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Lakes in Lunana with risks
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Watching the lakes
Although there is no immediate danger, the presence of a peculiar micro-organism
on the surfaces of glaciers could accelerate glacial melting and eventually lead to a glacial outburst, according to a preliminary survey report .
Out of more than 677 glaciers and 2674 glacial lakes lakes in Bhutan, about 24 are identified as potentially dangerous. Tshoju is identified as the longest glacier measuring about 13 kilometeres in length.
Tarina Lake Tarina Tsho
Luggi Lake Luggi Glacier Raphstreng Tsho
Luggi (Luggye) Lake Luggi (Luggye) Glacier Raphstreng Tsho


Lakes in Lunana with high GLOF (glacial lake outburst flood) risks

Of the four major lakes in Lunana experts have identified the Thorthormi (Thortomi) as potentially the most dangerous because of some weak points along its natural dam. They have also identified the safe and unsafe areas in the region, in case of a flood.

The developingThorthormi(Thortomi) lake (in the foreground) is 50-60 metres above the Raphstreng lake (Photo by Nozumo Naito, Nagoya University)

An Austria-Bhutan geological team which finalised its study this month pointed out that theThorthormi(Thortomi) glacier was melting and the lake, situated more than 4,500 metres above sea level, was growing.

If the lake did burst, perhaps in 10 years if preventive measures were not taken, it could also create a "cascading" effect and also pressure the Raphstreng lake, about 50 to 60 metres below it, into bursting, according to the department of geology and mines.

The result could be a flood with a downstream impact volume of 17-22 million cubic metres.Thorthormi(Thortomi) and Raphstreng, both sources of the Phochhu, are divided by a moraine dam which has risky segments. The Throthormi lake's southern flank was eroded by the 1994 flood. "Furthermore, a physical risk assessment of theThorthormi(Thortomi) supra-glacial lake is difficult because of the extremely dangerous crevices on the surface," said Dorji Wangda, the director of the department of geology and mines (DGM). "We cannot even carry our geo-physical instruments there."

A Japan-Bhutan survey team of glacier-microbiologists, glacio-ecologists and geologists recently reported that the potential of an outburst of the Throthormi lake was higher since the 1994 Luggye lake flood had made the left lateral moraine unstable.

As preventive measures the DGM, with its international partners, would create outlets so that the water will flow naturally.
Tarina Lunana glacial lake

The Austria-Bhtuan team had demarcated safe and unsafe zones for settlement in Lunana and the need for infrastructure between Tami Damchu and Khuruthang in Punakha valley.

If the lake burst the people along Lunana valley might have only 20 minutes to move out. Thenza, Denji, Tshojo, Lhedi, Shangsa and others villages were most risk prone areas. The team has identified the places where people could go for safety in case of a flood. It has also identified emergency helipads for rescue operations. Some of the other risk prone areas are the settlements along the river bank which are on the lower terraces. "The schools and resort in Khuruthang could be flooded and washed away," the Austrian professor Hausler said.

Punakha Dzong
"The Punakha dzong will be safe although the dzong premises could be flooded. Parts of Wangdue-Punakha road lying on low terraces will also be completely washed away, paralysing the rescue operations." The study team has recommended that these parts of the road be relocated to higher terraces. The demarcation represented a worst flood scenario. The department, with assistance from the flood warning unit and funds from the government of India, has installed two technical early warning systems in Lunana to warn the people downstream in time on the impending danger.

The 1994 flood took seven hours for the flood to reach Punakha, a distance of 90 kilometres from the Luggye lake. Scientists predict that if there is a flood this time it will take less time since the earlier flood had made the track for a smoother flood clearing the debris away.

Related Information
Raphstreng Tsho in Lunana
Bhutan's glaciers are retreating
Bhutan's Glaciers Pictures
Raphstreng Tsho in Lunana
Bhutan's glaciers are retreating
Luggye, Raphstreng,Thorthormiand Tarina
Punakha Dzong: Confluence of Mo Chhu and Pho Chhu
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