East Mareotis Tholus is a small volcano in Tempe Terra, Mars. This area is on the northeast edge of the Tharsis bulge that was built up by many large and small volcanoes.

One of the many questions we hope to address with HiRISE is the relative roles of the giant shield volcanoes (such as Olympus Mons) and smaller volcanic features (such as East Mareotis Tholus).

The anaglyph covers 4.4 x 6.9 km (2.7 x 4.9 miles) and the topography can be viewed using red-blue glasses. The elongated pit at the summit of the volcano is where the lava issued forth. The large circular hole just to the SW of the vent is an impact crater. The gouges in the ground to the SE of the volcano are tectonic fissures (called graben) that are now filled with sand dunes. The area is covered with large amounts of wind-blown dust, so it is not surprising that lava flows and other smaller volcanic features are not visible.

However, the smooth shape of the volcano, and the lack of lava layers exposed in the impact crater, allow for the possiblity that this volcano is composed largely of ash, rather than lava flows.

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.