This HiRISE image shows a graben (roughly 2.5 kilometers or 1.6 miles wide) cutting a ridge near Memnonia Sulci, a region of Mars west of the massive Tharsis volcanic province.

A graben is a trough created when two normal faults (faults dipping at an angle, with the overhanging wall sliding downwards) opposite each other lower the block of rock in between them. They are commonly associated with the tectonically-driven extension of a region and are also found in volcanic areas. Graben occur on many planets and moons, including Earth.

In this case, the graben (running roughly east-west, indicating extension in the north-south direction) is cutting a ridge, showing that the graben is more recent. The ridge may also be tectonic in origin, representing a different epoch and different type of tectonic activity.

Relationships like this can be used to determine the sequence of events in the history of the region. The graben walls can also expose the local rocks at depth; in this case there is no obvious indication of layering.
Written by: Colin Dundas

All of the images produced by HiRISE and accessible on this site are within the public domain: there are no restrictions on their usage by anyone in the public, including news or science organizations. We do ask for a credit line where possible: Image: NASA/JPL/University of Arizona

For information about NASA and agency programs on the Web, visit: http://www.nasa.gov. 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. Lockheed Martin Space Systems is the prime contractor for the project and built the spacecraft. The HiRISE camera was built by Ball Aerospace and Technology Corporation and is operated by the University of Arizona. The image data were processed using the U.S. Geological Survey’s ISIS3 software.