Abstract:
Among the more complex and devastating interactions between climate and hydromorphological processes
in mountain environments are landslide lake outburst floods (LLOFs), resulting from mass movements
temporarily blocking a drainage system. This work reviews these processes in the Himalayas and
highlights the high frequency of this type of phenomenon in the region. In addition, we analyse two recent
catastrophic trans-national LLOFs occurring in the Sutlej river basin during 2000 and 2005. Based on high
resolution satellite images, Tropical Rainfall Measuring Mission (TRMM), Moderate-Resolution Imaging
Spectroradiometer (MODIS) derived evolution of snowline elevation and discharge data we reconstruct
the timing and hydrometeorological conditions related to the formation and failure of landslide dams.
Results showed that the 2005 flood, originating from the outburst of the Parchu Lake, was not related to
heavy precipitation, but was likely enhanced by the rapid and late snowmelt of an unusually deep and
widespread snowpack. The flood in 2000 was triggered by the outburst of an unnamed lake located on the
Tibetan plateau, identified here for the first time. In this case, the outburst followed intense precipitation in
the lake watershed, which raised the level of the lake and thus caused the breaching of the dam. As stream
gauges were damaged during the events detailed discharge data is not available, but we estimated the peak
discharges ranging between 1100 m3 s 1 and 2000 m3 s 1 in 2005, and 1024 m3 s 1 and 1800 m3 s 1 in
2000. These events caused significant geomorphic changes along the river valleys, with observed changes in
channel width exceeding 200 m. Results also demonstrate that remotely-sensed data enables valuable
large-scale monitoring of lake development and related hydrometeorological conditions, and may there by inform early warning strategies, and provide a basis for flood risk reduction measures that focus on disaster
preparedness and response strategies.
