Icy Cliffs at the Martian North Pole

An ice cap about three kilometers (two miles) thick exists at the North Pole of Mars. In some locations its edge is a cliff about 800 meters (half a mile) high that is an almost-vertical wall of ice. With HiRISE images like this one we can look at this cliff face and see it is broken up into jagged blocks. Debris piles at the base of the cliff show where these blocks have fallen out. In the spring, we also sometimes see avalanches pouring down these cliff faces and this image was taken to search for more of them. No avalanches are visible this time., however. For reasons we don't understand, the number of avalanches varies from year to year and this spring appears to be a low-avalanche year. https://photojournal.jpl.nasa.gov/catalog/PIA25949