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Black and white animated drawing of a boy walking on the sand. He disappears. On Screen Text: One moment he was there, the next, he'd vanished.

Close up video footage of sand blowing in the wind. Then, a grassy sand dune. On Screen Text: Swallowed whole... by a hole? Impossible. That defied all geologic, well, logic.

Yellow police tape is stretched across the sand dune. It reads: Do Not Enter. Just beyond the dune, the flat beach and people in the water at the shoreline. On Screen Text: And yet, hours later, rescuers pulled the missing six-year-old from a cavity a dozen feet below the surface of Mount Baldy, a 126-foot-tall sand dune on the southern shore of Lake Michigan. Fortunately, the boy survived.

Photo of a woman in a red Indiana University t-shirt standing outside with two men in front of several news station microphones. On Screen Text: But the 2013 incident stunned the world, including IU Northwest geosciences professor Erin Argyilan and her colleagues.

Diagram of a sand dune. The image shows a mound of brown sand. Arrows labeled Wind show grains of sand moving across the earth. On the slope up it is labeled Sand eroded here. On the slope down it is labeled Sand deposited here in calm air. On Screen Text: The science of dunes had been studied and all but settled, or so it was thought.

Photo of a sand dune with small scrubby trees on top and the ocean beyond. On Screen Text: The migrating masses of sand are windblown into existence and generally solid.

Photo of a circular hole in the sand. On Screen Text: So what to make of the sinking hole at Mount Baldy?

A diagram drawn over an aerial image of Mount Baldy. It shows several red circles across the sand, including one labeled Site of boy's fall. On Screen Text: To find the answer, Argyilan and her students spent the next few years studying the site, painstakingly probing the sand for more holes, plotting them, and even mapping the dune's subsurface with radar.

A three dimensional computerized topographic diagram of Mount Baldy. On Screen Text: What she and the team discovered was quite literally groundbreaking.

A diagram drawn over an aerial image of Mount Baldy. It shows red lines marking the edge of the dune. The lines labeled 1938, 1972, 1998, and 2006 are each farther inland away from the ocean. On Screen Text: Over the prior 80 years, Mount Baldy had crept inland, eventually burying a thicket of large, black oak trees.

An animation of the hill of sand moving inland and covering a tree. The tree is now mostly buried in sand. It turns white as the branches above ground disappear. On Screen Text: Over time, the trees rotted from within, leaving their hollowed husks within the dune, which, in turn, created surface holes that collapse under weight.

Photos of several holes in the sand being measured. They are several inches wide and several feet deep. A hand holds up a piece of tree bark. On Screen Text: Argyilan named the phenomenon "dune decomposition chimneys," but it's been described colloquially as a "ghost forest.".

A visitor stands reading an informational display board about Mount Baldy. In front of her is the tall sand dune with the tops of trees sticking out of the sand. On Screen Text: The research continues today. Argyilan and her students are now studying the conditions that preserve the trees in collaboration with IU's Indiana Geological and Water Survey.

A photo of two children climbing on all fours the steep surface of a sand dune. On Screen Text: The work will hopefully help prevent future accidents.

Photo of the tall grass swaying in the wind over a sand dune. On Screen Text: It's all proof that IU Northwest ingenuity can get to the bottom of any mystery, and in this case, one very deep hole.

IU Day. Sand Trap: Solving a Shoreline Mystery.