The Geological Survey of India has through remote sensing and multispectral data found 13 of 486 glacial lakes in Uttarakhand to be vulnerable.
A glacial lake can breach causing outburst flood like the one in Chamoli on Sunday due to avalanche or landslip in its periphery, cloudburst in the catchment, a major quake and other geological factors, GSI’s Director-General Ranjit Rath said in New Delhi on Monday.
“The glaciers in the Himalayas are retreating under climate change scenario. This is a global phenomenon,” Dr. Rath said, adding that glacial lake outburst flood (GLOF) can result in the discharge of a huge volume of water leading to severe damage downstream.
“With the passage of time, some of the glacial lakes near the terminus often coalesce and form large glacial lakes dammed by glacial moraines. The moraines comprising loose boulders, gravels and sand admixture often containing dead ice impart inherent weakness to these dams.”
These lakes are quite common on the debris-covered Himalayan glaciers with their lower part moving very slowly and at times remaining almost stationary. Sudden triggering mechanisms make them burst out, he said.
Dr. Rath said the GSI had during 2014-16 undertaken the compilation of an inventory of glacial lakes of the Uttarakhand Himalaya to identify high-risk areas for GLOF. This was done as a follow-up of the Kedarnath tragedy in June 2013.
“We identified 486 glacial lakes excluding the supra-glacial lakes and 13 of these were found to be vulnerable,” he said.
According to the GSI’s inventory, 71 lakes of different sizes and types are in the upper reaches of Rishiganga and Dhauliganga valley.
“The GSI is in the process of finding out the focal point of this unfortunate flash flood event. Right now, it is not clear whether the flood is a typical GLOF or some temporary damming due to a landslip and avalanche that might have blocked the mainstream to form a temporary lake which got burst.”
He said a team of experts will assess the damage and the trigger factor responsible for the outburst once the water level recedes.
“The floodwater and mudflow will lose steam and cause less harm to life and property in the lower reaches. However, people living close to the river should be properly alerted,” Dr. Rath said.