Rift valley
Arift valleyis a linear shaped lowland between severalhighlandsor mountain ranges produced by the action of ageologic rift.Rifts are formed as a result of the pulling apart of thelithospheredue toextensional tectonics.The linear depression may subsequently be further deepened by the forces of erosion. More generally the valley is likely to be filled with sedimentary deposits derived from the rift flanks and the surrounding areas. In many casesrift lakesare formed. One of the best known examples of this process is theEast African Rift.[1]On Earth, rifts can occur at all elevations, from the sea floor to plateaus and mountain ranges incontinental crustor inoceanic crust.They are often associated with a number of adjoining subsidiary or co-extensive valleys, which are typically considered part of the principal rift valley geologically.
Earth's rift valleys
[edit]The most extensive rift valley is located along the crest of themid-ocean ridgesystem and is the result ofsea floor spreading.Examples of this type of rift include theMid-Atlantic Ridgeand theEast Pacific Rise.
Many existing continental rift valleys are the result of a failed arm (aulacogen) of atriple junction,although there are two, theEast African Riftand theBaikal Rift Zone,which are currently active, as well as a third which may be, theWest Antarctic Rift System.In these instances, not only the crust but entiretectonic platesare in the process of breaking apart forming 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 discontinuities 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, theDead Sealies in a rift which results from a leftward discontinuity in the left lateral-movingDead 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 assag pondsorlandslides.
Rift valley lakes
[edit]Many of the world's largest lakes are located in rift valleys.[2]Lake BaikalinSiberia,aWorld Heritage Site,[3]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.[4]Lake Tanganyika,second by both measures, is in theAlbertine Rift,the westernmost arm of the activeEast African Rift.Lake SuperiorinNorth America,the largestfreshwaterlakeby area, lies in the ancient and dormantMidcontinent Rift.The largest subglacial lake,Lake Vostok,may also lie in an ancient rift valley.[5]Lake NipissingandLake TimiskaminginOntarioandQuebec,Canadalie inside a rift valley called theOttawa-Bonnechere Graben.[6]Þingvallavatn,Iceland'slargest natural lake, is also an example of a rift lake.
Extraterrestrial rift valleys
[edit]Rift valleys are also known to occur on other terrestrial planets and natural satellites. The 4,000 km longValles Marinerison Mars is believed by planetary geologists to be a large rift system.[7][8]Some features of Venus, most notably, the 4,000 kmDevana Chasma[9]and a part of the western Eistla, and possibly also Alta and Bell Regio have been interpreted by some planetary geologists as rift valleys.[10][11]Some natural satellites also have prominent rift valleys. The 2,000 km longIthaca Chasmaon Tethys in the Saturn system is a prominent example. Charon'sNostromo Chasmais the first confirmed in the Pluto system, however large chasms up to 950 km wide observed on Charon have also been tentatively interpreted by some as giant rifts, and similar formations have also been noted on Pluto.[12]A recent study suggests a complex system of ancient lunar rift valleys, includingVallis RheitaandVallis Alpes.[13]The Uranus system also has prominent examples, with large 'chasma' believed to be giant rift valley systems, most notably the 1492 km longMessina Chasmaon Titania, 622 kmKachina Chasmataon Ariel,Verona Rupeson Miranda,[14]andMommur Chasmaon Oberon.[15]
References
[edit]- ^"The Ethiopian Rift Valley".Giacomo Corti-CNR.
- ^"The World's Greatest Lakes".Archived fromthe originalon 2020-06-19.Retrieved2020-06-18.
- ^"Lake Baikal – World Heritage Site".World Heritage.Retrieved2007-01-13.
- ^"The Oddities of Lake Baikal".Alaska Science Forum. Archived fromthe originalon 2012-04-19.Retrieved2007-01-07.
- ^Siegert, Martin J. (1999). "Antarctica's Lake Vostok".American Scientist.87(6): 510.Bibcode:1999AmSci..87..510S.doi:10.1511/1999.6.510.S2CID209833822.
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.
- ^John Grotzinger.... (2006).Understanding Earth.New York: W. H. Freeman.ISBN0-7167-7696-0.
- ^Anderson, Scott; Grimm, Robert E. (1998)."Rift processes at the Valles Marineris, Mars: Constraints from gravity on necking and rate-dependent strength evolution".Journal of Geophysical Research.103(E5): 11113.Bibcode:1998JGR...10311113A.doi:10.1029/98JE00740.ISSN0148-0227.
- ^Andrews-Hanna, Jeffrey C. (2012)."The formation of Valles Marineris: 3. Trough formation through super-isostasy, stress, sedimentation, and subsidence".Journal of Geophysical Research.117(E6): n/a.Bibcode:2012JGRE..117.6002A.doi:10.1029/2012JE004059.ISSN0148-0227.
- ^Kiefer, W. S.; Swafford, L. C. (2006). "Topographic Analysis Of Devana Chasma, Venus; Implications For Rift System Segmentation And Propagation".Journal of Structural Geology.28(12): 2144–2155.Bibcode:2006JSG....28.2144K.doi:10.1016/j.jsg.2005.12.002.
- ^Senske, D. A.; Schaber, G. G.; Stofan, E. R. (1992). "Regional topographic rises on Venus: Geology of Western Eistla Regio and comparison to Beta Regio and Atla Regio".Journal of Geophysical Research.97(E8): 13395.Bibcode:1992JGR....9713395S.doi:10.1029/92JE01167.ISSN0148-0227.
- ^Solomon, Sean C.; Smrekar, Suzanne E.; Bindschadler, Duane L.; Grimm, Robert E.; Kaula, William M.; McGill, George E.; Phillips, Roger J.; Saunders, R. Stephen; Schubert, Gerald; Squyres, Steven W.; Stofan, Ellen R. (1992). "Venus tectonics: An overview of Magellan observations".Journal of Geophysical Research.97(E8): 13199.Bibcode:1992JGR....9713199S.doi:10.1029/92JE01418.ISSN0148-0227.S2CID129537658.
- ^Dunn, Marcia (16 July 2015)."'Blowing my mind': Peaks on Pluto, canyons on Charon ".PhysOrg.
- ^Andrews-Hanna, Jeffrey C.; Besserer, Jonathan; Head III, James W.; Howett, Carly J. A.; Kiefer, Walter S.; Lucey, Paul J.; McGovern, Patrick J.; Melosh, H. Jay; Neumann, Gregory A.; Phillips, Roger J.; Schenk, Paul M.; Smith, David E.; Solomon, Sean C.; Zuber, Maria T. (2014). "Structure and evolution of the lunar Procellarum region as revealed by GRAIL gravity data".Nature.514(7520): 68–71.Bibcode:2014Natur.514...68A.doi:10.1038/nature13697.ISSN0028-0836.PMID25279919.S2CID4452730.
- ^ Chaikin, Andrew (2001-10-16)."Birth of Uranus' provocative moon still puzzles scientists".space.Imaginova Corp. p. 1. Archived fromthe originalon July 9, 2008.Retrieved2007-07-23.
- ^ Smith, B. A.; Soderblom, L. A.; Beebe, A.; Bliss, D.; Boyce, J. M.; Brahic, A.; Briggs, G. A.; Brown, R. H.; Collins, S. A. (4 July 1986)."Voyager 2 in the Uranian System: Imaging Science Results".Science.233(4759): 43–64.Bibcode:1986Sci...233...43S.doi:10.1126/science.233.4759.43.PMID17812889.S2CID5895824.
Further reading
[edit]- Bonatti, E (1985). "Punctiform initiation of seafloor spreading in the Red Sea during transition from a continental to an oceanic rift".Nature.316(6023): 33–37.Bibcode:1985Natur.316...33B.doi:10.1038/316033a0.S2CID4355790.
- Mart, Y.; Dauteuil, O. (2000). "Analogue experiments of propagation of oblique rifts".Tectonophysics.316(1–2): 121–132.Bibcode:2000Tectp.316..121M.doi:10.1016/s0040-1951(99)00231-0.
