Bursting of glacial lakes - a consequence of global warming: A case history from the Lunana area, Gasa Dzongkhag, Bhutan

The lower reaches of the Lunana area expose multiple folded migmatite and biotite gneiss of the Thimphu Group, extensively intruded by granitic and pegmatitic rocks. This sequence in the upper reaches of the Table Mountain is overlain by the Tethyan metasediments. The straight course of the Pho Chhu between Luggye and Lhedi lakes in the Lunana area is probably controlled by a fault. A N-S strike-slip fault during Quaternary seems to have formed the Raphstreng Lake as a pull apart sag-pond. Severe hot summers during the year 1994 led to excessive melting of glaciers. The exceptional melting contributed enormous amount of melt water to the lake basins, which caused breach of the morainic dam and consequent enlargement of the outlet of the Luggye Tsho and the Tshopda Tsho. The breach was followed by floods on October 7, 1994.