Why in news? A glacial outburst occurred in north Sikkim after the South Lhonak Lake burst due to incessant rains.

Highlights:

• Glacial outburst caused the rise of water levels in Teesta river that flooded at least four districts of Sikkim

What is Glacial Lake Outburst Flood?

• A glacial lake outburst flood (GLOF) is the sudden and destructive flood resulting from release of water that has collected in former glacier beds.
• Glacier melt is often channelled into rivers, but ice or the build-up of debris can form what is effectively a natural dam, behind which a glacial lake builds.
• If these natural dams are breached, large quantities of water can be released suddenly from the lakes, causing devastating flooding.

What are the reasons for GLOF?

• Glacier retreat: Glaciers retreat and melt water collects at the front of the glacier, forming a lake. These lakes can suddenly burst and create a fast-flowing Glacial Lake Outburst Flood (GLOF) that can spread over a large distance from the original site
• Avalanches or landslides: The massive redistribution of snow can sometimes cause a flash-flood; causing more damage to the surrounding areas, rivers become rerouted, and towns and ski resorts find themselves cut off until the damage and debris is cleared.
• Earthquakes: Seismic activity can trigger GLOFs by causing the ground to shake and destabilize natural barriers or by triggering avalanches or landslides that impact the damming material.
• Volcanic eruptions: Volcanic eruptions can melt ice and snow, creating temporary lakes on the volcano’s surface. These lakes can rapidly fill and overflow if the eruption generates enough heat to melt the ice and snow, leading to a GLOF.
• Climate change: Glaciers are retreating due to climate change. The increase in the anthropogenic footprint in the glaciers leads to the increasing threat of GLOFs, and over 200 glaciers in the Himalayas are vulnerable to outbursts. When a glacial lake bursts, its water flows into downstream areas at extreme speed.

What are the measures to overcome the GLOF?

• Robust hazard and risk assessment: It will provide the basis for prioritising, designing, and implementing risk management strategies with urgent up-to-date information to define the possible size and frequency of hazards in mountain regions, and identify vulnerable and exposed communities and infrastructure.
• Regular monitoring of glacial lakes : It is done using satellite observations is crucial for maintaining an up-to-date lake inventory for first-order GLOF risk assessment annual updating of lake. Inventories should be undertaken, particularly in monsoon affected areas where landslide dammed lakes are also a primary concern, while the length of time between comprehensive mapping efforts should not exceed 5 years.
• Regional cooperative initiatives: It should be considered regarding lakes located upstream in Tibet, and to a lesser extent in Nepal, as these lakes can threaten the IHR. Early identification of such trans boundary threats is important, to enable timely communication and exchange of information between neighbouring countries.
• Spatial planning: It is among the most efficient and sustainable disaster prevention measures in the long term. Hazard maps provide important tools for such land use planning by preventing (new) constructions in high hazard zones and allowing for the implementation of specific structural risk reduction measures
• Early Warning System : They are commonly agreed upon as the most effective approach to disaster risk reduction in communities that are exposed to climate-related disasters.
• Capacity Building : Efforts to develop capacities should focus both on training of professionals and practitioners, and strengthening academic education in relevant disciplines from natural and social science

Way forward

• Coordinated approach such as multiple agencies promptly sharing satellite images (that are trained towards the Himalayas) and a network of sensors to provide adequate warning. GLOF events can be anticipated as can monitor changes in the size of lakes with greater coordination.