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 (Frequently Asked Questions)

1. Explain the difference between illuviation and eluviation?

Ans: Illuvium-Illuvium is material that has been displaced through a soil profile by rainwater from one layer to another. Illuvium is material that has been displaced through a soil profile, from one layer to the next, by rainwater. Eluviation is the process of removing material from a soil layer. The substance may be transported mechanically or chemically. Illuviation is the name for the method of illuvium deposition. In contrast to alluviation, which is a horizontal running water movement, it is a water-assisted vertical transport. Alluvial deposits are the product of this process. Alluvial deposits, such as cutans, are a form of alluvial deposit. Organic matter, silicate clay, and iron and aluminum hydrous oxides are among the elements found in illuvium. Alluvial deposits of clays, oxides, and organics from distinctive soil horizons are known as "B horizons'' or "zones of illuviation" in the subsoil. Eluviation is the process of removing material from a soil layer. The substance may be transported mechanically or chemically. Illuviation is the name for the method of illuvium deposition.

2. What is soil illuviation? Explain the process of illuviation.

Ans: Illuviation is the buildup of dissolved or suspended soil materials in one region or substrate as a result of percolation (leaching) from another. Clay, iron, and humus typically wash out and leave a line of a different consistency and color. These lines are critical for determining the age and composition of rock strata. Water flows into the soil, causing illuviation. It transports clay, iron, hummus, calcium carbonate, and other minerals into small particles. These particles settle in the subsoil or zones close to the surface. Illuvial zones are the name given to these regions. Illuvium is the substance that has been transferred.

3. Where does eluviation happen?

Ans: Eluviation is much higher in humid climates with a lot of precipitation. In humid climates, the illuvial layers are found low in the soil profile, unlike in semiarid and arid climates where precipitation is scarce. In arid climates the illuvial layers are found closer to the surface.

The E horizon of the soil is the zone of the most eluviation. The soil here is very light in colour because the clay, chemicals, and organic matter are leached from it. This horizon is usually seen a lot more in sandy forest soils with high amounts of rainfall.

4. What are the factors that influence soil formation?

Ans: Soil profiles are influenced by five factors that interact with each other: parent material, climate, topography, organisms, and time. The interaction of these five factors gives each soil profile a distinctive character.

Parent Material

Parent soil refers to the geologic material from which soil horizons form. There are seven types: weathered bedrock, till, deposit, sand, loess, eolian, outwash, alluvium and local overwash.


There are soils, for example, that weather directly from the underlying rocks. Therefore this kind of soil gets its general chemistry from the original rocks. Soils very often take form in materials that have moved from some other place. Materials could have moved long distances or just a few feet. Windblown loess, a loosely compacted yellowish-grey deposit of sediment, are common in eastern China and the American Midwest.

On the other hand, Glacial till is material moved by a glacier. The texture of sediments along rivers are different. It depends on the speed of the stream. While slow streams, and stationary water bodies like lakes and ponds have fine textured materials like silt and clay, fast-moving streams and rivers have gravel, sand, and rocks. 

In the lower part of the soils, the materials mostly remain unchanged from when moving water, wind, or ice deposited them.


Soils vary, depending on the climate. The patterns of weathering and leaching change based on the temperature and moisture amounts. The intensity, timing, amount and precipitation influence soil formation.

Changes in temperature, seasonal or daily, affect biological activity, the rate of chemical reactions, effectiveness of moisture, and types of vegetation.

Other factors like wind also have an effect. Wind redistributes sand and other particles, especially in arid and semiarid regions.


Slope and aspects have an effect on the moisture and temperature of soil. Steep slopes that face the sun are considerably warm, and therefore the soils in these parts can get eroded and lose their topsoil. So, they may be thinner than soils that receive deposits from areas upslope.


Biological Factors

Soil formation is also hugely affected by plants, animals, micro-organisms, and human beings.

Plant roots open channels in the soils and different types of roots have different effects on soils. Grass roots, for example, are fibrous and grow near the soil surface. Thus they easily decompose, adding to the organic matter in the soil. Taproots open pathways through dense layers. Leaves from plants that fall on the surface decompose on the soil. 

Animals and microorganisms mix soils by forming burrows and pores. Micro-organisms cause chemical exchanges between the soil and roots. Humans can affect and mix the soil extensively.


The time taken for these factors to interact with the soil is important. The process of soil formation is continuous and slow, and the soil reflects the amount of time it has been exposed to the other factors.. Recently deposited material from a flood exhibits no features of soil development, as the previous soil surface and underlying horizons get buried. Areas above the active floodplain, while genetically similar to the floodplain, are relatively older, and so you see more development features in them.

It also affects soils on stable landscapes. The additions, alterations and removals in soil material, could either be slow or rapid, based on the climate, biological activity and landscape position.

5. Does soil contain air?

Ans: Yes, air is present in the space between the soil particles. The quantity of air varies based on the soil itself. Roots of plants and other organisms use the oxygen in this air for respiration. Sand particles cannot fit perfectly into each other, with no space between them. There is a good amount of space between sand particles that is filled with air. This is the reason why sandy soil can provide much more air to the root of a plant. Clay particles, on the other hand, pack in tightly together leaving very little space for air. This kind of soil provides much less air to the roots of plants that grow in it.