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Tsho Rolpa Lake in Rolwaling.

7. Other hazardous glacial lakes in Nepal and Tibet

The combination of a glacier hanging over a lake and a thin glacial dam, make such lakes extremely vulnerable to dam burst by a glacial slab falling in the lake after an earth quake. In Nepal and Tibet, a number of such lakes exist. A quick scouting of some 35% of Nepal using 1:50,000 maps, show that there are several more potential hazards similar to the Sabai Tsho Lake but fortunately they are generally smaller.
Examples of lakes at risk, roughly ordered in order of severity:
(1) Dudh Kund Lake, 6 km SSE of Sabai Tsho Lake in the Hinku Valley, measuring 1000 by 300 m.
(2) La Tsho Ogma and Kongma Lakes, 10 km NNW of the Tsho Rolpa Lake in Rolwaling, measuring 0.25 and 0.2 square km, resp.
(3) Naktok Tsho Lake, 5 km SSE/SE of Gokyo in the Everest Region, measuring 500 by 250 m;
(4) Chamlang Tsho Lake, 11 km ENE of the Sabai Tsho Lake in the Hunku Teng Valley, measuring 400 by 100 m.
(5) Lake 10 km NNE of the Lantrang Lirung Peak (7233 m) in the Langtang, measuring 500 by 250 m.
(6) Possibly the large Tilicho lake, near the Anapurna.

The risk will depend on the stability of the glacier, the slope on which the glacier hangs, the depth of the lake, the size of the lake, the thickness and strength of the glacial lake wall and the number of people living along the river valley down-streams.

According to Sherpa mountain guides, glacial lake bursts are quiet common in Nepal and Tibet. Major onces occur once every 5 to 10 years but generally do not kill many people as they happen in remote, poorly populated areas.

The Tsho Rolpa Lake in the Rolwaling area of Nepal, east of the Mount Everest Region, has been under surveillance for a number of years. This lake doesn't have a steeply hanging glacier but is very deep and large, and its moraine wall is instable. This has now been solved by building a canal (see Tsho Rolpa region entry) in the late nineties for controlled water flow which lowered the lake level by about 5 meters.

Gate in canal draining Tsho Rolpa Lake.

8. Land slide bursts

River valleys filled by land slides and subsequent burst of the lake formed, are more common. A catastrophe seems to happen on average once every three years but in 1998, due to the exceptionally heavy monsoon rains, there were at least two such major land slides.

9. Epilogue

The villagers were very happy to give their story. Apparantly, no officials visited them and only a helicopter flew by to inspect the valley and lake. Compensation for the lost houses, cattle and other damages is out of the question.
Remote mountain villagers in Nepal live a very simple life. One has the feeling (or fantasy) of returning to peaceful times of the Middle Ages or even earlier. Charming, but a hard life, especially when disasters strikes.

10. Acknowledgements

I would like to thank Lhakpa Geljen Sherpa of the village of Tangnag for the full report on the glacial lake burst and the Sherpa guides of the 1998 Trek to Mera Peak for back-ground information on glacial lake and land slide lake bursts.
Mr. Shree Kamal Dwivedi, Water and Energy Commission Secretariat, Kathmandu, provided the earth quake data with courtesy of Mr. Madhav Raj Pandey, National Seismological Centre, Department of Mines and Geology, Kathmandu.

11. References

Overview of harzardous glacial lakes in Nepal. Photograph of lake before the dam collapse from this site.


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