Inselbergs: Madikwe’s “island mountains”
by Leigh King – 23 July 2010
Visitors to Madikwe cannot help noticing that the landscape – particularly on the western side of the reserve – is dotted with small mountains or large hills that seem to suddenly protrude from otherwise fairly level terrain. Locals would probably call this geographical feature a “koppie”– a South African term for a small hill – but the Madikwe rangers and guides will almost certainly inform you that these protuberances are inselbergs. They might also tell you that the name derives from two German words: insel meaning “island”, and berg meaning “mountain”.
It is believed that early German explorers came upon these features in the vast arid spaces of Namibia, and gave them the name by which they are known in most of the world (http://www.geomorph.org). In the United States, the Native American term “monadnock” meaning “isolated mountain” is more frequently used.
The Penguin Dictionary of Physical Geography (1984) describes inselbergs as “prominent steep-sided hills of solid rock, rising abruptly from a plain of low relief” and notes that inselbergs are characteristic for tropical landscapes, particularly for the savannah zone. In fact, these rock features are found in a variety of climates including savannah, arid, sub-tropical, Mediterranean and Arctic.
Inselbergs occur when, for various geological reasons, a body of rock that is resistant to erosion lies inside a body of softer rock which is susceptible to weathering processes. When this latter rock is eroded the more resistant rock is left behind as an “isolated mountain”.
Inselbergs range in size and height – they can be mere metres, or thousands of metres high. They are found in granite and sedimentary landforms and this in turn influences their profiles. Those eroded in crystalline rocks are usually rounder and smoother, while those in eroded in sedimentary rocks are more block-shaped.
According to the US Army Corps of Engineers, “Inselbergs that have small-scale roughness can provide some level of cover and concealment. Because of their commanding positions over the surrounding desert terrain, they have often been used as observation posts during desert warfare. Although seldom trafficable by wheeled vehicles, they can be climbed on foot. Some larger inselbergs are shown on maps and appear on many forms of imagery, which makes them useful for navigation.”
Uluru (also known as Ayers Rock) in central Australia is probably the most well-known example of an inselberg. Although the inselbergs of Madikwe are not as large, nor do they have the historical and spiritual significance of this landmark, they are nevertheless fascinating and add another dimension to this malaria-free game reserve situated a few hours from Johannesburg and Pretoria.