Glacial Lake Outburst Flood

Primary reference(s)

Emmer, A., 2017. Glacier Retreat and Glacial Lake Outburst Floods (GLOFs). Accessed 7 October 2020.

Additional scientific description

The term glacial lake outburst flood (GLOF) is used here to refer to the catastrophic release of a water reservoir that has formed either at the side, in front, within, beneath or on the surface of a glacier. Dam structures that impound the water reservoir may be composed primarily of glacial ice, morainic debris, or bedrock (GAPHAZ, 2017).

GLOFs are characterised by extreme peak discharges, often several times in excess of the maximum discharges of hydrometeorological induced floods, with an exceptional erosion/transport potential. They can therefore turn into flow-type movements, such as GLOF-induced debris flow (Emmer, 2017; UN-SPIDER, no date).

Metrics and numeric limits

Not identified.

Examples of drivers, outcomes and risk management

Drivers: Key overarching determinants of GLOF susceptibility and the resulting event magnitude are the size of the glacier lake, the outburst mechanism (and related hydrograph), and the characteristics of the downstream torrent (determined by channel inclination and debris availability). Ice-dammed lakes can develop at the margin of an advancing (or surging) glacier, when side-valleys or depressions at the side of the glacier become truncated and blocked. Many such lakes formed in high mountain regions during the Last Glacial Maximum and more recently during and following the Little Ice Age. Over time, as the glaciers retreat, the support of the ice dam is removed and the lake may drain catastrophically or remain trapped behind lateral moraines of the former glacier (GAPHAZ, 2017; UN-SPIDER, no date).

Susceptibility and control measures: Various schemes have been proposed for assessing the susceptibility of glacial lakes to an outburst flood, mostly drawing on remotely sensed information to characterise semi-quantitatively the cryospheric environment, lake and dam area, and other geotechnical and geomorphic characteristics of the upstream catchment area of the lake. The potential for unstable rock and/or ice to impact into a lake can be determined using worst-case runout distances. Assessment approaches have mostly been developed and tailored towards regional implementation, especially for moraine dammed lakes, for which McKillop and Clague (2007) gave a comprehensive overview of many of the relevant susceptibility factors that may condition or trigger an outburst event (GAPHAZ, 2017).

Health impacts: The effects of flooding on health are extensive and significant, ranging from mortality and injuries resulting from trauma and drowning, to infectious diseases and mental health problems (acute and long-term). While some of these outcomes are relatively easy to track, ascertaining the human impact of floods is still weak. For example, it has been reported that two-thirds of deaths associated with flooding are from drowning, with the other third from physical trauma, heart attacks, electrocution, carbon monoxide poisoning and fire. Often, only immediate traumatic deaths from flooding are recorded (WHO, 2013).

Morbidity associated with floods is usually due to injuries, infections, chemical hazards and mental health effects (acute as well as delayed) (WHO, 2013). Hypothermia may also be a problem, particularly in children, if trapped in floodwaters for lengthy periods (WHO, no date). There may also be an increased risk of respiratory tract infections due to exposure (loss of shelter, exposure to flood waters and rain). Power cuts related to floods may disrupt water treatment and supply plants thereby increasing the risk of water-borne diseases as well as affecting proper functioning of health facilities, including cold chain (WHO, no date). Floods can potentially increase the transmission of the following communicable diseases: water-borne diseases (such as typhoid fever, cholera, leptospirosis and hepatitis A) and vector-borne diseases (such as malaria, dengue and dengue haemorrhagic fever, yellow fever, and West Nile Fever) (WHO, no date).

The longer-term health effects associated with a flood are less easily identified. They include effects due to displacement, destruction of homes, delayed recovery and water shortages (WHO, 2013).