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Caldera
CalderaA caldera is a large, usually circular depression at the summit of a volcano . Most calderas are formed by subsidence or sinking of the central part of the volcano; a rare few are excavated by violent explosions. Craters and calderas are distinct structures. Both are circular depressions at the tops of volcanoes, but a crater is much smaller than a caldera and is formed by the building up of material around a vent rather than by the subsidence of material below a cone. A volcano's summit may subside in two ways. First, eruptions of large volumes of pumice or magma , or subterranean drainage of the latter to other areas, may empty a chamber beneath the volcano into which a portion of the cone collapses. Second, the summit of the volcano may act as a thin roof over a large magma chamber that breaks under its own weight and sinks, partly or wholly, into the magma beneath. The term cauldron is sometimes reserved for calderas formed by the foundering of a cone summit in underlying magma. The largest volcanic structures in the world are resurgent calderas. Resurgent calderas form following intense volcanic eruptions comparable in violence to asteroid impacts. (None has occurred during historical times.) During such an eruption, vast ejections of volcanic material—in some cases, thousands of cubic miles of pumice and ash—excavate very wide underground chambers, much wider than the volcano itself. Large calderas, up to hundreds of square miles in extent, collapse into these chambers. After settling, the caldera floor resurges or bulges up again, lifted by the refilling magma chamber below. Is in the case of the 22 mile (35 km) wide Cerro Galan caldera in Argentina, which is visible as a whole only from orbit, resurgence has raised the center of the caldera to almost a mile (1500 m) above the point of lowest subsidence. Caldera complexes—overlapping calderas, some swallowing parts of others—are sometimes formed by repeated episodes of partial subsidence. Calderas and caldera complexes are common not only on Earth but on other bodies in the Solar System where volcanoes have erupted in the past or are presently erupting, including Mars, Venus, and Io. See also Silicic |
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"Caldera." World of Earth Science. 2003. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "Caldera." World of Earth Science. 2003. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1G2-3437800092.html "Caldera." World of Earth Science. 2003. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3437800092.html |
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caldera
caldera A large volcanic depression, usually several kilometres in diameter, formed primarily by the collapse of a magma chamber roof or, less frequently, by a volcanic explosion. A caldera often contains smaller craters, cones, and other types of volcanic vent. Small collapse craters less than 1 km in diameter are known as collapse pits. Calderas are often non-circular in shape. Many of the small number of volcanic craters on the Moon appear to be calderas, some of them at the heads of sinuous rilles. There are also huge calderas at the summits of many of the giant volcanoes of Mars. Olympus Mons has a complex of summit calderas more than 60 km in diameter, apparently the result of several collapse events. Similar features are found on the volcanoes of Venus.
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"caldera." A Dictionary of Astronomy. 1997. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "caldera." A Dictionary of Astronomy. 1997. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O80-caldera.html "caldera." A Dictionary of Astronomy. 1997. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-caldera.html |
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caldera
cal·de·ra / kalˈderə; kôl-; -ˈdi(ə)rə/ • n. a large volcanic crater, typically one formed by a major eruption leading to the collapse of the mouth of the volcano. |
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"caldera." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "caldera." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O999-caldera.html "caldera." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-caldera.html |
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caldera
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"caldera." World Encyclopedia. 2005. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "caldera." World Encyclopedia. 2005. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1O142-caldera.html "caldera." World Encyclopedia. 2005. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-caldera.html |
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caldera
caldera see crater . |
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"caldera." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. 26 May. 2012 <http://www.encyclopedia.com>. "caldera." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. (May 26, 2012). http://www.encyclopedia.com/doc/1E1-X-caldera.html "caldera." The Columbia Encyclopedia, 6th ed.. 2011. Retrieved May 26, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-X-caldera.html |
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