Repeated glacial lake outburst flood threatening the oldest Buddhist monastery in north-western Nepal

Abstract

Abstract. Since 2004, Halji village, home of the oldest Buddhist Monastery in north-western Nepal, has suffered from recurrent glacial lake outburst floods (GLOFs). A sudden englacial drainage of a supraglacial lake, located at a distance of 6.5 km from the village, was identified as the source of the flood. The topography of the lake basin was mapped by combining differential Global Positioning System (DGPS) measurements with a structure-from-motion (SFM) approach using terrestrial photographs. From this model the maximum filling capacity of the lake has been estimated as 1.06 × 10 6 m 3 with a maximum discharge of 77.8 m 3 s −1 , calculated using the empiric Clague-Mathews formula. A simulation of the flooded area employing a raster-based hydraulic model considering six scenarios of discharge volume and surface roughness did not result in a flooding of the village. However, both the village and the monastery are threatened by undercutting of the river bank formed by unconsolidated sediments, as it already happened in 2011. Further, the comparison of the GLOF occurrences with temperature and precipitation from the High Asia Reanalysis (HAR) data set for the period 2001-2011 suggests that the GLOF is climate-driven rather than generated by an extreme precipitation event. The calculation of geodetic mass balance and the analysis of satellite images showed a rapid thinning and retreat of Halji Glacier which will eventually lead to a decline of the lake basin. As the basin will persist for at least several years, effective mitigation measures should be considered. A further reinforcement of the gabion walls was suggested as an artificial lake drainage is not feasible given the difficult accessibility of the glacier.

Large drainages from short-lived glacial lakes in the Teskey Range, Tien Shan Mountains, Central Asia

“…Compared to many large proglacial lakes in the eastern Himalayas that exceed 0.1 km 2 (Komori et al, 2004;Nagai et al, 2017), 74 % of the lakes in the study region had area extents of less than 0.01 km 2 in 2014 (Narama et al, 2015). Nevertheless, in recent decades rapid drainage from such lakes in central Asian mountain ranges has caused severe damage, impacting residents in nearby mountain villages (Kubrushko and Staviskiy, 1978;Kubrushko and Shatravin, 1982;Baimoldaev and Vinohodov, 2007;Narama et al, 2009). More recently, catastrophic damage occurred in 1998 from a drainage of the Archa-Bashy glacial lake in the Alay Range of the GissarAlay region.…”

“…After drainage, vertical subsidence occurs along the subsurface channel in the debris landform. Such short-lived glacial lake types recur when their ice tunnel closes, similar to that on a supraglacial lake on a glacier or on a debris-covered glacier (Kropáček, et al, 2015;Benn et al, 2017;Narama et al, 2017). For example, at Angisay Glacier in the Teskey Range (Fig.…”

“…lake in front of them (Richardson et al, 2009;Komori et al, 2012;Rounce et al, 2017). In north-western Nepal, a supraglacial lake that developed temporally at a depression on a small alpine glacier caused a large drainage through an englacial conduit (Kropáček et al, 2015).…”

“…For example, at Angisay Glacier in the Teskey Range (Fig. 1), several floods occurred from the same glacial lake in 1974, 1975, and 1980(Kubrushko and Staviskiy, 1978Kubrushko and Shatravin, 1982). The repeated floods indicate that the lake water refills at the same lake basin due to a repeated closure of the ice-tunnel.…”

“…In the western Teskey Range of the Tien Shan mountains, several large floods occurred from a glacial lake at the Angisay Glacier in 1974, 1975, and 1980(Kubrushko and Staviskiy, 1978Kubrushko and Shatravin, 1982). Since then, large drainages have occurred at the Kashkasuu glacial lake in 2006, the western Zyndan lake in 2008, the Jeruy lake in 2013, and the Karateke lake in 2014.…”