Differential surface melting of a debris-covered glacier and its geomorphological control - A case study from Batal Glacier, western Himalaya

The spatially variable response of Himalayan glaciers is often linked with the melting rate caused by supraglacial debris cover on the glacier surface. Studies have identified the role of debris cover in inhibiting underneath ice melt, but the spatial distribution of debris thickness still needs to be discovered in the region. We conducted debris thickness estimation at 110 locations and in-situ mass balance measurements over Batal Glacier from Chandra basin in the semi-arid region of the western Himalaya from 2013 to 2019 to establish a relationship between ice ablation rates and debris thicknesses. Overall, the annual ablation for the debris-covered area varied between 1.3 and 1.8 m w.e. a-1, with a mean annual ablation of 1.6 m w.e. a-1 during 2013-2019. While the point ablation rate does not exceed 3 m w.e. a-1 at any specific glacier area throughout the observation period. The melt rate was attenuated up to 80 % under the debris thickness ranging from 2 to 72 cm. The formation and thickness of the debris increased linearly down the glacier, sparse in the centreline owing to supraglacial channels and ice walls, and higher at the margins due to the contribution from avalanches. Supraglacial water channels and ice cliffs along the centreline were also observed as persistent contributors to the ablation rate. However, a higher mean surface slope (12 degrees) of the ablation zone constraints the formation of supraglacial ponds. The area with patchy debris cover has an increased melt rate compared to the completely debris-covered area. Spatially distributed but reduced ice ablation under varying debris thickness underlines the influence of debris thickness on the underneath ice melt rate for Himalayan glaciers. Further studies on the evolution of supraglacial ponds and ice cliffs are required to understand the shrinking of glaciers in response to climate change in the western Himalaya.