An etchplain is a plain where the
bedrock
In geology, bedrock is solid rock that lies under loose material (regolith) within the crust of Earth or another terrestrial planet.
Definition
Bedrock is the solid rock that underlies looser surface material. An exposed portion of bedro ...
has been subject to considerable "etching" or
subsurface weathering. Etchplanation is the process forming etchplains. Contrary to what the name might suggest, etchplains are seldom completely flat and usually display some relief, as weathering of the bedrock does not advance uniformly. This means that weathering is unrelated to the flatness which might be derivative of various other processes of
planation including
peneplanation and
pediplanation.
Erosion of etchplains can result in the exposure of
inselberg
An inselberg or monadnock () is an isolated rock hill, knob, ridge, or small mountain that rises abruptly from a gently sloping or virtually level surrounding plain.
In Southern Africa a similar formation of granite is known as a koppie, a ...
s such as
bornhardt
A bornhardt () is a dome-shaped, steep-sided, bald rock outcropping at least in height and several hundred metres in width. They are named after Wilhelm Bornhardt (1864–1946), a German geologist and explorer of German East Africa, who first ...
and
tors.
Generally the topography exposed at a stripped etchplain, that is an etch surface,
after erosion of
regolith
Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestria ...
is one with many irregularities as result of
structurally defined areas of rock strength.
A distinction can be made between etchplains and etch surfaces as the latter may or may not be flat and can represent the landform arising from the stripping of an etchplain.
[
As climate changes, arid and semi-arid periods of pediplanation may alternate with more humid periods of etchplanation resulting in the formation of flattish surfaces (]peneplain
390px, Sketch of a hypothetical peneplain formation after an orogeny.
In geomorphology and geology, a peneplain is a low-relief plain formed by protracted erosion. This is the definition in the broadest of terms, albeit with frequency the usage ...
s) of mixed origin (polygenetic).
During wet seasons deep weathering
Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement) ...
is more pronounced producing regolith which is then stripped away by erosion during subsequent dry seasons. The rate of stripping must exceed that of regolith production by deep weathering, otherwise deep-seated basal surfaces would not be revealed.
The African Surface
The African Surface or African Erosion Surface is a land surface formed by erosion covering large swathes of Africa.Burke & Gunnell 2008, pp. 6–7. The type area of the surface lies in South Africa where the surface was first identified as such ...
formed 70–40 million years ago is an example of an etchplain.[
]
History of the concept
The term 'etchplain' or 'etched peneplain' was originally coined to describe surfaces in East Africa
East Africa, Eastern Africa, or East of Africa, is the eastern subregion of the African continent. In the United Nations Statistics Division scheme of geographic regions, 10-11-(16*) territories make up Eastern Africa:
Due to the historical ...
by E.J. Wayland in 1933 and Bailey Willis
Bailey Willis (March 31, 1857 in Idle Wild-on-Hudson, New York, United States – February 19, 1949 in Palo Alto, California) was a geological engineer who worked for the United States Geological Survey (USGS), and lectured at two prominent Amer ...
in 1936. This last geologist applied the term etched peneplain to the Tanganyika Plateau. Julius Büdel
Julius Büdel (8 August 1903 – 28 August 1983) was a German geomorphologist noted for his work on the influence of climate in shaping landscapes and landforms. In his work Büdel stressed the importance of inherited landforms in present-day ...
developed the concept further in the second half of the 20th century, but never did use the term 'etchplain'.landscape
A landscape is the visible features of an area of land, its landforms, and how they integrate with natural or man-made features, often considered in terms of their aesthetic appeal.''New Oxford American Dictionary''. A landscape includes the p ...
s in the tropics
The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in
the Southern Hemisphere at S. The tropics are also referred to ...
or with a tropical climate
Tropical climate is the first of the five major climate groups in the Köppen climate classification identified with the letter A. Tropical climates are defined by a monthly average temperature of 18 °C (64.4 °F) or higher in the coo ...
but since the 1980s it has also been used to describe flat weathered landscapes at higher latitudes.[
]
See also
*
*
References
Weathering landforms
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