First empirical assessment of ice content from Himalayan rock glaciers.

Climate warming in the Himalaya threatens glaciers and permafrost, with severe implications for the future sustainability of the region’s natural ‘water towers’ and connected ecological systems and human infrastructure. Recent work in high mountain environments has highlighted how rock glaciers are prevalent and contain globally valuable water supplies. Yet, over the Himalaya, information regarding their number, spatial distribution, morphometric characteristics and water content are scarce. Here, we present the first measured assessment of ice content in any Himalayan rock glacier. We use InSAR and Ground Penetrating Radar (GPR) surveys, respectively, to assess the current movement and ice content of a large rock glacier at Gokyo, central Nepal. This landform is situated at over 4700 m elevation and we show that parts of it are currently moving downslope at 75-100 cm per year; a figure in line with other rock glacier velocities in high arid mountains. This suggests that the rock glacier contains solid buried ice, and this is confirmed by our GPR surveys. We demonstrate the presence of massive ice units up to 250 m in length and 28 m in thickness underlies the rock glacier surface, representing an estimated total of up to 3.01 ×105 m3 of freshwater equivalent. We have recently reported that there are over 25,000 rock glaciers in the Himalayas. If the Gokyo rock glacier is representative for the region, then these landforms are likely to contain significant amounts of ice, and therefore will be of great hydrological value to downstream regions as climate change progresses and the buried ice slowly melts.