{{Short description|Vallis on Mars}} {{Infobox feature on celestial object |name = Nirgal Vallis |image = Nirgal Vallis based on day THEMIS.png |caption = Nirgal Vallis based on [[Thermal Emission Imaging System|THEMIS]] day-time image |coordinates = {{coord|28.4|S|42|W|globe:mars_type:landmark|display=inline,title}} |naming = the word for "Mars" in Babylonian }} '''Nirgal Vallis''' is a long river channel bordering the [[Coprates quadrangle]] and [[Margaritifer Sinus quadrangle]] of [[Mars]] at 28.4° south latitude and 42° west longitude. It is 610&nbsp;km long and is named after [[Nergal]], the [[Babylonian language|Babylonian]] god of war and counterpart to the Roman god of war [[Mars (mythology)|Mars]].<ref>{{gpn|4307|Nirgal Vallis}}</ref> Nirgal Vallis had a discharge of 4800 cubic meters/second.<ref>Irwin, J., R. Craddock, R. Howard. 2005. Interior channels in Martian valley networks: Discharge and runoff production. Geology: 33,489-492.</ref> The western half of Nirgal Valles is a branched system, but the eastern half is a tightly sinuous, deeply entrenched valley. Nirgal Valles ends at [[Uzboi Vallis]]. Tributaries are very short and end in steep-walled valley heads, often called "amphitheater-headed valleys." The shape of these valley heads is like [[cirques]] on the Earth.<ref>Baker, V. 1982. The Channels of Mars. University of Texas Press. Austin</ref>

Water from Nirgal Vallis contributed to a great flood that went through the rim of [[Holden (Martian crater)|Holden Crater]] and helped form a lake in the crater. It is estimated that Nirgal Vallis had a discharge of 4800 cubic meters/second.<ref>Irwin, J., R. Craddock, R. Howard. 2005. Interior channels in Martian valley networks: Discharge and runoff production. Geology: 33,489-492.</ref> Water from Nirgal Vallis was inbounded in [[Uzboi Vallis]] because the rim of Holden Crater blocked the flow. At a certain point the stored water broke through the rim of Holden and created a lake 200–250&nbsp;m deep.<ref name="Grant, J. 2010">Grant, J., R. Irwin, S. Wilson. 2010. Aqueous depositional settings in Holden crater, Mars In Cabrol, N. and E. Grin (eds.). 2010. Lakes on Mars. Elsevier. NY.</ref> Water with a depth of at least 50&nbsp;m entered Holden at a rate that 5-10 times the discharge of the Mississippi River.<ref name="Grant, J. 2002">Grant, J., T. Parker. 2002. Drainage evolution of the Margaritifer Sinus region, Mars. J. Geophysic. Res. 107, doi:10.1029/2001JE001678.</ref><ref>Komar, P. 1979. Comparisons of the hydraulics of water flows in Martian outflow channels with flows of similar scale on Earth. Icarus: 37, 156-181.</ref><ref>Grant, J. et al. 2008. HiRISE imaging of impact megabreccia and sub-meter aqueous strata in Holden Crater, Mars. Geology: 36, 195-198.</ref><ref>Irwin, et al. 2005. An intense terminal epoch of widespread fluvial activity on early Mars: 2. Increased runoff and paleolake development. J. Geophysical. Res. 110, E12S14, doi: 10.1029/2005JE002460.</ref> Terraces and the presence of large rocks (tens of meters across) support these high discharge rates.<ref name="Grant, J. 2010"/><ref name="Grant, J. 2002"/><ref>Boothroyd, J. 1983. Fluvial drainage systems in the Ladon Basin area: Margaritifer Sinus area, Mars. Geol. Soc. Am. Abstr. Programs 15, 530</ref><ref>Grant, J. 1987. The geomorphic evolution of Eastern Margaritifer Sinus, Mars. Adv. Planet. Geol. NASA Tech memo. 89871, 1-268.</ref><ref>Parker, T. 1985. Geomorphology and geology of the southwestern Margaritifer Sinus-northern Argyre region of Mars, California State University, M. S. Thesis, Los Angeles, California</ref>

<gallery class="center" widths="190px" heights="180px" > Margaritifer Sinus.png|Map showing locations Nirgal Vallis and other nearby valleys File:Nirgal Vallis 079A24.jpg|[[Viking program|Viking Orbiter 1]] image showing the entire valley </gallery>

== Nirgal Vallis and sapping== Nirgal Valles is one of the longest valley networks on [[Mars]]. It is so large that it is found on two quadrangles. Scientists are not sure about how all the ancient river valleys were formed. There is evidence that instead of rain or snow, the water that formed the valleys originated under ground. One mechanism that has been advanced is [[groundwater sapping|sapping]].<ref name=V07617003>{{cite web|title=Nirgal Vallis (Released 16 September 2003)|url=http://themis.asu.edu/zoom-20030916a|publisher=[[Arizona State University]]}}</ref> In this case, the ground just gives away as water comes out. Sapping is common in some desert areas in America's Southwest. It forms alcoves and stubby tributaries; these features are visible in the pictures below of Nirgal Vallis taken with [[Mars Odyssey]]'s [[THEMIS]].

<gallery class="center" widths="190px" heights="180px" > Image:Nirgal Vallis.jpg|Nirgal Vallis, as seen by THEMIS.

Image:Nirgal Vallis Close-up.JPG|Nirgal Vallis Close-up, as seen by THEMIS. </gallery>

==See also== * {{annotated link|Geology of Mars}} * {{annotated link|Groundwater on Mars}} * {{annotated link|Lakes on Mars}} * {{annotated link|List of quadrangles on Mars}} * {{annotated link|Vallis (planetary geology)|Vallis}} * {{annotated link|Uzboi-Landon-Morava|abbreviation=ULM}} * {{annotated link|Water on Mars}}

== References == {{Reflist}}

==External links== {{Commons category|Nirgal Vallis}} *{{Cite APOD |date=6 October 1997|title=Surveyor At Mars}}

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[[Category:Valleys and canyons on Mars]] [[Category:Coprates quadrangle]] [[Category:Margaritifer Sinus quadrangle]]