(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 ...

Smoke billows from the mouth of Mt. Shasta like a thunderous cough. Within moments, clear skies turn gray, and the sun vanishes behind thick, shifting layers of volcanic gas and ash. Visitors snap ...

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 ...