Nivation

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In geomorphology, weathering and erosion processes - subordinate also deposition and accumulation processes - are referred to as nivation (from Latin nivalis 'snowy'), which are accelerated and / or intensified by temporary and perennial snow patches in periglacial areas. The term is used with different broad definitions and is therefore controversial.

Concept history and definition

Matthes (1900) introduced the term nivation for the geomorphological processes on temporary and perennial patches of snow in the Bighorn Mountains ( Wyoming ) . The term was also transferred to the formation processes of temporary (temporary) and permanent (year-round permanent) snow patches in the periglacial areas of the polar regions. Later authors took the term much broader and related it in general to the formation of the landscape through snow: including the effect of snow on the ground through movement, pressure and the meltwater. Schunke (1974) saw nivation as a complex phenomenon consisting of frost splitting , solifluction , rinsing , cryoturbation and fall denudation .

In the mountains, nivation occurs over a large area above the tree line in the alpine and subnival altitudes, especially in unconsolidated deposits, and more rarely below the tree line . The main distribution, however, is in the periglacial areas of the polar regions.

Leveling processes and surface shapes

Leveling troughs on the northern slope of the Feldberg , snow valley vegetation, situation at the beginning of June

In the periglacial areas with unconsolidated surface sediments and permafrost soils , patches of snow dominate the geomorphological development of further areas in early summer and control the distribution of vegetation. The distribution of the snow patches is determined by the shape of the landscape itself, the dominant wind directions in winter and the depth of snow. Snow patches usually form again and again in the same positions, mostly in hollows, and only apper much later than the already snow-free surroundings. Melt water escapes below the snow patches and particularly moistens the soil there. As a result, frost-dynamic processes, such as intensive frost weathering, can start particularly well here. In addition, there is increased chemical weathering in the area of ​​the snow patches.

Other processes associated with snow patches are minor landslides and earth flow, niveo-aeolian sediment transport by wind, sediment transport by flowing water on the snow or in tunnels under the snow, erosion by the slowly moving snow and flowing water under the snow, solifluction and ablation .

The main geomorphological surface forms of the nivation are, depending on the slope, parallel or semicircular leveling hollows, leveling troughs or leveling niches (in flat relief), which can grow uphill through further slopes. Since patches of snow repeatedly form in the niches, these deepen and enlarge. Nivation terraces can develop as a special feature . Nivation funnels and leveling rinks form on steeper slopes.

At the lower edge of the niches, small earth walls can be formed by pushing together earthy material or by sliding earth over the snow. Rinsing can create stone pavement in the run-up to the snow patches, as well as alluvial erosion channels and ablate sediments in alluvial fans below the snow patches.

Extended meaning

In the broader sense of the term, snow heap moraines, avalanche tobels, broken leaves, snow and avalanche throw plaques are also included. However, most authors do not follow this broad definition.

Individual evidence

  1. ↑ a b Alexander Stahr and Thomas Hartmann: Landscapes and landscape elements in the high mountains. 398 pp., Springer Verlag 1999 ISBN 978-3-540-65278-6

literature

  • Hanne Hvidtfeldt Christiansen: Nivation forms and processes in unconsolidated sediments, NE Greenland. Earth Surface Processes and Landforms, 23: 751-760, New York 1998 doi : 10.1002 / (SICI) 1096-9837 (199808) 23: 8 <751 :: AID-ESP886> 3.0.CO; 2-A
  • Matthes, François Emile: Glacial sculpture of the Bighorn Mountains, Wyoming. United States Geological Survey 21st Annual Report 1899-1900, p. 167-190, Washington, 1900
  • Andrew Goudie: Nivation. In: Andrew Goudie: Encyclopedia of geomorphology, Volume 2. pp. 718-720, London et al. a., 2004 ISBN 0-415-32738-5
  • E. Schunke: Forming processes on patches of snow in the Icelandic highlands. Treatises of the Academy of Sciences in Göttingen, Mathematical-Physical Class, 3: 274-286, Göttingen 1974
  • Karl N. Thome: Introduction to the Quaternary. 287 pp., Springer, Berlin 1998 ISBN 3-540-62932-7
  • Colin E. Thorn: Nivation: A geomorphic chimera. In: Michael J. Clark, (Ed.): Advances in Periglacial Geomorphology . 5-31, Wiley, 1988 ISBN 0-471-90981-5
  • Colin E. Thorn and Kevin Hall: Nivation and cryoplanation: the case for scrutiny and integration. Progress in Physical Geography, 26 (4): 533-550, 2002 doi : 10.1191 / 0309133302pp351ra
  • Harald Zepp: Geomorphology: an introduction. 385 S., Paderborn, Munich a. a., Schöningh, 2008, ISBN 978-3-8252-2164-5 ISBN 978-3-506-97013-8