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Saltation
SaltationSaltation is the transportation of sand grains in small jumps by wind or flowing water . The term does not refer to salt, but is derived from the Latin saltare, to dance. Certain conditions are necessary for saltation. First, a bed of sand grains must be covered by flowing air or water, as in a streambed or windy desert . Second, this flow must be turbulent. In turbulent flow, a fluid swirls and mixes chaotically—and virtually all natural flows of water and air are turbulent. Third, some of the eddies in the turbulence must be strong enough to lift individual sand grains from the bottom. Fourth, the turbulence must not be so strong that grains cannot settle out again once suspended. An individual saltating grain spends most of its time lying at rest on the bottom. Eventually an eddy happens to apply enough suction to the upper surface of the grain to overcome its weight, lifting it into the current. The grain is carried for a short distance, and then allowed to settle to the bottom again by the ever-shifting turbulence. After a random waiting period, the grain is lifted, carried, and dropped again, always farther downstream. Grains too small to settle once suspended are carried indefinitely by the current; intermediate-size grains saltate; and grains too large to saltate either remain unmoved or move by sliding or rolling. Turbulent flow thus tends to sort grains by size. |
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"Saltation." World of Earth Science. 2003. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. "Saltation." World of Earth Science. 2003. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1G2-3437800526.html "Saltation." World of Earth Science. 2003. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1G2-3437800526.html |
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saltation
saltation Saltation (from the Latin ‘saltare’) is the process of particle transport by small bounces or leaps along a surface. Saltation occurs in both water and air, although there are some significant differences in the processes in the two media. In water, direct fluid lift and drag forces are responsible for entraining a grain into the fluid, whereas in air entrainment can also result from grain collision. The initial launch trajectory will be steep, though the angle of descent will be far more gentle. The impact of the saltating grain with the surface will be violent in air, normally resulting in multiple grains, up to six times the diameter of the impacting grain, being launched into the airstream. The force at which a grain is set in motion (the entrainment threshold), as well as the length and height of its subsequent leap, will be proportional to the shear velocity of the fluid and the size of the grain. In air the entrainment threshold will also be a function of grain impaction and configuration of the sediment surface. In water the impact of a saltating grain on a surface is far less violent, and does not normally result in further grains being launched into the fluid. This is because of the much lower density ratio between the fluid and the grain, and the greater viscosity of the water.
T. Linsey |
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PAUL HANCOCK and BRIAN J. SKINNER. "saltation." The Oxford Companion to the Earth. 2000. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. PAUL HANCOCK and BRIAN J. SKINNER. "saltation." The Oxford Companion to the Earth. 2000. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O112-saltation.html PAUL HANCOCK and BRIAN J. SKINNER. "saltation." The Oxford Companion to the Earth. 2000. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O112-saltation.html |
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saltation
saltation The hypothesis that the derived (apomorphic) characters of a species were all obtained simultaneously as a result of the random effects of mutation and recombination at the DNA level. Although popular in the early twentieth century, the saltation hypothesis is generally not accepted or supported by the fossil record.
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MICHAEL ALLABY. "saltation." A Dictionary of Zoology. 1999. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "saltation." A Dictionary of Zoology. 1999. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O8-saltation.html MICHAEL ALLABY. "saltation." A Dictionary of Zoology. 1999. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O8-saltation.html |
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saltation
saltation Major process of particle transport in either air or water, which involves an initial steep lift followed by travel and then a gentle descent to the bed. An essential requirement for the process is turbulent flow that can lift particles into the zone of relatively high downstream (downwind) velocity.
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AILSA ALLABY and MICHAEL ALLABY. "saltation." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "saltation." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O13-saltation.html AILSA ALLABY and MICHAEL ALLABY. "saltation." A Dictionary of Earth Sciences. 1999. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-saltation.html |
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saltation
saltation leaping, dancing. XVII. — L. saltātiō, -ōn-, f. saltāre dance, frequent. of salīre leap; see -ATION.
So saltatory XVII. — L. saltātōrius; hence saltatorial XVIII. |
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T. F. HOAD. "saltation." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. T. F. HOAD. "saltation." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O27-saltation.html T. F. HOAD. "saltation." The Concise Oxford Dictionary of English Etymology. 1996. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O27-saltation.html |
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saltation
saltation A major process of particle transport in air and water, which involves an initial steep lift followed by travel and then a gentle descent to the bed.
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MICHAEL ALLABY. "saltation." A Dictionary of Ecology. 2004. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "saltation." A Dictionary of Ecology. 2004. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O14-saltation.html MICHAEL ALLABY. "saltation." A Dictionary of Ecology. 2004. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O14-saltation.html |
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