Evolution and Controls of Large Glacial Lakes in the Nepal Himalaya

Abstract

Glacier recession driven by climate change produces glacial lakes, some of which are hazardous. Our study assesses the evolution of three of the most hazardous moraine-dammed proglacial lakes in the Nepal Himalaya-Imja, Lower Barun, and Thulagi. Imja Lake (up to 150 m deep; 78.4 × 10 6 m 3 volume; surveyed in October 2014) and Lower Barun Lake (205 m maximum observed depth; 112.3 × 10 6 m 3 volume; surveyed in October 2015) are much deeper than previously measured, and their readily drainable volumes are slowly growing. Their surface areas have been increasing at an accelerating pace from a few small supraglacial lakes in the 1950s/1960s to 1.33 km 2 and 1.79 km 2 in 2017, respectively. In contrast, the surface area (0.89 km 2 ) and volume of Thulagi lake (76 m maximum observed depth; 36.1 × 10 6 m 3 ; surveyed in October 2017) has remained almost stable for about two decades. Analyses of changes in the moraine dams of the three lakes using digital elevation models (DEMs) quantifies the degradation of the dams due to the melting of their ice cores and hence their natural lowering rates as well as the potential for glacial lake outburst floods (GLOFs). We examined the likely future evolution of lake growth and hazard processes associated with lake instability, which suggests faster growth and increased hazard potential at Lower Barun lake.

Heterogeneous Influence of Glacier Morphology on the Mass Balance Variability in High Mountain Asia

“…The results presented in this study are a broad regional overview, and more studies should be conducted on specific lake‐terminating glaciers to better understand the lake influence on the glacier dynamics and mass balance (King et al, ). Local studies are even more pressing because of the associated risk of GLOFs (Haritashya et al, ). In our study, we observe that there is no relationship between glacier‐wide mass balances of lake‐terminating glaciers and the degree of danger of the associated lakes.…”

“…Furthermore, the development of proglacial lakes at glacier termini is a topic of interest in HMA, as they are associated with enhanced glacier mass loss through subaqueous melting (e.g., Röhl, 2006), accelerated ice flows (e.g., King et al, 2018), and with potential hazardous glacier lake outburst floods (GLOFs; e.g., Haritashya et al, 2018). Compared with land-terminating glaciers, lake-terminating glaciers shrink faster in Sikkim (Basnett et al, 2013), have more negative rates of elevation changes in Bhutan, Everest region, and West Nepal (Gardelle et al, 2013), and have more negative mass balances in the Everest region (King et al, 2017).…”

Annual 30-meter Dataset for Glacial Lakes in High Mountain Asia from 2008 to 2017

“…Though the statistical systematic errors as computed are very large for the small lakes, it must be noted that the precision, 170 as formulated by Krumwiede et al (Krumwiede et al, 2014) and implemented in Haritashya et al (Haritashya et al, 2018)is a much smaller error bar. Precision is reduced from the systematic error by a factor of square root of the number of perimeter pixels defining a lake.…”

“…In monsoonaffected areas such as Nepal and Bhutan, monsoon cloud cover in July to mid-September means that most of those areas are 90 covered by clear-sky images only from late September to November. Southeast Tibet regions are problematic not only because the observation season is short but abundant cloud cover, which is formed by the warm humid airflow raised by topography (Haritashya et al, 2018;Qiao et al, 2016).…”

“…To explore potential factors that have influenced glacial lake distribution across HMA, we focus on proglacial and supraglacial lakes, for which the changes are closely related with glaciers and expansion is most rapid. Proglacial lakes frequently develop from the enlargement and coalescence of one or more supraglacial lakes (Haritashya et al, 2018;Thakuri et al, 2016). 255…”