A volcano is basically an opening in the earth’s (or any celestial body) crust through which magma, ash, and volcanic gases are ejected. Typically, volcanoes are located along the fault lines between the tectonic plates.
Perhaps the most common way to classify volcanoes is by their current state: active volcanoes, which are actively erupting magma; extinct volcanoes, which are dead or unlikely to erupt ever again; and lastly the dormant volcanoes, which are currently not active but can erupt in the future.
But the most effective way to classify various volcanoes is by their shapes and type of magma they erupt. Here, we have briefly discussed all major types of volcanoes that are currently known to us.
6. Shield Volcano
View of a Mauna Kea shield volcano | Image Courtesy: Wikimedia Commons
Shield volcanoes are differentiated from other volcano types by their unique broad and shield-like structure. Out of all volcano types, shield volcanoes erupt the most liquid (least viscous) lava which travels faster and much further from the vent. This result in a steady accumulation of broad lava sheets and thus establishing its distinct structure.
Most of our current knowledge on shield volcanoes are gained from studies conducted on the Hawaii island, the world’s largest shield volcano chain. They usually do not erupt catastrophically and ejects highly fluid basaltic lava.
Shield volcanoes also feature calderas, a large pot-like depression created after the magma chamber beneath the volcano is depleted. Due to the low viscosity, lava from a shield volcano is thin — sometimes less than 1 meter thick — and can travel much further while covering more ground.
Apart from Hawaii island, other prominent shield volcano chains in the world are Galápagos islands, Iceland and the East African Rift. Mauna Loa, the second largest volcano of the earth is an active shield volcano.
5. Cinder Cone Volcanoes
Izalco volcano in El Salvador
Cinder cone volcanoes, also known as ‘scoria cones’ are perhaps the simplest and most common type of volcano found on Earth. They are almost entirely made of small fragments of pyroclastics (volcanic rocks) mostly scoria and cinders which are ejected from the volcanic vent.
They are usually small, ranging somewhere from 30 to 400 meters in height, symmetrical in shape and have a bowl-shaped crater at their summit. Most cinder cone volcanoes erupt only once in their lifetime but for an extended period of time.
Parícutin, a cinder cone volcano located near the city of Uruapan in Mexico, came under the spotlight after it suddenly emerged on a cornfield in 1943. Few other examples of cinder cones are Sunset Crater in Arizona, United States and Cerro Negro in Nicaragua.
Mayon Volcano on December 29, 2009
Stratovolcanoes, often known as composite volcanoes, are characterized by their steep gradient and summit craters. They usually have a stratified structure caused by the steady accumulation of volcanic materials spilled during subsequent eruptions.
Such volcanoes exhibit both explosive as well as effusive eruptions. As it stands, stratovolcanoes are considered the most dangerous type of volcano on earth. Not only they usually erupt in a more explosive manner than shield volcanoes, the resulted ash and lahar (volcanic mudflow) from the explosion also pose a great threat to both climate and living beings.
Krakatoa volcano (located between the islands of Java and Sumatra) is perhaps the most well-known example of the stratovolcano, whose eruption in 1883 produced a massive shockwave comparable to the detonation of 200-megaton nuclear weapon. Other examples of stratovolcanoes are Mount Fuji in Japan and Mount Vesuvius in Italy. After the explosion, the summit crater of the volcano turned into a caldera.
3. Lava Domes
Lava or volcanic domes are small and circular bump created by slow eruptions of highly viscous lava. In most cases, these domes are created within the crater of active volcanoes, but they can also form independently as is the case with Lassen Peak, the largest lava dome on Earth.
Unlike shield volcanoes and even stratovolcanoes, the magma from the volcanic domes doesn’t flow far from the vent and continue to pile around it. However, they do explode violently.
2. Submarine and Sub-glacial Volcanoes
Glowing magma from a submarine volcano | Image Courtesy: NOAA
Submarine (underwater) and sub-glacial volcanoes, as their name suggest, are vents located under the Earth’s surface from which magma or lava is ejected. Their physical and eruption characteristics differ significantly from those above the surface.
Underwater volcanoes are mostly found near tectonically active mid-oceanic ridge and are responsible for about 75% of all lava outpour on earth. Submarine volcanoes, though far less in number, are also found in shallow water bodies and they often tend to blast molten matter high into the atmosphere.
Since water causes the molten magma to cool and solidify much faster than on the surface, it’s often that underwater magma turns into volcanic glass and then into pillow lava in later stages. Axial Seamount, located on the Juan de Fuca Ridge, is one of the youngest submarine volcanoes which last erupted in 2015.
Sub-glacial volcanoes are located well beneath giant ice sheets or glaciers. They have some unusual characteristics, such as the flattened summit and very steep sides supported by the surrounding ice. Over time, the ice sheet is melted by the rising lava and ultimately transforms into a lake.
While sub-glacial volcanoes are most common in Antarctica and Iceland, some are also found in western and northwestern regions of Canada.
Diagram of the Yellowstone Caldera
A supervolcano occurs when magma, rising from the Earth’s mantle, is trapped inside the crust and unable to break-out until it explodes under extensive pressure.
Supervolcanoes are perhaps the most dangerous type of volcano and are usually located at subduction and/or hotspots. These volcanoes often feature a caldera, such supervolcanoes are called megacaldera.
According to the scientific consensus, substantially large amounts of volcanic ash and sulfur produced during a supervolcano explosion can reduce global temperatures for a brief period of time (by increasing Earth’s albedo). It could also have a massive impact on living organisms.
Yellowstone Caldera in Yellowstone National Park, Lake Taupo in New Zealand, Ngorongoro Crater in Tanzania, and Lake Toba in Indonesia are few well-known examples of a supervolcano.
Volcanic eruption on Jupiter’s moon Io (Tvashtar Paterae region) captured by New Horizons in 2007 | Image Courtesy: NASA
Volcanoes and related activities have also been observed on celestial bodies in the solar system other than on earth. Researchers have discovered numerous shield volcanoes on both Mars and Venus. What’s more interesting is that the shield volcanoes on planet Mars bear a close resemblance to those on our planet.
Cryovolcanoes, a much-less known type of volcanoes, are found on Pluto and various celestial objects including Titan and Ceres. While there is no direct evidence, there are signs suggesting possible cryovolcanic activities on Europa and Enceladus. Instead of molten magma, cryovolcanoes ejects ammonia, methane, and water.