Anybody who's ever gone to a beach can tell you: sand moves. Anybody who's ever seen a field of sand dunes can tell you even better: sand moves a lot. It's one thing to know sand moves, but it's quite another to actually see the evidence right in front of you in the form of half-buried trees. These trees sprouted on fairly flat ground, but over time the sand dunes at Indiana Dunes National Park have shifted further inland, pushed by the winds across Lake Michigan, and are slowly burying the forest in front of them. Already trees are fully buried by the sands, making the dunes unstable when they rot and leave empty cavities that collapse without warning, causing more sand to shift. Dunes are active, flowing things, moving slowly but steadily one grain at a time. You just have to wait around long enough to see the proof yourself.
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