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.
Highlights
Rock glaciers are valley-floor and valley-side landforms consisting of ice–rock mixtures and are common in all arid and cold mountain regions
We develop an empirical rheological model for inferring ice content of rock glaciers and apply it to estimate the water storage 465 of rock glaciers situated in the Khumbu and Lhotse Valleys using surface-velocity-constraints derived from Interferometric Synthetic Aperture Radar (InSAR)
The main findings are summarised as follows: (1) An empirical rheological model is presented in this study for estimating ice content of rock glaciers using five input parameters, namely rock glacier area, width, surface slope angle, active layer thickness, and surface velocity, all of which can be obtained from readily available remote sensing products or emerging datasets. 470 (2) Mean downslope velocities of the rock glaciers situated in Khumbu and Lhotse Valleys ranged from 5 cm yr-1 to 30 cm yr1 and mostly remained stable during the observational period (2006–2020)
Summary
Rock glaciers are valley-floor and valley-side landforms consisting of ice–rock mixtures and are common in all arid and cold mountain regions. 30 research, was first noted by Corte (1976); despite this, research on the role of rock glaciers in maintaining hydrological stores in mountain catchments remains limited. In regions such as the Himalaya, recent research has argued that rock glaciers might represent the end member of an evolutionary process where some glaciers transition to debris-covered glaciers, a proportion of which will undergo further transition to rock glaciers (Jones et al, 2019; Knight et al, 2019). This process would be triggered by the paraglacial response
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