This website is devoted to the worldwide Study of Loess
Loess is a homogeneous, typically nonstratified, porous, friable, slightly coherent, often calcareous, fine-grained,silty, pale yellow or buff, windblown (aeolian) sediment. It consists of mainly quartz particles in the size range 15-75 micro-metres. It generally occurs as a widespread blanket deposit that covers areas of hundreds of square kilometers and tens of meters thick. Loess often stands in either steep or vertical faces. The term sometimes also refers to soils derived from such deposits. The word comes from the German Löss or Löß, Loess is an aeolian sediment which forms by the accumulation of wind-blown silt and lesser and variable amounts of either sand or clay. Glacial loess is derived from either glacial or glacial outwash deposits, where glacial activity has ground rocks mainly of granitic origin to a very fine dust. After drying, these deposits are highly susceptible to wind erosion, winnowing of their silts and clays, transportation of these sediments, and deposition some distance downwind from glacial deposits. The loess deposits found along both sides of the Missisippi River Alluvial Valley are a classic example of glacial loess Nonglacial loess consists of silt-size sediments eroded by wind from either deserts, dune fields, or playa lakes. The prolonged accumulation of wind-blown volcanic ash can form loess. Some types of nonglacial loess are 1) volcanic loess in Ecuador and Argentina; 2) tropical loess in northeastern Argentina, Brazil and Uruguay: 3) gypsum loess in northern Spain; 4) trade-wind loess in Venezuela and Brazil; and 5) anticyclonic gray loess in Argentina. The thick Chinese loess deposits are classic nonglacial (desert) loess with their sediments having been blown in from deserts in northern China. The loess covering the Great Plains of Nebraska, Kansas, and Colorado and is nonglacial desert loess. Nonglacial desert loess is also found in Australia and Arica.
Loess deposits may become very deep — a hundred metres or more in areas of China and the midwestern United States. Loess deposits are geologically unstable by nature, and will erode very readily. Even well-managed loess farmland can experience dramatic erosion of well over 25 tonnes per hectare per year.
Loess tends to develop into highly rich soils. Therefore under appropriate climatic conditions these areas are among the most agriculturally productive in the world.
Hungary has several areas that are covered by loess. At locations such as Dunaujvaros and Balatonakarattya, loess walls are exposed as "reefs" (see illustration). Similar formations exist in Bulgaria on the south bank of the Danube.
The central part of Belgium is also covered by thick loess stacks. An interesting loess site where late Middle and Late Pleistocene Neanderthal artifacts were found within the soils between the loess layers is Veldwezelt-Hezerwater.
Loess grains are angular, with little polishing or rounding, composed of crystals of quartz, feldspar, mica and other minerals. Because the grains are angular, loess will often stand in banks for many years without slumping. This soil has a characteristic called "vertical cleavage", which makes it easily excavated to form cave dwellings; this is still a popular method of making human habitations in some parts of China.
