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rift valley
rift valley An elongate trough, of regional extent, bounded by two or more faults. Many rifts on land are associated with alkaline volcanicity and, because their margins are uplifted, many are starved of clastic sediments and so contain lakes; the E. African rift system is an outstanding example. Some rifts are thought to be at the embryonic stage of ocean development of the Wilson cycle, whilst others may become ‘failed rifts’ (or ‘failed arms’) and fill with sediment to become aulacogens. The rift valley developed along the axis of slow-spreading oceanic ridges is known as the median valley (or axial rift or axial trough) and is associated with the production of basaltic magmas. Tibetan rifts form at the end of the Wilson cycle as a result of the northward indentation of India into Asia and the spreading of the thickening Tibetan crust. Graben (the German word for ‘ditch’) can be used synonymously for ‘rift valley’ and also for an infilled, fault-bounded trough of any size, with or without topographic expression.
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Cite this article
AILSA ALLABY and MICHAEL ALLABY. "rift valley." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "rift valley." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O13-riftvalley.html AILSA ALLABY and MICHAEL ALLABY. "rift valley." A Dictionary of Earth Sciences. 1999. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-riftvalley.html |
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rift valley
rift valley elongated depression, trough, or graben in the earth's crust, bounded on both sides by normal faults and occurring on the continents or under the oceans. The central flat block forming the trough slips downward relative to the crustal blocks on either side. The appearance is that of a fallen keystone in a broken arch. Rift valleys form by tensional forces, typically those associated with the initiation of plate separation (see plate tectonics ). The development of a rift valley in a continent is believed to be a precursor to the breakup of the continent and the development of a new ocean basin by seafloor spreading . Rift valleys, such as the Red Sea and the African rift valleys, are commonly the sites of volcanism and the locus of much earthquake activity. |
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Cite this article
"rift valley." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. "rift valley." The Columbia Encyclopedia, 6th ed.. 2011. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1E1-riftvall.html "rift valley." The Columbia Encyclopedia, 6th ed.. 2011. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-riftvall.html |
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rift valley
rift valley An elongate trough of regional extent, bounded by two or more faults. Many rifts on land are associated with volcanic activity and many contain lakes. The East African rift system is an outstanding example. Some rifts are thought to be at the embryonic stage of ocean development of the Wilson cycle; others may become ‘failed rifts’ (or ‘failed arms’) and fill with sediment to become aulacogens. The rift valley developed along the axis of a slow-spreading oceanic ridge is known as the median valley (or axial rift or axial trough). ‘Graben’ (the German word for ‘ditch’) can be used synonymously for ‘rift valley’ and also for an infilled, fault-bounded trough of any size.
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Cite this article
MICHAEL ALLABY. "rift valley." A Dictionary of Ecology. 2004. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. MICHAEL ALLABY. "rift valley." A Dictionary of Ecology. 2004. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O14-riftvalley.html MICHAEL ALLABY. "rift valley." A Dictionary of Ecology. 2004. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O14-riftvalley.html |
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rift valley
rift val·ley • n. a large elongated depression with steep walls formed by the downward displacement of a block of the earth's surface between nearly parallel faults or fault systems. |
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Cite this article
"rift valley." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 27 May. 2012 <http://www.encyclopedia.com>. "rift valley." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 27, 2012). http://www.encyclopedia.com/doc/1O999-riftvalley.html "rift valley." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 27, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-riftvalley.html |
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