Drumlin ( English drumlin from Irish. Droimnín ) - an elliptical hill, folded moraine , oriented along the movement of the glacier [1] . The term itself was first used in 1833.
Drumlins are composed of (mainly) the main moraine and boulder clay, which gave shape and smoothed ice moving over them. In some (but not all) cases they have a core of indigenous, mostly crystalline, rocks . Usually located in clusters in the areas of distribution of the Pleistocene ice cover and form a mine and a landscape of the cave.
The longline axis of the drumlins extends parallel to the direction of the former ice movement. The gentle and long slope faces the retreating glacier, the opposite - usually more pronounced, steep and high. The sizes of typical drumelins range from a few hundred meters to 2.5 km in length, 100-600 m in width, and a height of 10-45 m. There are also larger specimens.
Origin
Geomorphologists are considering several hypotheses for the formation of a drumlin . According to the basic theory, in the lower layers of the glacier there was accumulation of precipitation and the formation of a “blanket”, facilitating the movement of ice flow. Irregularity of the flow periodically arose when the lower layers lost mobility due to overload with detrital material and were blocked by the moving upper layers. Fragments of cracks in the marginal part of the glacier were filled with debris and subsequent projection of these clusters onto the surface of the main moraine . Thus, the upper layers processed material of the deposited moraine, creating the characteristic shape of drumlin. Such forms are widely distributed in landscapes of the main (bottom) moraines of the glaciation areas. [2] .
Notes
- ↑ Geological dictionary / O. AT . Petrov. - the third, revised and enlarged. - St. Petersburg: VSEGEI , 2010.
- ↑ GEOGRAPHICAL DICTIONARY of ecosystema.ru
Literature
- General geomorphology. Textbook. - 3rd ed., Pererab. and add./G. I. Levers. - M.
- Pazinich V.G. Ice age, ice sheets, gravitational collapse, water-ice flows and their consequences. Part one. Drumlins https://www.academia.edu/4254377/_GB._Ice_age_ice_sheets_the_gravitational_collapse_water-ice_deluge_and_their_consequences._Part_one._Drumlins