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The danger of glacial lakes

UNITED STATES (OBSERVATORY NEWS) — The ice has long formed the landscapes of the mountain ranges of South Asia. Now they melt and form huge lakes – the harbingers of impending catastrophic floods.

Flying on an airplane over Everest, you see how a series of snow-white peaks stretches to the very horizon. There is no such landscape anywhere else.

These are the colossal glaciers of the Himalayas. Not the first millennium, monsoons every summer generously wrap mountains with a blanket of fresh snow.

Alas, after only 80 years, you may not be able to admire these brilliant ice giants – ice caps risk completely disappearing.

This year, the International Center for Integrated Mountain Development published analytical materials predicting how climate change will affect the Himalaya glaciers, the Hindu Kush, Karakorum and Pamir mountain systems forming a gigantic arc that crosses Afghanistan, Pakistan, China, India, Nepal, Bhutan and Myanmar. The report contains a warning that, depending on the rate of global warming, by 2100 in the region will remain from one to two-thirds of the current 56 thousand glaciers.

The terrible prediction is relevant for 1.9 billion people in South Asia: glaciers for these people are the main source of water, which they use not only for drinking and at home, but also for agriculture, hydropower and tourism. However, the document also addresses another question: where will the huge mass of water formed from the melting of glaciers go – about 3850 cubic kilometers.

The answer is simple: the Himalayas, the landscape of which for a long time was formed by glaciers, quickly turn into a mountain range, where lakes play the main role. Another study found that from 1990 to 2010, more than 900 new lakes fed glaciers appeared in Asian mountain systems. They are formed in hard-to-reach areas, so scientists count them with the help of satellites, and these lakes appear so rapidly that experts can not even converge on any one digit.

“Everything happens much faster than we expected,” explains Elton Byers, a researcher at National Geographic, a mountain geographer at the University of Colorado at Boulder.

To understand how such lakes form, imagine that a glacier is a gigantic, powerful ice bulldozer that slowly plows a slope, scrubbing soil and leaving ridges of rock fragments on its sides. These ridges are called moraines. When the glacier melts and recedes, the moraines turn into natural dams, and water begins to rapidly fill the formed gutter.

“At first there are several ponds with meltwater,” says Byers, “which then merge to form a larger pond, and it turns into a lake, which, growing year after year, eventually reaches a volume of millions of cubic meters.”

As the lake fills, it risks going beyond the moraines that hold it, or, even worse, moraines can not stand it. Scientists call these phenomena glacial breakthrough floods, and the Sherpas gave it their name – chhu-gumha, which means “catastrophic flood.”

One of the most spectacular floods in the Himalayas occurred in Nepal, in the Khumbu region, on August 4, 1985: an ice avalanche crashing down from the Langmoche glacier came across a 1.5 km lake of Dig.

Most likely, the lake was less than 25 years old – in a photograph taken in 1961 by Swiss cartographer Edwin Schneider, only ice and debris are visible at the foot of the Langmoche glacier. When in 1985 an avalanche reached the lake, it raised a wave four to six meters high, the wave broke through the moraine, and more than five million cubic meters of water (the volume of two thousand Olympic pools) fell into the river.

Sherpa, who witnessed the flood, described it as a black mass of water, slowly moving down the valley and making a noise, “like a dozen helicopters.” At the same time, there was the smell of freshly plowed earth. The flood demolished 14 bridges, destroyed 30 houses and a new hydroelectric power station.

According to some reports, there were dead. Luckily, a natural disaster occurred during a holiday dedicated to the upcoming harvest: the river had only a few local residents, which helped to avoid more victims.

“Such floods have always occurred in these places,” says Byers. “However, never before in such a short period did so many dangerous lakes arise.” And they are so little studied! ”

The flood on Lake Dig has drawn attention to the dangers that lurk and other lakes of the Himalayas. The main objects of study were Rolpa in the Rolling Valley in Nepal and Image at the foot of Everest. Both lakes originate from the river, and settlements along which the popular trekking routes go to the base camp on Everest lie downstream of the rivers on the banks.

In the late 1980s, a group of scientists began researching these two lakes. Using satellite imagery, it was possible to establish that Imja was formed later than Lake Dig, tentatively in the 1960s, and expanded at an alarming rate. According to estimates given in one of the studies, from 2000 to 2007, its surface area increased by 10 hectares.

“The difficulty in exploring glacial lakes is that they pose different threats,” explains Paul Majewski, director of the Climate Change Institute at the University of Maine and head of the Nepal Glacier Expedition. To begin with, many moraines that hold water in glacial lakes are reinforced with blocks of ice that stabilize the overall structure. If the ice melts, the moraines, having lost their fortifications, can not stand it.

Almost quadrillion gallons of water are concentrated in glaciers. Residents of the region rightly ask themselves: will disaster happen? Where does all this water go when the glaciers melt?

The next threat: during the melting process, large voids may form in the retreating glacier. Sometimes these hidden ice caves are filled with water and connected by channels to surface water bodies. It is worth thawing the canal, water can go through it, and if dozens of such canals open at the same time, this threatens with powerful flooding.

Similar phenomena – floods caused by interglacial ducts – are not as terrible as glacial flash floods, but they occur much more often. And today they are still little studied. “Determining how water flows inside the glacier is not an easy task,” Maevsky explains.

But even insufficiently studied, it is the breakouts of lakes that are considered today the main threats. Without conducting research “in the field”, it is difficult for scientists to assess the level of danger. Remote lakes can sometimes be reached in just a few days on foot, while in the 2011 study, 42 lakes are listed only in Nepal, and all of them have a high or very high risk of flooding. And throughout the Himalayan mountain system, there can be more than a hundred such reservoirs.

Another country that knows firsthand the growing number of glacial lakes is Peru, a mountainous country that has
lost 50 percent of its glaciers over the past 30–40 years : thousands of inhabitants have died from lake breakouts. Now dams have been built on dozens of lakes in Peru, and water levels have been reduced. Along the way, hydropower plants and irrigation canals are being built here.

In Nepal, proponents of this approach face great difficulties.

The main difference between Peru and Nepal, according to the English geological hazard specialist John Reynolds, is logistics. John coordinated efforts to lower the water level at Rolpa, considered the most dangerous lake in Nepal.

“You can drive to Peru by car to the point from which you walk on foot to the lake for 24 hours,” he explains. “In Nepal, from the place of work to the nearest road, a walk will take about five to six days.”

The roll was removed so much that heavy equipment had to be delivered there by helicopter in parts and assembled on site. After the construction of a small dam with a gateway, engineers began the gradual descent of water from the lake. As a result of the work, the water level in the lake was reduced by three and a half meters — this is the first project to reduce the hydrological threat in the Himalayas. And in 2016, units of the Nepalese army were involved in a project to urgently lower the water level in Lake Imja.

According to Nepalese scientist Dhananjay Regmi, not only the largest lakes are dangerous. “As a rule, we worry about large lakes, and the lion’s share of natural disasters in recent years has occurred due to relatively small reservoirs in which no one has seen a threat,” Dhananjay clarifies.

However, Regmi sees opportunities for development in the growth of the area of ​​lakes. “Each lake has its own unique features, and each requires an individual approach,” he explains, adding that some lakes may well become a good source of mineral water in the future, while others can develop hydropower or tourism.

Elton Byers believes that there is already progress, and is optimistic about the future: “I do not mean only large-scale infrastructure projects such as lowering the level of Imji. Residents of remote highlands learn to adapt.”

So, he says, gabions are already being built in the Khumbu valley – baskets filled with stones from metal rods – helping to divert water flows from the settlements. In 2016, efforts were rewarded – when in the area located above the village of Chukhung, there was a sudden flood caused by interglacial ducts, the erected gabions resisted, diverting streams from several dwellings, and the village was saved.

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