What is Volcanism?
Volcanism is the process by which magma, molten rock, and ash are erupted from a volcano. Magma is produced by the partial melting of the Earth's mantle and crust, and it is the source of the materials that make up a volcano.
When magma rises to the surface and erupts, it can take the form of lava flows, ash, and pyroclastic materials such as pumice and tephra. Volcanoes can be found all over the world, and they come in a variety of shapes and sizes. Some are tall and cone-shaped, while others are flat and spread out over a large area.
The type of volcanism that occurs at a particular volcano is influenced by the type of magma that is present, the structure of the Earth's crust, and the tectonic setting in which the volcano is located.
Classification of Volcanoes
There are several different ways to classify volcanoes based on the mode of eruption. Here are a few common ways:
Explosive versus effusive: This classification is based on the type of eruption that occurs. Explosive eruptions are characterized by the explosive release of gases from magma, which produces a plume of ash, pumice, and other pyroclastic materials. Effusive eruptions, on the other hand, are characterized by the relatively calm and continuous flow of lava from the volcano.
Stratovolcano versus shield volcano: This classification is based on the shape of the volcano. Stratovolcanoes are tall, cone-shaped volcanoes that are formed by explosive eruptions of viscous magma. Shield volcanoes, on the other hand, are relatively flat volcanoes that are formed by the eruption of relatively fluid lava flows.
Active, dormant, and extinct: This classification is based on the current level of activity at a volcano. An active volcano is one that is currently erupting or has erupted recently. A dormant volcano is one that has not erupted for a long time, but it is still considered to be potentially active. An extinct volcano is one that is no longer considered to be active and is not expected to erupt again.
Fissure eruptions versus central vent eruptions: This classification is based on the location of the eruption. Fissure eruptions occur along a crack or fissure in the Earth's surface, while central vent eruptions occur at a single point on the volcano.
Lava dome versus caldera: This classification is based on the type of feature that is created by the eruption. A lava dome is a mound of solidified lava that is formed by the slow, viscous eruption of magma. A caldera is a large, circular depression that is formed by the collapse of a volcano into a magma chamber.
Various Volcanic Belts
There are several different types of volcanic belts, which are regions of the Earth's crust where volcanism is more common. Here are a few examples:
Subduction zone volcanic belts: These belts are found at the boundaries of tectonic plates where one plate is being subducted, or pushed beneath, another. Subduction zone volcanic belts are typically associated with explosive andesitic volcanoes, which are formed by the eruption of intermediate-silica magma. Examples of subduction zone volcanic belts include the Andes in South America and the Cascades in the Pacific Northwest of the United States.
Mid-ocean ridge volcanic belts: These belts are found at the boundaries of tectonic plates where two plates are moving apart, creating a gap that is filled by magma rising from the mantle. Mid-ocean ridge volcanic belts are typically associated with basaltic volcanoes, which are formed by the eruption of low-silica magma. The most well-known example of a mid-ocean ridge volcanic belt is the Mid-Atlantic Ridge.
Intraplate volcanic belts: These belts are found within the interior of a tectonic plate, away from the boundaries of plates. Intraplate volcanic belts are typically associated with basaltic volcanoes, and they are thought to be caused by the upwelling of hot, mantle-derived magma. Examples of intraplate volcanic belts include the Hawaiian Islands and the Galapagos Islands.
Hot spot volcanic belts: These belts are formed by the eruption of magma that is thought to be caused by a "hot spot" in the mantle. Hot spot volcanic belts are typically associated with basaltic volcanoes, and they are thought to be caused by the upwelling of hot, mantle-derived magma that is not associated with tectonic plate boundaries. An example of a hot spot volcanic belt is the Hawaiian-Emperor seamount chain.