Translated material
Subglacial Niagara
Scientists have uncovered the mystery of the disappearance of lakes in Greenland
American glaciologists managed to discover a unique natural phenomenon in Greenland. In July 2006, a lake with an area of 5.6 square meters disappeared on this icy island within 24 hours. km. Millions of tons of water literally fell through the ice and spread over the Greenland rocks. As scientists note, this leak in its scale was comparable in power and volume of falling water to Niagara Falls.The very fact of the existence of lakes in Greenland may surprise us, although there is nothing strange about it. At least for those who have been to Siberia in the summer, in areas with permafrost. Thawed several tens of centimeters of soil turn into swamps and lakes.
Greenland, the southern tip of which is located, by the way, at the latitude of Karelia and Finland, in the summer also turns into a country of a thousand lakes. The sun heats the glaciers, which begin to melt, and water fills the lowlands. Sometimes very large bodies of water form, but they are short-lived. With the arrival of cold weather, ice appears in their place again. But, as studies from space show, lakes suddenly disappear from time to time. It is impossible to see the full picture from a satellite: it is clear that water is flowing somewhere, but it is impossible to say how, where and why. To do this, you need to be in close proximity to the scene of the incident. The best is right on the shore of a glacial lake.
Sarah Des of Woods Hole Oceanographic Institution and Ian Jaufin of the University of Washington were lucky. Their monitoring equipment was placed next to a large lake in western Greenland, and in July 2006, sensors showed that the water level was falling sharply. 44 million cubic meters m of water flowed away somewhere literally in a day. Moreover, the main part of the lake disappeared in the first hour and a half. If the waterfall that was formed due to the fall of such a mass of water could be seen, it would be more powerful than Niagara. True, where the water went became clear only when the icy bottom of the lake was exposed.
It turned out that a huge crack had formed in the ice that was the lake bottom. It went right through to the very base, which is almost a kilometer deep into the Greenland ice sheet. And when the water reached the rocky bed of the glacier, something happened that each of us has seen many times in a cocktail glass - the ice floated up. There was no need for water to slowly erode the base or seep through the cracks; the laws of physics worked instantly. Within 24 hours, nature corrected the unnatural situation: since the ice is lighter than water, it means it must be on top, and the bottom of the lake became its ice “lid.” This cannot be seen in any body of water in the middle zone or in the polar countries: now the lake is covered with a kilometer-thick layer of perennial ice, which has surfaced and risen by 1.2 meters, and in the center of the former bottom - even by six meters.
However, even in this case, as scientists suggest, there is something like ice drift. Eternal ice, as is known, also flows, only very slowly. Mountain glaciers move down valleys for years until they descend so low that they melt. Greenlandic and Antarctic ice layers, many kilometers long, gradually slide towards the ocean and eventually huge blocks, breaking off from the tongue of the glacier, turn into icebergs. But, as Sarah Des points out, "if an ice sheet forms on rocks, it will flow slowly." But if you “lubricate” it, for example, with water, the situation will change dramatically.
The floating icy bottom of the lake now feels exactly the same as a person who decided to walk on an icy run-up in the midst of an unexpected thaw. Under the gigantic weight, the water spread in a thin layer over the rocks and thereby created a lubricating layer. And in fact, in this place the ice is now not creeping, but sliding towards the ocean. As glaciologists calculated, at the site of the former lake, the rate of creep of the Greenland shield doubled.
In addition, the strength of the ice now covering the lake has greatly decreased. Under the influence of water, the former bottom of the runaway Greenland lake now resembles a holey cheese. This means that the glacier will crack faster and more severely. Every year, the sun and warm winds from the south will again increasingly melt the surface of the shield, the water will continue to erode the glacier, and this cracking kilometer-long layer of ice will slide faster and faster towards the ocean.