Wednesday, June 12

Researchers Use Ground-Penetrating Radar to Understand Holes in Mount Baldy Dune

Illinois researchers are still searching for the reason for the many sudden holes forming in the dunes at Mount Baldy.

The area of the Indiana Dunes National Lakeshore was shut down for public visitation on when six-year-old Nathan Woessner was swallowed by a large hole in the dune. Though he recovered from the accident, he was buried in 11 feet of sand for 3½ hours before rescuers were able to get him out.

The incident sparked an ongoing research effort to discover the reason that holes are suddenly forming in the 126-foot-tall dune. Three of the effort’s primary researchers met in the cordoned-off area on Thursday to discuss recent findings.

A new wave of research that began Monday includes geological probes and ground-penetrating radar to build on radar data that the Environmental Protection agency collected from the site a year ago. The probe will collect soil samples and the GPR will give researchers a visual glimpse into the internal structure of the dune.

In the past 13 months, researchers have documented six holes on Mount Baldy. Most have been only about 2 inches wide and quickly fill with sand, but the larger ones can still be dangerous to casual hikers.

In fact, Indiana Geological Survey assistant director of research Todd Thompson was almost a victim of the hole formations himself on Wednesday when a 3-feet-deep hole opened up at his feet as he moved equipment across the dune.

At the moment, the working theory is that buried trees are decaying under the dune, causing shifts in the sand and opening up the many holes. Earlier research already uncovered an entire house buried by sand, among other structures. Similar holes have also appeared in Oregon, though researchers don’t yet know why.

Researchers are focusing their GPR and geological probe efforts on the 292-by-984-foot section of Mount Baldy where most of the holes have appeared, including the hole that nearly swallowed Woessner. Since the rescue activities were too urgent for anyone to take a measurement of that hole, researchers are hoping ground-penetrating radar will shed some light on what happened there.

“Ground penetrating radar is an excellent tool that can potentially locate voids under the surface,” says Stan Wood Jr,Subsurface Investigations at Wood Inspection Services. “Ground penetrating radar sends a signal down into the ground and the user can locate a baseline to establish whats normal, then figure out the abnormalities in the ground. Radar travels faster through air versus sand or dirt, so the voids would be able to be easily spotted.”

Scientists are interested in maintaining the safety and integrity of Mount Baldy, but they’re also very interested in understanding the unusual phenomena on the dune. Results of their research should be available in a few months, with a full analysis on it’s way in about a year. At this time, there’s no planned timetable for re-opening Mount Baldy to the public.

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