The state of six dangerous glacial lakes in the Nepalese Himalaya

Nitesh Khadka,Wenfeng Chen,Guoqing Zhang

doi:10.3319/tao.2018.09.28.03

Abstract

Glaciers in the Himalaya are increasingly retreating and thinning due to climate change. This process is the primary cause of glacial lakes expansion and has increased the possibilities of the glacial lake outburst floods (GLOFs) that have been responsible for heavy loss of life and damage to downstream infrastructures. This study examines the status of the existing potentially dangerous glacial lakes in the Nepalese Himalaya such as Imja Tsho, Tsho Rolpa, Thulagi, Chamlang South, Barun Tsho, and Lumding Tsho; which were more susceptible to GLOF after the devastating earthquake in 2015. We examined the evolution and decadal expansion rate of lakes from 1987 to 2016 using Landsat images. The results show significant expansion of Imja Tsho, Barun Tsho, and Lumding Tsho at the rates of 42.1, 46.8, and 32.9% respectively, during 2006 - 2016; while other glacial lakes (i.e., Chamlang South, Barun Tsho, and Lumding Tsho) are relatively stable. Although the current status of glacial lakes may be stable in term of burst risk, high expanding lakes must be prioritized for detail studies. Continuous model-based monitoring and risk assessment, mitigation measures and disaster management strategies are necessary for reducing the impact of GLOFs.

Highlights

The total glaciated area of Himalaya is ~22990 km2 (Bolch et al 2012) and there are more than 4000 glacial lakes in the Himalaya (Zhang et al 2015; Nie et al 2017)
An algorithm developed by Zhang et al (2017b) was used to delineate the boundaries of glacial lakes using Landsat images, which determines the optimal threshold of normalized difference water index (NDWI) images by Otsu method
Imja Tsho is formed at the lower tip of its mother glaciers (Imja-Lhotse Shar glaciers) and drains through a dam formed by the end moraine giving rise to the Imja Khola, a tributary of Dudh Koshi (ICIMOD 2011; Chen et al 2014)

Summary

Introduction

The total glaciated area of Himalaya is ~22990 km (Bolch et al 2012) and there are more than 4000 glacial lakes in the Himalaya (Zhang et al 2015; Nie et al 2017). Previous studies have found that the Himalayan glacial lakes display a complex episodic patterns of change (Nie et al 2017). The glacial lakes in the Himalaya are different from the glacier-fed large lakes found in Tibet, especially in the inner basin. The glacial lakes in Himalayas are usually connected with glacier terminus and have small area (Zhang et al 2015), glacier-fed lakes in Tibet have melting water supply within the basin, are far from glacier and are large in size (Zhang et al 2017a). Glacial lake studies in the Nepalese Himalaya are very important because these lakes are good indicators of the significant change of climate that has occured. Since the early 1970s there has been notable warming in the Nepalese Himalaya (Shrestha et al 1999); and since the early 1960s

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Discussion

Conclusion