Volcanoes: natural science

     

A volcano is an opening in the Earth"s surface through which lava, volcanic ash, & gases escape. Ancient people believed that volcanoes were under the control of the gods. In fact, the word volcano comes from Vulcan, the Roman god of fire.

Currently there are about 1,500 potentially active volcanoes worldwide. 169 of these are in the United States.

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Volcanic eruptions can cause death và widespread devastation. They can also bring benefits and provide:

Valuable mineral deposits lượt thích gold, aluminium, & nickel. Nutrient-rich fertile soils from volcanic ash. Geothermal energy—much of Iceland’s energy comes from geothermal sources. Lava flows that create land—in 2018, a new island appeared off the coast of Hawaii as a result of lava from Kilauea eruptions.

Anatomy of a Volcano

All volcanoes have some things in common:

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Did you know?

What is the difference between magma and lava?

Magma is molten rock stored in the Earth"s crust. Lava is molten rock that has reached the Earth’s surface through a volcanic vent.

Where volcanoes are found

The lithosphere is the outermost layer that surrounds the Earth. It consists of the crust & part of the mantle. This is broken into extremely large slabs called tectonic plates. For example, the North American Plate (includes most of North America, Greenland, and part of Siberia) is 75,900,000 square kilometers (29,305,000 square miles). These move around on the ductile layer beneath.

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Look at the bản đồ above to lớn see how the Earth’s surface is divided into seven major plates. Volcanoes are mostly (but not always) found where these tectonic plates meet, called the plate boundaries.

About 75 percent of the Earth’s active volcanoes are in the Ring of Fire. This 40,000-kilometer (25,000-mile) chain of volcanoes and seismically active sites circles the edges of the Pacific Ocean.

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How volcanoes form

We already know that volcanoes are formed mostly, but not always, at the boundaries of tectonic plates. Let’s look at the mechanisms behind this.


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An island arc volcano is a type of subduction zone volcano.

Island arc volcanoes occur when one plate descends, or subducts, under another plate. Subduction allows water from the subducting plate to be driven upward, off the subducting plate & into the mantle wedge. This lowers the melting point of the mantle, and it melts to form magma. This magma will rise và leak into the crust forming a volcano. This process can create a chain of volcanic islands.

Examples of island arcs are the Japanese islands & the Aleutian islands of Alaska.

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Cleveland Volcano, Aleutian Islands. Image credit: NASA


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About five percent of all known volcanoes size in the middle of plates, not at their edges. These intraplate volcanoes are caused by hot spots, unusually hot areas deep within the Earth. Magma rises from the hot spots and erupts as lava through cracks in the Earth"s surface forming volcanoes. As a plate moves slowly across a hot spot, a chain of volcanoes or volcanic islands can form.

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The islands of Hawaii & Samoa were formed in this way. Plates move about 5 centimeters a year so this is a slow process.

Satellite view of Hawaii archipelago (USA). Image credit: NASA


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Volcanoes called rift volcanoes are formed in spreading centers. In these zones, plates move away from each other, decreasing the pressure on the underlying mantle, allowing it lớn rise and melt, forming magma. Spreading centers can be found under the sea or on land.

On landWhen spreading centers develop within continents, they size new plate boundaries và trigger volcanic activity. Spreading may have created East Africa"s volcanic Great Rift Valley.

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Hills covered by volcanic ashes, Great Rift Valley, Tanzania, East Africa.Image credit: Aghezzi

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Under the sea The mid‐ocean ridge is a continuous, underwater seam of mountains & volcanoes that form where divergent tectonic plates meet. It stretches all around the globe and is more than 64,000 kilometers (40,000 miles) long. The tectonic plates are spreading apart allowing soft molten rock to lớn bubble up between the plates. Once this hardens it forms the seafloor. This process can also form volcanic islands. For example, Iceland was formed where the mid-ocean ridge met with a mantle plume – a ‘hotspot’ of abnormally hot rock in the mantle – & eruptions of lava built volcanoes & filled rift valleys.

Rift volcanoes generally issue nonviolent streams of lava, instead of explosively erupting. They also tend to lớn be shield volcanoes with gently sloping slides.

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Thingvellir Valley và Lake Thingvallavatn, Thingvellir National Park, Thingvellir, Iceland.Image credit: Emory Kristof


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When two plates come together, one of the plates may slide under another in a process called subduction.

Heat from deep in the Earth melts rock in the descending plate. At the same time, water is driven from the subducting slab into the overlying mantle wedge, lowering the melting point of the mantle, & melting it to khung magma. The molten rock rises through the plate above it & can burst out of the surface of the Earth as lava, gradually forming a volcano. Subduction volcanoes tend to be explosive stratovolcanoes. Hundreds of volcanoes rise from subduction zones encircling the Pacific Ocean. This famous belt is known as the Ring of Fire.
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Volcanoes of Bromo National Park, Java, Indonesia.Image credit: Manamana


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Cinder Cone
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Cinder cone volcanoes are relatively small, steep, cone-shaped hills made up mostly of partly burned ash & lava cinders. Cinder cones tend to lớn be explosive volcanoes but they can also produce lava.

Although larger volcanoes form very slowly, a cinder cone can develop rapidly. A good example is the Paricutín volcano in Mexico, which grew from a crack in a corn field to lớn a cone over 300 meters (984 feet) high over the course of one year in the 1940s. Cinder cones also have a shorter lifespan than slower-growing types of volcano.


Cinder Cone
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Photograph by J. Baylor Roberts

Cinder cone volcanoes are relatively small, steep, cone-shaped hills made up mostly of partly burned ash và magma cinders. Cinder cones tend lớn be explosive volcanoes but they can also produce lava.

Although larger volcanoes form very slowly, a cinder cone can develop rapidly. A good example is the Paricutín volcano in Mexico, which grew from a crack in a corn field lớn a cone over 300 meters (984 feet) high over the course of one year in the 1940s. Cinder cones also have a shorter lifespan than slower-growing types of volcano.


Cinder Cone
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Photograph by Saro17 / Getty Images

Cinder cone volcanoes are relatively small, steep, cone-shaped hills made up mostly of partly burned ash and magma cinders. Cinder cones tend to be explosive volcanoes but they can also produce lava.

Although larger volcanoes form very slowly, a cinder cone can develop rapidly. A good example is the Paricutín volcano in Mexico, which grew from a crack in a corn field khổng lồ a cone over 300 meters (984 feet) high over the course of one year in the 1940s. Cinder cones also have a shorter lifespan than slower-growing types of volcano.


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Shield volcanoes get their name from their shape which resembles a warrior"s shield lying on the ground. The shape comes from streams of lava that flow from a summit vent or group of vents và then cool down, forming smooth, gentle slopes. Their summits are nearly flat.

Examples are Kilauea in Hawaii & Piton de la Fournaise on Reunion Island in the Indian Ocean. Areas of the world with the most shield volcanoes include Hawaii, the Galapagos Islands, & Iceland.


Shield
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Photography by USGS / Getty Images

Shield volcanoes get their name from their shape which resembles a warrior"s shield lying on the ground. The shape comes from streams of lava that flow from a summit vent or group of vents and then cool down, forming smooth, gentle slopes. Their summits are nearly flat.

Examples are Kilauea in Hawaii & Piton de la Fournaise on Reunion Island in the Indian Ocean. Areas of the world with the most shield volcanoes include Hawaii, the Galapagos Islands, và Iceland.


Shield
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Photography by CORBIS / Getty Images

Shield volcanoes get their name from their shape which resembles a warrior"s shield lying on the ground. The shape comes from streams of lava that flow from a summit vent or group of vents & then cool down, forming smooth, gentle slopes. Their summits are nearly flat.

Examples are Kilauea in Hawaii and Piton de la Fournaise on Reunion Island in the Indian Ocean. Areas of the world with the most shield volcanoes include Hawaii, the Galapagos Islands, and Iceland.

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Composite volcanoes, also known as stratovolcanoes, are steep-­sided, symmetrical cones formed when pyroclastic eruptions (explosions of ash, cinders, và rock fragments) alternate with lava flows & layers build up over time. They usually have a central vent or a cluster of vents in a crater at their summit.

Mount Fuji in Japan, Mount St. Helens in Washington State, và Mount Etna in Italy are all composite volcanoes.


Composite
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Photograph by pxhidalgo

Composite volcanoes, also known as stratovolcanoes, are steep-­sided, symmetrical cones formed when pyroclastic eruptions (explosions of ash, cinders, and rock fragments) alternate with lava flows & layers build up over time. They usually have a central vent or a cluster of vents in a crater at their summit.

Mount Fuji in Japan, Mount St. Helens in Washington State, & Mount Etna in Italy are all composite volcanoes.


Composite
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Photograph by Fomin Sergey / EyeEm

Composite volcanoes, also known as stratovolcanoes, are steep-­sided, symmetrical cones formed when pyroclastic eruptions (explosions of ash, cinders, and rock fragments) alternate with lava flows and layers build up over time. They usually have a central vent or a cluster of vents in a crater at their summit.

Mount Fuji in Japan, Mount St. Helens in Washington State, và Mount Etna in Italy are all composite volcanoes.


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A caldera is a large oval or circular hollow that can size soon after an eruption. If the magma chamber has emptied over a short period of time, it won"t be able to tư vấn the weight of the mountain above it. This leads lớn a collapse above the magma chamber và the caldera forms.

The caldera may be encircled by steep cliffs and filled with lakes. Calderas can also khung on composite volcanoes và on the flat tops of shield volcanoes.


Caldera
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Photograph by Cavan Images

A caldera is a large oval or circular hollow that can form soon after an eruption. If the magma chamber has emptied over a short period of time, it won"t be able to tư vấn the weight of the mountain above it. This leads to a collapse above the magma chamber và the caldera forms.

The caldera may be encircled by steep cliffs và filled with lakes. Calderas can also size on composite volcanoes & on the flat tops of shield volcanoes.


Caldera
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Photograph by National Parks Service

A caldera is a large oval or circular hollow that can size soon after an eruption. If the magma chamber has emptied over a short period of time, it won"t be able to tư vấn the weight of the mountain above it. This leads to lớn a collapse above the magma chamber và the caldera forms.

The caldera may be encircled by steep cliffs & filled with lakes. Calderas can also size on composite volcanoes & on the flat tops of shield volcanoes.


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Lava domes are formed when very thick lava erupts through the volcano’s vent & then piles up around it. Lượt thích lava flows, there isn’t enough pressure for the volcano to erupt explosively. But unlike lava flows, where the faster-moving lava can flow for miles, the lava is so thick that it doesn"t flow very far.

These steep mounds can grow khổng lồ become several hundred meters high and be more than 1,000 meters (3,280 feet) in diameter.


Lava Dome
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Photograph by Ulet Ifansasti / Getty Images

Lava domes are formed when very thick lava erupts through the volcano’s vent and then piles up around it. Like lava flows, there isn’t enough pressure for the volcano to erupt explosively. But unlike lava flows, where the faster-moving lava can flow for miles, the lava is so thick that it doesn"t flow very far.

These steep mounds can grow lớn become several hundred meters high và be more than 1,000 meters (3,280 feet) in diameter.


Lava Dome
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Photograph by Mike Poland / USGS

Lava domes are formed when very thick lava erupts through the volcano’s vent & then piles up around it. Lượt thích lava flows, there isn’t enough pressure for the volcano lớn erupt explosively. But unlike lava flows, where the faster-moving lava can flow for miles, the lava is so thick that it doesn"t flow very far.

These steep mounds can grow to become several hundred meters high and be more than 1,000 meters (3,280 feet) in diameter.


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There are considerably more volcanoes underwater than on land. Most eruptions on the seafloor occur from fissures, for example along mid-ocean ridges & around Iceland. Other eruptions form cone­-shaped seamounts or sea mountains.

A seamount will occur where magma erupts through the seafloor & forms new seafloor. If the seamount grows out of the ocean it is known as a volcanic island. Hawaii is an example of a volcanic island.


Submarine
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Photograph by NOAA / NSF / WHOI

There are considerably more volcanoes underwater than on land. Most eruptions on the seafloor occur from fissures, for example along mid-ocean ridges và around Iceland. Other eruptions form cone­-shaped seamounts or sea mountains.

A seamount will occur where magma erupts through the seafloor & forms new seafloor. If the seamount grows out of the ocean it is known as a volcanic island. Hawaii is an example of a volcanic island.


Submarine
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Photograph by NOAA Okeanos Explorer Program, INDEX-SATAL 2010

There are considerably more volcanoes underwater than on land. Most eruptions on the seafloor occur from fissures, for example along mid-ocean ridges & around Iceland. Other eruptions form cone­-shaped seamounts or sea mountains.

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A seamount will occur where magma erupts through the seafloor và forms new seafloor. If the seamount grows out of the ocean it is known as a volcanic island. Hawaii is an example of a volcanic island.


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