Uttarakhand was shaken after a massive glacier broke off at Chamoli district on Sunday, triggering a massive flood that caused immense damage. Hundreds of people are reported to be missing from regions near Alaknanda and Dhauliganga rivers. Reports later revealed that the incident was, in fact, a glacial lake burst flood or GLOF. But what really is GLOF and how does it occur?
What are GLOFs?
According to the United Nations Spider Knowledge Portal, GLOF is a sudden release of a massive amount of water which is held in a glacial lake. In case you remember your geography classes, you’d remember that glaciers are essentially large bodies of ice moving slowly.
It leaves a considerable impression on the ground while it’s moving – This is at times filled with water and as the temperature gets warmer, more and more water is accumulated in these cavities.
How can GLOF’s occur?
GLOFs can occur for a variety of reasons – If there is a build-up of water pressure, an avalanche involving rocks and heavy snow, erosion, or earthquakes.
Global warming is another major reason that causes icy mountains to melt under high temperatures causing a rise in unstable moraines.
A 100-year old GLOF has an average discharge of 15,600 cubic metres per second which can be identical to monsoonal river discharges hundreds of kilometres downstream.
What Dr Ranjit Rath, Director General, Geological Survey of India said?
While addressing a press gathering at Shastri Bhawan in New Delhi, Dr Ranjit Rath, DG GSI said, "The glaciers in Himalaya are retreating under climate change scenario. Such a recession is a global phenomenon. With the passage of time, some of the glacial lakes near the terminus often coalesce together and form large glacial lakes dammed by glacial moraines. The constitution of the moraines comprising loose boulders, gravels, sand admixture often containing dead ice, imparts inherent weakness to these dams.”
He added, “These lakes are quite common on the debris-covered Himalayan glaciers wherein the lower part of the glacier moves very slowly and at times remains almost stationary. The breach glacial and outbursts, termed as Glacial Lake Outburst Flood (GLOF), can result in the discharge of a huge volume of water leading to severe damage in the areas falling in the downstream region.”
GSI is in the process of finding out the focal point of this unfortunate flash flood event:
As per the Inventory prepared by GSI on glacial lakes in Uttarakhand, a total of 71 lakes of different sizes and types are reported in the upper reaches of Rishiganga and Dhauliganga valley. 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 Glacial Lake Outburst Flood (GLOF) or some temporary damming due to a landslide and avalanche that might have blocked the mainstream to form a temporary lake which got burst. Once the water level recedes a team of experts will assess the damage as well as the triggering factor responsible for the outburst. As far as the lower reaches are concerned, by the time the floodwater and mudflow reach the lower path it will lose its steam and cause less harm to life and property, However, people living close to the river should be properly alerted.”