Ice reservoir
An ice reservoir , also a glacial reservoir or a glacier reservoir , is a lake in a valley or basin that is temporarily or permanently prevented from flowing off by glaciers .
Occurrence
Ice reservoirs are mostly formed in the immediate vicinity of a glacier on its edge. They can also form on, in and under a glacier. Ice reservoirs below a glacier are called subglacial . Due to the greater density of the water compared to the ice, they are quite stable. A well-known example of a subglacial lake is the Vostok Sea in Antarctica .
Ice reservoirs can be found in all glaciated areas of the world. In the Himalayas there are thousands of glacial lakes. 750 lakes are recorded for Alaska alone , an accumulation of ice reservoirs can be found in Siberia , especially in the Altai Mountains . A European example of an ice reservoir is the Märjelensee on the Great Aletsch Glacier , which was 78 m deep at the end of the 19th century.
Ice reservoirs and the like were much more widespread. a. during the last glacial periods (Weichsel-Würm and Saale-Riss) in the Pleistocene . In the meantime, the Fennoscandian Ice Sheet (also known as the Scandinavian Ice Sheet ) extended to northern Central Europe for a time, and the Alps were also widely glaciated. As a result, more or less extensive ice reservoirs formed in northern Germany as well as in the foothills of the Alps (partly also in the Alps themselves). Their size fluctuated widely and was between a few hundred square meters and several thousand square kilometers. A typical example of a very large European ice reservoir is the Baltic ice reservoir . About 14,000 years ago, in the area of today's Baltic Sea, there was a huge ice reservoir in front of the 2–3 km thick Scandinavian inland ice of the Vistula Ice Age . It was only around 10,000 years ago that the thawing ice barrier between the ocean and the ice reservoir released the central Swedish depression , causing the "Baltic ice reservoir" to leak.
Deposits
The existence of ice reservoirs that no longer exist today can be proven by means of typical lake deposits. Since the water in ice reservoirs generally does not flow or only flows very slowly, the deposits in ice reservoirs usually consist of fine-grained sediments , especially clay and silt . At the edge of the ice reservoirs, especially at the confluence of meltwater into the basin, there are also sand or even coarser material. Typical deltas are sometimes formed there. Due to the seasonal fluctuations in the amount of meltwater (almost nothing in winter, very large amounts in summer), much and coarser material was carried into the lakes in the summer months (silt). In winter, however, very fine material (clay) could settle in very calm conditions. So-called band clays ( warventones ) emerged, which today are often the only indicators of ice reservoirs in formerly glaciated areas. The seasonally controlled deposition of the ice reservoir sediments is the reason that they represent a valuable archive for the reconstruction of the history of the climate and glaciation. For example, the counting of the band clays of the Baltic Ice Reservoir enabled the exact reconstruction of the ice retreat in Scandinavia .
outbreaks
Since ice reservoirs are episodically or periodically affected by fluctuating water inflows, ice reservoirs overflow time and again, which in individual cases lead to catastrophic ice reservoir outbreaks when the released water masses suddenly shoot down into the valley. Another cause of eruptions is the lifting of the glacier by the 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 briefly exceed the water volume of even large currents on earth several times over.
Because of the remote location of most ice reservoirs, there are few descriptions or even photos of such eruptions.
Examples of eruptions of the present
-
Lake Argentino in the South Patagonian Andes
- Advance of the Perito Moreno Glacier , which dammed up part of the tributaries and split the lake in two
- Eruption in the 1950s with an outflow of 20,000 m³ of water per second over a period of a few hours
-
Russell Fjord in southern Alaska near Yakutat
- Advance of the Hubbard Glacier , which seals off the bay from the occasional sudden advance
- Eruptions in 1860 (storage height of 39 m); 1986 (water level 25 m and peak discharge of 104,500 m³ / s); 2002 (water level 18 m and peak discharge of 54,000 m³ / s).
-
Grímsvötn lakes in Iceland
- Locking off a depression at the edge of the Vatnajökull ice cap .
- Outbreak in 1996 through activities of Grímsvötn - volcano , in which part of the ice sheet broke off (peak flow of 45,000 m³ / s, the release of 3.4 billion cubic meters within two days)
Consequences of ice reservoir eruptions
The overflow of an ice reservoir is of economic importance when human settlements, industries and transport routes are affected; and it is of ecological importance when, for example, inlets are blocked by glaciers, the water behind the barrier is sweetened and ocean currents are changed.
The ecological effects can even lead to global climate changes, as the following studies show.
The most powerful known flood wave after ice reservoirs ran out occurred about 16,000 years ago in southern Siberia in the northern Altai in the Ob river system . It was preceded by several similar events, probably of a somewhat lesser extent, after the end of the last glacial maximum.
During the last Ice Age , an ice reservoir was formed in North America south of the Laurentide Ice Sheet , known as Lake Agassiz , after the co-discoverer of the Ice Age phenomenon. This ice reservoir covered an area of around 150,000 km², about the size of Greece , north of today's Great Lakes about 9,000 years ago .
On the basis of the traces of abrupt reservoir outbreaks at the time, it can be demonstrated that this ice reservoir, in addition to the 'normal' outflows to the south, west and northeast, occasionally also had abrupt eruptions in the northeast towards the North Atlantic . Scientific calculations are based on runoffs of 5,200,000 m³ / s in the short term, with up to 160,000 km³ of water being released. It can be assumed that the fresh water that was released at that time, due to its lower density, was superimposed on the salt water currents of the sea surface and thus markedly changed the global thermohaline circulation of the sea water. As a result, a temporary interruption of the Gulf Stream is suspected, which otherwise gives northern Europe a mild climate due to its warm water currents, with cooling and cold setbacks such as in the recent Dryas period .
See also
- Lech dl Dragon glacier lake in the Dolomites
literature
- Jürgen Herget : Ice reservoir eruptions - cause of catastrophic floods. In: Geographische Rundschau , 2/2003, pp. 14–20
Web links
Individual evidence
- ↑ Glacier lakes in Tibet threaten human life. In: science.orf.at . April 10, 2019, accessed May 9, 2019 .
- ↑ VR Baker : Global Late Quaternary Fluvial Paleohydrology: With Special Emphasis on Paleofloods and Megafloods. ( PDF; 1.2 MB ) In: John F. Shroder (ed.): Treatise on Geomorphology. Volume 9: Fluvial geomorphology. Elsevier, Amsterdam 2013, pp. 511-527.
- ↑ Keenan Lee: The Altai Flood. On: geology.mines.edu of October 4, 2004 ( PDF file ( Memento of August 11, 2011 in the Internet Archive )).
- ↑ Alexei N. Rudoy : Glacier-dammed lakes and geological work of glacial superfloods in the Late Pleistocene, Southern Siberia, Altai Mountains. In: Quaternary International. Vol. 87, No. 1, January 2002, pp. 119-140, doi : 10.1016 / S1040-6182 (01) 00066-0 .
- ↑ Alexei N Rudoy, VR Baker: Sedimentary effects of cataclysmic late Pleistocene glacial outburst flooding, Altay Mountains, Siberia. In: Sedimentary Geology. Vol. 85, No. 1-4, May 1993, pp. 53-62, doi : 10.1016 / 0037-0738 (93) 90075-G ( full text online ).
- ↑ Victor R. Baker, Gerardo Benito, Alexey N. Rudoy: Paleohydrology of late Pleistocene superflooding, Altai Mountains, Siberia. In: Science. January 15, 1993, Vol. 259, pp. 348-352 ( PDF file ).