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Evaluating the growth characteristics of a glacial lake and its degree of danger of outburst flooding: Imja Glacier, Khumbu Himal, Nepal

2009; Taylor & Francis; Volume: 63; Issue: 4 Linguagem: Inglês

10.1080/00291950903368367

1502-5292

Teiji Watanabe, Damodar Lamsal, Jack D. Ives,

Climate change and permafrost

Abstract The Imja Glacier Lake (Imja Tsho) (1.03 km2 in 2007) is repeatedly cited as one of the most dangerous glacial lakes in the Himalaya with a glacial lake outburst flood (GLOF) claimed to be imminent. Knowledge of lake development and its dynamics, however, is limited and forecasts of a possible outburst are not scientifically based. Nevertheless, prospects for such a catastrophe are repeatedly exaggerated, attracting alarmist mass media coverage. The paper provides an assessment of the lake expansion rates from 1956 to 2007. Stage 1 (1956–1975), slowest: coalescence of several small supra-glacial ponds; Stage 2 (1975–1978), a short period of most rapid expansion; Stage 3 (1978–1997), slow: gradual expansion of single lake; and Stage 4 (1997–2007), renewed acceleration: mainly eastward expansion into the glacier surface. The lake's water level has fallen from 5041 m to 5004 m (1964–2006). The results show that there is no immediate danger of catastrophic outburst although the dynamics of up-glacier and down-valley lake expansion, fluctuation of lake water level, and dead-ice morphology changes should be continuously and comprehensively monitored. Alarmist prognostications based solely upon rapid areal expansion are counterproductive. Keywords: glacial lakeglacial lake outburst flood (GLOF)HimalayaImja GlacierImja TshoKhumbu Himal Acknowledgements The Japan Science Society is thanked for providing financial support for part of the study. Thanks are due to Akiko Sakai of Nagoya University for providing the dead-ice topography data, and also Peter Messerli of the University of Bern and Katsuhiko Asahi of Ritsumeikan University who provided the information on the ground surface morphology and/or lake water level and ground photographs. TV Asahi Corporation, Tokyo, is thanked for providing oblique air photographs taken in 2007. Also, the United Nations University project on mountain hazards is thanked for providing support for the early stages of the survey. Notes 1. This paper was originally presented by the first author during the Tunis International Geographical Congress, August 2008.