Solifluction

Solifluction or soil flow is a form of erosion of the earth's surface, which occurs as slow, large-scale flow movements of loose rock material in the thawing zone of the permafrost and is related to periglacial processes and gelifluction .

Solifluid processes shape the landscape, especially in the subpolar arctic mountains of Eurasia and North America, extending into the tundra zone . In the middle and lower latitudes, as shaping processes, they take a back seat to the effects of precipitation and snow melt water. Since processes of solifluction outside the subpolar areas only occur between the forest and snow line of the high mountains, the geomorphological term of the solifluction stage was created for this .

For the general geomorphological definition of the term high mountains , the solifluction with the surface erosion by frost action is a determining feature, in addition to recent or Quaternary glaciation and the presence of a treasure trove of glacial forms as well as the climatic formation of an upper tree line.

Gelifluction on Svalbard

Basics

The cause is the thawing of topsoil layers above the permafrost area with a certain slope of the relief. The thawing layer (the active layer "active layer") of the soil is mostly saturated with water, since the permafrost in the subsoil prevents the water from seeping away . The water saturation reduces the friction in the soil substrate, which enables the downhill flow movement.

Solifluction is the most important erosion and transport process in the periglacial area. It is effective on very flat slopes from a slope of about 2 °.

In addition to water saturation, the solifluction is linked to a sufficiently high proportion of fine material (fine sands, silts, clays). Movement amounts of 5–10 centimeters per year can be achieved. In solifluction soils there are stones set parallel to the slope and often press structures.

In contrast to soil crawling, the downhill movement in solifluction occurs through actual flow processes that are caused by the water-saturated soil above the frozen subsoil and develop characteristic morphological forms on the surface. When crawling in the ground, the movement takes place exclusively through displacement, which is caused by the periodic effects of contraction and expansion.

Morphological forms

Solifluction is the decisive process that leads to the formation of periglacial layers (cover layers, rubble layers) such as the main layer common in Central Europe .

• Solifluction tongue: Soil substrates displaced downhill with solifluid usually have a tongue-like shape.
• Solifluction lobe : The bulge at the front of the solifluction area caused by the downward flow of the ground. The front of a solifluction tongue can also be seen as a praise. The form Riedel is called a fossil terrain form .
• Solifluction niche: Practically the area of ​​origin of the solifluidally displaced soil substrate. The relocation caused a dent in the slope above the solifluidally relocated material.

In the relief formation, the smooth slope formation is attributed to solifludial debris corrosion. Smooth slopes are particularly widespread in the arid regions, where often only the poleward layers are or have been glacial. On expositions facing the equator, there are smooth slopes several hundred meters high. A strong slope asymmetry with karen on the north side and smooth slopes on the south side is widespread, for example, in the dry mountains of the Mediterran up to the Hindu Kush.

During the Ice Ages there were valley asymmetries due to the climate, the asymmetrical valleys of the European hilly landscapes, with one flat and one steep slope. The steep slope is always the slope that is more exposed to the sun, which in the periglacial has become steeper due to the greater thawing depth and greater denudation of the solifluction due to the lateral undercut of a river.

Types and special shapes

• Time of day / season solifluction : Time of day solifluction is understood to mean a daily change in frost (freezing at night, daily thawing) and seasonal solifluction is understood to be a seasonal change of frost (summer / winter). Under certain conditions, humpback meadows could develop from this .
• Periglacial solifluction : Occurrence in arctic and subnival mountain areas in the vicinity of the large inland ice masses and high mountain glaciers.
• Free solifluction : easier soil flow in the absence of a closed, binding vegetation cover .

Garlands (form of bound solifluction) in the Swiss National Park on the Ofen Pass

• Bound solifluction : tearing of the sward and formation of demolition niches (lawn stairs) in the vegetation cover. Rolled up grass carpets can accumulate at the foot of the slope . In Switzerland this form of solifluction is called the garland .
• Kammeissolifluktion : Ground parts are lifted by growing ice at right angles to the surface of the terrain. When the comb ice thaws , the soil substrate settles down the slope. Depending on the inclination of the relief, this results in a slight downward offset.
• Microsolifluction / cryoturbation : In the event of a change of frost, material is also sorted in the upper soil layers in addition to soil movement. Cause of the formation of structured soils .
• Macrosolifluction : Similar to microsolifluction, but on steeper slopes and therefore with greater effect .

literature

• Carl Troll 1944: Structured Soils, Solifluction and Frost Climates of the Earth . Geological Review, 545–694.
• Lothar Eißmann : Periglacial processes and permafrost structures from six glacial periods of the Quaternary. A contribution to the periglacial geology from the point of view of the Saale-Elbe area (= Altenburger Naturwissenschaftliche Forschungen. Vol. 1, ISSN  0232-5381 = Treatises and reports from the Natural History Museum Mauritianum Altenburg. Special issue). Mauritianum, Altenburg 1981.
• Arno Semmel : Periglacial morphology (= income from research. Vol. 231). 2nd, unchanged edition. Scientific Book Society, Darmstadt 1994, ISBN 3-534-01221-6 .

Individual evidence

1. ^ Hermann Lautensach 1960: Carl Troll - A researcher's life. In: Geography. Volume 13, No. 4, Bonn 1959, pp. 245-258; here p. 250.
2. ^ Carl Rathjens 1982: Geography of the high mountains: 1. The natural space . Teubner Study Books Geography, Teubner, Stuttgart. ISBN 3-519-03419-0 Here p. 105
3. ^ Carl Rathjens 1982: p. 105.
4. ↑ Commision on Mountain Cartography The term high mountains
5. ^ Carl Rathjens 1982: p. 105
6. ↑ Spectrum Lexicon of Geography: Glatthang [1]
7. ↑ Spectrum Lexicon of Geography: Asymmetrical Valleys Asymmetrical Valleys