This long pit on the western flank of the Arsia Mons volcano shows a thick stack of volcanic layers.

This is probably a collapse pit that formed in a similar manner to how such pits form in Hawaii. Underlying large volcano complexes there is a large lava “plumbing system.” While active, these lava tubes can support the weight of overlying solidified lava layers. However, when volcanic activity slows down, and lava drains away, these lava tubes empty and often collapse.

Scientists can study the layers in the pit walls to learn things about the eruptions that built the volcano in this area.
Written by: Ross

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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.