Colluvium is the name for loose bodies of sediment

Sediment

Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

 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 grades into alluvium

Alluvium

Alluvium is loose, unconsolidated soil or sediments, eroded, deposited, and reshaped by water in some form in a non-marine setting. Alluvium is typically made up of a variety of materials, including fine particles of silt and clay and larger particles of sand and gravel...

 (deposits transported downslope by water). Coarse deposits due to rockfall at a cliff base are called talus (scree

Scree

Scree, 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 breccia

Breccia

Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....

s. Avalanche

Avalanche

An avalanche is a sudden rapid flow of snow down a slope, occurring when either natural triggers or human activity causes a critical escalating transition from the slow equilibrium evolution of the snow pack. Typically occurring in mountainous terrain, an avalanche can mix air and water with the...

s, mudslides, and landslide

Landslide

A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, 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 archaeology

Archaeology

Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...

 and soil science

Soil science

Soil 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 fragipan

Fragipan

A 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

Subsoil, or substrata, is 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 clay

Clay

Clay is a general term including many combinations of one or more clay minerals with traces of metal oxides and organic matter. Geologic clay deposits are mostly composed of phyllosilicate minerals containing variable amounts of water trapped in the mineral structure.- Formation :Clay minerals...

. 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 sites

Archaeological site

An 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 record.Beyond 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 deforestation

Deforestation

Deforestation is the removal of a forest or stand of trees where the land is thereafter converted to a nonforest use. Examples of deforestation include conversion of forestland to farms, ranches, or urban use....

 encourage a downward movement of material.

Sources

• Thomas Madigan, "The Geology of the MNRRA Corridor", p. 26, National Park Service
  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