Gelifluction

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Gelifluction on Svalbard

Gelifluction (from Latin gelare “freeze” and fluere “flow”) describes slow movements of substrate on slopes in the periglacial environment.

Often the terms gelifluction and solifluction are used synonymously, other sources use solifluction as a generic term for various periglacial processes and limit the term gelifluction to soak flow.

Gelifluction processes

Several sub-processes can be attributed to the soil movements called gelifluction under periglacial conditions,

Soak Flow

In the periglacial areas , the impregnation flow is usually the most important in quantitative terms. This is a viscous , laminar glide-flow process, in which soil particles or parts are more or less slowly shifted following the gradient.

The process of solifluction in general is linked to a high water content in a substrate rich in fine materials . These are achieved in the periglacial milieu, i.e. in the case of gelifluction, in particular through the damming effect of the ground ice, which is still frozen or frozen all year round, and through water accumulation during the snowmelt . A high water content reduces the cohesion of the soil particles. The flow pressure of laterally draining water, the pore water pressure , probably also plays a role , with water that is released during melting faster than it can drain off, leading to excess pore water pressure. Particularly important is the loosening of the structure through the volume expansion of the water during freezing and the formation of segregation ice, i.e. ice lenses or layers in the substrate that were formed by hygroscopic migration of the pore water towards the freezing front. The interaction of these diverse influences, which can complement and replace each other, has the effect that the saturation flow is not necessarily linked to water saturation, but can also take place when the flow limit is reached .

Contrary to popular belief, gelifluction is not linked to the appearance of permanently frozen ground; Especially on subsoil that is only seasonally frozen, particularly high movement rates of up to 1 meter per year were measured in the Alps, in contrast to values ​​between 1 and 12 centimeters per year that are usual in permafrost areas.

The widespread view that the masses moved by gel fluidization increase or decrease proportionally to the slope inclination is not generally applicable: On the contrary, the higher water saturation in the flat relief can (over) compensate for the more pronounced gravity components on the steeper slope.

General conditions of gelifluction

The adverse conditions in the affected areas may explain why there are only very few long-term series of measurements on gelifluction. In particular, a measuring field in the Alps that has been in operation for many years made it possible to quantify many influencing factors: accordingly, the slope of the slope plays a subordinate role there, and the vegetation only has a braking effect on the process when the degree of coverage is relatively high . In contrast, the lateral water supply, the roughness of the small relief and the dynamics of the snow cover proved to be important. H. the wind displacement of the snow and its ablation . These parameters determine the depth of penetration of the ground frost and thus the speed and thickness of the gelifluid movement.

Gelifluction sediments

The deposits resulting from gel fluidization can have very different forms, depending on whether they were subjected to other processes in addition to gel fluidization, such as rinsing or cryoturbation , which could have led to structural changes in the sediment.

Gelifluction sediments can otherwise be recognized by a typical property: The laminar movement causes the coarse parts of the soil skeleton to be aligned (regulated) with their longitudinal axes in the direction of movement, i.e. in the direction of the slope. Gelifluction sediments are also matrix- supported , i.e. H. it is a very fine-grained substrate, often with a predominance of silt . The segregation ice, which was important in the formation of the sediments, can often still be recognized by the flat structure of the bottom.

Active gelifluction areas are often characterized by praise as surface shapes. However, these are usually noticeably leveled as soon as the causal process no longer works. Thus, they can rarely serve as indicators of this process. Instead, gelifluction sediments appear as flat, horizontally poorly differentiated veils. The fact that a differentiation in layers of different facies is often possible vertically is less to be assigned to gelifluction than to differences in the added loess components .

Importance of gelifluction

The engineering-geological significance of the mass movements during construction work on unstable subsoil is evident. They influence the stability of the subsoil in the high latitudes, where use increases, in particular due to the extraction of raw materials . In some high mountains, the density of use is sometimes even greater, e.g. due to tourism . In particular, it can be important that the process in the event of malfunctions, e.g. B. shifts in weight in the course of construction work, can turn into faster movements up to mudslides and then gain even greater destructive power.

The importance of the gelifluction, which prevailed in the unglaciated areas of the middle latitudes during the Pleistocene glaciers , for today's locations is often neglected . Gelifluction was the dominant process in the formation of the periglacial layers , the most common starting material for the post-glacial soil formation in the low mountain range .

See also

Individual evidence

  1. ^ Henri Baulig: Peneplains and pediplains. In: Geological Society of America Bulletin. Vol. 68, No. 7, 1957, ISSN  0016-7606 , pp. 913-930, doi : 10.1130 / 0016-7606 (1957) 68 [913: PAP] 2.0.CO; 2 .
  2. ↑ a b c d Arno Semmel : Periglacial morphology (= results of research. Vol. 231). Scientific Book Society, Darmstadt 1985, ISBN 3-534-01221-6 .
  3. ↑ a b c d Hugh M. French: The Periglacial Environment. 3. Edition. Wiley, Chichester, et al. a. 2007, ISBN 978-0-470-86589-7 .
  4. ^ A b Albert Lincoln Washburn: Geocryology. A survey of periglacial processes and environments. Arnold, London 1979, ISBN 0-713-16119-1 .
  5. ^ Lewkowicz group: Slope processes . In: Michael J. Clark (Ed.): Advances in periglacial geomorphology. Wiley, Chichester, et al. a. 1988, ISBN 0-471-90981-5 , pp. 325-368.
  6. ^ A b Norikazu Matsuoka: Solifluction rates, processes and landforms: a global review. In: Earth Science Reviews. Vol. 55, No. 1/2, 2001, ISSN  0012-8252 , pp. 107-134, doi : 10.1016 / S0012-8252 (01) 00057-5 .
  7. ^ EC McRoberts: Slope stability in cold regions. In: Orlando B. Andersland, Duwayne M. Anderson (Eds.): Geotechnical engineering for cold regions. McGraw-Hill, New York NY et al. a. 1978, ISBN 0-070-01615-1 , pp. 363-404.
  8. ^ PJ Williams: Some investigations into solifluction features in Norway. In: The Geographical Journal. Vol. 123, No. 1, 1957, ISSN  0016-7398 , pp. 42-55.
  9. ↑ a b c Philipp Jaesche: Ground frost and gelifluction dynamics in an alpine periglacial area (Hohe Tauern, East Tyrol) (= Bayreuth geoscientific work. Vol. 20). Naturwissenschaftliche Gesellschaft Bayreuth, Bayreuth 1999, ISBN 3-98022-686-7 (At the same time: Bayreuth, Universität, Dissertation, 1999).
  10. ↑ K.-H. Emmerich 1990, cit. according to A. Kleber: Timing of the Central European upper layer ("Hauptlage") - a synthesis (deduced from analogues). In: Journal of Geomorphology. NF Vol. 48, No. 4, ISSN  0372-8854 , pp. 491-499.
  11. ↑ Heinz Veit, H. Stingl, K.-H. Emmerich, Brigitte John: Temporal and spatial variability of solifluidal processes and their causes. An interim report after eight years of solifluction measurements (1985–1993) at the “Glorer Hütte” measuring station, Hohe Tauern, Austria. In: Journal of Geomorphology. NF Supplement-Vol. 99, 1995, ISSN  0044-2798 , pp. 107-122.