MRO's Context camera (CTX) acquired the image at lower left on 18 November 2007 and the adjacent image on 14 February 2010, showing a large new slope streak in the aureole (giant landslide deposits) of Olympus Mons.
Slope streaks (dust avalanches) are common on Mars but this one is unusually wide and it began from an unusual extended/fuzzy source area. HiRISE acquired the follow-up image (right) 31 March 2010, revealing a small, pristine impact crater (blue arrow) in the fuzzy source area, which resembles the airblast patterns seen at many other new (recent year) impact sites. We've conclude that an impact event occurred sometime between the dates of the CTX images and triggered a large dust avalanche.
Photo credit: NASA/JPL/University of Arizona