volcano essay 200 words brainly

Activity 1: Volcano: Advantage or Disadvantage? Make a short essay about the statement: Volcano: Advantage or Disadvantage? To get 50 points, include the following words or phrases below in your essay and it must have a minimum of 200 words. -volcano - geothermal power plant - volcanic eruption -advantages -disadvantages - National Disaster Risk Reduction and Management Council (NDRRMC) - Philippine Institute of Volcanology and Seismology (PHIVOLCS) - geothermal energy​ -cost -steam

Provide energy

Volcanoes provide resources for energy extraction, also called geothermal resources.  Heat from the earth's crust is being converted to energy.  The big advantages to this type of energy are that it is very clean and the resources are nearly inexhaustible.Fertile soil

When a volcano erupts it throws out a lot of ash.  At short notice this ash can be very harmful to the environment, but on the long term the ash layer, which contains many useful minerals, will be converted to a very fertile soil. Nearly everywhere volcanoes are located people use the rich soil for farming.  Even after an eruption people still return because of the fertile soil around the volcano.Tourism

Volcanoes attract millions of visitors every year, for different reasons. Around the volcano may be warm bathing lakes, hot springs, bubbling mud pools and steam vents. Tourism creates jobs in shops, restaurants, hotels and tourist centers / national parks. Locals economies can profit from volcanism throughout the year, whereas skiing, for example, has only a limited winter season.                                                                                                                                

DISADVANTEGES•Sea - during a volcanic eruption earthquakes happen, and tsunamis may be created. Also, if it is a volcanic island, the island may be destroyed, and there is no escape.

•Lava flow - these are very slow moving, but destructive as they cannot be stopped and they set fire to everything in their path.

•Pyroclastic flow - these are impossible to outrun, travelling at about 300 km/h, and are extremely destructive.

•Mudflow/lahar - these are mud rivers that have the consistency of cement, and destroy everything in their path, including buildings.                                                                  

Explanation:

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

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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Science News Explores

Explainer: the volcano basics.

All volcanoes are not alike, but all do deserve respect

An ash burst coming from Washington’s Mount St. Helens in May 1982.

Lyn Topinka/ USGS

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By Sid Perkins

October 1, 2014 at 12:57 pm

A volcano is a spot in Earth’s crust where molten rock, volcanic ash and certain types of gases escape from an underground chamber. Magma is the name for that molten rock when it’s below ground. Scientists call it lava once that liquid rock erupts from the ground — and may start flowing across Earth’s surface. (It’s still “lava” even after it’s cooled and solidified.)       

Roughly 1,500 potentially active volcanoes exist across our planet, according to scientists at the U.S. Geological Survey, or USGS. About 500 volcanoes have erupted since humans have been keeping records.

Of all volcanoes that have erupted in the past 10,000 years, roughly 10 percent reside in the United States. Most of them exist in Alaska (particularly in the Aleutian Island chain), in Hawaii and in the Cascade Range of the Pacific Northwest.  

But volcanoes are not just an Earthly phenomenon. Several large volcanoes rise above the surface of Mars. Mercury and Venus both show signs of past volcanism. And the most volcanically active orb in the solar system is not Earth, but Io. It’s the innermost of the four largest moons of Jupiter. Indeed, Io has more than 400 volcanoes, some of which spew plumes of sulfur-rich material 500 kilometers (about 300 miles) into space.

(Fun fact: The surface of Io is small, only about 4.5 times the area of the United States. So its volcano density would be about comparable to 90 continuously active volcanoes erupting across the United States.)

Where do volcanoes form?

Volcanoes can form on land or below the sea. Indeed, Earth’s biggest volcano lies submerged a mile below the ocean’s surface. Certain spots on our planet’s surface are especially susceptible to volcano formation.

Most volcanoes, for instance, form at or near the edges — or boundaries — of Earth’s tectonic plates . These plates are large slabs of crust that jostle and scrape past each other. Their movement is driven largely by the circulation of the scalding, liquid rock in Earth’s mantle. That mantle is thousands of kilometers (miles) thick. It lies between our planet’s outer crust and its molten outer core.

The edge of one tectonic plate may begin sliding beneath a neighboring one. This process is known as subduction . The downward-moving plate carries rock back toward the mantle, where temperatures and pressures are very high. This disappearing, water-filled rock melts easily.

Because the liquid rock is lighter than the surrounding material, it will try to float back up toward Earth’s surface. When it finds a weak spot, it breaks through. This creates a new volcano.

Many of the world’s active volcanoes reside along an arc. Known as the “Ring of Fire,” this arc surrounds the Pacific Ocean. (In fact, it was the fiery lava erupting from volcanoes all along this boundary that inspired the arc’s nickname.) Along almost all sections of the Ring of Fire, a tectonic plate is shoving beneath its neighbor.

Many more of the world’s volcanoes, especially those located far from the edge of any plate, develop over or near broad plumes of molten material that rise up from Earth’s outer core. These are called “mantle plumes.” They behave very much like the blobs of hot material in a “lava lamp.” (Those blobs rise from the heat source at the bottom of the lamp. When they cool, they fall back towards the bottom.)

Many oceanic islands are volcanoes. The Hawaiian Islands formed over one well-known mantle plume. As the Pacific plate gradually moved northwest over that plume, a series of new volcanoes punched their way through to the surface. This created the island chain. Today, that mantle plume fuels volcanic activity on the island of Hawaii. It’s the youngest island in the chain. 

A small fraction of the world’s volcanoes form where Earth’s crust is being stretched apart, as it is in East Africa. Tanzania’s Mount Kilimanjaro is a prime example. In these thin spots, molten rock can break through to the surface and erupt. The lava they exude can build, layer upon layer, to create tall peaks.

How deadly are volcanoes?

Throughout recorded history, volcanoes have probably killed about 275,000 people, according to a 2001 study led by researchers at the Smithsonian Institution in Washington, D.C. Scientists estimate that almost 80,000 of the deaths — not quite one in every three — were caused by pyroclastic flows . These hot clouds of ash and rock sweep down a volcano’s slopes at hurricane speeds. Volcano-triggered tsunamis likely triggered another 55,000 deaths. These big waves can pose a threat to people living along coasts even hundreds of kilometers (miles) from the volcanic activity.

Many volcano-related deaths happen in the first 24 hours of an eruption. But a surprisingly high fraction — about two in every three — occurs more than a month after an eruption begins. These victims may succumb to indirect effects. Such effects might include famines when crops fail. Or people may return to a danger zone and then die in landslides or during follow-up eruptions.

Each of the past three centuries has seen a doubling of fatal volcanic eruptions. But volcanic activity has remained roughly constant during recent centuries. This suggests, the scientists say, that much of the increase in fatalities is due to population growth or to the decision of people to live (and play) near (or on) volcanoes.

For instance, nearly 50 hikers died on September 27, 2014, while climbing Japan’s Mount Ontake. The volcano unexpectedly erupted . Some 200 other hikers escaped to safety.

How big can a volcanic eruption be?

Some volcanic eruptions amount to small, relatively harmless puffs of steam and ash. At the other extreme are cataclysmic events. These can last for days to months, changing climate across the globe.

Early in the 1980s, researchers invented a scale to describe the strength of a volcanic eruption. This scale, which runs from 0 to 8, is called the Volcanic Explosivity Index (VEI). Each eruption gets a number based on the amount of ash spewed, the height of the ash plume and the power of the eruption.

For each number between 2 and 8, an increase of 1 corresponds to an eruption that’s ten times more powerful. For example, a VEI-2 eruption releases at least 1 million cubic meters (35 million cubic feet) of ash and lava. So a VEI-3 eruption releases at least 10 million cubic meters of material.

Small eruptions pose a threat only to nearby regions. Small clouds of ash might wipe out a few farms and buildings on the slopes of a volcano or on the surrounding plains. They also might smother crops or grazing areas. That could trigger a local famine.

Larger eruptions pose different types of hazards. Their ash can spew dozens of kilometers from the peak. If the volcano is topped with snow or ice, lava flows can melt it. That can create a thick mix of mud, ash, soil and rocks. Called a lahar, this material has a consistency like wet, newly mixed concrete. It can flow far from the peak — and destroy anything in its path.

Nevado del Ruiz is a volcano in the South American nation of Colombia. Its eruption in 1985 created lahars that destroyed 5,000 homes and killed more than 23,000 people. The lahars’ effects were felt in towns up to 50 kilometers (31 miles) from the volcano. 

A volcano’s threats can even extend into the sky. Ash plumes can reach altitudes at which jets fly. If ash (which actually is tiny bits of broken rock) gets sucked into an aircraft’s engine, high temperatures there can re-melt the ash. Those droplets can then solidify when they hit the engine’s turbine blades.

This will disrupt the flow of air around those blades, causing the engines to fail. (That’s not something anyone would like to experience when they are several kilometers in the air!) What’s more, flying into a cloud of ash at cruising speed can effectively sandblast a plane’s front windows to the point that pilots can no longer see through them.

Finally, a really big eruption can affect global climate. In a very explosive eruption, particles of ash can reach altitudes above where rains are available to quickly wash them from the air. Now, these ash bits can spread around the world, diminishing how much sunlight reaches Earth’s surface. This will cool temperatures globally, sometimes for many months.

Besides spewing ash, volcanoes also emit a witches’ brew of noxious gases, including carbon dioxide and sulfur dioxide. When sulfur dioxide reacts with the water vapor spewed by eruptions, it creates droplets of sulfuric acid. And if those droplets make it to high altitude, they too can scatter sunlight back into space, cooling climate even more.

It’s happened.

In 1600, for instance, a little-known volcano in the South American nation of Peru erupted. Its ash plumes cooled global climate so much that many parts of Europe had record-setting snowfalls the next winter. Large portions of Europe also suffered unprecedented floods the next spring (when the snow melted). Heavy rains and cool temperatures during the summer of 1601 ensured massive crop failures in Russia. The famines that followed lasted through 1603.

In the end, this one eruption’s impacts resulted in the deaths of an estimated 2 million people — many of them half a world away. (Scientists didn’t make the connection between the Peruvian eruption and the Russian famines until several years after the 2001 study that estimated the death tolls from all volcanoes in recorded history.)

More Stories from Science News Explores on Earth

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Summer ‘space hurricanes’ are emerging high above Earth’s magnetic poles

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Home — Essay Samples — Environment — Volcano — Exploring Volcanoes: From Formation to Societal Resilience

Exploring Volcanoes: from Formation to Societal Resilience

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Updated: 29 March, 2024

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Geography Notes

Essay on volcanoes: top 7 essays on volcanoes| disasters | geography.

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Here is a compilation of essays on ‘Volcanoes’ for class 7, 8, 9, 10. Find paragraphs, long and short essays on ‘Volcanoes’ especially written for school students.

Essay on Volcanoes

Essay Contents:

• Essay on the World Distribution of Volcanoes

Essay # 1. Concept of Vulcanicity :

The terms volcanoes, mechanism of volcanoes and vulcanicity are more or less synonymous to com­mon man but these have different connotations in geology and geography. ‘A volcano is a vent, or opening, usually circular or nearly circular in form, through which heated materials consisting of gases, water, liquid lava and fragments of rocks are ejected from the highly heated interior to the surface of the earth’.

According to A. Holmes and D.L. Holmes (1978) a volcano is essentially a fissure or vent, communicating with the interior, from which flows of lava, fountains of incandescent spray or explosive bursts of gases and volcanic ashes are erupted at the surface.

On the other hand, ‘the term vulcanicity covers all those processes in which molten rock mate­rial or magma rises into the crust or is poured out on its surface, there to solidify as a crystalline or semicrystaline rock’.

Some scientists have also used the term of vulcanism as synonym to the term of vulcanicity. For example, P.G. Worcester (1948) has maintained that ‘vulcanism includes all phenomena connected with the movement of heated material from the interior to or towards the surface of the earth.’

It is apparent from the above definitions of volcano and vulcanicity (vulcanism) that the later (vulcanicity) is a broader mechanism which is related to both the environments, endogenetic and exogenetic. In other words, vulcanicity includes all those processes and mechanisms which are related to the origin of magmas, gases and vapour, their ascent and appear­ance on the earth’s surface in various forms.

It is evident that the vulcanicity has two components which operate below the crustal surface and above the crust. The endogenetic mechanism of vulcanicity includes the creation of hot and liquid magmas and gases in the mantle and the crust, their expansion and upward ascent, their intrusion, cooling and solidification in various forms below the crustal surface (e.g., batholiths, laccoliths, sills, dykes, lopoliths, phacoliths etc.) while the exogenous mechanism includes the process of appearance of lava, volcanic dusts and ashes, fragmen­tal material, mud smoke etc. in different forms e.g., fissure flow or lava flood (fissure or quiet type of volcanic eruption), violent explosion (central type of volcanic eruption), hot springs, geysers, fumaroles, solfatara, mud volcanoes etc. It may be, thus, con­cluded that the vulcanicity is a broader mechanism which includes several events and processes which work below the crust as well as above the crust whereas volcano is a part of vulcanicity (vulcanism).

Essay # 2. Components of Volcanoes :

Volcanoes of explosive type or central eruption type are associated with the accumulated volcanic materials in the form of cones which are called as volcanic cones or simply volcanic mountains. There is a vent or opening, of circular or nearly circular shape, almost in the centre of the summital part of the cone.

This vent is called as volcanic vent or volcanic mouth which is connected with the interior part of the earth by a narrow pipe, which is called as volcanic pipe. Vol­canic materials of various sorts are ejected through this pipe and the vent situated at the top of the pipe. The enlarged form of the volcanic vent is known as volcanic crater and caldera. Volcanic materials include lavas, volcanic dusts and ashes, fragmental materials etc. (fig. 9.1).

Essay # 3. Types of Volcanoes:

There is a wide range of variations in the mode of volcanic eruptions and their periodicity.

Thus, vocanoes are classified on the basis of:

(i) The mode of eruption, and

(ii) The period of eruption and the nature of their activities.

(i) Classification on the Basis of the Nature of Volcanic Eruptions :

Volcanic eruptions occur mostly in two ways viz.:

(i) Violent and explosive type of eruption of lavas, volcanic dusts, volcanic ashes and fragmental materi­als through a narrow pipe and small opening under the impact of violent gases, and

(ii) Quiet type or fissure eruption along a long fracture or fissure or fault due to weak gases and huge volume of lavas.

Thus, on the basis of the nature and intensity of eruptions volcanoes are divided into two types e.g.:

(1) Central eruption type or explosive eruption type, and

(2) Fissure eruption type or quiet eruption type.

(1) Volcanoes of central eruption type:

Central eruption type or explosive eruption type of volcanoes occurs through a central pipe and small opening by breaking and blowing off crustal surface due to violent and explosive gases accumulated deep within the earth. The eruption is so rapid and violent that huge quantity of volcanic materials consisting of lavas, volcanic dusts and ashes, fragmental materials etc., are ejected upto thousands of metres in the sky.

These materials after falling down accumulate around the volcanic vent and form volcanic cones of various sorts. Such volcanoes are very destructive and are disastrous natural hazards.

Explosive volcances are further divided into 5 sub-types on the basis of difference in the intensity of eruption, variations in the ejected volcanic material and the period of the action of volcanic events as given below:

(i) Hawaiin type of volcanoes:

Such volcanoes erupt quietly due to less viscous lavas and non-violent nature of gases. Rounded blisters of hot and glowing mass/boll of lavas (blebs of molten lava) when caught by a strong wind glide in the air like red and glowing hairs. The Hawaiin people consider these long glassy threads of red molten lava as Pele’s hair (Pele is the Hawaiin goddess of fire).

Such volcanoes have been named as Hawaiin type because of the fact that such eruptions are of very common occurrence on Hawaii island. The eruption of Kilavea volcano of the southern Hawaii island in 1959-60 continued for seven days (from November 14 to 20, 1959) when about 30 mil­lion cubic metres of lavas poured out.

The intermittent eruptions continued upto December 21, 1959, when the volcano became dormant. It again erupted on January 13, 1960 and about 100 million cubic metres of lavas were poured out of one kilometre long fissure.

(ii) Strombolian type of volcanoes:

Such volca-noes, named after Stromboli volcano of Lipari island in the Mediterranean Sea, erupt with moderate inten­sity. Besides lava, other volcanic materials like pum­ice, scoria, bombs etc. are also ejected upto greater height in the sky. These materials again fall down in the volcanic craters. The eruptions are almost rhythemic or nearly continuous in nature but sometimes they are interrupted by long intervals.

(iii) Vulcanian type of volcanoes:

These are named after Vulcano of Lipari island in the Mediterranean Sea. Such volcanoes erupt with great force and inten­sity. The lavas are so viscous and pasty that these are quickly solidified and hardened between two eruptions and thus they crust over (plug) the volcanic vents.

These lava crusts obstruct the escape of violent gases during next eruption. Consequently, the violent gases break and shatter the lava crusts into angular fragments and appear in the sky as ash-laden volcanic clouds of dark and often black colour assuming a convoluted or cauli­flower shape (fig. 9.2c).

(iv) Peleean type of volcanoes:

These are named after the Pelee volcano of Martinique Island in the Caribbean Sea. These are the most violent and most explosive type of volcanoes. The ejected lavas are most viscous and pasty. Obstructive domes of lava are formed above the conduits of the volcanoes. Thus, every successive eruption has to blow off these lava domes. Consequently, each successive eruption oc­curs with greater force and intensity making roaring noise.

The most disastrous volcanic eruption of Mount Pelee on May 8,1902 destroyed the whole of the town of St. Pierre killing all the 28,000 inhabitants leaving behind only two survivors to mourn the sad demise of their brethren. Such type of disastrous violent erup­tions are named as nuee ardente meaning thereby ‘glowing cloud’ of hot gases, lavas etc., coming out of a vocanic eruption.

The nuee ardente spread laterally out of the mountain (Mount Pelee) with great speed which caused disastrous avalanches on the hillslopes which plunged down the slope at a speed of about 100 kilometres per hour. The annihilating explosive erup­tion of Krakatoa volcano in 1883 in Krakatoa Island located in Sunda Strait between Java and Sumatra is another example of violent volcanic eruption of this type.

(v) Visuvious type of volcanoes:

These are more or less similar to Vulcanian and Strombolian type of volcanoes, the difference lies only in the intensity of expulsion of lavas and gases. There is extremely vio­lent expulsion of magma due to enormous volume of explosive gases.

Volcanic materials are thrown up to greater height in the sky. The ejected enormous vol­ume of gases and ashes forms thick clouds of ‘cauli­flower form.’ The most destructive type of eruption is called as Plinian type because of the fact that such type of eruption was first observed by Plini in 79 A.D.

(2) Fissure eruption type of volcanoes:

Such vol­canoes occur along a long fracture, fault and fissure and there is slow upwelling of magma from below and the resultant lavas spread over the ground surface. The speed of lava movement depends on the nature of magma, volume of magma, slope of ground surface and temperature conditions. The Laki fissure eruption of 1783 in Iceland was so quick and enormous that huge volume of lavas measuring about 15 cubic kilometers was poured out from a 28-km long fissure. The lava flow was so enormous that it travelled a distance of 350 kilometres.

(ii) Classification on the Basis of Periodicity of Erup­tions :

Volcanoes are divided into 3 types on the basis of period of eruption and interval period between two eruptions of a volcano e.g.:

(i) Active volcanoes,

(ii) Dormant volcanoes, and

(iii) Extinct volcanoes.

(i) Active Volcanoes:

Active volcanoes are those which constantly eject volcanic lavas, gases, ashes and fragmental ma­terials. It is estimated that there are about more than 500 volcanoes in the world. Etna and Stromboli of the Mediterranean Sea are the most significant examples of this category. Stromboli Volcano is known as Light House of the Mediterranean because of continuous emission of burning and luminous incandescent gases.

Most of the active volcanoes are found along the mid- oceanic ridges representing divergent plate margins (constructive plate margins) and convergent plate margins (destructive plate margins represented by eastern and western margins of the Pacific Ocean). The latest eruption took place from Pinatubo volcano in June 1991 in Philippines. Mayon of Philippines re-erupted in Feb. 2000.

(ii) Dormant Volcanoes:

Dormant volcanoes are those which become quiet after their eruptions for some time and there are no indications for future eruptions but suddenly they erupt very violently and cause enormous damage to human health and wealth.

Visuvious volcano is the best example of dormant volcano which erupted first in 79 A.D., then it kept quiet upto 1631 A.D., when it suddenly exploded with great force. The subsequent eruptions occurred in 1803, 1872, 1906, 1927, 1928, and 1929.

(iii) Extinct volcanoes:

The volcanoes are con­sidered extinct when there are no indications of future eruption. The crater is filled up with water and lakes are formed. It may be pointed out that no volcano can be declared permanently dead as no one knows, what is happening below the ground surface.

Essay # 4. Mechanisms and Causes of Vulcanism:

As stated earlier the volcanic eruptions are asso­ciated with weaker zones of the earth surfaces repre­sented by mountain building at the destructive or convergent plate margins and fracture zones repre­sented by constructive or divergent plate boundaries at the splitting zones of mid-oceanic ridges and the zones of transform faults represented by conservative plate boundaries.

The mechanism of vulcanicity (vulcanism) and volcanic eruptions is closely associated with sev­eral interconnected processes such as:

(i) Gradual in­crease of temperature with increasing depth at the rate of 1°C per 32 m due to heat generated from the disintegration of radioactive elements deep within the earth.

(ii) Origin of magma because of lowering of melting point caused by reduction in the pressure of overlying superincumbent load due to fracture caused by splitting of plates and their movement in opposite direction.

(iii) Origin of gases and vapour due to heat­ing of water which reaches underground through per­colation of rainwater and melt-water (water derived through the melting of ice and snow).

(iv) The ascent of magma forced by enormous volume of gases and vapour, and

(v) Finally the occurrence of volcanic eruptions of either violent explosive central type or quiet fissure type depending upon the intensity of gases and vapour and the nature of crustal surface.

Theory of plate tectonics now very well explains the mechanism of vulcanism and volcanic eruptions. In fact, volcanic eruptions are very closely associated with the plate boundaries. It may be pointed out that the types of plate movements and plate boundaries also determine the nature and intensity of volcanic erup­tion. Most of the active fissure volcanoes are found along the mid-oceanic ridges which represent splitting zones of divergent plate boundaries (fig. 9.5).

Two plates move in opposite directions from the mid-oceanic ridges due to thermal convective currents which are originated in the mantle below the crust (plates). This splitting and lateral spreading of plates creates fractures and faults (transform faults) which cause pressure release and lowering of melting point and thus materials of upper mantle lying below the mid-oceanic ridges are melted and move upward as magmas under the impact of enormous volume of accumulated gases and vapour.

This rise of magmas along the mid-oceanic ridges (constructive or divergent plate bounda­ries) causes fissure eruptions of volcanoes and there is constant upwelling of lavas. These lavas are cooled and solidified and are added to the trailing ends of divergent plate boundaries and thus there is constant creation of new basaltic crust.

The volcanic eruptions of Iceland and the islands located along the mid- Atlantic ridge are caused because of sea-floor spread­ing and divergence of plates. It is obvious that diver­gent or constructive plate boundaries are always asso­ciated with quiet type of fissure flows of lavas because the pressure release of superincumbent load due to divergence of plates and formation of fissures and faults is a slow and gradual process.

It is apparent from the above discussion that the mid-oceanic ridges, representing splitting zones, are associated with active volcanoes wherein the supply of lava comes from the upper mantle just below the ridge because of differential melting of the rocks into tholeiitic basalts.

Since there is constant supply of basaltic lavas from below the mid-oceanic ridges and hence the volcanoes are active near the ridges but the supply of lavas decreases with increasing distance from the mid- oceanic ridges and therefore the volcanoes become inactive, dormant and extinct depending on their dis­tances from the source of lava supply, e.g., mid-oceanic ridges.

This fact has been validated on the basis of the study of the basaltic floor of the Atlantic Ocean and the lavas of several islands. It has been found that the islands nearer to the mid-Atlantic Ridge have younger lavas whereas the islands away from the ridge have older lavas. For example, the lavas of Azores islands Situated on either side of the mid-Atlantic Ridge are 4- million years old whereas the lavas of Cape Verde Island, located far away from the said ridge, are 120- million years old.

Destructive or convergent plate boundaries are associated with explosive type of volcanic eruptions. When two convergent plates collide along Benioff zone (subduction zone), comparatively heavier plate margin (boundary) is subducted beneath comparatively lighter plate boundary. The subducted plate margin, after reaching a depth of 100 km or more in the upper mantle, is melted and thus magma is formed.

This magma is forced to ascend by the enormous volume of accumulated explosive gases and thus magma appears as violent volcanic eruption on the earth’s surface. Such type of volcanic eruption is very common along the destructive or convergent plate boundaries which represent the volcanoes of the Circum-Pacific Belt and the Mid-Continental Belt.

The volcanoes of the island arcs and festoons (off the east coast of Asia) are caused due to subduction of oceanic crust (plate) say Pacific e below the continental plate, say Asiatic plate near Japan Trench.

Essay # 5. Hazardous Effects of Volcanic Eruptions :

Volcanic eruptions cause heavy damage to human lives and property through advancing hot lavas and fallout of volcanic materials; destruction to human structures such as buildings, factories, roads, rails, airports, dams and reservoirs through hot lavas and fires caused by hot lavas; floods in the rivers and climatic changes.

A few of the severe damages wrought by volcanic eruptions may be summarized as given below:

(1) Huge volumes of hot and liquid lavas mov­ing at considerably fast speed (recorded speed is 48 km per hour) bury human structures, kill people and ani­mals, destroy agricultural farms and pastures, plug rivers and lakes, burn and destroy forest etc. The great eruption of Mt. Loa on Hawaii poured out such a huge volume of lavas that these covered a distance of 53 km down the slope.

Enormous Laki Lava flow of 1783 A.D. travelled a distance of 350 km engulfing two churches, 15 agricultural farms and killing 24 per cent of the total population of Iceland. The cases of Mt. Pelee eruption of 1902 in Martinique Island (in Carib­bean Sea) (total death 28,000) and St. Helens eruption of 1980 (Washington, USA) are representative exam­ples of damages done by lava movement. The thick covers of green and dense forests on the flanks of Mt. St. Helens were completely destroyed due to severe forest fires kindled by hot lavas.

(2) Fallout of immense quantity of volcanic materials including fragmental materials (pyroclastic materials), dusts and ashes, smokes etc. covers large ground surface and thus destroys crops, vegetation and buildings, disrupts and diverts natural drainage sys­tems, creates health hazards due to poisonous gases emitted during the eruption, and causes killer acid rains.

(3) All types of volcanic eruptions, if not pre­dicted well in advance, causes tremendous losses to precious human lives. Sudden eruption of violent and explosive type through central pipe does not give any time to human beings to evacuate themselves and thus to save themselves from the clutches of death looming large over them. Sudden eruption of Mt. Pelee on the Island of Martinique, West Indies in the Caribbean Sea, on May 8, 1902 destroyed the whole of St. Pierre town and killed all the 28,000 inhabitants leaving behind only two survivors to mourn the sad demise of their brethren.

The heavy rainfall, associated with volcanic eruptions, mixing with falling volcanic dusts and ashes causes enormous mudflow or ‘lahar’ on the steep slopes of volcanic cones which causes sudden deaths of human beings. For example, great mud flow created on the steep slopes of Kelut volcano in Japan in the year 1919 killed 5,500 people.

(4) Earthquakes caused before and after the volcanic eruptions generate destructive tsunamis seis­mic waves which create most destructive and disas­trous sea waves causing innumerable deaths of human beings in the affected coastal areas. Only the example of Krakatoa in 1883 would be sufficient enough to demonstrate the disastrous impact of tsunamis which generated enormous sea waves of 30 to 40 m height which killed 36,000 people in the coastal areas of Java and Sumatra.

(5) Volcanic eruptions also change the radiation balance of the earth and the atmosphere and thus help in causing climatic changes. Greater concentration of volcanic dusts and ashes in the sky reduces the amount of insolation reaching the earth’s surface as they scat­ter and reflect some amount of incoming shortwave solar radiation. Dust veils, on the other hand, do not hinder in the loss of heat of the earth’s surface through outgoing long-wave terrestrial radiation.

The ejection of nearly 20 cubic kilometres of fragmental materials, dusts and ashes upto the height of 23 km in the sky during the violent eruption of Krakatoa volcano on August 27, 1883 formed a thick dust veil in the strato­sphere which caused a global decrease of solar radia­tion received at the earth’s surface by 10 to 20 per cent.

(6) A group of scientists believes that volcanic eruptions and fallout of dusts and ashes cause mass extinction of a few species of animals. Based on this hypothesis the mass extinction of dinosaurs about 60 million years ago has been related to increased world­wide volcanic activity. Acid rains accompanied by volcanic eruptions cause large-scale destruction of plants and animals.

Essay # 6. Volcanic Materials :

Volcanic materials discharged during eruptions include gases and vapour, lavas, fragmental materials and ashes.

(i) Vapour and Gases:

Steam and vapour consti­tute 60 to 90 per cent of the total gases discharged during a volcanic eruption.

Steam and vapour include:

(i) Phreatic vapour, and

(ii) Magmatic vapour whereas volcanic gases include carbon dioxide, nitrogen ox­ides, sulphur dioxide, hydrogen, carbon monoxide, etc.

Besides, certain compounds are also ejected with the volcanic gases e.g., sulphurated hydrogen, hydrochlo­ric acid, volatile chlorides of iron, potassium and other metallic matter.

(ii) Magma and Lava:

Generally, molten rock materials are called magmas below the earth’s surface while they are called lavas when they come at the earth’s surface.

Lavas and magmas are divided on the basis of silica percentage into two groups e.g.:

(i) Acidic magma (higher percentage of silica, and

(ii) Basic lava (low percentage of silica).

Lavas and magmas are also classified on the basis of light and dark coloured minerals into:

(i) Felsic lava, and

(ii) Mafic lava.

Basaltic or mafic lava is characterized by maxi­mum fluidity. Basaltic lava spreads on the ground surface with maximum flow speed (from a few kilome­tres to 100 kilometres per hour, average How speed being 45 to 65 km per hour) due to high fluidity and low viscosity. Basaltic lava is the hottest lava (1,000° to 1,200 C).

Lava flow is divided into two types on the basis of Hawaiin language e.g.:

(i) Pahoehoe, and

(ii) Aa Aa lava flow or block lava flow.

Pahoehoe lava has high fluidity and spreads like thin sheets. This is also known as ropy lava. On the other hand aa aa lava is more viscous. Pahoehoe lava, when solidified in the form of sacks or pillow, is called pillow lava.

(iii) Fragmental or Pyroclastic Materials:

Fragmental or pyroclastic materials thrown during explosive type of eruption are grouped into three categories:

(i) Essential materials include con­solidated forms of live lavas. These are also known as tephra which means ash. Essential materials are unconsolidated and their size is upto 1 mm.

(ii) Acces­sory materials include dead lavas,

(iii) Accidental materials include fragmental materials of crustal rocks.

On the basis of size pyroclastic materials are grouped into:

(i) Volcanic dust (finest particles),

(ii) Volcanic ash (2 mm in size),

(iii) Lapilli (of the size of peas) and

(iv) Volcanic bombs (6 cm or more in size), which are of different shapes viz. ellipsoidal, discoidal, cuboidal, and irregularly rounded.

The dimension of average volcanic bombs ranges from the size of a base-ball or basket-ball to giant size. Sometimes the volcanic bombs weigh 100 tonnes in weight and are thrown upto a distance of 10 km.

Essay # 7. World Distribution of Volcanoes :

Like earthquakes, the spatial distribution of volcanoes over the globe is well marked and well understood because volcanoes are found in a well-defined belt or zone (fig. 9.3). Thus, the distributional pattern of volcanoes is zonal in character.

If we look at the world distribution of volcanoes it appears that the volcanoes are associated with the weaker zones of the earth’s crust and these are closely associated with seismic events say earthquakes. The weaker zones of the earth are represented by folded mountains (western cordillera of North America, Andes, mountains of East Asia and East Indies) with the exceptions of the Alps and the Himalayas, and fault zones.

Volcanoes are also associated with the meeting zones of the continents and oceans. Occurrences of more volcanic eruptions along coastal margins and during wet season denote the fact that there is close relationship between water and volcanic eruption. Similarly, volcanic eruptions are closely associated with the activities of mountain building and fracturing.

Based on plate tectonics, there is close rela­tionship between plate margins and vulcanicity as most of the world’s active volcanoes are associated with the plate boundaries. About 15 per cent of the worlds’ active volcanoes are found along the construc­tive plate margins or divergent plate margins (along the mid-oceanic ridges where two plates move in opposite directions) whereas 80 per cent volcanoes are associ­ated with the destructive or convergent plate boundaries (where two plates collide). Besides, some volcanoes are also found in intraplate regions e.g., volcanoes of the Hawaii Island, fault zones of East Africa etc.

Like earthquakes, there are also three major belts or zones of volcanoes in the world viz.:

(i) Circum-Pacific belt,

(ii) Mid-continental belt, and

(iii) Mid-oceanic ridge belt (fig. 9.3).

(i) Circum-Pacific belt:

The circum-Pacific belt, also known as the ‘volcanic zones of the convergent oceanic plate margins’, includes the volcanoes of the eastern and western coastal areas of the Pacific Ocean (or the western coastal margins of North and South Americas and the eastern coastal margins of Asia), of island arcs and festoons off the east coast of Asia and of the volcanic islands scattered over the Pacific Ocean.

This volcanic belt is also called as the fire girdle of the Pacific or the fire ring of the Pacific. This belt begins from Erebus Mountain of Antarctica and runs north­ward through Andes and Rockies mountains of South and North Americas to reach Alaska from where this belt turns towards eastern Asiatic coast to include the volcanoes of island arcs and festoons (e.g., Sakhalin, Kamchatka, Japan, Philippines etc.).

The belt ulti­mately merges with the mid-continental belt in the East Indies. Most of high volcanic cones and volcanic mountains are found in this belt. Most of the volcanoes are found in chains e.g., the volcanoes of the Aleutian Island, Hawaii Island, Japan etc.

About 22 volcanic mountains are found in group in Ecuador wherein the height of 15 volcanic mountains is more than 4560 m AMSL. Cotopaxi is the highest volcanic mountain of the world (height being 19,613 feet). The other signifi­cant volcanoes are Fuziyama (Japan), Shasta, Rainier and Hood (western cordillera of North America), a valley of ten thousand smokes (Alaska), Mt St. Helens (Washington, USA), Kilavea (Hawaiiland), Mt. Taal, Pinatubo and Mayon (re-eruption in Feb. 2000) of Philippines etc.

Here volcanic eruptions are primarily caused due to collision of American and Pacific plates and due to subduction of Pacific plate below the Asiatic plate.

(ii) Mid-continental Belt:

Mid-continental belt is also known as ‘the vol­canic zones of convergent continental plate mergins’. This belt includes the volcanoes of Alpine mountain chains and the Mediterranean Sea and the volcanoes of fault zone of eastern Africa. Here, the volcanic erup­tions are caused due to convergence and collision of Eurasian plates and African and Indian plates.

The famous volcanoes of the Mediterranean Sea such as Stromboli, Visuvious, Etna etc. and the volcanoes of Aegean Sea are included in this belt. It may be pointed out that this belt does not have the continuity of volcanic eruptions as several gaps (volcanic-free zones) are found along the Alps and the Himalayas because of Compact and thick crust formed due to intense folding activity. The important volcanoes of the fault zone of eastern Africa are Kilimanjaro, Meru, Elgon, Birunga, Rung we etc.

(iii) Mid-Atlantic Belt:

Mid-Atlantic belt includes the volcanoes mainly along the mid-Atlantic ridge which represents the splitting zone of plates. In other words, two plates diverge in opposite directions from the mid-oceanic ridge. Thus, volcanoes mainly of fissure eruption type occur along the constructive or divergent plate mar­gins (boundaries).

The most active volcanic area is Iceland which is located on the mid-Atlantic ridge. This belt begins from Hekla volcanic mountain of Iceland where several fissure eruption type of volca­noes are found. It may be pointed out that since Iceland is located on the mid-Atlantic ridge representing the splitting zone of American plate moving westward and Eurasian plate moving eastward, and hence here is constant upwelling of magmas along the mid-oceanic ridge and wherever the crust becomes thin and weak, fissure flow of lava occurs because of fracture created due to divergence of plates.

The Laki fissure eruption of 1783 A.D. was so quick and enormous that huge volume of lavas measuring about 15 cubic kilometres was poured out from 28-km long fissure. Recently, Hekla and Helgafell volcanoes erupted in the year 1974 and 1973 respectively. Other more active volcanic areas are Lesser Antilles, Southern Antilles, Azores, St. Helena etc.

The dreadful and disastrous eruption of Mount Pelee occurred on May 8,1902 in the town of St. Pierre on the Martinique Island of West Indies in the Caribbean Sea. All the 28,000 inhabitants, except two persons, were killed by the killer volcanic eruption.

(iv) Intra-Plate Volcanoes:

Besides the aforesaid well defined three zones of volcanoes, scattered volca­noes are also found in the inner parts of the continents. Such distributional patterns of volcanoes are called as intraplate volcanoes, the mechanism of their eruption is not yet precisely known. Fig. 9.4 depicts the location of volcanoes of Pacific plate where one branch of volcanoes runs from Hawaii to Kamchatka.

Vulcanicity also becomes active in the inner parts of continental plates. Massive fissure eruption occurred in the north­western parts of North America during Miocene period when 1,00,000 cubic kilometres of basaltic lavas were spread over an area of 1,30,000 km 2 to form Columbian plateau. Similarly, great fissure flows of lavas covered more than 5,00,000 km 2 areas of Peninsular India. Parana of Barazil and Paraguay were formed due to spread of lavas over an area of 7,50,090 km 2 .

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125 Volcano Essay Topic Ideas & Examples

Inside This Article

Volcanoes are one of the most fascinating natural phenomena on Earth. From their explosive eruptions to the creation of new land, there is no shortage of topics to explore when it comes to volcanoes. If you are looking for inspiration for your next essay on volcanoes, look no further. Here are 125 volcano essay topic ideas and examples to get you started:

• The science behind volcanic eruptions
• The different types of volcanoes and how they form
• The role of plate tectonics in volcanic activity
• The impact of volcanic eruptions on the environment
• The history of volcanic eruptions around the world
• The cultural significance of volcanoes in different societies
• The relationship between volcanoes and climate change
• The benefits of living near a volcano
• The risks and challenges of living near a volcano
• The technology used to monitor and predict volcanic eruptions
• The impact of volcanic eruptions on air travel
• The economic impact of volcanic eruptions on local communities
• The history of volcano research and exploration
• The myths and legends surrounding volcanoes
• The impact of volcanic eruptions on wildlife and ecosystems
• The role of volcanoes in the formation of Earth's landforms
• The connection between volcanic activity and earthquakes
• The role of volcanic eruptions in shaping human history
• The impact of volcanic eruptions on agriculture and food security
• The relationship between volcanic eruptions and volcanic gases
• The role of volcanoes in the formation of mineral deposits
• The impact of volcanic eruptions on water quality
• The connection between volcanic eruptions and geothermal energy
• The impact of volcanic eruptions on tourism
• The history of famous volcanic eruptions, such as Mount Vesuvius and Mount St. Helens
• The impact of volcanic eruptions on indigenous communities
• The role of volcanoes in the creation of new land
• The impact of volcanic eruptions on global climate
• The relationship between volcanic eruptions and volcanic lightning
• The role of volcanoes in the formation of volcanic islands
• The impact of volcanic eruptions on human health
• The connection between volcanic activity and volcanic hotspots
• The role of volcanic eruptions in the formation of volcanic ash clouds
• The impact of volcanic eruptions on marine ecosystems
• The relationship between volcanic eruptions and volcanic mudflows
• The role of volcanic eruptions in the formation of volcanic craters
• The impact of volcanic eruptions on infrastructure and buildings
• The connection between volcanic activity and volcanic earthquakes
• The role of volcanic eruptions in the formation of volcanic domes
• The impact of volcanic eruptions on air quality
• The relationship between volcanic eruptions and volcanic gas emissions
• The role of volcanoes in the formation of volcanic arcs
• The impact of volcanic eruptions on soil fertility
• The connection between volcanic activity and volcanic tremors
• The role of volcanic eruptions in the formation of volcanic calderas
• The impact of volcanic eruptions on water resources
• The relationship between volcanic eruptions and volcanic tsunamis
• The role of volcanoes in the formation of volcanic rift zones
• The impact of volcanic eruptions on wildlife migration patterns
• The connection between volcanic activity and volcanic vents
• The role of volcanic eruptions in the formation of volcanic cones
• The impact of volcanic eruptions on indigenous knowledge and traditions
• The relationship between volcanic eruptions and volcanic seamounts
• The role of volcanoes in the formation of volcanic craters
• The impact of volcanic eruptions on human migration patterns
• The connection between volcanic activity and volcanic eruptions
• The role of volcanic eruptions in the formation of volcanic plateaus
• The impact of volcanic eruptions on geothermal energy production
• The relationship between volcanic eruptions and volcanic islands
• The role of volcanoes in the formation of volcanic plains
• The impact of volcanic eruptions on soil erosion
• The connection between volcanic activity and volcanic rocks
• The role of volcanic eruptions in the formation of volcanic ridges
• The impact of volcanic eruptions on biodiversity
• The relationship between volcanic eruptions and volcanic vents
• The role of volcanoes in the formation of volcanic ridges
• The impact of volcanic eruptions on human settlements
• The connection between volcanic activity and volcanic rifts
• The role of volcanic eruptions in the formation of volcanic chains
• The relationship between volcanic eruptions and volcanic cones
• The role of volcanoes in the formation of volcanic fields
• The impact of volcanic eruptions on wildlife habitats
• The role of volcanic eruptions in the formation of volcanic belts
• The impact of volcanic eruptions on cultural heritage sites
• The relationship between volcanic eruptions and volcanic ash clouds
• The impact of volcanic eruptions on agricultural productivity
• The role of volcanic eruptions in the formation of volcanic arches
• The relationship between volcanic eruptions and volcanic fissures
• The role of volcanoes in the formation of volcanic calderas
• The connection between volcanic activity and volcanic domes
• The role of volcanic eruptions in the formation of volcanic rift zones
• The connection between volcanic activity and volcanic plateaus
• The connection between volcanic activity and volcanic islands
• The role of volcanic eruptions in the formation of volcanic plains
• The relationship between volcanic eruptions and volcanic rocks

With so many interesting topics to choose from, you are sure to find the perfect subject for your volcano essay. Whether you are interested in the science behind volcanic eruptions, the cultural significance of volcanoes, or the impact of volcanic activity on the environment, there is a topic on this list that is sure to inspire you. Happy writing!

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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.

1.1 OVERVIEW OF THIS REPORT

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.

1.2 VOLCANOES IN THE UNITED STATES

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.

1.3 THE STRUCTURE OF A VOLCANO

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.

1.4 MONITORING VOLCANOES

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.

1.5 ERUPTION BEHAVIOR

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.

1.6 ERUPTION HAZARDS

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.

1.7 MODELING VOLCANIC ERUPTIONS

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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Essay on Volcano

Students are often asked to write an essay on Volcano in their schools and colleges. And if you’re also looking for the same, we have created 100-word, 250-word, and 500-word essays on the topic.

Let’s take a look…

100 Words Essay on Volcano

What is a volcano.

A volcano is a crack in the Earth’s surface. Through this crack, melted rock, ash, and gases can escape from deep inside the Earth. Think of it like a soda bottle. If you shake it and then open the top, everything rushes out. That’s similar to what happens during a volcanic eruption.

Types of Volcanoes

There are mainly three types: shield, cone, and composite. Shield volcanoes are broad and flat. Cone volcanoes are steep and pointy. Composite volcanoes are tall and can be very explosive. Each type acts differently when it erupts.

Why Do Volcanoes Erupt?

Deep inside the Earth, it’s so hot that rocks melt into liquid called magma. When magma is lighter than the rock around it, it moves up. If it reaches the Earth’s surface, it erupts. This can happen because of the Earth’s plates moving and creating pressure.

Living with Volcanoes

People live near volcanoes for the fertile soil, which is good for farming. But, living close to a volcano can be dangerous. Scientists help by monitoring volcanoes to predict eruptions and keep people safe.

250 Words Essay on Volcano

A volcano is a crack in the Earth’s surface where molten rock, ash, and gases from deep inside the Earth come out. Think of it like a soda bottle that’s been shaken up. When you open the cap, everything rushes out because of the pressure. In the same way, when a volcano erupts, it releases pressure from beneath the Earth’s crust.

There are different kinds of volcanoes, mainly based on their shape and how often they erupt. Some are called shield volcanoes because they’re broad and low, like a warrior’s shield. Others are called stratovolcanoes, which are tall and steep. They usually have more explosive eruptions. Then there are cinder cone volcanoes, which are smaller and made of bits of rock and ash.

Volcanoes erupt because of the movement of tectonic plates, which are big pieces of the Earth’s surface. When these plates move, they can cause magma from deep inside the Earth to push its way up to the surface. This magma then becomes lava when it comes out of the volcano.

The Impact of Volcanoes

Volcanoes can be dangerous, destroying homes and forests with their lava flows and ash. But they also create new land and bring important nutrients to the soil, which can help plants grow. Plus, the gases they release into the atmosphere can affect the Earth’s climate.

Understanding volcanoes helps us prepare for their eruptions and appreciate the powerful forces that shape our planet.

500 Words Essay on Volcano

Volcanoes: nature’s fiery breath.

Volcanoes are fascinating natural wonders that capture our imaginations. These colossal mountains showcase the immense power of nature, capable of awe-inspiring eruptions and destruction. Let’s explore the world of volcanoes and delve into some of their most intriguing aspects.

A Peek Inside a Volcano

Imagine a giant underground chamber filled with molten rock, known as magma. This magma is incredibly hot, and it’s constantly pushing against the Earth’s crust. When the pressure becomes too intense, it finds a way to escape, and that’s when a volcano erupts.

Types of Volcanic Eruptions

There are various types of volcanic eruptions, each with its own characteristics. Some eruptions are explosive, sending ash and lava soaring high into the air. Others are more gentle, with lava flowing slowly out of the volcano. Some eruptions produce glowing clouds of ash, called pyroclastic flows, which can race down the volcano’s slopes at high speeds.

Volcanic Hazards

While volcanoes can be a sight to behold, they also pose potential hazards. Lava flows can destroy entire villages and forests, and ash clouds can disrupt air travel. Volcanic eruptions can also trigger earthquakes, landslides, and tsunamis.

Predicting Volcanic Eruptions

Volcanoes and the environment.

Volcanic eruptions can have both positive and negative impacts on the environment. On the one hand, they can release harmful gases and ash into the atmosphere, which can affect air quality and climate. On the other hand, volcanic eruptions can create new landforms, provide fertile soil for agriculture, and support unique ecosystems.

Conclusion: The Majestic Force of Nature

Volcanoes are a powerful reminder of the Earth’s dynamic nature. They can be both destructive and awe-inspiring, showcasing the incredible forces that shape our planet. By studying volcanoes, we can better understand the Earth’s processes and prepare for potential hazards, while still appreciating their majestic beauty.

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volcanic eruption , an eruption of molten rock, hot rock fragments, and hot gases through a volcano , which is a vent in a planet’s or satellite’s crust. Volcanic eruptions can cause disastrous loss of life and property. They range from relatively gentle eruptions, as typically seen in Hawaiian volcanoes , to massively destructive ones, such as the eruption of Vesuvius that destroyed Pompeii in 79 ce . Volcanic eruptions have captured the imagination of people over millennia , and they feature in several mythologies as well as works of fiction. These eruptions also play a role in climate change , with expelled gases such as carbon dioxide contributing to global warming , while ash, dust, and gases such as sulfur dioxide can drive global temperatures down.

Volcanic eruptions occur as a result of heat moving under Earth’s surface . They often begin with an accumulation of gas-rich magma (molten underground rock) in reservoirs near Earth’s surface, though they may be preceded by emissions of steam and gas from small vents in the ground. Small earthquakes , which may be caused by a rising plug of dense, viscous magma oscillating against a sheath of more permeable magma, may also signal volcanic eruptions, especially explosive ones.

In some cases, magma rises in conduits to the surface as a thin and fluid lava , either flowing out continuously or shooting straight up in glowing fountains or curtains. The eruptions of Hawaii’s volcanoes fall into this category. In other cases, entrapped gases tear the magma into shreds and hurl viscous clots of lava into the air. In more violent eruptions, the magma conduit is hollowed out by an explosive blast, and solid fragments are ejected in a great cloud of ash-laden gas that rises tens of thousands of metres into the air. An example of this phenomenon is the 1980 eruption of Mount Saint Helens . Many explosive eruptions are accompanied by a pyroclastic flow , a fluidized mixture of hot gas and incandescent particles that sweeps down a volcano’s flanks, incinerating everything in its path. If the expelled ash or gases collect on a high snowfield or glacier , they may melt large quantities of ice , and the result can be a disastrous flood or landslide that rushes down a volcano’s slopes.

Volcanic eruptions can also result in secondary damage , beyond the direct loss to life and property from the eruption itself. Volcanic ash can cause respiratory illnesses such as silicosis and can be particularly harmful to infants and people with chronic lung diseases. Gases such as hydrogen chloride , carbon monoxide , and hydrogen fluoride can cause both short- and long-term problems. Eruptions can cause economic harm that affects workers’ livelihoods and can force mass migrations of people in affected regions. The 2010 eruption of Iceland’s Eyjafjallajökull also demonstrated the threat posed to jet aircraft by high clouds of volcanic ash; this eruption led aviation authorities to ground flights across northern and central Europe for several days.

Volcanoes can be classified by the manner in which they erupt. These six types of volcanic eruptions , starting with the least explosive, make up one classification system: Icelandic, Hawaiian, Strombolian, Vulcanian, Pelean, and Plinian. Each name corresponds to a region or to a specific volcano or historical eruption that exemplifies the type.

Volcanic eruptions are not limited to Earth. Jupiter’s moon Io is subject to strong gravitational forces due to Jupiter’s mass as well as interaction with Jupiter ’s other moons Europa and Callisto . These forces cause distortions in Io’s shape and make it the most volcanically active body in the solar system . Mars is also known for several volcanoes, with Olympus Mons being the largest known volcano in the solar system. The volcanoes of Mars are shield volcanoes , which have a relatively flat profile, as Mars’s low gravity allows for longer and more widespread lava flows. (According to some estimates, Olympus Mons has been built up by eruptions for more than a billion years, which has resulted in its 700-km [435-mile] diameter.)

Volcanoes and volcanic eruptions feature in several mythologies and cultural traditions, especially in regions with high volcanic activity . The word volcano is derived from the Latin Volcanus , or Vulcan , the name of the ancient Roman god of fire. The Māori people of New Zealand (Aotearoa)—which lies on the Pacific Ring of Fire —have, in their traditions, a god of volcanoes and earthquakes called Rūaumoko. Pele is the Hawaiian goddess of fire and volcanoes. In Norse mythology , Muspelheim is a hot, glowing land in the south, guarded by Surt, the fire giant.

Volcanic activity is a common feature in fiction too. In the Inferno section of The Divine Comedy (c. 1308–21), Dante describes Hell as an inverted cone, with the last and innermost circle a fiery lake, symbolic of a volcanic crater. In A Journey to the Centre of the Earth (1864) by Jules Verne , the protagonists commence their journey at the Snæfellsjökull volcano in Iceland, and they return to the surface by way of an eruption at Stromboli in the Mediterranean. Verne also set his The Mysterious Island (1874) on a volcanic island, and it ends with the volcano erupting, obliterating the island. In J.R.R. Tolkien ’s The Lord of the Rings trilogy (1954–55), the Dark Lord Sauron forges the One Ring of Power in the fiery pits of the volcano Mount Doom, where Frodo and Sam go to destroy the ring. The journey to Mount Doom is the primary plot element in the series.

The 1815 eruption of Mount Tambora in Indonesia—the largest volcanic eruption in recorded history—had a tremendous impact on the world’s climate as well as its culture . Tambora expelled as much as 150 cubic km (roughly 36 cubic miles) of ash, pumice and other rock, and aerosols into the atmosphere . These materials blocked substantial amounts of sunlight from reaching Earth’s surface, eventually reducing the average global temperature by as much as 3 °C (5.4 °F). The following year was called the “year without a summer.” It was during this bleak period that Mary Shelley and her literary circle were confined indoors in Geneva, when she conceived of her masterpiece Frankenstein (1818).

When Krakatoa , also in Indonesia, erupted in 1883, the Norwegian artist Edvard Munch , out on a walk, saw the sky turn blood red halfway across the world and later was inspired to paint The Scream in 1893.

Films have also included their fair share of volcanic eruptions as crucial plot points, from the eruption that ends the tribal conflict in One Million Years B.C. (1966) to the triggered-to-erupt volcanic base of the villain Blofeld in the James Bond film You Only Live Twice (1967) to the very obviously named Volcano (1997), in which Tommy Lee Jones and Anne Heche fight off lava from an erupting volcano in Los Angeles. Famous eruptions in history, such as those of Vesuvius and Mount Saint Helens, have featured in numerous films and TV programs.

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Attending a school event and the significance of the 2008 Presidential Election

Explanation:

Descriptive Essay: Attending a School Event

A school event that I attended and found significant was the annual talent show. The event took place in the school auditorium, which was filled with students, teachers, and parents. The talented performers showcased their skills in singing, dancing, and playing musical instruments. The atmosphere was buzzing with excitement and applause as each act impressed the audience. The event not only entertained but also brought the school community together, fostering a sense of pride and appreciation for the diverse talents of our fellow students.

Descriptive Essay: The Significance of the 2008 Presidential Election

The 2008 Presidential Election was a pivotal moment in United States history. It marked the election of Barack Obama as the first African American President, signifying a significant step towards racial equality. This election had a profound impact on the nation, inspiring hope and optimism for change. It symbolized progress and inclusivity, breaking barriers and shattering stereotypes. The 2008 Presidential Election demonstrated the power of democracy and the ability of individuals to come together to create meaningful change in society.

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200 words essay on bullying in schools​

bullying in schools

Explanation:

Bullying in the schools has negative effects on individual students and on the school climate as a whole. Bullying can cause long-term problems for both the victims of bullying and the bullies themselves. To explore the effects of bullying on adolescents, we will define bullying, identify the characteristics of bullies and victims, outline the extent and consequences of bullying, and present resources for further information and assistance.

Bullying is any behavior that is initiated by one or more students against a victim or victims that causes physical or psychological intimidation. Bullying behaviors can be classified as either direct (such as teasing, threatening, hitting, or stealing) or indirect (such as rumor spreading or social isolation). Boys typically employed direct methods of bullying, while girls tend to use in direct methods. Either way, behaviors must occur repeatedly overtime to be classified as bullying.

Characteristics of Bullies and Victims

There are specific behaviors that bullies tend to exhibit. The bullies often need to feel powerful and in control. They may feel no remorse when they inflict injury and suffering on others. Bullies tend to defy authority and are likely to break school rules. They seem to have little anxiety and appear to possess high self-esteem. Students who come from homes characterized by physical punishment tend to be more likely to exhibit these types of behaviors.

Victims also tend to exhibit specific characteristics. They are often anxious, insecure, cautious, and have low self-esteem. Victims tend to be socially isolated, and may lack social skills and friends. Because they tend to be weaker than their peers, either physically or socially, victims rarely retaliate against bullies. Students who have close ties with their parents/guardians or who have overprotective parents/guardians are more likely to be victimized by bullies.

Article - Bullying At School

Roses are red, violets are blue Bullying is bad don't you think so too?

Bullying has been a significant issue in the present schools, society, particularly among teenagers.  

Youngsters investing the vast majority of their energy at school this condition must be as sheltered as could be expected under the circumstances. Schools should be more proactive in tending to the issue of harassing on the grounds that numerous understudies are tormented from multiple points of view, the impacts can be fatal, and understudies merit a protected spot to learn. At schools kids are getting tormented from multiple points of view. This maltreatment happens due to menaces who decide to disregard the contrast among good and bad.

A few different ways to beat tormenting at school:  

1. stand up for individuals who harassed  

2. Make a move  

3. Converse with different students about this circumstance  

4. Converse with your teacher or principal

5. Converse with your parents or guardian or any counsellor

6. Bit and (review).  

Elevate harmony and to be a genuine guide to all the individuals who pick wrong way.

To conclude Roses are red, Violets are blue Be a Mate not a Harasser fool.

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