:en:Rift valley

The most extensive rift valley is located along the crest of the mid-ocean ridge system and is the result of sea floor spreading. Examples of this type of rift include the Mid-Atlantic Ridge and the East Pacific Rise.

Many existing continental rift valleys are the result of a failed arm (aulacogen) of a triple junction, although there are three, the East African Rift, Rio Grande rift and the Baikal Rift Zone, which are currently active, as well as a fourth which may be, the West Antarctic Rift System. In these instances, not only the crust but entire tectonic plates are 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, the Dead Sea lies in a rift which results from a leftward discontinuity in the left lateral-moving Dead Sea Transform fault. 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.

{{main|Rift lake}}

Many of the world's largest lakes are located in rift valleys.{{cite web|title=The World's Greatest Lakes|url=https://www.schoolofflyfishing.com/worlds-greatest-lakes/|access-date=2020-06-18|archive-date=2020-06-19|archive-url=https://web.archive.org/web/20200619121013/https://www.schoolofflyfishing.com/worlds-greatest-lakes/|url-status=dead}} Lake Baikal in Siberia, a World Heritage Site,{{cite web

|url=https://whc.unesco.org/en/list/754

|title=Lake Baikal – World Heritage Site

|publisher=World Heritage

|access-date=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

|url=http://www.gi.alaska.edu/ScienceForum/ASF9/986.html

|title=The Oddities of Lake Baikal

|publisher=Alaska Science Forum

|access-date=2007-01-07

|archive-date=2012-04-19

|archive-url=https://web.archive.org/web/20120419072226/http://www2.gi.alaska.edu/ScienceForum/ASF9/986.html

|url-status=dead

}} Lake Tanganyika, second by both measures, is in the Albertine Rift, the westernmost arm of the active East African Rift. Lake Superior in North America, the largest freshwater lake by 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 |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. |bibcode = 1999AmSci..87..510S |s2cid=209833822 }} Lake Nipissing and Lake Timiskaming in Ontario and Quebec, Canada lie inside a rift valley called the Ottawa-Bonnechere Graben.{{cite book|isbn=0-7167-7696-0|author=John Grotzinger ....|year=2006|publisher=W. H. Freeman|location=New York|title=Understanding Earth.}} Þingvallavatn, Iceland's largest natural lake, is also an example of a rift lake.

Rift valleys are also known to occur on other terrestrial planets and natural satellites. The 4,000 km long Valles Marineris on Mars is believed by planetary geologists to be a large rift system.{{cite journal|last1=Anderson|first1=Scott|last2=Grimm|first2=Robert E.|title=Rift processes at the Valles Marineris, Mars: Constraints from gravity on necking and rate-dependent strength evolution|journal=Journal of Geophysical Research|volume=103|issue=E5|year=1998|pages=11113|issn=0148-0227|doi=10.1029/98JE00740|bibcode=1998JGR...10311113A|doi-access=free}}{{cite journal|last1=Andrews-Hanna|first1=Jeffrey C.|title=The formation of Valles Marineris: 3. Trough formation through super-isostasy, stress, sedimentation, and subsidence|journal=Journal of Geophysical Research|volume=117|issue=E6|year=2012|pages=n/a|issn=0148-0227|doi=10.1029/2012JE004059|bibcode=2012JGRE..117.6002A|doi-access=free}} Some features of Venus, most notably, the 4,000 km Devana Chasma{{cite journal | last1 = Kiefer | first1 = W. S. | last2 = Swafford | first2 = L. C. | year = 2006 | title = Topographic Analysis Of Devana Chasma, Venus; Implications For Rift System Segmentation And Propagation | journal = Journal of Structural Geology | volume = 28 | issue = 12| pages = 2144–2155 | doi=10.1016/j.jsg.2005.12.002| bibcode = 2006JSG....28.2144K }} and a part of the western Eistla, and possibly also Alta and Bell Regio have been interpreted by some planetary geologists as rift valleys.{{cite journal|last1=Senske|first1=D. A.|last2=Schaber|first2=G. G.|last3=Stofan|first3=E. R.|title=Regional topographic rises on Venus: Geology of Western Eistla Regio and comparison to Beta Regio and Atla Regio|journal=Journal of Geophysical Research|volume=97|issue=E8|year=1992|pages=13395|issn=0148-0227|doi=10.1029/92JE01167|bibcode=1992JGR....9713395S}}{{cite journal|last1=Solomon|first1=Sean C.|last2=Smrekar|first2=Suzanne E.|last3=Bindschadler|first3=Duane L.|last4=Grimm|first4=Robert E.|last5=Kaula|first5=William M.|last6=McGill|first6=George E.|last7=Phillips|first7=Roger J.|last8=Saunders|first8=R. Stephen|last9=Schubert|first9=Gerald|last10=Squyres|first10=Steven W.|last11=Stofan|first11=Ellen R.|title=Venus tectonics: An overview of Magellan observations|journal=Journal of Geophysical Research|volume=97|issue=E8|year=1992|pages=13199|issn=0148-0227|doi=10.1029/92JE01418|bibcode=1992JGR....9713199S|s2cid=129537658}} Some natural satellites also have prominent rift valleys. The 2,000 km long Ithaca Chasma on Tethys in the Saturn system is a prominent example. Charon's Nostromo Chasma is 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.{{cite web|last1=Dunn|first1=Marcia|title='Blowing my mind': Peaks on Pluto, canyons on Charon|url=http://phys.org/news/2015-07-mind-peaks-pluto-canyons-charon.html|publisher=PhysOrg|date=16 July 2015}} A recent study suggests a complex system of ancient lunar rift valleys, including Vallis Rheita and Vallis Alpes.{{cite journal|last1=Andrews-Hanna|first1=Jeffrey C.|last2=Besserer|first2=Jonathan|last3=Head III|first3=James W.|last4=Howett|first4=Carly J. A.|last5=Kiefer|first5=Walter S.|last6=Lucey|first6=Paul J.|last7=McGovern|first7=Patrick J.|last8=Melosh|first8=H. Jay|last9=Neumann|first9=Gregory A.|last10=Phillips|first10=Roger J.|last11=Schenk|first11=Paul M.|last12=Smith|first12=David E.|last13=Solomon|first13=Sean C.|last14=Zuber|first14=Maria T.|title=Structure and evolution of the lunar Procellarum region as revealed by GRAIL gravity data|journal=Nature|volume=514|issue=7520|year=2014|pages=68–71|issn=0028-0836|doi=10.1038/nature13697|pmid=25279919|bibcode=2014Natur.514...68A|s2cid=4452730}} The Uranus system also has prominent examples, with large 'chasma' believed to be giant rift valley systems, most notably the 1492 km long Messina Chasma on Titania, 622 km Kachina Chasmata on Ariel, Verona Rupes on Miranda,

{{cite web

|last=Chaikin

|first=Andrew

|date=2001-10-16

|title=Birth of Uranus' provocative moon still puzzles scientists

|work=space.com

|publisher=Imaginova Corp

|pages=1

|access-date=2007-07-23

|url=http://www.space.com/scienceastronomy/solarsystem/miranda_creation_011016-1.html

|url-status=dead

|archive-url=https://web.archive.org/web/20080709020909/http://www.space.com/scienceastronomy/solarsystem/miranda_creation_011016-1.html

|archive-date=July 9, 2008

}}

and Mommur Chasma on Oberon.

{{cite journal| doi = 10.1126/science.233.4759.43| last1 = Smith| first1 = B. A.| last2 = Soderblom| first2 = L. A.| last3 = Beebe| first3 = A.| last4 = Bliss| first4 = D.| last5 = Boyce| first5 = J. M.| last6 = Brahic| first6 = A.| last7 = Briggs| first7 = G. A.| last8 = Brown| first8 = R. H.| last9 = Collins| first9 = S. A.| date = 4 July 1986| title = Voyager 2 in the Uranian System: Imaging Science Results| journal = Science| volume = 233| issue = 4759| pages = 43–64| pmid = 17812889| bibcode = 1986Sci...233...43S| s2cid = 5895824| ref = {{sfnRef|Smith Soderblom et al.|1986}}| url = https://zenodo.org/record/1230972}}

• {{cite journal | last1 = Bonatti | first1 = E | year = 1985 | title = Punctiform initiation of seafloor spreading in the Red Sea during transition from a continental to an oceanic rift | journal = Nature | volume = 316 | issue = 6023| pages = 33–37 | doi=10.1038/316033a0| bibcode = 1985Natur.316...33B| s2cid = 4355790 }}

• {{cite journal | last1 = Mart | first1 = Y. | last2 = Dauteuil | first2 = O. | year = 2000 | title = Analogue experiments of propagation of oblique rifts | journal = Tectonophysics | volume = 316 | issue = 1–2| pages = 121–132 | doi=10.1016/s0040-1951(99)00231-0| bibcode = 2000Tectp.316..121M }}

{{Structural geology}}

Category:Tectonic landforms