- Rift valley
A rift valley is a linear-shaped lowland between highlands or mountain ranges created by the action of a geologic
riftor fault. This action is manifest as crustal extension, a spreading apart of the surface which is subsequently further deepened by the forces of erosion. Rifts can occur at all elevations, from the seafloor to plateaus and mountain ranges. They can occur in continental crustor in oceanic crust. Rift valleys are often associated with a number of adjoining subsidiary or co-extensive valleys which are typically considered geologically part of the principal rift valley.
The most extensive rift valley is located along the crest of the
mid-ocean ridgesystem and is the result of seafloor spreading. Examples of this type of rift include the Mid-Atlantic Ridgeand the East Pacific Rise.
Many existing continental rift valleys are the result of a failed arm (
aulacogen) of a triple junction, although there are two, the East African Riftand the Baikal Rift Zone, which are currently active, as well as a third which may be, the West Antarctic Rift. In these instances, not only the crust, but also entire tectonic plates are in the process of breaking apart to create new plates. If they continue, continental rifts will eventually become oceanic rifts.
Other rift valleys are the result of bends or discontinuities in horizontally-moving (strike-slip) faults. When these bends or discontinuitues are in the same direction as the relative motions along the fault, extension occurs. For example, for a right lateral-moving fault, a bend to the right will result in stretching and consequent subsidence in the area of the irregularity. In the view of many geologists today, the
Dead Sealies in a rift which results from a leftward discontinuity in the left lateral-moving Dead Sea Transformfault. Where a fault breaks into two strands, or two faults run close to each other, crustal extension may also occur between them as a result of differences in their motions. Both types of fault-caused extension commonly occur on a small scale, producing such features as sag ponds or landslides.
The largest freshwater lakes in the world are all located in rift valleys. [cite web
title=The World's Greatest Lakes
Lake Baikalin Siberia, a World Heritage Site, [cite web
title=Lake Baikal - World Heritage Site
accessdate=2007-01-13] , lies in an active rift valley. Baikal is both the deepest lake in the world and, with 20% of all of the liquid freshwater on earth, has the greatest volume. [cite web
title=The Oddities of Lake Baikal
publisher=Alaska Science Forum
Lake Tanganyika, second by both measures, is in the "Albertine Rift", the westernmost arm of the active Great Rift Valleyof East Africaand Southwest Asia. Lake Superiorin North America, the largest freshwater lakeby area, lies in the ancient and dormant Midcontinent Rift. The largest subglacial lake, Lake Vostok, may also lie in an ancient rift valley. [cite journal |last=Siegert |first=Martin J. |year=1999 |title=Antarctica's Lake Vostok |journal=American Scientist |volume=87 |issue=6 |pages=510 |doi=10.1511/1999.6.510 |url=http://www.americanscientist.org/template/AssetDetail/assetid/15820/page/3;jsessionid=baa9...#26308 |accessdate=2007-12-12 |quote=The best explanation is that Lake Vostok may lie in a rift valley, as does Lake Tanganyika in East Africa and Lake Baikal in Russia. The geography of Lake Vostok is indeed consistent with this notion, in that the lake has a crescent shape, just like Tanganyika and Baikal, and the side walls of the lake are relatively steep, at least on one side. ] Lake Nipissingand Lake Timiskamingin Ontarioand Quebec, Canadalie inside a rift valley called the Ottawa-Bonnechere Graben.
* Bonatti, E., 1985. Punctiform initiation of seafloor spreading in the Red Sea during transition from a continental to an oceanic rift. Nature, 316: 33-37.
* Mart, Y., Dauteuil, O., 2000. Analogue experiments of propagation of oblique rifts. Tectonophysics, 316: 121-132.
Wikimedia Foundation. 2010.
См. также в других словарях:
Rift-Valley — (engl. für „Grabenbruch“) bezeichnet: den Großen Afrikanischen Grabenbruch eine Provinz in Kenia, siehe Rift Valley (Kenia) … Deutsch Wikipedia
Rift Valley — (engl. für „Grabenbruch“) bezeichnet: den Großen Afrikanischen Grabenbruch eine Provinz in Kenia, siehe Rift Valley (Kenia) … Deutsch Wikipedia
Rift Valley — (la) ou Rift (le) suite de dépressions de l Afrique de l Est, jalonnant une faille qui s allonge de la vallée du Jourdain au Malawi; la Rift Valley est occupée par des plaines étroites et de nombreux lacs (V. Grands Lacs). De nombreuses… … Encyclopédie Universelle
Rift Valley — GREAT RIFT VALLEY … English World dictionary
rift-valley — see rift n.2 4 … Useful english dictionary
rift valley — rift .valley n a valley with very steep sides, formed by the cracking and moving of the Earth s surface … Dictionary of contemporary English
rift valley — rift ,valley noun count a valley with steep sides, produced when the land between two parallel cracks in the ground sinks … Usage of the words and phrases in modern English
rift valley — Geol. 1. graben. 2. a subsea chasm extending along the crest of a mid ocean ridge, locus of the magma upwellings that accompany seafloor spreading. [1890 95] * * * Elongated trough formed by the subsidence of a segment of the Earth s crust… … Universalium
rift valley — noun a valley with steep sides; formed by a rift in the earth s crust • Hypernyms: ↑valley, ↑vale • Instance Hyponyms: ↑Great Rift Valley * * * noun, pl ⋯ leys [count] geology : a long, steep valley formed when two parallel rifts form in the… … Useful english dictionary
rift valley — UK / US noun [countable] Word forms rift valley : singular rift valley plural rift valleys a valley with steep sides, produced when the land between two parallel cracks in the ground sinks … English dictionary