Composite Volcano

A composite volcano forms in subduction zones when a crustal plate is forced into the mantle and begins to melt. Andesite, dacite and rhyolite lavas are the primary types of lava that form these volcanoes. Eruptions on the volcanoes often alternate between tephra and lava flows. 

Mount Shasta is a composite volcano. Photo by Myrna Martin

Subduction zone volcanoes

Geologists often use the term stratovolcanoes to describe the mountains that form in subduction zones. The volcanoes form on the continental side of a subduction zone.

The melting oceanic crust forms pools of molten rock in a magma chamber. The magma, molten rock, in the magma chamber is lighter than the volcano rocks that surround it. The magma works its way to the summit where it erupts as tephra or in thick lava flows.

Lava eruptions on stratovolcanoes

Andesite, dacite and rhyolite are the three major types of lava that creates these large volcanic mountains on the continents. These three types of lava have a high percentage of quartz and are associated with large violent eruptions.

Stratovolcanoes will often alternate between explosive eruptions and thick lava flows. This combination of eruptions produces the classical look of a composite volcano.

Growth of the volcano

The summit of a stratovolcano has steep sides. Andesite, dacite and rhyolite create slowing thick lava flows that usually cool on the upper slopes of a volcano.

The base of these volcanoes is wide and has gentle slopes due to erosion. As the volcano grows in size large amounts of the pyroclastic material erodes away. The eroded pyroclastic material is carried down the slopes by erosion where it is deposited at the base of the volcano.

More Links to Volcano Facts

Yellowstone Caldera The Yellowstone Caldera is the location of three supervolcano eruptions.

Iceland Volcanoes  Find out more about Grimsvotn volcano, Hekla volcano and Katla volcano which are the most dangerous volcanoes on Iceland. 

Composite Volcano  These volcanoes form on the continental side of subduction zones. 

Super Volcanoes  Super volcanoes are places where massive volcanic eruptions occur. These eruptions can alter the weather and cause mini ice ages.


Dome Volcano  A dome volcano is small and often forms inside the caldera of a stratovolcano. 

Volcano Facts  Find out lots of fascinating facts and trivia about volcanoes on this webpage.

Home Page  The Science Site contains information on our planet, volcanoes, science projects, earthquakes and much more.

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