How volcanoes form

Volcanoes are geological structures through which magma rises from within the Earth. These usually originate at 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.

What are volcanoes

A volcano can be defined as a mountain with 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, they are made up of lava flows and fragmented material , but they can form in different ways depending on where volcanoes are formed, as we will see below.

How a volcano is formed step by step

As we indicated, there are different ways in which a volcano can form depending on where it is located, among other factors, but the steps are generally the same:

Volcano formation processes

  • 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 to the 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.

Steps in the formation of volcanoes

  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.

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. Here you can learn more about what magma is, types, where it is found and how it is formed .
  • 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 its different types, it can be done, for example, by the types of volcanoes according to their activity , existing the following:

  • Active volcanoes: they are those that at any moment can erupt, 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.

The different types of volcanoes can also be classified according to 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 basaltic type and have 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 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 interactions of magma and water, causes large amounts of ash, bombs, blocks and steam to be produced.

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 magma cools on 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.

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