The influence of water percolation through crevasses on the thermal regime of Himalayan mountain glaciers

Abstract. In cold and arid climate, small glaciers with cold accumulation zone are often thought to be entirely cold based. However, Ground Penetrating Radar (GPR) measurements on Rikha Samba Glacier in the Nepal Himalaya reveal a large amount of temperate ice that seems to be influenced by the presence of crevassed areas. We used a coupled thermo-mechanical model forced by a firn model accounting for firn heating to interpret the observed thermal regime. We show that the addition of water percolation and refreezing in crevassed areas using a simple energy conservative approach is able to explain the observations. Model experiment shows that both steady and transient thermal regimes are significantly affected by latent heat release in crevassed areas. It makes half of the glacier base temperate, resulting in the dynamics mainly controlled by basal friction instead of ice deformation. Timescale of thermal regime change in response to warming climate is also greatly diminished with a potential switch from cold to temperate basal ice in 50–60 years in the upper part of the glacier while it would take 100–150 years without the crevasses effect. This study highlights the crucial role of water percolation through the crevasses on the thermal regime of glaciers and validates a simple method to take it into account in glacier thermo-mechanical models.