 "EXPLAINED: GLOF And LLOF – Understanding The Devastation Unleashed By Himalayan Lakes; Can They Be Prevented?")
Uttarkashi: An Indian Army personnel carry out rescue operations following a landslide triggered by heavy rainfall at Dharali in Uttarkashi (PHOTO: IANS) The Himalayas are increasingly coming under the glare for glacier-related catastrophes, usually with such jargon as GLOF and LLOF—abbreviations of the risks associated with glacial and landslide-dammed lakes. Though widely debated, are they identical, or is there a vital distinction? This article explored what GLOF and LLOF consist of, how they vary, and their past record of massive catastrophes in India.
These two categories of floods result from the sudden outbursts of water from mountain lakes but have distinct mechanisms of formation and impact.
GLOF (Glacial Lake Outburst Flood)
Definition: A GLOF is caused by the sudden collapse of a natural dam containing a glacial lake (created through ice melting, which may consist of moraine, ice, or rock) allowing a burst of water to flow downstream, leading to disastrous floods.
Mechanism: Glaciers melt into lakes. If the structural integrity of the moraine dam is weakened by heavy rainfall, earthquakes, or internal structural flaws, the dam may fail, causing a catastrophic flood wave.
Threat: GLOFs can result in extensive damage over long distances, impacting river systems, demolishing infrastructure such as roads and houses, and seriously threatening downstream communities.
Definition: An LLOF is formed when a landslide dams a river or valley and forms a temporary lake. When the natural dam created by the landslide material breaks, the stored water suddenly comes out.
Process: An earth mass movement (landslide) blocks the natural flow of a river, and water comes to be stored upstream. The landslide dam, if unstable or overwhelmed by a heavy rainfall, bursts.
Threat: LLOFs are more localized in impact but frequently are high-velocity flows that carry large amounts of debris with them, and thus are very destructive right next to the breach point.
Scientific Fact: GLOFs, as per the International Centre for Integrated Mountain Development (ICIMOD), have the potential to discharge 10-100 cubic meters of water per second per event, while LLOFs range from 1-10 cubic meters per second.
Example Difference: The 2013 Kedarnath disaster was a typical case of a big GLOF, while the 2021 Chamoli event, although a glacier was involved, possessed characteristics of debris-laden flow like some LLOF mechanisms, although its trigger mechanism was complicated.
The Indian Himalayan area is extremely prone to such glacial and landslide-driven calamities. Let's have a glance at some major incidents:
GLOF Events
Location: Kedarnath, Uttarakhand.
Impact: Excess of 5,700 lives were lost and over 1,000 sq km of area was ruined.
Cause: Heavy precipitation (350 mm) blended with glacial melting made the lake's natural moraine dam weak.
Fact: A study by ISRO found debris spread over 20-22 km.
Location: Kumaon region, Uttarakhand.
A glacial lake burst triggered floods in the Alaknanda river, impacting various villages.
Cause: A mix of snowmelt and earthquakes.
Fact: The incident entailed a release of 10-15 cubic meters of water per second.
Location: Rishiganga Valley, Uttarakhand.
Impact: A glacial event resulted in around 200 fatalities and the collapse of the Tapovan dam.
Cause: Initially considered to be a GLOF, subsequent studies indicated it was a multifaceted event initiated by a rock and ice avalanche, forming a temporary lake that burst.
Fact: Around 15 million cubic meters of debris at a rate of 20 meters per second.
LLOF Events
Location: Kinnaur, Himachal Pradesh.
Impact: Landslide formed a temporary lake on the Sutlej river, which later breached and resulted in floods.
Cause: Monsoon rains (150 mm) and unstable soil conditions.
Fact: The event involved 5-10 cubic meters of water per second and affected 25 people.
Location: Mandi, Himachal Pradesh.
Impact: A landslide blocked a stream, and its subsequent breach destroyed 500 hectares of land.
Cause: A cloudburst (100 mm per hour).
Fact: Approximately 10-15 houses were destroyed.
ICIMOD (2023): The Hindu Kush-Himalayan area has more than 2,000 glacial lakes, out of which 200 are recognized as being high-risk. The risk of GLOF events is on the rise by 10-15% per year.
ISRO Landslide Atlas (2023): There are 147 landslide-prone districts in India, enhancing the threat of LLOF events.
IPCC (2021): Glaciers are melting by 0.5-1% every year due to climate change, heightening the risk of GLOF events.
Wadia Institute of Himalayan Geology: Almost 70% of Himalayan slopes are prone to seismic and climate-related hazards.
Future Threat: Estimates show that 30-40% of the glaciers would melt by 2050, thus possibly doubling the number of GLOF and LLOF occurrences. Almost 100,000-120,000 square kilometers of the Himalayas fall under the fragile category.
Solutions:
Improved Monitoring: Use satellites and sensors for real-time monitoring of glacial lakes.
Limited Construction: Ban constructions in areas prone to landslides.
Forest & Water Management: Enforce strong forest protection measures and enhance natural drainage systems.
Local Preparedness: Offer extensive disaster management training to local people to respond immediately.
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