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Landslides cost human lives every year: in the northern Indian state of Uttarakhand, rescue workers recover the first victims after the flash flood
Photo: Raja Gupta / EPA-EFE / Shutterstock
As if out of nowhere, the tidal wave rushes down a valley and sweeps everything with it - trees, houses, bridges, dams.
A cell phone video shows the full extent of the disaster that occurred in northern India.
The amateur filmmakers witnessed a devastating flash flood in the state of Uttarakhand, in which several people were killed and more than 170 are still missing.
The masses of water carried away bridges and road sections.
Two power plants were buried under the floods and rock masses.
Numerous villages in the affected region have been evacuated.
Such disasters occur again and again in the high mountains.
But climate change could increase the risk of landslides, flash floods and avalanches - not only in the Himalayas, but also in the Andes and the Alps.
Geologists and glaciologists therefore observe major movements of glaciers, rock and scree slopes around the world with concern.
With satellite images and seismic measuring devices they try to monitor the often inaccessible areas.
The causes of the disasters are not always clear: Initially, the authorities in India spoke of a "broken glacier" that had slipped into a river and triggered the flash flood.
However, several researchers now assume that it was a stone and ice avalanche, which probably hit an overhanging glacier or ice masses, then raced on and ultimately triggered a flash flood in the valley.
The reason for the water masses are probably two destroyed waterworks and the melting ice masses of the avalanche.
However, it is still unclear whether a glacier crashed on debris or, conversely, sliding earth masses broke off a glacier.
"The ice-rubble avalanche started at a height of 5600 meters and hit the waterworks at 3800 meters - there are unbelievable forces at work and frightening speeds," geologist Kristen Cook describes the disaster to SPIEGEL.
She conducts research at the GFZ German Research Center for Geosciences in Potsdam and has already recorded the eruption of a glacial lake with seismometers on the Nepalese side of the high mountains in 2016.
At that time there was a flash flood because the natural dam of a mountain lake had broken.
100,000 tons of water were set in motion and tumbled down the valley.
How destructive the floods are, Cook then assessed in the specialist magazine "Science"
out.
Danger to life from shrinking glaciers
The glaciers in the Himalayas have been shrinking rapidly for years due to climate change.
According to a 2019 study, the ice giants lose an average of eight billion tons of ice a year.
Of the thousands of glaciers in the largest mountain range in the world, at least a third of the glacier mass will have disappeared by the end of the century.
Researchers follow the death of glaciers in all high mountains.
The reason is rising average temperatures, also in higher altitudes.
Depending on the region, the ice masses are several hundred meters thick and sometimes thousands of square kilometers in size.
Glaciers have less volume in summer than in winter, where ice and snow are deposited.
But due to climate change, the melting exceeds this natural fluctuation - there is a net loss of ice.
The first glaciers have already been declared “dead”: In 2019, residents in Iceland put up a memorial plaque for the 700-year-old Okjökull glacier, which has almost completely melted.
The retreat of the ice tongues is well documented and has fatal consequences.
Due to the higher temperatures, they retreat and their meltwater runs down the mountain slopes, collects in mountain lakes or is dammed up by rocky rubble.
As a result, the number of mountain lakes has increased over the past hundred years.
This, in turn, can be dangerous for the people in the valley - for example if the natural debris dams break or rocks and rubble are set in motion, as in the current case in northern India.
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"It is too early to say something about the contribution of climate change to the disaster in India," said Canadian geomorphologist Dan Shugar.
He is observing the disaster in India via satellite.
However, recent research has shown that there is a clear connection between the retreat of glaciers and the increase in landslide areas.
This increases the likelihood of debris avalanches, according to the study.
According to researchers, a possible cause of landslides is also the melting of ice in rock crevices.
This then sets the stones in motion.
"Insane Power of Destruction"
Every year people die in the Alps from landslides or avalanches.
Most of the time, the victims are lonely hikers who ignore warnings.
In 2018, an entire mountain village in the French Alps had to be supplied by an airlift.
It was cut off from the outside world by a landslide.
"It is likely that such catastrophes will pile up worldwide in the next few decades," said glaciologist Andrea Fischer from the Austrian Academy of Sciences (ÖAW) in an interview with SPIEGEL.
She works for the Institute for Interdisciplinary Mountain Research.
In the Alps, too, there are glacier breaks, avalanches and landslides at greater intervals.
Such catastrophes would always have occurred at higher altitudes - albeit at large intervals of several decades.
The reason for this are natural melting processes and falling rocks that cause movement in the mountains.
If temperatures rise as a result of climate change or if it thaws and freezes again at irregular intervals, this increases the risk of thawing permafrost or full glacial lakes, which can then pour into valleys, says glaciologist Fischer, who observes the phenomenon of landslides in the Alps .
As the glaciers retreat, they also expose rubble and the thawing of the permafrost - a permanently frozen layer of soil in the high mountains or the Arctic Circle - loosens the ground.
"When the ground melts, rubble and mud are released, which can slide through snow or water," says Fischer.
This rubble-ice avalanche then moves down into the valley and carries with it more and more debris.
"These landslides and debris avalanches are incredibly destructive and are the most dangerous events in high mountains for human settlements," says the glaciologist.
This mechanism can be observed in all high mountains, says GFZ researcher Cook.
In the Himalayas the probability is only higher because there are more glaciers and rubble volumes.
Avalanches and floods are therefore far more dangerous.
Unlike in the Himalayas, however, the Alps are much better studied.
"Almost every square meter is monitored here," says Alpine expert Fischer.
In this way, the mountain residents can be better warned in advance.
The researchers are also collecting data in order to be able to make statements about the frequency and intensity of such mountain disasters.
However, the researchers have not yet been able to determine an accumulation of landslides.
The series of measurements are too short.
According to Fischer, it will likely hit areas at lower altitudes first, as temperatures there rise faster than freezing point.
"In the past, most of the villages in the high mountains were situated higher up because people knew that it was safer there," says glaciologist Fischer.
Today, many settlements have been built in valleys, including along rivers.
"Here we need good warning systems and in case of doubt we have to evacuate quickly."
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