On the origin of the drumlins of the South German Alpine Foreland

Abstract

The drumlins formed during the last (Würmian) glaciation in the South German Alpine Foreland are situated in distinct topographic positions. These drumlins are found on the gently ascending Molasse socles between the glacially incised basins, and behind the terminal moraines of the (in the Rhein glacier area so-called) Inner Young Terminal Moraines. The former position has been explained as a result of differential ice thicknesses between the basins and the Molasse interfluves. The latter position remained problematical. Recent investigations in the frontal area of the past Iller glacier indicate that: (1) the formation of the drumlins date from one distinct glacier re-advance (the Luiblings Phase), and (2) the permafrost table within near-surface sediments, at the time of drumlin formation, was at a sufficient depth not to have any influence upon the formative processes at surface level. The drumlins, therefore, formed because the glacier re-advanced over decaying permafrost within non-lithified Pleistocene sediments, whereas in the past the ice had advanced over frozen ground and later over unfrozen ground. This situation, as found in front of the Iller glacier, is not an exceptional case. In comparing three other areas—the western Rhein glacier area, the Inn-Chiemsee area and the eastern flank of the Iller glacier—a general conformity of both landforms and glacial processes was found to exist. However, where slight variations do occur adequate explanations can be made.