Many areas in the world are
covered by hundreds of almost nine feet high, dome-like mounds with a diameter
of ten to over hundred feet. In Washington state, the hillocks are called
Mima-mounds after the Mima Prairie in Thurston County. In California and Oregon,
they are named hogwallow-mounds, prairie-mounds in New Mexico and Colorado and
pimple-prairies in the southeastern states. In South Africa, they are called
"heuweltjies" or just little hills, in Brazil “campos de murundus” or
the fields of mounds. In the Alps there are hump-meadows and even Australia has
its own earth-mounds.
Various theories have been
proposed over time to explain the strange little hills. First explorers
believed that the Mima mounds were prehistoric burial sites, but no human remains
were ever found there. In recent times, geologists explained the mounds as soil
disturbed by earthquakes, sinkholes caused by chemical weathering, formed by
glacial or periglacial activity, sediment accumulated around former tree stumps
or the action of animals. Burrowing animals like
gophers, insects or worms are
indeed able to modify entire landscapes and this theory is supported by some
recent computer models - by simulating
the behaviour of burrowing mammals, a program can produce
virtual mounds. Now, though, new research is suggesting another possible
animal responsible for the mounds in the Australian outback: birds.
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