The sedimentation It is the accumulation of solid materials, caused by natural or experimental processes. For example: alluvium, dunes, sedimentary islands.
Different materials from rock erosion can be transported by various agents (wind, water, glaciers) to a place where they are deposited. The continuous deposit of materials, has as a consequence the accumulation, that is the sedimentation.
The gravity it intervenes in the sedimentation processes, since it is the force that causes the materials, suspended in the wind or water, to fall again.
However, gravity intervenes along with other forces. The Stokes law points out that particles settle more easily if they meet any of these characteristics:
- Larger diameter of the particle.
- Higher specific weight of the solid compared to the liquid in which it is suspended.
- Lower viscosity of the liquid medium. This means, for example, that a particle of the same size and specific gravity will settle faster in water than in oil.
Sedimentation occurs when the agent that transported the materials loses energy. For example, when the wind stops or the flow of a river decreases.
The accumulation of a new material on the accumulation of another material is called stratification and it is a form of sedimentation.
There are specific places on the earth’s surface where sediments accumulate, due to their geographical characteristics. These places are called sedimentary media or sedimentary environments and differs from all nearby areas, both in physical, chemical and biological aspects. Sedimentary media can be continental, transitional, or marine.
Besides being a natural phenomenon, sedimentation can be artificially reproduced. When carried out under laboratory conditions, it can also be called decantation, and consists of the separation of suspended particles that have a higher specific weight than the liquid medium.
Examples of sedimentation
- Water purification (artificial sedimentation). It is based on Stokes’ law, which is why an attempt is made to increase the diameter of the particles suspended in the water, uniting one with the other. This is achieved thanks to the coagulation and flotation processes (which occur naturally in the blood but are artificially produced in the water).
- Sewage treatment (artificial sedimentation). Solid matter, organic or not, is removed from the water. The sedimentation process makes it possible to reduce between 40 and 60% of the suspended solids.
- Sand trap (artificial sedimentation). A so-called discrete or granular sedimentation occurs. This means that the particles settle as individual units, with no interaction with each other (as opposed to coagulation).
- Alluvium. Continental sedimentary medium. The solid material is transported and deposited by a stream of water. These solids (which can be sand, gravel, clay or silt), accumulate in the riverbeds, in plains where a flood has occurred or in deltas.
- Dunes. Aeolian sedimentation (continental sedimentary environment). Dunes are accumulations of sand caused by the action of the wind. They can reach heights of up to 15 meters.
- Sedimentary islands. Rivers transport solid materials suspended in water, but since they do not always flow at the same speed, solids can settle in certain areas, forming islands. They are part of the deltas but can also be present far from the mouth of the rivers.
- Moraines (continental glacial sedimentation). A moraine is the accumulation of sediment formed by a glacier. Since most of the ice formations from glaciations no longer exist, moraines can be found in valleys that have been created by glaciers that are no longer there.
- Geological reefs (marine sedimentary environment). They are accumulations of sediments built by the interaction of certain organisms with their environment. They are supported by a frame. For example, coral reefs are the accumulation of corals and calcareous algae that grow on top of each other.
- Delta (transitional sedimentary medium). It is the mouth of a river whose cause is divided into multiple arms that separate and come together again, forming islands and channels. When the islands are formed by the sedimentation process, the water opens new paths to continue its course, forming the new arms and channels.
- Slopes (marine sedimentary environment). They are geographical accidents that are between 200 and 4000 meters below sea level. They are formed by the accumulation of solid materials that are transported from the continents, thanks to the force of marine currents. These materials form valleys, mountains, and canyons. They are usually in the shape of a sloping plain, in planes similar to steps.