Colluvium (also ore material or ore soil) is a common name for loose, unconsolidated deposits that are deposited at the foot of hillsides as a result of torrential landslides. The colluvium usually consists of a heterogeneous range of rock types and sediments ranging from silt to clay fragments. The term is also used to refer to deposits formed on hillsides as a result of non-concentrated surface runoff or rock erosion.
Internal processes
Colluviation refers to the accumulation of sediment, which is the subject of this article, at the base of a slope. Colluvium is a loosely compacted angular material that accumulates at the base of steep slopes or hillsides. It accumulates in gentle fan-shaped accumulations either at the base or inside ravines and depressions on hillsides. These accumulations can be several meters thick and often contain buried soils (paleosols), rough beds, and sequences of cut andfilling.
Meaning in geology
Dense aggregations can maintain a very rich "record" of long-term paleoclimate changes based on paleosols and plant and animal remains, invertebrates and vertebrates, which are often found in such deposits. These fossils provide a very broad picture of previous geological and environmental conditions.
Dense colluvium accumulations often contain well-preserved and sometimes deeply buried archaeological deposits, which are clearly visible in some places in Cherokee County, Iowa, and at the Coster Site, Greene County, Illinois. Coluvium may also be rich in rocks that have been transported down from glaciers and therefore may indicate past stages of colder and/or wetter weather. Deposits of colluvium detritus can reveal the composition of the soil and indicate the processes of chemical weathering.
Eluvium, colluvium, deluvium, proluvium, alluvium
The definitions of all the deposits listed in the title are interdependent and interrelated. The differences between them are important for the correct determination of the geomorphological processes that have taken place in a particular geological setting. Alluvium is sand, clay or other similar material resulting from sedimentation caused by water flowing along the rock. The difference between colluvium and alluvium has to do with the involvement of running water. Alluvium, in particular, refers to geomorphological processes associated with flowing water, and therefore it is usuallyis a fine-grained clay and silt material that is able to capture water flows and eventually settle. For the same reasons, alluvium tends to sort well as well, while the material this article focuses on does not. Colluvium/Delluvium differ from each other in the same ways.
The cuts of bedrock filled with this material are the cause of many small landslides on steep mountain slopes. They can form a U-shaped or V-shaped trough, as local bedrock variations show areas in them that are more weathered than other places on the slope. Such formations are typical for rocks rich in colluvium, eluvium, deluvium.
When the weathered rock turns into soil, the difference in level between the soil level and the hard bedrock becomes larger. Such is the effect of eluvium on hard rocks, but colluvium acts on them differently. When water and thick soil are introduced, the entire rock becomes less dense, and the soil flows out in the form of a landslide. With each landslide, more bedrock is cleared away, and the depression gets deeper. After a while, the colluvium fills the depression and the sequence begins again.
Other features
Colluvium is very often soil and debris that accumulates at the base of a slope as a result of mass depletion or rock erosion. It usually contains corner fragments that are not sorted by size and may contain rock slabs that dip back towardsslope, indicating both their place of origin and their fall during transport. At the edges of valleys, colluvium can be mixed with alluvium and almost indistinguishable from it.
Other differences
They often form at the foot of steep slopes and are discovered during drilling, exploration of small streams. The differences between alluvium and colluvium are mainly based on topography. Alluvium is mapped where the slope deposition surface is parallel to the main drainage. The colluvium is marked on the map when the surface of the deposit deviates from the adjacent hills towards the main drainage line.
More examples
The subject of the article is often described as uncompacted material at the bottom of a cliff or slope, usually only moved by gravity. It is not stratified and is not usually sorted: its composition depends on the source of the rock, and its dimensions vary considerably. Such deposits include debris and scree.
Colluvium is also a free-flowing, non-stratified, poorly sorted, heterogeneous mixture of various sizes, accumulating at the bottom and at the base of slopes. There are three basic scenarios for its occurrence:
- land runoff occurs when soil saturation is exceeded during heavy rains;
- soil movements cause it to pile up;
- downslope displacement of soil as a direct result of plowing.
Colluvium is still poorly sorted garbage that accumulated inbases of slopes, in depressions or along small streams due to gravity, soil creep, etc. It consists primarily of material that has rolled, slid, or fallen downhill under the force of gravity.
Scree
Accumulation of rock debris is called scree. Rock fragments usually have an angular shape, in contrast to rounded, water-worn cobblestones and stones. Very often it is detritus carried by various processes, which is still near or on the slope of the source. Heterogeneous materials of any particle size typically consist of fragments of soil and/or rock accumulated on lower slopes and are brought there by gravity, soil creep, leaf flow, rainfall, s alt accumulation.
Natural slope deposits resulting from the gradual accumulation over short distances of uplifted soil materials are colluvium. At least, sometimes it is defined that way. It is often deposited on slopes perpendicular to the flow of rivers. Rivers are often poor in clay.
Conclusion
There are a lot of definitions of colluvium. Deposits of this type are very important for determining the age of rocks. Also, they often contain many fossils and small soil formations, perfectly preserved, which have passed through the depths of centuries. Not only geologists are studying this material, but also archaeologists, paleontologists, speleologists and surveyors. Sometimes, however, he connectswith catastrophic events such as landslides. In most cases, colluvium is a harmless formation that does not contain any toxins (despite its partially organic origin). Therefore, if you notice a high content of this breed somewhere near your home, then do not worry.
