Earth and Moon

Types of volcanoes

Types of volcanoes

Volcanoes have been classified into several large groups or types, although there are some that do not fit exactly into any of them.

Lava does not always go outside in the same way. Sometimes it does so violently, with large explosions and huge masses of gases, smoke, ashes and incandescent rocks that can be projected several kilometers high.

Other times it spills smoothly, like when the milk boils in the saucepan and we don't put out the fire in time.

The most common types

Depending on the temperature of the magmas, the amount of volatile products that accompany the lavas and their fluidity or viscosity, the types of eruptions can be:

Hawaiian, of very fluid lavas and without explosive gaseous detachments. The lava overflows when it passes the crater and glides easily, forming true currents over long distances.

Strombolian. Lava is fluid, with abundant and violent gaseous detachments. Because gases can be easily released, no sprays or ashes occur. When lava overflows along the crater edges, it descends its slopes and ravines, but does not reach as much extension as in Hawaiian-type eruptions.

Vulcanian, type of volcano releases large amounts of gases from a little fluid magma that consolidates rapidly. The explosions are very strong and pulverize the lava, producing a large amount of ashes that are thrown into the air accompanied by other materials. When lava goes outside it quickly consolidates, but the gases that break off break and crack its surface, which is therefore rough and irregular.

Vesuvian, also called plinian: The gas pressure is so strong that it produces very violent explosions. It forms burning clouds that, when cooled, precipitate in the form of ashes. These volcanoes can bury cities, as happened with Pompeii and Herculaneum due to the activity of the Vesuvius volcano, from which they take their name. They alternate eruptions of pyroclast and lava flows, forming layers that can reach large dimensions.

Freatomagmatic These volcanoes are found in shallow waters, seas or lakes. They may have a lake inside their crater and sometimes form atolls. Its eruptions are very violent and with solid fragments, since the energy of the volcano and that of the suddenly heated water vapor are added. Magma is little viscous and basaltic.

Peleano. Among the volcanoes of the Antilles is the one of the Pelada Mountain (Montagne Pelée) of the Martinique island due to its eruption in 1902, which caused the destruction of its capital, San Pedro. Its lava is extremely viscous and consolidates very quickly, completely covering the crater. The enormous pressure of the gases, which do not find an outlet, lifts this plug that rises forming a large needle.

Special eruptions

Not all volcanic eruptions fit into one of the four common types. Some deserve special attention.

The most formidable volcanic explosion known to date was that of the Krakatoa volcano. It caused a tremendous explosion and huge tidal waves. It is believed that these types of eruptions are due to the contact of the ascending lava with water or wet rocks.

On the other hand, volcanic eruptions occur on the ocean floor whose lava, if they reach the surface, can form volcanic islands. These tend to be short-lived in most cases, due to the isostatic balance of the lavas upon cooling and by marine erosion. Some current islands such as the Cyclades (Greece), have this origin.

There are volcanoes that cause a large number of victims, because their craters are occupied by lakes or covered with snow. When recovering its activity, the water mixed with ashes and other remains, is thrown forming torrents and avalanches of mud, which destroy, everything they find in its path.

A current example was the eruption of the Nevado de Ruiz (Colombia) in 1985. The summit was covered by an ice cap and, as the lava ascended, the layers were reheated, forming mud castings that invaded the Lagunilla river valley and they buried the city of Armero.

Finally, the fissural eruptions are those that originate along a dislocation of the earth's crust, which can have several kilometers. The lavas that flow along the break are fluid and cover large areas, forming large plateaus or traps, one kilometer or more thick and thousands of square kilometers of surface. A good example of fissural volcanism is the Deccan plateau (India).

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