Ice-Dammed Lakes and Outburst Floods, Karakoram Himalaya: Historical Perspectives on Emerging Threats

The largest glacier impoundments in the Karakoram Himalaya are by ice dams formed where tributary glaciers block main rivers. These can cause outburst floods that spread destruction far through the mountains and into the lowlands. More than 90 out-bursts from impoundments behind such dams have been identified. Of the largest and most destructive, 17 were on the upper Indus River and 10 on the Yarkand. Unlike "dangerous lakes" recently reported elsewhere in the Himalaya, these events are associated with advancing glaciers, in some cases glacial surges. The lakes are short-lived, rarely surviving more than one summer. Their outburst styles and flood waves exhibit distinctive features. This paper summarizes the behavior and current status of advances of more than a dozen glaciers with histories of large impoundments. Recent developments are assessed in relation to historical records and the Karakoram glacier environment. Destructive outburst floods have already occurred on the Yarkand and may be imminent on the Indus. Problems of predicting dangerous outbursts are outlined, uncertainties raised by limited and mainly older investigations. Implications of global climate change appear different for these hazards in this region than reports of dangerous glacial lakes elsewhere in the Himalaya.