Diffluence stage

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A diffluence level (sometimes also transfluence level ) is a terrain level created in connection with a diffluence - i.e. the branching of a glacier  - through glacial erosion in a valley . There are two different definitions of a so-called stage:

  • on the one hand there is a step below the branch point, which is directed against the general slope of the valley and which is caused by the thinness and friction there;
  • on the other hand, the step in the valley slope of the main valley to the opening of the hanging side valley of the branching smaller branch.

A diffluence stage is the counterpart to a confluence stage that can occur at the junction of former glaciers.

Occasionally the term “transfluence level” is also used when a distinction is made between diffluence and transfluence - the latter expression is used when the crossing already takes place at the source of the valley and glacier ice thus reaches another valley system via a main watershed .

Descending step down the valley below the branch point

According to this definition, which can be found almost exclusively in today's literature, a diffluence stage can arise in the main stream of the glacier behind the diffluence, i.e. below the point at which part of the glacier's ice masses took a different path. The reason for this is considered to be that there is less glacial erosion, particularly deterion , due to the reduced ice pressure and lower flow velocity . In this way, a terrain level opposite to the general slope of the valley could arise. It should be noted, however, that during and after the retreat of the glacier a glacial and fluvial filling takes place, which can cover this step, which would only be detectable by seismic investigations. It should also be noted that there are also other glacial processes that create depressions and thus also steps.

Valley slope to the Diffluenzpass

Albrecht Penck , who established the term “Diffluenz” at the beginning of the 20th century, used the term “Diffluenzstufe”, at least initially, exclusively for the ascent from the main valley to the gap in the Diffluenzpass . This becomes clear from the following quote:

The steps of confluence are seen in the hanging mouths of side valleys; the steps of diffluence are hanging openings of those valleys which were entered by a branch of the ice. The height of both kinds of steps will generally be more considerable, the greater the difference between the main glacier and its affluent or diverting branch.

“Stages of confluence can be recognized as hanging mouths of side valleys; Diffluence stages are hanging openings in the valleys into which a branch of the ice flow has penetrated. The height of both types of steps is fundamentally more important, the greater the difference between the main stream and the incoming or outgoing branch. "

An example of such a differential stage can be found at the Brünig Pass . At this point, ice from the ice age Aar glacier left the Aare valley to the north and reached the Sarner Aa valley via this pass .

Individual evidence

  1. ^ A b Eduard Gerber: The longitudinal profile of the alpine valleys. In: Geographica Helvetica. Volume 11, 1956, pp. 160-215 ( online )
  2. ^ A b Albrecht Penck: Glacial features in the surface of the Alps. In: Journal of Geology. Volume 13, 1905, pp. 1-19 ( online ).
  3. ↑ David Leslie Linton: The Forms of Glacial Erosion. In: Transactions and Papers (Institute of British Geographers). No. 33, 1963, pp. 1-28 ( abstract ).
  4. ↑ Harald Zepp: Geomorphology: An Introduction. 5th edition, Verlag Ferdinand Schöningh, Paderborn 2011, ISBN 978-3-8385-3593-7 , p. 198 ( Google books )
  5. ↑ Diffluence level at Spektrum.de
  6. ↑ Diffluence level at geodz.de
  7. ↑ Julia A. Jackson, James P. Mehl, Klaus KE Neuendorf: Glossary of geology. Springer Verlag, Berlin 2005, ISBN 0-922152-76-4 , p. 179. ( Google books )
  8. ↑ Heribert Louis: On the theory of glacial erosion in valleys. In: Ice Age u. Present. Volume 2, 1952, pp. 12-24 ( online )
  9. ↑ Frank Preusser, Jürgen M. Reitner, Christian Schlüchter: Distribution, geometry, age and origin of overdeepened valleys and basins in the Alps and their foreland. In: Swiss Journal of Geosciences. Volume 103, 2010, pp. 407-426 ( online )
  10. ^ Albrecht Penck, Eduard Brückner: The Alps in the Ice Age. Tauchnitz Verlag, Leipzig 1901–1909, Volume III, p. 811
  11. ^ William Morris Davis, Alfred Rühl: The explanatory description of land forms. Teubner Verlag, Leipzig and Berlin 1912, p. 445 ( online )
  12. ↑ Map section with Brünig Pass at geo.admin.ch