Glacier, released circa 200 million tons of water into the Colonia river. The lake has rapidly refilled, suggesting high risk of further GLOFs. Indeed, the peak discharge was estimated to surpass 3000 m3

/second. Such events

may in the future endanger continued hydropower devel- opment in the region (Dussaillant et al., 2010).

Large glacier lakes do not necessarily imply high risk of flooding, however, and GLOF risks depend on site-spe- cific factors such as moraine-dam stability and triggering mechanisms. Given the physical and economic damage that glacial hazards can cause, it is important to be able to identify and define the degree of hazard objectively. Over the last decade or so significant advances have been made in the use of Remote Sensing techniques to map, classify and categorize glacial lakes. These methods have been used not only to monitor changes in the glacial lake systems but also to identify areas where lakes have the potential to form and grow perhaps two to three decades into the future, based on the rate of ice flow, low sur- face gradient of the debris-covered glacier, and negative mass balance. Similarly, advances in ground-based sur- vey methods, such as the use of geophysical techniques, have helped to provide information about the integrity of the moraines themselves. It has been demonstrated that by using Multi-Criteria Analysis it is possible to gauge the degree of glacial hazard quantitatively. By analysing a given glacial lake system, basic threshold parameters such as lake volume, moraine dimensions, etc., can be determined. Similarly, parts of the same environment that could trigger a lake outburst, for instance, can also be identified and rated so that a hazard score can be as- signed by which it can be graded. This affords a method of prioritising lakes objectively within a whole catchment or region. As climate continues to change, the nature of glacial hazards in a given region also has the potential to alter with time. Debuttressing of steep rock slopes as

 Figure 9: ASTER image of retreating glaciers and mo- raine-dammed lakes in Bhutan (28 October 2009). The large lake to the right (Luggye Tsho) partially drained in 1994, carving the prominent flood track and causing wide- spread damage and loss of life downstream.

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