Why Melting Glaciers Are Making Floods More Dangerous

Living beneath the world’s spectacular, ice-capped mountains has always carried risks, but the devastating flood wave that tore through communities along the Nepal-China border this week highlights how life downstream from glaciers is becoming more unpredictable and dangerous.

It is too soon to determine what role climate change may have played in the specific disaster. What is clear, scientists say, is that mountain environments are changing rapidly as temperatures rise, melting glaciers and destabilizing slopes in ways that can trigger cascading disasters.

Nepal’s steep Himalayan terrain, narrow valleys and powerful rivers have long made the country vulnerable to floods and landslides. But scientists say Wednesday’s event was unusually destructive.

An enormous section of glacier roughly 2,000 feet wide broke away from Langtang Lirung mountain in northern Nepal, accompanied by a landslide, according to satellite analysis. The collapse sent a mixture of ice, water, rock and sediment thousands of feet down the mountain.

The resulting surge was so powerful that the ground shook strongly enough for the event to initially be mistaken for an earthquake.

The torrent of ice, water, rock, silt and sand swept through narrow gorges, destroying homes, buildings, power plants, bridges and roads. Hundreds of people have died, while many more remain missing.

Scientists say events like this could become more common as the planet warms.

“Whether this particular event can be tied to climate change or not, this is what we expect,” said Dan Shugar, a geologist at the University of Calgary in Canada. “This is what climate change looks like.”

The risks are not limited to Nepal.

There are more than 200,000 mountain glaciers around the world, and researchers estimate that up to half could disappear by the end of this century even if ambitious climate targets are met.

In the Hindu Kush Himalaya region, which includes Nepal, the rate of glacier ice loss has doubled since 2000, according to research from the International Centre for Integrated Mountain Development.

As glaciers shrink, they can become increasingly unstable. Rising temperatures can also thaw permafrost, the mixture of soil, rock and ice that helps hold steep mountain slopes together.

Richard Waller, a physical geographer at Keele University in England, compared the high mountains to shattered bedrock held together by ice-filled joints. As that ice melts, large sections of mountainsides can become unstable and collapse.

Glacial lakes present another danger. These lakes form as glaciers melt and can eventually overflow or burst, sending huge amounts of water and debris downstream.

A glacial lake outburst in a similar part of Nepal last year killed at least 11 people.

Rainfall is another factor. As the atmosphere warms, it can hold more moisture, increasing the potential for intense precipitation. In mountain regions, more extreme precipitation can fall as rain rather than snow, increasing the threat of landslides and erosion.

Scientists say these dangers are found well beyond the Himalayas.

Glacier and permafrost hazards threaten mountainous areas from the European Alps to the Andes. In Alaska, the Mendenhall Glacier above Juneau drains toward Suicide Basin, a glacial lake that has repeatedly burst and sent floodwaters downstream toward the city.

In Switzerland last year, the village of Blatten was buried after a glacier collapse sent millions of tons of ice and rock down a mountainside. Scientists believe thawing permafrost may have contributed to the collapse.

Early warning systems can help save lives, but predicting exactly when a glacier or mountainside will fail remains extremely difficult.

Nepal’s warning systems likely saved many lives during the latest disaster, according to Hannah Cloke, a professor of meteorology and climate change at the University of Reading. But she said there can be very little time between a triggering event high in the mountains and the arrival of a flood wave downstream.

One scientist estimated that the flood wave near the Nepal-China border traveled nearly 14 miles at about 120 mph.

Nepal has roughly 3,000 glaciers, making comprehensive monitoring extremely challenging, according to ICIMOD analyst Prashant Baral.

There is some hope that new satellite monitoring systems could provide a major improvement in detecting dangerous changes in glaciers and mountain slopes.

As people continue to live, work and travel in mountain regions, scientists say better monitoring and earlier warnings will become increasingly important as a warming planet changes the risks associated with the world's glaciers.