A study of decadal scale glacier changes of the Lunana glacier system in Bhutan, Himalaya, with considerations to glacial lake outburst floods (GLOFs)
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- Master theses 
This study assesses changes in glacier area, velocity, and geodetic mass balance for a selection of glaciers in the Lunana glacier system of Bhutan, Himalaya. It takes considerations to Glacial Lake Outburst Floods (GLOFs) by creating a glacial lake inventory of two important potential dangerous glacial lakes, Raphstreng Tsho and Luggye Tsho. Bhutan is located in the eastern parts of the HKH region and is known for its earlier GLOF events. The precipitation in Bhutan is driven by the Indian monsoon resulting in 60% annual precipitation, the high amount of rainfall results in rockfalls that covers large valley glacier tongues with debris. I studied the glacier area changes between 1976, 1996 and 2018 using freely available Landsat satellite imagery, SAR Sentinel 1&2, the SRTM Digital Elevation Model (DEM) and HMA DEM. The geodetic mass balance was calculated between 1976, 2000 and 2018/9 (for selected glaciers) using DEM constructed from high-resolution stereo images, Pléiades and SPOT, granted from the European Space Agency, as well as using the already accessed SRTM DEM and a Hexagon DEM courtesy of King, et al. (2019). The glacier velocity was generated using SAR TerraSAR-X data from 2016 and shows an average yearly displacement over the Lunana glacier system. The glacial lake time series for Raphstreng Tsho and Luggye Tsho where studied between 1993 and 2018 using a stack of freely available Landsat imagery. The results of this study, show a variety of decadal glacial changes over Lunana glacier system, with glaciers lowering on an average by 0.48± 0.08 m a-1 between 1976 and 2018/9 which calculates to a geodetic mass balance of -0.41 ± 0.068 m w.e. a-1. The system had a total average of 12.73% area of reduction for all glaciers, between the same time period. The Lunana glacier system consists of both debris-covered glaciers in the south and debris-free glaciers in the north, and as a result, the glacier changes vary between the two regions. Between 1976 – 2018/9 the southern region had an average surface melt of 0.76 ± 0.07 m a-1 which calculates to a geodetic mass balance of -0.65 ± 0.06 m w.e. a-1 and a 12.65% area of reduction. For the Northern region, the average surface melt was measured to be 1.26 ± 0.07 m a-1 which calculates to a geodetic mass balance of 1.07 ± 0.06 m w.e. a-1 and a 12.80% area of reduction. The glacier velocity was calculated to be at average of 3.05 ± 0.73 m a-1 over the south region and 3.78 ± 0.73 m a-1 over the north region. The Luggye glacier 1, located in the southern parts of Lunana glacier system, is the main input source for glacier meltwater to Luggye Tsho an ice-moraine dam proglacial lake which outburst in 1994 due to hydrostatic pressure. Between 1976 and 2018/9, the Luggye glacier 1 has had a considerable loss in surface elevation by 1.19 ± 0.07 m a-1 which calculates to a geodetic mass balance of 1.01 ± 0.069 m w.e. a-1. The 1994 GLOF event discharged over 18 million m3 of water, destroying infrastructure, flooding villages and houses which killed 21 humans. Today, Luggye Tsho is classified to yield over 1.41 km2 of water, an increase from its former state of 1.12 km2 in 1993, just before the event. This study cannot affirm if PDGLs such as Luggye Tsho is to outburst in the future, but it does affirm its growth in lake area and its input source from glacier melt over Luggye glacier, and that it should be monitored in case of potential outbreak. This can be done by doing repeated analysis of glacier velocity and calculation of glacier mass balance, as this would calculate the input source amount of meltwater to Luggye Tsho.