Mud flow levitation on Mars: Insights from laboratory simulations

Sediment mobilisation occurring at depth and ultimately manifesting at the surface, is a process which may have operated on Mars. However, the propagation behaviour of this mixture of water and sediments (hereafter simply referred to as mud) over the martian surface, remains uncertain. Although most of the martian surface is below freezing today, locally warmer surface temperatures do occur, and our current knowledge suggests that similar conditions prevailed in the recent past. Here, we present the results of experiments performed inside a low pressure chamber to investigate mud propagation over a warm (similar to 295 K) unconsolidated sand surface under martian atmospheric pressure conditions (similar to 7 mbar). Results show that the mud boils while flowing over the warm surface. The gas released during this process can displace the underlying sand particles and hence erode part of the substrate. This "entrenched" flow can act as a platform for further mud propagation over the surface. The escaping gas causes intermittent levitation of the mud resulting in enhanced flow rates. The mud flow morphologies produced by these phenomena differ from those produced when mud flows over a frozen martian surface as well as from their terrestrial counterparts. The intense boiling removes the latent heat both from the mud and the subsurface, meaning that the mud flow would eventually start to freeze and hence changing again the way it propagates. The diverse morphology expressed by our experimental mudflows implies that caution should be exercised when interpreting flow features on the surface of Mars and other celestial bodies. (C) 2020 Elsevier B.V. All rights reserved.