photo of pebbly ground with pebbles arranged in regular circlesStrange patterns can arise in the pebbly ground of cold landscapes. Now, writes Hannah Hickey (@hickeyh), scientists can explain how these patterns of circles, lines or gently undulating shapes form. The rocks are slowly pushed into place by the random growth of needles of ice along the ground, proved the researchers, whose experiments and computer modeling revealed how the concentration and size of stones, the height of the ice needles and the ground slope interact over dozens of freeze-thaw cycles to give rise to the patterns. Photo by Bernard Hallet/University of Washington, used with permission