Extreme floods caused by meltwater from glaciers are likely to cause more fatalities globally due to climate change, according to research at a Scottish university.
Meltwater from glaciers settles into natural hollows in the landscape that are vacated by glaciers as they recede, and the water becomes dammed by deposits of mud, sand and gravel deposited by the glaciers.
These lakes are known as moraine-dammed lakes, but the "dams" can be unstable and result in a flood downstream when they are weakened or breached, which can have devastating consequences for communities and infrastructure downstream.
The new study documents a marked increase in the frequency of these events since the 1980s, rising from 5.2 glacial lake outburst floods (Glofs) per year (1981-1990) to 15.2 Glofs per year (2011-2020).
We have time to act to prevent them - but we have to act fast
Dr Simon Cook, University of Dundee
The University of Dundee's glaciology and geohazards expert, Dr Simon Cook, warned they had increased three-fold by 2011.
More than 200 unrecorded incidents, similar to the floods in the Himalayan state of Sikkim in India, in 2023, which killed 55 people, were uncovered by an international team of researchers.
The research team, led by experts at the Chinese Academy of Sciences, studied satellite images and documentary records across a 120-year period to identify 609 incidents of glacial meltwater lakes bursting their dams and causing floods.
During the period 1900-2020, 400 events had been identified and recorded in previous inventories of Glofs, which has since increased to 609.
Research found that such incidents had increased three-fold since 2011.
More than 100 of the Glofs recorded caused damage downstream, and there have been more than 13,000 fatalities globally, with the highest number of damaging floods occurring in High Mountain Asia and in the Tropical Andes.
The research, co-authored by Dr Cook, has been published in Nature Communications.
The research found a strong, lagged relationship between Glof frequency and temperature such that temperature increase leads to an increase in Glof frequency between five and 20 years later.
The updated Glof inventory also showed that approximately 70% of these events have been triggered by ice avalanches and rockfalls landing in a lake and causing a wave of water to then overtop the dam.
Dr Cook said: "The concerning thing this research shows is that the number of these incidents remains relatively steady between the 1900s to around 1970.
"Then from the 1970s, when we know climate warming has accelerated, they start to creep up, before a threefold increase between 2011-2020.
"There's a time delay of around five to 20 years from the warming happening and the flood incidents taking place. That means that we know there will be many more glacial floods to come.
"We have time to act to prevent them - but we have to act fast.
"As the climate warms, not only are we seeing the shrinkage of glaciers and the ponding of meltwater to form these glacial lakes, but we're also seeing the stability of mountain slopes being threatened.
"Steep, cold glaciers loosen up and generate ice avalanches, and the rock and sediment in the mountain walls become more prone to failure because the permafrost here is warming and thawing meaning that we get more landslides into the lakes.
"These factors conspire to make Glofs more likely to occur in a warming world.
"With global temperatures continuing to rise, and recent progress in tackling climate change stalling at the Cop30 meeting, Glofs will remain a threat to people and infrastructure in the world's high-mountain regions."