Volcanoes are one of the Earth's most interesting and destructive natural phenomena.

Beneath the surface crust of the Earth, lies a zone of molten rock (called magma) and lava; when a fissure opens up, the material rushes up the tube and spews itself on the surface - a volcano. The magma forms a hill or mountain around the opening fissure, and the burning gas, ash, and hot lava may erupt with or without warning.

Unlike a mere lava seep, though, a volcanic eruption spews dust, rock, gas, and other materials into the surrounding areas, and itself can do much damage when it is in the active phase. For example, the volcano located in Pompeii, Italy, erupted shortly before the turn of the 1st Millennium and totally destroyed the city. In the United States during the 1980s, Washington State's Mount St. Helens darkened the sky for extended periods and for miles around with a thick, black ash.

There are about 800 places in the world where volcanoes are active, including 80 of them below the sea. One large undersea belt circles the Pacific Ocean, and others run east-west through Indonesia and the Mediterranean Sea.

It is likely that undersea volcanoes lifted the crustal plate and pushed up the Hawaiian Islands, as well as several others. Mauna Loa, in Hawaii, is the planet's largest volcano.

Not just the Earth, but the solar system, as well, houses numerous volcanoes. The most active body in our solar system is not the Earth but Jupiter's moon, Io; at one point, the Voyager space probes detected eight active volcanoes on the surface, most likely due to the pull of Jupiter's nearby gravity field, which distorted the moon's fragile crust.