Glacial Lake Outburst Floods (GLOFs) | An Emerging Threat in a Warming World

Climate change refers to long-term shifts in temperature, precipitation and weather patterns. These shifts can be natural, due to changes in the sun’s activity or large volcanic eruptions as well as anthropogenically driven. Since the 1800s, human activities have been the main driver of climate change, primarily due to the burning of fossil fuels. The burning of fossil fuels generates greenhouse gas emissions (e.g., carbon dioxide and methane) that act like a blanket wrapped around the Earth, trapping the sun’s heat and raising atmospheric temperatures.

Climate scientists have shown that humans are responsible for virtually all global heating over the last 200 years. The average temperature of the Earth’s surface is now about 1.1°C warmer than it was in the late 1800s (Pre-Industrial Revolution) and warmer than at any time in the last 100,000 years (Holocene Epoch). Climate change has an increasingly large impact on the earth’s surface system and surrounding environment.

For instance, the amplified warming has contributed to significant retreat of ice bodies/or glaciers, thawing of permafrost, and sea ice decline, intense storms, droughts, and other weather extremes. Climate change threatens people with increased flooding, extreme heat, increased food and water scarcity, more disease, economic losses, etc. The World Health Organization (WHO) calls climate change the greatest threat to global health in the 21^st century.

Climate change has had a profound impact on snow/ice/glaciers worldwide, causing them to recede at an unprecedented rate. As global temperatures rise, glaciers melt more rapidly than they can accumulate new snow, leading to a net loss in glacier mass, known as glacier recession. Glacier recession has several significant impacts.

Firstly, it contributes to sea-level rise. Secondly, glacier recession can alter water availability. Lastly, glacier recession can lead to the formation of glacial lakes. When these glacial lakes burst, they can cause devastating floods in downstream areas generally called Glacial Lake Outburst Floods (GLOFs). GLOF is a type of outburst flood occurring when the water dammed by a glacier or a glacial moraine is released suddenly.

This can happen due to various reasons such as erosion, build-up of water pressure, avalanche of rock or heavy snow/or hanging glacier,  earthquakes, volcanic eruptions under the ice, or massive displacement of water in a glacial lake when a large portion of an adjacent glacier/or surrounding slope collapses into it. The terminal glacial moraine dam is inherently week and susceptible to failure under suitable triggers as it comprises poorly sorted and unconsolidated glacial material consisting of partly dead glacier ice within the debris material. Glacier/or moraine dams can break easily because they are generally weak structures and the pressure build-up can cause it to rupture and subsequently to fail.

When such natural dams break owing to pressure from accumulating water and external triggering agents, water gushes down in a powerful flow due to the built-up hydrostatic pressure and can lead to flash flooding and debris flow in downstream areas. This phenomenon is becoming increasingly common due to climate change and poses a significant threat to established infrastructure and communities living in downstream areas of the mountainous regions, globally. GLOFs remain a persistent threat to downstream communities and infrastructure, besides other flora and fauna.

GLOF events cause disastrous floods and claim thousands of lives including human lives. They occur when the water levels of glacial lakes breach their boundaries, causing large amounts of water to flow into nearby streams and rivers and hit the settlements downstream. They are generally rapid events, lasting for hours to days, and cause large downstream river discharges. When the water flows downstream suddenly with a high force, any human or natural structure in its wake is destroyed, including villages, power plants, road network, bridges and other infrastructure, etc.

Peak flows as high as 15,000 cubic meters per second have been recorded in such events. Increasing glacial melting because of climate change, alongside other environmental effects of climate change (viz. permafrost melting) mean that regions with glaciers are likely to see increased flooding risks from GLOFs.

This is especially true in the Himalayas, which is geologically more active as well. As per a recent study, about 15 million people, mostly in China, India, Pakistan, Peru, etc. are at risk from this type of cryospheric hazard. As the planet continues to warm, the frequency and intensity of GLOFs are projected/or expected to increase.

GLOFs are a significant and increasing hazard in the Himalayan region as well. The Himalayas are home to over 5,000 glacial lakes, of which more than 200 are considered vulnerable to outbursts – meaning these lakes are Potentially Dangerous Glacial Lakes (PDGL). The increasing threat of GLOFs in the Himalayas is attributed to climate change and the increase of anthropogenic footprints on glaciers and glaciated areas.

Glaciers in the Himalayas are shrinking very fast at the rate of 20 meters per year due to global warming and thereby, increasing the threat of GLOFs. GLOFs have occurred several times in the Himalayan region, causing significant damage to infrastructure and loss of life. Examples of previous GLOF events reported from the region include the Cirenmaco GLOF (11 July 1981), Jinco GLOF (27 August 1982), Dig Tsho GLOF (4 August 1985), Tam Pokhari (Sabai-Tsho) GLOFs (3 September 1998), and Jialongco GLOF (23 May and 29 June 2002). Moreover it is pertinent to note that during last decade, the Indian Himalayan region has witnessed many disastrous GLOF events. For instance, Kedarnath GLOF occurred on 17 June 2013.

It was triggered by an outburst from a lake formed by the right lateral moraine of the Chorabari Glacier and caused severe damage to the village of Kedarnath in the Indian Himalaya. Similarly, the Gya GLOF occurred on 6 August 2014, in the Gya village of Ladakh Himalaya. It was triggered when the glacial lake of the Gya glacier burst, causing a flood that hit the village of Gya, carried away a bridge and destroyed houses and farmlands in downstream areas.

Last year, on 3 October 2023, the South Lhonak Lake in the Himalayan state of Sikkim breached, resulting in a GLOF that ravaged four districts killing at least 42 people in addition to more than 77 people missing and destroying infrastructure in the area. Generally, GLOFs result in the destruction of major hydropower projects, thereby causing socioeconomic decline.

GLOFs pose a significant threat in the highly glaciated areas of Jammu and Kashmir, and Ladakh also. The retreat of glaciers owing to climate change has led to the formation of a large number of glacial lakes and rapid expansion of existing lakes in various mountain ranges including those of Jammu and Kashmir and Ladakh, making the region vulnerable to GLOFs. Experts have noted that there are more than 100 glacial lakes spread across different mountain ranges of these UTs, most of them located in Ladakh and Chenab valley.

The number and size of these lakes have shown an increase over time due to the enhanced melting of the mother glaciers under the changing climate. The valley of Kashmir, located in this region, is also home to numerous glacial lakes. As per our recent study, the total count of lakes, as well as their spatial extent, showed a discernible increase from 253 in 1990 to 324 in 2018, with a growth rate of 21.4%. The lake area has increased from 18.84 km² in 1990 to 22.13 km² in 2018 with a growth rate of 14.7%. Some of the stunning lakes are Krishnasar, Gangabal, Gadsar, Satsar, Shountsar and Vishansar.

These glacial lakes make the region vulnerable to GLOFs under changing climatic conditions, receding glaciers, degrading permafrost, extreme weather events and active Himalayan tectonics. Moreover, most water requirements are also met by glacier resources in this region. Therefore, the threat of glacier loss vis a vis GLOFs is not only an environmental concern but also a significant risk to water security.

In a recent development, Focused Glacial Lake Outburst Flood (GLOF) Monitoring Committee (FGMC) was constituted by the Government of Jammu and Kashmir to review the current status of glaciers and glacial lakes in the region. The committee is tasked with identifying the vulnerable glacial lakes in terms of GLOF, as per the information provided by the National Disaster Management Authority. This committee will play a crucial role in monitoring and managing the threat of GLOFs in the region.

The National Institute of Hydrology (NIH), Roorkee and its Regional Centres have been actively involved in research and training programs related to Glacial Lake Outburst Floods (GLOFs). They have organized workshops and training programs on various aspects of hydrology, including the impact of climate change and the management of glacial and mountain hazards. One of the significant contributions of NIH, Roorkee has been the organization of a brainstorming workshop on the “Preparation of Guidelines for Management of Glacial Hazards & Risks especially GLOF & LLOFs” jointly with the National Disaster Management Authority (NDMA), Delhi. This workshop was aimed at preparing guidelines (SOP) for managing the risks associated with GLOFs.

As for the Standard Operating Procedure (SOP) for GLOF monitoring, it provides a standard working tool for operators, managers, and other stakeholders engaged during GLOF events. The SOP covers various aspects, including the objectives of GLOF monitoring and warning, management and operation of GLOF monitoring and warning, repair and maintenance of GLOF Early Warning System (EWS) facilities, and monitoring and dissemination of warnings. While NIH contributes to the understanding and management of GLOFs, the implementation of SOPs for GLOF monitoring would involve multiple stakeholders, including local authorities and communities guided by the specific geographical and climatic conditions of the area.

It is important to mention that NIH has a well-established “Western Himalayan Regional Centre (WHRC)” at Jammu. WHRC is looking after the Western Himalayan Region and has a well-equipped Glacial Research Field Station in Leh District, Ladakh. The RC focuses on several key objectives that address the unique challenges faced by the Western Himalayan Region (comprising the UTs of Jammu & Kashmir and Ladakh as well as the State of Himachal Pradesh and hilly parts of Uttrakhand) such as hydrological and disaster risk reduction including the Climate Change Impact Analysis, Flood and River Basin Modelling, Mountain Hazards Susceptibility Analysis including Landsides and GLOFs, Cryosphere Studies and Disaster Risk Reduction (DRR), etc.  These objectives guide WHRC’s research and development initiatives, helping to address the region’s unique hydrological challenges, geological and cryospheric hazards under changing climatic conditions towards sustainable water resource and disaster management in the region.

Climate change is not only an environmental, social, economic, and political issue that affects every aspect of our lives but also a global challenge that requires urgent attention and action to mitigate the impacts.  In the Himalayas, the glacier mass loss rates have persistently increased during recent years in response to climate warming. As per studies, an increase in summer temperature explains the long-term trend in glacier mass loss and now appears to mainly drive mass loss even in regions formerly sensitive to both temperature and precipitation.

Climate change is causing significant glacier recession, which in turn is leading to changes in water availability, and increased risk of GLOFs. As such, GLOFs represent a catastrophic phenomenon of the Himalayas and pose a risk to downstream communities and infrastructure, etc. Himalayan glaciers are melting fast, with a 40 percent increase in their melt water discharge recorded in the last decade. As the planet continues to warm, the glacier recession and glacial lake formation vis a vis the frequency and intensity of GLOFs are projected to increase.

Similarly, the threat of GLOFs in Jammu and Kashmir and Ladakh region is becoming real and significant under rapid glacier loss and permafrost degradation due to changing climatic conditions. As such, the above cited disastrous events are a stark reminder of the risks posed by glacial lakes in the Himalayan region, particularly in the context of climate change, retreat of glaciers and increasing anthropogenic developmental activities in the fragile Himalayan ecosystem.

It therefore, underscores the need for comprehensive monitoring of glacial lakes and the implementation of early warning systems to mitigate the risks associated with GLOFs. Additionally, there is also a need for sustainable land-use planning and adaptation of disaster risk reduction measures in vulnerable regions like Himalayas. It is crucial that we understand and address these emerging threats to mitigate its impacts and safeguard our future, well in time.

By Dr. Riyaz Ahmad Mir (He is a Scientist at National Institute of Hydrology, Western Himalayan Regional Centre, J&K, Jammu)