Colluvium (also colluvial material or colluvial soil) is a general name for loose, unconsolidated

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s that have been deposited at the base of hillslopes by either rainwash, sheetwash, slow continuous downslope creep, or a variable combination of these processes. Colluvium is typically composed of a heterogeneous range of rock types and sediments ranging from

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension (chemistry), suspension with water. Silt usually ...

rock Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wale ...

fragments of various sizes. This term is also used to specifically refer to sediment deposited at the base of a hillslope by unconcentrated

surface runoff Surface runoff (also known as overland flow or terrestrial runoff) is the unconfined flow of water over the ground surface, in contrast to ''channel runoff'' (or ''stream flow''). It occurs when excess rainwater, stormwater, meltwater, or other ...

or sheet erosion.

Location

Colluviation refers to the buildup of colluvium at the base of a hillslope.Jackson, JA, J Mehl, and K. Neuendorf (2005) ''Glossary of Geology'' American Geological Institute, Alexandria, Virginia. 800 pp. Goodie, AS (2003) ''Colluvium'' in A. S. Goodie, ed., pp. 173, Encyclopedia of Geomorphology Volume 1, A–I. Routledge, New York, New York. 1200 pp. Colluvium is typically loosely consolidated angular material located at the base of a steep hill slope or cliff. Colluvium accumulates as gently sloping aprons or fans, either at the base of or within gullies and hollows within hillslopes. These accumulations of colluvium can be several meters in thickness and often contain buried soils (

paleosol In Earth science, geoscience, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The definition of the term in geology and paleontology is slightly different from its use in soil science. In geo ...

s), crude bedding, and cut and fill sequences.

Importance

Thick accumulations of colluvium may preserve a rich record of long term paleoclimatic change based on the paleosols and the remains of plants and animals, invertebrate and vertebrates that they often contain. These fossils indicate previous geologic and environmental settings. Thick accumulations of colluvium often contain well-preserved and sometimes deeply buried archaeological deposits as excavated at the Cherokee Sewer Site,

Cherokee County, Iowa Cherokee County is a county located in the U.S. state of Iowa. As of the 2020 census, the population was 11,658. The county seat is Cherokee. The county was formed on January 15, 1851, from open territory. It was named after the Cherokee peopl ...

, and the Koster Site, Greene County, Illinois.Anderson, D, and HA Semken (1980) ''The Cherokee Excavations: Holocene Ecology and Human Adaptations in Northwestern Iowa.'' Academic Press, New York.Angel JR (1990) ''Koster site archaeology I: stratigraphy and landscape evolution.'' Research Series. vol. 8. Center for American Archeology, Kampsville, Illinois. Colluvium can also be rocks that have been transported downward from

glacier A glacier (; or ) is a persistent body of dense ice, a form of rock, that is constantly moving downhill under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires ...

s and so can indicate past stages of cooler and/or wetter weather. Deposits of detrital colluvium can reveal the soil composition and signify processes of chemical weathering.

Compared to alluvium

The definitions of colluvium and

alluvium Alluvium (, ) is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluvium is also sometimes called alluvial deposit. Alluvium is ...

are interdependent and reliant on one another. Distinctions between the two are important in order to properly define the

geomorphic Geomorphology () is the scientific study of the origin and evolution of topography, topographic and bathymetry, bathymetric features generated by physical, chemical or biological processes operating at or near Earth#Surface, Earth's surface. Ge ...

processes that have occurred in a specific geological setting. Alluvium is sand, clay, or other similar detrital material deposited by running water. The distinction between colluvium and alluvium relates to the involvement of running water. Alluvium specifically refers to the geomorphic processes involved with flowing water and so alluvium is generally fine-grained clay and silt material that has the capacity to be entrained in water currents and eventually deposited. For these same reasons, alluvium is also generally well sorted material while colluvium is not.

References

External links

*Anonymous (2007
''Field Analysis:Is this a colluvial deposit''

Soil Analysis Support System for Archaeology
{{Webarchive, url=https://web.archive.org/web/20130225073507/http://www.sassa.org.uk/index.php/Soil_Analysis_Support_System_for_Archaeology , date=2013-02-25 , Natural Environment Research Council, United Kingdom. Geomorphology Sedimentology

Location

Importance

Compared to alluvium

See also

References

External links