Avalanches occurring on North Polar Scarps, Mars. 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 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 m (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). Cameras orbiting Mars have taken thousands of images that have enabled scientists to put together pieces of Mars%u2019 geologic history. However, most of them reveal landscapes that haven%u2019t changed much in millions of years. Some images taken at different times of year do show seasonal changes from one image to the next; however, it is extremely rare to catch such a dramatic event in action. (Another, unrelated, active process that has been captured by Mars cameras are dust devils.) Observing currently active processes is often a useful tool in unlocking puzzles of the past for scientists studying the Earth. Working from primarily still images, it is harder for scientists studying Mars to rely on this tool. The HiRISE image of avalanching debris is a very rare opportunity to directly do so. The scarp in this image is on the edge of the dome of layered deposits centered on Mars%u2019 north pole. From top to bottom this impressive cliff is over 700 m (2300 ft) tall and reaches slopes over 60 degrees. The top part of the scarp, to the left of the images, is still covered with bright (white) carbon dioxide frost which is disappearing from the pola