Research continues as Indiana’s Mount Baldy reveals secrets of dune dynamics

Post by IU Northwest media communications specialist Erika C. Rose

Erin Argyilan has no doubt covered miles while traversing the sand dunes of the Indiana Dunes National Lakeshore over the past several years.

After logging all those miles, there was perhaps no happier day for the Indiana University Northwest geologist than the day she stumbled over an 8-foot hole hidden beneath the fine sand.

In 2013, Nathan Woessner, a 6-year-old boy from Sterling, Ill., was rescued after falling into a similar hole and being trapped under 11 feet of sand. It was, in fact, the boy’s close call that sparked all those miles Argyilan covered as she sought answers to the mystery.

Erin Argyilan

Erin Argyilan (Photo by Liz Kaye, IU Communications)

Argyilan’s discovery was a defining moment that validated more than a year of research. She had believed that the mysterious holes revealing themselves atop the 120-foot-tall Mount Baldy were caused by rotting oak trees buried beneath the shifting dune. And while her outings exploring the dune yielded many small holes here and there, each giving her hypothesis more credibility, it wasn’t until she could photograph a buried branch leading to a hollowed-out tree trunk that Argyilan could so convincingly prove what she believed to be true.

It was well known that the moving dune had, over time, buried a 70- or 80-year-old forest. Everyone had assumed that any trees buried under the sand would simply decompose. The discovery was that the rotting trees somehow maintained a hollow and hazardous structure and that their collapse could create holes in the dune.

The resulting study, published in the journal Aeolian Research, made the discovery official and gave the phenomenon a name: dune decomposition chimneys. Argyilan and her colleagues introduced the discovery to the world at the Geological Society of America conference in November. Argyilan’s co-authors, including IU Northwest associate professor of biology Peter Avis, contributed their specialized expertise — such as Avis’ knowledge of fungus living within the trees — to make the case.

More dune discoveries to come

The discovery laid the groundwork for more research, which promises to be equally historic. Argyilan and colleagues are well into the second phase of their research. This time they are investigating exactly how the holes — or, more accurately, tree branches and trunks — are able to maintain their hollow shape. Figuring out how this happens, and what conditions contribute to it, will have significant implications for understanding similar phenomena in sand dunes throughout the world.

Argyilan reveals a couple of key factors that are informing the researchers’ early hypotheses, such as the formation of calcium carbonate “cement” between the trees and surrounding sand. Since the sand is made up primarily of quartz, a non-reactive mineral, she wonders how the cement is being created.

“Where is that coming from?” she ponders. “It’s not in the sand. Is it the tree itself? Is it the fungus? The sediment? What is the key factor that is making this happen? The work we are doing now will show the pathway for how the materials got there. It’s still an evolving system throughout the time that it is encapsulated within the dune.”

Argyilan’s early speculation is that human activity is somewhat to blame.

“This has not really been studied before,” Argyilan says. “This is significant because there are actually a lot of places around the country, not just the Indiana Dunes, where dunes are covering trees. Learning about the real mechanisms behind it will help us assess risk in other locations.”

The ‘official university’ of the Indiana Dunes

Largely due to Argyilan and her colleagues’ discoveries, and because the Indiana Dunes lakeshore offers the perfect lab environment for students and faculty, it’s hardly a stretch to refer to IU Northwest as the Indiana Dunes’ university — the place where the dynamics of dunes are observed, explained and researched. Students are doing real science at the very place where the world’s most significant work on the dunes originated, under the wing of the scientists who published it.

Students like Eric Torness, a sophomore geology student who is working with Argyilan to analyze the chemical components of Mount Baldy’s soil and sand. He said that working under Argyilan is giving him the experience he needs for his application to graduate school.

“Dr. Argyilan has been a big part of my success at IU Northwest,” Torness said. “I was doing senior-level research as a freshman. The opportunities we get here on a smaller campus are amazing.”

Torness anticipates receiving a double bachelor’s degree in geology and atmospheric sciences in 2019.

He hopes to attend graduate school at the University of Colorado in Boulder, ultimately pushing toward a degree in planetary science and a job at NASA.

“I don’t want students leaving this university thinking they haven’t done what ‘real’ geology students do,” Argyilan said. “Especially with the dunes in our backyard, they are truly engaging in relevant scientific research.”

Other happenings on Mount Baldy

This summer, National Park Services officials are keeping Mount Baldy closed while they wait for another study, expected soon from the Indiana Geological Survey. The study, which commenced two years ago, will yield a 3-D map of the internal architecture of the dune.

The Indiana Geological Survey, a research institute of Indiana University based in Bloomington, brought two ground-penetrating radar systems to Mount Baldy two years ago. The 100-megahertz and 250-MHz rigs were used to image the internal structure of the dune, similar to how a CT scan would image the inside of a body. The researchers also used a Geoprobe to bring up sediment from deep inside the dune.

Argyilan said the Indiana Geological Survey researchers have done phenomenal things with their technology, including digitizing every single tree and landmark from a collection of 1938 photographs. That includes the tree that produced the hole that Nathan Woessner fell into in 2013. She anticipates that one day, visitors to the Indiana Dunes could view a simulation of the dune moving over the forest since 1938.

“What we can do now is amazing,” she said. “We are going to understand everything about the dune.”

Of course, from now on, Argyilan says she will always be expecting the unexpected.

This article originally appeared in Indiana University Northwest News.

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