Ascreaus Mons is one of the giant shield volcanoes in the Tharsis region of Mars. Based on earlier lower resolution images, this location seemed to be ideal for examining how different types of lava flows interacted.
The smoother ground on the northwest side of the image is probably a lava flow with a relatively smooth crust much like “pahoehoe” lava flows in Hawaii.
The rugged terrain in the southwestern part of the image is indicative of a highly disrupted crust, possibly like what Hawaiians call an “aa” flow. Instead of confirming these hypotheses, HiRISE shows that the lava flow details are obscured by dust. The dust is carved into a curious network of scallops that are too small to have been seen by previous cameras.
Written by: Laszlo Kestay (16 June 2010)
More info and image formats at http://hirise.lpl.arizona.edu/PSP_002209_1865
Image: NASA/JPL/University of Arizona