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Dune dynamics discovered here


First came the groundbreaking discovery that decomposing oak trees are the source of holes in Mt. Baldy; now, IU Northwest’s Dunes expert is leading a second study to answer ‘how’ and ‘why’

Monday Jun 20, 2016


Erin Argyilan has no doubt covered miles while traversing the sand dunes of Indiana’s 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 eight-foot hole hidden beneath the fine sand.

The same scare happened to a six-year-old boy there in 2013, and he was later rescued after being trapped under 11-feet of sand. It was, in fact, the boy’s tragedy that sparked all those miles covered by Argyilan as she sought answers to the mystery, however, Argyilan felt much differently about the scare.

She was, frankly, elated.

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

The discovery wasn’t so much that the moving dune had, over time, buried a 70- or 80-year-old forest. Everyone had just assumed that any trees buried under the sand would simply decompose. The mystery was more about how the decomposing trees maintained a hollow, and hazardous, structure.

The resulting study, published in Aeolian Research in 2015, made the discovery official and the phenomenon got an official 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’s own Peter Avis, Ph.D., contributed their specialized expertise, such as Avis’s knowledge of fungus living within the trees, to make the case.

More dune discoveries to come

The ground-breaking discovery merely 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, to investigate exactly how the holes, or more accurately, trees branches and trunks, are able to maintain their hollow shape. Figuring out how this happens, and what conditions contribute, will have significant implications for understanding similar phenomena in sand dunes throughout the world, thus giving geologists a new body of knowledge to help them understand not just that trees are the reason, but what’s happening to them within the dune.

Argyilan reveals a couple of key facts that are forming the researchers’ early hypotheses, such as the presence of calcium carbonate “cement” forming between the trees and surrounding sand. Since the sand is made up of primarily quartz, a non-reactive mineral, she wonders about this.

“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 the discoveries of Argyilan and her colleagues, and because the Indiana Dunes 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. The students here 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 Mt. Baldy’s soil and sand. He says 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 towards 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 Mt. Baldy

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

The IGS, a research institute of Indiana University, has brought two ground-penetrating radar systems to Mt. Baldy two years ago. The 100 Mhz 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 IGS researchers have done phenomenal things with their technology, including digitizing every single tree and landmarks from a collection of 1938 photographs, including the very one that Nathan Woessner fell into in 2013. She anticipates that one day, visitors to the Indiana Dune 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.

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