Colluvium

Colluvium (lat .: the alluvial) is the name for a layer of loose sediments , usually several decimetres thick , which arise mainly from soil material that has been redistributed by alluvial deposits or other mostly loamy or sandy loose sediments. Younger colluvia are often humic , but this is not an essential feature. As long as there are no dominant features of a new soil development in the colluvium, it is called Kolluvisol in soil science .

Definition of terms

In the German-speaking world, colluvial sediments are generally understood to be the result of anthropogenic soil erosion caused by flowing water and, in part, by wind movement. In the Anglo-American area, the term colluvium stands for all types of sloping sediments that can also be of Ice Age origin and that were not created by flowing water. Nevertheless z. T. by German-speaking scientists Holocene colluvia, d. H. those that arose under the influence of humans are called Holocene Colluvium . For a better differentiation of the formation processes, material displaced by the wind is called aeolium .

Emergence

Soil erosion mainly occurs on unprotected soil surfaces and when there is no vegetation . This is e.g. B. the case when fields are exposed for too long. Therefore, the formation of culluvia is often increased by agriculture . Deep plowing, plowing in the direction of the fall line and other types of tillage have a beneficial effect on erosion. It can have extremely damaging effects on entire landscapes through loss of humus and sediment removal . The soil material is loosened by flowing water (precipitation) and shifted down the slope following gravity. When the slope decreases, it is deposited again sorted according to the grain size . Coarser particles are deposited at a higher flow speed, i.e. earlier, and finer particles only later at lower transport speeds. The fine material often ends up in streams, ditches or lakes and is deposited there or transported on. Whole soil aggregates (mixtures of grain sizes) can also be displaced colluvially. This greatly attenuates the sorting effect.

Historical and prehistoric colluvia

In the course of the landscape's development, numerous colluvia have often been deposited on top of one another. They are therefore relics of human settlement and some contain archaeological finds or indicators of former soil-forming processes. This means that these deposits can be viewed as geo-archives of landscape history and their analysis can be used to reconstruct earlier landscape conditions.

Occurrence

Colluvia are often found in Central Europe due to the climatic conditions and the long history of use since the Neolithic . Colluvia can be found in almost all landscapes currently or formerly used for arable farming, but especially in the old settlements , for example in the Eifel and the Moselle region , in the Kraichgau, in the Black Forest or on the Swabian Alb .

In highly structured landscapes (e.g. in the young moraine area at the edge of the break-off to the Oderbruch ), colluvia several meters thick can often be found, which testify to earlier erosion events caused by heavy rain . A well-studied example is the Biesdorf throats near Wriezen on the edge of the Oderbruch. The 5 m deep and 50 m long gorge is no older than the trees, and its alluvial deposits downstream are accordingly young .

See also

• Alluvial fans
• Debris

literature

• Characteristics of Brandenburg floors - Kolluvisol. Ministry for Rural Development, Environment and Consumer Protection of the State of Brandenburg (PDF; 1.2 MB)
• Fritz Scheffer: Textbook of soil science / Scheffer / Schachtschabel . rework. and exp. by Hans-Peter Blume u. a.,. 15th edition. Spectrum Akademischer Verlag, Heidelberg - Berlin 2002, ISBN 3-8274-1324-9 , pp. 37, 469 .

Web links

• Kolluvisol from limestone solution residue (Baden-Württemberg) (PDF file; 3.00 MB)
• Erosion and colluvia on the northern slope of the Rigi. Interprävent 1988 (PDF file; 1.68 MB)

Individual evidence

1. ^ Ad-hoc working group Soil: Soil-scientific mapping instructions . 5th edition. Schweizerbart'sche Verlagbuchhandlung, Stuttgart 2005.
2. ↑ Arno Kleber: “Kolluvium” does not equal “colluvium” . In: Journal of Geomorphology, NF Volume 50 , 2006, p. 541-542 .
3. ↑ Leopold, M. & J. Völkel (2007): Colluvium: definition, differentiation and their possible suitability to reconstruct Holocene climate data . Quaternary International, 162-163: 133-140.
4. ^ Frank Press, Raymond Siever: General geology. Introduction to the earth system. 3rd edition, Spektrum Akademischer Verlag, ISBN 3827403073
5. ↑ Stolz, C., Grunert, J., Fülling, A. (2012): The formation of alluvial fans and young floodplain deposits in the Lieser catchment, Eifel Mts., Western German Uplands: A study of soil erosion budgeting. The Holocene 22, 3, 267-280.
6. ↑ Examples for Trockental-Kolluvium in Kraichgau, pp. 21–24
7. ↑ Colluvium of loess loam and lime - solution residues (Black Forest)  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.