Dead ice
As dead ice is called glacial ice, which with the active glacier is no longer connected, as a result, no longer moved and is mostly covered with sediment.
Use of terms
Colloquially, the term dead ice is generally applied to glacier ice that is no longer moving. In the language of science, however, it is common to distinguish between stagnant ice and dead ice. Stagnant ice can still have contact with the active glacier. In any case, it has not or has not yet been covered with sediment. Dead ice, on the other hand, has lost contact with the active glacier and was covered with sediments (mostly meltwater sands from the glacier).
Emergence
Dead ice occurs because the ice on a melting glacier does not thaw evenly. Even when most of the ice has melted, more or less large blocks always remain in the formerly ice-covered area. This is very often the case, especially in areas with locally increased ice thickness, such as tongue basins or glacial channels . Melt water flowing in from the active glacier deposits material (mostly sand ) next to and finally above the ice blocks . This is how the ice becomes dead ice.
Preservation and melting
Since the sand cover acts as insulation against solar radiation, dead ice usually only melts very slowly. In addition, the formation of a permafrost soil can preserve the dead ice in the ground for several millennia. Extreme cases with about 70,000 years old dead ice have been documented from northwestern Siberia. Only with further warming does the permafrost dissolve and the dead ice melts.
With today's glaciers without permafrost in the area, the time until the dead ice finally melts depends on the climatic conditions, on possible shading in deep valleys and on the amount and type of overlying sediments. Melting here can also take years or even decades.
As the subsurface melts, the surface slowly sags above the dead ice and a dead ice hole or kettle can form. If the bottom of the boiler is below the groundwater level, a dead lake is created .
Dead ice can also subsequently also deposited sediments (z. B. glazifluviale sands or flight Sande by pauses). Dead ice forms can therefore also be found on Sandern near the former edge of the ice .
Evidence of dead ice
Geologically
The detection of melted dead ice is usually not easy to carry out geological-sedimentologically. Since dead ice kettles are often low-lying areas with high groundwater levels , excavations can rarely be carried out. If it is possible, especially at the edges of the basin, there are expansion phenomena in the sediments. A reliable indication of formerly existing ice blocks are faults in the sediment layers. The thawing of the ice caused the deposits to sag.
Geomorphologically
Hollow forms that were closed on all sides in the formerly glaciated areas are usually interpreted as kettle kettles. This interpretation is safe when the boilers occur in areas where such boilers do not normally exist, such as sand areas and glacial valleys . The meltwater would normally spill such cauldrons quickly. A previously existing block of dead ice is the most plausible explanation for the preservation of such a hollow shape.
Dead ice kettle (dead ice hole)
Small, completely closed hollow shapes are generally referred to as dead ice kettles or holes, the formation of which is attributed to the spilling and subsequent thawing of a block of dead ice. Due to their small size (less than 1 hectare) they usually have a rather regular, rounded shape. But they can be more than ten meters deep. Today many of them contain small bodies of water ( brooks ).
distribution
The formation of dead ice is a process that can be observed very frequently in the melting areas of glaciers, which is why dead ice kettles occur worldwide in all newly glaciated areas. Outside of Germany, they are found in large numbers in southern Sweden and North America, for example .
Germany
During the Ice Age, with its repeated ice advances in northern and southern Germany, dead ice was a widespread phenomenon of ice retreat. Above all, the hollow forms of the most recent glaciation - called the Würm Ice Age in southern Germany and the Vistula Ice Age in northern Germany - are still quite fresh and very numerous in the areas that were formerly covered by ice. They are therefore very widespread in northern Brandenburg , Mecklenburg-Western Pomerania and in the Bavarian Alpine foothills .
Southern Germany
The dead ice blocks that melted at the end of the last ice age gave rise to smaller lakes, for example the Osterseen south of the Starnberger See or the Eggstätter lakes northwest of the Chiemsee . Also in Upper Bavaria , in the Hague, there is a Toteiskesselweg with two routes - one to Höhenberg, the other to Limberg. Numbered boulders mark the way. You can see different stages of siltation (pond, Großseggenried, moor, swamp meadow). A beautiful example of a funnel-like kettle (diameter approx. 50 m) can be found right next to the federal road 471 near Grafrath in the Fürstenfeldbruck district . You can also admire a dead ice hole near Ebersberg .
In Upper Swabia, the Blitzenreuter Lake District along the B32 with the Dornacher Ried and the Schreckensee is worth mentioning. Buchsee, Bibersee, Vorsee and Schreckensee are considered to be dead ice holes.
Northern Germany
In Berlin and Brandenburg in particular, many, if not most, lakes have to assume that their basins will be preserved by dead ice, as they are located within glacial valleys or sand areas. Especially within the Berlin glacial valley there are numerous lakes (including Müggelsee , Langer See ( Dahme ), Rummelsburger See ), the preservation of which in the glacial valley can only be explained by preservation by means of dead ice. On the Baltic island of Fehmarn , the ponds Kriegssoll and Ratssoll were created by dead ice, in Mölln in southern Schleswig-Holstein the Grundlose Kolk .
Austria
- The Meerauge in the Southern Limestone Alps: In a small high valley in the Carinthian Karawanken , the Bodental , there is a smaller kettle hole with national fame. It is known as the " sea eye ". Its turquoise-blue water color and the rising bubbles have always stimulated people's imagination. Popularly one suspected of an underground connection to another lake or even to the sea.
- In the Tyrolean low mountain range there are numerous remains of dead ice ( e.g. Lanser See , Viller Moor , Wirtssee near Grinzens)
See also
Web links
Individual evidence
- ↑ Stolz, C. (2012): Holocene sediment fillings of silted up brooks and floodplain deposits south of Flensburg. Geomorphological investigations in the valley of the Jarplunder Au. - Natural and regional studies 119, 10–12: 150–161.
- ^ "Wolfsgrube" near Grafrath (Bavaria)
- ↑ Toteisloch in the city forest near Ebersberg (Bavaria) South of it, the Steinsee and in Glonn the Kastensee have formed from dead-ice holes.
- ↑ - ( Memento of the original from December 10, 2015 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ - ( Memento of the original from December 17, 2015 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ - ( Memento of the original from January 31, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
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