Editing Valles Marineris (section)

== Formation ==

The most agreed upon theory today is that Valles Marineris was formed by [[rift]] [[Fault (geology)|fault]]s, later enlarged by erosion and collapsing of the rift walls, similar to how the [[East African Rift]] was formed. The formation of Valles Marineris is thought to be closely tied with the formation of the [[Tharsis]] Bulge. The Tharsis Bulge was formed from the [[Noachian epoch|Noachian]] to Late [[Hesperian epoch|Hesperian]] period of Mars, in three stages.

[[Image:Valles Marineris & outflow channels MOLA zoom 64.jpg|thumb|right|400px|Topographic map of Valles Marineris with its associated [[outflow channel]]s and their surroundings, based on MOLA altimetry data]]

The first stage consisted of a combination of volcanism and [[isostatic uplift]]; soon, however, the [[volcano|volcanism]] loaded the crust to a point at which the crust could no longer support the added weight of Tharsis, leading to widespread [[graben]] formation in the elevated regions of Tharsis. The second stage consisted of more volcanism and a loss of [[isostasy|isostatic equilibrium]]; the source regions of the volcanism no longer resided underneath Tharsis, creating a very large load. Finally, the crust failed to hold up Tharsis and radial fractures formed, including at Valles Marineris. The third stage mainly consisted of more volcanism and asteroid impacts. The crust, having already reached its failure point, just stayed in place and younger volcanoes formed. Tharsis volcanism involved very low viscosity [[magma]], forming shield volcanoes similar to those of the [[Hawaii|Hawaiian Island chain]], but, because there is minor or no current active plate tectonics on Mars, the hotspot activity led to very long histories of repeated volcanic eruptions at the same spots, creating some of the largest volcanoes in the solar system, including the biggest, [[Olympus Mons]].<ref name=Cattermole>{{cite book |last= Cattermole|first= Peter John |title=Mars: the mystery unfolds |publisher=[[Oxford University Press]] |date=2001 |page=[https://archive.org/details/marsmysteryunfol00catt/page/103 103-104] |isbn=0-19-521726-8 |url-access=registration |url= https://archive.org/details/marsmysteryunfol00catt }}</ref>

[[Landslide]]s have left numerous deposits on the floor of Valles Marineris and contributed to widening it. Possible triggers of [[landslides]] are quakes caused by tectonic activity or impact events. Both types of events release seismic waves that accelerate the ground at and below the surface. Mars is much less tectonically active than Earth, and [[marsquake]]s are unlikely to have provided seismic waves of the required magnitude.<ref name = "Akers_2012">{{cite conference
 | first = C. | last = Akers | author2 = Schedl, A. D. | author3 = Mundy, L.
 | title = What Caused the Landslides in Valles Marineris, Mars?
 | book-title = 43rd Lunar and Planetary Science Conference
 | page = 1932 | date = 2012 | url = http://www.lpi.usra.edu/meetings/lpsc2012/pdf/1932.pdf
 | access-date = 2013-02-11}}</ref> Most sizable craters on Mars date to the [[Late Heavy Bombardment]], 4.1 to 3.8 billion years ago (the Noachian period), and are older than the landslide deposits in Valles Marineris. However, three craters (including the crater [[Oudemans (crater)|Oudemans]]) have been identified, on the basis of their proximity and later dates, as ones whose formation may have caused some of the landslides.<ref name = "Akers_2012"/>
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[[File:016vallesmarineris.jpg|thumb|800px|center|Valles Marineris in mosaic of [[Thermal Emission Imaging System|THEMIS]] infrared images from  ''[[2001 Mars Odyssey]]'']]

===Former formation hypotheses===
Hypotheses about the formation of Valles Marineris have changed over the years.<ref>Cabrol, N. and E. Grin (eds.).  2010.  Lakes on Mars.  Elsevier. NY</ref>  Ideas in the 1970s were erosion by [[water]] or [[thermokarst]] activity. Thermokarst activity may have contributed, but erosion by water is a problematic mechanism because liquid water cannot exist in most current Martian surface conditions, which typically experience about 1% of Earth's atmospheric pressure and a temperature range of {{convert|148|K|°C °F|abbr=on}} to {{convert|310|K|°C °F|abbr=on}}. Many scientists however agree that [[Water on Mars|liquid water]] flowed on the Martian surface in the past, when atmospheric conditions were different. Valles Marineris may have been enlarged by flowing water at that time. Another hypothesis by McCauley in 1972 was that the canyons formed by withdrawal of subsurface magma. Around 1989, a formation hypothesis by tensional fracturing was proposed.{{by whom|date=November 2024}}