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Olympus Mons, the largest volcano in the Solar System is a shield volcano built up by lava flow after lava flow. Like the larger shield volcanoes Mauna Loa and Etna on Earth, many of these lava flows carried the liquid lava in open channels.
In some places these channels break down and the lava spills out, forming a broad fan. In the center of this HiRISE image (PSP_003331_2005), you can see a lava channel that has fed many overflows to both sides. The lava was traveling from the southeast toward the north and northwest.
When viewed at full-resolution, the HiRISE image shows a very irregular surface. This is caused by a thick layer of very small particles that are being moved around by the wind. The linear features that could be mistaken for dunes in lower resolution images turn out to look more like wind-eroded ridges, called "yardangs" by geologists.
Acquisition date: 4 April 2007
Local Mars time: 3:29 PM
Degrees latitude (centered): 20.4°
Degrees longitude (East): 224.7°
Range to target site: 270.5 km (169.1 miles)
Original image scale range: 54.1 cm/pixel (with 2 x 2 binning) so objects ~162 cm across are resolved
Map-projected scale: 50 cm/pixel and north is up
Emission angle: 6.6°
Phase angle: 68.8°
Solar incidence angle: 63°, with the Sun about 27° above the horizon
Solar longitude: 218.0°, Northern Autumn
NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft. The High Resolution Imaging Science Experiment is operated by the University of Arizona, Tucson, and the instrument was built by Ball Aerospace and Technology Corp., Boulder, Colo.