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Volcanoes are geological structures through which magma rises from within the Earth. These usually originate in the limits of the tectonic plates as a consequence of their movement, although there are also so-called hot spots, which are volcanoes located in places where there are no movements between plates.

If you want to know more information about these formations that connect the center of the Earth with the outside, both on land and on the seabed, what types of volcanoes there are and why a volcano erupts and what volcanic eruptions are like, continue reading this interesting AgroCorrn article in which we clarify how volcanoes form and much more.

What are valcanes and how are they formed

It is an opening or rupture in the earth’s crust, through which magma or molten rock is expelled in the form of lava, volcanic ash and gases from the interior of the earth at high temperatures.

They are usually formed at the edge of tectonic plates and there are different processes for the formation of a volcano :

  • Continental boundary volcanoes: when the subduction process occurs, that is, an oceanic plate (denser) subducts to a continental plate (thinner). In this process, the subduced material melts, forming magma that will rise through fissures to be expelled outside.
  • Mid-ocean ridge volcanoes: those that form when tectonic plates separate and create an opening through which the magma generated in the upper mantle emerges, driven by convention currents.
  • Hot spot volcanoes: are those generated by the existence of ascending magma plumes that cross the crust and accumulate in ocean beds, forming islands like the Hawaiian ones.

In general, we can say that volcanoes can be of different types depending on some characteristics of their formation, such as the place or the exact process, but that there are aspects of the formation of volcanoes that are basic in all of them. This is how a volcano forms :

  1. At highly elevated temperatures, magma forms inside the planet.
  2. It rises to the top of the earth’s crust.
  3. It exits through fissures in the earth’s crust and through the main crater in the form of an eruption.
  4. Pyroclastic materials accumulate on the surface of the earth’s crust, forming the main volcanic cone.

To learn more about the formation of volcanoes, we encourage you to read these other AgroCorrn articles on What are the main seismic and volcanic zones in the world and What is the Pacific Ring of Fire .

Parts of a volcano

A volcano is made up of different parts:

  • Circular conduit or chimney: conduit through which the magma rises until it reaches the crater.
  • Crater: it is a depression with steep walls that is located at the top of the volcano. Lava, ash and pyroclastic materials are emitted through the crater.
  • Caldera: it is a large depression that forms when an eruption occurs, creating instability within the volcano due to the absence of structural support and the soil ends up collapsing inward. Not all volcanoes have a caldera, and it ends up being larger than the crater.
  • Parasitic cone : this cone is formed by the emission of magma from secondary vents, that is, the magma does not come from the main conduit. The secondary chimneys are formed as the volcano matures, due to the fissures that are produced at the base of the volcano or along the flanks.
  • Fumaroles: it is a chimney that only emits gas, that is, no magma is expelled through it.
  • Magmatic chamber: zone inside the earth’s crust where magma is found before rising to the surface.
  • Lava: it is the magma that rises to the surface with a high temperature and in contact with the air cools and solidifies. This lava contributes together with the rocks and the ash to the formation of the conical body of the volcano that has been formed thanks to all the eruptions that have occurred over time.

Types of volcanoes

To classify the types of volcanoes, it can be done according to their activity , existing the following:

  • Active volcanoes: are those that can erupt at any time, these are in a state of latency.
  • Inactive volcanoes: they show some signs of activity, among them they usually include fumaroles, hot springs or those volcanoes that between eruptions have been inactive for a long time. That is, for it to be considered inactive, centuries must have passed since the last eruption.
  • Extinct volcanoes: thousands of years must have passed to consider that a volcano is extinct, although this does not ensure that at some point it can wake up.

Although they can also be classified by their volcanic eruption :

  • Hawaiian: the lavas that this type of volcano emits are expelled by the crater or by the fissures that are in the flanks of the volcano. These lavas are of the basaltic type and have a low gas content.
  • Icelandic: it originates from eruptions in fissures and the relief they present is flat, since the lavas that are deposited are very fluid and have it successively in horizontal layers.
  • Strombolian: this type of volcano is when its explosions are separated in time by states of calm that can vary their extension.
  • Peleano: they are volcanoes with violent eruptions, the result of the solidification of a viscous magma right in the chimney, creating a plug that does not let the magma and gases escape. This plug increases the pressure, since the magma inside it accumulates and ends up producing a large explosion.
  • Pliniano: it is characterized by an explosion of gases, which consecutively emits a large amount of pumice at a high altitude, about 20 km above the crater.
  • Vulcanian: it is a volcano in which there are violent eruptions, in which the water interacts with the magma, giving a small fragmentation in the magma. These magma and water interactions produce large amounts of ash, bombs, blocks, and steam.






How a volcanic eruption occurs

The eruption is one of the main characteristics of volcanoes that help us to classify and study them. Within the different mechanisms of volcanic eruptions there are 3:

  • Magmatic eruption: it is produced by the release of the gas contained in the magma due to a decompression effect, this causes the density to fall, making it possible for the magma to exit upwards.
  • Phreatomagmatic eruption: it occurs when the magma cools in contact with water, when this happens the magma there is an explosive increase in the surface and the magma is fractionated.
  • Phreatic eruption: it occurs when the water in contact with the magma evaporates, thanks to the evaporation surrounding materials and particles are expelled and only the magma remains.

For more information on volcanic eruptions, their definition and types , don’t miss this other article. In addition, if you want to discover more curiosities about volcanoes, we recommend you read these other posts about The heart of volcanoes, an inexhaustible source of energy and What are the most dangerous volcanoes in the world (you can see a video about them below).

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