Nirgal Vallis Tributaries
Nirgal Vallis Tributaries
ESP_033814_1525  Science Theme: Fluvial Processes
Nirgal Vallis is one of the largest and longest valley networks on Mars (approximately 400 kilometers in length). Oriented roughly east-west and located north of the Argyre impact basin, its western region contains numerous short, theater-headed tributaries that merge into a long, sinuous, and deeply entrenched main valley that extends eastward to Uzboi Vallis.

The area in this image features the western-most tributaries. Valley heads are steep and abrupt with blunt terminations. Although Nirgall Vallis formed long ago, likely by flowing water, abundant wind-blown sediments transformed into the dune fields that now line the valley floors. However, the distinctive valley pattern shape with steep walls and flat floors led many to propose that ground water flowed out to the surface along the valley heads and walls of the numerous tributaries. This process, known as sapping, begins with ground water flowing along subsurface fractures or permeable layers and carrying out sediments with it as it emerges at the cliff face.

Eventually, the loss of support from beneath undermines the cliff face, causing it to slump into the valley. With continued sapping, tributaries grow progressively in a headward direction. This kind of erosion is common in the Colorado Plateau of the Southwestern United States and helped form the distinctive shape of the Grand Canyon. Wrinkle ridges intersecting several tributaries may have provided additional avenues for ground water flow into the valley system.

Written by: Ginny Gulick  (20 November 2013)

This is a stereo pair with ESP_034091_1525.
Acquisition date
13 October 2013

Local Mars time

Latitude (centered)

Longitude (East)

Spacecraft altitude
255.8 km (159.0 miles)

Original image scale range
54.2 cm/pixel (with 2 x 2 binning) so objects ~163 cm across are resolved

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50 cm/pixel and North is up

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Solar incidence angle
57°, with the Sun about 33° above the horizon

Solar longitude
35.0°, Northern Spring

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North azimuth:  96°
Sub-solar azimuth:  48.2°
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NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, Calif., manages the Mars Reconnaissance Orbiter for NASA’s Science Mission Directorate, Washington. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona.