Explain the causes of glacial lake outburst flood. 2025
A glacial lake outburst flood (GLOF) is a release of meltwater from a moraine- or ice-dam glacial lake due to dam failure. GLOFs often result in catastrophic flooding downstream, with major geomorphic and socioeconomic impacts.
GLOFs have three main features:
Some of the largest floods in Earth’s history have been GLOFs. They have caused large-scale landscape change, and even altered regional climate by releasing huge quantities of freshwater to the oceans.
Today, GLOFs pose a risk downstream communities and infrastructure. In Peru alone, GLOFs were responsible for ~32,000 deaths in the 20th century. They have killed hundreds to thousands of people in other mountain regions (e.g. the Himalayas), and destroyed roads, bridges, and hydroelectric developments.
An increasing hazard
Importantly, the general global trend of glacier shrinkage through the 20th and 21st centuries has seen the number and size of glacial lakes increase, at the same time as human activities have expanded further into glaciated catchments. The study of how GLOFs occur and their impacts is therefore important for future hazard mitigation.
Glacial lake settings
There are two main settings in which glacial lakes form: (1) behind moraine dams, and (2) behind ice dams.
Moraine-dammed lakes
Moraine-dammed lakes form during periods of glacier retreat from a moraine. As a glacier margin retreats, water collects in the topographic low between the ice-front and the abandoned frontal and/or lateral moraine. Most existing moraine-dammed lakes (such as the Imja Tsho glacial lake in Nepal formed when mountain glaciers began to retreat from large moraine ridges constructed during the Little Ice Age
Moraine-dam failures
The failure of glacier and moraine dams depends on two main factors: (1) the integrity of the dam, and (2) the nature of trigger mechanisms
Moraine dams tend to be narrow and sharp-crested. As such, they are more likely to fail than broader dam types, such as ice-contact fans or landslides Most moraines are made up of loose, poorly sorted, permeable sediment, and some contain ice cores. Unconsolidated sediments are susceptible to failure, especially if saturated, while the melting of ice cores may cause moraines to subside over time. Despite these weaknesses, where a moraine is low, wide, and armoured by large rock material it may survive intact for hundreds or even thousands of years.
Displacement waves
Outburst floods in moraine-dammed settings are often caused by the sudden input of material into a lake causing displacement of water and overtopping of the dam. Displacement (or seiche) waves are commonly triggered by avalanches or rockfalls, or calving of a lake-terminating glacier.
Other triggers include, the rapid input of meltwater from an glacier upstream, heavy rainfall or snowmelt events that rapidly raise the lake level, or earthquakes that destabilise the moraine dam
