Volcano

a mountain or hill from which lava, heated rock material, and gases are ejected. The term was applied first to Mount Etna, the supposed home of Vulcanus, the god of fire. The material ejected is apt to give a volcano the form of a cone. The opening is surrounded usually by a pit-shaped cavity called a crater. The crater of Mauna Loa in Hawaii is 13,000 feet wide and 800 feet deep. Frequently there are many additional small openings. Within ten miles of the main crater, Mount Etna has over two hundred small vents. Many volcanoes have been quiet so long that they are regarded as extinct. Many such cold, lofty peaks exist in the Sierra Nevada Mountains of California. Volcanoes not lately in a state of eruption but which are thought likely to be resting only are termed dormant.

Volcanoes vary greatly in height. Some are scarcely above sea level. Vesuvius is 4,000 feet high. Cotopaxi in the Andes is the highest active volcano. It rises through the clouds to an altitude of 20,000 feet. There are over three hundred active volcanoes. They are widely distributed. A series encircles the Pacific Ocean; a second series runs east and west, including the volcanoes of the West Indies, the Canaries, the Azores, and the Mediterranean region. Where the Pacific circle crosses the east and west series volcanic activity is marked. The region of greatest volcanic activity is that of Java and adjacent islands. Latitude appears to have no influence. Erebus within the Antarctic Circle reddens the southern sky, and Mount Hecla in Iceland rivals Vesuvius in activity.

Pompeii was overwhelmed by an eruption of Vesuvius in 79. Late in August, 1883, an eruption in an island in the Strait of Sunda created a cavity into which the sea rushed with violence, setting waves in motion that overwhelmed and drowned villages. The cause of eruption is not known with certainty but it is believed that internal heat forms gases that expand and drive out the molten material as exploding powder drives the bullet from a gun.

See Lava; Basalt; Hecla; Etna; Vesuvius; Pompeii; Cotopaxi; Stromboli; Geysers