An avalanche is captured in progress by the the HiRISE camera aboard the Mars Reconnaissance Orbiter.

Yes, this really is an avalanche in progress and not an artist concept. The HiRISE has captured avalanches before at least since 2008. Thanks to the great resolution possible with HiRISE, the imaging team can zoom in on these areas quite nicely.

The information given with the images pegs the reddish cloud at 600 feet (200 meters) across. You can get all of the details AND a huge assortment of images sizes to suit your desktop at the HiIRISE page for this image. Natually you can get the full res versions too.