Drumlin

Drumlins (of Irish droimnín [ drim'n'i ː n ' ] "little back ", " ridge " ) are elongated hills of drop-shaped floor plan, the longitudinal axis is the Eisbewegungsrichtung a ( glacial ) glacier. Typical dimensions a length of several 100 to several 1000 m at a height of 10 to be specified in each individual case more than 40 m. The streamlined bodies were formed under an actively moving glacier. They are part of the ground moraine. Drumlins often occur as groups in a fan shape or staggered.

Formation

In the ablation zone of a glacier outweighs the deposition of material, not the ablation. It is usually formed as a glacial till unconsolidated sediment, which are deformed by ice pressure. The interface between the glacier and its deformable surface is wavy after Helmholtz 's law. If the moraine now is a plastic mixture of water and sediments, and the glacier encounters a rocky knolls or a slope that is ground moraine may issue under the pressure built up water so that the subglacial sediments solidify. In other cases, existing surveys and sediments were like older tertiary sands or existing moraines of former glacial phases by a later glacier " overrun". In both cases, they get their streamlined shape by the movement of the glacier.

Dissemination

In Central Europe drumlins are mainly known from the alpine Vergletscherungsgebiet. The Lake Constance region northwest of Konstanz and north of Lindau, the Eberfinger Drumlinfeld near Weilheim, Upper Bavaria and the Zurich Oberland are examples of drumlin landscapes. In northern Germany, drumlins, however, are a rare phenomenon. Ernst Th Seraphim localized some drumlins in northern Teutoburg Forest in the area between Borgholzhausen and Versmold and between Bielefeld, Rheda- Wiedenbrück and ET ​​There are some Drumlingebiete in Jungmoränengebiet Northern Ireland, Poland and the Baltic States, but also there only a few percent of the ground moraine cover. It is controversial whether there is in the Brandenburg Grundmoränenlandschaften drumlins. A candidate there is the little Rummelsberg.

Drumlins are widespread, however in North America.

Similar shapes

In contrast to the drumlins are less streamlined and very elongated Oser caused by melt water, which flowed under the glacier.

The drumlins also the lookalike moutonnées not consist of loose material, but from hard rock and have a slightly different shape. They are a form of glacial erosion.