Reviewing Scientific Assessment Data On Imja Glacial Lake And GLOF For The Activity Of Component I Of Community Based Flood And Glacial Lake Outburst Risk Reduction Project
Himalayan glaciers cover about three million hectares or 17% of the mountain area as compared to 2.2% in the Swiss Alps. They form the largest body of ice outside the polar caps and are the source of water for the innumerable rivers that flow across the Indo-Gangetic plains. Himalayan glacial snowfields store about 12,000 km3 of freshwater. About 15,000 Himalayan glaciers form a unique reservoir which supports perennial rivers such as the Indus, Ganga and Brahmaputra which, in turn, are the lifeline of millions of people in South Asian countries (Pakistan, Nepal, Bhutan, India and Bangladesh) (IPCC WGII AR4).
Glaciers are highly sensitive to climate change due to their relatively quick response. Climate cooling results in glacier advancement and warming leads to glacier retreat; so they are excellent indicators of climate change. Hence, recent glacial retreat and concomitant glacial lake formations/expansions in mountain areas serve as an example and infallible testimony of climate change. As glaciers retreat, lakes commonly form behind the newly exposed terminal moraine. The rapid accumulation of water in these lakes can lead to a sudden breach of the moraine dam. The resultant rapid discharge of huge amount of water and debris is known as a glacial lake outburst flood (GLOF). These GLOF events may result into catastrophic damage to the downstream areas.
In Nepal there are 3,808 glaciers with a total area of 4,212 sq.km and 1,466 glacial lakes. Nine lakes were mapped in the Nepalese part of the Mahakali River basin with a total area of 0.137 sq.km; 742 lakes were mapped in the Karnali basin with a total area of 29.147 sq.km — the largest number and greatest lake area in any one basin; 116 glacial lakes were mapped in the Gandaki basin with a total area of 9.538 sq.km — the largest average size in any basin (0.082 sq.km); and 599 lakes were mapped in the Koshi basin with a total area of 25.958 sq.km. Similarly, the majority of lakes are moraine-dammed (975 lakes occupying 72% of the total lake area); supra-glacial lakes are mostly small with an average size of 0.009 sq.km and these represent only 1.5 % of the total glacial lake area; erosion lakes represent 17% of the total lake area; and other glacial lakes represent 9.5%.
This report on Imja Glacial Lake is based upon information gathered through personal communication and published reports from different organizations working on glacial lake issues such as International Centre for Integrated Mountain Development (ICIMOD), Water and Energy Commission Secretariat (WECS), Department of Hydrology and Meteorology (DHM), United Nations Development Program (UNDP), World Bank and Kathmandu University. It also reviewed and analyzed almost all studies carried out on Imja and Tsho Rolpa Glacial Lakes of Nepal. It also gathered information of Raphstreng, Luggye and Thorthormi Glacial Lakes of Bhutan and few glacial lakes of Cordillera Blanca, Peru. Almost all glacial lakes in Nepal and Bhutan are formed in 1950s and then gradually grown up along with warming climate in this region.