volcanic eruption essay introduction

ENCYCLOPEDIC ENTRY

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

Volcanic eruption

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

Photograph by Chris Johns

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

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

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

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

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

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

Chapter: summary.

Volcanoes are a key part of the Earth system, and open a window into the inner workings of the planet. More than a dozen volcanoes are usually erupting on Earth at any given time. Some of these eruptions are devastating, killing people, damaging homes and infrastructure, altering landscapes, and even disrupting climate. Fortunately, many eruptions are preceded by signs of unrest (precursors) that can be used to anticipate eruptions and support disaster planning.

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. Eruption behaviors are diverse (e.g., violently explosive or gently effusive, intermittent or sustained, last hours or decades) and may change over time at a volcano. More accurate and societally useful forecasts of eruptions and their hazards are possible by using new observations and models of volcanic processes.

At the request of managers at the National Aeronautics and Space Administration, the National Science Foundation (NSF), 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.

These four tasks are closely related. Improved understanding of volcanic processes guides monitoring efforts and improves forecasts. In turn, improved monitoring provides the insights and constraints to better understand volcanic processes. This report identifies key science questions, research and observation priorities, and approaches for building a volcano science community capable of tackling them. The discussion below first summarizes common themes among these science questions and priorities, and then describes ambitious goals (grand challenges) for making major advances in volcano science.

KEY QUESTIONS AND RESEARCH AND OBSERVATION PRIORITIES

Many fundamental aspects of volcanoes are understood conceptually and often quantitatively. Plate tectonics and mantle convection explain where volcanoes occur. We understand how magma is initially created in Earth’s mantle, how it rises toward the surface, that it can be stored and evolve in magma chambers within the crust, and that a number of processes initiate eruptions. We understand in general terms why some magmas erupt explosively and others do not, and why some volcanoes erupt more often than others. High-resolution observations and models combined provide a detailed and quantitative picture of eruptions once they begin.

Our understanding is incomplete, however, especially those aspects of volcano behavior that define the timing, duration, style, size, and consequences of eruptions. Additional questions relate to our ability to forecast eruptions. What processes produce commonly observed geophysical and geochemical precursors? What factors determine if and when unrest will be followed by eruption? How rapidly do magmas mobilize prior to eruption? Which volcanoes are most likely to erupt in coming years and decades? And we are only beginning to decipher the impacts of large volcanic eruptions on Earth’s climate and biosphere.

Our understanding of the entire life cycle and diversity of volcanoes—from their conception in the mantle to their periods of repose, unrest, and eruption to their eventual demise—is poised for major advances over the next decades. Exciting advances in our ability to observe volcanoes—including satellite measurements of ground deformation and gas emissions, drone observations, advanced seismic monitoring, and real-time, high-speed acquisition of data during eruptions—await broad application to volcanic systems. Parallel advances in analytical capabilities to decipher the history of magmas, and in conceptual, experimental, and numerical models of magmatic and volcanic phenomena, both below and above ground, will provide new insights on the processes that govern the generation and eruption of magma and greatly improve the quality of short-term, months to minutes, forecasts. The time is ripe to test these models with observations from new instrumentation, data collected on fine temporal and spatial scales, and multidisciplinary synthesis.

Four common themes emerged from the research priorities detailed in the following chapters:

• Develop multiscale models that capture critical processes, feedbacks, and thresholds to advance understanding of volcanic processes and the consequences of eruptions on Earth systems.

Advances will come from measurements of physical and chemical properties of magmas and erupted materials, deciphering the history of magmas (before and during eruption) recorded in their crystals and bubbles, and developing new models that account for the numerous interacting processes and vast range of scales, from microscopic ash particles and crystals, to eruption columns that extend to the stratosphere.

• Collect high-resolution measurements at more volcanoes and throughout their life cycle to overcome observational bias.

Few volcanoes have a long record of monitoring data. New and expanded networks of ground, submarine, airborne, and satellite sensors that characterize deformation, gases, and fluids are needed to document volcanic processes during decade-long periods of repose and unrest. High-rate, near-real-time measurements are needed to capture eruptions as they occur, and efficient dissemination of information is needed to formulate a response. Both rapid response and sustained monitoring are required to document the life cycle of volcanoes. Monitoring and understanding volcanic processes go hand-in-hand: Different types of volcanoes have different life cycles and behaviors, and hence merit different monitoring strategies.

• Synthesize a broad range of observations, from the subsurface to space, to interpret unrest and forecast eruption size, style, and duration.

Physics-based models promise to improve forecasts by assimilating monitoring data and observations. Progress in forecasting also requires theoretical and experimental advances in understanding eruption processes, characterization of the thermal and mechanical properties of magmas and their host rocks, and model validation and verification. Critical to eruption forecast-

ing is reproducing with models and documenting with measurements the emergent precursory phenomena in the run-up to eruption.

• Obtain better chronologies and rates of volcanic processes.

Long-term forecasts rely on understanding the geologic record of eruptions preserved in volcanic deposits on land, in marine and lake sediments, and in ice cores. Secondary hazards that are not part of the eruption itself, such as mud flows and floods, need to be better studied, as they can have more devastating consequences than the eruption. Understanding the effects of eruptions on other Earth systems, including climate, the oceans, and landscapes, will take coordinated efforts across disciplines. Progress in long-term forecasts, years to decades, requires open-access databases that document the full life cycle of volcanoes.

GRAND CHALLENGES

The key science questions, research and observation priorities, and new approaches highlighted in this report can be summarized by three overarching grand challenges. These challenges are grand because they are large in scope and would substantially advance the field, and they are challenges because great effort will be needed. Figure S.1 illustrates these challenges using the example of the 2016 eruption of Pavlof volcano, Alaska. The volcanic hazards and eruption history of Pavlof are summarized by Waythomas et al. (2006) .

A principal goal of volcano science is to reduce the adverse impacts of volcanism on humanity, which requires accurate forecasts. Most current eruption forecasts use pattern recognition in monitoring and geologic data. Such approaches have led to notable forecasts in some cases, but their use is limited because volcanoes evolve over time, there is a great diversity of volcano behavior, and we have no experience with many of the potentially most dangerous volcanoes. A major challenge is to develop forecasting models based instead on physical and chemical processes, informed by monitoring. This approach is used in weather forecasting. Addressing this challenge requires an understanding of the basic processes of magma storage and ascent as well as thresholds of eruption initiation. This understanding and new discoveries will emerge from new observations, experimental measurements, and modeling approaches. Models are important because they capture our conceptual and quantitative understanding. Experiments test our understanding. Relating models to observations requires multiple types of complementary data collected over an extended period of time.

Determining the life cycle of volcanoes is key for interpreting precursors and unrest, revealing the processes that govern the initiation and duration of eruptions, and understanding how volcanoes evolve between eruptions. Our understanding is biased by an emphasis over the last few decades of observation with modern instruments, and most of these well-studied eruptions have been small events that may not scale to the largest and most devastating eruptions. Strategic deployment of instruments on volcanoes with different characteristics would help build the requisite knowledge and confidence to make useful forecasts. For every volcano in the United States, a realistic goal is to have at least one seismometer to record the small earthquakes that accompany magma movement. Even in the United States, less than half of potentially active volcanoes have a seismometer, and less than 2 percent have continuous gas measurements. Global and daily satellite images of deformation, and the ability to measure passive CO 2 degassing from space would fill critical observational gaps. Geologic and geophysical studies are required to extend understanding of the life cycle of volcanoes to longer periods of time. On shorter time scales, satellite measurements, emerging technologies such as drones, and expansion of ground-based monitoring networks promise to document processes that remain poorly understood.

The volcano science community needs to be prepared to capitalize on the data and insights gained from eruptions as they happen. This will come from effective integration of the complementary research and monitoring roles by universities, the USGS, and other government agencies. Volcano science is fundamentally interdisciplinary and the necessary expertise is spread across these institutions. The science is also international, because every volcano provides insights on processes that drive eruptions. Volcanic eruptions can have global impacts and so demand international collaboration and cooperation. New vehicles are needed to support interdisciplinary research and training, including community collaboration and education at all levels. Examples of similar successful programs in other fields include NSF’s Cooperative Studies of the Earth’s Deep Interior program for interdisciplinary research and National Earthquake Hazards Reduction

Program for federal government agency–academic partnerships.

Results of the above investments in science will be most evident to the public in improved planning and warning and, ideally, a deeper appreciation of this amazing natural phenomenon.

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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7.6: Effects of Volcanic Eruptions on Humans and on Earth Systems

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• Steven Earle
• Vancover Island University via BCCampus

Humans have a love-hate relationship with volcanoes. For many reasons humans are attracted to areas with active volcanism, but for several others that we’ve already discussed, they would be wise to stay away.

The key reason that humans like living around potentially active volcanoes is that the soil tends to be fertile, and thus there is the potential to grow enough food to live. For example, some parts of the area around Mt. Merapi in Indonesia (Figure 7.0.1) can support subsistence populations of 8 to 10 people per hectare. [1] In comparison, the typical farm in the United States can feed just under 1 person per hectare ( US Farm Bureau ).

Volcanic soil is good for a number of reasons. One is that volcanic ash and rock fragments are rich in volcanic glass and under weathering conditions glass breaks down quickly to clay minerals so that productive soil can form within 200 to 300 years in favorable climates. [2] Another is that the clays that form from volcanic parent materials are effective at holding onto nutrients such as phosphorous. A third is that volcanic lava or tephra are typically quite rich in some important plant nutrients, such as magnesium and sulphur. Volcanic regions all over the world are know for their fertile soils. Some examples, apart from Indonesia, include the volcanic areas in Italy, much of northern New Zealand, Japan, Hawaii, parts of Africa, and much of the Caribbean.

Volcanoes are also valued for their scenic beauty and recreational opportunities. An example is the Mt. Garibaldi area of southwestern British Columbia (Figure 7.6.1), but there are hundreds of other scenic volcanoes around the world, some of which are immense tourist and hiker attractions (Figure 7.6.2). Many volcanoes are also venues for a wide range of winter sports, and for hot springs, spas and mudbaths. Volcanic regions are also an excellent source of geothermal heat for both electricity and district heating, and of hydroelectric energy from streams.

Many volcanoes are also venues for a wide range of winter sports, and for hot springs, spas and mudbaths. Volcanic regions are also an excellent source of geothermal heat for both electricity and district heating, and of hydroelectric energy from streams. Figure 7.6.3 provides an overview of some of the ways that humans interact with volcanoes, and some of the risks associated with living nearby.

Volcanism and Earth Systems

As already noted in Chapter 1 and Chapter 3 , volcanic eruptions contribute to the Earth’s systems in important ways. For starters, it is widely believed that the water in the Earth’s oceans is at least partly derived from volcanism, and the Earth would not have much in the way of systems without water.

Some of the key roles of volcanic eruptions in Earth systems are as follows:

• Cycling solids (mostly silicates) from depth in the mantle and the crust to surface,
• Cycling volatiles (water and gases) from depth, and thereby influencing organisms and the climate,
• Ejecting both solids and volatiles high into the atmosphere,
• Cycling thermal energy from depth,
• Creating solid surfaces (e.g., islands) that will be colonized by organisms, and
• Creating sloped surfaces (mountains) that influence weather and climate patterns, and will be eroded and weathered.

All of these products subsequently contribute to other Earth system processes in myriad ways.

Media Attributions

• Figure 7.6.1 Photo by Isaac Earle, used with permission, CC BY 4.0
• Figure 7.6.2 Mt. Fuji Summit by Derek Mawhinney, public domain image via Wikimedia Commons, https://commons.wikimedia.org/wiki/F...uji_Summit.jpg
• Figure 7.6.3 Steven Earle, CC BY 4.0
• Dahlgren, R., Saigusa, M., & Ugolini, F. (2004). The nature, properties and management of volcanic soils. Advances in Agronom y, 82 , 114-183. https://doi.org/10.1016/S0065-2113(03)82003-5 ↵
• (Dahlgern et al., 2004) ↵

8a. Introduction to Volcanoes

Karla Panchuk and Steven Earle

Learning Objectives

After reading this chapter and answering the Questions For Review at the end, you should be able to:

• Explain what a volcano is.
• Describe the different kinds of materials produced by volcanoes.
• Describe the structures of shield volcanoes, composite volcanoes, and cinder cones.
• Explain how the style of a volcanic eruption is related to magma composition.
• Describe the role of plate tectonics in volcanism and magma formation.
• Summarize the hazards that volcanic eruptions pose to people and infrastructure.
• Describe how volcanoes are monitored, and the signals that indicate a volcano could be ready to erupt.

Why Study Volcanoes?

Volcanoes are awe-inspiring natural events. They have instilled fear and fascination with their red-hot lava flows, and cataclysmic explosions. In his painting The Eruption of Vesuvius (Figure 8.2), Pierre-Jacques Volaire captured the stunning spectacle of the eruption on Mt. Vesuvius on 14 May 1771. He also captured some stunningly casual spectating being done by tourists and their dog (lower left).

As Volaire’s painting suggests, curiosity alone would be enough to make people want to learn why volcanoes happen and how they work. However, there are other reasons why we should know more about volcanoes. One reason is that studying volcanoes helps us understand the evolution of the Earth system- not just Earth’s geological features, but past changes in climate, and even the causes of mass extinctions. Another reason is the critical need to study the hazards posed by volcanoes to people and infrastructure. Over the past few decades, volcanologists have made great strides in their ability to forecast volcanic eruptions and predict the consequences, saving thousands of lives.

Licenses and Attributions

“Physical Geology, First University of Saskatchewan Edition” by Karla Panchuk is licensed under CC BY-NC-SA 4.0 Adaptation: Renumbering, Remixing

https://openpress.usask.ca/physicalgeology/

8a. Introduction to Volcanoes Copyright © 2021 by Karla Panchuk and Steven Earle is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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Volcanic eruptions.

Photo by R.E. Stinson.

Introduction

Volcanic eruptions are among the most awesome of all natural phenomena on Earth. They may be strangely beautiful as fountains of glowing-red lava rise above a vent to feed a lava flow that spreads rapidly downhill. Or they may consist of terrifying explosions that send clouds of scorching hot ash high into the atmosphere or roaring down a volcano’s slopes and destroying everything in its path. While a great range in the type, style, and violence of volcanic eruptions exists, they all are part of one of the most fundamental geologic processes that builds and shapes Earth’s crust. The place to begin an exploration of the diversity of the different types and kinds of volcanic eruptions is with the definition. A volcanic eruption is the expulsion of gases, rock fragments, and/or molten lava from within the Earth through a vent onto the Earth’s surface or into the atmosphere.

USGS illustration.

Some volcanic eruptions consist of mostly gas emissions, others are relatively quiet discharges of fluid lava, and yet others are cataclysmic explosions. Different kinds of eruptions leave characteristic deposits that, in turn, build different types of volcanoes. A magma’s composition, viscosity, and gas content, the eruption rate, and the size of the magma reservoir determines many aspects of eruptions, including how explosive they are. National parks are great places to observe current volcanic activity.

• Kilauea in Hawai’i Volcanoes National Park was active from 1983 to 2018, and has had shorter periods of eruption since then.
• Katmai National Park and Preserve in Alaska is one of the world’s most active volcanic areas with 10 volcanoes that have had historic eruptions.
• The most recent eruption at the Lassen volcanic center in California occurred in 1917.

A number of other national parks contain volcanoes that have had prehistoric eruptions. Volcanoes in many other parks erupted in the even more distant past. Today, these mountains evoke peace and serenity that belies the violence in their history.

• Mount Mazama exploded about 7,550 years ago to form Crater Lake.
• Capulin Volcano erupted just over 54,000 years ago.
• The Valdez Caldera erupted 1.25 million years ago.

Whether active or ancient, volcanic landforms found in national parks result from their eruption dynamics, with the volcanoes themselves and the lava flows and other deposits they leave behind serving as tangible evidence of the volcanic processes that formed them.

Generation and Rise of Magma

The melted rock (magma) that is erupted in volcanoes does not come from the Earth’s core or even from deep within the mantle. There are also no permanent pools of melted rock found within the crust or mantle. Instead, magma produced from partial melting of the upper mantle. The heat that causes the partial melting comes from several sources; most importantly, from decay of radioactive elements, such as uranium, thorium, and potassium. Once magma is generated, it rises buoyantly because it is lighter than the surrounding rock. It moves in slow-moving balloons or diapirs; or in planar fractures (dikes). Sometimes it pools at the base of the crust, and other times it continues to rise to form magma chambers. Shallow magma chambers may form in regions of neutral buoyancy, i.e., areas where the pressure within the magma body equals the pressure outside it. Magma typically begins to crystallize while they are being stored in magma chambers, forming a liquid-crystal mush. Eruptions from a shallow magma body may be triggered by injection of more magma into the chamber, by overpressure from increased volatile (gas) content, or by some other factor.

Composition & Viscosity

Volcanic eruptions are inherently physical processes given that they are the emission of gas, magma, and rock from within the Earth. Yet many aspects of eruptions are actually controlled by magma chemistry. In fact, the composition of the magma, as well as its gas content, largely determines whether an eruption is explosive, and the magnitude of that explosivity. Magma composition impacts nearly everything about a volcano, with viscosity of the melt being one of the most important factors that determines eruption dynamics, and even the shape of a volcanic edifice. Viscosity is the internal friction, or resistance to flow—or how “thick and sticky” or “thin and runny” a lava is.

• Lavas with low viscosity such as those erupted at Kilauea in Hawai’i Volcanoes National Park flow easily, with flow fronts that move up to 6 miles (10 km) per hour. Speeds in channels or lava tubes on steep slopes can be as fast as 19 miles (30 km) per hour.
• Highly viscous lavas do not spread out to form wide lava flows, but instead form steep-sided domes immediately above a vent, such as the dome at Novarupta in Katmai National Park .

Modified from NASA illustration.

Silica (SiO2) content has the greatest impact on magma viscosity. Most igneous rocks are made predominately of silica with concentrations ranging from about 45 to 78% by weight. Specifically, silica is arranged in tetrahedrons (Si04 complexes). Silica tetrahedrons can share oxygen atoms to form chains or networks in a melt. Higher concentrations of silica leads to longer and more complex chains. The greater abundance of complex chains of silica tetrahedrons have a greater propensity to tangle with one another. This impedes their ability to flow past one another, somewhat akin to tangling of long strands of spaghetti.

Therefore, the general rule is that magmas with high silica content are highly viscous, and ones with low silica have low viscosity (e.g., are inviscid ). The presence of other elements, particularly sodium and potassium, can lower viscosity in rhyolitic magmas because they interfere with silica’s ability to form complex chains. Similarly, the presence of water in the melt (which is common) can also decrease viscosity. In general the viscosity of a low silica magma like basalt is thousands of times more viscous than liquid water. High silica melts can be many orders of magnitude more viscous than basalts. Their relatively low viscosities are why basalts are generally extruded in quiet (effusive) or mildly explosive eruptions. On the other hand, eruptions of high silica magmas are likely to be explosive (due to both high viscosity and higher gas content).

NPS photo by B. Seibert.

Photo by Lanny Simpson, Alaska High Mountain Images.

Gas content & exsolution

Courtesy of James St. John (Flickr)

Magmas typically contain small amounts of dissolved gas ( volatiles ). Water and carbon dioxide are the most common volatiles, although sulfur dioxide, hydrogen sulfide, and others may be present. Until a magma nears the Earth’s surface, the enormous pressure of the overlying rock keeps gases dissolved. Near the surface, the pressure decreases and they can exsolve from the melt, ultimately forming gas bubbles in a process called vesiculation . This exsolution of magmatic gases as a magma ascends towards the surface is one of the forces that propels volcanic eruptions. The release of pressure as a magma nears the Earth’s surface is similar to the release of pressure in a carbonated beverage when it is opened. The exsolution of carbon dioxide from soda pop due to the release of confining pressure when the can is opened is like the expansion and exsolution of gases that propels eruptions. Higher volatile contents increase the likelihood of explosive eruptions compared to eruptions of magma with lower concentrations of gases. Viscosity is also important because gases can escape more easily from thin fluids than thick ones, as can be observed in the spattering that can happen when making jam (a more viscous liquid) versus the simple boiling of water. In general, the higher the viscosity and the higher the gas content, the more explosive the eruption will be.

USGS photo.

• In the eruptions that build some cinder cones, the vesiculation of basaltic magma from expanding and exsolving gas throws blobs of magma perhaps tens to hundreds of feet into the air that then cool and fall around the vent as cinders.
• In highly explosive eruptions of silicic magmas, vesiculation can completely shatter the erupting material into tiny bits called volcanic ash in columns that rise tens of thousands of feet into the atmosphere. For example, the April 21, 1989 eruption of Redoubt Volcano in Lake Clark National Park and Preserve formed an eruption column that ascended to a height of 62,000 feet (19 km).

Rate of Eruption

The rate of eruption can also influence how explosive an eruption is. If magma ascends slowly from deep within the crust, it is possible for the dissolved gases to escape nonviolently over time. But when magma ascension and eruption rate is rapid, the dissolved gases must escape all at once and the eruption is more explosive. Likewise, a soda gently fizzes when the gases dissolved in it are slowly released. Yet it explodes violently when carbon dioxide exsolves rapidly, such as happens after a can is shaken. It is the sudden release of energy by gas under pressure by rapid exsolution that is one of the main drivers of explosive eruptions.

Size of Magma Reservoir

The size of the magma body beneath a volcano has a strong controlling factor in the magnitude of eruptions because the availability of magma can strongly constrain its size. Small magma bodies simply cannot sustain large eruptions because there is not enough material available. Cinder cones, even exceptionally large ones like Sunset Crater Volcano, only tap small magma sources. The volume of erupted rock material erupted In 1085 CE to form Sunset Crater Volcano about was 0.12 cubic miles (0.52 cubic km) in volume in contrast to the largest eruption at Yellowstone 2.1 million years ago that expelled nearly 600 cubic miles (2,450 cubic km) of material.

Volcanic Activity

An erupting volcano may include varying types of activity, along with a range of intensity. Volcanic activity includes earthquakes caused by magma movement, gas emissions, effusive emissions of lava, and cataclysmic eruptions. Most geologists use the term eruption to encompass a whole period of volcanic activity which is bracketed by quiet intervals. The Smithsonian Institute has set an arbitrary interval of three months of complete inactivity of a volcano to separate one eruption from another. Eruptions generally consist of eruptive pulses and eruptive phases.

• Eruptive pulses are single explosions that may last a few seconds to minutes.
• Eruptive phases consist of numerous eruptive pulses that generate a pulsating eruptive column or lava flow, and may last from a few hours to days.

An eruption may consist of many eruptive pulses and last a few days, months, or even years.

Active, Dormant & Extinct

Volcanologists describe volcanoes as being active, dormant, or extinct based on how recently they erupted and whether they are likely to do so again.

• Active : A volcano is considered potentially active if it has erupted during the last 10,000 years. Some volcanoes may have dormant periods between eruptions greater than 10,000 years, but 10,000 years is a convenient cut-off date for activity and is used by convention. An active volcano is currently erupting, or is one that has erupted in historic time. Even though Mount Rainier hasn’t had a significant eruption for a thousand years, it is considered to be an active volcano.
• Dormant : A volcano that is not erupting now, but is considered likely to erupt in the future. There is no precise distinction between active and dormant volcanoes. Sometimes dormant volcanoes are described as being potentially active. Mount Rainier and the El Malpais National Monument volcanic field are considered dormant.
• Extinct : An extinct volcano is one that is not expected to erupt again in the future. Sometimes the determination of whether a volcano is extinct is based on the amount of time since its last eruption. Alternatively, some types of volcanoes such as cinder cones typically only erupt once. For example, Capulin Volcano, a cinder cones, is extinct.

Last updated: July 18, 2022

• Earth Science

Volcano Eruption

Volcanoes are ruptures in the crust of our planet Earth that allow hot gases, molten lava and some rock fragments to erupt by opening and exposing the magma inside. In this piece of article, we will be discussing how and why volcanoes erupt.

How Do Volcanoes Erupt?

It is so hot deep within the earth that some rocks slowly melt and turn into a thick flowing matter known as magma. Since it is lighter than solid rock, the magma rises and collects in magma chambers. Eventually, some magma pushes through fissures and vents on the earth’s surface. Hence, a volcanic eruption occurs, and the erupted magma is known as lava.

We need to understand the Earth’s structure to know how volcanoes erupt. At the top lies the lithosphere, the outermost layer that consists of the upper crust and mantle. The thickness of the crust ranges from 10km to 100km in mountainous locations and mainly consists of silicate rock.

See the video below to know more about the causes of volcanic eruptions.

Why Do Volcanoes Erupt?

The Earth’s mantle within the crust is classified into different sections depending on individual seismology. These include the upper mantle, which ranges between 8 – 35 km to 410 km; the transition zone ranges from 400 to 660 km; the lower mantle lies between 660 – 2891 km.

The conditions change dramatically from the crust to the mantle location. The pressures rise drastically and temperatures rise up to 1000 o C. This viscous and molten rock gets collected into large chambers within the Earth’s crust.

Since magma is lighter than surrounding rock, it floats up towards the surface and seeks out cracks and weakness in the mantle. It finally explodes from the peak point of a volcano after reaching the surface. When it is under the surface, the melted rock is known as magma and erupts as ash when comes up.

Rocks, lava and ash are built across the volcanic vent with every eruption. The nature of the eruption mainly depends on the viscosity of the magma. The lava travels far and generates broad shield volcanoes when it flows easily. When it is too thick, it makes a familiar cone volcano shape. If the lava is extremely thick, it can build up in the volcano and explode, known as lava domes.

Causes of Volcanic Eruption

We know that the mantle of the Earth is too hot, and the temperature ranges from 1000° Celsius to 3000° Celsius. The rocks present inside melt due to high pressure and temperature. The melted substance is light in weight. This thin lava comes up to the crust since it can float easily. Since the density of the magma between the area of its creation and the crust is less than the enclosed rocks, the magma gets to the surface and bursts. The magma is composed of andesitic and rhyolitic components along with water, sulfur dioxide, and carbon dioxide in dissolved form. By forming bubbles, excess water is broken up with magma. When the magma comes closer to the surface, the level of water decreases and the gas/magma rises in the channel. When the volume of the bubbles formed is about 75%, the magma breaks into pyroclasts and bursts out. The three main causes of volcanic eruptions are: The buoyancy of the magma Pressure from the exsolved gases in the magma Increase in pressure on the chamber lid Hope you are familiar with why volcanoes erupt and the cause of the volcanic eruption. Stay tuned to BYJU’S to learn about types of volcanoes, igneous rocks, and much more.

Frequently Asked Questions – FAQs

What is lava.

When a volcanic eruption occurs, the erupted magma is known as lava.

State true or false: The nature of the eruption mainly depends on the viscosity of the magma.

What are the causes of volcanic eruption.

The causes of the volcanic eruption are:

• The buoyancy of the magma
• Pressure from the dissolved gases in the magma
• Increase in pressure on the chamber lid

Define magma.

How is earth’s mantle classified.

• The upper mantle – ranges between 8 – 35 km to 410 km
• Transition zone ranges from 400 to 660 km
• Lower mantle lies between 660 – 2891 km

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Select the correct answer and click on the “Finish” button Check your score and answers at the end of the quiz

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• A vent, hill or mountain from which molten or hot rocks with gaseous material have been ejected
• Also craters, depressions, hills or mountains formed by removal of pre-existing material or by accumulation of ejected materials

The Philippines sits on a unique tectonic setting ideal to volcanism and earthquake activity. It is situated at the boundaries of two tectonic plates – the Philippine Sea Plate and the Eurasian plate –  both of which subduct or dive beneath the archipelago along the deep trenches along its east and west seaboard.

• Tephra fall or ashfall and ballistic projectiles
• Pyroclastic density currents or PDCs (pyroclastic flow, pyroclastic surge, base surge)
• Lateral blast
• Volcanic gas
• Lahar, flooding
• Debris avalanche, landslide
• Volcanic tsunami
• Ground deformation (subsidence, fissuring)
• Secondary explosion
• Secondary PDCs and ashfall

Volcanic Hazards

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Essay on volcanoes | geology.

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

Essay Contents:

• Essay on the Volcanoes and Atmospheric Pollution

Essay # 1. Introduction to Volcanoes :

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Essay # 2. Location of Volcanoes:

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

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

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

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

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

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Essay # 3 . formation of volcanoes :.

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

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

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

Essay # 4 . Volcanic Landforms :

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

Four types of volcanic landforms are formed:

i. Ash and Cinder Cones or Explosion Cones:

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

ii. Lava Cones:

These are formed from slowly upwelling lava.

These are of two types:

(a) Steep Sided Volcanoes:

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

(b) Shield Volcanoes:

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

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

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

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

iv. Shield Volcanoes:

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

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

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

v. Plateau Basalts or Lava Plains:

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

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

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

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

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

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

Essay # 5 . Major Gases Emitted by Volcanoes :

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

Essay # 6 . Lightning and Whirlwinds :

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

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

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

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

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

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

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

Essay # 8 . Volcanic Products :

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

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

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

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

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

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

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

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

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

i. Hot springs:

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

ii. Smoker:

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

iii. Geyser:

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

iv. Mud volcano:

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

v. Solfatara:

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

vi. Fumarole:

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

vii. Mofette:

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

Various terms used while describing volcanic features are given below:

i. Magma Chamber:

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

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

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

iv. Crater:

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

v. Caldera:

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

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

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

viii. Pyroclastic Flow :

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

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

ix. Seamounts :

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

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

Essay # 9 . Source of the Explosive Energy :

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

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

Essay # 10 . Classification of Pyroclastics :

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

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

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

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

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

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

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

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

i. Agglomerate:

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

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

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

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

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

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

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

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

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

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

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

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

Essay # 15. Classification of Volcanic Activity:

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

Essay # 16. Cone Topped and Flat Topped Volcanoes:

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

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

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

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

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

Essay # 17. Types of Volcanoes :

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

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

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

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

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

Essay # 18. Violence of Volcanic Eruptions :

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

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

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

Essay # 19. Famous Volcanoes around the World :

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

Essay # 20. Volcanic Hazards :

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Essay # 21. Volcanoes and Atmospheric Pollution :

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

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

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

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

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

i. Global Warming :

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

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

ii. Geothermal Energy :

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

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

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

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

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

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

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

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

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

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

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

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

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

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

iii. Phenomena Associated with Volcanism :

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

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

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

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

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

Related Articles:

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

Science , Essay , Geology , Volcanoes , Essay on Volcanoes

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Ever since we were small kids, we always were fascinated about what was in the sky. Ever thought about what is going on beneath the land on which we stand? Let us dive down inside the Earth’s surface and familiarize ourselves with a phenomenon known as the Volcano. You may have seen Volcanic eruptions in movies. Let us learn volcanoes in detail.

Introduction to Volcanoes

Volcanoes are openings on the Earth’s crust through which molten metal comes out. Volcanoes form on the boundaries of the tectonic plates that continuously move inside the Earth. There are 17 such tectonic plates inside the Earth’s Crust. The Earth is divided into several parts such as the Crust, Upper Mantle, Mantle, Outer Core, Inner Core. These tectonic plates exist in the Mantle region inside the Earth. Earthquakes also occur because of the movement of such tectonic plates. Places on the Earth that are on the edges of these tectonic plates are affected the most as these regions are subjected to more amount of underground activity. According to geographical studies, volcanoes generally exist in places where the tectonic plates are either converging or diverging. Volcanic eruption results in polluting the environment as it includes harmful gases and other hot toxic elements including ash.

Formation of Volcanoes and Volcanic Eruptions

Volcanoes are scattered across the planet. Almost about 1500 volcanoes are there on the Earth’s crust and several others are there on the ocean bed. All volcanoes emit gases no matter where they are present. The journey of these emissions begins deep down near the core of the Earth. The core is as hot as the surface of the Sun. Above the core is the mantle layer which is fully present of rocks. The Earth’s core is of very high temperature, because of which the heat converts some portion of the rocky mantle into Magma which has a lower density than the surrounding rocky environment and as a result, it travels upwards and burst out through the openings on the earth’s crust which we know as a volcanic eruption. Once this magma reaches Earth’s surface it is known as lava and has a temperature of near about.

Classification of Volcanoes

There are various kinds of volcanoes primarily classified on the shape and size basis. They are-

• Strato Volcanoes: These appear as tall steep mountains over the earth’s crust.
• Shielded Volcanoes: These appear as dome-shaped over the ground.
• Calderas: These types of volcanoes have large depressions and look like plateaus. A continuous amount of smoke keeps coming out from these types of volcanoes.
• Ocean- ridges: These are underwater chains of volcanic mountains that exist deep inside the ocean bodies.

Again based on eruptions volcanoes are classified as active or inactive type volcanoes. The volcanoes which erupt on regular basis are termed as active volcanoes and the ones which erupted after a long time (maybe during historical times) are referred to as inactive or dormant type volcanoes.

Ring of Fire

The Ring of Fire is nothing but the path that traces the boundaries of several tectonic plates around the Pacific Ocean which consist of about the world’s 75% of the volcanoes. The Ring of fire covers up regions from Eastern Asia to both North and South America. It is a long chain of about 25000 miles and touches some parts of New Zealand as well.

Famous Volcanic Eruptions

Since the inception of Earth, there has been a lot of volcanic eruptions which were also catastrophic for mankind. Some of them are:

• Mount Vesuvius in 79 A.D in Italy.
• Mount Ruiz in 1985 in Columbia.
• The Mount Tambora in 1815 in Indonesia.
• Mount Pelee in 1902 in the Caribbean Islands.
• Mount Krakatoa in 1883 in Indonesia.

In America, there is the famous Yellowstone National Park which consists of the supervolcano. Scientists think that if this supervolcano erupts then it will destroy almost half of the planet. Also, this supervolcano is said to have erupted about 7 lakh years ago.

Effects of Volcanic Eruption on the Environment

Volcanic eruptions releases tons of harmful and toxic elements into the atmosphere. These harmful gases include oxides of carbon and sulfur which have a deadly impact on the ozone layer. Nitrogen dioxide formed also affects the environment. Again, gas emissions as a result of the volcanic eruptions lead to the creation of acid rain as well. Also, aerosols are injected into the Earth’s Atmosphere. When high-temperature ash is thrown out into the environment then sometimes it happens that those particles hit the aeroplanes flying in the sky.

Again when pyroclastic materials mix up with the water in the nearby lakes and rivers, it affects the marine life as well as pollutes the water bodies. Earthquakes are also a result of a high VEI type volcanic eruption. These types of earthquakes are volcano-tectonic earthquakes. These types of earthquakes can have a reading of as high as 7 on the Richter scale. Tsunamis are also a consequence of a devastating volcanic eruption.

Volcanic Eruptions In Solar System

As Earth is a planet and volcanic eruptions have been taking place since its inception, so it is quite obvious that the other planets also experience such a phenomenon. Mars is said to have several dormant type volcanoes. Some moons of Jupiter are said to have an active volcanic system. The planet Venus has a Basalt surface which has been generated because of several volcanoes erupting together. In a nutshell, we can say that a celestial body whose core is hot enough to generate molten metal will experience volcanic eruptions.

FAQs about Volcanoes

Q.1. What is VEI?

Answer: VEI is the volcanic explosivity index. This property depicts various factors of a volcanic eruption such as the volume of lava, gas, and other emissions from the volcano. The VEI scale begins from 0. The most destructive volcanic eruption has a rating of 8 on the VEI scale. Mount Tambora in Indonesia erupted in 1815 with a VEI scale of 7. Also, this was the most destructive Strato volcanic eruption ever witnessed by mankind. This leads to earthquakes and tsunamis as well. This volcanic eruption immediately killed around 10,000 people and later around with various diseases coming into the picture took away more than 1,00,000 lives.

Q.2. What are tectonic plates?

Answer: The tectonic plates are large pieces on the Earth’s crust and upper mantle region which move and collide continuously with each other. The formation of tectonic plates is considered to begin about 3.2 billion years ago. Because of the movement of these tectonic plates, mountains and plateaus, volcanoes form.

Q.3.  What is a pyroclastic flow?

Answer: When a volcano erupts, lots of toxic elements(gases) and molten metal having very high temperature coming out of the volcano opening and flows down through the outer volcanic surface. This can burn down anything in its path. This phenomenon is the pyroclastic flow. The speed of such flow is as high as 725 kilometres per hour.

Q.4. What are aerosols?

Answer: Aerosols are the suspension of solid particles or liquid droplets in another gaseous medium. The volcanic eruptions include aerosols, i.e. solid particles mix with harmful gases and eject out.

Q.5. What is Basalt?

Answer: Basalt is an igneous rock that forms by the cooling of the lava rich in elements such as iron and magnesium.

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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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Community and Authority Response to Volcanic Eruptions Essay

Introduction, location of buildings, reluctance to evacuation, economy preference, distrust with investigations conducted and public ignorance, works cited.

Volcanic eruption is one of the natural phenomena that pose a lot of threats to the public. However, the eruption may at times be beneficial to the country and community living around as it may attract tourists. For many years, there have been numerous fatalities resulting from volcanic eruptions. Those who escape the death, have suffered other ailments due to being exposed to volcanic ash and other toxic gases that accompany volcanic eruptions. With the world having the capacity to predict and determine the volcanic activity of most mountains, there have always been early warnings to people and the government for a potential volcanic eruption.

This is vital to help society, as well as the government, prepare for ways to evacuate people from the area before the actual eruption takes place. However, despite there being early warnings of volcanic eruptions, the community living in these areas has not taken the dangers of the eruption seriously. The authorities in these areas have also been found to be reluctant in addressing the matter. This is concerning the structure and location of buildings, government and society response to crisis after eruptions, and others.

The dangers of volcanic eruptions call for people to locate their buildings away from mountains that are identified as volcanic active. The fact that it is difficult to predict the exact date and time that the mountain is likely to explode, underlines the need for people to situate their buildings away from the mountain to avoid being trapped. This has not been the case in most countries where there are mountains identified as volcanic active.

People have gone to an extent of building living houses at the foot of these mountains. This has predisposed them to the dangers of being trapped in case of volcanic eruptions. Despite the scientists warning of signs of volcanic activity in these mountains as well as the dangers of the eruption, people have not taken heed to protect themselves (Alexander 67). The government and other authorities in these regions have also taken no measures to ensure that people are safe. With most people daring to take risks to enrich themselves, they are likely to construct and operate businesses in any region. This calls for the government to come up with regulations to curb this habit.

Because of the dangers of volcanic eruption, the government needs to come up with regulations governing people on how and where to construct their buildings in areas identified to be volcanic active. This has not been the case. People have been left to construct their buildings whenever they feel to best suit them making them vulnerable to these dangers. The ignorance from the society, as well as other authorities responsible for responding to emergencies, led to the loss of life during the Mt. St. Helen eruption.

The mountain having been identified as volcanic activity, required the agents responsible for responding to such catastrophes to be always prepared to avoid cases of damages resulting due to poor response after the eruption. Federal Emergency Management Agency (FEMA) and Department of Emergency Services (DES) ought to ensure that it was always prepared to respond to any tragedy (Chester, Angus, Wetton & Wetton pp. 168-196). This is by ensuring that they always have the required resources, funds, and expertise needed to deal with a volcanic eruption. Ignorance from the management and government at large led to these departments being caught unprepared after the eruption.

Despite the public and government learning serious lessons from the eruption, still, some of the leaders in the United States government seem to take the issue lightly. This is evident by remarks from Louisiana governor Bobby Jindal who argued that there was no need for the government to invest heavily in monitoring volcanic activities in Alaska. The sentiments have come at a time when Redoubt Mountain which is one of the volcanic active mountains is expected to erupt. Despite the economic hardships and fatalities that resulted from volcanic eruptions in the country twenty years ago, Jindal still seems not to take the dangers of volcanic eruptions seriously.

Before and after a volcanic eruption, people are requested to evacuate the affected area in fear of further eruption and health hazards posed by gases emitted during the eruption. Most of the gasses are said to be corrosive and they corrode eye tissues. In addition, some gases emitted during a volcanic eruption are poisonous if inhaled. To avoid these problems, it calls for all people to evacuate the affected areas. These gases and ash may remain in the air for a long period.

Going back to the affected area a few days after evacuation may not help in preventing some of the health hazards caused by eruptions. Even after people being informed about the health implications of volcanic eruptions, they have been reluctant to evacuate the affected areas. It has led to the government going to an extent of applying force to make people leave the area. After leaving, people have been found to take limited time before going back to their homes (Chester pp. 319-328). This has been the case even in the recent eruption that occurred in Iceland. Poor conditions in refuge places have been attributed to the desire by people to go back to their homes after evacuation.

The authorities have not been serious in considering other dangers accompanied by volcanic eruption such as respiratory problems, social disruption, and disease outbreaks. As a result, no measures are usually taken to ensure the well-being of the evacuated persons leading to most of them going back to their homes shortly after the evacuation exercise.

Volcanic eruptions lead to most of the economic activities in the affected areas being brought to a halt. No trade goes on with people fearing further eruptions. This affects the country and the society adversely especially those that rely on trade. After the volcanic eruption in Iceland, flights that use that route were suspended. This led to trade between different countries coming to a stop. People and countries complained of their products expiring due to them being unable to access the market. With people wishing to enrich themselves, they have ignored health hazards resulting from the eruption and went on with their trade.

For instance, after airline companies in Iceland and other places realized the loss they were incurring they called the suspension and resumed their activities event without being guaranteed that it was safe for them to embark on their normal activities (Forsloff 432). Some pilots even undermined the implications of flying planes across the cloud of ash in the air and argued that they could fly below the cloud and still go on with their business as usual.

Despite people being warned that the mountain may have further eruptions in the future, people have taken the opportunity to visit them and take photos to sell later. Event after people being evacuated, they have all returned b to their homes and are making visits to the site. There have been warnings that toxic fumes that were emitted in the air are still in there and inhaling them would lead to respiratory problems.

However, people have not taken the issue seriously. They are making frequent visits to the site even without ensuring that they have worn protective gears and carried artificial oxygen to ensure that they do not inhale fluorine, sulfur, and carbon dioxide gas that is still in the air (Lavigne et. al pp. 273-287). There is a presence of lava flow in Hrunagil but this is not deterring people from visiting the mountain. The fact that it is long since a volcanic eruption occurred in the region has made most of the people take the initiative of visiting the site without putting into consideration the dangers they expose themselves to.

Over time, there have been rumors of certain mountains facing volcanic eruptions only to find that they do not occur. This has led to the public not being serious with the given results. People have been found to evacuate their homes and come back a few days later once they realize that the mountain is taking a long to erupt. For instance, there were rumors that Mt. Kelud in Indonesia showed signs of erupting (Masel-Walters, Wilkins & Walters 129).

The signs were very precise with water in crates lakes fount on top of the mountain becoming extremely hot. There was the presence of gases on top of the mountain as well as the occurrence of several earthquakes. People even claimed that the top of the mountain had started changing its shape in preparedness for eruption. After people were informed of the danger, they were reluctant to evacuate the place. As a measure by the government to avoid fatalities and other damages in case of an eruption, troops were sent to the scene to forcefully evacuate the residents. However, with time, the eruption failed to occur leading to the government declaring that the place was safe for people to go back home.

Currently, the mountain is not being monitored due to ignorant from the government and the society around the area (Tobin & Whiteford 28-48). The fact that it is difficult to predict the exact time when the mountain will erupt poses the society in great danger of being caught unawares.

Despite Indonesian mountains being known for volcanic eruptions, people have gone to an extent of living on their slopes in a bid to use their fertile volcanic soils in planting. Even after being warned that the mountain is likely to erupt, these people are found to be unwilling to leave their crops. Some people in the country have survived various volcanic eruptions. To them, they consider themselves as capable of protecting themselves from the dangers of a volcanic eruption.

These people are never willing to evacuate from the mountain till the actual eruption takes place (Wallace-Hadrill pp. 311-337). To mitigate damages resulting from a volcanic eruption, the Indonesian government has been found to actively draw off water from crater lakes on top of the mountain as well as dig tunnels around the mountain to divert lava flow. They have overlooked the fact that the eruption may lead to the emission of hot ashes and other toxic gases into the air posing a threat to the public. Their action has been used by people in the area to justify their reasons for not leaving their homes.

Another incidence that brought out the level of ignorance among the people living in volcanic-prone areas is the Pompeii eruption. Despite people having seen and warned of eruption, it caught them unprepared. People went on with their daily activities paying no attention to the mountain even after seeing smoke appearing at the top of the mountain.

Fatalities and property damage resulting from volcanic eruptions are attributed to the high level of ignorance among society and authorities on the dangers of volcanic eruptions. Despite people being warned of volcanic active mountains, they still go to an extent of building their homes on the slopes of these mountains. The government and other authorities responsible for addressing emergencies have been reluctant to equip their staff with the necessary expertise and resources.

This has led to them not effectively responding to eruption emergencies. After realizing that a certain mountain is about to erupt, society declines to take the initiative of evacuating the place. There are instances where people were forced to evacuate their homes by troops. The need by people to continue with their economic activities has led to them ignoring the dangers of eruptions. After evacuation, the society is found to go back to their homes even before they are assured that the place is secure.

Alexander, David. Confronting catastrophe: new perspectives on natural disaster . England: Terra Publishing.

Chester, David, Angus, Duncan, Wetton, Philip & Wetton, Roswitha. “Response of the Anglo-America military authorities to the eruption of Vesuvius, 1944.” Journal of Historical Geography , 33.1 (2007): 168-196.

Chester, David. “Theology and disaster studies: The need for dialogue.” Journal of Volcanology and Geothermal Research, 146.4 (2005): 319-328.

Forsloff, Carol. “Jindal vs. the volcano reveals Louisiana governor’s ignorance.” Digital Journal, (2009).

Lavigne, Franck, Coster, Benjamin, Juvin, Nancy, Flohic, Francois, Gaillard, Jean-Christophe, Texier, Paulline, Morin, Julie & Sartohadi, Junun. “People’s behavior in the face of volcanic hazards: Perspective from Javanese communities, Indonesia.” Journal of Volcanology and Geothermal Research , 172.3 (2008): 273-287.

Masel-Walters, Lynne, Wilkins, Lee & Walters, Tim. Bad tidings: communication and catastrophe . New Jersey: Lawrence Erlbaum Associates, Inc., Publishers.

Tobin, Graham & Whiteford, Linda. “Community resilience and volcano hazard: The eruption of Tungurahua and evacuation of the Faldas in Ecuador.” Disasters , 26.1 (2002): 28-48.

Wallace-Hadrill, Andrew. Houses and Society in Pompeii and Herculaneum. Princeton: Princeton University Press, 1994.

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IvyPanda. (2021, December 20). Community and Authority Response to Volcanic Eruptions. https://ivypanda.com/essays/community-and-authority-response-to-volcanic-eruptions/

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Science Projects > Earth & Space Projects > Introduction to Volcanoes  

Introduction to Volcanoes

An introduction to volcanoes.

You’ve probably heard in the news about volcanic eruptions, or you might remember when Mount St. Helens erupted in 1980.

(Volcanoes can alter the landscape of a town, county, even country!)

Perhaps you’ve even seen an active volcano. Although they are often a destructive force, volcanoes are an amazing facet of creation. They come in a variety of shapes, sizes, and eruption types.

Why Do Volcanoes Erupt?

Volcanoes erupt when magma , red-hot liquid rock, seeps up through a vent in the earth.

More violent eruptions occur when pyroclastic material – a mixture of magma, rocks, ash, and hot gases – is exploded upward by pressure caused by underground gases and magma.

When magma flows above the surface of the earth, it is called lava . Usually lava changes from bright red to duller red, gray, or black as air causes it to cool and solidify.

Volcanic eruptions vary in size and display. There are six common types of eruptions, with differing features:

• Plinian eruptions usually have thick lava and high gas content. They can shoot pyroclastic material high into the air, moving at hundreds of feet per second. These eruptions can last for hours or even days.
• Hawaiian eruptions are not usually very explosive; instead, they produce streams of slow-moving lava. An interesting feature of Hawaiian eruptions are ‘fire fountains’, huge fountains of magma being spewed into the air. These fountains last anywhere from a few minutes to a few hours.
• Strombolian eruptions put on an impressive display but are not usually very dangerous. During these eruptions, lava is shot fifty to a few hundred feet into the air and is accompanied by booming noises. These eruptions do not produce much lava flow.
• Vulcanian eruptions do not have much lava flow either, but they tend to be larger than Strombolian ones. They produce a lot of ash and spit out ‘bombs’ of hard pyroclastic material.
• Hydrovolcanic eruptions occur when water vapor hits hot magma and gases, and forms huge steam clouds that rise from the volcano.
• Fissure eruptions occur when magma leaks up through a long crack in the ground. They are associated with ‘curtains of fire” – magma being spewed up to a small height all along a fissure.

There are also different shapes and sizes of volcanoes.

Stratovolcanos are usually very high, with pointy tops. They are formed by repeated explosions, usually Plinian, and by slow-moving lava. Eruptions from these volcanoes are usually very large but occur infrequently.

Mount Vesuvius, which buried the Roman city of Pompeii in 79 AD (creating an instant fossil record ) is a stratovolcano.

Shield-type volcanoes are usually spread out over a large area and have gently sloping sides. They are caused by minor explosions (usually Hawaiian) and erupt more frequently than stratovolcanoes. Most of the major volcanoes in Hawaii are shield volcanoes.

Scoria Cones are the most common volcano type, usually caused by Strombolian eruptions. They are shaped like upside-down cones, with slightly squished tops. Scoria cones usually erupt only once.

Try These Volcano Projects:

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Essay on Volcanic Eruption | Geography

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

Essay on Volcanic Eruption

1. essay on the introduction to volcanic eruption:.

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

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

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

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

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

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

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

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

2. Essay on the Effects of Volcanic Eruption:

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

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

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

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

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

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

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

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

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

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

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

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

3. Essay on the Types of Volcanic Eruption:

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

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

1. Magmatic Eruptions:

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

2. Strombolian Eruptions:

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

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

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

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

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

3. Vulcanian Eruption:

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

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

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

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

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

4. Pel é an Eruption:

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

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

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

Some other examples include the following:

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

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

iii. The 1956 eruption of Bezymianny;

iv. The 1968 eruption of Mayon Volcano;

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

5. Hawaiian Eruption:

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

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

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

6. Surtseyan Eruption:

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

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

Several Specific Characteristics:

i. Physical nature of magma – viscous; basaltic.

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

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

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

v. Structures built around vent – tuff rings

7. Plinian Eruption:

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

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

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

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

8. Phreatomagmatic Eruptions :

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

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

9. Submarine Eruption:

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

10. Sub-Glacial Eruption:

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

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

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

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

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

11. Phreatic Eruption :

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

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

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

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Ocean Heat Has Shattered Records for More Than a Year. What’s Happening?

There have been record temperatures every day for more than a year. Scientists are investigating what’s behind the extraordinary measurements.

Daily Global Sea Surface Temperatures

Source: Climate Reanalyzer , Climate Change Institute at the University of Maine, based on data from NOAA Optimum Interpolation Sea Surface Temperature (OISST) Note: Data through April 8, 2024. By The New York Times

By Delger Erdenesanaa

The ocean has now broken temperature records every day for more than a year. And so far, 2024 has continued 2023’s trend of beating previous records by wide margins. In fact, the whole planet has been hot for months, according to many different data sets.

“There’s no ambiguity about the data,” said Gavin Schmidt, a climatologist and the director of the NASA Goddard Institute for Space Studies. “So really, it’s a question of attribution.”

Understanding what specific physical processes are behind these temperature records will help scientists improve their climate models and better predict temperatures in the future.

Last month, the average global sea surface temperature reached a new monthly high of 21.07 degrees Celsius , or 69.93 degrees Fahrenheit, according to the Copernicus Climate Change Service, a research institution funded by the European Union.

“March 2024 continues the sequence of climate records toppling for both air temperature and ocean surface temperatures,” Samantha Burgess, deputy director of Copernicus, said in a statement this week.

The tropical Atlantic is abnormally warm, helping set the stage for a busy hurricane season, according to an early forecast by scientists at Colorado State University. Higher ocean temperatures provide more energy to fuel stronger storms.

Global temperatures are rising long-term because the burning of fossil fuels adds greenhouse gases, which warm the planet, to the atmosphere. So far, climate change has raised the global average temperature by about 1.2 degrees Celsius, or 2.2 degrees Fahrenheit, above the preindustrial average temperature. And because it takes more energy to heat up water than air, the oceans have absorbed the vast majority of the planet’s warming from greenhouse gases.

But the “massive, massive records” set over the past year are beyond what scientists would expect to see even considering climate change, Dr. Schmidt said.

What’s different now, compared with this time last year, is that the planet is dealing with the effects of an El Niño event that began in July. El Niño events are natural climate patterns associated with elevated temperatures.

“The temperatures that we’re seeing now, the records being broken in February and March, are actually much more in line with what we would expect,” compared with those of last year, Dr. Schmidt said. “Let’s see what happens by the summer.”

El Niño is weakening and expected to dissipate soon. What happens to global average temperatures then would help shed light on the temperatures of 2023, he said.

In addition to climate change and El Niño, there are a couple of other factors that might be contributing to these dizzying records.

One is a recent reduction in aerosol pollution from container ships traversing the ocean, following new international fuel standards that took effect in 2020. Ironically, aerosols have a cooling effect in the atmosphere, and had been helping to mask the true extent of climate change until now.

There was also the huge eruption of the underwater Hunga Tonga-Hunga Haʻapai volcano in 2022. Volcanic eruptions that happen on land send up plumes of soot and aerosols, which block sunlight and temporarily cool the atmosphere. But because this volcano was submerged under the Pacific Ocean, its eruption also sprayed millions of tons of water vapor into the upper atmosphere. Water vapor is a powerful greenhouse gas.

‘It’s Super Spectacular.’ See How the Tonga Volcano Unleashed a Once-in-a-Century Shockwave.

A new simulation gives a detailed look at a shockwave that circled the planet for days.

“It was the most explosive eruption since Krakatau, and usually the year after is when you see the impacts,” said Sean Birkel, an assistant professor at the University of Maine Climate Change Institute, who created a climate data visualization tool called Climate Reanalyzer. He suspects the warming effect of the volcanic eruption has been larger than early estimates suggested, noting that the eruption may have affected atmospheric circulation and helped amplify the El Niño that developed in 2023. But, he added, more research is needed.

Dr. Schmidt pointed out that when scientists put together their estimates so far of how much the volcanic eruption, the reduced shipping pollution, El Niño and climate change should warm the planet, the numbers don’t add up .

“There could be still something missing,” he said, like other sources of aerosol pollution having improved more than researchers know, or Earth’s climate having more internal variability than expected, or global warming amplifying the effects of El Niño.

Several groups of scientists are working to get a clearer picture, Dr. Schmidt said, and he expects results to start being published in the next few months.

Nadja Popovich contributed reporting.

Delger Erdenesanaa is a reporter covering climate and the environment and a member of the 2023-24 Times Fellowship class, a program for journalists early in their careers. More about Delger Erdenesanaa

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