Changes in Soil Cohesion Due to Water Vapor Exchange: A Proposed Dry-Flow Trigger Mechanism for Recurring Slope Lineae on Mars

Recurring slope lineae (RSL) are seasonal flows on steep slopes on Mars. Their formation mechanism is unknown, but dry granular flows are a likely explanation. Any proposed trigger for these flows must be consistent with the observed temperature dependence of RSL: more active in warmer months or when sun-facing. Here, we use atmospheric modeling and laboratory experiments to explore a potential mechanism that involves both wet and dry processes at Hale Crater, a known RSL location. We propose that dry flows are triggered by changes in soil cohesion due to the loss of water. When surface temperature and humidity were experimentally simulated, salts likely found in the soil only completely dehydrated during the active season for RSL. We propose that the loss of water from soil in warmer months (or when illuminated) lowers soil cohesion and maximum stability angle. Slope failure may occur, exposing darker underlying material and creating RSL.