In the referential image above, two avalanches were captured in action by the Mars Reconnaissance Orbiter. The larger of these two (B) is around 180 meters wide, extends about 190 meters and the cliff heights are around 700 meters tall. The White material on the top that appears as snow is actually carbon dioxide frost which is currently receding as the Martian Spring moves closer. It is this very process which may be the cause of such falls as the carbon dioxide frost expands and contracts with the changing seasonal temperatures. Despite these seasonal changes, most areas of the Martian surface have likely been unchanged for millions of years, so it is quite rare to capture such cataclysmic activities in a single image from orbit.
IMAGE NOTE: The images above are listed as RGB, but the accompanying text describes all the images as “false color”. Guess – maybe it means the colors are natural but exaggerated? See below for 1440x900 landscape wallpaper.