Natural dams and outburst floods of the Karakoram Himalaya

ABSTRACT Glacier dams and outburst floods (jokulhlaups) have been reported in many glacierized mountain regions, and may create hazards for human populations. Specially large and dangerous examples occur where the rivers of extensive ice-free zones are blocked. This hydrological anomaly has been rare in modern times except for two areas: the southern Alaska-Yukon ranges and Karakoram Himalaya. In the Karakoram some 30 glaciers may form substantial dams on the Upper Indus and Yarkand river systems. Many more interfere with the flow of rivers in a potentially dangerous way. There is evidence of some 35 disastrous jokulhlaups since 1826. Rarer landslide dams have resulted in the largest dam-burst floods. The paper provides a record of known dams and related events, and identifies the glaciers involved. It indicates the role of the regional environment in the widespread potential for these glacier dams and catastrophic outbursts. Some data are given on the dimensions of past dams and the nature and impact of the flood waves. No dams were reported from the mid 1930's until 1978 when satellite imagery showed a 6 km glacier lake on the Upper Yarkand. The absence of dams in recent decades relates to a general glacier recession here. Renewed activity creates serious problems for water resource development and settlement growth that occurred in the recent, unusually favourable period.