presentation of volcano

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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Volcanoes and Associated Vocabulary

Volcanoes – View From Space

3 Types of Volcanoes

Volcano Facts

Parts of a Volcano

Volcanic cones

See Also: Earthquakes , Yellowstone National Park

Free Games & Learning Activities about Volcanoes for Kids

For Teachers

Lots of Lessons – Volcanoes

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Volcanoes, explained

These fiery peaks have belched up molten rock, hot ash, and gas since Earth formed billions of years ago.

Volcanoes are Earth's geologic architects. They've created more than 80 percent of our planet's surface, laying the foundation that has allowed life to thrive. Their explosive force crafts mountains as well as craters. Lava rivers spread into bleak landscapes. But as time ticks by, the elements break down these volcanic rocks, liberating nutrients from their stony prisons and creating remarkably fertile soils that have allowed civilizations to flourish.

There are volcanoes on every continent, even Antarctica. Some 1,500 volcanoes are still considered potentially active around the world today; 161 of those—over 10 percent—sit within the boundaries of the United States .

But each volcano is different. Some burst to life in explosive eruptions, like the 1991 eruption of Mount Pinatubo , and others burp rivers of lava in what's known as an effusive eruption, like the 2018 activity of Hawaii's Kilauea volcano. These differences are all thanks to the chemistry driving the molten activity. Effusive eruptions are more common when the magma is less viscous, or runny, which allows gas to escape and the magma to flow down the volcano's slopes. Explosive eruptions, however, happen when viscous molten rock traps the gasses, building pressure until it violently breaks free.

How do volcanoes form?

The majority of volcanoes in the world form along the boundaries of Earth's tectonic plates—massive expanses of our planet's lithosphere that continually shift, bumping into one another. When tectonic plates collide, one often plunges deep below the other in what's known as a subduction zone .

As the descending landmass sinks deep into the Earth, temperatures and pressures climb, releasing water from the rocks. The water slightly reduces the melting point of the overlying rock, forming magma that can work its way to the surface—the spark of life to reawaken a slumbering volcano.

Not all volcanoes are related to subduction, however. Another way volcanoes can form is what's known as hotspot volcanism. In this situation, a zone of magmatic activity —or a hotspot—in the middle of a tectonic plate can push up through the crust to form a volcano. Although the hotspot itself is thought to be largely stationary, the tectonic plates continue their slow march, building a line of volcanoes or islands on the surface. This mechanism is thought to be behind the Hawaii volcanic chain .

Where are all these volcanoes?

Some 75 percent of the world's active volcanoes are positioned around the ring of fire , a 25,000-mile long, horseshoe-shaped zone that stretches from the southern tip of South America across the West Coast of North America, through the Bering Sea to Japan, and on to New Zealand.

This region is where the edges of the Pacific and Nazca plates butt up against an array of other tectonic plates. Importantly, however, the volcanoes of the ring aren't geologically connected . In other words, a volcanic eruption in Indonesia is not related to one in Alaska, and it could not stir the infamous Yellowstone supervolcano .

What are some of the dangers from a volcano?

Volcanic eruptions pose many dangers aside from lava flows. It's important to heed local authorities' advice during active eruptions and evacuate regions when necessary.

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One particular danger is pyroclastic flows, avalanches of hot rocks, ash, and toxic gas that race down slopes at speeds as high as 450 miles an hour . Such an event was responsible for wiping out the people of Pompeii and Herculaneum after Mount Vesuvius erupted in A.D. 79 .

Similarly, volcanic mudflows called lahars can be very destructive. These fast-flowing waves of mud and debris can race down a volcano's flanks, burying entire towns.

Ash is another volcanic danger. Unlike the soft, fluffy bits of charred wood left after a campfire, volcanic ash is made of sharp fragments of rocks and volcanic glass each less than two millimeters across. The ash forms as the gasses within rising magma expand, shattering the cooling rocks as they burst from the volcano's mouth. It's not only dangerous to inhale , it's heavy and builds up quickly. Volcanic ash can collapse weak structures, cause power outages, and is a challenge to shovel away post-eruption.

Can we predict volcanic eruptions?

Volcanoes give some warning of pending eruption, making it vital for scientists to closely monitor any volcanoes near large population centers. Warning signs include small earthquakes, swelling or bulging of the volcano's sides, and increased emission of gasses from its vents. None of those signs necessarily mean an eruption is imminent, but they can help scientists evaluate the state of the volcano when magma is building.

However, it's impossible to say exactly when, or even if, any given volcano will erupt. Volcanoes don't run on a timetable like a train. This means it's impossible for one to be “overdue” for eruption —no matter what news headlines say.

What is the largest eruption in history?

The deadliest eruption in recorded history was the 1815 explosion of Mount Tabora in Indonesia. The blast was one of the most powerful ever documented and created a caldera —essentially a crater—4 miles across and more than 3,600 feet deep. A superheated plume of hot ash and gas shot 28 miles into the sky, producing numerous pyroclastic flows when it collapsed.

The eruption and its immediate dangers killed around 10,000 people. But that wasn't its only impact. The volcanic ash and gas injected into the atmosphere obscured the sun and increased the reflectivity of Earth, cooling its surface and causing what's known as the year without a summer. Starvation and disease during this time killed some 82,000 more people, and the gloomy conditions are often credited as the inspiration for gothic horror tales, such as Mary Shelley's Frankenstein .

Although there have been several big eruptions in recorded history, volcanic eruptions today are no more frequent than there were a decade or even a century ago. At least a dozen volcanoes erupt on any given day. As monitoring capacity for—and interest in—volcanic eruptions increases, coverage of the activity more frequently appears in the news and on social media. As Erik Klemetti, associate professor of geosciences at Denison University, writes in The Washington Post : “The world is not more volcanically active, we’re just more volcanically aware.”

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A huge volcano near Naples has been convulsing. What does it mean?

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About Volcanoes

Volcanoes are openings, or vents where lava, tephra (small rocks), and steam erupt onto the Earth's surface. Volcanic eruptions can last days, months, or even years. 

What is a volcano?

Many mountains form by folding, faulting, uplift, and erosion of the Earth's crust. Volcanic terrain, however, is built by the slow accumulation of erupted lava. The vent may be visible as a small bowl shaped depression at the summit of a cone or shield-shaped mountain. Through a series of cracks within and beneath the volcano, the vent connects to one or more linked storage areas of molten or partially molten rock (magma). This connection to fresh magma allows the volcano to erupt over and over again in the same location. In this way, the volcano grows ever larger, until it is no longer stable. Pieces of the volcano collapse as rock falls or as landslides.

How do volcanoes erupt?

Molten rock below the surface of the Earth that rises in volcanic vents is known as magma, but after it erupts from a volcano it is called lava. Magma is made of molten rock, crystals, and dissolved gas—imagine an unopened bottle of soda with grains of sand inside. The molten rock is made of the chemicals oxygen, silicon, aluminum, iron, magnesium, calcium, sodium, potassium, titanium, and manganese. After cooling, liquid magma may form crystals of various minerals until it becomes completely solid and forms an igneous or magmatic rock.

Originating many tens of miles beneath the ground, magma is lighter than surrounding solid rock. It is driven towards Earth's surface by buoyancy, it is lighter than the surrounding rock, and by pressure from gas within it. Magma forces its way upward and may ultimately break though weak areas in the Earth's crust. If so, an eruption begins.

Magma can be erupted in a variety of ways. Sometimes molten rock simply pours from the vent as fluid lava flows. It can also shoot violently into the air as dense clouds of rock shards (tephra) and gas. Larger fragments fall back around the vent, and clouds of tephra may move down the slope of the volcano under the force of gravity. Ash, tiny pieces of tephra the thickness of a strand of hair, may be carried by the wind only to fall to the ground many miles away. The smallest ash particles may be erupted miles into the sky and carried many times around the world by winds high in the atmosphere before they fall to the ground.

How many volcanoes are there?

USGS scientists monitor over 160 active and potentially active volcanoes in the United States. Some of these are erupting now and others could erupt at some point in the future. Most of these volcanoes are located in Alaska, a state where eruptions occur almost every year. The rest of the volcanoes are located throughout the American West, and in Hawaii (see our  volcano activity map  for their locations). Kīlauea volcano on the Island of Hawai‘i is one of the most active volcanoes on Earth. It has been erupting almost nonstop since 1983!

There are about 1,350 potentially active volcanoes worldwide, not counting the volcanoes under the oceans. About 500 of these have erupted in the past 100 years. Many of these are located around the Pacific Ocean in what is known as the "Ring of Fire." In the U.S., volcanoes along the west coast and in Alaska (Aleutian volcanic chain) are part of the Ring of Fire, while Yellowstone and Hawaiian volcanoes form over a "hot spot."

See the  Eruption, Earthquakes, and Emissions  around the world since 1960.

What are the main types of volcanoes?

Cinder cone.

Cinder cones are the simplest type of volcano. They are made of small pieces of solid lava, called cinder, that are erupted from a vent. The ground shakes as magma rises from within the Earth. Then, a powerful blast throws molten rocks, ash, and gas into the air. The rocks cool quickly in the air and fall to the earth to break into small pieces of bubbly cinder that pile up around the vent. They accumulate as a small cinder cone that can be as high as a thousand feet above the surrounding ground. If the wind is blowing during the eruption, cinder is carried downwind before it's deposited into an oval shape. Eruptions that form cinder cones also feed lava flows that spread outward from the eruptive vent. When you climb a cinder cone you can usually find the bowl-shaped crater marking the location of the vent. If eruptions of cinder and lava flows happen repeatedly from the same vent, the overlapping layers can form a composite volcano (stratovolcano). When looking at a map, you will find that thousands of cinder cones exist in western North America and in other volcanic areas of the world.

Composite Volcano (Stratovolcano)

Some of the Earth's grandest mountains are composite volcanoes—sometimes called stratovolcanoes. They are usually tall with steep even sides and are made out of repeating layers of lava flows, volcanic ash, cinders, blocks, and volcanic bombs. Some composite volcanoes rise over 8,000 feet above their surroundings, but they reach much higher elevations when compared to the level of the sea (called above sea level). Ojos del Salado in Chile is the tallest composite volcano on Earth with a summit elevation (height above sea level) of 22,615 feet; the tallest in the U.S. is Mount Rainier in Washington State with a summit elevation of 14,410 feet. Some of the most famous and beautiful mountains in the world are composite volcanoes, including Mount Fuji in Japan, Mount Cotopaxi in Ecuador, Mount Shasta in California, Mount Hood in Oregon, and Mount St. Helens in Washington.

Shield Volcano

Shield volcanoes are built almost entirely of fluid lava flows. Lava pours out of vents in all directions, either from the summit (top) or along two to three rift zones (fractures) that radiate out from the summit like spokes on a bicycle wheel. As lava flows overlap one another, they construct a broad, gently sloping dome shape that from far away appears similar to a warrior's shield. Shield volcanoes build up slowly by the growth of thousands of lava flows that spread widely over great distances, and then cool as thin sheets. On Earth, some of the most massive volcanoes are shield volcanoes. In northern California and Oregon, many shield volcanoes are up to 3 or 4 miles wide and as tall as 1,500 to 2,000 feet. The Hawaiian Islands are made of a chain of shield volcanoes including Kīlauea and the world's largest active volcano, Mauna Loa. Looking at pictures of volcanoes, you can usually identify them by shape as being a shield volcano or stratovolcano.

A volcano can host many lava domes over a long period of time, so these are technically not a "volcano type" but rather an eruption phenomenon. Lava domes are technically lava flows made up of lava that is too thick to flow away from the vent. Lava squeezes out of the vent and accumulates as a giant pile over and around the vent. Some domes form pointy spines, while others appear as a giant muffin, as opening flower petals, or as steep-sided stubby flows or tongues. Lava domes often grow within craters or upon the flanks of large steep-sided composite volcanoes. Lava domes can be dangerous. They grow largely by expansion from within. As fresh magma fills the inside, the cooler and harder outer surface shatters and spills hot rock and gases down the mountainside. The circle-shaped Novarupta Dome that formed during the 1912 eruption of Katmai Volcano, Alaska, measures 800 feet across and 200 feet high. This dome was one of the last squirts of lava to emerge during a much larger and long-term eruption. The eruption at Katmai was the largest and most violent eruption ever to occur within the United States.

• Earth Science

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

What Are Volcanoes?

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

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

Formation of Volcanoes

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

Different Stages of Volcanoes

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

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

Volcanoes are categorised into three main categories:

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

Reason Behind the Eruption of Volcanoes

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

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

Types of Volcanoes

These are grouped into four types:

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

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

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

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

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

The video about the eruption of volcanoes

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Teach Earth Science

Science Partnership of the East Bay

Introduction to Volcanoes This unit introduces volcanology and the relationship between the occurrence of volcanoes and plate tectonics. In addition, factors that affect the mode of eruption (tectonic setting, viscosity, etc.) are also described. Lastly, volcanic hazards are reviewed.

Workshop Presentations

Volcano Basics - reviews the basics about volcanoes, lava composition and viscosity and the relationship with plate tectonics. .

PowerPoint Click to download the MS Powerpoint file (21.1 Mbytes)

PDF Click to view or download the presentation in PDF (5.5 Mbytes)

HT ML Cl ick to view the presentation in html format.

Online Lecture. Click here to view a streaming lecture covering the basics of volcanoes (~51 minutes).

Volcano Hazards - reviews volcano monitoring and volcano hazards.

PowerPoint Click to download the MS Powerpoint file (39 Mbytes)

PDF Click to view or download the presentation in PDF (28 Mbytes)

Online Lecture. Click here to view a streaming lecture that discusses the monitoring of volcanoes and volcanic hazards (~23 minutes).

Classroom Activities

Flour Box Volcano Deformation Model PDF In this classroom activity or demo, volcanic deformation can be modeled including inflation, formation of a caldera and the development of fractures from rising magma. From the Teacher’s Interactive Resource Guide to the DVD Lava Flows and Lava Tubes: What They Are, How They Form. www.volcanovideo.com Click here to view a video demonstration of a version of this demonstration from the U.S. Geological Survey

Gelatin Model of Magma Instrusion PDF This activity demonstrates the intrusion of magma (chocolate sauce into country rock (plain gelatin). Click here to view a video demonstration of this activity. This activity is from Teachers on the Leading Edge

The Great Viscosity Race. In this activity, students modle the effect of composition, temperature and partial crystallization on the viscosity of magma/lava.

• Student Data Sheet PDF Word Document
• Teacher Instructions Coming Soon

How Fast is the Pacific Plate Moving? PDF Word Document In this activity, students examine geochronological data for lava flows that form the Hawaiian Islands and use that data and the distances of the islands from the Hawaiian mantle hotspot to detemine the rate that the Pacific Plate is moving over. This activity permits students to apply mathematical concepts (e.g. rate) to a scientific question about the rate of motion of the Pacific plate over the Hawaiian hotspot . Teacher Key

Online Media Resources

Plate Tectonics: The Hawai'ian Archipelago This video introduces the formation of Hawai'i from a mantle hot spot. WGBH Educational Foundation

Lava Sampling on Kilauea Volcano, Hawai'i This video introduces volcanism at Kilauea and how volcanologists sample lava for analysis. WGBH Educational Foundation and Peace River Films, Inc.

Volcanic Views This short excerpt discusses volcanism at Kilauea and includes eruption video from the recent vent Pu'u O'o. WNET.ORG

Mount St. Helens This video summarizes volcanic activity at Mt. St. Helens since the large 1980 eruption. Idaho Public Television

Possible Ice Volcano on Titan This video discusses radar imagery from Titain and the possible existence of an ice volcano (cryovolcano). NASA

Sibley Volcanic Regional Preserve This video discusses Sibley Volcanic park in Berkeley. KQED Quest

Photovolcanica.com This website contains spectacular images of volcanic eruptions (and penguins!).

Videos of Volcanic Eruptions

Mt. Lassen 1915 Eruption. The YouTube video above shows rare film footage of the eruption of Mt. Lassen in 1915. Lassen is one of only two historic volcanic eruptions to occur in the lower 48 (Mount St. Helens is the other).

Pahoehoe basalt lava flow . This YouTube video shows a low viscosity basalt lava flow.

Aa basalt lava flow . This YouTube video shows a high viscosity aa basalt lava flow. Note how viscous this lava flow is compared to the pahoehoe flow.

Pahoehoe flow over aa flow. This YouTube video shows a fluid pahoehoe lava flow covering an older aa surface. The volcanoes of Hawaii are built from successive pahoehoe and aa flows.

Pillow lava flow . This YouTube video shows a submarine pillow basalt lava flow. When the lava is extruded into water, it forms a glassy crust. The force of the flowing lava fractures the crust and the flow surges forward. Submarine basalt flows form pillow-shaped or lobate shapes.

Mount St. Helens 1980 Eruption . This YouTube video shows the massive 1980 eruption. This video was created from a series of still photos. Careful examination of the video shows the sequence of events that resulted in this eruption. As lava intruded into the volcano, a visible bulge formed on the flank of the volcano. An earthquake (due to the movement of magma) caused a landslide on the unstable bulge. As the flank of the volcano slid down, it exposed the lava inside the volcano. The sudden decompression caused the gas dissolved in the lava to be released and resulted in a large pyroclastic eruption. The blast flattened trees and stuctures for a 230 square mile area.

Mount St. Helens Lava Dome . This YouTube video from the USGS shows a 4-year time lapse movie of the growth of the lava dome inside the central crater on Mount St. Helens. The andesitic lava extruding in the crater is very viscous forming steep domes that collapse and are replaced by more lava pushed up from the interior of the volcano.

Unzen Pyroclastic Flow . This dramatic YouTube video shows a pyroclastic flow on Mt. Unzen in Japan that results from the collapse of the lava dome.

Batu Tara Volcano Pyroclastic Flow . This YouTube video shows a small pyroclastic flow. Note how the pyroclastic flow travels down the volcano within a stream valley until it reaches the ocean.

Mt. Ontake 2014 Pyroclastic Flow. This dramatic YouTube video shot by mountain climbers records a pyroclastic flow which resulted in 34 casualties.

Mt. Kuchinoerabujima 2015 Eruption. This YouTube video shows a pyroclastic eruption caught by a webcam. Note the pyroclastic flows down the flanks of the volcano.

Japanese Lahar Flows. This YouTube video shows three lahars (volcanic mud flows). Lahars can travel long distances from an eruption and represent a significant hazard.

Mt. Semeru Lahar Flow 2003. This YouTube video shows a small lahar flowing down a stream valley on Mt. Semeru in Indonesia.

Useful Websites

USGS Volcano Hazards Program volcanoes.usgs.gov/ T his USGS site is the main entry point for information on volcanoes including realtime maps of eruption alerts.

United States Geological Survey (USGS) www.usgs.gov/ The USGS is a federal agency within the U.S. Department of the Interior and has primary responsibility for geological (hazards, resources, etc.) and environmental issues of national and regional importance.

The Educational Multimedia Visualization Center emvc.geol.ucsb.edu/ This website contains terrific animations illustrating tectonic plate motion. UCSB

Teachers on the Leading Edge orgs.up.edu/totle/ There are many resources and activities developed by this professional development program for middle school science teachers.

NGSS Disciplinary Core Ideas

Grade 2 ESS2.B: Plate Tectonics and Large-Scale System Interactions. Maps show where things are located. One can map the shapes and kinds of land and water in any area.

Grade 4 ESS2.B: Plate Tectonics and Large-Scale System Interactions. The locations of mountain ranges, deep ocean trenches, ocean floor structures, earthquakes, and volcanoes occur in patterns. Most earthquakes and volcanoes occur in bands that are often along the boundaries between continents and oceans. Major mountain chains form inside continents or near their edges. Maps can help locate the different land and water features areas of Earth.

Middle School ESS1.C: The History of Planet Earth. Tectonic processes continually generate new ocean sea floor at ridges and destroy old sea floor at trenches. (HS.ESS1.C GBE),(secondary) ESS2.B: Plate Tectonics and Large-Scale System Interactions. Maps of ancient land and water patterns, based on investigations of rocks and fossils, make clear how Earth's plates have moved great distances, collided, and spread apart.

High School ESS1.C: The History of Planet Earth. Continental rocks, which can be older than 4 billion years, are generally much older than the rocks of the ocean floor, which are less than 200 million years old.

ESS2.B: Plate Tectonics and Large-Scale System Interactions. Plate tectonics is the unifying theory that explains the past and current movements of the rocks at Earth's surface and provides a framework for understanding its geologic history.

SS2.A: Earth Materials and Systems. Evidence from deep probes and seismic waves, reconstructions of historical changes in Earth's surface and its magnetic field, and an understanding of physical and chemical processes lead to a model of Earth with a hot but solid inner core, a liquid outer core, a solid mantle and crust. Motions of the mantle and its plates occur primarily through thermal convection, which involves the cycling of matter due to the outward flow of energy from Earth's interior and gravitational movement of denser materials toward the interior.

Common Scientific Misconceptions

Magma comes from molten layer beneath Earth's crust (older cosmologies, Franklin's idea, as well as popular literature such as Dante's Inferno, and some religious tracts).

Magma comes from deep within Earth's mantle (common textbook and earth science educational movies use of 'deep' terminology, older cosmology of passage-filled Earth')

Magma comes from Earth's outer core (this one tends to increase as students realize there is no molten layer in the mantle).

Basalt's origin is connected to the presence of seawater (original concept and name, coupled with its association with oceanic crust and oceanic hotspots vs. continental) Volcanic eruptions are rare events (media coverage is biased by location and death tolls).

Volcanoes are dominantly tropical features (Gilligan Island phenomena, common depiction)

Most deaths during volcanic eruptions are due to suffocation from smoke or poisonous gases (older scientific hypothesis until 1902 Pelee eruption, real life knowledge that many deaths in fires due to smoke inhalation, as well as being specifically mentioned as such in secondary education earth science films, all primarily legacy of Pompeii casts).

Most deaths during volcanic eruptions are due to fear and panic during evacuation (real life knowledge of crowds, Hollywood depictions).

Most magma forms as rock melts due to an increase in temperature (in real life this is the way most things melt, coupled with knowledge that temperature rises within Earth).

Most magma forms as rock is subjected to great pressure deep within the Earth (since increased pressure makes rock easier to deform or convect, even greater pressure should turn it to liquid - or so it seems).

Wind blowing across the tops of volcanic mountains can cause eruption, similar to wind blowing over opening of a flute (older cosmology dating back to Greeks)

Most volcanoes are tall peaks with craters at summit (bias of photographic record, pretty volcanoes most photographed, subduction volcanoes more accessible than submarine)

Whole idea of common use of active, dormant and extinct terms having geologic validity. Volcanoes are only hazards, not important long-term resources.

☺ Like this page? Want something different? Tell me what you think jeff.seitz@csueastbay.edu

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Volcanoes and volcanism

Nov 09, 2014

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Volcanoes and volcanism. Volcanoes represent venting of the Earth’s interior Molten magma rises within the Earth and is erupted either quietly (lavas) or violently (pyroclastics). Terminology

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Presentation Transcript

Volcanoes and volcanism • Volcanoes represent venting of the Earth’s interior • Molten magma rises within the Earth and is erupted either quietly (lavas) or violently (pyroclastics)

Terminology Magma – molten rock sometimes containing suspended minerals and dissolved gases. Magma forms when temperatures rise sufficiently high for melting to occur in the Earth’s crust or mantle. Volcano – a vent at the surface in which magma, solid rock, and gases erupt. Lava – magma that reaches the surface and pours out over the landscape.

A-Characteristics of Magma Composition – Controlled by the abundant elements in Earth (Si, Al, Fe, Ca, Mg, Na, K, H, and O). Most common types of magma are: basaltic (~50% SiO2), andesitic (60% SiO2) and rhyolitic (70% SiO2) Magma that solidify on the surface are called extrusive rocks and rocks that solidify below the surface are called intrusive. ~70 - 75% of all magma erupted by volcanoes is basaltic the rest is split between andesitic and rhyolitic.

Characteristics of Magma Rock classification chart - USGS

Characteristics of Magma Dissolved Gases Comprise a small percentage of the magma (0.2 to 3 wt.%). Although not present in abundance these gases strongly influence the eruption style and explosiveness of the magma. Dominantly H2O and CO2 with small amounts of nitrogen, chlorine, sulfur and argon. Temperature Ranges from ~800 C to ~1200 C Viscosity a substances resistance to flow **dependent on temperature and composition

The Viscosities of Foods as Analogs for Silicate Melts From: Baker D. et al. (2004) J. Geosc. Education

Explosive Eruptions vs. Effusive Eruptions • Three factors effect the explosivity of a volcano • Temperature of magma • High-temperature, less explosive • Composition of magma • Less silica, less explosive • Gas content of magma • Less gas, less explosive fluidity

Volcano types

Volcano types: cinder cones • Cinder cones are volcanoes which erupt only during one episode • They are explosive, but small in size • The cone is a pile of pyroclastic debris which piles up at the angle of repose

Volcano types: cinder cones • The cinders are generally of basaltic composition • The eruptive activity typically lasts a few months or years

Volcano types: shield volcanoes • Shield volcanoes are broad, gently sloping volcanoes • They are composed mainly of basaltic lava flows • This is a view of Mauna Loa, Hawaii, from the cinder cones of Mauna Kea Mauna Loa is the tallest volcano on Earth, as measured from the sea floor

Shield volcanoes on Mars • Other planets also have shield volcanoes • This is the largest shield volcano in the solar system, Olympus Mons on Mars • Check out the scale !

Shield volcanoes: Earth vs. Mars • Red = Hawaiian chain, which is superimposed on Olympus Mons • this says it pretty well, I think ! Mauna Loa is about here

Volcano types: stratovolcanoes • Stratovolcanoes consist of alternating layers of lava and pyroclastics • They are dominantly andesitic in composition • These volcanoes are typical of subduction zones Mt. St. Helens (pre-1980)

Volcanic landforms Volcano types: calderas A large depression generally caused by the removal of large quantities of magma from beneath a volcano causing the ground to collapse into an empty space. Aniakchak Caldera, Alaska, formed during an enormous explosive eruption that expelled more than 50 km3 of magma about 3,450 years ago. The caldera is 10 km in diameter and 500-1,000 m deep. Subsequent eruptions formed domes, and explosion pits on the caldera floor.

Now we need to answer……… A-How and where do magmas and volcanoes form ? What tectonic environment do these volcanoes occur in and why?

How and why do magmas and volcanoes form? -Global distribution of volcanoes

1-Magma generation at hot spots • Basaltic magmas at hot spots are derived from deep within the mantle • the magmas are fed by deep mantle plumes which are stationary relative to the drifting tectonic plates

Intraplate Volcanism USGS

Hawai’i • Best example of intraplate volcanism • More lava is extruded here constantly than anywhere else on Earth!

A Bigger Picture • Looking at Hawai’i, and volcanic seamounts nearby (underwater volcanic islands) Current Hawaiian Islands

What is a hot spot? • Some mantle anomaly allows the oceanic or continental lithosphere to melt where it would not normally melt • The anomaly (usually) stays stationary • The plate(s) moves over it

The Hawai’ian Hot Spot University of North Dakota • Islands and seamounts get older as you move away from the hotspot

Hawaiian island trail Does the kink represent a change in plate direction?

2-Magma generation at mid-ocean ridges • In these zones, the mantle rises and melts, producing magma of silicate composition • the magma continues to rise, and erupts mainly as basaltic lava flows **volcanism and earthquakes are separate issues

This rifting process is dramatic on Iceland • Iceland is literally being torn apart by rifting of the two plates… • yet its center is continually renewed by new magma from the mantle… • the same thing is going on under the ocean

One result of these processes • Krafla volcano erupts frequently, producing spectacular fountains of fluid lava

3-Magma generation at subduction zones • During subduction, the subducted oceanic plate is heated as it plunges into the mantle • At a depth of 80-120 km, melting begins, and volcanoes are produced which parallel the subduction zone Andesitic to Dacitic magmas are typical of these volcanoes

Volcanic landforms Stratovolcanoes -explosive eruptions -viscous lava -built of interlayered lava and pyroclastic material -usually andesitic in composition Mt. Fuji, Japan

Volcanoes and Plate Tectonics

Stratovolcano

Stratovolcano eruptions Pinchincha, Ecuador Anak Krakatau, Indonesia

Indonesia Population: 215 million World’s fourth most populous nation. 60% on island of Java Krakatau Volcanoes: 79 active - 20% of the world total -600 eruptions since 1800

Krakatau Eruption Krakatau Height 2575 ft (785 m) Circa 1880 August 27th, 1883 • Blast 10,000 greater than at Hiroshima • >36,000 people killed • 18 Cubic Km material ejected The explosion blew away the northern two-thirds of the island and it was almost instantaneously followed by the collapse of the unsupported volcanic chambers which formed the huge underwater caldera

Other Features: calderas

NOW, WHAT ABOUT RHYOLITIC VOLCANISM? • SiO2 contents are even greater than is the case in andesitic magmas, therefore....... viscosities are even greater. • So, Incredible resistance to flow!

NOW, WHAT ABOUT RHYOLITIC VOLCANISM? • In addition, rhyolitic magmas tend to be richer in H2O, because they form by partial melting of the crust, and melting is only possibly there if H2O is present. • In other words, rhyolitic magmas exsolve more H2O (more bubbles form as the magmas rise), yet the bubbles cannot expand owing to the high viscosity of the magma (they must expand as pressure decreases, i.e., as the magmas rise through the crust) • Recipe for a major disaster!!!

Yellowstone National Park, Wyoming,offers an excellent example of rhyolitic volcanism

Yellowstone National Park, Wyoming, • The volcanic eruptions, as well as the continuing geothermal activity, are a result of a large chamber of magma located below the caldera's surface. • The magma in this chamber contains gases that are kept dissolved only by the immense pressure that the magma is under. • If the pressure is released to a sufficient degree by some geological shift, then some of the gases bubble out and cause the magma to expand. • This can cause a runaway reaction. If the expansion results in further relief of pressure, for example, by blowing crust material off the top of the chamber, the result is a very large gas explosion.

Geysers and fumaroles!

The H2O is of near-surface origin, but the heat is due to a batholith (still partially molten) not far below the surface

Uplift and ring fracture formation Initial eruptive stage along ring fractures Collapse alongside eruption Remaining lava extruded Smith and Bailey Resurgent dome forms Calderas can host lakes -Active hydrothermal systems Life Cycle of a Caldera

SUMMARY • Calderas are primarily rhyolitic • largest explosive eruptions are caldera-related • lava is cool and viscous, rises slowly, allowing pressure to build up • gas percolates slowly through the viscous magma, does not have an easy way to vent • Stratovolcanoes are dacitic-andesitic • have eruptions of intermediate explosivity • can undergo lava flows if lava is mafic enough and hot enough • lava domes if lava is more felsic and cooler • gas does vent, but slowly, through fissures • Shield volcanoes are usually basaltic • lava is very hot and fluid • gases easily pass through magma to be released into the atmosphere • experience gentle, effusive activity • fountaining if pressure builds, usually at the start of an eruption

Volcanic activity • In the following slides, I will give you some examples of volcanic activity: • lava flows, including flood basalts • lava domes • pyroclastic falls and pyroclastic flows • lahars and debris avalanches • volcanic gases

Volcanic activity: lava flows • This is a basalt lava flow in a channel • Due to its low silica content and high temperature, it is quite fluid (but stickier than maple syrup) • Yet lava usually flows fairly slowly

Pahoehoe lava Do you want to walk on pahoehoe ? This is a Hawaiian term for smooth, ropy lava It generally exhibits fluid-like textures

Aa lava • This type of lava is quite blocky on the surface, and comparatively cool • Yet below the surface, the lava is fairly massive and much hotter • Do you want to walk on aa ?

Fire fountaining • Sometimes, basaltic lava can contain lots of gas • Then, small explosive eruptions form fire fountains • As partially liquid drops fall back to the ground, they may coalesce to form a lava flow

Flood basalts • The previous examples represent small-scale activity • But basaltic eruptions can be huge, forming lava plateaus • These huge outpourings may occur quickly (1-3 Ma) and may contribute to mass extinctions

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Volcanoes and Earthquakes - Plate Tectonics.

Subject: Geography

Age range: 16+

Resource type: Lesson (complete)

Last updated

7 September 2024

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Pack contains a 23 slide PPT and two task sheets that the students can answer using information from the PPT.

There is enough material here for 2-3 lessons.

PPT contains:

• diagram showing the structure of the earth - crust, mantle, outer core, inner core
• world map showing main tectonic plates
• embedded video showing how the world will change in the next 200 million years due to tectonic plate movement
• the case of the Mesosaurus - proof of plate tectonics?
• map showing main areas of volcanic and earthquake activity and the Ring of Fire
• link to online website showing recent earthquake activity
• three types of plate boundaries explanation and diagrams - divergent/constructive, convergent/destructive, and transform/conservative.

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