Heuweltjie

Heuweltjies are a class of soil surface feature that occurs widely in the south-western Cape of South Africa. They may be recognised as large mounds above or near the surface of the landscape. Like other similar-looking phenomena, such as Mima mounds and fairy circles, from which they have been poorly distinguished, particularly in early literature, they have been the subject of a wide range of speculation and of debate that has not yet been settled conclusively.

It is quite certain that not all types of heuweltjies have the same cause and nature. For one thing, the various organisms and circumstances that have been proposed to cause them do not occur throughout their range. For another, they differ in nature; some for example have been seen as improving soil fertility, an opinion documented at least as long ago as the early 20th century, whereas others seem to inhibit plant growth.

Possible theories and discussions on the topic include the following:

One theory is that heuweltjies are fossil termite mounds. Within this hypothesis, there are two conflicting opinions on the origins of heuweltjies, one maintaining that heuweltjies were built by the harvester termite Microhodotermes viator, the other that heuweltjies were built by a now possibly extinct termite species. The earliest radiocarbon dates on heuweltjies suggest an age of about 30,000 or even 40,000 B.P.

Another theory is that heuweltjies are created by burrowing (fossorial) animals. Variants of this hypothesis are that the animals are mole-rats in the families Bathyergidae and Rhizomyinae; termites; or a combination of mole-rats and termites. In a review paper, Walter Whitford and Fenton Kay state that while the mounds appear to have been created by termites, mammals (aardvarks) partially maintain the mounds by feeding on and living in them. They show a (log-log) correlation between the surface area of mounds including Mima mounds, badger digs, bison wallows, mole-rat, prairie-dog and banner-tail kangaroo rat mounds, with the longevity of the disturbance ('', i.e. disturbance of soil by living agents including animals, roots, etc.): a heuweltjie of 100–1000 square metres is 1000–10,000 years old.

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