They might look like the footprints of giants or of alien visitors, but the quasi-geometric shapes adopted by some elongated lakes or ponds have a natural explanation.rnThe shores of such water bodies are washed by high-angle waves, which make them prone to instability caused by erosion and deposition of shoreline sand or gravel, say Andrew Ashton of the Woods Hole Oceanographic Institution in Massachusetts and his colleagues. Their simulations show that this process creates cusp-shaped capes and spits, and that the effect of these on wave patterns often leads to cusps on opposite shores 'attracting' one another. The cusps ultimately link up, forming bridges that divide the water body into a series of smaller, often oval, lakes.
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