Abstract
Abstract In the Nepalese Himalaya, there is little information on the number, spatial distribution and morphometric characteristics of rock glaciers, and this information is required if their hydrological contribution is to be understood. Based on freely available fine spatial resolution satellite data accessible through Google Earth, we produced the first comprehensive Nepalese rock glacier inventory, supported through statistical validation and field survey. The inventory includes the location of over 6000 rock glaciers, with a mean specific density of 3.4%. This corresponds to an areal coverage of 1371 km 2 . Our approach subsampled approximately 20% of the total identified rock glacier inventory ( n = 1137) and digitised their outlines so that quantitative/qualitative landform attributes could be extracted. Intact landforms (containing ice) accounted for 68% of the subsample, and the remaining were classified as relict (not containing ice). The majority (56%) were found to have a northerly aspect (NE, N, and NW), and landforms situated within north- to west-aspects reside at lower elevations than those with south- to- east aspects. In Nepal, we show that rock glaciers are situated between 3225 and 5675 m a.s.l., with the mean minimum elevation at the front estimated to be 4977 ± 280 m a.s.l. for intact landforms and 4541 ± 346 m a.s.l. for relict landforms. The hydrological significance of rock glaciers in Nepal was then established by statistically upscaling the results from the subsample to estimate that these cryospheric reserves store between 16.72 and 25.08 billion m 3 of water. This study, for the first time, estimates rock glacier water volume equivalents and evaluates their relative hydrological importance in comparison to ice glaciers. Across the Nepalese Himalaya, rock glacier to ice glacier water volume equivalent is 1:9, and generally increases westwards (e.g., ratio = 1:3, West region). This inventory represents a preliminary step for understanding the spatial distribution and the geomorphic conditions necessary for rock glacier formation in the Himalaya. With continued climatically-driven ice glacier recession, the relative importance of rock glaciers in the Nepalese Himalaya will potentially increase.
Highlights
2 3 The Hindu Kush-Himalayan (HKH) region contains ~54,000 glaciers covering an area of ~60,000 km2 (Bajracharya 4 and Shrestha, 2011), constituting the most extensive glacier coverage outside of the polar regions and forming 5 the “Asian water towers” (Immerzeel et al, 2010)
HKH glaciers have generally undergone mass loss between 19808 2010 (Bajracharya et al, 2015), with estimated glacial mass change rates of -26±12 Gt yr-1 (2003-2009) (Gardner 9 et al, 2013), while substantial further long-term glacial mass losses are projected under climate warming (Bolch 10 et al, 2012; Jiménez Cisneros et al, 2014; Huss and Hock, 2015; Shrestha et al, 2015)
Compilation of the DDA/I-DL inventory 84 85 Whereas automated and semi-automated techniques have enabled mapping and monitoring of clean-ice glaciers from optical satellite image data (e.g., Bolch and Kamp, 2006; Bhambri and Bolch, 2009; Shukla et al, 2010), these approaches are generally unsuitable for mapping debris-covered glaciers (e.g., Alifu et al, 2015)
Summary
2 3 The Hindu Kush-Himalayan (HKH) region contains ~54,000 glaciers covering an area of ~60,000 km (Bajracharya 4 and Shrestha, 2011), constituting the most extensive glacier coverage outside of the polar regions and forming 5 the “Asian water towers” (Immerzeel et al, 2010). 17 Rock glaciers are cryospheric landforms formed by gravity-driven creep of ice-supersaturated accumulations of rock debris, incorporating a perennially frozen mixture of poorly sorted angular-rock debris and ground ice (Haeberli et al, 2006) They are characterised by a seasonally frozen, clastic blocky surficial layer 0.5 to 5 m thick that thaws each summer (known as the active layer) (Bonnaventure and Lamoureux, 2013; Pourrier et al, 2014). The genesis of rock glaciers remains contested; this controversy has been between the permafrost school (purely periglacial-origin) vs the continuum school (glacial- and periglacial-origin), and has previously been summarised and discussed in detail (see Berthling, 2011) Discussion of this is beyond the scope of this study; here we adopt the inclusive, and non-genetic, terms discrete debris accumulations ( DDAs) and ice-debris landforms ( I-DLs) to incorporate rock glaciers, protalus lobes and protalus ramparts.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
