A cloud of dust rises in the wake of a Martian avalanche in this images from the Mars Reconnaissance Orbiter. Image: NASA/JPL-Caltech/University of Arizona

Cameras orbiting Mars as part of NASA's High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter have captured four avalanches in action.

Material, likely including fine-grained ice and dust, has detached from a 700-metre high cliff and cascaded to gentler slopes below. The clouds of fine material that have risen into the air have been captured by the HiRISE cameras. In just one HiRISE image, at least four avalanches in the northern polar regions, where it is now spring, have been observed. In the main image the path of the falling material can be seen, possibly originating from just below the carbon dioxide frost encrusted surface and tumbling the 700 metres to the shallower slopes below. The billowing debris cloud is around 180 metres across and extends out 190 metres from the base of the cliff. Shadows towards the lower left of each cloud show that these features are three-dimensional and are hanging above the ground and in front of the cliff face, and are not markings on the ground.

The trigger mechanism for the avalanches is not confirmed, but it is likely that the disappearance of the carbon dioxide frost and the expansion and contraction of ice in response to temperature changes may be the cause. Other possibilities include a nearby Mars-quake or meteorite impact, or perhaps vibrations caused by a different debris fall in the area.

Another view from the Mars Reconnaissance Orbiter of a Martian Avalanche. Image: NASA/JPL-Caltech/University of Arizona

Most of the images taken by Mars orbiting cameras record few changes to the surface, revealing landscapes millions of years old. With the exception of a few seasonal changes and the occasional dust devil, it is extremely unlikely that such a dynamic event as an avalanche is captured by still photography. Events like these are useful in trying to unlock the secrets of active processes that occur on other planets.