stratovolcanoes
Composite volcanoes are also called stratovolcanoes. This is because they are formed by alternating layers strata of magma and ash Figure below . The magma that creates composite volcanoes tends to be thick. The steep sides form because the lava cannot flow too far from the vent. The thick magma may also create explosive eruptions. Ash and pyroclasts erupt into the air. Much of this material falls back down near the vent. This creates the steep sides of stratovolcanoes. The composition of magma that erupts at composite volcanoes is usually felsic rhyolite or intermediate andesite .