A lone shark cruises a sandy shoreline in the Maldives in this image from photographer Tim Burgess. Its path parallels the footsteps left by humans on the beach. Between the beach’s sand and the ocean’s deeper water, there’s a narrow stripe of sand ripples. Constantly formed and reformed by the crashing waves, these ripples act like miniature dunes. Any time a flat particle bed endures a passing flow above a critical speed, it will form ripples like these. (Image credit: T. Burgess/OPOTY; via Colossal)
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