A rapidly growing moraine-dammed glacial lake on Ngozumpa Glacier, Nepal

Abstract

Moraine-dammed glacial lakes are becoming increasingly common in the Himalaya as a result of glacier mass loss, causing concern about glacier lake outburst flood risk. In addition to extant lakes, the potential exists for many more to form, as more glaciers ablate down to the level of potential moraine dams. In this paper, we document the recent rapid growth of, a moraine-dammed lake on Ngozumpa Glacier, Nepal. Using a combination of ground-based mapping and sonar surveys, aerial photographs (<1m resolution), and ASTER imagery (15m resolution), processes and rates of lake expansion have been determined. The lake first formed between 1984 and 1992 when collapse of an englacial conduit allowed water to accumulate at the level of a gap in the lateral moraine, ~km from the glacier terminus. Lake growth was initially slow, but since 2001 it has undergone exponential growth at an average rate of 10%y−1. In 2009, the lake area was 300,000m2, and its volume was at least 2.2million m3. Calving, subaqueous melting, and melting of subaerial ice faces all contribute to the expansion of the lake; but large-scale, full-height slab calving is now the dominant contributor to growth. Comparison with other lakes in the region indicate that lake growth will likely continue unchecked whilst the spillway remains at its current level and may attain a volume of hundreds of millions of cubic metres within the next few decades.