includes many of the islands in it. Other volcanic areas are the island of West Indies, those of the West coast of Africa, the Mediterranean region and Iceland.

Most volcanoes occur around or near the margins of the continents and so these areas re regarded as weak zones of the earth’s crust where lavas can readily work their way upward. There are over 400 active volcanoes and many more inactive ones. Numerous submarine volcanoes also exist.

Since it is not possible to examine the magma reservoir which fees a volcano our information must be obtained by studying the material ejected by the volcano. This material consists of three kinds of products, viz. liquid lava, fragmented pyroclasts and gases. There may exist a special problem in studying the gases, both in collecting them under hazardous conditions or impossible conditions.

It may also be difficult to ascertain that the gases collected are true volcanic gases and are not contaminated with atmospheric gases. Investigation of the composition of extruded rock leads to a general, although not very detailed, correlation between composition and intensity of volcanic eruption.

In general, the quite eruptions are characteristic of those volcanoes which emit basic or basaltic lavas, whereas the violent eruptions are characteristic of volcanoes emitting more silicic rocks.

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Essay # 3 . formation of volcanoes :.

The term volcano is used to mean both the opening in the earth’s crust, i.e. the vent through which the eruption of magma occurs as well as the hill built- up by the erupted material. Volcanoes occur where the cracks in the earth’s crust lead to the magma chamber.

The liquid magma which is lighter than the surrounding rocks is under high pressure is pushed up towards the surface through these cracks. In this process the gases dissolved in the magma which expand are released providing an upward push to the magma.

Section of a Volano

As the magma gets closer to the surface, due to the reducing confining pressure to overcome, the magma and the gases flow faster. The magma, depending on its viscosity may quietly pour to the surface in the form of a flood of molten rock or it may explosively spurt out the molten rock to considerable heights as showers on the surrounding region with solid rock fragments and globs of molten rock. The liquid magma discharged to the surface is called lava.

Erupting Volcano

Essay # 4 . Volcanic Landforms :

Many surface features of volcanic origin are created. These features range from towering peaks and huge lava sheets to small and low craters. The features created by a volcano vary depending on the type of eruption, the material erupted and the effects of erosion.

Four types of volcanic landforms are formed:

i. Ash and Cinder Cones or Explosion Cones:

These appear where explosive eruptions take place. When very hot solid fragments from a central crater (or a subsidiary crater) are ejected. A concave cone of height not exceeding 300 m is formed.

ii. Lava Cones:

These are formed from slowly upwelling lava.

These are of two types:

(a) Steep Sided Volcanoes:

These are formed from sticky acid lava which gets hardened quickly. The highly viscous lava which is squeezed out makes spines like tower.

(b) Shield Volcanoes:

These show gently sloping dome features. These are formed from runny lava which flows long distances, before getting hardened.

iii. Composite Cones or Strato-Volcanoes or Strato Cones:

These volcanoes have concave cone shaped sides of alternating ash and lava layers. These are common in most very high volcanoes. In some cases solid lava may plug the main pipe to the crater. Then pent up gases may blast the top off.

When the magma chamber empties, the summit of the volcano collapses. As a consequence, the feature produced is a vast shallow cavity called a Caldera. Strato volcanoes are the accumulated products of many volcanoes. Chemically most of these products are andesite. Some are dacite and a few are basalt and rhyolite. Due to this chemical mix and characteristic interlayering of lava flows, this volcano is called strato volcano.

iv. Shield Volcanoes:

When a volcano vent produces many successive basaltic lava flows stacked one on top of another in eruptive order, the resulting landform is called a shield volcano. A cinder cone and its associated lava flow can be thought of as the initial building blocks of a shield volcano.

A cinder cone is monogenetic because it forms from a single short-lived eruption (of a few years to a decade or two in duration). In contrast, a shield volcano that is an accumulation of the products of many eruptions over a period of say thousands to hundreds of thousands of years is polygenic.

On land these volcanoes have low angle cones. When they form under water they start with a steeper shape because the lava freezes much faster and does not travel far. The shape fattens to the shield form as the cone builds above the sea level.

v. Plateau Basalts or Lava Plains:

These form the bulk of many volcanic fields. These are features which occur where successive flows of basic lava leaks through fissures, over land surface and then cools and hardens forming a blanket-like feature.

The surface appearance of a flow provides information on the composition and temperature of the magma before it solidified. Very hot low viscosity basalt flows far and fast and produces smooth ropy surfaces. Cooler and less-fluid basalt flows form irregular, jagged surfaces littered with blocks.

The lava flows have blanketed to about 2000 m thickness covering 6,50,000 sq.km. in the Indian Deccan Plateau. Such lava flows have also created the U.S. Columbia River Plateau, the Abyssinian Plateau, the Panama Plateau of South America and the Antrim Plateau of Northern Ireland.

Magmas like dacite and rhyolite that have high silica contents are cooler and more viscous than basalt and hence they do not flow far resulting in the features, lobes, pancakes and domes. Domes often plug up the vent from which they issued, sometimes creating catastrophic explosions and may create a crater.

Eroded volcanoes have their importance. They give us a glimpse of the interior plumbing along which the magma rose to the surface. At the end of an eruption, magma solidifies in the conduits along which it had been rising. The rock so formed is more resistant than the shattered rock forming the walls and hence these lava filled conduits are often left behind when the rest of the volcano has been eroded away.

The filling of the central vertical vent is somewhat circular in section and forms a spire called a neck. The filling of cracks along which lava rose forms nearly vertical tabular bodies called dikes. Sometimes magma works its way along cracks that are nearly horizontal, often along bedding planes of sedimentary rocks. This results in the formation of table-like bodies called sills.

Volcanic Landforms

Essay # 5 . Major Gases Emitted by Volcanoes :

Volcanic gases present within the magma are released as they reach the earth’s surface, escaping at the major volcanic opening or from fissures and vents along the side of the volcano. The most prevalent gases emitted are steam, carbon dioxide and hydrogen sulphide. Carbon dioxide is an invisible, odourless poisonous gas. The table below shows the gases emitted from volcanoes.

Gases Emitted from Volcanoes

Essay # 6 . Lightning and Whirlwinds :

Lightning flashes accompany most volcanic eruptions, especially those involving dust. The cause of this lightning is believed to be either contact of sea water with magma or generation of static electricity by friction between colliding particles carried in the erupting gases. Lightning is characteristic of vulcanian eruptions and is common during glowing avalanches.

Whirlwinds are seen during many volcanic eruptions. They are seen above hot lavas. Sometimes they form inverted cones extending a little below the eruption cloud. Energy for the whirlwinds might be from the hot gases and lava, high velocity gas jets in the eruption, heat released into the atmosphere during falls of hot tephra or where lava flows into the sea creating steam.

Essay # 7 . Features Produced by the Escape of Gases from Volcanic Lavas :

The gases of volcanic lavas produce several interesting features while they escape. They expand in the lava of the flow and thus cause the formation of Scoriaceous and Pumiceous rocks. By their explosion, they blow the hardened lava above them in the conduit, into bits and thus produce pyroclastic material.

They form clouds above volcanoes, the rain from which assists in the production of mud flows. When the volcano becomes inactive, they escape aiding in the formation of jumaroles, geysers and hot springs. Scoriaceous rocks are extremely porous. They are formed by the expansion of the steam and other gases beneath the hardened crust of a lava. The final escape of the gases from the hardening lava leaves large rounded holes in the rock.

Pumice is a rock also formed by the expansion and escape of gases. In pumice, many of the holes are in the form of long, minute, closed tubes which make the rock so light that it will float on water.

These tubes are formed by the expansive force of large amounts of gases in an extremely viscous lava that cools very rapidly, forming a glassy rock. Pumice is the rock that is usually formed from the lava ejected from explosive volcanoes. It can be blown to kilometres by explosions.

Essay # 8 . Volcanic Products :

Volcanoes give out products in all the states of matter – gases, liquids and solids.

Steam, hydrogen, sulphur and carbon dioxide are discharged as gases by a volcano. The steam let out by a volcano condenses in the air forming clouds which shed heavy rains. Various gases interact and intensify the heat of the erupting lavas. Explosive eruptions cause burning clouds of gas with scraps of glowing lava called nuees ardentes.

The main volcanic product is liquid lava. Sticky acid lava on cooling, solidifies and hardens before flowing long distances. Such lava can also block a vent resulting in pressure build-up which was relieved by an explosion. Basic fluid lava of lesser viscosity flows to great distances before hardening.

Some lava forms are produced by varying conditions as follows. Clinkery block shaped features are produced when gas spurted from sluggish molten rock capped by cooling crust. These are called Aa.

Pahoehoe is a feature which has a wrinkled skin appearance caused by molten lava flowing below it.

Pillow lava is a feature resembling pillows. This feature piles up when fast cooling lava erupts under water.

Products in explosive outbursts are called Pyroclasts. These consist of either fresh material or ejected scraps of old hard lava and other rock. Volcanic bombs include pancake-flat scoria shaped on impacting the ground and spindle bombs which are twisted at ends as they whizzle through the air. Acid lava full of gas formed cavities produces a light volcanic rock.

Pumice which is so light it can float on water. The product Ignimbrite shows welded glassy fragments. Lapilli are hurled out cinder fragments. Vast clouds of dust or very tiny lava particles are called volcanic ash. Volcanic ash mixed with heavy rain creates mudflows.

Sometimes mudflows can bury large areas of land. Powerful explosions can smoother land for many kilometres around with ash and can hurl huge amount of dust into the higher atmosphere. Violent explosions destroy farms and towns, but volcanic ash provides rich soil for crops.

i. Hot springs:

The underground hot rocks heat the spring waters creating hot springs. The hot springs shed minerals dissolved in them resulting in crusts of calcium carbonate and quartz (geyserite).

ii. Smoker:

This is a submarine hot spring at an oceanic spreading ridge. This submarine spring emits sulphides and builds smoky clouds.

iii. Geyser:

Periodically steam and hot water are forced up from a vent by super-heated water in pipe like passage deep down. Famous geysers are present in Iceland and Yellowstone National Park.

iv. Mud volcano:

This is a low mud cone deposited by mud-rich water gushing out of a vent.

v. Solfatara:

This is a volcanic vent which emits steam and sulphurous gas.

vi. Fumarole:

This is a vent which emits steam jets as at Mt. Etna, Sicily and Valley of Ten Thousand smokes in Alaska.

vii. Mofette:

This is a small vent which emits gases including carbon dioxide. These occur in France, Italy and Java.

Various terms used while describing volcanic features are given below:

i. Magma Chamber:

Magma is created below the surface of the earth (at depth of about 60 km) and is held in the magma chamber until sufficient pressure is built-up to push the magma towards the surface.

This is a pipe like passage through which the magma is pushed up from the magma chamber.

This is the outlet end of the pipe. Magma exits out of the vent. If a vent erupts only gases, it is called fumarole.

iv. Crater:

Generally the vent opens out to a depression called crater at the top of the volcano. This is caused due to the collapse of the surface materials.

v. Caldera:

This is a very big crater formed when the top of an entire volcanic hill collapses inward.

When the erupted materials cover the vent, a volcanic dome is created covering the vent. Later as the pressure of gas and magma rises, another eruption occurs shattering the dome.

A mountain-like structure created over thousands of years as the volcanic lava, ash, rock fragments are poured out onto the surface. This feature is called volcanic cone.

viii. Pyroclastic Flow :

A pyroclastic flow (also known as nuee ardentes (French word) is a ground hugging, turbulent avalanche of hot ash. pumice, rock fragments, crystals, glass shards and volcanic gas. These flows can rush down the steep slopes of a volcano at 80 to 160 km/li, burning everything in their path.

Temperatures of these flows can reach over 500°C. A deposit of this mixture is also often referred to as pyroclastic flow. An even more energetic and dilute mixture of searing volcanic gases and rock-fragments is called a pyroclastic surge which can easily ride up and over ridges.

ix. Seamounts :

A spectacular underwater volcanic feature is a huge localized volcano called a seamount. These isolated underwater volcanic mountains rise from 900 m to 3000 m above the ocean floor, but typically are not high enough to poke above the water surface.

Seamounts are present in all the oceans of the world, with the Pacific ocean having the highest concentration. More than 2000 seamounts have been identified in this ocean. The Gulf of Alaska also has many seamounts. The Axial Seamount is an active volcano off the north coast of Oregon (currently rises about 1400 m above the ocean floor, but its peak is still about 1200 m below the water surface.

Essay # 9 . Source of the Explosive Energy :

The energy for the explosive violence comes from the expansion of the volatile constituents present in the magma, the gas content of which determines the degree of commination of the materials and the explosive violence of the eruption.

This energy is expanded in two ways, firstly in the expulsion of the materials into the atmosphere and secondly, due to expansion within the magma leading to the development of vesicles. The most important gas is steam, which may form between 60 to 90 per cent of the total gas content in a lava. Carbon dioxide, nitrogen and sulphur dioxide occur commonly and hydrogen, carbon monoxide, sulphur and chlorine are also present.

Essay # 10 . Classification of Pyroclastics :

Pyroclastics refer to fragmental material erupted by a volcano. The larger fragments consisting of pieces of crystal layers beneath the volcano or of older lavas broken from the walls of the conduit or from the surface of the crater are called blocks.

Volcanic bombs are masses of new lava blown from the crater and solidified during flight, becoming round or spindle shaped as they are hurled through the air. They may range in size from small pellets up to huge masses weighing many kilonewtons.

Sometimes they are still plastic when they strike the surface and are flattened or distorted as they roll down the side of the cone. Another type called bread crust bomb resembles a loaf of bread with large gaping cracks in the crust.

This cracking of the crust results from the continued expansion of the internal gases. Many fragments of lava and scoria solidified in flight drop back into the crater and are intermixed with the fluid lava and are again erupted.

In contrast to bombs, smaller broken fragments are lapilli (from Italian meaning, little stones) about the size of walnuts; then in decreasing size, cinders, ash and dust. The cinders and ash are pulverized lava, broken up by the force of rapidly expanding gases in them or by the grinding together of the fragments in the crater, as they are repeatedly blown out and dropped back into the crater after each explosion.

Pumice is a type of pyroclastic produced by acidic lavas if the gas content is so great as to cause the magma to froth as it rises in the chimney of the volcano. When the expansion occurs the rock from the froth is expelled as pumice. Pumice is of size ranging from the size of a marble to 30 cm or more in diameter. Pumice will float in water due to many air spaces formed by the expanding gases.

Lava fountains in which steam jets blow the lava into the air produce a material known as Pele’s hair which is identical with rock wool which is manufactured by blowing a jet of steam into a stream of molten rock (Rock wool is used for many types of insulation).

Coarse angular fragments become cemented to form a rock called volcanic breccia. The finer material like cinders and ash forms thick deposits which get consolidated through the percolation of ground water and is called tuff. Tuff is a building stone used in the volcanic regions. It is soft and easily quarried and can be shaped and has enough strength to be set into walls with mortar.

i. Agglomerate:

The debris in and around the vent contains the largest ejected masses of lava bombs which are embedded in dust and ash. A deposit of this kind is known as agglomerate. The layers of ash and dust which are formed for some distance around the volcano and which builds its cone, become hardened into rocks which are called tuffs.

Ash includes all materials with size less than 4 mm. It is pulverized lava, in which the fragments are often sharply angular and formed of volcanic glass; these angular and often curved fragments are called shards.

Since the gas content of ash on expulsion is high it has considerable mobility on reaching the surface; it is also hot and plastic, the result of these conditions being that the fragments often become welded together. The finest of ash is so light that wind can transport it for great distances.

The table below sets out a general classification of pyroclastic rocks based on the particle size of the fragments forming the rocks.

essay on volcano in short

The chart in Fig. 15.3 summarizes the names of the common magmas and their associated ranges in silica. A very important property of magma that determines the eruption style and the eventual shape of the volcano it builds, is its resistance to flow, namely its viscosity.

Magma viscosity increases as its silica content increases. Eruptions of highly viscous magmas are violent. The highly viscous rhyolite magma piles up its ticky masses right over its eruptive vent to farm tall steep sided volcanoes.

On the contrary the basaltic magma flows great distances from its eruptive vent to from low, broad volcanic features. Magma in the intermediate viscosity spectrum say the andesite magma tends to form volcanoes of profile shapes between these two extremes.

An additional important ingredient of magma is water. Magmas also contain carbon dioxide and various sulphur-containing gases in solution. These substances are considered volatile since they tend to occur as gases at temperatures and pressures at the surface of the earth.

As basaltic magma changes composition toward rhyolite the volatiles become concentrated in the silica-rich magma. Presence of these volatiles (mainly water) in high concentration produces highly explosive volcanoes. It should be noted that these volatiles are held in magma by confining pressure. Within the earth, the confining pressure is provided by the load of the overlying rocks.

As the magma rises from the mantle to depths about 1.5 km or somewhat less, the rock load is reduced to that extent that the volatiles (mainly water) start to boil. Bubbles rising through highly viscous rhyolitic magma have such difficulty to escape their way, that many carry blobs of magma and fine bits of rock with them and they finally break free and jet violently upward resulting in a violent buoyant eruption column that can rise to kilometres above the earth.

The fine volcanic debris in such a powerful eruption gets dispersed within the upper atmosphere, hide the sunlight affecting the weather. The greater the original gas concentration in a magma and the greater the volume rate of magma leaving the vent, the taller is the eruption column produced.

The gases escaping from magma during eruption mix with the atmosphere and become part of the air humans, animals and plants breath and assimilate. However as magma cools and solidifies to rock during eruption, some of the gas remains trapped in bubbles creating vesicles. Generally all volcanic rocks contain some gas bubbles. A variety of vesicular rhyolite is pumice. Pumice is vesicular to such an extent, it floats in water.

Essay # 15. Classification of Volcanic Activity:

A classification of volcanic activity based on the type of product is shown in Fig. 15.4. The basic subdivision is based on the proportions of the gas, liquid and solid components, which can be represented on a triangular diagram. The four basic triangles represent the domain of four basic kinds of volcanic activity.

Classification of Eruptions

Essay # 16. Cone Topped and Flat Topped Volcanoes:

Generally rhyolite volcanoes are flat-topped because rhyolite magma which is extremely viscous, oozes out of the ground, piles up around the vent and then oozes away a bit to form a pancake shape. In contrast basalt volcanoes generally feed lava flows that flow far from the vent, building a cone.

Basaltic tephra (large particles of different size) is a spongy-looking black, rough material of pebble or cobble. Commercially this tephra is known as cinder and is used for gardening and rail-road beds. In some situations basaltic volcanoes develop flat top profile.

Flat topped volcanoes of basalt can form when there is an eruption under a glacier. Instead of getting ejected as tephra to form a cone, it forms a cauldron of lava surrounded by ice and water and eventually solidifying. When the ice melts, a steep-sided, table-shaped mountain known as a tuya remains. Volcanoes of this type are common in Iceland and British Columbia, where volcanoes have repeatedly erupted under glaciers.

Surprisingly, the Pacific ocean is a home to many flat-topped undersea basaltic mountains. These are called seamounts. How these seamounts were formed was a mystery for a long time. Surveying and dredging operations revealed that most seamounts were formerly conical volcanoes projecting above the water.

Geologists found that the conical volcanoes got lowered due to subsidence and the tops of the volcanoes came near the sea water level and the powerful waves mowed them flat. Continued subsidence caused them to drop below the water surface.

Essay # 17. Types of Volcanoes :

There are many types of volcanoes depending on the composition of magma especially on the relative proportion of water and silica contents. If the magma contains little of either of these, it is more liquid and it flows freely forming a shallow rounded hill.

Large water content with little silica permits the vapour to rapidly rise through the molten rock, throwing fountains of fire high into the air. More silica and less water in the magma make the magma more viscous. Such magma flows slowly and builds-up a high dome.

High content of both water and silica create another condition. In such a case the dense silica prevents the water from vaporizing until it is close to the surface and results in a highly explosive way. Such an eruption is called a Vulcan eruption.

Other types of eruption are named after people or regions associated with them. Vesuvian eruption named after Vesuvius is a highly explosive type occurring after a long period of dormancy. This type ejects a huge column of ash and rock to great heights upto 50 km.

A peleean eruption named after the eruption of Mt. Pelee in Martin que in 1902 is a highly violent eruption ejecting a hot cloud of ash mixed with considerable quantity of gas which flows down the sides of the volcano like a liquid. The cloud is termed nuee ardente meaning glowing cloud. Pyroclastic or ash flow refers to a flow of ash, solid rock pieces and gas. Hawaiian eruptions eject fire fountains.

Essay # 18. Violence of Volcanic Eruptions :

Volcanic activity may be classified by its violence, which in turn is generally related to rock type, the course of eruptive activity and the resulting landforms. We may in general distinguish between lava eruptions associated with basic and intermediate magmas and pumice eruptions associated with acid magmas.

The percentage of the fragmentary material in the total volcanic material produced can be used as a measure of explosiveness and if calculated for a volcanic region can be adopted as an Explosion Index (E), useful for comparing one volcanic region with others. Explosion Index for selected volcanic regions by Rittmann (1962) are shown in the table below.

Explosion Index for Selected Volcanic Regions

Newhall and Self (1982) proposed a Volcanic Explosivity Index (VEI) which helps to summarize many aspects of eruption and is shown in the table below.

Volcanic Explosivity Index

Essay # 19. Famous Volcanoes around the World :

Many volcanoes are present around the world. Some of the largest and well known volcanoes are listed in the table below.

Famous Volcanoes Around the World

Essay # 20. Volcanic Hazards :

Volcanic eruptions have caused destruction to life and property. In most cases volcanic hazards cannot be controlled, but their impacts can be mitigated by effective prediction methods.

Flows of lava, pyroclastic activity, emissions of gas and volcanic seismicity are major hazards. These are accompanied with movement of magma and eruptive products of the volcano. There are also other secondary effects of the eruptions which may have long term effects.

In most cases volcanoes let out lava which causes property damage rather than injuries or deaths. For instance, in Hawaii lava flows erupted from Kilauea for over a decade and as a consequence, homes, roads, forests, cars and other vehicles were buried in lavas and in some cases were burned by the resulting fires but no lives were lost. Sometimes it has become possible to control or divert the lava flow by constructing retaining walls or by some provision to chill the front of the lava flow with water.

Lava flows move slowly. But the pyroclastic flows move rapidly and these with lateral blasts may kill lives before they can run away. In 1902, on the island of Martinique the most destructive pyroclastic flow of the century occurred resulting in very large number of deaths.

A glowing avalanche rushed out of the flanks of Mount Pelee, running at a speed of over 160 km/h and killed about 29000 people. In A.D. 79 a large number of people of Pompeii and Herculaneum were buried under the hot pyroclastic material erupted by Mount Vesuvius.

The poisonous gas killed many of the victims and their bodies got later buried by pyroclastic material. In 1986, the eruption of the volcano at Lake Nyos, Cameroon killed over 1700 people and over 3000 cattle.

When magma moves towards the surface of the earth rocks may get fractured and this may result in swarms of earthquakes. The turbulent bubbling and boiling of magma below the earth can produce high frequency seismicity called volcanic tremor.

There are also secondary and tertiary hazards connected with volcanic eruptions. A powerful eruption in a coastal setting can cause a displacement of the seafloor leading to a tsunami. Hazardous effects are caused by pyroclastic material after a volcanic eruption has ceased.

Either melt water from snow or rain at the summit of the volcano can mix with the volcanic ash and start a deadly mud flow (called as lahar). Sometimes a volcanic debris avalanche in which various materials like pyroclastic matter, mud, shattered trees etc. is set out causing damage.

Volcanic eruptions produce other effects too. They can permanently change a landscape. They can block river channels causing flooding and diversion of water flow. Mountain terrains can be severely changed.

Volcanic eruptions can change the chemistry of the atmosphere. The effects of eruption on the atmosphere are precipitation of salty toxic or acidic matter. Spectacular sun set, extended period of darkness and stratospheric ozone depletion are all other effects of eruptions. Blockage of solar radiation by fine pyroclastic material can cause global cooling.

Apart from the above negative effects of volcanisms there are a few positive effects too. Periodic volcanic eruptions replenish the mineral contents of soils making it fertile. Geothermal energy is provided by volcanism. Volcanism is also linked with some type of mineral deposits. Magnificent scenery is provided by some volcanoes.

The study of volcanoes has great scientific as well as social interest. Widespread tephra layers inter-bedded with natural and artificial deposits have been used for deciphering and dating glacial and volcanic sequences, geomorphic features and archeological sites.

For example, ash from Mt. St. Helens Volcano in Washington travelled at least 900 km into Alberta. North American Indians fashioned tools and weapons out of volcanic glass, the origin of which is used to trace migratory and trading routes.

Volcanoes are windows through which the scientists look into the interiors of the earth. From volcanoes we learn the composition of the earth at great depths below the surface. We learn about the history of shifting layers of the earth’s crust. We learn about the processes which transform molten material into solid rock.

From the geological historical view point, volcanic activity was crucial in providing to the earth a unique habitat for life. The degassing of molten materials provided water for the oceans and gases for the atmosphere – indeed, the very ingredients for life and its sustenance.

Essay # 21. Volcanoes and Atmospheric Pollution :

During eruptions volcanoes inject solid particles and gases into the atmosphere. Particles may remain in the atmosphere for months to years and rain back on to the earth. Volcanoes also release chlorine and carbon dioxide.

The main products injected into the atmosphere from volcanic eruptions however are volcanic ash particles and small drops of sulphuric acid in the form of a fine spray known as aerosol. Most chlorine released from volcanoes is in the form of hydrochloric acid which is washed out in the troposphere. Volcanoes also emit carbon dioxide.

During the times of giant volcanic eruptions in the past the amount of carbon dioxide released may have been enough to affect the climate. In general global temperatures are cooler for a year or two after a major eruption.

A large magnitude pyroclastic eruption such as a caldera-forming event can be expected to eject huge volumes of fine ash high into the atmosphere where it may remain for several years, carried around the globe by strong air currents in the upper atmosphere.

The presence of this ash will increase the opacity of the atmosphere, that is, it will reduce the amount of sunlight reaching the earth’s surface. Accordingly, the earth’s surface and climate will become cooler. Various other atmospheric effects may be observed. Particularly noticeable is an increase in the intensity of sunsets.

i. Global Warming :

Besides blocking the rays of the sun, the vast clouds of dust and ash that result from a volcanic eruption can also trap ultraviolet radiation within the atmosphere causing global warming.

Volcanic eruptions usually include emissions of gases such as carbon dioxide which can further enhance this warming. Even if it lasted only for a relatively short time, a sudden increase in temperature could in turn have contributed to extinctions by creating an environment unsuitable for many animals.

ii. Geothermal Energy :

Geothermal energy is the heat energy trapped below the surface of the earth. In all volcanic regions, even thousands of years after activity has ceased the magma continues to cool at a slow rate. The temperature increases with depth below the surface of the earth. The average temperature gradient in the outer crust is about 0.56° C per 30 m of depth.

There are regions however, where the temperature gradient may be as much as 100 times the normal. This high heat flow is often sufficient to affect shallow strata containing water. When the water is so heated such surface manifestations like hot springs, fumaroles, geysers and related phenomena often occur.

It may be noted that over 10 per cent of the earth’s surface manifests very high heat flow and the hot springs and related features which are present in such areas have been used throughout the ages, for bathing, laundry and cooking.

In some places elaborate health spas and recreation areas have been developed around the hot-spring areas. The cooling of magma, even though it is relatively close to the surface is such a slow process that probably in terms of human history, it may be considered to supply a source of heat indefinitely.

Temperatures in the earth rise with increasing depth at about 0.56°C per 30 m depth. Thus if a well is drilled at a place where the average surface temperature is say 15.6°C a temperature of 100°C would be expected at about 4500 m depth. Many wells are drilled in excess of 6000 m and temperatures far above the boiling point of water are encountered.

Thermal energy is stored both in the solid rocks and in water and steam filling the pore spaces and fractures. The water and steam serve to transmit the heat from the rocks to a well and then to the surface.

In a geothermal system water also serves as the medium by which heat is transmitted from a deep igneous source to a geothermal reservoir at a depth shallow enough to be tapped by drilling. Geothermal reservoirs are located in the upward flowing part of a water – convective system. Rainwater percolates underground and reaches a depth where it is heated as it comes into contact with the hot rocks.

On getting heated, the water expands and moves upward in a convective system. If this upward movement is unrestricted the water will be dissipated at the surface as hot springs; but if such upward movement is prevented, trapped by an impervious layer the geothermal energy accumulates, and becomes a geothermal reservoir.

Until recently it was believed that the water in a geothermal system was derived mainly from water given off by the cooling of magma below the surface. Later studies have revealed that most of the water is from surface precipitation, with not more than 5 per cent from the cooling magma.

Production of electric power is the most important application of geothermal energy. A geothermal plant can provide a cheap and reliable supply of electrical energy. Geothermal power is nearly pollution free and there is little resource depletion.

Geothermal power is a significant source of electricity in New Zealand and has been furnishing electricity to parts of Italy. Geothermal installations at the Geysers in northern California have a capacity of 550 megawatts, enough to supply the power needs of the city of San Francisco.

Geothermal energy is versatile. It is being used for domestic heating in Italy, New Zealand and Iceland. Over 70 per cent of Iceland’s population live in houses heated by geothermal energy. Geothermal energy is being used for forced raising of vegetables and flowers in green houses in Iceland where the climate is too harsh to support normal growth. It is used for animal husbandry in Hungary and feeding in Iceland.

Geothermal energy can be used for simple heating processes, drying or distillation in every conceivable fashion, refrigeration, tempering in various mining and metal handling operations, sugar processing, production of boric acid, recovery of salts from seawater, pulp and paper production and wood processing.

Geothermal desalinization of sea water holds promise for abundant supply of fresh water. In some areas it is a real alternative to fossil fuels and hydroelectricity and in future may help meet the crisis of our insatiable appetite for energy.

iii. Phenomena Associated with Volcanism :

In some regions of current or past volcanic activity some phenomena related to volcanism are found. Fumaroles, hot springs and geysers are the widely known belonging to this group. During the process of consolidation of molten magma either at the surface or at some depths beneath the surface gaseous emanations may be given off.

These gas vents constitute the fumaroles. The Valley of Ten Thousand Smokes in Alaska is a well-known fumarole and is maintained as a national monument. This group of fumaroles was formed by the eruption of Mount Katmai in 1912. This valley of area of about 130 square kilometres contains thousands of vents discharging steam and gases.

These gases are of varied temperatures and the temperatures vary from that of ordinary steam to superheated steam coming out as dry gas. Many of the gases escaping from the vents may be poisonous, such as hydrogen sulphide and carbon monoxide which are suffocating and may settle at low places in the topography. For example, the fumaroles at the Poison Valley, Java discharge deadly poisonous gases.

Solfataras are fumaroles emitting sulphur gases. At some places, the hydrogen sulphide gases undergo oxidation on exposure to air to form sulphur. The sulphur accumulates in large amount so that the rocks close to the solfataras may contain commercial quantities of sulphur.

Hot springs are also phenomena associated with volcanic activity. Waters from the surface which penetrate into the ground can get heated either by contact with the rocks which are still hot or by gaseous emanations from the volcanic rocks. The water so heated may re-emerge at the surface giving rise to hot springs. In some situations the hot springs may be intermittently eruptive. Such intermittently hot springs are called geysers.

Related Articles:

  • Lava: Types and Eruptions | Volcanoes
  • Submarine and Sub Glacial Eruptions | Volcanoes

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Your burning questions about volcanoes, answered

Asu experts explain these molten mysteries.

lava erupting out of volcano

Volcano! That little word brings so much to our minds — streams of lava and clouds of ash, rumbling mountains, the might of a planet’s fiery underbelly, and our own nervous anticipation, curiosity and fear.

In fact, if it seems like more and more people have volcanoes on the brain, there’s a good reason.

It’s not necessarily that the number of volcanic eruptions is increasing, though media coverage of dangerous eruptions, such as the one in Indonesia on Aug. 10 or other recent ones in New Zealand and the Philippines, may make it appear that way. Scientists can’t say without more data from Earth’s history.

What is certain is that humans (and our stuff) take up more space on the planet than ever before, putting more people in the paths of volcanoes.

“The impact of volcanic eruptions is increasing,” volcanologist Amanda Clarke said. “As the global population grows, more people are being affected by eruptions, so we care about them more.”

Despite their growing effect on our lives, volcanoes seem to retain their air of mystery, leaving many of us with questions. Where do they come from? What causes eruptions? How do scientists predict them?

Clarke and fellow volcanologist Christy Till — both faculty in the Arizona State University  School of Earth and Space Exploration  — answer these questions and more to help us understand how to safely live in the shadows of these mighty forces of nature.

graphic of Mount St. Helens showing magma chamber and plates beneath

Click to view larger image. Illustration by Shireen Dooling

How does a volcano form?

There are two sides to the making of a volcano: what happens below ground and what happens above.

Events below ground have to do with plate tectonics. This is the theory that the Earth’s crust — the outer shell on which we live — is broken up into plates that move around on top of Earth’s mantle like ice cubes in a glass of water. Scientists see it as the force behind earthquakes, mountains, continent migration and volcano formation.

“Scientists for a long time have scratched their heads trying to figure out why these volcanoes occur where they do.”  — Christy Till

There are three basic types of tectonic environments where volcanoes grow.

The first is a convergent plate boundary, where two plates crash and an oceanic plate slips underneath another plate, bringing water and carbon dioxide into the mantle. This triggers a magma-melting process and creates more explosive volcanoes. This process created the Ring of Fire, an arch of volcanoes that wraps around the Pacific Ocean.

The second, a divergent plate boundary, occurs when a gap opens up between two plates. The gap is filled in by the mantle underneath, causing magma to melt. These volcanoes are common on the ocean floor and erupt continuously as the plates keep going their separate ways.

Volcanoes that form in the middle of a plate are called hot spot volcanoes.

“Scientists for a long time have scratched their heads trying to figure out why these volcanoes occur where they do,” Till said. “Our best guess is that there’s magma or mantle rising up underneath, and for some reason, it’s just hotter than in other places, so we get a volcano.”

Above ground, the part of the volcano we can see is formed by eruptions.

For example, Mount St. Helens, a composite volcano in Washington, grew over time as layers of debris from a mix of effusive eruptions (think gooey lava) and explosive eruptions (think pumice stone and ash) built on top of each other.

Sunset Crater, a cinder cone volcano in Arizona, ejected glowing fountains of lava and ash when it erupted, which then fell around the crater to create its steep slopes.

And Kilauea, a shield volcano in Hawaii, formed its wide but shallow slopes as its lava spread out in all directions and built up in layers over time.

However, the type of eruption, and therefore volcano, circles back to another underground element.

“The composition of the magma, and the process deep in the earth that forms it, controls the eruption style to a large extent,” Till said.

What is magma?

Magma is the molten material that sits under or inside the Earth’s crust. (Lava is magma that has reached the surface through a volcano.) Till’s lab, the  Experimental Petrology and Igneous processes Center , looks at how magma forms on Earth and on other planets, as well as the underground processes that lead up to an eruption.

One of the surprises that researchers have learned in the last 10 years, she says, is that the magma below a volcano is not the cauldron of bubbling, liquid goo we might imagine.

“In fact, what’s below a volcano is more like a slushie. In a slushie, you have mostly ice crystals and some liquid, and at first, it’s hard to suck it through a straw because it’s mostly ice. You have to wait until it melts a little to get it through a straw.”

Magma, too, is composed of crystals (the geological kind) with just a little bit of liquid. Something must happen to the magma underground to warm it up, making it liquid enough to erupt. To study those processes, Till gathers samples of those crystals, which she likens to “little black boxes,” from volcanic deposits on the surface and examines them with microscopes.

“These crystals have little zones in them, much like tree rings. They can tell us about the temperature, pressure and composition of the magma chamber, and also how long before an eruption these specific events happened,” she said.

Video by ASU Research

What happens during a volcanic eruption?

First, a fresher, hotter, more liquid magma rises from deeper in the Earth’s mantle and warms the slushie magma in the volcano’s chamber. One way for it to arrive there is via an earthquake, which might push up fresh magma or open new pathways for it to travel upward. However, not every earthquake can warm a magma chamber and cause an eruption, Till notes.

“There’s also a possibility that the seismic waves passing through the crust can kind of jiggle a magma body and cause it to fizz. Just like with a soda, those bubbles can generate overpressure and buoyancy, driving an eruption,” Clarke said.

As the new and old magmas mix, the crystal mush heats up and comes to the surface. It could be an effusive eruption of syrupy, flowing lava, or it could be an explosive eruption of ash, cinders and hunks of molten rock known as lava bombs. The amount of gas in the body of magma determines how violent the eruption is.

For those that are more explosive, the volcano could generate an ash cloud that travels great distances, which could have indirect effects like roof damage, bad air quality or crop devastation. It could also unleash the significantly more destructive pyroclastic flow, which is a searing wave of dense ash and gases that rushes along the ground, killing and burning everything in its path.

“The plume is the big footprint, but only indirectly dangerous,” Clarke said. “The pyroclastic flows are the smaller footprint, but much more dangerous.”

If the volcano is near a body of water, there is another opportunity for additional destruction — pyroclastic flows entering the sea can cause tsunamis.

How do scientists predict eruptions?

“The bread and butter of prediction is seismic data,” Clarke said. Volcanologists take seismic stations, which measure vibrations in the earth, and distribute them all around a volcano to get the best read on what’s happening underneath.

Another important tool is the tiltmeter, which, as its name suggests, measures any miniscule changes in the level of the earth. Typically, before a volcano erupts, the ground around it inflates slightly, which scientists call deformation.

Observatories typically also monitor gas emissions, such as sulfur dioxide and carbon dioxide, which may indicate changes happening deeper in the volcano.

“If you want to know what a volcano is capable of doing in the future, the first thing you have to do is look at what it did in the past.”  — Amanda Clarke

And finally, cameras — both standard and thermal — help volcanologists keep an eye on activity. Clarke explains that thermal cameras are especially helpful for tall volcanoes whose tops may often be obscured by clouds.

“Using these kinds of data together, you can even predict how much magma there is, and at what depth,” Clarke said.

Having an idea of what a particular volcano can do once it’s ready to erupt is also a critical piece of prediction that allows volcanologists to make safety recommendations.

“If you want to know what a volcano is capable of doing in the future, the first thing you have to do is look at what it did in the past,” Clarke said.

Researchers do this by collecting ash deposits from a wide area and dating them. This gives them an idea of how large a volcano’s eruptions were and how frequently they occurred. However, the method has its limitations. Hardened magma is much harder to date than ash, and supervolcanoes have eruptions so large that the ash travels thousands of miles, making it difficult to determine their true size.

There’s also the trouble of inconsistent eruptions. Volcanoes tend to fluctuate in the size of their eruptions; a big one may be followed by several smaller ones before another large one happens. That’s why it’s crucial, Clarke said, to look over long timespans for an accurate picture of a volcano’s history.

How far in advance scientists can predict an eruption depends on a host of factors, one of which is whether the eruption is large or small. Large eruptions are farther apart, so they might have longer warning times — from weeks away to even decades — while the magma slowly heats up after the last eruption. Small eruptions are closer together, so their warning times are shorter — months to hours. However, an abundance of data means that those predictions are typically more precise than for large eruptions.

graphic of erupting ash cloud with chemical elements highlighted

How can you stay safe in an area with volcanic activity?

Clarke has seen too many volcanic eruptions to count, but she says that her time on the island of Montserrat while getting her PhD was when she learned how to be safe around them.

“I think some people take a bit of a macho attitude about trying to get close to volcanoes,” she said.

Proper precautions, she argues, help people stay alive.

“The main thing is to understand what the local observatories and scientists are doing. They collect data. They know what’s going on,” she said.

Till has not experienced a volcanic eruption and, despite an academic interest in seeing one, is largely happy to keep it that way.

“I’ve been to volcanoes that could erupt at any time, but I was fortunate enough not to be there when they were erupting,” she said. Like Clarke, by checking in with observatories, she’s managed to keep herself safe in dangerous environments.

In the U.S., you can find the latest reports on activity at the  U.S. Geological Survey website . Abroad, other nations may have an equivalent database online, or you can visit the Smithsonian’s  Global Volcanism Program website , which gathers data from around the world.

These resources can help you find out what the alert level is in the area (and what colored or numbered alert system locals use), and whether there has been any activity recently. Clarke said it’s not a good idea to assume that other groups are communicating with the local observatory and recommends always checking for yourself.

“If you get a permit from the forest service to hike to a crater, that doesn’t mean it’s safe. That doesn’t mean they’ve checked the data.”

What do classifications like active, dormant and extinct mean?

Not much, it turns out.

Clarke explains that people used to classify a volcano as “active” if it had erupted in historic time. The problem with this is that historic time varies from culture to culture, because it refers to the time when written records became available. Volcanoes in Italy have extensive documentation going back thousands of years, but volcanoes in the U.S. don’t have as deep of a written history.

“Having had a historic eruption is a meaningless classification, because there’s no number that goes along with that,” Clarke said.

A dormant volcano is one that is active but not currently erupting, while an extinct volcano has not erupted in historic time and is unlikely to erupt in the future.

A handier — and globally applicable — way to determine if a volcano is active is whether it has erupted during the Holocene, our present epoch which began over 11,000 years ago. However, this marker ultimately has its own flaws. A volcano can have an incredibly long lifespan, sometimes lasting millions of years. Silence in recent millennia doesn’t mean its erupting days are over.

“Whether it erupted in the Holocene is meaningless when it comes to someplace like Yellowstone or the Valles Caldera, whose timescales are way longer than we even have the capacity to document,” Clarke said.

Can a volcanic eruption be stopped?

Ideas for stopping eruptions range from venting gases to relieve volcanic pressure to plugging the top like a cork in a bottle. However, these concepts remain untested, and most volcanologists don’t take such efforts seriously.

What has found some success, though, is using barriers to redirect lava and pyroclastic flows away from towns and important structures. Clarke gives the example of Heimaey, a harbor town in Iceland that experienced a nearby eruption in 1973. The resulting lava flow threatened to close off the bay that was their main economic resource.

“As it started to enter the bay, they got out all the water hoses they had and sprayed it, and it solidified there. They used the lava itself as a barrier,” Clarke said.

Do volcanoes affect the climate?

Volcanic eruptions have both positive and negative effects on the climate. For example, their plumes carry gases like sulfur dioxide, which reach above the clouds into the stratosphere. There, the gas forms into droplets of sulfuric acid.

“The sulfur compounds can be circulated around the globe, and they can filter out the sun’s light and heat to cool global temperatures,” Clarke said.

Researchers speculate that such an event — an 1815 eruption of Mount Tambora in Indonesia — was behind the 1816 “year without a summer” that caused low temperatures and heavy rains in Europe and North America, leading to food shortages.

Whether an eruption can have a worldwide effect may depend on the size and composition of the ash cloud, as well as the volcano’s position on Earth. The cooling effect is always temporary. The longest documented cooling period lasted about three years, though Clarke believes that super eruptions in Earth’s history may have had longer temperature effects.

If you’re thinking that this sounds like a good way to combat today’s warming temperatures, you’re not alone. Some scientists are beginning to research the possibilities of solar engineering — a strategy inspired by volcanoes that would use planes to spray sulfur dioxide into the stratosphere.

Another climate effect of volcanoes is that their ash makes super fertile soil, creating lush environments in the areas surrounding them. The plants and trees that grow in this rich soil capture and store carbon dioxide from the atmosphere.

“What’s in fertilizer? Phosphorus, nitrogen and potassium. Those are abundant in volcanic products,” Clarke said. “Basically, they act as a fertilizer just like you might buy at Agway or ACE Hardware.”

Nutrients from falling ash easily leach into the soil, she adds, making it an excellent delivery system as well.

What are volcanoes like on other planets?

graphic of volcanoes on other planetary bodies

Planets, and moons as well, can have volcanoes very different from those on Earth. Jupiter’s moon Io has more volcanic activity than any other object in our solar system; its lava fountains can be many miles high. And the dwarf planet Ceres has ice volcanoes, or cryovolcanoes. They erupt water instead of magma, which freezes on its surface.

“The compositions of planets are different, so the kinds of magma they have are different, which then gives them unique eruptive behavior,” Till said.

Her lab works to understand the magma of other celestial bodies by creating it in a special device called a piston cylinder, which simulates conditions on the interior of a planet.

“In the same way that you’d mix flour and sugar and eggs to make a cake, we mix silica and magnesium and iron and other elements in the proportion we want to study. Then we put them in our equivalent of an oven to make magma at high pressures and temperatures,” Till said. “When we do this, we can discover how magmas on other planets are different.”

Her team has begun work on a new project that will study the types of magma that may exist on planets outside our solar system, known as exoplanets. Knowing more about their magma will give researchers glimpses into those planets’ volcanic behavior.

“Over 4,000 exoplanets have been confirmed in the last five years or so, and we’re just starting to investigate them,” Till said. “It’s an exciting time.”

Top photo from Shutterstock.

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70 Volcano Essay Topic Ideas & Examples

🏆 best volcano topic ideas & essay examples, 📌 most interesting volcano topics to write about, 👍 good research topics about volcano, ❓ essay questions about volcanoes.

  • The Economic Impact of the Icelandic Volcano Eruptions on the International Economy So, it may be completed that even though the shutdown of the European airspace negatively affected the economics of the whole world and GDP level of the countries, there were the ways for solving the […]
  • Eruption of Mount Saint Helen Volcano Helens volcano, looking at its history, the explosion, the immediate consequences of the eruption, and the historic impact on the climate and human life. We will write a custom essay specifically for you by our professional experts 808 writers online Learn More
  • Hawaii – A Volcano in the Sea All the volcanoes in Hawaii are shield volcanoes. They are large and have shallow-sloping sides – almost like a warrior’s shield.
  • Sparks Fly Over Theory That Volcano Caused Salmon Boom However, for the theory to be credible the volcanic ashes must be rich in iron and spread ashes to oceanic regions that have a limited concentration of iron.
  • The Volcano and Aurora in Iceland In other words, the volcano Hekla was erupting from the surface of the earth while the natural light was shining from the sky.
  • Haleakalā Volcano and Wai’anapanapa State Park Haleakal is a large shield volcano that is situated in the east of the Island of Maui and basically comprises this part of Maui.
  • Review of Related Literature of Volcano Tourism in the Philippines
  • The Human Response During a Calamity in A Living God by Lafcadio Hearn and The Volcano Next Door by Michael Finkel
  • Investigating the Rate of Lava Flows Down the Side of a Volcano
  • The Dangers of Living Too Close to a Volcano
  • The Characteristics of Mount Vesuvius, the Only Active Volcano on the European Mainland
  • Causes and Effect of Volcano Eruption
  • The Most Famous Mount Kilauea Volcano in Hawaii
  • The Devastation a Volcano Can Create Shown in In a Volcanoes Path
  • What Fundamental Parameters Determine the Vigor or Violence with Which a Volcano Erupts
  • The History and Possible Threats of Nyiragongo in The Volcano Next Door, a Book by Michael Finkel
  • Volcano Eruptions Types
  • Understanding How A Volcano Forms and Erupts
  • Volcano: The Eruption and Healing of Mount St. Helens Critical
  • The Mount Saint Helens and the Volcano Area in Washington State
  • Planet and Live Erupting Volcano
  • The Mount St. Helen and Mount Pinatubo Volcano Eruptionss
  • The Most Active Volcano Of The Philippines
  • An Active Super Volcano Lying Underneath Yellowstone Nation Park
  • The Vesuvius Volcano Eruption and the Activities of the Cities Pompeii and Herculaneum
  • Why This Volcano Eruption in the Philippines May Be Especially Deadly
  • Sitting on a Volcano: Domestic Violence in Indonesia Following Two Volcano Eruptions
  • Volcanoes: Volcano and Broad Domed Volcano
  • The Lack of Volcano Physics in the Movies
  • A Look at the Destructive Power of a Volcano
  • An Analysis of the Destructive Power of a Volcano as One of the Most Violent and Deadly of All Natural Forces
  • The Importance and Role of Hydrothermal Vents and Underwater Volcano
  • Yellowstone: Volcano and Lieutenant Gustavus Doane
  • The Devastating Effects of Volcano Eruptions in the U.S
  • An Analysis of the Eruption of the Mount St. Helens Volcano on the 18th of May, 1980
  • Volcanoes: Volcano and Eruptions Explosive Eruptions
  • Volcanoes : The Volcano Of Tambora
  • An Analysis of the Question Whether Germany Was Dancing on a Volcano
  • The Three Systems to Faults Present in the Nevado del Ruiz Volcano Region
  • An Analysis of the Soufriere Hills Volcano Eruption on Montserrat Island in 1997
  • Why Can’t Toxic or Nuclear Waste Be Disposed of in Volcanoes?
  • What Are the Four Basic Types of Volcanoes?
  • What Exactly Are Super Volcanoes?
  • Where Do Volcanoes Exist and How They Have Formed?
  • Which Is the World’s Largest Volcano?
  • What Causes Hotspot Volcanoes?
  • What Are the Most Beautiful Volcanoes in the World?
  • Which Are the Most Dangerous Volcanoes That Could End the World?
  • Why Are Some Volcanoes More Hazardous Than Others?
  • Are Volcanoes the Main Cause of Global Warming?
  • What Would Be the Side Effects of Dumping Our Trash in Active Volcanoes?
  • Is It Possible There Are Active Volcanoes on the Moon?
  • Why Are There So Many Volcanoes in the Philippines?
  • Is It Possible for Extinct Volcanoes to Ever Become Dormant or Active Again?
  • Why Do Most Volcanoes and Earthquakes Occur at Plate Boundaries?
  • What Are the Hazards Caused by Volcanoes?
  • Why Are Plug Dome Volcanoes Considered Especially?
  • What Are Most Dangerous Volcanoes in the US and Why?
  • Why Can’t We Harvest Energy From Volcanoes?
  • What Is the Most Interesting Thing About the Volcanoes?
  • What Islands Have Volcanoes on Them?
  • What Are the 3 Main Types of Volcanoes and Their Characteristics?
  • Could the Earth Survive Without Volcanoes?
  • Which Continent Does Not Have Volcanoes?
  • Why Do Volcanoes Erupt on Mountains and Not on Flat Land?
  • How Are Underwater Volcanoes Different From Land Volcanoes?
  • How Often Do “Extinct” Volcanoes Become Active?
  • Where Are the Most Active Volcanoes Located?
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  • How Do Volcanoes Influence Climate?
  • Chicago (A-D)
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National Academies Press: OpenBook

Volcanic Eruptions and Their Repose, Unrest, Precursors, and Timing (2017)

Chapter: 1 introduction, 1 introduction.

Volcanoes are a key part of the Earth system. Most of Earth’s atmosphere, water, and crust were delivered by volcanoes, and volcanoes continue to recycle earth materials. Volcanic eruptions are common. More than a dozen are usually erupting at any time somewhere on Earth, and close to 100 erupt in any year ( Loughlin et al., 2015 ).

Volcano landforms and eruptive behavior are diverse, reflecting the large number and complexity of interacting processes that govern the generation, storage, ascent, and eruption of magmas. Eruptions are influenced by the tectonic setting, the properties of Earth’s crust, and the history of the volcano. Yet, despite the great variability in the ways volcanoes erupt, eruptions are all governed by a common set of physical and chemical processes. Understanding how volcanoes form, how they erupt, and their consequences requires an understanding of the processes that cause rocks to melt and change composition, how magma is stored in the crust and then rises to the surface, and the interaction of magma with its surroundings. Our understanding of how volcanoes work and their consequences is also shared with the millions of people who visit U.S. volcano national parks each year.

Volcanoes have enormous destructive power. Eruptions can change weather patterns, disrupt climate, and cause widespread human suffering and, in the past, mass extinctions. Globally, volcanic eruptions caused about 80,000 deaths during the 20th century ( Sigurdsson et al., 2015 ). Even modest eruptions, such as the 2010 Eyjafjallajökull eruption in Iceland, have multibillion-dollar global impacts through disruption of air traffic. The 2014 steam explosion at Mount Ontake, Japan, killed 57 people without any magma reaching the surface. Many volcanoes in the United States have the potential for much larger eruptions, such as the 1912 eruption of Katmai, Alaska, the largest volcanic eruption of the 20th century ( Hildreth and Fierstein, 2012 ). The 2008 eruption of the unmonitored Kasatochi volcano, Alaska, distributed volcanic gases over most of the continental United States within a week ( Figure 1.1 ).

Finally, volcanoes are important economically. Volcanic heat provides low-carbon geothermal energy. U.S. generation of geothermal energy accounts for nearly one-quarter of the global capacity ( Bertani, 2015 ). In addition, volcanoes act as magmatic and hydrothermal distilleries that create ore deposits, including gold and copper ores.

Moderate to large volcanic eruptions are infrequent yet high-consequence events. The impact of the largest possible eruption, similar to the super-eruptions at Yellowstone, Wyoming; Long Valley, California; or Valles Caldera, New Mexico, would exceed that of any other terrestrial natural event. Volcanoes pose the greatest natural hazard over time scales of several decades and longer, and at longer time scales they have the potential for global catastrophe ( Figure 1.2 ). While


the continental United States has not suffered a fatal eruption since 1980 at Mount St. Helens, the threat has only increased as more people move into volcanic areas.

Volcanic eruptions evolve over very different temporal and spatial scales than most other natural hazards ( Figure 1.3 ). In particular, many eruptions are preceded by signs of unrest that can serve as warnings, and an eruption itself often persists for an extended period of time. For example, the eruption of Kilauea Volcano in Hawaii has continued since 1983. We also know the locations of many volcanoes and, hence, where most eruptions will occur. For these reasons, the impacts of at least some types of volcanic eruptions should be easier to mitigate than other natural hazards.

Anticipating the largest volcanic eruptions is possible. Magma must rise to Earth’s surface and this movement is usually accompanied by precursors—changes in seismic, deformation, and geochemical signals that can be recorded by ground-based and space-borne instruments. However, depending on the monitoring infrastructure, precursors may present themselves over time scales that range from a few hours (e.g., 2002 Reventador, Ecuador, and 2015 Calbuco, Chile) to decades before eruption (e.g., 1994 Rabaul, Papua New Guinea). Moreover, not all signals of volcanic unrest are immediate precursors to surface eruptions (e.g., currently Long Valley, California, and Campi Flegrei, Italy).

Probabilistic forecasts account for this uncertainty using all potential eruption scenarios and all relevant data. An important consideration is that the historical record is short and biased. The instrumented record is even shorter and, for most volcanoes, spans only the last few decades—a miniscule fraction of their lifetime. Knowledge can be extended qualitatively using field studies of volcanic deposits, historical accounts, and proxy data, such as ice and marine sediment cores and speleothem (cave) records. Yet, these too are biased because they commonly do not record small to moderate eruptions.

Understanding volcanic eruptions requires contributions from a wide range of disciplines and approaches. Geologic studies play a critical role in reconstructing the past eruption history of volcanoes,


especially of the largest events, and in regions with no historical or directly observed eruptions. Geochemical and geophysical techniques are used to study volcano processes at scales ranging from crystals to plumes of volcanic ash. Models reveal essential processes that control volcanic eruptions, and guide data collection. Monitoring provides a wealth of information about the life cycle of volcanoes and vital clues about what kind of eruption is likely and when it may occur.


At the request of managers at the National Aeronautics and Space Administration (NASA), the National Science Foundation, and the U.S. Geological Survey (USGS), the National Academies of Sciences, Engineering, and Medicine established a committee to undertake the following tasks:

  • Summarize current understanding of how magma is stored, ascends, and erupts.
  • Discuss new disciplinary and interdisciplinary research on volcanic processes and precursors that could lead to forecasts of the type, size, and timing of volcanic eruptions.
  • Describe new observations or instrument deployment strategies that could improve quantification of volcanic eruption processes and precursors.
  • Identify priority research and observations needed to improve understanding of volcanic eruptions and to inform monitoring and early warning efforts.


The roles of the three agencies in advancing volcano science are summarized in Box 1.1 .

The committee held four meetings, including an international workshop, to gather information, deliberate, and prepare its report. The report is not intended to be a comprehensive review, but rather to provide a broad overview of the topics listed above. Chapter 2 addresses the opportunities for better understanding the storage, ascent, and eruption of magmas. Chapter 3 summarizes the challenges and prospects for forecasting eruptions and their consequences. Chapter 4 highlights repercussions of volcanic eruptions on a host of other Earth systems. Although not explicitly called out in the four tasks, the interactions between volcanoes and other Earth systems affect the consequences of eruptions, and offer opportunities to improve forecasting and obtain new insights into volcanic processes. Chapter 5 summarizes opportunities to strengthen

research in volcano science. Chapter 6 provides overarching conclusions. Supporting material appears in appendixes, including a list of volcano databases (see Appendix A ), a list of workshop participants (see Appendix B ), biographical sketches of the committee members (see Appendix C ), and a list of acronyms and abbreviations (see Appendix D ).

Background information on these topics is summarized in the rest of this chapter.


The USGS has identified 169 potentially active volcanoes in the United States and its territories (e.g., Marianas), 55 of which pose a high threat or very high threat ( Ewert et al., 2005 ). Of the total, 84 are monitored by at least one seismometer, and only 3 have gas sensors (as of November 2016). 1 Volcanoes are found in the Cascade mountains, Aleutian arc, Hawaii, and the western interior of the continental United States ( Figure 1.4 ). The geographical extent and eruption hazards of these volcanoes are summarized below.

The Cascade volcanoes extend from Lassen Peak in northern California to Mount Meager in British Columbia. The historical record contains only small- to moderate-sized eruptions, but the geologic record reveals much larger eruptions ( Carey et al., 1995 ; Hildreth, 2007 ). Activity tends to be sporadic ( Figure 1.5 ). For example, nine Cascade eruptions occurred in the 1850s, but none occurred between 1915 and 1980, when Mount St. Helens erupted. Consequently, forecasting eruptions in the Cascades is subject to considerable uncertainty. Over the coming decades, there may be multiple eruptions from several volcanoes or no eruptions at all.

The Aleutian arc extends 2,500 km across the North Pacific and comprises more than 130 active and potentially active volcanoes. Although remote, these volcanoes pose a high risk to overflying aircraft that carry more than 30,000 passengers a day, and are monitored by a combination of ground- and space-based sensors. One or two small to moderate explosive eruptions occur in the Aleutians every year, and very large eruptions occur less frequently. For example, the world’s largest eruption of the 20th century occurred approximately 300 miles from Anchorage, in 1912.

In Hawaii, Kilauea has been erupting largely effusively since 1983, but the location and nature of eruptions can vary dramatically, presenting challenges for disaster preparation. The population at risk from large-volume, rapidly moving lava flows on the flanks of the Mauna Loa volcano has grown tremendously in the past few decades ( Dietterich and Cashman, 2014 ), and few island residents are prepared for the even larger magnitude explosive eruptions that are documented in the last 500 years ( Swanson et al., 2014 ).

All western states have potentially active volcanoes, from New Mexico, where lava flows have reached within a few kilometers of the Texas and Oklahoma borders ( Fitton et al., 1991 ), to Montana, which borders the Yellowstone caldera ( Christiansen, 1984 ). These volcanoes range from immense calderas that formed from super-eruptions ( Mastin et al., 2014 ) to small-volume basaltic volcanic fields that erupt lava flows and tephra for a few months to a few decades. Some of these eruptions are monogenic (erupt just once) and pose a special challenge for forecasting. Rates of activity in these distributed volcanic fields are low, with many eruptions during the past few thousand years (e.g., Dunbar, 1999 ; Fenton, 2012 ; Laughlin et al., 1994 ), but none during the past hundred years.


Volcanoes often form prominent landforms, with imposing peaks that tower above the surrounding landscape, large depressions (calderas), or volcanic fields with numerous dispersed cinder cones, shield volcanoes, domes, and lava flows. These various landforms reflect the plate tectonic setting, the ways in which those volcanoes erupt, and the number of eruptions. Volcanic landforms change continuously through the interplay between constructive processes such as eruption and intrusion, and modification by tectonics, climate, and erosion. The stratigraphic and structural architecture of volcanoes yields critical information on eruption history and processes that operate within the volcano.

Beneath the volcano lies a magmatic system that in most cases extends through the crust, except during eruption. Depending on the setting, magmas may rise


1 Personal communication from Charles Mandeville, Program Coordinator, Volcano Hazards Program, U.S. Geological Survey, on November 26, 2016.


directly from the mantle or be staged in one or more storage regions within the crust before erupting. The uppermost part (within 2–3 km of Earth’s surface) often hosts an active hydrothermal system where meteoric groundwater mingles with magmatic volatiles and is heated by deeper magma. Identifying the extent and vigor of hydrothermal activity is important for three reasons: (1) much of the unrest at volcanoes occurs in hydrothermal systems, and understanding the interaction of hydrothermal and magmatic systems is important for forecasting; (2) pressure buildup can cause sudden and potentially deadly phreatic explosions from the hydrothermal system itself (such as on Ontake, Japan, in 2014), which, in turn, can influence the deeper magmatic system; and (3) hydrothermal systems are energy resources and create ore deposits.

Below the hydrothermal system lies a magma reservoir where magma accumulates and evolves prior to eruption. Although traditionally modeled as a fluid-filled cavity, there is growing evidence that magma reservoirs may comprise an interconnected complex of vertical and/or horizontal magma-filled cracks, or a partially molten mush zone, or interleaved lenses of magma and solid material ( Cashman and Giordano, 2014 ). In arc volcanoes, magma chambers are typically located 3–6 km below the surface. The magma chamber is usually connected to the surface via a fluid-filled conduit only during eruptions. In some settings, magma may ascend directly from the mantle without being stored in the crust.

In the broadest sense, long-lived magma reservoirs comprise both eruptible magma (often assumed to contain less than about 50 percent crystals) and an accumulation of crystals that grow along the margins or settle to the bottom of the magma chamber. Physical segregation of dense crystals and metals can cause the floor of the magma chamber to sag, a process balanced by upward migration of more buoyant melt. A long-lived magma chamber can thus become increasingly stratified in composition and density.

The deepest structure beneath volcanoes is less well constrained. Swarms of low-frequency earthquakes at mid- to lower-crustal depths (10–40 km) beneath volcanoes suggest that fluid is periodically transferred into the base of the crust ( Power et al., 2004 ). Tomographic studies reveal that active volcanic systems have deep crustal roots that contain, on average, a small fraction of melt, typically less than 10 percent. The spatial distribution of that melt fraction, particularly how much is concentrated in lenses or in larger magma bodies, is unknown. Erupted samples preserve petrologic and geochemical evidence of deep crystallization, which requires some degree of melt accumulation. Seismic imaging and sparse outcrops suggest that the proportion of unerupted solidified magma relative to the surrounding country rock increases with depth and that the deep roots of volcanoes are much more extensive than their surface expression.


Volcano monitoring is critical for hazard forecasts, eruption forecasts, and risk mitigation. However, many volcanoes are not monitored at all, and others are monitored using only a few types of instruments. Some parameters, such as the mass, extent, and trajectory of a volcanic ash cloud, are more effectively measured by satellites. Other parameters, notably low-magnitude earthquakes and volcanic gas emissions that may signal an impending eruption, require ground-based monitoring on or close to the volcanic edifice. This section summarizes existing and emerging technologies for monitoring volcanoes from the ground and from space.

Monitoring Volcanoes on or Near the Ground

Ground-based monitoring provides data on the location and movement of magma. To adequately capture what is happening inside a volcano, it is necessary to obtain a long-term and continuous record, with periods spanning both volcanic quiescence and periods of unrest. High-frequency data sampling and efficient near-real-time relay of information are important, especially when processes within the volcano–magmatic–hydrothermal system are changing rapidly. Many ground-based field campaigns are time intensive and can be hazardous when volcanoes are active. In these situations, telemetry systems permit the safe and continuous collection of data, although the conditions can be harsh and the lifetime of instruments can be limited in these conditions.

Ground-based volcano monitoring falls into four broad categories: seismic, deformation, gas, and thermal monitoring ( Table 1.1 ). Seismic monitoring tools,

TABLE 1.1 Ground-Based Instrumentation for Monitoring Volcanoes

including seismometers and infrasound sensors, are used to detect vibrations caused by breakage of rock and movement of fluids and to assess the evolution of eruptive activity. Ambient seismic noise monitoring can image subsurface reservoirs and document changes in wave speed that may reflect stress. changes. Deformation monitoring tools, including tiltmeters, borehole strainmeters, the Global Navigation Satellite System (GNSS, which includes the Global Positioning System [GPS]), lidar, radar, and gravimeters, are used to detect the motion of magma and other fluids in the subsurface. Some of these tools, such as GNSS and lidar, are also used to detect erupted products, including ash clouds, pyroclastic density currents, and volcanic bombs. Gas monitoring tools, including a range of sensors ( Table 1.1 ), and direct sampling of gases and fluids are used to detect magma intrusions and changes in magma–hydrothermal interactions. Thermal monitoring tools, such as infrared cameras, are used to detect dome growth and lava breakouts. Continuous video or photographic observations are also commonly used and, despite their simplicity, most directly document volcanic activity. Less commonly used monitoring technologies, such as self-potential, electromagnetic techniques, and lightning detection are used to constrain fluid movement and to detect

ash clouds. In addition, unmanned aerial vehicles (e.g., aircraft and drones) are increasingly being used to collect data. Rapid sample collection and analysis is also becoming more common as a monitoring tool at volcano observatories. A schematic of ground-based monitoring techniques is shown in Figure 1.6 .

Monitoring Volcanoes from Space

Satellite-borne sensors and instruments provide synoptic observations during volcanic eruptions when collecting data from the ground is too hazardous or where volcanoes are too remote for regular observation. Repeat-pass data collected over years or decades provide a powerful means for detecting surface changes on active volcanoes. Improvements in instrument sensitivity, data availability, and the computational capacity required to process large volumes of data have led to a dramatic increase in “satellite volcano science.”

Although no satellite-borne sensor currently in orbit has been specifically designed for volcano monitoring, a number of sensors measure volcano-relevant


TABLE 1.2 Satellite-Borne Sensor Suite for Volcano Monitoring

NOTE: AIRS, Atmospheric Infrared Sounder; ALOS, Advanced Land Observing Satellite; ASTER, Advanced Spaceborne Thermal Emission and Reflection Radiometer; AVHRR, Advanced Very High Resolution Radiometer; CALIPSO, Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation; COSMO-SkyMed, Constellation of Small Satellites for Mediterranean Basin Observation; GOES, Geostationary Operational Environmental Satellite; IASI, Infrared Atmospheric Sounding Interferometer; MISR, Multi-angle Imaging SpectroRadiometer; MLS, Microwave Limb Sounder; MODIS, Moderate Resolution Imaging Spectroradiometer; OMI, Ozone Monitoring Instrument; OMPS, Ozone Mapping and Profiler Suite; SAGE, Stratospheric Aerosol and Gas Experiment.

parameters, including heat flux, gas and ash emissions, and deformation ( Table 1.2 ). Thermal infrared data are used to detect eruption onset and cessation, calculate lava effusion rates, map lava flows, and estimate ash column heights during explosive eruptions. In some cases, satellites may capture thermal precursors to eruptions, although low-temperature phenomena are challenging to detect. Both high-temporal/low-spatial-resolution (geostationary orbit) and high-spatial/low-temporal-resolution (polar orbit) thermal infrared observations are needed for global volcano monitoring.

Satellite-borne sensors are particularly effective for observing the emission and dispersion of volcanic gas and ash plumes in the atmosphere. Although several volcanic gas species can be detected from space (including SO 2 , BrO, OClO, H 2 S, HCl, and CO; Carn et al., 2016 ), SO 2 is the most readily measured, and it is also responsible for much of the impact of eruptions on climate. Satellite measurements of SO 2 are valuable for detecting eruptions, estimating global volcanic fluxes and recycling of other volatile species, and tracking volcanic clouds that may be hazardous to aviation in near real time. Volcanic ash cloud altitude is most accurately determined by spaceborne lidar, although spatial coverage is limited. Techniques for measuring volcanic CO 2 from space are under development and could lead to earlier detection of preeruptive volcanic degassing.

Interferometric synthetic aperture radar (InSAR) enables global-scale background monitoring of volcano deformation ( Figure 1.7 ). InSAR provides much higher spatial resolution than GPS, but lower accuracy and temporal resolution. However, orbit repeat times will diminish as more InSAR missions are launched, such as the European Space Agency’s recently deployed Sentinel-1 satellite and the NASA–Indian Space Research Organisation synthetic aperture radar mission planned for launch in 2020.



Eruptions range from violently explosive to gently effusive, from short lived (hours to days) to persistent over decades or centuries, from sustained to intermittent, and from steady to unsteady ( Siebert et al., 2015 ). Eruptions may initiate from processes within the magmatic system ( Section 1.3 ) or be triggered by processes and properties external to the volcano, such as precipitation, landslides, and earthquakes. The eruption behavior of a volcano may change over time. No classification scheme captures this full diversity of behaviors (see Bonadonna et al., 2016 ), but some common schemes to describe the style, magnitude, and intensity of eruptions are summarized below.

Eruption Magnitude and Intensity

The size of eruptions is usually described in terms of total erupted mass (or volume), often referred to as magnitude, and mass eruption rate, often referred to as intensity. Pyle (2015) quantified magnitude and eruption intensity as follows:

magnitude = log 10 (mass, in kg) – 7, and

intensity = log 10 (mass eruption rate, in kg/s) + 3.

The Volcano Explosivity Index (VEI) introduced by Newhall and Self (1982) assigns eruptions to a VEI class based primarily on measures of either magnitude (erupted mass or volume) or intensity (mass eruption rate and/or eruption plume height), with more weight given to magnitude. The VEI classes are summarized in Figure 1.8 . The VEI classification is still in use, despite its many limitations, such as its reliance on only a few types of measurements and its poor fit for small to moderate eruptions (see Bonadonna et al., 2016 ).

Smaller VEI events are relatively common, whereas larger VEI events are exponentially less frequent ( Siebert et al., 2015 ). For example, on average about three VEI 3 eruptions occur each year, whereas there is a 5 percent chance of a VEI 5 eruption and a 0.2 percent chance of a VEI 7 (e.g., Crater Lake, Oregon) event in any year.

Eruption Style

The style of an eruption encompasses factors such as eruption duration and steadiness, magnitude, gas flux, fountain or column height, and involvement of magma and/or external source of water (phreatic and phreatomagmatic eruptions). Eruptions are first divided into effusive (lava producing) and explosive (pyroclast producing) styles, although individual eruptions can be simultaneously effusive and weakly explosive, and can pass rapidly and repeatedly between eruption styles. Explosive eruptions are further subdivided into styles that are sustained on time scales of hours to days and styles that are short lived ( Table 1.3 ).

Classification of eruption style is often qualitative and based on historical accounts of characteristic eruptions from type-volcanoes. However, many type-volcanoes exhibit a range of eruption styles over time (e.g., progressing between Strombolian, Vulcanian, and Plinian behavior; see Fee et al., 2010 ), which has given rise to terms such as subplinian or violent Strombolian.


Eruption hazards are diverse ( Figure 1.9 ) and may extend more than thousands of kilometers from an active volcano. From the perspective of risk and impact, it is useful to distinguish between near-source and distal hazards. Near-source hazards are far more unpredictable than distal hazards.

Near-source hazards include those that are airborne, such as tephra fallout, volcanic gases, and volcanic projectiles, and those that are transported laterally on or near the ground surface, such as pyroclastic density currents, lava flows, and lahars. Pyroclastic density currents are hot volcanic flows containing mixtures of gas and micron- to meter-sized volcanic particles. They can travel at velocities exceeding 100 km per hour. The heat combined with the high density of material within these flows obliterates objects in their path, making them the most destructive of volcanic hazards. Lava flows also destroy everything in their path, but usually move slowly enough to allow people to get out of the way. Lahars are mixtures of volcanic debris, sediment, and water that can travel many tens of kilometers along valleys and river channels. They may be triggered during an eruption by interaction between volcanic prod-


TABLE 1.3 Characteristics of Different Eruption Styles


ucts and snow, ice, rain, or groundwater. Lahars can be more devastating than the eruption itself. Ballistic blocks are large projectiles that typically fall within 1–5 km from vents.

The largest eruptions create distal hazards. Explosive eruptions produce plumes that are capable of dispersing ash hundreds to thousands of kilometers from the volcano. The thickness of ash deposited depends on the intensity and duration of the eruption and the wind direction. Airborne ash and ash fall are the most severe distal hazards and are likely to affect many more people than near-source hazards. They cause respiratory problems and roof collapse, and also affect transport networks and infrastructure needed to support emergency response. Volcanic ash is a serious risk to air traffic. Several jets fully loaded with passengers have temporarily lost power on all engines after encountering dilute ash clouds (e.g., Guffanti et al., 2010 ). Large lava flows, such as the 1783 Laki eruption in Iceland, emit volcanic gases that create respiratory problems and acidic rain more than 1,000 km from the eruption. Observed impacts of basaltic eruptions in Hawaii and Iceland include regional volcanic haze (“vog”) and acid rain that affect both agriculture and human health (e.g., Thordarson and Self, 2003 ) and fluorine can contaminate grazing land and water supplies (e.g., Cronin et al., 2003 ). Diffuse degassing of CO 2 can lead to deadly concentrations with fatal consequences such as occurred at Mammoth Lakes, California, or cause lakes to erupt, leading to massive CO 2 releases that suffocate people (e.g., Lake Nyos, Cameroon).

Secondary hazards can be more devastating than the initial eruption. Examples include lahars initiated by storms, earthquakes, landslides, and tsunamis from eruptions or flank collapse; volcanic ash remobilized by wind to affect human health and aviation for extended periods of time; and flooding because rain can no longer infiltrate the ground.


Volcanic processes are governed by the laws of mass, momentum, and energy conservation. It is possible to develop models for magmatic and volcanic phenomena based on these laws, given sufficient information on mechanical and thermodynamic properties of the different components and how they interact with each other. Models are being developed for all processes in volcanic systems, including melt transport in the mantle, the evolution of magma bodies within the crust, the ascent of magmas to the surface, and the fate of magma that erupts effusively or explosively.

A central challenge for developing models is that volcanic eruptions are complex multiphase and multicomponent systems that involve interacting processes over a wide range of length and time scales. For example, during storage and ascent, the composition, temperature, and physical properties of magma and host rocks evolve. Bubbles and crystals nucleate and grow in this magma and, in turn, greatly influence the properties of the magmas and lavas. In explosive eruptions, magma fragmentation creates a hot mixture of gas and particles with a wide range of sizes and densities. Magma also interacts with its surroundings: the deformable rocks that surround the magma chamber and conduit, the potentially volatile groundwater and surface water, a changing landscape over which pyroclastic density currents and lava flows travel, and the atmosphere through which eruption columns rise.

Models for volcanic phenomena that involve a small number of processes and that are relatively amenable to direct observation, such as volcanic plumes, are relatively straightforward to develop and test. In contrast, phenomena that occur underground are more difficult to model because there are more interacting processes. In those cases, direct validation is much more challenging and in many cases impossible. Forecasting ash dispersal using plume models is more straightforward and testable than forecasting the onset, duration, and style of eruption using models that seek to explain geophysical and geochemical precursors. In all cases, however, the use of even imperfect models helps improve the understanding of volcanic systems.

Modeling approaches can be divided into three categories:

  • Reduced models make simplifying assumptions about dynamics, heat transfer, and geometry to develop first-order explanations for key properties and processes, such as the velocity of lava flows and pyroclastic density currents, the height of eruption columns, the magma chamber size and depth, the dispersal of tephra, and the ascent of magma in conduits. Well-calibrated or tested reduced models offer a straightforward ap-


proach for combining observations and models in real time in an operational setting (e.g., ash dispersal forecasting for aviation safety). Models may not need to be complex if they capture the most important processes, although simplifications require testing against more comprehensive models and observations.

  • Multiphase and multiphysics models improve scientific understanding of complex processes by invoking fewer assumptions and idealizations than reduced models ( Figure 1.10 ), but at the expense of increased complexity and computational demands. They also require additional components, such as a model for how magma in magma chambers and conduits deforms when stressed; a model for turbulence in pyroclastic density currents and plumes; terms that describe the thermal and mechanical exchange among gases, crystals, and particles; and a description of ash aggregation in eruption columns. A central challenge for multiphysics models is integrating small-scale processes with large-scale dynamics. Many of the models used in volcano science build on understanding developed in other science and engineering fields and for other ap-


plications. Multiphysics and multiscale models benefit from rapidly expanding computational capabilities.

  • Laboratory experiments simulate processes for which the geometry and physical and thermal processes and properties can be scaled ( Mader et al., 2004 ). Such experiments provide insights on fundamental processes, such as crystal dynamics in flowing magmas, entrainment in eruption columns, propagation of dikes, and sedimentation from pyroclastic density currents ( Figure 1.11 ). Experiments have also been used successfully to develop the subsystem models used in numerical simulations, and to validate computer simulations for known inputs and properties.

The great diversity of existing models reflects to a large extent the many interacting processes that operate in volcanic eruptions and the corresponding simplifying assumptions currently required to construct such models. The challenge in developing models is often highlighted in discrepancies between models and observations of natural systems. Nevertheless, eruption models reveal essential processes governing volcanic eruptions, and they provide a basis for interpreting measurements from prehistoric and active eruptions and for closing observational gaps. Mathematical models offer a guide for what observations will be most useful. They may also be used to make quantitative and testable predictions, supporting forecasting and hazard assessment.


Volcanic eruptions are common, with more than 50 volcanic eruptions in the United States alone in the past 31 years. These eruptions can have devastating economic and social consequences, even at great distances from the volcano. Fortunately many eruptions are preceded by unrest that can be detected using ground, airborne, and spaceborne instruments. Data from these instruments, combined with basic understanding of how volcanoes work, form the basis for forecasting eruptions—where, when, how big, how long, and the consequences.

Accurate forecasts of the likelihood and magnitude of an eruption in a specified timeframe are rooted in a scientific understanding of the processes that govern the storage, ascent, and eruption of magma. Yet our understanding of volcanic systems is incomplete and biased by the limited number of volcanoes and eruption styles observed with advanced instrumentation. Volcanic Eruptions and Their Repose, Unrest, Precursors, and Timing identifies key science questions, research and observation priorities, and approaches for building a volcano science community capable of tackling them. This report presents goals for making major advances in volcano science.

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  • Earth Science

A volcano is a landform (usually a mountain) where molten rock erupts through the surface of the planet. There are a huge number of active volcanoes present worldwide. In this article, we will learn about the definition, formation and types of volcanoes.

What Are Volcanoes?

A volcano is a landform, a mountain, where molten rocks erupt through the surface of the planet. The volcano mountain opens downwards to a pool of molten rocks underneath the surface of the earth.


Pressure builds up in the earth’s crust and this is the reason why eruptions occur. Gases and igneous rocks shoot up and splash over or fill the air with lava fragments. The volcano eruption can cause hot ash, lateral blasts and lava flow, mudslides, and more.

Formation of Volcanoes

A volcano mountain is formed by the surface eruption of magma from within the earth’s upper mantle. The magma that erupts to the surface and forms a lava flow that deposits ash. As the volcano continues to erupt, a new layer of lava is added to the surface, accumulating to form a mountain.

Different Stages of Volcanoes

They tend to be conical although there are a variety of forms, depending upon:

  • The nature of the material erupted
  • The type of eruption
  • The amount of change since the eruption

Volcanoes are categorised into three main categories:

  • Active Volcanoes: A volcano will be classified as an active volcano if at the present time it is expected to erupt or is erupting already.
  • Dormant Volcanoes: The classification of volcanoes which is called dormant would be a volcano that is not erupting or predicted to erupt in the near future.
  • Extinct Volcanoes: An extinct volcano is a volcano that no one expects will ever have another eruption.

Reason Behind the Eruption of Volcanoes

The volcano eruption begins with the formation of magma in the lower section of the earth’s crust. The earth’s crust is made up of massive slabs called plates, which fit together like a jigsaw puzzle. The friction during the movement of plates causes earthquakes and volcanic eruptions.


With pressure, it travels upwards with tremendous force hitting solid rocks and other materials and creates a new passage to the earth’s surface. Once the magma reaches the air it is called lava.

Types of Volcanoes

These are grouped into four types:

  • Cinder cones
  • Composite volcanoes
  • Shield volcanoes
  • Lava volcanoes

Cinder Cones: These are the simplest type of volcano. They occur when particles and blobs of lava are ejected from a volcanic vent. The lava is blown violently into the air, and the pieces rain down around the vent. Over time, this builds up a circular or oval-shaped cone, with a bowl-shaped crater at the top. Cinder cone volcanoes rarely grow larger than about 1,000 feet above their surroundings.

Composite Volcanoes: Composite volcanoes are some of the Earth’s grandest mountains, and they are also called stratovolcanoes. They are typically symmetrical cones of large dimension built of alternating layers of lava flows, steep-sided, volcanic ash, blocks, bombs, and cinders and may rise as much as 8,000 feet above their bases.

Shield Volcanoes: A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They have very gentle slopes and are developed horizontally. Shield volcanoes are built by effusive eruptions, which flow out in all directions. They almost never have violent eruptions, with basic lava simply flowing out.

Lava Domes: Lava domes are the fourth type of volcano that we are going to discuss. Unlike composite and shield volcanoes, lava domes are of tiny stature. They are formed when the lava is too viscous to flow to a great distance. As the lava dome slowly grows, the outer surface cools and hardens as the lava continues to pile within. Eventually, the internal pressure can shatter the outer surface, causing loose fragments to spill down its sides. Generally, such lava domes are found on the flanks of larger composite volcanoes.

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Volcanoes: A Very Short Introduction

Volcanoes: A Very Short Introduction

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Volcanoes: A Very Short Introduction explains how volcanoes work and how volcanologists forensically decipher the processes involved. Volcanic eruptions are amongst the most dramatic expressions of the powerful tectonic forces at work in the Earth beneath our feet. However, volcanism encompasses much more than just volcanoes themselves. On a planetary scale, it is an indispensable heat release mechanism; shaping landscapes, releasing gases into the atmosphere, and allowing the conditions for life on Earth. Thus, this VSI also considers how volcanoes interact with other physical processes on the Earth, with life, and with human society.

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Smart English Notes

Essay on Volcano for Students and Children in English

Essay on volcano.

A volcano is a mountain with an opening in the top called a crater which allows hot liquidly magma, volcanic ash and gases to escape out from inside the earth and burst from the crust (surface) when a volcano erupts. The red fiery substance that erupts out of a volcano is ash and molten rock. The volcanic rocks are called Magma. It has a very hot liquid rock which is very deep inside the earth. The Earth pushes magma as lava and when it cools down it becomes solid. The earth’s temperature is always so hot that rock melts to become liquid magma.

Volcanoes have many different shapes. Some are:

Shield Volcanoes formed from the flows of watery lava. They have very gentle slopes e.g. Mount Kilimanjaro is the world’s tallest volcanic mountain.


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Cinder Cones are the very smallest kinds of volcanoes. They are formed when the earth pushes the cinder from its inside. E.g. Paricutin (below) is a cinder cone.

Stratovolcanoes are the most common ones. They are made up of layers of ash and lava from the past eruptions e.g. Mount Fuji and Mount Vesuvius.

When volcanoes erupt, they can have catastrophic consequences for the regions and people near them. The devastation they leave behind accounts for the complete extinction of the surrounding landscape. In the last 500 years, volcanic eruptions have killed around 200,000 people.

Buildings are destroyed, people are displaced, people are killed, plant and animal life is destroyed, and the poisonous gases emitted by volcanoes can cause death and diseases such as pneumonia in those who survive.

The world’s tallest volcano is the Ojos del Salado, Chile’s volcano. The Muano Loa in Hawaii is the world’s largest volcano.

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Essay on Volcanic Eruption | Geography

essay on volcano in short

In this essay we will discuss about: 1. Introduction to Volcanic Eruption 2. Effects of Volcanic Eruption 3. Types.

Essay on Volcanic Eruption

1. essay on the introduction to volcanic eruption:.

Explosive eruptions can inject large quantities of dust and gaseous material (such as sulphur dioxide) into the upper atmosphere, where sulphur dioxide is rapidly converted into sulphuric acid aerosols. Whereas volcanic pollution of the lower atmosphere is removed within days by the effects of rainfall and gravity, stratospheric pollution may remain there for several years, gradually spreading to cover much of the globe.

The volcanic pollution results in a substantial reduction in the direct solar beam, largely through scattering by the highly reflective sulphuric acid aerosols. This can amount to tens of per cent. The reduction, is however, compensated for by an increase in diffuse radiation and by the absorption of outgoing terrestrial radiation (the greenhouse effect). Overall, there is a net reduction of 5 to 10% in energy received at the Earth’s surface.

Clearly, this volcanic pollution affects the energy balance of the atmosphere whilst the dust and aerosols remain in the stratosphere. Observational and modelling studies of the likely effect of recent volcanic eruptions suggest that an individual eruption may cause a global cooling of up to 0.3°C, with the effects lasting 1 to 2 years. Such a cooling event has been observed in the global temperature record in the aftermath of the eruption of Mount Pinatubo in June 1991.

The climate forcing associated with individual eruptions is, however, relatively short-lived compared to the time needed to influence the heat storage of the oceans. The temperature anomaly due to a single volcanic event is thus unlikely to persist or lead, through feedback effects, to significant long-term climatic changes.

Major eruptions have been relatively infrequent this century, so the long-term influence has been slight. The possibility that large eruptions might, during historical and pre-historical times, have occurred with greater frequency, generating long-term cooling, cannot, however, be dismissed. In order to investigate this possibility, long, complete and well-dated records of past volcanic activity are needed. One of the earliest and most comprehensive series is the Dust Veil Index (DVI) of Lamb (1970), which includes eruptions from 1500 to 1900.

When combined with series of acidity measurements in ice cores (due to the presence of sulphuric acid aerosols), they can provide valuable indicators of past eruptions. Using these indicators, a statistical association between volcanic activity and global temperatures during the past millennia has been found. Episodes of relatively high volcanic activity (1250 to 1500 and 1550 to 1700) occur within the period known as the Little Ice Age, whilst the Medieval Warm Period (1100 to 1250) can be linked with a period of lower activity.

Bryson (1989) has suggested a link between longer time scale volcanic variations and the climate fluctuations of the Holocene (last 10,000 years). However, whilst empirical information about temperature changes and volcanic eruptions remains limited, this, and other suggested associations discussed above , must again remain speculative.

Volcanic activity has the ability to affect global climate on still longer time scales. Over periods of millions or even tens of millions of years, increased volcanic activity can emit enormous volumes of greenhouse gases, with the potential of substantial global warming. However, the global cooling effects of sulphur dioxide emissions will act to counter the greenhouse warming, and the resultant climate changes remain uncertain. Much will depend upon the nature of volcanic activity. Basaltic outpourings release far less sulphur dioxide and ash, proportionally, than do the more explosive (silicic) eruptions.

2. Essay on the Effects of Volcanic Eruption:

There are many different types of volcanic eruptions and associated activity – phreatic eruptions (steam-generated eruptions), explosive eruption of high-silica lava (e.g., rhyolite), effusive eruption of low-silica lava (e.g., basalt), pyroclastic flows, lahars (debris flow) and carbon dioxide emission. All of these activities can pose a hazard to humans. Earthquakes, hot springs, fumaroles, mud pots and geysers often accompany volcanic activity.

The concentrations of different volcanic gases can vary considerably from one volcano to the next. Water vapour is typically the most abundant volcanic gas, followed by carbon dioxide and sulphur dioxide. Other principal volcanic gases include hydrogen sulfide, hydrogen chloride, and hydrogen fluoride. A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen, carbon monoxide, halocarbons, organic compounds, and volatile metal chlorides.

Large, explosive volcanic eruptions inject water vapour (H 2 O), carbon dioxide (CO 2 ), sulphur dioxide (SO 2 ), hydrogen chloride (HCl), hydrogen fluoride (HF) and ash (pulverized rock and pumice) into the stratosphere to heights of 16-32 kilometres (10-20 mi) above the Earth’s surface. The most significant impacts from these injections come from the conversion of sulphur dioxide to sulphuric acid (H 2 SO 4 ), which condenses rapidly in the stratosphere to form fine sulfate aerosols.

The aerosols increase the Earth’s albedo—its reflection of radiation from the Sun back into space – and thus cool the Earth’s lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere. Several eruptions during the past century have caused a decline in the average temperature at the Earth’s surface of up to half a degree (Fahrenheit scale) for periods of one to three years — sulphur dioxide from the eruption of Huaynaputina probably caused the Russian famine of 1601 – 1603.

One proposed volcanic winter happened c. 70,000 years ago following the super-eruption of Lake Toba on Sumatra Island in Indonesia. According to the Toba catastrophe theory to which some anthropologists and archeologists subscribe, it had global consequences, killing most humans then alive and creating a population bottleneck that affected the genetic inheritance of all humans today.

The 1815 eruption of Mount Tambora created global climate anomalies that became known as the “Year without a summer” because of the effect on North American and European weather. Agricultural crops failed and livestock died in much of the Northern Hemisphere, resulting in one of the worst famines of the 19th century. The freezing winter of 1740-41, which led to widespread famine in northern Europe, may also owe its origins to a volcanic eruption.

It has been suggested that volcanic activity caused or contributed to the End-Ordovician, Permian-Triassic, Late Devonian mass extinctions, and possibly others. The massive eruptive event which formed the Siberian Traps, one of the largest known volcanic events of the last 500 million years of Earth’s geological history, continued for a million years and is considered to be the likely cause of the “Great Dying” about 250 million years ago, which is estimated to have killed 90% of species existing at the time.

The sulfate aerosols also promote complex chemical reactions on their surfaces that alter chlorine and nitrogen chemical species in the stratosphere. This effect, together with increased stratospheric chlorine levels from chlorofluorocarbon pollution, generates chlorine monoxide (CIO), which destroys ozone (O 3 ). As the aerosols grow and coagulate, they settle down into the upper troposphere where they serve as nuclei for cirrus clouds and further modify the Earth’s radiation balance.

Most of the hydrogen chloride (HCl) and hydrogen fluoride (HF) are dissolved in water droplets in the eruption cloud and quickly fall to the ground as acid rain. The injected ash also falls rapidly from the stratosphere; most of it is removed within several days to a few weeks. Finally, explosive volcanic eruptions release the greenhouse gas carbon dioxide and thus provide a deep source of carbon for biogeochemical cycles.

Gas emissions from volcanoes are a natural contributor to acid rain. Volcanic activity releases about 130 to 230 teragrams (145 million to 255 million short tons) of carbon dioxide each year. Volcanic eruptions may inject aerosols into the Earth’s atmosphere. Large injections may cause visual effects such as unusually colourful sunsets and affect global climate mainly by cooling it.

Volcanic eruptions also provide the benefit of adding nutrients to soil through the weathering process of volcanic rocks. These fertile soils assist the growth of plants and various crops. Volcanic eruptions can also create new islands, as the magma cools and solidifies upon contact with the water.

Ash thrown into the air by eruptions can present a hazard to aircraft, especially jet aircraft where the particles can be melted by the high operating temperature. Dangerous encounters in 1982 after the eruption of Galunggung in Indonesia, and 1989 after the eruption of Mount Redoubt in Alaska raised awareness of this phenomenon. Nine Volcanic Ash Advisory Centers were established by the International Civil Aviation Organization to monitor ash clouds and advise pilots accordingly. The 2010 eruption of Eyjafjallajokull caused major disruptions to air travel in Europe.

3. Essay on the Types of Volcanic Eruption:

During a volcanic eruption, lava, tephra (ash, lapilli, solid chunks of rock), and various gases, are expelled from a volcanic vent or fissure.

Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behaviour has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types.

1. Magmatic Eruptions:

Magmatic eruptions produce juvenile clasts during explosive decompression from gas release. They range in size from the relatively small fire fountains on Hawaii to > 30 km Ultra Plinian eruption columns, bigger than the eruption that buried Pompeii.

2. Strombolian Eruptions:

Strombolian eruptions are relatively low-level volcanic eruptions, named after the Italian volcano Stromboli, where such eruptions consist of ejection of incandescent cinder, lapilli and lava bombs to altitudes of tens to hundreds of meters. They are small to medium in volume, with sporadic violence.

They are defined as “…Mildly explosive at discrete but fairly regular intervals of seconds to minutes…”

The tephra typically glows red when leaving the vent, but its surface cools and assumes a dark to black colour and may significantly solidify before impact. The tephra accumulates in the vicinity of the vent, forming a cinder cone. Cinder is the most common product, the amount of volcanic ash is typically rather minor. The lava flows are more viscous and therefore shorter and thicker, than the corresponding Hawaiian eruptions; it may or may not be accompanied by production of pyroclastic rock.

Instead the gas coalesces into bubbles, called slugs, that grow large enough to rise through the magma column, bursting near the top due to the decrease in pressure and throwing magma into the air. Each episode thus releases volcanic gases, sometimes as frequently as a few minutes apart. Gas slugs can form as deep as 3 kilometers, making them difficult to predict.

Strombolian eruptive activity can be very long-lasting because the conduit system is not strongly affected by the eruptive activity, so that the eruptive system can repeatedly reset itself. For example, the Paricutin volcano erupted continuously between 1943-1952, Mount Erebus, Antarctica has produced Strombolian eruptions for at least many decades, and Stromboli itself has been producing Strombolian eruptions for several thousand years.

3. Vulcanian Eruption:

Vulcanian eruptions are a type of volcanic eruption characterised by a dense cloud of ash-laden gas exploding from the crater and rising high above the peak. They usually commence with phreatomagmatic eruptions which can be extremely noisy due the rising magma heating water in the ground. This is usually followed by the explosive clearing of the vent and the eruption column is dirty grey to black as old weathered rocks are blasted out of the vent. As the vent clears, further ash clouds become grey-white and creamy in colour, with convolution of the ash similar to those of plinian eruptions.

The tephra is dispersed over a wider area than that from Strombolian eruptions. The pyroclastic rock and the base surge deposits form an ash volcanic cone, while the ash covers a large surrounding area. The eruption ends with a flow of viscous lava. Vulcanian eruptions may throw large metre-size blocks several hundred metres, occasionally up to several kilometres.

The term Vulcanian was first used by Giuseppe Mercalli, witnessing the 1888-1890 eruptions on the island of Vulcano. His description of the eruption style is now used all over the world. Mercalli described vulcanian eruptions as “…Explosions like cannon fire at irregular intervals…”

Their explosive nature is due to increased silica content of the magma. Almost all types of magma can be involved, but magma with about 55% or more silica (basalt-andesite) is most common. Increasing silica levels increase the viscosity of the magma which means increased explosiveness.

Vulcanian eruptions are dangerous to persons within several hundred metres of the vent. One feature of this type of eruption is the “Volcanic bomb.” These can be blocks often 2 to 3 m in dimensions. At Galeras a vulcanian eruption ejected bombs which impacted with several volcanologists who were in the crater and many died or suffered terrible.

4. Pel é an Eruption:

Peléan eruptions are a type of volcanic eruption. They can occur when viscous magma, typically of rhyolitic or andesitic type, is involved, and share some similarities with Vulcanian eruptions. The most important characteristics of a Peléan eruption are the presence of a glowing avalanche of hot volcanic ash, a pyroclastic flow. Formation of lava domes is another characteristical feature. Short flows of ash or creation of pumice cones may be observed as well.

The initial phases of eruption are characterised by pyroclastic flows. The tephra deposits have lower volume and range than the corresponding Plinian and Vulcanian eruptions. The viscous magma then forms a steep-sided dome or volcanic spine in the volcano’s vent.

The dome may later collapse, resulting in flows of ash and hot blocks. The eruption cycle is usually completed in few years, but in some cases may continue for decades, like in the case of Santiaguito. The 1902 explosion of Mount Pelée is the first described case of a Peléan eruption, and gave it its name.

Some other examples include the following:

i. The 1948-1951 eruption of Hibok-Hibok;

ii. The 1951 eruption of Mount Lamington, which remains the most detailed observation of this kind;

iii. The 1956 eruption of Bezymianny;

iv. The 1968 eruption of Mayon Volcano;

v. And the 1980 eruption of Mount St. Helens.

5. Hawaiian Eruption:

A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relative gentle, low level eruption, so called because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high temperature at the vent. Very little amount of volcanic ash is produced. This type of eruption occurs most often on hotspot volcanoes such as Kilauea, though it can occur near subduction zones (e.g. Medicine Lake Volcano in California, United States.) Another example of Hawaiian eruptions occurred on Surtsey from 1964 to 1967, when molten lava flowed from the crater to the sea.

Hawaiian eruptions may occur along fissure vents, such as during the eruption of Mauna Loa Volcano in 1950, or at a central vent, such as during the 1959 eruption in Kilauea Iki Crater, which created a lava fountain 580 meters (1,900 ft) high and formed a 38 meter cone named Pu’u Pua’i. In fissure-type eruptions, lava spurts from a fissure on the volcano’s rift zone and feeds lava streams that flow downslope. In central-vent eruptions, a fountain of lava can spurt to a height of 300 meters or more (heights of 1600 meters were reported for the 1986 eruption of Mount Mihara on Izu Ôshima, Japan).

Hawaiian eruptions usually start by formation of a crack in the ground from which a curtain of incandescent magma or several closely spaced magma fountains appear. The lava can overflow the fissure and form pahoehoe style of flows. Eruptions from a central cone can form small lightly sloped shield volcanoes, for example the Mauna Loa.

6. Surtseyan Eruption:

A Surtseyan eruption is a type of volcanic eruption that takes place in shallow seas or lakes. It is named after the island of Surtsey off the southern coast of Iceland.

These eruptions are commonly phreatomagmatic eruptions, representing violent explosions caused by rising basaltic or andesitic magma coming into contact with abundant, shallow groundwater or surface water. Tuff rings, pyroclastic cones of primarily ash, are built by explosive disruption of rapidly cooled magma. Other examples of these volcanoes-Capelinhos, Faial Island, Azores; and Taal Volcano, Batangas, Philippines.

Several Specific Characteristics:

i. Physical nature of magma – viscous; basaltic.

ii. Character of explosive activity – violent ejection of solid, warm fragments of new magma; continuous or rhythmic explosions; base surges.

iii. Nature of effusive activity – short, locally pillowed, lava flows; lavas may be rare.

iv. Nature of dominant ejecta – lithic, blocks and ash; often accretionary lapilli; spatter, fusiform bombs and lapilli absent.

v. Structures built around vent – tuff rings

7. Plinian Eruption:

Plinian eruptions, also known as ‘Vesuvian eruptions’, are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79, which killed Pliny the Elder.

Plinian eruptions are marked by columns of gas and volcanic ash extending high into the stratosphere, a high layer of the atmosphere. The key characteristics are ejection of large amount of pumice and very powerful continuous gas blast eruptions. Key characteristics are ejection of large amount of pumice and very powerful continuous gas blast eruptions.

Short eruptions can end in less than a day, but longer events can take several days to months. The longer eruptions begin with production of clouds of volcanic ash, sometimes with pyroclastic flows. The amount of magma erupted can be so large that the top of the volcano may collapse, resulting in a caldera. Fine ash can deposit over large areas. Plinian eruptions are often accompanied by loud noises, such as those generated by Krakatoa.

The lava is usually rhyolitic and rich in silicates. Basaltic lavas are unusual for Plinian eruptions; the most recent example is the 1886 eruption of Mount Tarawera.

8. Phreatomagmatic Eruptions :

Phreatomagmatic eruptions are the result of thermal contraction from chilling on contact with water. The products of phreatomagmatic eruptions are believed to have more regular shard shapes and be finer grained than the products of magmatic eruptions because of the different eruptive mechanism.

There is debate about the exact nature of the eruptive style. Fuel-coolant reactions may be more critical to the explosive nature than thermal contraction. Fuel coolant reactions fragment the material in contact with a coolant by propagating stress waves widening cracks and increasing surface area leading to rapid cooling rates and explosive thermal contraction.

9. Submarine Eruption:

A submarine eruption is a type of volcanic eruption where lava erupts under an ocean. Most of the Earth’s volcanic eruptions are submarine eruptions, but few have been documented because of the difficulty in monitoring submarine volcanoes. Most submarine eruptions occur at mid-ocean ridges and near hotspots.

10. Sub-Glacial Eruption:

A sub-glacial eruption is a volcanic eruption that has occurred under ice, or under a glacier. Sub-glacial eruptions can cause dangerous floods, lahars and create hyaloclastite and pillow lava. Only five of these types of eruptions have been recorded in recent history. Sub-glacial eruptions sometimes form a sub-glacial volcano called a tuya. Tuyas in Iceland are called Table Mountains because of their flat tops. Tuya Butte, in northern British Columbia is an example of a tuya.

A tuya may be recognized by its stratigraphy, which typically consists of a basal layer of pillow basalts overlain by hyaloclastite breccia, tuff, and capped off by a lava flow. The pillow lavas formed first as a result of subaqueous eruptions in glacial melt-water. Once the vent reaches shallower water, eruptions become phreatomagmatic, depositing the hyaloclastite breccia. Once the volcano emerges through the ice, it erupt lava, forming the flat capping layer of a tuya.

The thermodynamics of sub-glacial eruptions are very poorly understood. Rare published studies indicate that plenty of heat is contained in the erupted lava, with 1 unit-volume of magma sufficient to melt about 10 units of ice. However, the rapidity by which ice is melted is unexplained, and in real eruptions the rate is at least an order of magnitude faster than existing predictions.

Antarctica eruption-On January, 2008, the British Antarctic Survey that scientists led by Hugh Corr and David Vaughan, reported (in the journal Nature Geoscience) that 2,200 years ago, a volcano erupted under Antarctica ice sheet (based on airborne survey with radar images).

The biggest eruption in the last 10,000 years, the volcanic ash was found deposited on the ice surface under the Hudson Mountains, close to Pine Island Glacier. The ash covered an area the size of New Hampshire and was probably deposited from a 12 km high ash plume. Researchers have detected a mountainous peak some 100 meters beneath the surface believed to be the top of the tuya associated with this eruption.

11. Phreatic Eruption :

A phreatic eruption, also called a phreatic explosion or ultra-vulcanian eruption occurs when rising magma makes contact with ground or surface water. The extreme temperature of the magma [anywhere from 600 to 1,170°C (1,112 to 2,138°F)] causes near-instantaneous evaporation to steam resulting in an explosion of steam, water, ash, rock, and volcanic bombs. At Mount St. Helens hundreds of steam explosions preceded a 1980 plinian eruption of the volcano. A less intense geothermal event may result in a mud volcano. In 1949, Thomas Jaggar described this type of activity as a steam-blast eruption.

Phreatic eruptions typically include steam and rock fragments; the inclusion of lava is unusual. The temperature of the fragments can range from cold to incandescent. If molten material is included, the term phreatomagmatic may be used. These eruptions occasionally create broad, low-relief craters called maars. Phreatic explosions can be accompanied by carbon dioxide or hydrogen sulfide gas emissions. The former can asphyxiate at sufficient concentration; the latter is a broad spectrum poison. A 1979 phreatic eruption on the island of Java killed 149 people, most of whom were overcome by poisonous gases.

It is believed the 1883 eruption of Krakatoa, which obliterated most of the volcanic island and created the loudest sound in recorded history, was a phreatic event. Kilauea, in Hawaii, has a long record of phreatic explosions; a 1924 phreatic eruption hurled rocks estimated at eight tons up to a distance of one kilometer. Additional examples are the 1963-65 eruption of Surtsey, the 1965 eruption of Taal Volcano, and the 1982 Mount Tarumae eruption.

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A mountain at the end of a snowy expanse.

Empty Roads and Spewing Lava: 4 Months Into Iceland’s Eruptions

Volcanic eruptions are continuing in the Reykjanes Peninsula in Iceland. Streets are empty and the Blue Lagoon resort remains closed.

The plume from a volcanic eruption as viewed from Route 41 near the town of Kalfatjorn in western Iceland on Wednesday. Credit...

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Claire Moses

By Claire Moses

Photographs by Tony Cenicola

  • March 29, 2024

The scene is as spectacular as it is dangerous: flowing rivers of shimmering lava and a dramatic plume of toxic gas.

That image has been the reality for much of the past four months in the Reykjanes Peninsula in southern Iceland, which the country’s tourism website has called a “geological wonder where lighthouses outnumber villages.”

A series of volcano eruptions began in December after hundreds of earthquakes shook the peninsula, cracking open a fissure that sent lava spewing into a residential neighborhood for the first time in more than four decades. The volcanic system has erupted several more times since then.

Grindavik, a fishing town of more than 3,500 people about 30 miles southwest of the country’s capital, Reykjavik, has been evacuated, and the nearby Blue Lagoon, a popular geothermal spa, has been largely closed since early November.

A mountain looms over a collection of short buildings that stand amid a snowy, rocky terrain.

While much of life goes on in the rest of Iceland, the eruptions have had an effect beyond the peninsula, disrupting the tourism operations of a country that relies heavily on visitors .

Icelandair said it has seen a negative impact on bookings because of the threat of the eruptions. While the overall number of passengers carried by the airline in February increased compared to last year, the number flying to Iceland dropped by 8 percent, according to the airline.

While the eruptions continue, the situation has been “steady” this week, according to the Icelandic Meteorological Office, the country’s weather service. But lava continues to flow from three craters toward Grindavik, the service said.

The eruptions also produce high levels of gas pollution. The concentration of sulfur dioxide in the air is “very unhealthy,” according to the Met Office, which added that “people are likely to experience respiratory symptoms if exposed.”

The Blue Lagoon, a spa and hotel complex in Grindavik, is closed at the moment. It first temporarily shut its doors in November after thousands of earthquakes, signs of the impending eruption, hit the region.

The resort has reopened occasionally, but has been closed for more than 85 days since then, the hotel said in an email. It is currently on its sixth closure since Nov. 9.

Lava damaged several houses in Grindavik when it breached a defense wall that was supposed to route it away from the town.

Around the town, earthquakes caused cracks in the streets. Breaks in the roads have been filled with gravel.

The authorities continue to warn visitors to stay away from the eruption site. “The edges of the new lava field are unstable and large chunks of lava can fall suddenly,” the Met Office said.

Claire Moses is a reporter for the Express desk in London. More about Claire Moses

Tony Cenicola is a Times photographer. More about Tony Cenicola



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