Indiana Dunes National Lakeshore

Photo: carful ... Cowboy State-r/Flickr

Every year hundreds if not thousands of people climb the 125-foot-tall sand dune known as Mount Baldy in Indiana Dunes National Lakeshore park, but last Friday something happened that has never occurred before. A hole appeared in the sand, swallowing a 6-year-old boy visiting from Illinois. He sank 11 feet into the sand, and rescuers took three hours to reach and save him.

Mount BaldyYoung Nathan Woessner, who remains in critical but stable condition at a nearby hospital, may have survived the ordeal thanks to an air pocket that provided him with oxygen.

Now the National Park Service is investigating how and why this occurred. Park ranger Bruce Rowe told the Associated Press that they think the dune, which moves several feet every year, may have encompassed a tree trunk, which slowly decayed and left room for the sand to shift and settle, creating the hole. Rangers have seen trees become covered by the dune, but this is the first time a hole has ever been observed.

Mount Baldy, on the shores of Lake Michigan, has several marked trails, one of which leads to the summit. The official National Park Service description of the site refers to the trees on the dune's south slope, saying "without vegetation to hold the sand, Mount Baldy will continue its deliberate march inland." The park service describes the dune as "starving," saying more sand erodes than arrives on waves. The Army Corps of Engineers has added sand to it four times, most recently in 1996.

Rowe said rescuers did not find evidence of a tree where they rescued Woessner, but he told the AP that they did find a lot of bark. He said that was not definitive enough to rule out other possibilities. A geochemist with the Illinois Geological Survey said other dunes have been affected by underground water discharge, creating "piping" or cavities that can collapse.

Mount Baldy is currently closed to further hiking while the park service investigates further. Woessner remains on a ventilator, but doctors say there is no evidence of brain injury and he could be released in the next two weeks.

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Inset image: The 125-foot-tall Mount Baldy sand dune in Michigan City, Indiana, photographed in 2009. (Photo: Tom Gill/Flickr)