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Inselbergs
Inselbergs are residual hills, which stand above the general plateau level. The term iselberg is a German word for “island mountain”. It was first used in 1900 by B.W. Bornhardt to describe steep sided residual hills rising abruptly above the monotonous plains of East Africa. They are erosional features and are found in most parts of Africa.
They are formed as the young soft rocks which lie above the ancient hard basement rocks are acted on by the rivers and other agents of erosion. Over time, they are worn away leaving the very ancient hard rocks standing as isolated groups of hills.
Most inselbergs are formed from massive igneous intrusions of granitic rock. Others occur in areas of ancient metamorphic rocks. Inselbergs occur in both arid and humid lands. In arid lands, their formation is understood to be through a process known as pediplanation. This involves the destruction of the initial surface by back wearing and parallel retreat. As the process of parallel retreat continues, pediments (gently sloping surface or rock usually bare or with a very thin accumulation of debris) are extended until a residual hill or inselberg is formed between them. An inselberg therefore represents the remains of an initial or older surface.
When Inselbergs are completely worn away a continuous plain called a pediplain remain. Several types of inselbergs are identified:
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Whale back is a large, low and elongated inselberg.
- A smaller type is called turtle back.
- Tor comprises of small piles of rounded boulders.
- Bornhardt is a collapsed inselberg with a conical profile.
- Kopje is an Afrikaan word for an isolated, steep-sided pile of large boulder.