The flash flood that killed dozens of people and left hundreds missing in the Himalayas of India on Sunday was far from the first such disaster to occur among the world's high-mountain glaciers. In a world with a changing climate, it won't be the last.
Shrinking and thinning of glaciers is one of the most documented signs of the effects of global warming caused by emissions of greenhouse gases, scientists say. Glacial retreat in mountains around the world has been measured, sometimes at a rate of 100 feet or more each year. In the Himalayas, the most glaciated mountain range and home to about 600 billion tons of ice, the rate of retreat has accelerated over four decades.
Over the long term, there are concerns about what the loss of glaciers will mean for billions of people around the world who rely on them at least in part for water for drinking, industry and agriculture. But the more acute fear is for the safety of the people who live near them.
Ice lost is water released, and in the Himalayas, as elsewhere, some of that water is trapped in lakes as it runs down mountainsides, dammed by rocky debris the glaciers leave behind. Worldwide, as more ice has melted, the resulting lakes have increased in number, and the total volume of water in them has grown by 50% since 1990.
"Climate change, we believe with 100% surety, has to be the reason these lakes are forming and increasing," said Umesh K. Haritashya, who studies glacial hazards at the University of Dayton in Ohio.
While it is too early to directly link the disaster in Uttarakhand to climate change, destabilization resulting from melting ice may have been responsible.
Although the Indian government claimed that an avalanche that poured into a river and created the flood was caused by "calving," or breaking, of a glacier at high elevation, scientists who analyzed satellite images from before and after the disaster said the collapse of an equally high rock slope was more likely the cause.
In addition, when this mass of rock and now-melting ice reached the valley floor, it quite likely encountered huge amounts of sediments deposited by a landslide in 2016, the scars from which are visible in satellite images. That sediment would have mixed with the incoming debris, worsening the flooding's impact.
"From what I've been able to see, the chain of events may have started in 2016," said Mylène Jacquemart, a glacier researcher at the University of Colorado.