Revisiting 1985 Dig Tsho GLOF site: Himalayan GLOF risk assessment by ICIMOD

The memories of the sudden flood of black water that washed away their entire livelihood still haunt Lhakpa Chamjee and Ang Maya, even though the ICIMOD research team estimates Dig Tsho lake to be considerably more safe at the moment.

23 years after the GLOF occurred on 4 August 1985, ICIMOD's research team revisited the Dig Tsho Glacial Lake Outburst Flood (GLOF) site and downstream river banks on 10th April 2008 as part of the ongoing Eco Everest expedition (www.ecoeverest.net.np). The Dig Tsho GLOF site is in the Langmoche and Bhote Koshi valleys. The purpose of the visit was to study the present conditions.

The analysis of temporal series of satellite images show that the size of the Dig Tsho lake seems stable. The present observations show that further retreat of the steep Langmoche glacier will not cause the lake to further expand at the far end as the glacier retreat will only expose the bed rock. The present outlet of the lake is at the same level as the Langmoche river bed and a large mass failure at breach area that can close the outlet causing rise of the lake water level can be ruled out. This observation supports the view that a second outburst from Dig Tsho Lake seems unlikely.

Even though the likelihood of a second GLOF from Dig Tsho is small the threat of GLOFs in general in the valley remains, as there are several other glacial lakes in the vicinity. These are growing rapidly, and could potentially reach a stage where an outburst could happen. Such events threaten the very livelihoods of local people and economy. Regular scientific monitoring with in-situ measurements of these lakes is necessary to take preventive measures to safeguard the mountain communities and the environment. As part of the EcoEverest Expedition the ICIMOD research team will conduct a detailed field investigation and establish a pilot early warning system in Imja lake, in collaboration with Department of National Park and Wildlife Conservation and Keio University of Japan.