A Glacial Lake Outburst Flood (GLOF) has been suspected as the cause behind the recent flash floods in Chamoli district of Uttarakhand. A GLOF occurs when the water dammed by a glacier or a moraine is suddenly released, leading to a potentially catastrophic flooding downstream. The National Disaster Management Authority (NDMA) had released guidelines in October 2020 on how to handle and mitigate the destructive force of GLOFs.
The Formation of Glacial Lakes
Glacial lakes are primarily formed at the lower end of a glacier. As the glaciers shift and flow, they erode the surrounding soil and sediment, creating grooves and depressions. These indents are then filled by meltwater from the glacier, forming a lake. There are several types of glacial lakes such as supraglacial, proglacial and subglacial which respectively form on the surface, in front, and underneath the ice.
These lakes can impact the movement of the glacier by reducing friction, promoting basal sliding, and influencing the albedo effect which leads to an increase in surface melt. Additionally, these lakes pose a hazard when their unstable moraine and ice dams fail, triggering a GLOF.
Rise in Glacial Lake Numbers
Due to rising global temperatures and consequent receding glaciers, scientists have witnessed a rapid increase in the number of glacial lakes, which pose a significant risk due to their potential to create large scale flooding and destruction. The disaster at Kedarnath in 2013 was one such example where a breach in a large glacial lake triggered devastating flash floods. A study by the Central Water Commission (CWC) found a significant number of glacial lakes and water bodies in the Indus, Ganga, and Brahmaputra basins.
Guidelines for Reducing GLOF Risk
The NDMA has laid out guidelines to mitigate risk posed by the GLOFs. Among the measures proposed include identifying potentially dangerous lakes through field observations, records of past events and geological characteristics. NDMA also calls for promoting the use of Synthetic-Aperture Radar imagery to detect changes in water bodies.
In order to structurally manage the potentially hazardous lakes, the NDMA recommends reducing the volume of water with methods such as controlled breaching, pumping or siphoning out water, and tunneling through the moraine barrier or under an ice dam.
Proactive Measures and Community Involvement
NDMA also suggests establishing a broad framework for construction in vulnerable zones and enhancing early warning systems. The authority calls for training local manpower which often plays a vital role in search and rescue before specialized teams arrive. Community involvement includes planning and setting up emergency shelters, distributing relief packages, identifying missing people, and addressing the needs for food, healthcare, water supply etc. Moreover, implementation of comprehensive modern alarm systems using cell and smartphones is also encouraged.
