Rotting trees possible cause of sand dunes’ mystery holes

SOUTH BEND, Ind. — Mysterious holes that forced the closure of a massive dune at an Indiana national park after a 6-year-old boy fell into one and nearly died were caused by sand-covered trees that left cavities behind as they decayed over the years, researchers have found.

Fungi on the covered trees formed a sort of cement that allowed the sand to keep its hollowed out shape as the wood decayed and collapsed inward, leaving holes more than 10 feet deep in the dune known as Mount Baldy at the Indiana Dunes National Lakeshore, according to a study published in December by Erin Argyilan, who heads Indiana University Northwest’s department of geosciences. She said the phenomenon likely explains similar holes found in migrating dunes in Oregon and Michigan.

Although she determined the holes to be more of a nuisance than a hazard, Argyilan said they could present an unseen geological hazard in heavily visited natural places like Mount Baldy. The popular dune has been closed except for small ranger-led tours since the July 2013 rescue of the Illinois boy, who was trapped under sand for more than three hours.

The question facing the National Park Service is whether to keep Mount Baldy closed to the unsupervised public or to find a way to safely reopen it, at least partially.

Bruce Rowe, a spokesman for the park, declined to comment on Argyilan’s study or an ongoing Indiana Geological Survey study that supports her findings. He said it wouldn’t be appropriate to comment until the agency had the chance to review both. G. William Monaghan, a senior research scientist at the IGS, said he hopes to have its completed study to the Park Service by Aug. 1.

Monaghan said the IGS study, which Argyilan is also involved in, will include a map of potentially hazardous areas based on 1930s photos that show the location of trees before the sand buried them. The scientists said reopening Mount Baldy would be a risk-management decision that the Park Service would have to make.