crater, circular, bowl-shaped depression on the earth's surface. (For a discussion of lunar craters, see moon.) Simple craters are bowl-shaped with a raised outer rim. Complex craters have a raised central peak surrounded by a trough and a fractured rim.
Many of the largest craters are formed by the impact of meteorites. Impacting at speeds in excess of 10 mi/sec (16 km/sec), a meteorite creates pressures on the order of millions of atmospheres, producing shock waves that blast out a circular hole and often destroy the meteorite. Meteor, or Barringer, Crater, near Winslow, Arizona, c.3/4 mi (11/5 km) in diameter and 600 ft (180 m) deep, is probably the best-known crater of this type. Of the more than 160 impact craters identified on earth, the largest are at Manicouagan, Quebec; Vredefort, South Africa; and Chicxulub (off the coast of the Yucatán peninsula), Mexico. Others include the Chesapeake Bay impact crater, Virginia; Chubb Crater, Quebec; Lake Bosumtwi, Ghana; Brent Crater, Ontario; and Kebira, SW Egypt. Two sizable impact events occurred in the 20th cent., both in Siberia. In 1908 in the Tunguska Basin near Lake Baykal one occurred that caused vast destruction of timber from its blast, and the other in 1947 at Sikhote-Alin also caused great damage. Craters that have been obliterated by erosion over thousands of years, leaving only a circular scar on the earth's surface, are called astroblemes. The fractured rock of buried impact craters (e.g., Chicxulub) may become a trap for oil and natural gas.
Craters are also commonly formed at the surface opening, or vent, of erupting volcanoes, particularly of the type called cinder cones, where the lava is extruded rather explosively. Virtually all volcanoes display a crater, called a sink, around the vent; this is believed to be a collapse feature caused by molten lava subsiding as an eruption phase diminishes. Volcanic craters formed in these ways are relatively small, usually less than 1 mi (1.6 km) in diameter, and represent only a small fraction of the cone's diameter at the base. A caldera is a much larger crater, typically ranging from 3 to 18 mi (5–30 km) in diameter, and represents a considerable fraction of the volcano's basal diameter. In a few instances, however, tremendous volcanic eruptions have left calderas 50 mi (80 km) or so, such as that that forms much of Yellowstone National Park or the basin of Lake Toba, Sumatra, Indonesia. Most calderas are formed by the collapse of the central part of a cone during great eruptions. A few small calderas have been formed by explosive eruptions in which the top of a volcano was blown out. Some volcanic craters are created by a combination of these events. Formed thousands of years ago, the caldera that contains Crater Lake, Oreg., is 6 mi (9.7 km) in diameter. In recent times, caldera-producing eruptions occurred at Krakatoa, Indonesia, in 1883 and Katmai, Alaska, in 1912.
See also tektite.
See P. Hodge, Meteorite Craters and Impact Structures of the Earth (1994).
1. General term for a circular, funnel-shaped depression, up to 1km in diameter, produced by volcanic processes by which gases, tephra, and lava are or have been ejected. Several types are recognized: a crater at the summit of a volcanic cone marks the site of magma degassing and ejection of material; a maar, often occupied by a lake, results from explosive activity; and a caldera is a large volcanic depression greater than 1 km in diameter.
2. Near-circular depression produced by the impact of an extraterrestrial body, e.g. Meteor Crater, Arizona. Meteorite craters are formed by the explosion outward and upward of material compressed and heated strongly by the energy of impact, and so usually are circular at the time they form. They are characterized by topographically raised rims and by ejecta blankets which show inverted stratigraphy with respect to the target rocks. See also SHATTER CONES.
cra·ter / ˈkrātər/ • n. 1. a large, bowl-shaped cavity in the ground or on the surface of a planet or the moon, typically one caused by an explosion or the impact of a meteorite or other celestial body. ∎ a large pit or hollow forming the mouth of a volcano. ∎ a cavity or hole in any surface. 2. a large bowl used in ancient Greece for mixing wine. • v. [tr.] form a crater in (the ground or a planet): he has the offensive power to crater the enemy's runways.
Cra·ter / ˈkrātər/ Astron. a small and faint southern constellation (the Cup), between Hydra and Leo, said to represent the goblet of Apollo. ∎ [as genitive] (Cra·te·ris / krāˈti(ə)ris/ ) used with a preceding letter or numeral to designate a star in this constellation: the star Delta Crateris.