Scenarios for the formation of Chasma Boreale, Mars

Abstract

The martian polar caps feature large chasmata and smaller trough systems which have no counterpart in terrestrial ice sheets. Chasma Boreale cuts about 500 km into the western part of the north-polar cap, is up to 100 km wide and up to 2 km deep. One possible formation mechanism is by a temporary heat source under the ice due to tectono-thermal or volcanic activity, which melts the ice from below. It is demonstrated by model simulations that this process is feasible, a moderately increased heat flux of 0.5–1 W m −2, sustained over at least tens of thousands of years, producing a topographic depression which resembles the real chasma. Associated meltwater discharge rates are small ( < 1 km 3 a −1 ), but can exceed 10 km 3 a −1 if a stronger heat flux of 10 W m −2 is assumed. Local ice-flow velocities during the process of chasma formation can exceed 1 m a −1 at the head and scarps of the chasma. However, if the thermal anomaly shuts down, glacial flow quickly decreases, so that the chasma can stay open for an indefinite amount of time without an ongoing, sustaining process under the climate conditions of the most recent millions of years.