Changes in Imja Tsho in the Mount Everest region of Nepal

M A Somos-Valenzuela,D C Mckinney,A C Byers,D R Rounce

doi:10.5194/tc-8-1661-2014

Abstract

Abstract. Imja Tsho, located in the Sagarmatha (Everest) National Park of Nepal, is one of the most studied and rapidly growing lakes in the Himalayan range. Compared with previous studies, the results of our sonar bathymetric survey conducted in September of 2012 suggest that its maximum depth has increased from 90.5 to 116.3 ± 5.2 m since 2002, and that its estimated volume has grown from 35.8 ± 0.7 to 61.7 ± 3.7 million m3. Most of the expansion of the lake in recent years has taken place in the glacier terminus–lake interface on the eastern end of the lake, with the glacier receding at about 52 m yr−1 and the lake expanding in area by 0.04 km2 yr−1. A ground penetrating radar survey of the Imja–Lhotse Shar glacier just behind the glacier terminus shows that the ice is over 200 m thick in the center of the glacier. The volume of water that could be released from the lake in the event of a breach in the damming moraine on the western end of the lake has increased to 34.1 ± 1.08 million m3 from the 21 million m3 estimated in 2002.

Highlights

The rate of formation of glacial lakes in the Nepal Himalaya has been increasing since the early 1960s (Bolch et al, 2008; Watanabe et al, 2009; Bajracharya and Mool, 2009)
Everest) and Makalu Barun national parks of Nepal have grown substantially during the past several decades (Bajracharya et al, 2007). Accompanying this increase in the number and size of glacial lakes is an associated increase in the risk of glacial lake outburst flood (GLOF) events (Ives et al, 2010; Shrestha and Aryal, 2011)
The appearance and possible danger posed by new glacial lakes in this region has prompted national and regional groups to begin assessing engineering and nonengineering methods to mitigate increasing GLOF risks to communities, infrastructure, and landscapes downstream of the lakes (e.g., UNDP, 2013)

Summary

Introduction

The rate of formation of glacial lakes in the Nepal Himalaya has been increasing since the early 1960s (Bolch et al, 2008; Watanabe et al, 2009; Bajracharya and Mool, 2009). GLOFs are the sudden release of a large amount of glacial lake water into a downstream watercourse, many orders of magnitude higher than the normal flow due to a moraine damming the lake (Carrivick and Rushmer, 2006). They can cause severe damage to downstream communities, infrastructure, agriculture, economic activities, and landscapes because of the sheer magnitude and power of the flood and debris flows produced (Bajracharya et al, 2007). The appearance and possible danger posed by new glacial lakes in this region has prompted national and regional groups to begin assessing engineering and nonengineering methods to mitigate increasing GLOF risks to communities, infrastructure, and landscapes downstream of the lakes (e.g., UNDP, 2013)

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