Silt

Silt [6]

Definition

Silt is a granular sediment that can be transported and deposited by water, ice, and wind. Silt particles are larger than clay, but smaller than sand. To be classified as silt, a particle must be between .002 to .05 mm [1]. Similarly to clay, sand, and gravel, silt is found in soil. Silt can also occur as sediment mixed in suspension with water. Because of silt’s spherical shape, it retains a large amount of water. Silty soil is known to be more fertile than other soils, and many species of organisms thrive in it.

Loess [7]

Formation

Silt-producing mechanisms include frost shattering (Freeze-Thaw Weathering), comminution during transport, eolian abrasion, salt weathering, and glacial grinding. Windblown silt blankets the land in many parts of the world [2]. Large deposits of silt, such as this, are known as loess. Loess landscapes are usually a sign of past glacial activity, including areas such as the Great Plains. Silt can accumulate quickly in areas that lack vegetation, which can disrupt ecosystems. Silt also settles in still water, resulting in build ups like deltas. The main mineral origin of silt is quartz and feldspar [3]. The formation and movement of silt are constantly altering ecosystems.

Identification

Silt soil is fine and feels like flour when dry. When silt is wet it becomes a smooth mud that can be easily molded into shapes. When silt soil is very wet, it blends seamlessly with water, and forms puddles of mud [4]. Silt particles are very small, so they have a very smooth soil texture. Silty soil drains well, but not as quickly as sand. Silts sparkly appearance can be observed using a hand lens. Pure silts are identified by their lack of cohesion. Silts and clays are distinguished by their plasticity [5].

Field Identification

[8]

See also

• Clay
• Loam
• Founders of Soil Concepts
• Humus
• Microorganisms
• Pedogenesis
• Soil
• Soil Textures
• Soil Properties
• Jenny Equation

References

[1] National Geographic Society. “Silt.” National Geographic Society, 9 Oct. 2012, www.nationalgeographic.org/encyclopedia/silt/.

[2] Wright, Janet S. "“Desert” loess versus “glacial” loess: quartz silt formation, source areas and sediment pathways in the formation of loess deposits." Geomorphology 36.3-4 (2001): 231-256.

[3] Wright, J. S., Smith, B. J. & Whalley, W. B. Mechanisms of loess-sized quartz silt production and their relative effectiveness: Laboratory simulations. Geomorphology 23, 15-34 (1998).

[4] Wentworth, Chester K. "A scale of grade and class terms for clastic sediments." The journal of geology 30.5 (1922): 377-392.

[5] NRCS, USDA. "National soil survey handbook, title 430-VI." (2007).

[6] “Silt: Environmental Impact.” Rashid's Blog: An Educational Portal, 8 May 2016, rashidfaridi.com/2016/03/04/silt-environmental-impact/.

[7] “Loess Hills.” Iowa Geological Survey, 11 July 2017, www.iihr.uiowa.edu/igs/loess-hills/?doing_wp_cron=1525843720.4534800052642822265625.

[8] “Choosing a Topsoil Mix for Your Yard or Garden.” Washington Rock Quarries, 23 Mar. 2017, www.wa-rock.com/choosing-topsoil-mix-yard-garden/.