Perennial Frost Mounds in Gusev Crater (Mars)

Frost mound is a generic term for all mounds involving: volumetric expansion of water when changing to ice; hydrostatic and/or hydraulic pressure of groundwater; and forces of crystallization during freezing. The variety of structures (perennial and seasonal) includes pingos, hydrolaccoliths, palsas, hummocks, frost and icing blisters, and icing mounds. Round to elongated mounds are observed in Gusev crater (Aeolis subquadrangle of Mars). These structures can be compared with terrestrial frost mounds, and show morphologic similarities with pingos. They are located north to a 20-km impact crater, 50 km downstream of the Ma'adim Vallis mouth. This region is one of the lowest points in Gusev crater, and is characterized by upheavals of the floor extending over a narrow band of 45 kmx 40 km that joins with the northern part of the Gusev rim. The mounds are concentrated in a large cluster, with a density of 1 per 7.6 sq km. They display different stages of evolution, from fresh looking structures that comprise the majority of the cluster to scars of partially collapsed features.