20-EPN2-023: FLUME-ET: Fluidisation of mass flows by metastable volatiles on extra-terrestrial bodies
Visit by Lonneke Roelofs and Tjalling de Haas, Utrecht University (Netherlands) to TA2.4 Planetary Environment Facilities (PEF), AU (Denmark)
Dates of visit: 03-28 October 2022
Report summary: Martian gullies are alcove-channel-fan systems which have been hypothesised to be formed by the action of liquid water and brines, the effects of sublimating CO2 ice or a combination of these processes. Recent activity and new flow deposits in these systems have shifted the leading hypothesis from water-based flows to CO2-driven flows. This shift in thinking is supported by the low availability of atmospheric water under present Martian conditions and the observation that gully activity occurs at times when CO2 ice is present.
We recently performed novel experiments in the Mars chamber at the Open University in the UK that have shown that this hypothesis holds; sediment can be mobilised and fluidised by sublimating CO2 ice under Martian atmospheric pressure. However, if these experiments work on a larger scale and if these granular-gas flows are able to erode the underlying surface and can explain the formation of Martian gully systems over the long term remained unknown. Therefore, we conducted an additional series of experiments in a larger flume that test the capacity of CO2-driven granular flows under Martian atmospheric conditions to erode sediment.
These experiments were conducted in a 4 m long flume in the Aarhus Mars Simulation Wind Tunnel. Our experiments show that CO2-driven granular flows can erode loose sediment under a range of different slopes and CO2-ice fractions. The results also show that incorporation of warmer sediment increases fluidisation of the mixture, reflected by an increase in gas pore pressure in the flow. These results thus prove that morphological evolution in the gully systems on Mars can be explained by CO2-driven granular flows.