Colluvium (also ore material or ore soil) is a common name for loose, unconsolidated sediments that are deposited at the foot of hillsides as a result of storm landslides. Colluvium usually consists of a heterogeneous series of rock types and deposits, ranging from silt to clay fragments. This term is also used to refer to deposits formed on hillsides as a result of unconcentrated surface runoff or rock erosion.
Internal processes
Colluviation refers to the accumulation of sediment, which is devoted to the article, at the base of the slope. Colluvium is a poorly compacted angular material that accumulates at the base of steep slopes or cliffs of hills. It accumulates in the form of gentle clusters of fan-shaped either at the base or inside the ravines and depressions on the hillsides. These clusters can be several meters thick and often contain buried soils (paleozols), coarse occurrences, as well as sequences of cutting and filling.
Value in geology
Dense accumulations can preserve very meaningful “records” of long-term paleoclimatic changes based on paleozols and the remains of plants and animals, invertebrates and vertebrates, which are often found in such deposits. These fossils provide a very broad picture of previous geological and natural conditions.
Dense clusters of colluvium often contain well-preserved, and sometimes deeply buried archaeological deposits, which are clearly visible in some places in Cherokee County, Iowa, and on the Bonfire site, County Green, Illinois. Colluvia can also be rich in rocks that have been transported down from the glaciers and, therefore, may indicate past stages of colder and / or wetter weather. Colluvium detritus deposits can reveal soil composition and indicate chemical weathering processes.
Eluvium, Colluvium, Deluvium, Proluvium, Alluvium
The definitions of all the sediments listed in the heading are interdependent and interconnected. The differences between them are important for the correct determination of the geomorphological processes that occurred in a particular geological setting. Alluvium is sand, clay, or other similar material formed as a result of sedimentation due to water draining along a rock. The difference between colluvium and alluvium is associated with the involvement of running water. Alluvium, in particular, refers to geomorphological processes associated with running water, and therefore, as a rule, it is a fine-grained clay and silt material that is able to capture water flows and ultimately precipitate. For the same reasons, alluvium is also usually well sorted, while the material to which this article is devoted is not. Colluvium / deluvium differ from each other in the same way.
The excavations 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, since local variations of bedrocks show areas in them that are more susceptible to atmospheric influences than other places on the slope. Similar formations are characteristic of rocks rich in colluvium, eluvium, and deluvium.
When weathered rock turns into soil, the difference in level between soil level and hard bedrock becomes larger. Such is the effect on hard rocks of eluvium, but the 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 and more bedrock is being cleared, and the trench is becoming deeper. After some time, the colluvium fills the cavity, and the sequence begins again.
Other characteristics
Colluvium is very often soil and debris that accumulate at the base of the slope as a result of mass depletion or erosion of the rock. It usually contains angular fragments that are not sorted by size, and may contain rock slabs that sink back to the slope, indicating both their origin and fall during transport. On the edges of the valleys, the colluvium can mix with alluvium and hardly differ from it.
Other differences
They are often formed at the foot of steep slopes and are discovered during drilling, research of small streams. The differences between alluvium and colluvium are mainly based on topography. Alluvium is mapped where the surface of the incline is parallel to the main drainage. Colluvium is marked on the map when the surface of the field deviates from adjacent hills to the main drainage line.
Other examples
The subject of an article is often described as loose material at the bottom of a cliff or slope, usually moved only by gravity. It is not stratified and usually not sorted: its composition depends on the source of the rock, and its size varies considerably. Such deposits include rubbish and scree.
Colluvium is also a loose, non-stratified, poorly sorted, heterogeneous mixture of various sizes, accumulating in the lower part and at the base of the slopes. There are three basic scenarios of its occurrence:
- land runoff occurs when excess soil saturation occurs during heavy rains;
- soil movements cause it to accumulate;
- soil displacement downhill as a direct result of plowing.
Colluvium is still poorly sorted garbage that accumulated at the base of slopes, in depressions or along small streams under the influence of gravity, creep of the soil, etc. It consists mainly of material that rolled, slid, or fell down a slope under the influence of gravity.
Scree
Accumulations of debris are called scree. Fragments of the rock usually have an angular shape, in contrast to the rounded, worn-out cobblestones and stones. Very often, it is detritus carried by various processes, which is still nearby or on the slope of the source. Heterogeneous materials of any particle size, as a rule, consist of fragments of soil and / or rocks accumulated on the lower parts of the slopes and get there under the influence of gravity, creep of the soil, leaf flow, rainfall, and accumulation of salts.
Natural deposits on the slopes resulting from the gradual accumulation of elevated soil materials over short distances are colluvium. At least sometimes it is defined that way. It is often deposited on the slopes perpendicular to the flow of rivers. Rivers are often clay depleted.
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 preserve many fossils and small soil formations, perfectly preserved, passing through the depth of centuries. The study of this material is carried out not only by geologists, but also archaeologists, paleontologists, cavers and geodesists. Sometimes, however, he is associated with such catastrophic events 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 house, then do not worry.