Proglacial lake
An Ice Lake, also Glazialstausee or glacier dam, is a lake in a valley or basin, which is prevented by glaciers temporarily or permanently flowing away.
Occurrence
Eisstauseen arise mostly in the immediate run-up to a glacier at its edge. You can also form in and under a glacier. Eisstauseen beneath a glacier is called subglacial. Due to the greater density of water compared to the ice, they are quite stable. A well-known example of a subglacial lake is Lake Vostok in Antarctica.
Eisstauseen found in all glaciated regions of the world. Just for Alaska are detected 750 lakes, an accumulation of Eisstauseen found in Siberia, and there especially in the Altai Mountains. A European example of an Ice Lake is the Märjelensee at the Great Aletsch Glacier, the end of the 19th century was still a lake depth of 78 m had.
More widespread were Eisstauseen during the Ice Age. During the glaciations formed in many places, both in Northern Germany and in the foothills of the Alps ( in some cases also in the Alps even ) more or less extensive Eisstauseen. Their size fluctuated widely and ranged from a few hundred square meters to several thousand square kilometers. A typical example of a very large European Ice Lake is the Baltic Ice Lake. About 14,000 years ago, existed on the territory of today's Baltic Ice Lake before a huge 2-3 km thick Scandinavian ice the Vistula glaciation. It was not until about 10,000 years ago was the defrost ice barrier between the ocean and the free agent Swedish Ice Lake Valley, what the " Baltic Ice Lake " brought to leak.
Deposits
The existence of no longer existing Eisstauseen can be detected using typical lacustrine deposits. Since the water is not or only very slowly flows into Eisstauseen in general, the deposits of Eisstauseen usually consist of fine-grained sediments, mainly clay and silt. On the edge of Eisstauseen, especially at the confluence of melt water into the basin but also occur sands or even coarser material. In part, there form from typical Delta. Due to the seasonal fluctuations in meltwater volume ( almost nothing in winter, very large quantities in the summer ) was much coarser material and also entered in the summer months in the lakes ( silt ). In winter, however, very fine material could be in very calm conditions settle down ( sound). It emerged so-called Bändertone ( Warventone ), which often are the only indicators of Eisstauseen in glaciated areas today. The seasonally controlled deposition of Eisstauseesedimente is the reason that they represent a valuable archive for the reconstruction of climate and glacial history. For example, the count of the Baltic Ice Bändertone enabled the accurate reconstruction of the Eisrückzuges in Scandinavia.
Outbreaks
Since Eisstauseen are episodically or periodically affected by fluctuating water supply, it always comes back to overflowing of Eisstauseen, leading in some cases to catastrophic Ice Lake outbreaks when the released water masses suddenly shoot into the valley. Another original cause for outbreaks is the lifting of the glacier by meltwater, again due to the differences in density between ice and water so that the water can flow under the ice. The resulting floods can temporarily exceed the volume of water, even for large currents of the earth several times over.
Because of the remote location of most Eisstauseen there are few descriptions and even photos of such outbreaks.
Examples of the present outbreak
- Lago Argentino in the Andes südpatagonischen Advance of the Perito Moreno glacier that dammed a portion of the inflows and brought about a division of the lake
- Outbreak in the 1950s with an outflow of 20,000 cubic meters of water per second over a period of several hours
- Russell Fjord in southern Alaska near the town of Yakutat Advance of Hubbard Glacier, sealing off the bay with occasional sudden incursions
- Outbreaks in 1860 ( dam height of 39 m); 1986 ( dam height 25 m and peak flow of 104,500 m³ / sec); 2002 ( dam height 18 m and peak flow of 54,000 m³ / sec).
- Grímsvötn lakes in Iceland Sealing off a depression at the edge of the ice cap of Vatnajökull.
- Outbreak in 1996 through activities of the Grímsvötn volcano, in which a portion of the ice sheet broke off ( peak flow of 45,000 m³ / sec, release of 3.4 billion cubic meters within two days )
Consequences of Ice Lake outbreaks
The overflow of a Eisstausees is of economic importance when human settlements, industries and roads are affected; and it is of environmental significance if, for example inlets are blocked by glaciers, aussüßt the water behind the barrier and ocean currents are changed.
The ecological effects can sometimes even lead to effective global climate change, as the following studies show.
During the last Ice Age Ice Lake had a North American Laurentide ice sheet south of the formed which is called Lake Agassiz, after the co-discoverer of the phenomenon of ice ages. This Ice Lake covered about 9000 years ago north of the modern Great Lakes an area of 150,000 km ², about the size of Greece.
On the basis of traces of former abrupt reservoir outbreaks can be shown that this Ice Lake occasionally had sudden outbursts in the northeast next to the 'normal' drains to the south, west and north- east to the north Atlantic. Scientific calculations assume outflows, which have 5.200.000 m³ / sec be short-term, in which up to 160,000 km ³ of water have been given. It is assumed that at the time the released fresh water has settled due to its lower density of the salt water of the ocean currents, thus changing the global thermohaline circulation of the sea water significantly. As a result, a temporary interruption of the Gulf Stream is suspected, the other northern Europe due to its hot water flow brings a mild climate, with a cooling and refrigeration setbacks such as the younger Dryas.