The unusual giant craters several kilometers long recently found in Antarctica did not arise from past asteroid impacts, but from the accumulation of melt water on the surface of glaciers in parts of the continent, according to an article in the journal Nature Climate Change.
“In January 2015, all the media began to report on the discovery of a mysterious crater in the land of King Baudouin in the east of Antarctica, which, as journalists said, was most likely caused by a meteorite fall.
I looked at the photographs of this structure and immediately thought that it was the result of the melting of water, not the fall of a celestial body,”said Jan Lenaerts from the Catholic University of Leuven (Belgium).
In recent years, climatologists have begun to pay more and more attention to the melting ice cap of the southern polar cap, which until recently was considered relatively stable. As satellite and aircraft observations show, in fact this is not so - the ice in the west of Antarctica is melting, splitting into pieces and collapsing today, and East Antarctica, considered inaccessible, is also under threat of rapid disappearance.
Lehnerts and colleagues worked out why the eastern Antarctic ice sheets are melting faster than climate models and calculations predict by examining a mysterious three-kilometer crater discovered in the King Baudouin Glacier in January 2015 by one of the survey planes of the Alfred Wegener Institute, the American oceanographic organization.
About a year later, the authors of the article visited this structure, measured its depth and comprehensively studied it, discovering that in fact this "crater" did not arise as a result of a meteorite falling, but due to the emergence of a subglacial lake, the melt waters of which made their way to the surface and towards the waters of the ocean.
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All the water from this lake, as shown by the study of its "shores", flowed into the ocean by the time it was photographed by an airplane, which hid its essence from the scientists and the public who discovered it. The discovery of such a large lake forced scientists to analyze photographs of this part of the ice massif obtained using the Terra and Aqua probes. It turned out that next to this "crater" there are 55 more similar structures hidden under snow and ice.
Their discovery surprised the authors of the article, and they tried to explain their appearance by analyzing all the processes that are currently taking place in East Antarctica, using the climate model of the region developed by them.
As it turned out, two things were to blame for the formation of these lakes - strong winds, which always blow in one direction in this part of the continent, and an increase in temperatures as a result of global warming, which was further enhanced by such winds. Thanks to both, the melting of ice at the foot of the glacier located directly above the surface of Antarctica has actually doubled in recent years, which explains the appearance of such lakes.
Strong winds, scientists explain, play another role - they blow snow off the surface of the so-called "blue" perennial ice, reflecting less light than the snow itself. This further exacerbates melting and makes glaciers in eastern Antarctica more vulnerable to heat and light than scientists previously believed.
The melt water itself also warms the glaciers in this part of the continent and makes them as vulnerable to destruction as their “cousins” on the Antarctic Peninsula, which has recently begun to free itself of ice.
Tibet is melting too
The series of avalanches and landslides that claimed the lives of ten Tibetans this July were triggered by changes in the region's glaciers caused by global warming, scientists say in an article published in the Journal of Glaciology.
“Considering the speed with which these avalanches descended and what areas they covered, I think that this could only happen if the foothills of the glaciers were wetted by melt water. Unfortunately, today we cannot predict which other glaciers are in the same state, which prevents us from making forecasts for subsequent avalanches,”said Lonnie Thompson of Ohio State University (USA).
In May and the first months of summer, Tibet was reported by Xinhua as a series of relatively weak earthquakes and several avalanches and landslides that claimed the lives of ten local residents who grazed livestock in the vicinity of the glaciers. Despite all the efforts of the Chinese rescuers, their lives could not be saved.
Thompson, a renowned American paleoclimatologist, and his colleagues found a possible reason for the increased frequency of avalanches and landslides in Tibet, and explained their unusually large scale, collecting and studying all the information about one of such avalanches, which descended on July 17 this year near the village of Aru in the south east of Tibet.
After examining the photographs taken by the Sentinel-2 satellite shortly before the avalanche, scientists discovered that a huge piece of ice mass 6 kilometers long and 2.5 kilometers wide broke off from the Aru glacier. This huge mass of ice, according to eyewitnesses, completely "slid" from the slopes of the mountains in just 4-5 minutes, and warmed under itself the valley, in which there were people at that moment.
A similar scenario surprised scientists - the Aru glacier was considered one of the most stable ice massifs in Asia, the area of which was decreasing much more slowly than the glaciers in the Himalayas and other high mountain regions. The rapid avalanche, in turn, led scientists to assume that something similar to what happened in the Karmadon Gorge in 2002, when the film crew of Sergei Bodrov Jr. died there, near the village of Aru.
Scientists believe that the catastrophe in North Ossetia and avalanches and landslides in Tibet occurred because melt water penetrated into the foothills of the glaciers, which "lubricated" them and made them slide over soils and rocks much faster than they did before. Accordingly, if the slope is steep enough - about 15 degrees in this case, the lower part of the glacier can simply "break away" and slide down in a matter of moments.
How could this happen? According to Thompson, global warming is to blame for this, which has led to an increase in temperatures in Tibet and other mountains by 1.5-2 degrees Celsius over the past 50 years, and to an increase in the amount of summer precipitation several times over the past five to six years. …
Accordingly, the rains, combined with higher air and soil temperatures, will force the base of the glaciers to melt and form flows of melt water at the boundary between ice and soil. It is almost impossible to predict when this process will lead to the sliding of the glacier, which should prompt scientists and the authorities of countries where there are such glaciers to continuously monitor them, Thompson concludes.
