The flood that killed dozens of people and left hundreds missing in India’s Himalayas on Sunday was far from the first disaster to occur among the world’s high mountain glaciers. In a world with a changing climate, it will not be the last.
The shrinking and narrowing of glaciers is one of the most documented signs of the effects of global warming caused by greenhouse gas emissions, scientists say. Glacial retreat in mountains around the world has been measured, sometimes at a rate of 30 meters or more each year. In the Himalayas, the most glacier mountain range and with around 600 billion tons of ice, the rate of retreat has accelerated over the past four decades.
In the long run, there are concerns about what the loss of glaciers will mean for billions of people around the world who depend on them, at least in part, for drinking water, industry and agriculture. But the most acute fear is for the safety of the people who live close to them.
“Climate change, we believe with 100 percent certainty, must be the reason why these lakes are forming and growing,” said Umesh K. Haritashya, who studies glacial risks at the University of Dayton in Ohio.
Glacial lakes are a serious danger. The dam of debris can collapse with the weight of the water or with an earthquake; or an avalanche above the lake can send ice and rock into it. Either way, the result could be a sudden and catastrophic explosion of water that can destroy communities and infrastructure in the downstream valleys.
Explosive floods, as they are known, have occurred throughout history. In Uttarakhand, a 2013 explosion led to floods, destroyed villages and killed several thousand people. Elsewhere in the subcontinent, flooding in the mountains in 1929 affected the Indus River almost 500 miles away. In the Andes, Peru, floods related to glaciers have killed about 30,000 people since the 1940s.
In Switzerland and some other countries, engineers have built siphons to drain lakes that pose specific threats to communities or infrastructure. But all over the world, these projects are few and far between and are oppressed by the increasing number of glacial lakes.
Rising temperatures affect more than glaciers, however. Thawing and refreezing of ice trapped in rock fractures on mountain slopes can cause the slopes to become unstable and more prone to collapse.
“We are seeing more and more high cases of rocks and mountains in the high mountains not as stable as we imagined,” said Dan Shugar, a geomorphologist at the University of Calgary, Canada.
Although it is too early to directly link the disaster in Uttarakhand to climate change, the destabilization resulting from melting ice may have been responsible.
Although the Indian government claims that an avalanche that fell into a river and created the flood was caused by the “birth”, or breakdown, of a high-altitude glacier, scientists who analyzed satellite images before and after the disaster said the collapse of an equally high rock slope was the most likely cause.
Dave Petley, vice president of innovation at the University of Sheffield in Britain who has long been studying landslides, said such slopes often contain many rock fractures, and the ice acts like a glue that holds them together. “As the weather is heating up, this ice is degrading in the summer,” he said. “The rock mass becomes very weak because the glue that is holding is no longer there.”
A mystery is the origin of all the water for the flood, which combined with sediments to create a mud wall that flowed down the Rishiganga River, sweeping houses and people and leaving two hydroelectric projects in ruins.
Many scientists initially thought that such a large amount of water must be the result of a flood. But satellite images prior to the disaster showed no signs of any major lakes.
Petley said the rock fall – which was probably in the order of tens of millions of cubic meters of debris – is likely to hit a glacier, fragmenting it. “These rock avalanches are very energetic and chaotic,” he said.
What was now an avalanche of ice rock continued down the hill, generating immense heat from the friction. This heat probably melted much of the ice. “That’s probably where all the water came from,” he said.
Heavy snow cover in the region, some of which began to melt days before the disaster, may also have contributed, some researchers said.
In addition, when this mass of melting rock and ice hit the valley floor, it most likely found large amounts of sediment deposited by a landslide in 2016, the scars of which are visible on satellite images. This sediment would have mixed with the incoming debris, worsening the impact of the flood.
“From what I could see, the chain of events may have started in 2016,” said Mylène Jacquemart, a glacier researcher at the University of Colorado.
And while this particular chain of events may seem like a unique event, it is not, said Jacquemart. A deadly landslide in 2017 that hit the village of Santa Lucía in Chile followed a similar pattern, she said.
“It’s not like we’ve never seen anything like this before,” she said.
Floods and the collapse of slopes subject to melting are not the only hazards related to glaciers linked to climate change. A glacier is a river of ice, and the ice acts as a buttress for the slopes on both sides. As a glacier recedes and tapers, these slopes lose their support. The result can be a sudden collapse and an avalanche of ice rocks when the debris from the hillside reaches the glacier.
Scientists raised the alarm last year about the possibility of such a disaster in Prince William Sound, Alaska, not far from Anchorage. A kilometer-long slope along a fjord had lost most of its support due to the receding ice, increasing the risk of a landslide in the fjord. The resulting sudden tsunami can be deadly to any hunter or fishing boat in the area and can destroy coastal villages.
The faster melting of glaciers is also causing some glaciers to flow faster, as the melt water 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 breaks off unexpectedly, Jacquemart said.
Two of those detachments took place two months apart in 2016 in the Aru mountain range in Tibet, she said.