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 bed ...
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, an ...
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 firs ...
and
tors.
Generally the topography exposed at a stripped etchplain, that is an etch surface,
after erosion of
regolith 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 ( peneplains) of mixed origin (polygenetic).
During wet seasons deep weathering 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 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, also known as Eastern Africa or the East of Africa, is a region at the eastern edge of the Africa, African continent, distinguished by its unique geographical, historical, and cultural landscape. Defined in varying scopes, the regi ...
by E. J. Wayland in 1934 and Bailey Willis in 1936. This last geologist applied the term etched peneplain to the Tanganyika Plateau. Julius Büdel 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 human-made features, often considered in terms of their aesthetic appeal.''New Oxford American Dictionary''. A landscape includes th ...
s in the tropics
The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...
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 or higher in the coolest month, featuring hot te ...
but since the 1980s it has also been used to describe flat weathered landscapes at higher latitudes.[
]
See also
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*
References
Weathering landforms
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