Experts refer to the different types of glacial lakes based on dam type and the process by which the lake was formed. Glacial lakes within two kilometres of glaciers are directly fed by glacier melt. In this report – which focuses on different types of moraine-dammed glacial lakes – mapping shows that most glacial lakes are within five kilometres of glaciers. Among the different types of glacier lakes, end moraine–dammed lakes are mostly closer to or in contact with glaciers and, as such, have higher risk for glacial lake outburst floods (GLOFs)

Climate change in the past few decades has increased the development of pro-glacial lakes by damming melt water or causing existing glacial lakes to expand and merge. These are lakes formed in front of or on the margins of glaciers and ice sheets. The report finds that the expansion or formation of new lakes at the margin of shrinking glaciers has increased the risk of GLOFs. Although GLOFs are not a recent phenomenon in the HKH, their impact on lives, property, and livelihood support systems has increased over the years. While more than 50 glacial lake outburst events have been recorded in the HKH, records are available only for a part of Bhutan, China, Nepal, and Pakistan.

This report provides baseline data for researchers to carry out further studies to determine the risk of GLOFs in the five basins. With further research, glacial lake change can be monitored, critical lakes identified, and hazard and GLOF risk levels assessed. This will support decision makers in the region in reducing risks of potential GLOFs in the future. It will also help to target future research focus on lakes considered more vulnerable – based on factors like their proximity to glaciers and the type of moraine damming the lake. ”Putting this kind of information in the hands of decision makers will contribute to managing water resources in higher altitude areas and to reducing risk by identifying potentially dangerous lakes. This information will help to save lives and property,” said Sudan Maharjan, a remote sensing specialist at ICIMOD and the study’s lead author.

The report is based on mapping of glacial lakes of the Amu Darya, Indus, Ganges, Brahmaputra, and Irrawaddy river basins, including the Mansarovar Interior Basin, using Landsat images mostly from 2005. The report identified that there are now more and larger lakes in the eastern part of the HKH. The Brahmaputra basin has the highest number of glacial lakes followed by the Indus, Ganges, Amu Darya, and Irrawaddy basins. The report also includes all glacial lakes in the landforms that were previously under glacier – known as paleo-glaciation landforms – many of which are bedrock–dammed lakes. The Brahmaputra basin contains the highest number of this type of lake. The Ganges and Amu Darya basins contain the largest number of moraine–dammed lakes, which comprise nearly one third of all lakes in the HKH. Moraine–dammed lakes are important to monitor closely since they are more likely to breach under slight triggers, given their weak and unconsolidated boundaries formed by moraine from glacial retreat. Researchers investigate such lakes to determine GLOF risk, whereas bedrock–dammed lakes are the focus of future water availability studies.

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1. Distribution of glacial lakes in the HKH 2. Number and area of glacial lakes in major river basins of the HKH 3. Lead author Sudan Bikash Maharjan and co-author Finu Shrestha discuss the outcome of their work. Photo: Jitendra Bajracharya.

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