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 (1 1/5 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.