Abstract. Wide outflow channels occur both in Siberia and on the planet Mars. In Siberia, thermal erosion results from ground thawing produced by the heat transfer from the flow of water to the frozen ground. We suggest that relatively warm floods on Mars could enlarge outflow channels by a combination of thermal and mechanical erosion along frozen river banks. A onedimensional model is proposed to estimate the thermal erosion efficiency. A first test of this model is a comparison of results with experiments carried out in a cold chamber. A hydraulic channel allows measurements of the thawing line propagation, as well as the thermal erosion rate, in simulated ground ice that is subjected to warm water flow. Various laboratory simulations demonstrate the validity of the mathematical model for the range of laboratory conditions. This model is then applied to a range of possible current and ancient Martian conditions.

In the Arctic, thermal erosion results from ground thawing produced by heat transfer when water is flowing upon the frozen ground. A mathematical model has been proposed to determine the efficiency of the process and the rate of thermal erosion. Considering a constant heat-transfer coefficient, the resulting thermal flux at the groundsurface produces ground thaw, and the unfrozen sediments can be removed by the water flow. A particular case of an ablation model consists of an immediate removing of sediments by a strong flow and by the action of gravity. An experimental hydraulic device was built to test the authors' theoretical ablation model, describing a fluvial thermalerosionprocess. The effect of different parameters (Reynolds number, water temperature, ground-ice temperature) on the rate of thermal erosion for samples of frozen sand was investigated. Results from the experiments are in agreement with theoretical estimates using the mathematical model. Moreover, this study shows a hierarchy of parameters in terms of efficiency of the fluvial thermal-erosion process.A discussion of the possible effects of the contaminants on the erosion rate leads the authors to propose two kinds of experiments: a contaminated frozen sample eroded by a water flow, varying in this case the thermophysical properties of the sample (density, specific heat capacity, a latent heat, and change of phase), and an experiment consisting of erosion of a frozen sample by contaminated flow. This second case is also complex due to many mechanical, hydrodynamic and thermal interactions at the ground surface. This paper reports results of thermal erosionfrom experiments with icesaturated sand. A pure ice sample is used to determine the heat-transfer coefficient.