Nirgal Vallis is a long river channel bordering the
Coprates quadrangle and
Margaritifer Sinus quadrangle
The Margaritifer Sinus quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The Margaritifer Sinus quadrangle is also referred to as MC-19 (Mars Chart-19) ...
of
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
at 28.4° south latitude and 42° west longitude. It is 610 km long and is named after
Nergal, the
Babylonian god of war and counterpart to the Roman god of war
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
. Nirgal Vallis had a discharge of 4800 cubic meters/second. 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
A (; from the Latin word ') is an amphitheatre-like valley formed by glacial erosion. Alternative names for this landform are corrie (from Scottish Gaelic , meaning a pot or cauldron) and (; ). A cirque may also be a similarly shaped landform ...
on the Earth.
Water from Nirgal Vallis contributed to a great flood that went through the rim of
Holden Crater and helped form a lake in the crater. It's estimated that Nirgal Vallis had a discharge of 4800 cubic meters/second. 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 m deep.
[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.] Water with a depth of at least 50 m entered Holden at a rate that 5-10 times the discharge of the Mississippi River.
[Grant, J., T. Parker. 2002. Drainage evolution of the Margaritifer Sinus region, Mars. J. Geophysic. Res. 107, doi:10.1029/2001JE001678.] Terraces and the presence of large rocks (tens of meters across) support these high discharge rates.
[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]
Margaritifer Sinus.png, Map showing locations Nirgal Vallis and other nearby valleys
File:Nirgal Vallis 079A24.jpg, Viking Orbiter 1 image showing the entire valley
Nirgal Vallis and sapping
Nirgal Valles is one of the longest valley networks on
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...
. 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
sapping
Sapping is a term used in siege operations to describe the digging of a covered trench (a "sap") to approach a besieged place without danger from the enemy's fire. (verb) The purpose of the sap is usually to advance a besieging army's positio ...
.
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
''2001 Mars Odyssey'' is a robotic spacecraft orbiting the planet Mars. The project was developed by NASA, and contracted out to Lockheed Martin, with an expected cost for the entire mission of US$297 million. Its mission is to use spectro ...
's
THEMIS
In Greek mythology and religion, Themis (; grc, Θέμις, Themis, justice, law, custom) is one of the twelve Titan children of Gaia and Uranus, and the second wife of Zeus. She is the goddess and personification of justice, divine order, fai ...
.
Image:Nirgal Vallis.jpg, Nirgal Vallis, as seen by THEMIS.
Image:Nirgal Vallis Close-up.JPG, Nirgal Vallis Close-up, as seen by THEMIS.
See also
*
*
*
*
*
*
*
References
External links
*
{{Authority control
Valleys and canyons on Mars
Coprates quadrangle
Margaritifer Sinus quadrangle