Each Martian spring, the northern polar cap undergoes warming from the sun. The ices sublimate into the thin atmosphere and leave behind dust and rocks. This image shows the edge of the ice cap at the left and a dust cloud from an avalanche of this dust and rock debris at the right. The avalanche had just occurred when the image was recorded.
This next image shows two avalanches caught in the act in the same 2008 image strip. A narrow portion of an image strip is at the far left. Two locations are selected and enlarged revealing the two avalanches. Both are enlarged one final time.
Join me below for some additional details about these events captured on Mars.
The images of avalanches of ice and rock in the northern polar regions of Mars have been captured by NASA Mars Reconnaissance Orbiter’s (MRO) High Resolution Imaging Science Experiment (HiRISE). MRO launched in 2005. The mission timeline originally called for an end in 2009. But, the mission is now designated at ongoing.
The rare events are of value to Mars scientists analysing the effects of seasons on the landscape and provide information on the geological activity of the planet. These avalanches occurred along a steep scarp, or cliff, around the North Polar Region. Surface ice can be found in large quantities. The HiRISE instrument was being used to assess seasonal changes around the North Pole when four areas of activity were seen along the scarp. This scarp is a high cliff over 700 m tall and slopes at over 60 degrees. It is the pinkish brown region extending from the white ices at the left to the center part of the image. A mixture of ice, rock and dust slid down the slope and ejected a plume of dust at the bottom of the cliff. The dust cloud is about 180 meters across and reaches about 190 meters beyond the base of the cliff. The dust clouds are large 3D structures reaching into the Martian atmosphere. Their shadows can be seen to their lower left.
The Martian landscape does not change very much. Unlike the Earth, it doesn't have a thick atmosphere eroding the surface. It lacks the water we have on Earth to cause large erosion effects. Mars also has very little geological activity and tectonic movement. No major earthquakes or present volcanic activity has been detected by the craft which are monitoring and studying Mars.
So why are there avalanches? HiRISE scientists have some ideas:
• Disappearance of carbon dioxide frost dislodges rocks
• Expansion and contraction of ice
• Small Mars-quakes
• Nearby meteorite impact
• Vibrations from other avalanches
Seasonal change seems the most likely trigger. As the North Polar Region warms, solid carbon dioxide, “dry ice”, sublimes. It goes from the solid frozen state to the vapor state without melting. This loosens the larger rocks at the upper edge of the cliff. Thermal expansion and contraction of water ice can do the same thing and loosen rocks.
Each of the recent spring seasons on Mars, the spacecraft has captured avalanches in action. This first image is from November 2011. The image below it is from 2010.
The image of the November 2011 avalanche came from the PDS image release of February 2012. This release covers MRO orbits 25,000 to 25,399. One of my favorite parts of this image release is the anaglyph set. These are images viewed with red and blue colored filters over your eyes to give the effect of depth. (Red over left eye. Blue over right eye.)
The PDS is the curator for images of planetary missions at NASA.
The Imaging Node of the Planetary Data System is the curator of NASA's primary digital image collections from past, present and future planetary missions. The node provides to the NASA planetary science community the digital image archives, necessary ancillary data sets, software tools, and technical expertise necessary to fully utilize the vast collection of digital planetary imagery.