Part of the main street in Hilo, Hawaii, was flattened by a tsunami in April 1946. That big wave was triggered by a quake near the Aleutian Islands, where the edges of two tectonic plates continue to collide. Bettmann/Corbis hide caption

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The granulated surface of the lake bed known as the Racetrack is a favorite destination for tourists — and for scientists who want to investigate trails left by the meandering stones. Momatiuk - Eastcott/Corbis hide caption

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Scenes from the Apostle Islands National Lakeshore in Bayfield, Wis., where Lake Superior's ice is thick enough to walk to the area's sea caves for the first time in five years. Derek Montgomery for MPR News hide caption

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The Cathedral Spires in the Black Hills of South Dakota are just one of innumerable formations across the planet that speak to the Earth's ancient history. K. Scott Jackson/Ohio Water Science Center/USGS hide caption

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