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The Raphstreng Tsho in Lunana is one of the "dangerous" lakes

The Raphstreng Tsho glacial lakein the Pho Chhu Riversub-basin measured 1.6 km long, 0.96 km wide and was 80 metres deep in 1986. The latest figures (1995) show the lake has swollen to be 1.94 km long, 1.13 km wide and has a depth of 107 metres. Its neighboring glacier could generate a GLOF up to two-and-a-half-times that which caused major devastation in October 1994. The 43 other glacial lakes, pin pointed in the survey and deemed to be in a dangerous state, show similar patterns.

Later, in 1999, a joint study by Austrian and Bhutanese experts concluded that the risk of an immediate outburst from the lake was "low" compared with theThorthormi (Thortomi) Tsho. Lying to the east of the Raphstreng Tsho, theThorthormi (Thortomi) Tsho and its off-shoots at the moment is considered "very dangerous" by experts after its southern flank was eroded by the 1994 flood and recommends close monitoring all summer till November every year

Outbursts from the main lake's dam would have similar impact downstream as the Luggye Tsho flood. To contain the lake, the department of geology and mines plans to open an outlet from one of its dam's side."This will be done to channel excess amount of water when glaciers melt," said the director of the department, Dorji Wangda.

Other than that the department has carried out "hazard zonation map" where to-be affected areas along the Lunana valley have been identified and settlements cautioned from starting any constructions. Re-settlement of villages affected by the 1994 flood was also recommended but officials say farmers were reluctant to move because of sentimental attachments. As a result pictorial manuals are distributed to help villagers evacuate in case of an impending flood. Satellite Phones were installed and a wireless station set up along with two watchmen to monitor the lakes. Moreover work at the site, which is above 4,000 meters above sea level, is aggravated by the harsh climate. Dorji Wangda said that the rough terrain to the site, which takes more than 11 days to walk, is also proving difficult, "especially when you have heavy equipment to carry."

In 994 the partial outburst from the Luggye Tsho caused the Pho Chhu flood which claimed 23 lives in Punakha valley and damaged a part of the Punakha dzong. The flood relief measure cost the government Nu 43 million. In Lunana 12 houses were damaged and 964.74 acres of pasture land wiped out. Yaks, grain, bridges, water mills, chortens and a temple were part of the toll.

Two major floods in the past, both from the Pho Chhu, are also remembered - one in the summer of 1950, lasting about 24 hours, and another in 1960 that lasted for five days. They are known to have caused by glacial lake outbursts. Meanwhile, the chances of a near-future glacial outburst from Lunana seem to pivot on the rising global climate and the toil of geologists.

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