Loess ( /ˈloʊ.əs, lʌs, lɛs/, or UK: /lɜːrs/; from German Löss
[lœs]) is a clastic, predominantly silt-sized sediment that is formed
by the accumulation of wind-blown dust. 10% of the Earth's land
area is covered by loess or similar deposits.
Loess is an aeolian sediment formed by the accumulation of wind-blown
silt, typically in the 20–50 micrometer size range, twenty
percent or less clay and the balance equal parts sand and silt that
are loosely cemented by calcium carbonate. It is usually homogeneous
and highly porous and is traversed by vertical capillaries that permit
the sediment to fracture and form vertical bluffs.
The word loess, with connotations of origin by wind-deposited
accumulation, came into English from German Löss ([lœs]), which can
be traced back to Swiss German and is cognate with the English word
loose and the German word los. It was first applied to
valley loess about 1821.
3 History of research
6 Large areas of loess deposits and soils
6.2 Central Asia
6.4 New Zealand
6.5 United States
7 See also
9 Further reading
10 External links
Loess near Hunyuan,
Shanxi province, China.
Loess is homogeneous, porous, friable, pale yellow or buff, slightly
coherent, typically non-stratified and often calcareous.
are angular with little polishing or rounding and composed of crystals
of quartz, feldspar, mica and other minerals.
Loess can be described
as a rich, dust-like soil.
Loess deposits may become very thick, more than a hundred meters in
China and tens of meters in parts of the Midwestern United
States. It generally occurs as a blanket deposit that covers areas of
hundreds of square kilometers and tens of meters thick.
Loess often stands in either steep or vertical faces. 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, a
popular method of making human habitations in some parts of China.
Loess will erode very readily.
In several areas of the world, loess ridges have formed that are
aligned with the prevailing winds during the last glacial maximum.
These are called "paha ridges" in America and "greda ridges" in
Europe. The form of these loess dunes has been explained by a
combination of wind and tundra conditions.
Loess comes from the German Löss or Löß, and ultimately from
Alemannic lösch meaning loose as named by peasants and masons along
History of research
The term "Löß" was first described in Central
Europe by Karl Cäsar
von Leonhard (1823–1824) who reported yellowish brown, silty
deposits along the
Rhine valley near Heidelberg. Charles Lyell
(1834) brought this term into widespread usage by observing
similarities between loess and loess derivatives along the loess
bluffs in the
Rhine and Mississippi. At that time it was thought
that the yellowish brown silt-rich sediment was of fluvial origin
being deposited by the large rivers. It wasn't until the end of the
19th century that the aeolian origin of loess was recognized (Virlet
D'Aoust 1857), especially the convincing observations of loess in
Ferdinand von Richthofen
Ferdinand von Richthofen (1878). A tremendous number
of papers have been published since then, focusing on the formation of
loess and on loess/palaeosol (older soil buried under deposits)
sequences as archives of climate and environment change. These
water conservation works were carried out extensively in
China and the
China has been continued since 1954. (Liu TS,
Loess and the environment)
Much effort was put into the setting up of regional and local loess
stratigraphies and their correlation (Kukla 1970, 1975,
1977). But even the chronostratigraphical position of the
last interglacial soil correlating to marine isotope substage 5e has
been a matter of debate, owing to the lack of robust and reliable
numerical dating, as summarized for example in Zöller et al.
(1994) and Frechen, Horváth & Gábris (1997) for the
Austrian and Hungarian loess stratigraphy, respectively.
Since the 1980s, thermoluminescence (TL), optically stimulated
luminescence (OSL) and infrared stimulated luminescence (IRSL) dating
are available providing the possibility for dating the time of loess
(dust) deposition, i.e. the time elapsed since the last exposure of
the mineral grains to daylight. During the past decade,
luminescence dating has significantly improved by new methodological
improvements, especially the development of single aliquot
regenerative (SAR) protocols (Murray & Wintle 2000) resulting
in reliable ages (or age estimates) with an accuracy of up to 5 and
10% for the last glacial record. More recently, luminescence dating
has also become a robust dating technique for penultimate and
antepenultimate glacial loess (e.g. Thiel et al. 2011, Schmidt et
al. 2011) allowing for a reliable correlation of loess/palaeosol
sequences for at least the last two interglacial/glacial cycles
Europe and the Northern Hemisphere (Frechen 2011).
Furthermore, the numerical dating provides the basis for quantitative
loess research applying more sophisticated methods to determine and
understand high-resolution proxy data, such as the palaeodust content
of the atmosphere, variations of the atmospheric circulation patterns
and wind systems, palaeoprecipitation and palaeotemperature.
According to Pye (1995), four fundamental requirements are
necessary for the formation of loess: a dust source, adequate wind
energy to transport the dust, a suitable accumulation area, and a
sufficient amount of time.
Periglacial (glacial) loess is derived from the floodplains of glacial
braided rivers that carried large volumes of glacial meltwater and
sediments from the annual melting of continental icesheets and
mountain icecaps during the spring and summer. During the autumn and
winter, when melting of the icesheets and icecaps ceased, the flow of
meltwater down these rivers either ceased or was greatly reduced. As a
consequence, large parts of the formerly submerged and unvegetated
floodplains of these braided rivers dried out and were exposed to the
wind. Because these floodplains consist of sediment containing a high
content of glacially ground flour-like silt and clay, they were highly
susceptible to winnowing of their silts and clays by the wind. Once
entrained by the wind, particles were then deposited downwind. The
loess deposits found along both sides of the
Alluvial Valley are a classic example of periglacial loess.
During the Quaternary, loess and loess-like sediments were formed in
periglacial environments on mid-continental shield areas in
Siberia, on the margins of high mountain ranges like in
on semi-arid margins of some lowland deserts like in China.
In England, periglacial loess is also known as brickearth.
Non-glacial loess can originate from deserts, dune fields, playa
lakes, and volcanic ash.
Some types of nonglacial loess are:
Desert loess produced by aeolian attrition of quartz grains 
Volcanic loess in Ecuador and Argentina;
Tropical loess in Argentina, Brazil and Uruguay;
Gypsum loess in Spain;
Trade wind loess in Venezuela and Brazil;
Anticyclonic loess in Argentina.
The thick Chinese loess deposits are non-glacial loess having been
blown in from deserts in northern China. The loess covering the
Great Plains of Nebraska, Kansas, and
Colorado is considered to be
non-glacial desert loess. Non-glacial desert loess is also found
in Australia and Africa.
Loess tends to develop into very rich soils. Under appropriate
climatic conditions, it is some of the most agriculturally productive
terrain in the world.
Soils underlain by loess tend to be excessively drained. The fine
grains weather rapidly due to their large surface area, making soils
derived from loess rich. One theory states that the fertility of loess
soils is due largely to cation exchange capacity (the ability of
plants to absorb nutrients from the soil) and porosity (the air-filled
space in the soil). The fertility of loess is not due to organic
matter content, which tends to be rather low, unlike tropical soils
which derive their fertility almost wholly from organic matter.
Even well managed loess farmland can experience dramatic erosion of
well over 2.5 kg /m2 per year. In
China the loess deposits which
Yellow River its color have been farmed and have produced
phenomenal yields for over one thousand years. Winds pick up loess
particles, contributing to the
Asian Dust pollution problem. The
largest deposit of loess in the United States, the
Loess Hills along
the border of
Iowa and Nebraska, has survived intensive farming and
poor farming practices. For almost 150 years, this loess deposit was
farmed with mouldboard ploughs and fall tilled, both intensely
erosive. At times it suffered erosion rates of over 10 kilograms per
square meter per year. Today this loess deposit is worked as low till
or no till in all areas and is aggressively terraced.
Large areas of loess deposits and soils
An outcrop of loess in Patagonia
Much of Argentina is covered by loess. Two areas of loess are usually
distinguished in Argentina: the neotropical loess north of latitude
30° S and the pampean loess.
The neotropical loess is made of silt or silty clay. Relative to the
pampean loess the neotropical loess is poor in quartz and calcium
carbonate. The source region for this loess is thought by some
scientists to be areas of fluvio-glacial depostis the Andean foothills
formed by the Patagonian Ice Sheet. Other researchers stress the
importance of volcanic material in the neotropical loess.
The pampean loess is sandy or made of silty sand.
Tajikistan up to Almaty, Kazakhstan, spans an area of
multiple loess deposits.
Loess Plateau (simplified Chinese: 黄土高原; traditional
Chinese: 黃土高原; pinyin: huángtǔ gāoyuán), also known as the
Huangtu Plateau, is a plateau that covers an area of some
640,000 km² in the upper and middle of China's
Yellow River and
China proper. The
Yellow River was so named because the loess forming
its banks gave a yellowish tint to the water. The soil of this
region has been called the "most highly erodible soil on earth".
Loess Plateau and its dusty soil cover almost all of Shanxi,
Gansu provinces, the Ningxia Hui Autonomous Region, and
parts of others.
Extensive areas of loess occur in New Zealand. The basis of loess
stratigraphy was introduced by
John Hardcastle in 1890 
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Map showing the distribution of loess in United States.
Loess Hills of
Iowa owe their fertility to the prairie topsoils
built by 10,000 years of post-glacial accumulation of organic-rich
humus as a consequence of a persistent grassland biome. When the
valuable A-horizon topsoil is eroded or degraded, the underlying loess
soil is infertile, and requires the addition of fertilizer in order to
The loess along the
Mississippi River near Vicksburg, Mississippi,
consist of three layers. The Peoria Loess, Sicily Island Loess, and
Loess accumulated at different periods of time during
the Pleistocene. Ancient soils, called paleosols, have developed in
the top of the Sicily Island
Loess and Crowley's
Ridge Loess. The
lowermost loess, the Crowley's
Ridge Loess, accumulated during the
late Illinoian Stage. The middle loess, Sicily Island Loess,
accumulated during early Wisconsin Stage. The uppermost loess, the
Peoria Loess, in which the modern soil has developed, accumulated
during the late Wisconsin Stage. Animal remains include terrestrial
gastropods and mastodons.
Börde – North German loess regions
Gäue – South German loess regions
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Look up loess in Wiktionary, the free dictionary.
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Wikisource has the text of the 1920
Encyclopedia Americana article
2006, The Secret of China’s Vast
Loess Plateau Suburban Emergency
Management Project, Chicago, Illinois.
2007, New European
Loess Map. Helmholtz Centre for Environmental
Research, Leipzig, Germany.
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Loess Hills, Iowa
U.S. Geological Survey, 2006, Eolian History of North America Why is
loess important to study?
Loess Hills of Western Iowa
Loess Hills of Roztocze
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