Bathymetric survey of Imja Lake, Nepal in 2012

Abstract

Imja Lake is one of the most studied lakes in the Himalaya as well as one of the most rapidly evolving glacial lakes in Nepal. Many researchers have studied the lake and the potential of a glacier lake outburst flood from the lake. One of the important factors in assessing the outburst flood risk is the volume that could be released in the flood and good bathymetric data is necessary to estimate that value. This work reports on the 2012 bathymetric survey of Imja Lake and the rate of expansion that has been observed in the lake over the last two decades, since 1992. The survey was somewhat hampered by the extensive iceberg coverage of the lake in September 2012, but a good estimate of the bottom bathymetry and the current volume was obtained. When compared to previous surveys, it is very clear that the lake bottom has continued to deepen as the ice beneath the lake has melted. The average depth has increased by 62% since 2002 and continues to increase at a rate of 1.8 m/yr. The maximum depth has increased 28% since 2002 and is increasing currently at a rate of 5.8 m/yr. Perhaps more important in terms of glacier lake outburst flood risk is the continued rapid areal expansion of the lake which has expanded 41% since 2002 and is growing at a rate of 0.02 km2/yr. This expansion has resulted in an additional 6 million m3 of water for an outburst flood event, and increasing the maximum possible flood volume to 36.3 million m3 a 73% increase from what was calculated using 2002 data.