(CNN) — Here's some background information about volcanoes, mountains that open downward to a reservoir of molten rock. Facts: More than 80% of the Earth's surface, both above and below sea level, is ...

A volcano is an opening in the Earth's crust that allows molten rock, gases, and debris to escape from below the surface. The molten rock that rises in volcanic vents is known as 'magma', and after it ...

Lava is molten rock from a volcano that reaches the Earth’s surface. Liquid rock below the Earth’s surface is referred to as magma. More than 50% of the world’s active volcanoes above sea level ...