Caught in Action: Avalanches on North Polar Scarps (PSP_007338_2640) Credit: NASA/JPL/University of Arizona

From the HiRISE Website

The image to the left shows the context of where these avalanches occurred, with white boxes indicating the locations of the more detailed image portions shown to the right (all images are false color). Material, likely including fine-grained ice and dust and possibly including large blocks, has detached from a towering cliff and cascaded to the gentler slopes below. The occurrence of the avalanches is spectacularly revealed by the accompanying clouds of fine material that continue to settle out of the air. The largest cloud (upper images) traces the path of the debris as it fell down the slope, hit the lower slope, and continues downhill, forming a billowing cloud front. This cloud is about 180 meters (590 feet) across and extends about 190 m (625 ft) from the base of the steep cliff. Shadows to the lower left of each cloud illustrate further that these are three dimensional features hanging in the air in front of the cliff face, and not markings on the ground (sun is from the upper right).

This is pretty impressive. Actually seeing an avalanche as it happens in such detail on another planet!

The white snow like substance on the left at the top of the enourmous 700m sheer cliff is actually carbon dioxide frost. HiRISE claim that either a mars-quake or a meterite triggered the avalanche.

This image is part of 9.9 Terabytes worth of imagery recently returned from Mars