Abstract
<jats:p>Mass wasting, the downslope movement of soil and rock, is a common geomorphic process on terrestrial bodies. Many extraterrestrial mass wasting landforms are associated with ice and frost, and their deposit slopes are frequently too gentle for material to move without some form of fluidisation. Ice sublimation is one mechanism proposed for driving mass wasting below the angle of repose. However, the roles of ambient pressure and gravity on the fluidisation, dynamics, and mobility and morphology of sublimation-driven flows remain poorly understood. We present experiments on CO2-sublimation-driven mass flows under extraterrestrial pressure environments in a low-pressure chamber, accounting for effects of simulated reduced gravity with low-density sediments. Results demonstrate that lower ambient pressures increase the volume flux of sublimating ice, enhancing fluidisation, flow mobility and runout. The gas velocity required for fluidisation is lower in flows of low-density sediments compared to flows of higher-density sediments, because it requires a lower gas velocity to lift low-density, or low-gravity, particles. In our experiments, flows transition into a bubbling fluidisation regime at pressures ≤40 mbar, exhibiting gas bubbles, surges, and outbursts. When atmospheric pressures are further reduced (3 mbar), the further enhanced gas velocity causes gas bubbles to merge into slugs which lift up particles, increasing flow depth and inducing multiple flow surges, particularly in flows of low-density particles. These multi-surge flows may form deposits with multiple lobes. This work suggests that sublimation can be an effective driver for mass wasting on planets, asteroids and dwarf planets with low ambient pressures and gravity. Plain Language Summary Mass movements, or the downhill movement of loose material, are common on planetary surfaces across the Solar System. Many of these landforms occur in areas with ice or frost and on slopes too gentle for dry material to move unaided. Ice sublimation, where ice transitions directly into gas, might help the material flow more easily by reducing the friction between the sediment particles. Yet, how gravity and atmospheric pressure affect this process remains unclear. We conducted experiments using sublimating CO2 ice to fluidise granular flows in a low-pressure chamber, using low-density sediments to mimic reduced gravity. Results show that at lower atmospheric pressures, the flows become more fluid and travel further, especially with low-density materials compared to higher-density ones. This is because there is less force needed to lift the low-density, or low-gravity, particles. Moreover, flows behave differently with signs of gas bubbles and eruptions at 40 mbar, indicating the bubbling regime. At even lower pressures (3 mbar), the gas bubbles merge into larger ones, lifting the particles, characterising what is known as the slugging regime. Our work suggests that sublimation plays an important role in mass movements on planets, asteroids and dwarf planets with low ambient pressures and gravity.</jats:p>