A Volcanic Bomb Is A

What is a volcano?

A volcano is an opening in the Earth's surface through which lava, volcanic ash, and gases escape. Ancient people believed that volcanoes were nether the command of the gods. In fact, the word volcano comes from Vulcan, the Roman god of burn.

Currently there are nigh 1,500 potentially active volcanoes worldwide. 169 of these are in the United states of america.

Video courtesy of Spotmatik Ltd / Shutterstock

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

Valuable mineral deposits similar gilt, aluminium, and nickel.
Food-rich fertile soils from volcanic ash.
Geothermal free energy—much of Iceland'due south free 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 accept some things in common:

Illustration of the anatomy of a volcano

Did you know?

What is the difference between magma and lava?

Magma is molten rock stored in the Globe's chaff.
Lava is molten rock that has reached the Earth'southward surface through a volcanic vent.

Where volcanoes are found

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

Map of where volcanoes are found

Expect at the map above to meet how the Earth'southward surface is divided into seven major plates. Volcanoes are mostly (just not e'er) establish where these tectonic plates meet, called the plate boundaries.

About 75 percent of the Earth'due south 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 Sea.

Video courtesy of National Geographic Partners

How volcanoes form

We already know that volcanoes are formed by and large, simply non always, at the boundaries of tectonic plates. Permit'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 ane plate descends, or subducts, under another plate.
- Subduction allows water from the subducting plate to be driven up, off the subducting plate and into the mantle wedge.
- This lowers the melting bespeak of the pall, and it melts to grade magma.
- This magma volition rise and leak into the crust forming a volcano.
- This process can create a concatenation of volcanic islands.
Examples of island arcs are the Japanese islands and the Aleutian islands of Alaska.
Cleveland Volcano, Aleutian Islands.
Image credit: NASA

Nearly five per centum of all known volcanoes form in the middle of plates, not at their edges. These intraplate volcanoes are caused by hot spots, unusually hot areas deep within the World.

Magma rises from the hot spots and erupts every bit lava through cracks in the Earth'due south surface forming volcanoes.

Every bit a plate moves slowly across a hot spot, a concatenation of volcanoes or volcanic islands can grade.
The islands of Hawaii and Samoa were formed in this way. Plates movement nigh 5 centimeters a year so this is a slow procedure.

Satellite view of Hawaii archipelago (U.s.a.).
Image credit: NASA

Volcanoes called rift volcanoes are formed in spreading centers. In these zones, plates motion away from each other, decreasing the pressure on the underlying drapery, assuasive it to ascent and melt, forming magma. Spreading centers can be found under the sea or on land.

On land
When spreading centers develop within continents, they class new plate boundaries and trigger volcanic activity. Spreading may accept created Eastward Africa's volcanic Great Rift Valley.
Hills covered past volcanic ashes, Nifty Rift Valley, Tanzania, East Africa.
Prototype credit: Aghezzi
Under the ocean
The mid‐ocean ridge is a continuous, underwater seam of mountains and volcanoes that class where divergent tectonic plates run across. It stretches all around the world and is more than 64,000 kilometers (twoscore,000 miles) long. The tectonic plates are spreading autonomously allowing soft molten rock to chimera up between the plates. One time this hardens it forms the seafloor. This process can besides form volcanic islands. For example, Republic of iceland was formed where the mid-ocean ridge met with a drapery plumage – a 'hotspot' of abnormally hot stone in the curtain – and eruptions of lava congenital volcanoes and filled rift valleys.

Rift volcanoes more often than not consequence irenic streams of lava, instead of explosively erupting. They as well tend to be shield volcanoes with gently sloping slides.
Thingvellir Valley and Lake Thingvallavatn, Thingvellir National Park, Thingvellir, Iceland.
Image credit: Emory Kristof

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When 2 plates come together, one of the plates may slide under another in a procedure called subduction.
- Heat from deep in the Earth melts rock in the descending plate. At the same fourth dimension, water is driven from the subducting slab into the overlying mantle wedge, lowering the melting point of the drape, and melting information technology to form magma.
- The molten rock rises through the plate in a higher place it and tin burst out of the surface of the World every bit lava, gradually forming a volcano.
- Subduction volcanoes tend to be explosive stratovolcanoes. Hundreds of volcanoes ascent from subduction zones encircling the Pacific Body of water. This famous belt is known as the Band of Burn.
Volcanoes of Bromo National Park, Coffee, Indonesia.
Image credit: Manamana

Types of volcano

Cinder cone
Shield
Composite
Caldera
Lava dome
Submarine

Video courtesy of Wead / Shutterstock

Cinder cone volcanoes are relatively minor, steep, cone-shaped hills made up by and large of partly burned ash and lava cinders. Cinder cones tend to exist explosive volcanoes but they tin can also produce lava.

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

Cinder cone volcanoes are relatively minor, steep, cone-shaped hills made upwards more often than not of partly burned ash and magma cinders. Cinder cones tend to be explosive volcanoes but they can as well produce lava.

Although larger volcanoes form very slowly, a cinder cone can develop apace. A good example is the Paricutín volcano in Mexico, which grew from a crack in a corn field to a cone over 300 meters (984 feet) high over the class of one year in the 1940s. Cinder cones likewise take a shorter lifespan than slower-growing types of volcano.
Photograph by Saro17 / Getty Images

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

Although larger volcanoes form very slowly, a cinder cone tin can develop rapidly. A good case is the Paricutín volcano in United mexican states, which grew from a crack in a corn field to a cone over 300 meters (984 feet) loftier over the class of 1 year in the 1940s. Cinder cones also take a shorter lifespan than slower-growing types of volcano.

Video courtesy of Rick Ray

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 almost flat.

Examples are Kilauea in Hawaii and Piton de la Fournaise on Reunion Isle in the Indian Ocean. Areas of the world with the virtually shield volcanoes include Hawaii, the Galapagos Islands, and Republic of iceland.
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 pinnacle vent or group of vents and so cool downward, forming smoothen, gentle slopes. Their summits are about flat.

Examples are Kilauea in Hawaii and Piton de la Fournaise on Reunion Isle in the Indian Body of water. Areas of the earth with the most shield volcanoes include Hawaii, the Galapagos Islands, and Iceland.
Photography past CORBIS / Getty Images

Shield volcanoes go their name from their shape which resembles a warrior'south 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 downwards, forming smooth, gentle slopes. Their summits are about flat.

Examples are Kilauea in Hawaii and Piton de la Fournaise on Reunion Isle in the Indian Body of water. Areas of the earth with the nearly shield volcanoes include Hawaii, the Galapagos Islands, and Iceland.

Video courtesy of fitopardo / Getty Images

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

Mount Fuji in Japan, Mount St. Helens in Washington State, and Mount Etna in Italia are all composite volcanoes.
Photo by pxhidalgo

Blended volcanoes, also known equally stratovolcanoes, are steep-sided, symmetrical cones formed when pyroclastic eruptions (explosions of ash, cinders, and rock fragments) alternate with lava flows and layers build upward over fourth dimension. They unremarkably take a key vent or a cluster of vents in a crater at their elevation.

Mountain Fuji in Japan, Mountain St. Helens in Washington Country, and Mountain Etna in Italy are all blended volcanoes.
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 stone fragments) alternating with lava flows and layers build upward over fourth dimension. They unremarkably have a central vent or a cluster of vents in a crater at their peak.

Mount Fuji in Nihon, Mountain St. Helens in Washington Land, and Mount Etna in Italy are all composite volcanoes.

Video courtesy of BBC Universal / Getty Images

A caldera is a big oval or circular hollow that can form before long after an eruption. If the magma sleeping accommodation has emptied over a short catamenia of fourth dimension, it won't be able to support the weight of the mountain above it. This leads to a collapse above the magma bedroom and the caldera forms.

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

A caldera is a big oval or circular hollow that can grade before long after an eruption. If the magma chamber has emptied over a curt period of time, it won't be able to back up the weight of the mount above it. This leads to a collapse in a higher place the magma bedroom and the caldera forms.

The caldera may be encircled past steep cliffs and filled with lakes. Calderas can also form on blended volcanoes and on the apartment tops of shield volcanoes.
Photograph by National Parks Service

A caldera is a large oval or round hollow that can course soon after an eruption. If the magma bedroom has emptied over a short period of time, it won't exist able to support the weight of the mount to a higher place information technology. This leads to a collapse above the magma chamber and the caldera forms.

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

Video courtesy of Stefan Schuetz / Getty Images

Lava domes are formed when very thick lava erupts through the volcano'south vent and then piles upward around information technology. Like lava flows, in that location isn't enough force per unit area for the volcano to erupt explosively. Just unlike lava flows, where the faster-moving lava tin 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 loftier and be more than 1,000 meters (three,280 anxiety) in bore.
Photograph by Ulet Ifansasti / Getty Images

Lava domes are formed when very thick lava erupts through the volcano'south vent and then piles upward 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 information technology doesn't flow very far.

These steep mounds can grow to go several hundred meters loftier and be more than than i,000 meters (iii,280 feet) in diameter.
Photograph by Mike Poland / USGS

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 tin can flow for miles, the lava is so thick that information technology doesn't flow very far.

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

Video courtesy of Body of water Today / Smithsonian Institution / NOAA

In that location are considerably more volcanoes underwater than on land. Near eruptions on the seafloor occur from fissures, for example along mid-ocean ridges and around Iceland. Other eruptions class cone-shaped seamounts or sea mountains.

A seamount will occur where magma erupts through the seafloor and forms new seafloor. If the seamount grows out of the ocean it is known every bit a volcanic island. Hawaii is an example of a volcanic island.
Photo by NOAA / NSF / WHOI

There are considerably more than volcanoes underwater than on country. Well-nigh eruptions on the seafloor occur from fissures, for example along mid-bounding main ridges and around Iceland. Other eruptions form cone-shaped seamounts or ocean mountains.

A seamount volition occur where magma erupts through the seafloor and 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 isle.
Photograph by NOAA Okeanos Explorer Program, Index-SATAL 2010

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

A seamount will occur where magma erupts through the seafloor and 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.

Did you lot know?

Blended volcano eruptions are the almost catastrophic. Lava pours out from fissures or cracks in the volcano'due south walls, strengthening the cone and forming a seal every bit it hardens. Pressure gradually builds up within the cone and the consequence is a violent explosion of pyroclastic fabric from the volcano's vents.

How volcanoes erupt

We know that volcanic eruptions can be

fairly calm lava flows, calm enough for scientists to stand nigh and observe, or
violently explosive, powerful enough to blow mountains autonomously.

What decides how violent the eruption will exist?

This is decided by the physical properties of the magma:

Viscosity: how thick or runny it is
Gas contents: the amount of dissolved gas in it

Viscous magma

illustration of magma inside science beaker

Viscosity describes how runny the magma or lava is. Viscosity is afflicted by the corporeality of silica (SiO₂ as well known as silicon dioxide) in the magma.

Silica molecules form long chains in the magma; these get tangled together, making it difficult for the magma to slide past itself. The more silica, the more viscous the magma, the slower it will move.

Dissolved gases

illustration of gases inside science beaker

In the Earth's crust the magma is at a college pressure than at the Earth's surface, so information technology is possible for gases (h2o vapour and carbon dioxide) to be dissolved in information technology.

Equally lava moves upward towards the Globe's surface, the gas tries to escape because the pressure level on information technology is decreasing. Call back about what happens when you shake a bottle of soda!

Did y'all know?

The 1883 eruption of Krakatoa measured 6 out of 8 on the Volcanic Explosion Index with an estimated strength comparable to 200 megatons of TNT (trinitrotoluene, an explosive). The atomic bomb that devastated Hiroshima had a force of 20 kilotons. Krakatau was almost ten thousand times more than explosive than the bomb.

Types of Eruption

The post-obit summarizes how the properties of viscosity and the amount of gases dissolved in the magma control what kind of eruption happens and what kind of volcano results.