Formation of long-distance water ice avalanches on Mars

摘要

At the high northern latitudes of Mars, there are two impact craters (70.3 degrees N 266.45 degrees E and 67.25 degrees N 249.45 degrees E) with lobate moraine-like ridges (LMLR) on the inner slopes. In addition to these craters, a nearby plain (74 degrees N 95 degrees E) also displays remnants of water ice layered deposits with similar series of lobate ridges. The formation of these ridges has been hypothesized to be caused by either viscoplastic flow of CO2 ice deposits or a catastrophic down-slope movement of an H2O ice massif, which produced long-distance avalanches or fast-running glacier surges. In past climatic epochs, the formation of water ice massifs on high latitudes was possible under low (20 degrees) planet obliquity. Destabilization of water ice massifs on the craters' steep inner slopes could lead to down-slope movement, followed by the destruction of the massifs and the production of long-distance water ice avalanches or surges. In this work, we focus on the avalanche formation hypothesis. The down-slope movement of a water ice massif has several possible causes, with the main one being excessive accumulation of water ice on slopes, which then reaches a critical unstable condition. Modeling of long-distance avalanche processes in Martian environments was carried out with Rapid Mass Movement Simulation (RAMMS:AVALANCHE) software, using the graphanalytical method of estimating avalanche velocity and maximum distance. As a result of the modeling, the volume of down-slope movement was defined, confirming the that LMLR were formed by the catastrophic downslope movement of H2O ice masses in the form of long-distance avalanches.