The HiRISE team from the Mars Reconnaissance Orbiter has captured a few avalanches on Mars, some actually while in progress. But this latest landslide is a little different. Above is a dust avalanche that created a streak on the slopes of Olympus Mons, the solar system’s largest volcano. While scientists believe some of the previous avalanches seen on Mars occur due to the expansion and contraction of ice from seasonal temperature differences, this one was caused by an impact event. This HiRISE image was taken on March 31, 2010 and reveals a small, pristine impact crater (blue arrow). “It shows a fuzzy source area, which resembles the airblast patterns seen at many other recent impact sites,” said Alfred McEwen, Principal Investigator for HiRISE. “The crater is only about 4.5 meters across, meaning the bolide was only about a half a meter wide, so it didn’t take much to trigger this landslide.”
MRO’s Context Camera (CTX) took an image of this area on Nov. 18, 2007 (left) and the adjacent image on Feb. 14, 2010, which shows a large new avalanche. HiRISE then took the follow-up image in March. McEwen said slope streaks , or dust avalanches are common on Mars, but this one is unusually wide and began from an unusual extended or “fuzzy” source area. This made HiRISE team conclude that an impact event occurred sometime between the dates of the CTX images and triggered the large dust avalanche.
“Sometimes, these dust avalanches are easily triggered,” McEwen told Universe Today. “We’ve seen them caused just by dust devils. The dark area was created by an atmospheric blast associated with the impact event, with the bolide coming in at about 10 km per second that distributes the dust. You can see that the upper most fresh dust on the surface is bright, so this landslide disturbed either bare substrate or compacted, older dust.
Planetary scientists say that landslides or avalanches on Mars can also be caused by small Mars-quakes or the sublimation of carbon dioxide frost which dislodges rocks.
Sources: HiRISE, phone conversation with Alfred McEwen.