An Overflow Channel from Athabasca Vallis
NASA/JPL/UArizona
An Overflow Channel from Athabasca Vallis
ESP_029864_1880  Science Theme: Fluvial Processes
A MOC image over this area showed a channel spilling out of the larger Athabasca Vallis (trending east-west at the north end of this image) and flowing to the south.

The channel splits into multiple branches, creating about ten streamlined mesas. Vague bumps were visible on the channel floor in the MOC image--perhaps large boulders that were deposited by floodwaters?

Our HiRISE image reveals the bumps to be rootless cones that form from lava-water interaction. The entire channel system appears to be coated by lava. There are two leading hypotheses for the origin of these channels: (1) they were carved by water and later coated by lava, or (2) the channels were eroded by the lava itself. If eroded by lava, a source of water was still needed to create the rootless cones, but could have been a much smaller quantity of water than that needed to carve the channels.

(The MOC image can be viewed here, but note that it needs to be flipped left-right to correct the geometry.)



Written by: Alfred McEwen  (9 January 2013)
 
Acquisition date
09 December 2012

Local Mars time
15:26

Latitude (centered)
7.745°

Longitude (East)
154.244°

Spacecraft altitude
274.6 km (170.6 miles)

Original image scale range
55.1 cm/pixel (with 2 x 2 binning) so objects ~165 cm across are resolved

Map projected scale
50 cm/pixel and North is up

Map projection
Equirectangular

Emission angle
5.1°

Phase angle
61.4°

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

Solar longitude
222.1°, Northern Autumn

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North azimuth:  97°
Sub-solar azimuth:  340.2°
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POSTSCRIPT
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.