Photograph by National Park Service
Published August 14, 2014
Decomposing trees, dilapidated houses, and other items buried over 70 years by a rapidly moving sand dune could be responsible for a sudden and mysterious hole that swallowed a six-year-old boy at Indiana Dunes National Lakeshore last summer.
That is the working theory of a team of scientists who are scrambling to figure out how and why the boy was buried under 11 feet (3.4 meters) of sand for 3.5 hours on June 12, 2013. The fine, silky grains dropped out from under him as he explored Mount Baldy, the most popular destination at the national park about 60 miles (96.6 kilometers) southeast of Chicago.
As a result, scientists are using ground-penetrating radar that shoots as far as 75 feet (22.9 meters) below the dune's surface to build a detailed, three-dimensional map of trees, buildings and more that could be buried there. They're also combing old aerial photos and historical records for clues to what is hidden beneath the sand and could, therefore, collapse. (See "Singing Sand Dunes Explained.")
"There may be houses underneath where we're standing," said G. William Monaghan, as he stood atop the 142-foot (43.3-meter) dune on the south shore of Lake Michigan. Monaghan is senior research scientist at Indiana Geological Survey at Indiana University Bloomington, and one of three lead investigators on the Mount Baldy mystery.
While the boy is alive and well, Mount Baldy remains closed indefinitely to the park's nearly two million annual visitors.
A Dune Biopsy
Already, the investigative team has found a home that was buried by sand after the Mount Baldy area joined the national lakeshore in the early 1970s. Researchers suspect more remain, perhaps with barns and sheds, as the houses stood uninhabited after the park service—and the dune—took over. (See pictures of sand dunes from around the world.)
While about six more holes have been discovered since last summer, others may have gone unnoticed, researchers said.
Scientist Todd Thompson, assistant director of research for Indiana Geological Survey, compared the entire process to a CT scan. CT scans combine x-ray images taken from various angles to produce a detailed picture of bones and tissues in the body. They commonly are used to find tumors and other problems.
Then, "if you see something, you need to go do a biopsy," Thompson said.
On a sand dune, that biopsy means taking core samples of the dune, which involves sticking long, hollow plastic tubes deep into the sand at various locations to pull up the layers of sand, dirt, or anything else buried there. Monaghan said he wouldn't be surprised to find a shingle.
A few different factors are responsible for Mount Baldy's rapid and continuing shift southwest, as the dune has moved about 394 feet (120 meters) in the past 70 years, researchers said. (See "Dune May Doom 'Star Wars' Set.")
The first contributor is nature: The south shore of Lake Michigan collects sediment from around the lake, which helped build and maintain the dune in the first place, researchers said. The fine sand is naturally picked up and carried by the wind and water, ever shifting the dune.
But development at the harbor in nearby Michigan City, Indiana, has stopped a lot of sediment that once landed at Mount Baldy from making it all the way there, Thompson said. That reduces the amount of new sand coming in and replenishing the dune. (See also "How (And Why) to Build a Dune.")
In addition, scientists said, park visitors have enjoyed Mount Baldy for decades. Those years of hiking, sliding and picnicking on the dune have eliminated much of the natural vegetation that once grew there and helped hold the fine sand in place.
Still, Mount Baldy is the only place that Erin Argyilan, the third investigator, said she has ever heard of sudden and deep holes appearing in the sand dune, which disappear almost as quickly. Argyilan is associate professor of geology at Indiana University Northwest.
The event last summer, Argyilan said, "really was hard for me to wrap my brain around."
A final report on the $90,000 investigation, paid for by the National Park Service, is expected next summer.
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