The flash flood that left dozens dead and hundreds missing in the Himalayas of India on Sunday was by no means the first disaster among the world’s high mountain glaciers. In a world with a changing climate, this will not be the last.
Shrinkage and thinning of glaciers is one of the most documented signs of the effects of global warming caused by greenhouse gas emissions, scientists say. The retreat of ice in mountains around the world has been measured, sometimes at a velocity of 100 feet per year. In the Himalayas, the most spotted mountain range and home to about 600 billion tons of ice, the rate of retreat has accelerated over the past 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 at least partially rely on it for water for drinking, industry and agriculture. But the sharper is the fear of the people who live near them.
“Climate change, we believe with 100 percent sponsorship, should be the reason why these lakes are forming and increasing,” said Umesh K. Haritashya, who studies the dangers of ice at the University of Dayton in Ohio.
Ice smears are a serious danger. The debris can collapse due to the weight of the water or an earthquake; or an avalanche above the lake can send ice and rock into it. Either way, the result could be a sudden, catastrophic eruption of water that could wipe out communities and infrastructure in valleys downstream.
Eruption floods, as they are known, have occurred throughout history. In Uttarakhand, an eruption in 2013 led to flooding, destroying villages and killing thousands of people. Elsewhere on the subcontinent, eruptions in the mountains in 1929 hit the Indus River nearly 500 kilometers further. In the Andes, Peru, some 30,000 people are expected to have been killed by glacier-related floods since the 1940s.
In Switzerland and some other countries, engineers have built siphons to drain lakes that pose particular threats to communities or infrastructure. But worldwide, such projects are rare and are overwhelmed by the increase in the number of glaciers.
However, rising temperatures affect more than glaciers. Thawing and re-freezing of ice trapped in rock fractures on mountain slopes can cause the slopes to be destabilized and more likely to collapse.
“We are seeing more and more in the high mountains cases of rock and mountains that are not as stable as we would think,” said Dan Shugar, a geomorphologist at the University of Calgary in Canada.
Although it is still too early to link the disaster in Uttarakhand directly to climate change, destabilization due to melting ice may have been responsible.
Although the Indian government has claimed that an avalanche that plunged into a river and caused the flood was caused by ‘calving’ a high-altitude glacier, scientists using satellite images from before and after the disaster analysts said equally high rock slope was probably the cause.
Dave Petley, vice president of innovation at the University of Sheffield in Britain, who has long studied landslides, said such slopes contain many rock fractures and ice acts like a glue holding them together. “As the climate warms, this ice destroys in the summer,” he said. “The rock mass becomes so weak because the glue that is together is no longer there.”
One mystery is the source of all the water for the flood, which along with sediment creates a mud wall that runs down the Rishiganga River, sweeping away houses and people and leaving two hydroelectric projects in ruins.
Many scientists at first thought that such a large amount of water must be the result of an eruption. But satellite images from before the disaster showed no signs of large lakes.
Dr Petley said the rock fall, probably in the order of ten million cubic meters of debris, hit and fragmented a glacier. “These rock avalanches are very energetic and chaotic,” he said.
What was now a rock-ice avalanche continued downhill, generating friction over time. This heat probably melted a lot of the ice. “This is probably where all the water comes from,” he said.
Heavy snow cover in the region, some of which began to melt in the days before the disaster, may also have contributed, some researchers said.
Moreover, when this mass of rock and now melting ice reached the valley floor, it most likely encountered in 2016 large amounts of sediments deposited by a landslide, the scars of which are visible in satellite images. This sediment would have mixed with the incoming debris, exacerbating the impact of the flood.
“According to what I could see, the events possibly started in 2016,” said Mylène Jacquemart, a glacier researcher at the University of Colorado.
And while this particular series of events may seem like a one-time event, it is not, Drs. Jacquemart said. A fatal mudslide in 2017 that hit the town of Santa Lucía in Chile followed a similar pattern, she said.
“It’s not like we’ve ever seen anything like it,” she said.
Eruption floods and the collapse of slopes subject to thawing are not the only dangers associated with glaciers with climate change. A glacier is an ice river and the ice serves as a fulcrum for the slopes on either side. As a glacier recedes and becomes thinner, these slopes lose their support. The result can be a sudden collapse and an ice-rock avalanche if the slope debris hits the glacier.
Scientists last year sounded the alarm about the possibility of such a disaster in Prince William Sound in Alaska, not far from Anchorage. A slope of one kilometer along a fjord lost most of its support due to ice falling back, which increased the risk of a landslide in the fjord. The resulting sudden tsunami could be fatal to hunters or fishing boats in the area and could destroy coastal villages.
Faster melting of glaciers also causes some glaciers to flow faster, as meltwater acts as a lubricant between the ice and the underlying rock. In some cases, they flowed so fast that the front of the glacier simply broke off unexpectedly, Dr. Jacquemart said.
Two such divisions took place within two months of each other in the 2016 Aru Series in Tibet, she said.