Abstract

Rocks with maximum dimensions between 5 and 50 cm, which have moved distances of 35 cm to 400 m over the dry, mudcracked upper surface of the seasonal lake at Magdalenasmeer in South Africa, have left well defined traces on the argillaceous material. This phenomenon is postulated to reflect a slick muddy lake surface that developed during the passing of a cold front in the middle of the winter season, and which developed as a result of dew precipitation related to high humidity, and two subsequent freezing nights. The resultant slick surface is thought to have represented a combination of damp mud polygons and ice-filled cracks in between, and movement of the rocks was as a result of gusts of wind on the second freezing night.

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