This image shows a terraced fan (center left) located adjacent to a short valley. Terraced fans are rare deposits on Mars: they have only been seen in a few dozen locations.

On Earth, terraced fans are found in alluvial environments and in deltas. When water flowing down steep slopes, such as mountains or hills, encounters a flatter surface, the sediments carried by the water are deposited along the shallow slopes to form alluvial fans. Deltas can also produce terraced fans when water from rivers and streams meets oceans or lakes; a delta deposit results at the contact between the confined, fast-moving water (river/stream) and the open body of water (ocean/lake).

The fact that this Martian terraced fan is found adjacent to a valley supports the hypothesis that water was the mechanism that transported and deposited the material that now forms the fan. It is unclear, however, if this fan formed in an alluvial or deltaic environment, or by some other process.
Written by: Cathy

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.