Mount Baldy Investigation Continues
One of the most popular attractions in the Indiana Dunes National Lakeshore has remained closed for over a year. Last July, a 6-year-old boy visiting the park was buried under 11 feet of sand for over 3 hours before being pulled from the dune with only minor injuries. Researchers immediately began searching for the cause of the collapsing sand, and discovered several smaller holes in the process. Now, over a year later, theories are being explored, but answers are still elusive.
Mount Baldy inside the Indiana Dunes National Lakeshore is moving. Changes in wind direction, lake level, and human activity are all contributing to the dune’s migration south away from the shoreline. But last summer the dune began moving in a way no one had recorded before.
Erin Argyilan, Ph.D., an associate professor of geology at Indiana University northwest in Gary, says the phenomenon initially left her baffled. “Some sort of hole or cavity that could somehow stay open really was hard for me to wrap my brain around.”
Holes, or collapse features, began showing up along an East – West line on the slip face of the dune, the side which faces the lake.
Researcher Todd A. Thompson, Ph.D., assistant director of research for the Indiana Geological Survey, discovered one of the holes while walking along the dune. “I stepped on to the ground, continued walking, didn’t even realize it, and when we came back later on, a hole that was 18 by 22 centimeters had opened up and we were able to follow that hole down 1.4 meters.”
Now, a team of researchers with The Indiana Geological Survey and Indiana University are trying to determine why the holes are appearing. They’re using high tech equipment to gather two types of data. The first is a series of images using ground penetrating radar which will allow them to internally map the dune.
Argyilan says, “Every 10 meters we’re taking this ground penetrating radar. It lets us see what we call the internal structure of the dune, how the sand falls, the bed forms. We can see any buried soils underneath. And by doing so many lines every 10 meters, what we’ll do is we’ll actually build a 3-dimensional model of what the dune actually looks like.”
Thompson adds, “So this would be somewhat similar to you getting a CAT scan done of your brain.”
The second kind of collection involves sampling the dune itself. Long thin tubes known as GeoProbes are pushed down into the ground to obtain a cross section of the sand and soil below.
“That cylinder collects sediment in it, and we bring it back up to the surface,” says Thompson. “We can do what we say ‘ground – truth it,’ we can see what it actually is.”
The result so far is a theory which researchers are continuing to investigate. The dune, which migrates several feet per year, has likely moved over top of vegetation and even homes which once stood along the shore.
Argyilan explains, “We can see in the aerial photographs from 1939 that the landscape was largely stabilized and there was a narrow band, probably about 150 – 200 meters, of open sand close to the lake. So what’s happened over time is that there’s been more disturbance. That area of open sand has actually moved farther to the south. So the old stable landscape is now buried underneath anywhere from about 20 to 70 feet of bare open sand.”
Thompson says “There were houses in there. There were trails in there. There were little small garages, maybe some barns. You know we may, we may push a GeoProbe down in and come up with some shingles.”
G. William Monaghan, Ph.D., is a senior research scientist at the Indiana geological Survey. He explains how such vegetation could eventually create holes in the dune. “You can see the canopy of these trees and it’s got leaves on it of course, but it’s also got a whole network of branches. When those branches start to decay, the dune starts to settle. And if conditions are just right, the dune will settle but maybe leave some void, some opening. So normally this process of decay and settling with the dune occurs in increments. But occasionally apparently it can also occur in large scale catastrophic events, and we think that’s what happened.”
Researchers currently believe there is a narrow area of Mount Baldy where the depth, ground composition and other conditions are right to allow the holes to form, and eventually they may stop altogether. Most of the holes are too small to pose a threat to visitors, but park officials remain cautious.
“The problem that we have now is there’s very little information out there, well pretty much no information, about holes appearing and staying open in dunes,” says Argyilan. “So we need to understand the process and that’s where the science is going to lead us, and then there can be management decisions based on that.”
Monaghan concludes, “I really hope that this will shed some light unto the past several hundred years of dune activity here, and fit into some bigger research projects that we have. I’m very excited to be doing this work.”
National park officials say safety is their top concern, and the dune will remain closed as long as necessary. However there are many other features of the national park which remain open.