Facts

Volcano Types

Caldera

Calderas are huge craters usually formed by a collapsed volcano or the collapse of the roof of a magma chamber. Examples of a caldera are: Santorini and Crater Lake.

Cinder Cone

These aren’t very large volcanoes but they’re made up of layers of lava and scoria emitted by strombolian eruptions. It is common to find them as vents on major volcanoes as well as individually, and are usually typically black in colour. Examples of cinder cones are: Paricutin and Cerro Negro.

Complex Volcano

Large volcanic structures which consist of multiple lava domes or stratovolcanoes formed at different times. Examples of a complex volcano are: Pacaya and Dukono.

Compound Volcano

A volcanic structure with multiple vents confined within a small area as a result of vent migration. Example of a Compound Volcano: Zhupanovsky

Fissue Vents

These are just basically cracks in the ground which are caused by the upwelling of magma in the earth’s crust which then erupts volcanic material. These are commonly found at continental rift zones/mid ocean ridge zones as well as on the flanks of volcanoes. Examples of fissue vent volcanoes are: Ardoukoba and Laki.

Lava Dome

Steep sided dome shaped mounds made out of slow moving viscous lava which forms over a vent and hardly flows far. These are notorious for causing major explosive eruptions or pyroclastic flows. Examples of lava domes are: Soufriere Hills and Santiaguito.

Pyroclastic Cone

These can be very similar to Cinder Cones and they are either found as vents on volcanoes, or individually. They’re made up of layers of fine particles and volcanic bombs. Typically grey in colour. Examples of a Pyroclastic Cone are: Carran-los Venados and the Tavurvur cone in the Rabaul Caldera.

Shield Volcano

So called because they are shaped like a warrior’s shield. They have gentle smooth slopes which were built up by layers of liquid basaltic lava. Examples of a shield volcano are: Mauna Loa, Kilauea, and Piton de la Fournaise.

Somma Volcano

A partially filled caldera with a newer central cone in it. Example of a somma volcano: Ebeko.

Stratovolcano

These are the typical shapes of volcanoes with steep sides made up of layers of lava, tephra, pyroclastic flows, and lahars. Examples of a stratovolcano are: Fuji, Merapi, and Popocatepetl.

Sub Glacial Volcano

Volcanoes which are under the ice. When a volcanic activity occurs, the ice melts giving way to surtseyan explosions of when magma comes into contact with meltwater. An example of a sub-glacial volcano is: Grimsvotn.

Submarine Volcano

There are many of these around the oceans of the world. Because they are so deep under the sea level, the pressure of the deep water limits their eruption force. They will produce pillow lavas unless they are on subduction zones. They can also come in the form of an underwater fumerole called a “Black Smoker”. Examples of submarine volcanoes: Kick-Em-Jenny and Bayonnaise Rocks.

Tuff Cone

Similar to a cinder cone except they are less common and are formed by explosions when magma comes into contact with water. Example of a tuff cone: Surtsey.

Eruption Types

Hawaiian

These types of eruptions usually occur at hotpot volcanoes such as in Hawaii, Reunion Island, Iceland, or the Galapagos Islands. They typically occur when liquid basaltic magma erupts as lava fountains which are known to spurt hundreds of metres high into the air or as lava lakes which can fill a crater.

Lahar

Pretty much like mud. They form when large quantities of water comes together with volcanic debris and can flow down the slopes at high speeds. A prime example of a lahar eruption was at Nevado del Ruiz in Colombia in 1985.

Nuee Ardente

Similar to a pyroclastic flow these glowing clouds of avalanches are made out of hot gas, ash, and incandescent material. The lighter fraction of gases and ash cauliflowers upwards as the nuee ardente flows down the slopes.

Pelean

These involve lava domes more than the volcano itself. Lava domes are known to have steep sides and grow vertically making the lava dome subject to collapse. When a lava dome explodes or collapses, huge chunks of incandescent material rolls down the slopes at roaring speeds causing nuee ardentes or pyroclastic flows which devastate anything in their path.

Phreatic

These are steam eruptions without any magmatic ejections which are usually caused when groundwater over vents are rapidly heated by the magma underground. Although not major, phreatic eruptions are very common among most volcanoes. Sometimes in some cases, they are a sign that dormant volcanoes are about to come back to life.

Phreatomagmatic

Caused by interactions of magma coming in contact with water saturated rocks. They are known to emit large amounts of steam and gases.

Phreatoplinian

An ash eruption caused possibly by the interaction of viscous magma with water. Alot of steam is emitted.

Plinian

This is the most violent and largest eruption which is caused by viscous magma rich in gas. A tall eruption column is produced as a result of a powerful explosion of ash, gas, and other material being ejected high up into the atmosphere.

Pyroclastic Flow

Pyroclastic flows are one of the most dangerous forms of volcanic eruption made out of hot clouds of gas, ash, and volcanic material which roll down the slopes of a volcano at roaring speeds. They are produced either when a lava dome collapses, or when a dense eruption column collapses under it’s own weight. Very common at subduction zone volcanoes.

Strombolian

These are produced by medium-low magma and occur when gas bubbles build up in the magma chamber then cause explosions of incandescent material into the air (One after another) when the bubbles rise and come into contact with the more cooler viscous lava on the surface.

Sub-glacial

Sub-glacial eruptions occur when volcanoes hidden under the ice causes the ice to melt eventually giving way for the activity to break out on the surface and into the atmosphere.

Submarine

The force of submarine volcano eruptions are limited due to the fact that they lay deep under the sea where the pressure is greater. They can either come in the form of an explosive eruption or as pillow lavas at hotspots whereas the magma rapidly cools as it comes into contact with the deep sea water.

Surtseyan

These are caused when water interacts with magma producing explosions of fine grained tephra. Explosions look like tails of thick dirt mixed with ash and steam. Surtsey volcano off coast of Iceland when it was in it’s early stages is a prime example of this.

Vulcanian

Caused by explosions of large amounts of gas through viscous magma. This type of eruption is known to eject ash, gas, and lava bombs at considerable distances.

Lava Types

A’a Lava

A more common form of lava flow which cools to a rough jagged surface.

Block Lava

So-called because it comes in the form of blocks of slow moving viscous magma typically produced by subduction volcanoes.

Pahoehoe Lava

Fluid lava which is typically found on hotspot volcanoes with a smooth ropy texture to the surface.

Pillow Lava

Found on the ocean floor, these form a roundish suface which piles on top of each other caused by the rapid cooling of magma when it comes in contact with the seawater.

Eruptive Status

Active

There are a few perceptions of what a definition of an active volcano is, one of them is that a volcano which had erupted within the past 500 years is considered to be active, another is that a volcano is active if it is displaying any form of volcanic activity, and another is that a volcano is considered active if an eruption had occurred in recent years. While an active volcano may erupt frequently more than others, there are a few in the world which are in a state of permanent or near-permanent eruptive activity.

Dormant

A potentially active volcano which hasn’t erupted for a long period of time. A dormant volcano may either erupt again one day, or it may become extinct the longer the period of time it doesn’t display any activity.

Extinct

If a volcano has not displayed any form of activity for centuries then they may be classed as extinct. It has however been known on rare occasions for a thought-to-be extinct volcano to come back to life after centuries of inactivity.

Location of Volcanoes

Volcanic activity has always been associated with tectonic plate movements on Earth which have been going on for millions of years. Volcanoes are located within 5 different zones in which you will find within or on the edge of each tectonic plate. They are: Hotspots, Continental Margins, Island Arcs, Mid Oceanic ridges, and Continental Rifts.

Fig13
Diagram showing volcanism associated with tectonic plate movements. SOURCE: USGS.

Hotspot Volcanoes

These are normally located in the middle of a plate and are formed by the upwelling of magma inside the earth known as Mantle Plumes. They usually produce liquid basaltic magma which typically forms a shield volcano. The volcanoes of Hawaii, Galapagos Islands, and Reunion Island are examples of hotspot volcanoes.

Continental Margin Volcanoes

Continental Margin volcanoes are formed as a result of which an oceanic plate is subducted beneath the larger continental plate into the mantle causing partially melted material to rise to the surface, this is called the subduction zone. They typically form Lava Domes and Stratovolcanoes which tend to be the most explosive volcanoes. The volcanoes of the Cascades and Andes mountains are examples of Continental Margin volcanoes.

Island Arc Volcanoes

Another form of subduction zone volcanoes. They work in the same way as Continental Margin volcanoes except an oceanic plate is subducted beneath another oceanic plate forming volcanic islands. Lava Domes and Stratovolcanoes are typically formed. The volcanoes of Indonesia, Japan, and Aleutian Islands are examples of Island Arc volcanoes.

Mid Oceanic Ridge Volcanoes

These volcanic structures form along a long line of fissues running along through the middle of the ocean caused by the upwelling of liquid basaltic magma. Black Smokers are found here and in some cases, volcanic structures form above the surface of the ocean creating islands. The volcanoes of Iceland are a prime example of Mid Oceanic Ridge volcanoes.

Continental Rift Volcanoes

When a landmass splits, it seperates from each other creating a rift valley. Down on the rift valley floor the crust thins out allowing the upwelling of magma to create volcanoes. The volcanoes of East Africa are examples of Continental Rift volcanoes.

Fig31
Diagram showing tectonic plate boundaries and hotspots of the world. SOURCE: USGS.

Super Volcanoes

Super volcanoes are rare and amongst the hardest to spot but are known to cause catastrophic eruptions which dramatically affects the Earth’s climate with an eruption cycle of hundreds of thousands of years. Notable super volcanoes include Lake Toba on the island of Sumatra in Indonesia, Lake Taupo in New Zealand, and perhaps the most famous one of all, Yellowstone National Park which lies in Wyoming, USA. Yellowstone National Park is well known for it’s Geysers and it is said that a giant magma chamber lies beneath the national park with an eruption cycle of 600,000 years.

Most Fatalities Caused By Eruption

 Year

 Volcano

 Estimated number of deaths caused by eruption

 1815

 Tambora, Indonesia

 92,000

 1883

 Krakatau, Indonesia

 36,417

 1902

 Pelee, Martinique

 28,000

 1985

 Nevado del Ruiz, Colombia

 22,000

 1792

 Unzen, Japan

 15,188

 1783

 Laki, Iceland

 10,521

 1586

 Kelut, Indonesia

 10,000

 1902

 Santa Maria, Guatemala

 6,000

 1919

 Kelut, Indonesia

 5,110

 1929

 Santiaguito, Guatemala

 5,000

 1822

 Galunggung, Indonesia

 4,011

 1631

 Vesuvius, Italy

 3,500

 79 AD

 Vesuvius, Italy

 3,360

 1711

 Awu, Indonesia

 3,000

 1672

 Merapi, Indonesia

 3,000

 1772

 Papandayan, Indonesia

 2,957

 1951

 Lamington, Papua New Guinea

 2,942

 1856

 Awu, Indonesia

 2,806

 1982

 El Chichon, Mexico

 2,500

 1977

 Nyiragongo, DR Congo

 2,000

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