Colluvium is the name for loose bodies of
sedimentSediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers...
that have been deposited or built up at the bottom of a low-grade slope or against a barrier on that slope, transported by gravity. The deposits that collect at the foot of a steep slope or cliff are also known by the same name. Colluvium often outerfingers with
alluviumAlluvium is soil or sediments deposited by a river or other running water...
(deposits transported downslope by water). Coarse deposits due to rockfall at a cliff base are called
talus* Talus , sloped portion of a fortified wall* Talus, California, community in Inyo County* Talus bone, ankle bone, connecting the leg to the foot* Talus, planet in the Star Wars universe...
(
screeScree, also called talus, is a term given to an accumulation of broken rock fragments at the base of crags, mountain cliffs, or valley shoulders. Landforms associated with these materials are sometimes called scree slopes or talus piles...
) and if lithified are talus
brecciaBreccia is a rock composed of angular fragments of minerals or rocks in a matrix , that may be similar or different in composition to the fragments. The word is a loan from italian, and in that language indicates both loose gravel and stone made by cemented gravel...
s.
Colluvium is the name for loose bodies of
sedimentSediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers...
that have been deposited or built up at the bottom of a low-grade slope or against a barrier on that slope, transported by gravity. The deposits that collect at the foot of a steep slope or cliff are also known by the same name. Colluvium often outerfingers with
alluviumAlluvium is soil or sediments deposited by a river or other running water...
(deposits transported downslope by water). Coarse deposits due to rockfall at a cliff base are called
talus* Talus , sloped portion of a fortified wall* Talus, California, community in Inyo County* Talus bone, ankle bone, connecting the leg to the foot* Talus, planet in the Star Wars universe...
(
screeScree, also called talus, is a term given to an accumulation of broken rock fragments at the base of crags, mountain cliffs, or valley shoulders. Landforms associated with these materials are sometimes called scree slopes or talus piles...
) and if lithified are talus
brecciaBreccia is a rock composed of angular fragments of minerals or rocks in a matrix , that may be similar or different in composition to the fragments. The word is a loan from italian, and in that language indicates both loose gravel and stone made by cemented gravel...
s.
AvalancheAn avalanche is a rapid flow of snow down a slope, from either natural triggers or human activity. Typically occurring in mountainous terrain, an avalanche can mix air and water with the descending snow...
s, mudslides, and
landslideA landslide is a geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
s are processes that deposit colluvium. This build-up process is called
colluviation.
Colluvium normally forms humps at the base of mountains or fan-shaped deposits similar in shape to alluvial fans that cover former ground surfaces. This process is an important phenomenon in the fields of
archaeologyArchaeology or archeology is the science that studies human cultures through the recovery, documentation, analysis, and interpretation of material culture and environmental data, including architecture, artifacts, biofacts, and landscapes...
and
soil scienceSoil science is the study of soil as a natural resource on the surface of the earth including soil formation, classification and mapping; physical, chemical, biological, and fertility properties of soils; and these properties in relation to the use and management of soils.Sometimes terms which...
.
Many colluvial soils tend to have a
fragipanA fragipan is a diagnostic horizon in USDA soil taxonomy. They are altered subsurface soil layers that restrict water flow and root penetration. Fragipans are similar to a duripan in how they affect land-use limitations...
associated with them that are a brittle
subsoil----Subsoil Sub:under or beneath.Soil:Earth and groundis the layer of soil under the topsoil on the surface of the ground. The subsoil may include substances such as clay and/or sand that has only been partially broken down by air, sunlight, water,wind etc., to produce true soil...
layer typically high in
clayClay is a naturally occurring material composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried and/or fired...
. One theory of fragipan formation is the smearing of soil during the colluvial process causing the clays to seal the surface between the moving portion of soil and the stationary soil on which it slides.
Ancient sitesAn archaeological site is a place in which evidence of past activity is preserved , and which has been, or may be, investigated using the discipline of archaeology and represents a part of the archaeological recordBeyond this, the definition and geographical extent of a 'site' can vary widely,...
can be preserved beneath colluvium if later changes in the landscape such as
deforestationDeforestation is the clearance of naturally occurring forests by the processes of logging and/or burning of trees in a forested area. There are several reasons deforestation occurs: trees or derived charcoal can be sold as a commodity and used by humans, while cleared land is used as pasture,...
encourage a downward movement of material.
Sources
- Thomas Madigan, "The Geology of the MNRRA Corridor", p. 26, National Park Service
The National Park Service is the U.S. federal agency that manages all national parks, many national monuments, and other conservation and historical properties with various title designations...
, Retrieved July 23, 2007