Silt Soil
Silt is solid, dust-like sediment which is carried by wind or water or ice. Silt is composed of rock and mineral molecules that are bigger than clay but smaller than sand. Individual silt particles are so small that they are less likely to be seen with the naked eye. To be categorized as silt, a particle must be smaller than (.002 inches) across. Silt is most commonly found in soil, along with other kinds of sediment such as sand, clay and gravel. Silt sand or soil is slippery when wet, but not rocky or grainy. It is often referred to as fine silt because of being a non-plastic soil material.
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Occurrence of Silt
Let’s see the three main processes that form silt:
Silt soil occurs when rock is weathered, or worn away, by water and ice. As flowing water carries tiny rock splinters, they scrape against the bottom and sides of stream beds, working away more rock.
The particles mince against each other, getting smaller and smaller until they become silt-size.
Glaciers can also weather away rock particles to form silt. Ultimately, wind can carry rock particles through a canyon or a landscape, thrusting the particles to grind against the canyon wall or one another.
All three processes cause the formation of silt.
Soil and Its Different Types
Soil is formed by various particles such as clay, loam, humus, rock, gravel, sand and silt. Let’s discuss the types of soil in detail.
1. Sand
The widely used construction material, sand consists of particles of rock and hard minerals, like silicon dioxide. They are the biggest type of soil particles, where each particle is visible to plain sight. The large, comparatively stable sand-particle size enhances soil aeration, encourages drainage in tight soils and helps plants thrive or tilt.
When rubbed between the fingers, the larger particle sand size provides wet or dry sandy soil a grainy texture and even makes the soil crumbly and light when stuck together in your hand. The shape of sand particles is flat, rounded, elongated, angular, and subangular with a texture that is smooth, rough or polished.
2. Silt
Silt is a sediment substance with a size mediated between sand and clay. Transported by water during floods, the river silt creates a fertile deposit on the valley floor.
Being non-plastic or having low plasticity because of its fineness, silt soil allows it to be formed into balls or any desired shape when wet.
3. Clay
Finest of all the soil particles, clay measures less than 0.002 mm in size and is formed from the chemical decomposition of rocks. This fine-grained, cohesive soil glues together and creates a sticky texture when wet or dry.
Clay retains a high amount of water due to the spaces found between clay particles. Clay shrinks when getting dry but expands when in contact with water. Organic clay is extremely compressible and has very high strength when dry, which is why it is utilized in construction as mud mortar.
4. Loam
A mixture of clay, sand and silt is known to have to favour air circulation, water retention, drainage and fertility. These soils are greatly fertile, easy to work with and offer good drainage. Depending on their predominant constitution they can be either sandy or clay.
Black Silt
Silt is granular soil whose mineral origin is quartz and feldspar. It is quite amazing to know that the fertile black river silt situated on the Nile river's banks is a symbol of rebirth, linked with the Egyptian god Anubis.
Tank Silt
One of the silt types of soil, is fine soil transported from surface runoff during rainfall from catchment areas along with crop residue and is deposited as sediment in the tank water and decomposed over a period of time. Tank silt is believed to be rich in organic matter. However, the poor physical, chemical and biological property of the soil elevates the ill effects of climatic change, which substantially affects the rain-fed cropping.
Fun Facts
Silty soil is generally more fertile than other types of soil, which also makes it good for growing crops. Enough clay content makes the soil too stiff for plants to flourish.
Silt soil encourages air circulation and water retention.
When there aren't abundant trees, rocks, or other materials to prevent erosion, silt can accumulate quickly.
The surplus of silt can also upset some ecosystems.
The important and national symbol of India and Vietnam – Lotus plants have their roots in silty wetlands; however, their big, showy flowers blossom above water.
Many species of frog lie torpid during the cold winters by embedding themselves in a layer of soft silt at the bottom of a pond or lake. Since the Water at the bottom does not freeze, and the silt renders some insulation, or warmth, for the animal.
In some parts of the world, agriculture has blossomed in river deltas, where silt sediments are rich, and along the sides of rivers where annual floods freshen up silt.
The Nile River Delta in Egypt is one classic example of a highly fertile area where farmers are harvesting crops for thousands of years utilizing river silt.
FAQs on Silt
1. What is silt in geography?
In geography, silt refers to granular material of a size between sand and clay. It is composed of fine rock and mineral particles that are transported and deposited by agents like water, wind, or ice. When you feel silt, it has a smooth, floury, or silky texture, especially when wet, but is not sticky like clay.
2. How is silt formed through natural processes?
Silt is primarily formed through the mechanical weathering and erosion of rocks. As water flows in rivers or glaciers move, they carry rock fragments. These fragments grind against each other and the riverbed, breaking down into progressively smaller particles. When the velocity of the transporting agent (like wind or water) decreases, these fine particles, known as silt, settle and get deposited.
3. What are the key properties of silt soil?
Silt soil has several distinct properties that make it unique:
Texture: It feels smooth and almost soapy or floury when wet.
Particle Size: Silt particles are smaller than sand but larger than clay, typically ranging from 0.002 to 0.05 mm in diameter.
Water Retention: It holds water well but has better drainage than clay soil, making it highly fertile and ideal for agriculture.
Erodibility: Silt is easily transported by wind and water, making it prone to erosion if not managed properly.
4. How does silt differ from sand and clay?
The primary difference between silt, sand, and clay lies in their particle size and texture. Sand has the largest particles, feeling gritty and coarse. Clay has the smallest particles, feeling sticky when wet and hardening when dry. Silt falls in the middle; its particles are larger than clay but smaller than sand, giving it a smooth, non-sticky, flour-like texture.
5. Why is silt important for agriculture and the environment?
Silt is crucial for forming some of the world's most fertile lands. When rivers flood, they deposit a layer of silt on their floodplains, creating rich alluvial soils that are perfect for farming (e.g., the Nile River delta). Wind-blown silt deposits, known as loess, also form highly productive agricultural regions. Environmentally, this process of deposition builds up landforms like river deltas and floodplains, creating vital habitats.
6. What is siltation and can it be harmful?
Yes, while silt is naturally beneficial, an excess amount can be harmful. Siltation is the process where water bodies like rivers, lakes, and reservoirs become filled with excessive silt and other sediments. This can be accelerated by human activities like deforestation and construction. The negative effects include:
Reducing the water storage capacity of dams and reservoirs.
Making water cloudy (increasing turbidity), which harms aquatic life by blocking sunlight and clogging fish gills.
Clogging irrigation canals and navigation channels.
7. How does silt contribute to the formation of a river delta?
A river delta is formed at the mouth of a river where it meets a larger, slower-moving body of water like a sea or lake. As the fast-flowing river slows down upon entry, it loses the energy required to carry its sediment load. Consequently, it drops the heavier particles first (like sand) and then the lighter particles like silt and clay. Over thousands of years, this continuous deposition of silt builds up new land, forming the characteristic fan-shape of a delta.
