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淤泥

2018-11-19 21:30:42     所属分类:地质学

淤泥Silt),又称沉泥,是泥土的基本组成成分之一。地质学中,淤泥是介于沙土及黏土之间,长约2到62微米、直径4到9微米的一种颗粒状物料英语granular material,主要由石英及长石这两种矿物组成[1]。淤泥可能以土壤的成分或悬浊水体内的沉积物两种形式出现。当河道泛滥,又或被山崩时的泥石流带动,淤泥会在流动时随同水体在沿途沉积成为土壤。由于淤泥的比表面积属中度,非黏粘,有好像塑胶那样带弹性。当完全干燥时,淤泥会变回粉尘般的幼细,但潮湿后立即又变回黏滑。在手持的放大镜下,淤泥清晰可见,往往带有尖锐的外表。当以牙齿咬或以舌头触摸时,这种棱角亦能感觉到,而这亦是分辨水中的淤泥或黏土的一种方法。

目录

  • 1 来源
  • 2 粒径大小的条件
  • 3 Environmental impacts
  • 4 文化象征
  • 5 参考文献
  • 6 参看
  • 7 外部链接

来源

淤泥是通过对其原石施以各种物理过程而产生。这些物理过程能够通过利用原石内沙粒大小的石英晶体中的缺陷,将这些石英沙粒再细分[2]。这些物理过程包括有:岩石表岩屑的风化作用[3]霜冻作用英语frost shattering[4]卤虫成形术英语haloclasty[5]。当中主要的过程是岩石在被水体运输时造成的磨损作用,例如:河流粉碎、风成磨损英语Attrition (weathering)和冰川研磨[6]。在半干旱环境[7]中,产生了大量的淤泥。干燥后的淤泥又名粉砂,特别是由冰川作用形成的淤泥。矿物学上,淤泥的主要成分是石英和长石。主要由淤泥组成的沉积岩被称为粉砂岩英语siltstone。强烈地震造成的液化是悬浮在水中的淤泥,水流动力从地下开始向上推。

粒径大小的条件

按巫登–温特瓦分级(Udden–Wentworth scale),淤泥的粒径属于粉砂级的3.9至62.5 µm之间,比黏土大,但比沙粒小。国际标准化组织的ISO 14688将淤泥的粒径定为2 µm-6 µm 到 20 µm-63 µm,然后再分为幼粒、中等和粗粒三等。实际上,淤泥在化学上的成分与黏土完全不同;此外淤泥的粒径在各个方向都大致相同,这一点亦是与黏土不同。再者,淤泥的尺寸往往重叠,即有多种不同粒径的粉砂混合在一起。反而黏土由通过静电力保持在一起的薄板状颗粒形成,因此具有内聚力;相反淤泥并没有这种内聚力。根据美国农业部(USDA)的土壤质地分类系统(Soil Texture Classification system)沙土和淤泥以0.05 mm的颗粒为分野[8]。这套由美国农业部开发的系统后来亦为粮食及农业组织(FAO)所采纳。 In the Unified Soil Classification System英语Unified Soil Classification System (USCS) and the AASHTO英语AASHTO Soil Classification system, the sand–silt distinction is made at the 0.075 mm particle size (i.e., material passing the #200 筲箕). Silts and clays are distinguished mechanically by their 塑性变形.

Environmental impacts

A silted lake located in 艾肖尔斯特, 德国

Silt is easily transported in 水 or other liquid and is fine enough to be carried long distances by air in the form of 灰尘. Thick deposits of silty material resulting from deposition by 风蚀 are often called 黄土. Silt and clay contribute to 浊度 in water. Silt is transported by 溪s or by water currents in the 洋. When silt appears as a pollutant in water the phenomenon is known as siltation英语siltation.

Silt, deposited by annual floods along the 尼罗河, created the rich, fertile soil that sustained the 古埃及ian civilization. Silt deposited by the 密西西比河 throughout the 20th century has decreased due to a system of 堤, contributing to the disappearance of protective 湿地 and barrier islands英语barrier islands in the 密西西比河三角洲 region surrounding 新奥尔良.[9]

In southeast Bangladesh, in the 诺阿卡利县, cross dams were built in the 1960s whereby silt gradually started forming new land called "chars". The district of Noakhali has gained more than 73平方千米(28平方英里) 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 multi-agency operation building roads, 涵洞s, embankments, cyclone shelters, toilets and ponds, as well as distributing land to settlers. By fall 2010, the program will have allotted some 100平方千米(20,000英亩) to 21,000 families.[10]

A main source of silt in urban rivers is disturbance of soil by 建筑施工 activity.[11] A main source in rural rivers is 侵蚀作用 from plowing of farm fields, 皆伐 or 刀耕火耨 treatment of 森林s.[来源请求]

文化象征

尼罗河河岸上的黑色淤泥在古埃及是重生的象征,往往与埃及诸神英语Egyptian pantheon之一的阿努比斯(Anubis)相关 [12]

参考文献

  1. ^ Assallay, A.M.; Rogers, C.D.F.; Smalley, I.J.; Jefferson, I. Silt: 2-62um,9-4phi.. Earth-Science Reviews. 1998, 45: 61–88. 
  2. ^ Moss, A J; Green, P. Sand and silt grains: Predetermination of their formation and properties by microfractures in quartz. Australian Journal of Earth Sciences. 1975, 22 (4): 485–495. Bibcode:1975AuJES..22..485M. doi:10.1080/00167617508728913. 
  3. ^ Nahon, D; Trompette, R. Origin of siltstones:glacial grinding versus weathering. Sedimentology. 1982, 29: 25–35. Bibcode:1982Sedim..29...25N. doi:10.1111/j.1365-3091.1982.tb01706.x. 
  4. ^ Lautridou, J P; Ozouf, J C. Experimental frost shattering: 15 years of research at the Centre de Geomorphologie du CNRS. Progress in Physical Geography. 1982, 6 (2): 215–232. doi:10.1177/030913338200600202. 
  5. ^ Goudie, A S; Viles, H A. The nature and pattern of debris liberated by salt weathering: a laboratory study. Earth Surface Processes and Landforms英语Earth Surface Processes and Landforms. 1995, 9: 95–98. Bibcode:1984ESPL....9...95G. doi:10.1002/esp.3290090112. 
  6. ^ Wright, J S; Smith, B J; Whalley W B. Mechanisms of loess-sized quartz silt production and their relative effectiveness: laboratory simulations. Geomorphology. 1998, 45: 15–34. Bibcode:1998Geomo..23...15W. doi:10.1016/S0169-555X(97)00084-6. 
  7. ^ Haberlah, D. A call for Australian loess. AREA. 2007, 39 (2): 224–229. doi:10.1111/j.1475-4762.2007.00730.x. 
  8. ^ 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. [2006-05-31]. (原始内容存档于2006-05-27). 
  9. ^ Mississippi River. USGS Biological Resources. [2006-03-08]. (原始内容存档于2005-10-28). 
  10. ^ Bangladesh fights for survival against climate change. [October 22, 2009]. (原始内容存档于February 12, 2010). 
  11. ^ Leedy, Daniel L.; Franklin, Thomas M.; Maestro, Robert M. Planning for Urban Fishing and Waterfront Recreation. U.S. Department of the Interior, Fish and Wildlife Service, Eastern Energy and Land Use Team. 1981. (原始内容存档于2017-12-24) (英语). 
  12. ^ Hart 1986, p. 22; Freeman 1997, p. 91.

参看

  • 侵蚀控制
  • Nonpoint source pollution英语Nonpoint source pollution
  • Sediment control英语Sediment control
  • Silt fence英语Silt fence
  • Siltation英语Siltation

外部链接


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