In total, four avalanches were imaged. The particulate in the avalanche is believed to be fine-grained ice and dust, even large chunks of rock. The picture at left shows clouds of dispersing, fine material in the air, falling to the ground.
Credit: NASA/JPL/University of Arizona
Of all the orbiting equipment around Mars, most pictures are of the ancient geological past, from millions of years ago. This is a rare moment when Martian geological activity is caught as it happens. The only other significant active events that can be seen as they happen are the Martian dust devils, mini-tornado like winds on the Martian surface.
The escarpment imaged by HiRISE is over 2,300 feet high (700m) and has an angle of slope of over 60 degrees. The top piece of the scarp, at left in the image, is covered in bright white carbon dioxide frost. This frost retreats as the Martian spring approaches. By comparing this picture with prior pictures taken of the area before the avalanche, an understanding of the processes and rates of erosion can be gained. The interaction of carbon dioxide ice and gas as well as water can be studied to understand how the polar landscape has evolved and its implications for the geological history for the rest of the planet.
The HiRISE is onboard NASA’s Mars Reconnaissance Orbiter. The images were captured on February 19.
The HiRISE science team has a very interesting blog, though at times a bit technical, but not too much so, commenting on these findings and others at http://hirise.lpl.arizona.edu/HiBlog/ .