Mount St. Helens erupting on May 18, 1980

Spectacular and beautiful Koryaksky volcano on the Kamchatka peninsula, eastern Russia

A volcano is a mountain where lava (hot, liquid rock) comes from a magma chamber under the ground.

Most volcanoes have a volcanic crater at the top. When a volcano is active, materials come out of it. The materials include lava, steam, gaseous sulfur compounds, ash and broken rock pieces.

When there is enough pressure, it causes the volcano to erupt. The pressure blows off the top of the volcano. The magma comes out, sometimes quickly and sometimes slowly.