The breach can be caused by several reasons — in this particular case, for instance, an avalanche was reported in the region two days ago.
A glacial lake burst, a cloud burst or an avalanche, the impact of climate change or “development” — scientists are not sure what triggered the sudden surge of water near Chamoli in Uttarakhand Sunday morning that briefly raised fears of a repeat of the 2013 disaster in the state.
By evening, the prospect of largescale flooding and destruction had receded. And, as scientists prepared to travel to the site in the high mountains north of Chamoli to ascertain the cause of the incident, the scenario being most talked about was what glaciologists like to call a GLOF, or glacial lake outburst flood. It is a reference to flooding caused downstream due to a breach in a glacial lake.
Retreating glaciers, like several in the Himalayas, usually result in the formation of lakes at their tips, called proglacial lakes, often bound only by sediments and boulders. If the boundaries of these lakes are breached, it can lead to large amounts of water rushing down to nearby streams and rivers, gathering momentum on the way by picking up sediments, rocks and other material, and resulting in flooding downstream.
GLOF events are not unusual, but their impact depends on the size of the proglacial lake that burst, and location. The breach can be caused by several reasons — in this particular case, for instance, an avalanche was reported in the region two days ago.
But while GLOF is being considered to be the most likely trigger for Sunday’s event, there are questions surrounding this possibility. “We don’t know of any big glacial lakes in this region. An avalanche is quite common, and there could have been one, but an avalanche on its own would not result in an increase in the flow of water in the river. The water has to come from a source, and as of now, we do not know what this source is,” said Professor H C Nainwal, a glaciologist at the Hemwati Nandan Bahuguna Garhwal University in Srinagar, Uttarakhand.
“We would have to visit the area to find out what exactly happened. Till then, we can only speculate,” he said.
Argha Banerjee, a glaciologist who works at the Indian Institute of Science Education and Research (IISER), Pune, said it was possible that a glacier lake was present in the area but not known to scientists.
Source: The Indian Express