Glacier Lake Bursts in Bhutan

Upper drainage of Mochu, showing glacier lakes. (Source: Google Earth)
Upper drainage of Mochu, showing glacier lakes. (Source: Google Earth)

On the morning of Sunday 28 June, an earthquake in India caused a Glacial Lake Outburst Flood in northern Bhutan.  Local residents alerted officials, who activated warning systems and ordered evacuations downstream. Rivers  rose to high levels, but no fatalities occurred. By Monday night, the rivers had begun to fall.

Map of 27 June earthquake, courtesy of the USGS
Map of 28 June earthquake, courtesy of the USGS

The United States Geological Survey reported an earthquake of 5.5 on the modified Richter scale at 7:05 AM local time, at 17km north-northeast of the town of Basugaon, in Assam State, India and 22 km south of the town of Gelephu in  Sarpang District, Bhutan.

Light to moderate shaking was reported from Nepal and Bangladesh as well as Bhutan and India. Sonam Choden in Thimphu in western Bhutan reported on Facebook “the earthquake rocked my husband right back on to sleeping.” Sangay Wangchuk, who lives in Jakar in central Bhutan, wrote “Ap Naka wags its tail again.” Ap Naka means “father earthquake,” referring to the common belief that the earth is held by a giant male spirit whose movements cause earthquakes.

The immediate damage in Bhutan was negligible, and even in India it was slight. Three persons sustained minor injuries when an old wall collapsed near the railway station in Kokrajhar, Assam, injuring three people. At an ancient temple in Chirang district, Assam, a sculpture of a lion was knocked off its base.

A glacial lake, Lemthang Tsho, located about 95 km northwest of the epicenter, burst later that day. This lake, also known as Shinchila Tsho, is located in Laya County in Gasa District in northern Bhutan, close to the border with China.   According to Kuensel, Kinley Dorji, a county official  in Laya, stated that mushroom collectors in the high pastures near glaciers had called him to let him know about the outburst from the lake, which is one of the sources of the Mochu, a major river of Central Bhutan. He, in turn, alerted district officials in Gasa and in Punakha and Wangdue, two large districts downstream on the Mochu. He also spoke with police, hospitals and officials at a large hydroelectric station at Punatsangchu.

Flooding on the Mochu River, courtesy of Kuensel via Facebook
Flooding on the Mochu River, courtesy of Kuensel via Facebook

Officials at the three major gauges along the Mochu monitored the water levels closely. They began sounding the sirens around 6:30 pm, even before the rivers reached the level for alerts, because they were concerned about additional risks from the monsoon rains, which had been heavy during the preceding weeks. The sirens caused panic among many residents, and they were turned off after more than an hour. The Prime Minster ordered evacuations along the Mochu River and at the hydropower station at 9:30pm, and reports suggest that these were largely complete within an hour. Patients at a hospital close to the river were moved to a military hospital at higher ground.

The river peaked late that evening, with high waters at Punakha a bit before midnight and at Wangdue later on. Fortunately, the towns were not damaged. The historic fortress or dzong of Punakha had been partially destroyed by a glacier lake outburst flood in 1994, so residents were concerned. The residents returned to their homes the next morning. Power, which had been cut in Punakha, was also restored.

Teams traveled through the area on 29 and 30 June to examine the damage. They reported that six wooden bridges had been washed out, isolating some villages and Laya town, and impeding the assessment efforts. Several groups of mushroom collectors were stranded on the far side of the now-empty Lemthang Tsho lake.

Karma Dupchu , the chief of the Hydrology Division within Department of Hydrometeorology,  will send a delegation to the glacier lakes high in the Mochu drainage, to see which of them burst, and to assess the relative importance of the earthquake and the heavy rains in causing the flood.

Rebuilding efforts already began by 30 June, as shown by a tweet from the Prime Minister Tshering Tobgay




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