Nirgal Vallis
Encyclopedia
Nirgal Vallis is a long river channel in the Coprates quadrangle
and the Phoenicis Lacus quadrangle
of Mars at 28.4° south latitude and 42° west longitude. It is 496 km long and is named after the word for "Mars" in Babylonian. 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.
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Coprates quadrangle
The Coprates quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey Astrogeology Research Program...
and the Phoenicis Lacus quadrangle
Phoenicis Lacus quadrangle
The Phoenicis Lacus quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey Astrogeology Research Program. The Phoenicis Lacus quadrangle is also referred to as MC-17 ....
of Mars at 28.4° south latitude and 42° west longitude. It is 496 km long and is named after the word for "Mars" in Babylonian. 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
Uzboi Vallis
Uzboi Vallis is a valley on Mars. It is named after a dry river valley in USSR, now in Turkmenistan.The valley begins on the northern rim of the Argyre basin, and cuts through several craters, before ending at Holden crater....
. 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.
Nirgal Vallis and sapping
Nirgal Valles is one of the longest valley networks on Mars. It is so large that it is found on more than one quadrangle. 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. 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 THEMISThemis
Themis is an ancient Greek Titaness. She is described as "of good counsel", and is the embodiment of divine order, law, and custom. Themis means "divine law" rather than human ordinance, literally "that which is put in place", from the verb τίθημι, títhēmi, "to put"...
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