Nivation

The term refers to Nivation in geomorphology weathering and erosion processes, also subordinated to deposition and accumulation processes are intensified accelerated by temporary and perennial snow patches in periglacial and / or. The term has, however, experienced different definitions and is therefore not without controversy.

Conceptual history and definition

For the geomorphological processes of temporary and perennial snow patches in the Bighorn Mountains (Wyoming) led Matthes (1900) the term Nivation one. The term was also applied to the formation processes of temporary and perennial snow patches in the polar regions Periglazialgebiete. Later writers have much broader the term; on the landscape shaping by snow in general, the effect of snow on the ground by movement, pressure and meltwater. Schunke (1974 ) saw in the Nivation a complex phenomenon of frost wedging, solifluction, rinsing, and Kryoturbation Sturzdenudation.

In the mountains Nivation occurs over a large area above the tree line in the alpine and subnivalen height on stage, especially in unconsolidated deposits, rare even below the tree line. The main distribution lies in the periglacial the polar regions.

Nivationsprozesse and surface forms

In the periglacial with unconsolidated surface sediments and permafrost in the early summer snow patches dominate the geomorphological development of vast areas and control the distribution of vegetation. The distribution of snow patches in turn is determined by the landform itself, due to the dominant wind directions in winter and the snow depth. Snow patches form usually always in the same positions, usually in hollows and apern only from much later than the already snow- free environment. Below the snow patches occur from melt water and soak the ground there in particular. This can take place in particular here frost dynamic processes, such as an intense frost weathering. In addition also enhanced chemical weathering in the field of snow patches.

Other impacts associated with patches of snow processes are smaller landslides and Erdfließen, niveo - aeolian sediment transport, sediment transport by flowing water on the snow or in tunnels under the snow, erosion by the slow-moving snow and running water under the snow, solifluction and Abluation.

The main geomorphological landforms of Nivation are hang parallel depending on slope, or semicircular Nivationsmulden, Nivationswannen or Nivationsnischen ( in shallow relief) that can grow by more crashes slope uphill. The fact that repeatedly form in these niches snow patches, deepen and enlarge these niches and on. A special feature is Nivationsterrassen can form. On steeper slopes to Nivationstrichter and Nivationsrunsen form.

At the bottom of the niches can form small earthworks by pushing together of earthy material, or by landslides of earth over the snow. By Abluation can form stone pavement, and of alluvial gullies and alluvial fans below the snow patches in the run-up to the snow patches.

In the broader sense of the term also Schneehaldenmoränen, avalanche Tobel, Blattanbrüche, snow and Lawinenschurf - Plaiken be included as well. However, most authors do not follow this broad definition.