Glacier Lake Outburst Floods

What are Glacial Lake Outburst Floods?

A Glacial Lake Outburst Flood (GLOF) is a catastrophic release of water from a glacier lake, i.e. a water reservoir that has formed either at the side, in front, within, beneath or on the surface of a glacier. The dam that impounds the water body may be composed primarily of  debris, bedrock or glacial ice.

Ice-dammed lakes can develop at the margin of an advancing glacier, when side-valleys or depressions at the side of the glacier become blocked. Many such lakes formed in the past during former Ice Ages. Many ice-dammed glacier lakes form and  drain repeatedly. Lake Merzbacher in Kyrgyzstan, which drains every year, is one of the most famous and best investigated ice-dammed glacier lakes in the world. Over time, as glaciers retreat, the support of the ice dam is removed and the lake may drain catastrophically, or remain trapped behind piles of debris (moraines) left behind by the former glacier. The recent 2013 GLOF disaster in Kedarnath, India, involved failure of such a lake.

Outbursts from lakes at the surface (supraglacial), within or beneath a glacier, have also been described across most mountain regions of the world, often triggered by heavy rainfall or enhanced melt during warm weather. Recent studies from the Tien Shan have shown that frequent monitoring is required to identify rapidly evolving dangerous situations. In Central Asia, these highly dynamic lakes, that can form and drain rapidly, are termed “non-stationary” lakes, and represent a special challenge for early warning and response strategies.

The widespread retreat of mountain glaciers over the past century resulted in the formation of numerous new glacier lakes trapped behind moraines in many mountain regions of the world. Some of these lakes are spectacularly large with volumes of up to 100 million m3, and depths exceeding 200 m.  Large piles of steep glacial moraine are unstable, and can contain slowly thawing ice, meaning they can be weak and prone to failure. Intense rain or snowmelt or the generation of tsunami waves from landslides into the lake are common triggers of GLOFs from moraine dammed lakes. Earthquakes are a concern, because they both trigger landslides into a lake, or directly destabilise a dam.

In rare instances, tsunami waves from large landslides can overtop a moraine dam and cause an outburst event without actually destroying  the dam, meaning that the threat of secondary events remains. For lakes dammed by solid rock, tsunami  waves are the only mechanism by which a catastrophic flood may be initiated, as the dam structures themselves are considered stable.

Once initiated, GLOFs tend to mobilise large amounts of debris and can transport massive boulders, particularly in the steep river sections. This is particularly true for floods from moraine dammed lakes, which frequently transform into debris or mud flows. Several transitions of these flow types, depending on the steepness and therefore erosive power of the river, are typical for GLOFs . Importantly,GLOFs typically produce discharge values, erosive forces and hence also impacts that are far greater than normal seasonal floods. However, unlike seasonal floods, GLOFs tend to rapidly lose their power downstream which has implications for potential impacts and losses on the lowlands. Nevertheless, flood paths extending up to hundred kilometers and even more have been observed, including events involving more than one country (transboundary GLOFs), while secondary hazards can occur owing to erosion of river banks,blocking of river channels and impacts into downstream lakes.

Given potential future expansion of lakes as the climate warms and glaciers melt, and the rapidly increasing exposure of residential, tourism, transport, and hydropower infrastructure higher into the alpine valleys, a significant increase in future GLOF risk is anticipated globally. Therefore, robust scientific assessments are urgently needed to underpin the design of response and mitigation strategies by national- and regional stakeholders.

This text is a plain-language summary of the paragraph of GLOFs from the GAPHAZ guidelines.

GAPHAZ 2017: Assessment of Glacier and Permafrost Hazards in Mountain Regions – Technical Guidance Document. Prepared by Allen, S., Frey, H., Huggel, C. et al. Standing Group on Glacier and Permafrost Hazards in Mountains (GAPHAZ) of the International Association of Cryospheric Sciences (IACS) and the International Permafrost Association (IPA). Zurich, Switzerland / Lima, Peru, 72 pp.

Suggested readings:

Allen, S. K., Linsbauer, A., Randhawa, S. S., Huggel, C., Rana, P. and Kumari, A.: Glacial lake outburst flood risk in Himachal Pradesh, India: an integrative and anticipatory approach considering current and future threats, Nat. Hazards, 84(3), 1741–1763, doi:10.1007/s11069-016-2511-x, 2016.

Benn, D. I., Bolch, T., Hands, K., Gulley, J., Luckman, A., Nicholson, L. I., Quincey, D., Thompson, S., Toumi, R. and Wiseman, S.: Response of debris-covered glaciers in the Mount Everest region to recent warming, and implications for outburst flood hazards., Earth Sci. Rev., 114, 156–174, 2012.

Carey, M., Huggel, C., Bury, J., Portocarrero, C. and Haeberli, W.: An integrated socio-environmental framework for glacier hazard management and climate change adaptation: lessons from Lake 513, Cordillera Blanca, Peru, Clim. Change, 112, 733–767, 2012.

Cenderelli, D. A. and Wohl, E. E.: Flow hydraulics and geomorphic effects of glacial-lake outburst floods in the Mount Everest region, Nepal, Earth Surf. Process. Landforms, 28(4), 385–407, doi:10.1002/esp.448, 2003.

Emmer, Adam & Mergili, Martin & Veh, Georg. Glacial Lake Outburst Floods: Geomorphological Agents and Hazardous Phenomena. 10.1016/B978-0-12-818234-5.00057-2, 2021.

Frey H, Haeberli W, Linsbauer A, Huggel C, Paul F.: A multi-level strategy for anticipating future glacier lake formation and associated hazard potentials. Natural Hazards and Earth System Science 10:339–352.  httpss://, 2010.

Frey, Holger: Glacier lake outburst floods. In: Richardson, Douglas; Castree, Noel; Goodchild, Michael F; Kobayashi, Audrey; Liu, Weidong; Marston, Richard A. (Eds.) The international encyclopedia of geography: people, the earth, environment, and technology, 2017.

Huggel, C., Haeberli, W., Kääb, A., Bieri, D. and Richardson, S.: An assessment procedure for glacial hazards in the Swiss Alps, Can. Geotech. J., 41, 1068–1083, 2004a.

Kargel, J., Leonard, G., Shugar, D. H., Haritashya, U. K., Bevinton, A. and Fielding, E. J.: Geomorphic and geologic controls of geohazards induced by Nepal’s 2015 Gorkha earthquake, Science (80-. )., 351, doi:10.1126/science.aac8353, 2016.

Narama, C., Duishonakunov, M., Kääb, A., Daiyrov, M. and Abdrakhmatov, K.: The 24 July 2008 outburst flood at the western Zyndan glacier lake and recent regional changes in glacier lakes of the Teskey Ala-Too range, Tien Shan, Kyrgyzstan, Nat. Hazards Earth Syst. Sci., 10(4), 647–659, 2010.

Narama, C., Daiyrov, M., Tadono, T., Yamamoto, M., Kääb, A., Morita, R., Ukita, J. and Shan, T.: Seasonal drainage of supraglacial lakes on debris-covered glaciers in the Tien Shan Mountains, Central Asia, 2017.

Quincey, D. J., Richardson, S. D., Luckman, A., Lucas, R. M., Reynolds, J. M., Hambrey, M. J. and Glasser, N. F.: Early recognition of glacial lake hazards in the Himalaya using remote sensing datasets, Glob. Planet. Change, 56, 137–152, 2007.

Richardson, S. D. and Reynolds, J. M.: An overview of glacial hazards in the Himalayas, Quat. Int., 65/66, 31–47, 2000a.

Richardson, S. D. and Reynolds, J. M.: Degradation of ice-cored moraine dams: implications for hazard development, in Debris-covered Glaciers. Proceedings of a workshop held at Seattle, Washington, U.S.A., edited by M. Nakawo, C. F. Raymond, and A. Fountain, pp. 187–198, IAHS Publication, Wallingford., 2000b.

Rounce, D. R., Byers, A. C., Byers, E. A. and Mckinney, D. C.: Brief communication: Observations of a glacier outburst flood from Lhotse Glacier, Everest area, Nepal, Cryosph., 11, 443–449, doi:10.5194/tc-11-443-2017, 2017.

Schwanghart, W., Worni, R., Huggel, C., Stoffel, M. and Korup, O.: Uncertainty in the Himalayan energy–water nexus: estimating regional exposure to glacial lake outburst floods, Environ. Res. Lett., 11(7), 74005, doi:10.1088/1748-9326/11/7/074005, 2016.

Suraj Mal, Simon K. Allen, Holger Frey, Christian Huggel, A. P. Dimri: Sector wise Assessment of Glacial Lake Outburst Flood Danger in the Indian Himalayan Region, Mountain Research and Development, 41(1), R1-R12, 2021.


Early Warning Systems


Disaster Risk Reduction


Disaster risk reduction (DRR) aims at preventing and reducing the risks arising from a potential disaster. Disaster risk reduction strategies focus on one or several of the three components of risk, namely (1) the hazard (e.g. of a glacier lake outburst), (2) the exposure of people and assets, and (3) the vulnerability of people and assets (figure 1). For the risk reduction of glacier lake outburst floods (GLOFs), hazard reduction strategies try to lower the probability of a  GLOF to happen, and/or to lessen the magnitude of a potential GLOF. This can be achieved for example by lowering the water level and volume of glacial lakes or by reinforcing and stabilizing the dams of such lakes. Disaster risk reduction can also act on exposure, for example, through hazard mapping that informs communities of hazard-prone areas, and through adjusted land use planning. Disaster risk reduction can finally be achieved by a reduction of vulnerability of people and systems. For instance, capacity building and education about the processes, their causes, impacts and dangers of GLOFs as well as mock drills to foster proper preparedness in case of a GLOF, can reduce people’s vulnerability to disasters.

Figure 1: Concept of risk reduction based on the International Panel on Climate Change (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC), Adjusted from Abram et al., 2019. The arrows indicate a reduction of one of the three components of risk (i.e., hazard, exposure and vulnerability) and the subsequent reduction of risk (lighter shaded areas). 



A process, phenomenon or human activity that may cause loss of life, injury or other health impacts, property damage, social and economic disruption or environmental degradation Hazards may be natural, anthropogenic or socionatural in origin (UNDRR: httpss:// Within the GLOFCA project, we are confronted with natural hazards originating from the outburst of glacier lakes (see theme What is a GLOF).


A disaster is a serious disruption of the functioning of a community or a society at any scale due to hazardous events interacting with conditions of exposure, vulnerability and capacity, leading to human, material, economic and or environmental losses and impact (UNDRR: httpss://


The situation of people, infrastructure, housing, production capacities and other tangible human assets located in hazard-prone areas. Measures of exposure can include the number of people or types of assets in an area. These can be combined with the specific vulnerability and capacity of the exposed elements to any particular hazard to estimate the quantitative risks associated with that hazard in the area of interest. (httpss://


The ability of a system, community or society exposed to hazards to resist, absorb, accommodate, adapt to, transform and recover from the effects of a hazard in a timely and efficient manner, including through the preservation and restoration of its essential basic structures and functions through risk management. (httpss://


In the context of climate impacts, the IPCC defines risk as the potential for adverse consequences of a climate-related hazard, on lives, livelihoods, health and well-being, ecosystems and species, economic, social and cultural assets, services, and infrastructure. Risk results from the interaction of the three components (1) hazard and the likelihood of its occurrence, (2) the exposure of any kind of assets, and (3) the vulnerability of the affected asset or system. 


Vulnerability is defined as the conditions determined by physical, social, economic and environmental factors or processes which increase the susceptibility of an individual, a community, assets or systems to the impacts of hazards (UNDRR: httpss:// 

Disaster Risk Management (DRM):

Disaster risk management is the application of disaster risk reduction policies and strategies to prevent new disaster risk, reduce existing disaster risk and manage residual risk, contributing to the strengthening of resilience and reduction of disaster losses (UNDRR: httpss://

Disaster Risk Reduction (DRR):

Disaster risk reduction (DRR) is the policy objective of disaster risk management, and its goals and objectives are defined in disaster risk reduction strategies and plans (UNDRR: httpss://

GLOF DRR examples in the high mountain context

Glacier lake outburst flood (GLOF) disaster risk reduction (DRR) includes a variety of different approaches and strategies. 

GLOF hazard reduction is based on measures that can be implemented at the glacial lake or at sites on potential impact areas downstream. Such measures can aim at the drainage, lowering or regulation of lakes and the artificial fortification and stabilization of the lake dam, as well as at flow channel adaptation or erosion control, for example. One of the most important structural measures for reducing GLOF hazard is the reduction of the water volume in glacial lakes and increase of the freeboard at the dam, which can be done through pumping or siphoning out the water from the lake, controlled breaching, construction of an outlet control structure, and/or making a tunnel through the moraine barrier or under an ice dam, as well as sediment infilling into the lake (figure 2). Artificial dams are built to increase dam freeboard and to prevent a lake outburst due to the direct impact of a displacement wave and protection from erosion at the dam, as well as unexpected increase in water levels. They are often implemented in combination with open cuts or tunnels in order to regulate the water level. 


Figure 2: Top left: Channel deepening works at lake No. 6 in the Kishi Almaty River basin, Ile Alatau, Kazakhstan in 1997. Top right: Clearing and deepening of the drainage channel of a moraine lake in Kazakhstan. Bottom left: Construction works on water pump installation for the drainage of moraine lake No. 13 in the Ulken Almaty river basin, Kazakhstan. Bottom right: Running siphons draining a moraine lake in Kazakhstan. Photos provided by Kazselezashita, Kazakhstan.

GLOF exposure reduction concentrates on the people and assets at stake rather than on the hazard itself, and therefore does not affect the physical processes of GLOFs. Exposure can be reduced on the very short term through evacuations or on the long term through relocation or spatial planning (Figure 3). Early warning systems (EWS) are non-structural measures, lowering the GLOF risk by reducing the damage potential through monitoring of the hazard and warning and evacuation of the population in case of a lake outburst. An EWS’ main objective is to avoid harm to human lives. EWS, as most other risk reduction measures, cannot reduce risks to zero, they should ideally be accompanied by other risk reduction measures, in particular appropriate land-use planning. 

GLOF vulnerability reduction acts on the conditions determined by physical, social, economic and environmental factors or processes which increase the susceptibility of an individual, a community, assets or systems to the impacts of hazards (UNDRR: httpss:// GLOF vulnerability reduction, thus, aims at the reduction and mitigation of the effects of GLOFs. This can be achieved through, for instance, knowledge generation, information and communication, capacity building, good governance (e.g. the strengthening of institutions, clarifications of roles and responsibilities), fostering of economic diversity, different preparedness and disaster relief plans, and insurances and compensations for losses. Comprehensive EWS, including risk understanding, communications and response capacity, are also effective on vulnerability reduction (figure 3). 


Figure 3: Top: Calculation of water height and potentially affected zones for different debris flow scenarios (Zaginaev et al., 2019). Bottom left: Monitoring system for early warning at lake Faverge, Switzerland ( Bottom right: Ground observation works at lake No. 1 in the Turgen river basin, Ile Alatau in Kazakhstan in 2020. Photo provided by Kazselezashita, Kazakhstan.

Sendai framework

The Sendai Framework for Disaster Risk Reduction 2015-2030 is an agreement that was adopted by the United Nations member states in 2015 in the city of Sendai, Japan. It is a high level international policy instrument that sets goals and guides disaster risk reduction. The Sendai Framework aims to achieve a substantial reduction of disaster risk and losses in lives, livelihoods and health and in the economic, physical, social, cultural and environmental assets of persons, businesses, communities and countries. It outlines seven clear targets and four priorities for action to prevent new and reduce existing disaster risks. The four priorities are: (i) Understanding disaster risk; (ii) Strengthening disaster risk governance to manage disaster risk; (iii) Investing in disaster reduction for resilience and; (iv) Enhancing disaster preparedness for effective response, and to “Build Back Better” in recovery, rehabilitation and reconstruction (UNDRR: httpss://


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Emmer, A., Vilímek, V., & Zapata, M. L. (2018). Hazard mitigation of glacial lake outburst floods in the Cordillera Blanca (Peru): the effectiveness of remedial works. Journal of Flood Risk Management, 11, S489–S501. httpss:// Lenk Gemeinde. Überwachungssystem. httpss:// Accessed: 25.04.2022.

Haeberli, W., Schaub, Y., & Huggel, C. (2017). Increasing risks related to landslides from degrading permafrost into new lakes in de-glaciating mountain ranges. Geomorphology, 293, 405–417. httpss://

Huggel, C., Cochachin, A., Drenkhan, F., Fluixá-Sanmartín, J., Frey, H., García Hernández, J., Jurt, C., Muñoz, R., Price, K., & Vicuña, L. (2020). Glacier Lake 513, Peru: Lessons for early warning service development. WMO Bulletin, 69(1), 45–52. httpss://

IPCC. (2018). Special Report: Global Warming of 1.5°C. Annex 1: Glossary.

NDMA. (2020). National Disaster Management Authority Guidelines. Management of Glacial Lake Outburst Floods (GLOFs).

Zaginaev, V., Falatkova, K., Jansky, B., Sobr, M., & Erokhin, S. (2019). Development of a potentially hazardous pro-glacial lake in Aksay Valley, KyrgyzRange, Northern Tien Shan. Hydrology, 6(1). httpss://

Further reading

Amendola, A., Linnerooth-Bayer, J., Okada, N., & Shi, P. (2008). Towards integrated disaster risk management: Case studies and trends from Asia. Natural Hazards, 44(2), 163–168. httpss://

Carey, M., Huggel, C., Bury, J., Portocarrero, C., & Haeberli, W. (2012). An integrated socio-environmental framework for glacier hazard management and climate change adaptation: Lessons from Lake 513, Cordillera Blanca, Peru. Climatic Change, 112(3–4), 733–767. httpss://

Carey, M., McDowell, G., Huggel, C., Jackson, J., Portocarrero, C., Reynolds, J. M., & Vicuña, L. (2015). Integrated Approaches to Adaptation and Disaster Risk Reduction in Dynamic Socio-cryospheric Systems. In Snow and Ice-Related Hazards, Risks, and Disasters (pp. 219–261). httpss://

Cuellar, A. D., & McKinney, D. C. (2017). Decision-making methodology for risk management applied to Imja Lake in Nepal. Water (Switzerland), 9(8), 14–16. httpss://

Emmer, A., Vilímek, V., & Zapata, M. L. (2018). Hazard mitigation of glacial lake outburst floods in the Cordillera Blanca (Peru): the effectiveness of remedial works. Journal of Flood Risk Management, 11, S489–S501. httpss://

Fakhruddin, B., & Basnet, G. (2018). Community Based Flood and Glacial Lake Outburst Risk Reduction Project (CFGORRP) in Nepal. Final Report. httpss://

Frey, H., Huggel, C., Bühler, Y., Buis, D., Burga, M. D., Choquevilca, W., Fernandez, F., García Hernández, J., Giráldez, C., Loarte, E., Masias, P., Portocarrero, C., Vicuña, L., & Walser, M. (2016). A robust debris-flow and GLOF risk management strategy for a data-scarce catchment in Santa Teresa, Peru. Landslides, 13(6), 1493–1507. httpss://

Gurung, S., Joshi, S. D., & Parajuli, B. (2021). Overview of an early warning system for Glacial Lake outburst flood risk mitigation in Dudh-Koshi Basin, Nepal. Sciences in Cold and Arid Regions, 13(3), 206–219. httpss://

Haeberli, W., Kääb, A., Mühll, D. V., & Teysseire, P. (2001). Prevention of outburst floods from periglacial lakes at Grubengletscher, Valais, Swiss Alps. Journal of Glaciology, 47(156), 111–122. httpss://

Huggel, C., Cochachin, A., Drenkhan, F., Fluixá-Sanmartín, J., Frey, H., García Hernández, J., Jurt, C., Muñoz, R., Price, K., & Vicuña, L. (2020). Glacier Lake 513, Peru: Lessons for early warning service development. WMO Bulletin, 69(1), 45–52. httpss://

Ikeda, N., Narama, C., & Gyalson, S. (2016). Knowledge sharing for disaster risk reduction: Insights from a glacier Lake workshop in the Ladakh Region, Indian Himalayas. Mountain Research and Development, 36(1), 31–40. httpss://

NDMA. (2020). National Disaster Management Authority Guidelines. Management of Glacial Lake Outburst Floods (GLOFs).

Portocarrero Rodríguez, C. A. (2014). The Glacial Lake Handbook. Reducing risk from dangerous glacial lakes in the Cordillera Blanca, Peru.

Rana, B., Shrestha, A. B., Reynolds, J. M., Aryal, R., Pokhrel, A. P., & Budhathoki, K. P. (2000). Hazard assessment of the Tsho Roipa Glacier Lake and ongoing remediation measures. In Journal of Nepal Geological Society (Vol. 22). httpss://

Shrestha, B. B., & Nakagawa, H. (2014). Assessment of potential outburst floods from the Tsho Rolpa glacial lake in Nepal. Natural Hazards, 71(1), 913–936. httpss://

Somos-Valenzuela, M. A., McKinney, D. C., Byers, A. C., Rounce, D. R., & Portocarrero, C. (2013). Modeling Mitigation Strategies for Risk Reduction at Imja Lake, Nepal (Issue CRWR Online Report 13-06).

UNISDR. (2015). Sendai Framework for Disaster Risk Reduction 2015-2030.

Wang, S., & Zhou, L. (2017). Glacial Lake Outburst Flood Disasters and Integrated Risk Management in China. International Journal of Disaster Risk Science, 8(4), 493–497. httpss://