Indian authorities are reporting at least 40 deaths in flash floods caused by the overflow of a glacial lake in the Himalayas, a phenomenon that is becoming more common as climate change occurs, scientists say.
• Also read: India: At least 40 dead after a lake in the Himalayas overflows
Here is an update on glacial lake flooding and associated risks to populations in several regions of Asia:
What is a Glacial Lake Flood?
A flood or sudden outflow of a glacial lake is the sudden release of water that has accumulated in ancient glacial valleys.
These lakes are formed by retreating glaciers, a natural phenomenon that is exacerbated by warmer temperatures due to human-caused climate change.
Water from melting glaciers is often discharged into rivers, but ice or accumulations of debris can form a natural dam behind which a glacial lake forms.
If these natural dams are breached, large amounts of water can suddenly escape from the lakes and cause devastating floods.
What causes these separations?
According to Lauren Vargo, glacier expert and scientist at the Antarctic Research Center in New Zealand, the natural dams that hold back glacial lakes can be breached for a variety of reasons.
The causes could be “a snow avalanche or a landslide causing a wave in the lake, or overfilling of the lake (…) due to rain or melting glaciers,” she told AFP.
Sometimes the dam gradually weakens over time or breaks after an event such as an earthquake. Breakups are very unpredictable “because they can be caused by many different factors,” she added.
What are the effects of climate change?
Climate change is causing glaciers to disappear. Half of Earth’s 215,000 glaciers are expected to melt by the end of the century, although warming can be limited to 1.5 degrees Celsius.
According to a 2020 study based on satellite data, the volume of glacial lakes has increased by 50% in 30 years.
The more lakes are created and the larger they are, the greater the danger to the downstream population.
Climate change not only leads to the formation of glacial lakes, but can also create conditions that cause dams to fail.
“Flooding can be caused by melting glaciers or heavy rainfall. We know this is happening more frequently because of climate change,” notes Lauren Vargo.
How dangerous are these floods?
The particular danger of glacial lake flooding is related to its unpredictability.
“The likelihood of a lake triggering a flash flood is difficult to accurately quantify without detailed and local studies,” warns an international study examining the issue this year.
According to the study published in Nature Communications, 15 million people live within 50 kilometers of a glacial lake and within one kilometer of possible flooding from a breach.
The highest risk is in the “High Mountains of Asia,” an area that partially covers twelve countries, including India, Pakistan, China and Nepal.
This is partly because more people live near glacial lakes in the region than in other parts of the world, making warning times even shorter.
But it also reflects the vulnerability of these populations, who may be poorer and less prepared for the sudden arrival of catastrophic floods.