Model Results (IMAGE) University of Washington Caption Two different computer models predict the long-term distribution of stones on freezing ground depending on the stones’ initial concentration. The left column starts with 20% stone coverage, which creates islands, shown here in white; the middle rows have 30% and 40% stone coverage, which creates labyrinths and worm-like shapes; and the fourth column is 80% stone coverage, which gives no pattern. The right column shows 20% stone coverage on a slightly sloping ground; the stones tend to form lines. Credit Li et al./PNAS Usage Restrictions With credit License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.