Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment (also known as suspended load) in a surface water body. It may also exist as soil deposited at the bottom of a water body.

Source[link]

Silt is created by a variety of physical processes capable of splitting the generally sand-sized quartz crystals of primary rocks by exploiting deficiencies in their lattice.^[1] These involve chemical weathering of rock^[2] and regolith, and a number of physical weathering processes such as frost shattering^[3] and haloclasty.^[4] The main process is abrasion through transport, including fluvial comminution, aeolian attrition and glacial grinding.^[5] It is in semi-arid environments ^[6] that substantial quantities of silt are produced. Silt is sometimes known as 'rock flour' or 'stone dust', especially when produced by glacial action. Mineralogically, silt is composed mainly of quartz and feldspar. Sedimentary rock composed mainly of silt is known as siltstone.

Grain size criteria[link]

In the Udden-Wentworth scale (due to Krumbein), silt particles range between 0.0039 to 0.0625 mm, larger than clay but smaller than sand particles. ISO 14688 grades silts between 0.002 mm and 0.063 mm. In actuality, silt is chemically distinct from clay, and unlike clay, grains of silt are approximately the same size in all dimensions; furthermore, their size ranges overlap. Clays are formed from thin plate-shaped particles held together by electrostatic forces, so present a cohesion. According to the USDA Soil Texture Classification system, the sand-silt distinction is made at the 0.05 mm particle size.^[7] The USDA system has been adopted by the Food and Agriculture Organization (FAO). In the Unified Soil Classification System (USCS) and the AASHTO Soil Classification system, the sand-silt distinction is made at the 0.075 mm particle size (i.e. material passing the #200 sieve). Silts and clays are distinguished mechanically by their plasticity.

Silt deposits around house and car in New Orleans left by flooding from a breach in the London Avenue Canal

Environmental impacts[link]

Silt is easily transported in water or other liquid and is fine enough to be carried long distances by air in the form of dust. Thick deposits of silty material resulting from aeolian deposition are often called loess (a German term) or limon (French). Silt and clay contribute to turbidity in water. Silt is transported by streams or by water currents in the ocean. When silt appears as a pollutant in water the phenomenon is known as siltation.

Silt, deposited by annual floods along the Nile River, created the rich, fertile soil that sustained the Ancient Egyptian civilization. Silt deposited by the Mississippi River throughout the 20th century has decreased due to a system of levees, contributing to the disappearance of protective wetlands and barrier islands in the delta region surrounding New Orleans.[1]

In south east Bangladesh, in the Noakhali district, cross dams were built in the 1960s whereby silt gradually started forming new land called "chars." The district of Noakhali has actually gained more than 28 square miles (73 km²) of land in the past 50 years.

With Dutch funding, the Bangladeshi government began to help develop older chars in the late 1970s, and the effort has since become a multiagency operation building roads, culverts, embankments, cyclone shelters, toilets and ponds, as well as distributing land to settlers. By fall 2010, the program will have allotted some 27,000 acres (100 km²) to 21,000 families.^[8]

A main source of silt in urban rivers is disturbance of soil by construction activity.^{[citation needed]} A main source in rural rivers is erosion from plowing of farm fields, clearcut logging or slash and burn treatment of forests.^{[citation needed]}

See also[link]

Wikimedia Commons has media related to: Silt

• Erosion control
• Nonpoint source pollution
• Sediment control
• Silt fence
• Siltation
• Clay

References[link]

1. ^ Moss, A J; Green, P (1975). "Sand and silt grains: Predetermination of their formation and properties by microfractures in quartz". Australian Journal of Earth Sciences 22 (4): 485–495. DOI:10.1080/00167617508728913. 
2. ^ Nahon, D; Trompette, R (1982). "Origin of siltstones:glacial grinding versus weathering". Sedimentology 29: 25–35. DOI:10.1111/j.1365-3091.1982.tb01706.x. 
3. ^ Lautridou, J P; Ozouf, J C (1982). "Experimental frost shattering: 15 years of research at the Centre de Geomorphologie du CNRS". Progress in Physical Geography 6 (2): 215–232. DOI:10.1177/030913338200600202. 
4. ^ Goudie, A S; Viles, H A (1995). "The nature and pattern of debris liberated by salt weathering: a laboratory study". Earth Surface Processes and Landforms 9: 95–98. DOI:10.1002/esp.3290090112. 
5. ^ Wright, J S; Smith, B J; Whalley W B (1998). "Mechanisms of loess-sized quartz silt production and their relative effectiveness: laboratory simulations". Geomorphology 45: 15–34. DOI:10.1016/S0169-555X(97)00084-6. 
6. ^ Haberlah, D (2007). "A call for Australian loess". AREA 39 (2): 224–229. DOI:10.1111/j.1475-4762.2007.00730.x. 
7. ^ "Particle Size (618.43)". National Soil Survey Handbook Part 618 (42-55) Soil Properties and Qualities. United States Department of Agriculture - Natural Resource Conservation Service. http://soils.usda.gov/technical/handbook/contents/part618.html#43. Retrieved 2006-05-31. 
8. ^ http://pulitzercenter.org/openitem.cfm?id=1973

Getatchew Mekurya
Background information
Born	1935 (age 76–77)
Origin	Addis Ababa, Ethiopia
Genres	Ethiopian music, jazz
Instruments	Saxophone
Years active	1949–present
Associated acts	The Ex, Either/Orchestra, Addis Ababa Municipality Band

Getatchew Mekurya (Amharic: ጌታቸው መኩሪያ) (born 1935)^[1] is an Ethiopian jazz saxophonist.

Early career[link]

Mekurya began his musical studies on traditional Ethiopian instruments such as the krar and the masenqo, and later moved on to the saxophone and clarinet. Upon reaching adolescence, he began his professional career in 1949 as a part of the Municipality Band in Addis Ababa. In 1955 he joined the house band at Addis' Haile Selassie I Theatre, and in 1965 joined the famous Police Orchestra. He was also one of the first musicians to record an instrumental version of shellela, a genre of traditional Ethiopian vocal music sung by warriors before going into battle. Mekurya took the shellela tradition seriously, often appearing onstage in a warrior's animal-skin tunic and lion's mane headdress. He continued to refine his instrumental shellela style, recording an entire album in 1970, Negus of Ethiopian Sax, released on Philips Ethiopia during the heyday of the Ethiojazz movement. Mekurya continued to work alongside many of the biggest orchestras in the Ethiopian capital, accompanying renowned singers Alemayehu Eshete, Hirut Beqele, and Ayalew Mesfin.

Recent career, collaborations with The Ex and others[link]

Mekurya reached an international audience when his album Negus of Ethiopian Sax was re-released as part of the Ethiopiques CD series. Mekurya's playing style has been compared to free jazz, but developed in isolation from it during the early 1950s.^[2][3] Mekurya has said he is unfamiliar with either Ornette Coleman or Albert Ayler.^[3][4]

The album Negus of Ethiopian Sax caught the ears of Dutch avant-garde/punk band The Ex who invited the septuagenarian sax player to perform at their 25th anniversary show in Amsterdam in November 2004. In turn, Mekurya asked the Ex to be the backup band for his 2006 album, Moa Anbessa. The Ex and Mekuria toured The Netherlands, Belgium and France together in 2006 and 2007, and then the United States in 2008 and Canada in 2009.^[5]

Getatchew Mekurya has added his distinctive sound to collaborations with numerous other contemporary artists, including British Tamil singer Susheela Raman and Boston jazz ensemble Either/Orchestra.^[3] He still lives in Addis Ababa, and regularly performs at the Sunset Bar at the Sheraton Addis.

Discography[link]

• "Shellela" 45 (late 1950s)^[2]
• Ethiopiques Volume 14: Negus of Ethiopian Sax (recorded in 1970, originally released on Philips Ethiopia in 1972)
• Ethiopiques Volume 20: Either/Orchestra Live in AddisMekuria appears on the track "Shellella" (recorded in 2004)
• Moa Anbessa (with The Ex and other guests) (2006)
• Getatchew Mekurya & The Ex + Guests [DVD, Ethiosonic/Buda Musique] (2007)

References[link]

External links[link]

Wikimedia Commons has media related to: Getatchew Mekuria