Composite Volcanoes

By David Olmstead
Composite Volcano Information - Mount Rainier

Composite volcanoes are also called strato-volcanoes. It is a member of the volcanic landforms family.  As the name suggests, they are composed of lava flows and pyroclastic materials of intermediate composition which includes volcanic ash, cinders, blocks and fragments of rock. It should not be confused with shield volcanoes or cinder cones because they not only differ in composition but also the shapes. Unlike the other two, composite volcanoes are deep sided near their summits.They can have an inclination of up to 30 degrees but their slopes decreases towards the base where they may be no more than 5 degrees.

Composite volcanoes assume different shapes. The most common ones include the following information;

1. Concave as witnessed in the Agna volcano.
2. A pyramidal e.g. the Stromboli volcano
3. Convex- concave as in the Vesavius
4. Some will form as multiple summits e.g. the Shasta.
5. Helmet shaped- Mount Rainier.
6. Perfect Cone shape of Mayon Volcano of the Philippines

Formation of composite volcanoes

They result from alternating layers of the composite materials like lava volcanic ash.   A significant characteristic of the composite volcano is the process through which the magma from inside the earth’s surface transits to the top of the land.  The volcano is built up by repeated accumulation of materials that erupts through the conduit and also increases in the sizes of lava and other materials. Normally volcanoes have have craters on their top which contains a central vent or a group of vents.

Why do composite volcanoes erupt violently?

It is true that composite volcanoes erupt explosively and you will be impressed by this information.This is attributed to the viscous magma. When the magma comes to the earth’s crust, it results in clogging of the crater pipe thus causing the gas in the pipe to be locked up. This will cause pressure mount up and eventually violent eruptions occur.In some instances, the lava solidifies within fissures thus forming dykes.The dykes act as ribs thus giving strength to the volcano.

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