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Keywords:

  • Mars;
  • avalanche;
  • geomorphology;
  • sand dunes;
  • seasonal processes

In the sand dunes in the north polar sand sea of Mars, sand avalanches that appear as wedge-shaped alcoves can be seen above fan-shaped deposits. The avalanches, which are typically several meters across, are currently actively forming, with new alcoves showing up in recent images taken in consecutive Mars years. Some scientists have proposed that these sand avalanches occur when frozen carbon dioxide (CO2) sublimates, triggering the downslope flow (mass wasting) of sand grains and rock that had been lying on top of the CO2 frost. However, Horgan and Bell now suggest that these alcoves may actually have been formed by wind-driven movement of sand, not by CO2 sublimation.