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How are volcanoes formed?

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Volcano eruptions cone cylinder composite volcanoes
The Mayon Volcano in the Philippines
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Volcanoes are actually mountains that get bigger and bigger

It sounds like a term straight out of Star Trek: "volcano" comes from Vulcan, the Roman god of fire. Vulcan lived inside the earth beneath Hiera, an island, which is now referred to as Vulcano. The Japanese call volcanoes kazan whereas the Indonesian refer to them as gunung api. Volcan is Spanish for volcano.

Learning about volcanoes is one of the introductions to understanding our earth and exploring geology. Teachers use many resources to teach about earth science. Volcanoes are fascinating and frightening and capture the imagination of both young students and adults. Volcanoes are mountains that build up and get taller and taller. 

Eventually, the volcano will erupt. When that happens, magma or molten rock, that comes from within the earth breaks through to the surface of the earth. An erupting cross section model of a volcano is an excellent tool for demonstrating how a volcano evolves.

When you walk outside into your yard, you are standing on the crust of the earth, which is actually a thin layer. Underneath the crust is an extremely hot region called the mantle. The mantle is almost completely solid but it can form pockets of hot gasses and liquid rock. The magma or molten rock surrounds the solid rock, and it is buoyant. It slowly works through the crust of the earth and creates a volcano.

When magma reaches the surface it spreads out onto the surface and this creates a volcano. When the magma becomes flat, lava flows out. Most of the Pacific Ocean area volcanoes are composite. This means they contain layers of lava and ashes.

The main types of volcanoes are shield, composites and cinder cones. They are formed by the eruption of lava, gases from the central vent and volcanic ash. Some lava is thick and cannot travel far. This type of lava creates cinder cone shaped volcanoes. A cinder cone volcano starts out when there is an eruption from a vent in the surface of the land and that develops into a steep sloped circular mountain as cinders from later eruptions create a cone around the vent.

The type of volcano that ultimately evolves depends on how big the crack in the crust is and the kind of lava that spews out. Some lava is quite fluid and can flow for long distances and creates a volcano called a shield volcano, such as is found in Hawaii. A shield volcano is made up of basaltic lava that is low viscosity and easily and rapidly flows from the central vent. A shield volcano can be huge but its structure is simple and includes stacked, low-angle lava flows around the central vent.

When a volcano is particularly energetic it will spit ash, rock and magma high into the air. When this material falls back down around the vent, it builds up and a volcano is created. Essentially, a volcano is comparable to a large pile of debris surrounding a volcanic vent. A volcanic vent is an opening in the crust of the earth. This is where volcanic gases and molten lava escape from and into the atmosphere or onto the surface of the land.

The majority of volcanoes have a circular, central vent that is located close to the summit crater. The summit crater is a conduit for continuing volcanic creation.

There are large, elongated fissures or plantar vents from which basaltic lavas erupt, which cool and then form oceanic crust, continental flood basalts and oceanic plateaus. Oceanic crust is newly created at the axial fissures that are located along the globe-encircling ocean ridge system. Hydrothermal provinces and small ducts and cracks in the volcanic provinces act as vents for the gas, lava and water that is escaping and this results in smaller scale volcanic features such as hot springs, geysers, gaseous fumaroles and rootless splatter cones called homitos.


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