MAY 20, 2018 @ 11:30 AM 484 2 Free Issues of Forbes
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.