Modelling rock glacier velocity and ice content, Khumbu and Lhotse Valleys, Nepal

Abstract. Rock glaciers contain significant amount of ground ice and serve as important freshwater resources as mountain glaciers melt in response to climate warming. However, current knowledge about ice content in rock glaciers has been acquired mainly from in situ investigations in limited study areas, which hinders a comprehensive understanding of ice storage in rock glaciers situated in remote mountains and over local or regional scales. In this study, we develop an empirical rheological model to infer ice content of rock glaciers using readily available input data, including rock glacier planar shape, surface slope angle, active layer thickness, and surface creep rate. We apply the model to infer the ice content of five rock glaciers in Khumbu and Lhotse Valleys, north-eastern Nepal. The inferred volumetric ice fraction ranges from 57.5 % to 92 %, with an average value between 71 % to 75.3 %. The total water volume equivalent in the study area lies between 10.61 and 16.54 million m3. Considering previous mapping results and extrapolating from our findings to the entire Nepalese Himalaya, the total amount of water stored in rock glaciers ranges from 8.97 to 13.98 billion m3, equivalent to a ratio of 1 : 17 between the rock glacier and glacier reservoirs. Due to the accessibility of the input parameters of the model developed in this study, it is promising to apply the approach to permafrost regions where previous information about ice content of rock glaciers is lacking.