GULLIES AND SLOPE STREAKS ON MARS: INSIGHTS INTO THEIR ORIGINS FROM FIELD STUDIES IN THE ANTARCTIC DRY VALLEYS

The Antarctic Dry Valleys (ADV) represent a hyperarid, extremely cold polar desert environment that is an excellent terrestrial analogs for Mars. We investigated analogs to martian gullies and slope streaks in the South Fork of the Upper Wright Valley during the 2006-2007 austral summer field season. For gullies, we asked the questions: Do ADV gullies have the same morphology as those on Mars? What is the nature and origin of the fluids carving the gullies (e.g., groundwater, saline springs, snowmelt)? Do the ADV gullies provide insight into the formation of recent, and perhaps current gullies on Mars? We found that ADV gullies contained the major feature of Mars gullies (alcove, channel and fan), that they formed due to top-down melting of glacial ice, perennial snowpack, and annual wind-blown snow trapped in the topographic lows, such as channels. Flow took place during daily melting of snow patches entrapped in the trough when atmospheric temperatures exceeded the melting point. Snowmelt flowed down the channels, soaked into the channel floor and margins producing a hyporheic zone, and moved along the top of the ice table at 20-30 cm depth. Daily melting produced surface flow that moved sediment within the channels to produce distal fans. These characteristics suggest that gullies on Mars could be related to melting of surface snow and ice deposits, in the absence of deep groundwater sources and springs. Once formed, lifetimes of gullies can be extended by trapping and melting of wind-blown snow in the channel floor. For slope streaks, we examined orbital images and found features similar in appearance and scale to those seen on Mars. We asked the questions: Is there evidence for dust avalanches, dry debris flows, wet debris flows? Does water play a role? We found no evidence for dust avalanches or debris flows. Instead, the low albedo of the ADV slope streaks is due to moist soil. ADV slope streaks form from snowpack meltwater that soaks into the ground, becomes saline, travels downslope along the top of the ice table, and wicks to the surface above the subsurface flow. On Mars, melting of surface and shallow subsurface snow and ice and flow of saline solutions may explain slope streaks. ADV terrestrial analogs of martian gullies and slope streaks provide important models for formational processes.