Volcanoes known for explosive eruptions are called composite volcanoes, or stratovolcanos. Composite volcanoes have steep sides, with cones that are often symmetrical. The cones are made of layers of ash, lava and rock from previous eruptions.
Explosive eruptions are caused when gas builds up under the volcano's surface, or dome, along with large quantities of thick magma.
Pyroclastic flows are extremely hot mixtures of volcanic debris and gases that flow close to the ground. These flows can reach speeds of 450 mph depending on the ratio of gases to solids.
Lava flows can have temperatures as high as 2,000 degrees. Pieces of hardening lava released from the explosion, and mudflows caused by rapidly melting snow, can destroy the natural environment and completely cover villages and towns.
Rhyolitic volcanoes, such Chile's Chiaten volcano which erupted in 2008, are the most dangerous. They have an extremely thick magma consisting of mainly silica and can take 10,000 years to build enough pressure to explode, often with little warning. The people in Chile had only 30 hours.
Over the past 300 years, more than 260,000 people have died as a result of volcanic eruptions.
