Meaning of Eluviation
Eluviation meaning is the downward percolation of water through soil horizons that transports soil content from upper layers to lower levels, and illuviation is the deposition of this material (illuvial deposit) in lower levels. Eluviation is the movement of water that removes dissolved or suspended material from a layer or layers of soil when rainfall exceeds evaporation. Leaching is the term used to describe the loss of material in the solution.
Eluviation Definition
The transportation of dissolved or suspended material within the soil by the movement of water as rainfall exceeds evaporation.
Eluvium or alluvial deposits are volcanic deposits and soils formed by in situ weathering or weathering combined with gravitational movement or deposition in geology.
Eluviation or leaching is the method of removing materials from geological or soil horizons. There is a distinction between how this word is used in geology and soil science. Eluviation is the downward percolation of water through soil horizons that transports soil content from upper layers to lower levels, and illuviation is the deposition of this material (illuvial deposit) in lower levels. The extracted material is meaningless in geology, and the deposit (alluvial deposit) is the material that remains. When precipitation exceeds evaporation, eluviation occurs.
An alluvial zone or illuvial horizon is a soil horizon created by eluviation. The illuvial horizon is a light-colored region in a standard soil profile that is either at the lower part of the A horizon or within a distinct horizon (E horizon) below the A, where the process is most strong and rapid (depending on background and literature). While eluviation theoretically occurs in both, some sources consider the alluvial zone to be the A horizon plus the (distinct) E horizon. The strict illuvial horizon (E horizon) is usually light grey, clay-free, low in organic matter, and high in salt and sand particles made up of quartz and other resistant minerals.
Alluvial ore deposits, including tungsten and gold placer deposits, are created by settling and enriched by winnowing or removing lower-density materials. Alluvial deposits are diamonds found within the yellow ground (weathered parts of kimberlites). Residual or alluvial deposits of cassiterite and columbite-tantalite can also be found. The Pitinga tin deposit, an alluvial deposit in Brazil, is one of the world's largest tin mines. In Ontario, weathering supergene enrichment of an apatite-rich carbonatite has resulted in a large alluvial phosphate ore deposit.
Eluviation of Soil
Water pushes tiny colloidal-sized materials into the soil as it moves through it. Eluviation is the movement or leaching of materials such as clay, iron, or calcium carbonate. The region of eluviation, also known as the E horizon or eluviation layer of soil, is the area where the materials have been extracted. Alluvial zones have fewer nutrients for plant growth. In forested soils, E horizons are common.
Different forms of soil exist, each with its own set of characteristics. Any soil has layers, or horizons, as you can see if you dig far enough (O, A, E, B, C, R). When you combine the horizons, you get a soil profile. Each profile, like a biography, tells a tale about a soil's life. Most soils have three main horizons (A, B, and C), as well as an organic horizon in some cases (O). The following are the horizons:
O (Humus or Organic): Organic matter, primarily decomposing leaves. Some soils have a thin O horizon, while others have a dense O horizon or none at all.
A (Topsoil): Mostly minerals from the parent material, with some organic matter. Plants and other organisms can thrive in this material.
E (Eluviate): Leached of clay, minerals, and organic matter, leaving a concentration of sand and silt particles of quartz or other resistant materials – contained in older soils and forest soils.
B (Subsoil): Minerals leached (moved down) from the A or E horizons and deposited in the B.
C (Parent Material): The deposit that formed the soil at the Earth's surface.
R (Bedrock): A mass of rock, such as granite, basalt, quartzite, limestone, or sandstone, that serves as the parent material for some soils when it is close enough to weather. This isn't dirt, because it's under the C horizon.
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FAQs on Eluviation
1. What exactly is eluviation in soil?
Eluviation is the process where rainwater moving downwards through the soil picks up and carries away fine mineral particles, like clay and silt, and organic matter from the upper layers of the soil. Think of it as a natural washing-out process that happens within the soil itself.
2. What is the main difference between eluviation and illuviation?
The easiest way to remember the difference is with 'E' for Exit and 'I' for Into.
- Eluviation is the removal or 'exit' of materials from a soil layer.
- Illuviation is the accumulation or 'deposit' of those same materials into a lower soil layer.
3. In which soil layer does most eluviation happen?
Most eluviation takes place in the E horizon, which lies just below the topsoil (A horizon). This layer is often called the 'zone of eluviation' because this is where the most significant loss of minerals and clay occurs. As a result, the E horizon is typically lighter in colour and has a coarser texture than the layers above or below it.
4. How is eluviation different from the process of leaching?
While they are similar, there is a key difference. Leaching refers to the dissolving of soluble minerals in water and their removal from the soil completely. In contrast, eluviation is the physical movement of insoluble, suspended particles (like clay) from one horizon to another within the soil profile. Leaching removes materials entirely, while eluviation just relocates them to a lower layer.
5. What kind of climate promotes the most eluviation?
Eluviation is most intense in humid climates with high amounts of rainfall. The constant flow of water through the soil profile is necessary to transport the clay and mineral particles downwards. In arid or dry climates, there isn't enough water movement to cause significant eluviation.
6. Why is understanding eluviation important in Geography?
Understanding eluviation is crucial because it is a fundamental process of soil formation. It helps explain why soils develop distinct layers, or horizons. The process directly affects soil fertility, texture, and structure by moving key nutrients and materials, which in turn determines what kind of vegetation can grow in a region.
7. Can you give a real-world example of what a heavily eluviated soil looks like?
A classic example is a podzol soil, often found in coniferous forests with cool, humid climates. If you were to dig a profile of this soil, you would see a very pale, ash-coloured E horizon just below the dark topsoil. This pale layer is a clear visual sign of intense eluviation, where iron, aluminium, and organic matter have been washed out, leaving behind mostly light-coloured quartz sand.
