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Picture Book: Glacial Lake Breach, Mera Peak region, Nepal, October 1998.

Female Tamang porters; background a glacial lake breach in the natural moraine wall of the Sabai Tso Lake.

Three young female porters, carrying about 15 kg each. This is a light load as it is the second last day of the trek to Mera Peak. They are now returning. Tomorrow we will arrive in Lukla.

Loads for female porters are normally 20-25 kg, for men between 30 and 40 kg, depending if they want to take an additional 35% for extra pay. Their dresses were very clean for the last three weeks, until a few days ago. Normally they would wash them every few days.

Inseveral isolated camps in the mountains surrounded by barren rocks, they were chanting at night. Their crisp and clear girl voices carried a long way in the cold, dead calm, freezing nights. Songs were about hardship and missing loved ones.

I recorded an hour of their songs.

In the back ground is a 100 meter high glacial dam with a 50 meter deep breach that was formed in early September 1998, a month ago, see below for the dam before and after the breach. This was formed by a big piece of the hanging glacier falling in the lake, see below. For two hours the water was flowing over the dam, undermining it, and then the dam burst. The lake is a half square km in size and the lake level dropped by 50 m. The lake level went down in a matter of a few hours. The enormous amount of water released made a devastating flood some 200 wide and 10 m high, carrying boulders of up to 2 m. Only the biggest rocks, some 3-5 m across, seemed to have hardly moved.

The main cause of the glacial instability was the warm monsoon summer weakening the hanging mountain glacier, see picture below. An earth quake, very common in this area, may have finally triggered it.

Most glacial lakes in the Himalayas have a breach. Those still full of water, could burst any time so they are under surveillance. A famous example is the Tso Rolpa Lake in Rolwaling, about 30 km to the West from here, which has a 100 meter high dam and a size of 1.4 square kms.

Also see: Detail description Sabai Tso glacial lake outflood, September 1998.

Sabai Tsho Lake before (left) and ....................................................................................... after (right) the breach.

Overview of the lake before the breach. Hanging glacier piece that broke of above the lake, right side.

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