A new remote hazard and risk assessment framework for glacial lakes in the Nepal Himalaya

David R Rounce,Daene C Mckinney,Alton C Byers,C Scott Watson,Jonathan M Lala

doi:10.5194/hess-20-3455-2016

Abstract

Abstract. Glacial lake outburst floods (GLOFs) pose a significant threat to downstream communities and infrastructure due to their potential to rapidly unleash stored lake water. The most common triggers of these GLOFs are mass movement entering the lake and/or the self-destruction of the terminal moraine due to hydrostatic pressures or a buried ice core. This study initially uses previous qualitative and quantitative assessments to understand the hazards associated with eight glacial lakes in the Nepal Himalaya that are widely considered to be highly dangerous. The previous assessments yield conflicting classifications with respect to each glacial lake, which spurred the development of a new holistic, reproducible, and objective approach based solely on remotely sensed data. This remote hazard assessment analyzes mass movement entering the lake, the stability of the moraine, and lake growth in conjunction with a geometric GLOF to determine the downstream impacts such that the present and future risk associated with each glacial lake may be quantified. The new approach is developed within a hazard, risk, and management action framework with the aim that this remote assessment may guide future field campaigns, modeling efforts, and ultimately risk-mitigation strategies. The remote assessment was found to provide valuable information regarding the hazards faced by each glacial lake and results were discussed within the context of the current state of knowledge to help guide future efforts.

Highlights

Glacial lake outburst floods (GLOFs) unleash stored lake water, often causing enormous devastation downstream that can include high death tolls as well as the destruction of valuable lands and costly infrastructure
As the number and area of glacial lakes continue to increase (Bajracharya and Mool, 2009; Bolch et al, 2011; Gardelle et al, 2011; Carrivick and Tweed, 2013), assessing the risk associated with these potential GLOFs becomes increasingly important
This study explored the use of two computationally inexpensive flood models: the Modified Single Flow direction (MSF) model developed by Huggel et al (2003) and the Monte Carlo Least Cost Path (MC-LCP) model developed by Watson et al (2015)

Summary

Introduction

Glacial lake outburst floods (GLOFs) unleash stored lake water, often causing enormous devastation downstream that can include high death tolls as well as the destruction of valuable lands and costly infrastructure. As the number and area of glacial lakes continue to increase (Bajracharya and Mool, 2009; Bolch et al, 2011; Gardelle et al, 2011; Carrivick and Tweed, 2013), assessing the risk associated with these potential GLOFs becomes increasingly important. This is especially true in the Himalaya, where a global assessment of the socio-economic impacts resulting from glacier outburst floods found that Nepal and Bhutan had the greatest economic consequences at the national level despite experiencing fewer floods than other parts of the world (Carrivick and Tweed, 2016). Events that occur over a relatively short time period, i.e., minutes to days, such as mass movement entering the lake, intensive rainfall, or intensive snowmelt, are referred to as dynamic events, while other events that occur over longer periods of time are referred to as self-destruction or long-term causes (Yamada, 1998; Emmer and Cochachin, 2013). Emmer and Cochachin (2013) highlight the complexity of these self-

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