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crater,circular, bowl-shaped depression on the earth's surface. (For a discussion of lunar craters, see moonmoon,
natural satellite of a planet (see satellite, natural) or dwarf planet, in particular, the single natural satellite of the earth. The Earth-Moon System
The moon is the earth's nearest neighbor in space.
..... Click the link for more information. .) 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 meteoritesmeteorite,
meteor that survives the intense heat of atmospheric friction and reaches the earth's surface. Because of the destructive effects of this friction, only the very largest meteors become meteorites.
..... Click the link for more information. . 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 190 impact locations identified on earth, the largest craters by diameter (80 mi/130 km or greater) are at Vredefort, South Africa; and Chicxulub (off the coast of the Yucatán peninsula), Mexico. Others include Acraman Crater, South Australia; Brent Crater, Ontario; the Chesapeake Bay impact crater, Virginia; Chubb Crater, Quebec; Lake Bosumtwi, Ghana; and Manicouagan, Quebec; and Popigai Crater, Siberia. Two sizable impact events occurred in the 20th cent., both in Siberia. In 1908 in the Tunguska BasinTunguska Basin,
c.400,000 sq mi (1,036,000 sq km), Krasnoyarsk Territory and Sakha Republic, E central Siberian Russia, between the Yenisei and Lena rivers. It has a huge untapped coal reserve.
..... Click the link for more information. 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 astroblemesastrobleme
, large, circular structure ranging from c. 1-2 mi to 40 mi (.8–64 km) in diameter. Astroblemes are found at numerous places on the earth's surface, e.g., Meteor, or Barringer, Crater in Arizona, Brent Crater in Ontario, and Vredefort Ring in South Africa.
..... Click the link for more information. . 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 volcanoesvolcano,
vents or fissures in the earth's crust through which gases, molten rock, or lava, and solid fragments are discharged. Their study is called volcanology. The term volcano
..... Click the link for more information. , 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; the pressure that a caldera collapse produces on a magma chamber helps drive such 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 tektitetektite
, naturally occurring, silica-rich (65%–80% SiO2) glass resembling obsidian and sometimes shale, and is normally jet black to olive green. They appear as small rounded or elongated objects that often have aerodynamic shapes and range from a fraction of
..... Click the link for more information. .
See P. Hodge, Meteorite Craters and Impact Structures of the Earth (1994).
Crater(kray -ter) (Cup) A small inconspicuous constellation in the southern hemisphere near Leo, the brightest stars being of 3rd and 4th magnitude. Abbrev.: Crt; genitive form: Crateris; approx. position: RA 11.5h, dec –l5°; area: 282 sq deg.
a bowl- or funnel-shaped depression with a diameter measuring between dozens of meters and several kilometers and a depth from a few meters to hundreds of meters. Craters form during volcanic eruptions, as a result of the impact of meteorites, and as a result of large man-made explosions. Volcanic craters are usually located on the peaks or slopes of volcanoes. At the bottom of the crater are one or several vents through which lava and other volcanic products rising along an outlet channel from the magmatic center reach the surface. Sometimes the bottom of the crater is covered with a lake of lava or a small, newly formed volcanic cone.
The craters on the moon and Mars are round depressions surrounded by circular ridges; their diameters are up to 100–200 km and they are up to several kilometers deep. A distinction is made among them between craters formed during the impact of meteorites and asteroids and craters of volcanic origin (similar to the earth's volcanic craters and calderas).
(the Cup), a constellation of the southern hemisphere; its brightest star has a visual stellar magnitude of 3.6. The constellation is most easily viewed in March; it is visible from the central and southern regions of the USSR. (SeeSTELLAR SKY.)