Erin Argyilan was wrapping up a scientific study of wind speeds on Mount Baldy last year when she saw a circle of beachgoers on their knees halfway up the hulking sand dune. They appeared to be digging frantically.
It had been a gorgeous afternoon: sunny, mid-70s. All day, a breeze had rolled off Lake Michigan and up the dune’s rumpled face. Rising 126 feet off the beach, Mount Baldy is one of the tallest lakefront dunes in the world and the most popular attraction at the Indiana Dunes National Lakeshore, a national park that straggles for 15 miles along the industrial southern shore of Lake Michigan, between Gary and Michigan City, Indiana.
For many of the park’s two million yearly visitors, the grueling hike up Baldy’s slip-sliding slope—and the dead run down—is a rite of passage. But on that July afternoon, Argyilan, an athletic 38-year-old geoscientist at Indiana University Northwest, who was then seven months pregnant with her first child, sensed that something was amiss. She strode up to the site of the commotion and saw a man in swim trunks clawing at the sand. “He’s here,” the man kept saying. “He’s right here.” His wife, who appeared to be in shock, was calling out to God. Their 6-year-old son, they said, had vanished down a hole.
Argyilan saw no sign of an opening or even upturned sand, which you’d expect if someone had dug a hole. As for natural cavities, dunes aren’t supposed to have any. Unlike hard rock, which can dissolve to form caverns and sinkholes, dunes are just big piles of sand formed as wind stacks one grain atop the next.
“This doesn’t make any sense,” Argyilan told a pair of fieldworkers from the National Park Service, who’d been helping lug around her 45-pound wind meter. Someone had called 911, and soon police and firefighters were clambering over Baldy’s crest with shovels.
Argyilan, a former CrossFit trainer with a nose stud and shoulder tattoo, was no milquetoast. As Hurricane Sandy bore down the October before, she’d summited Baldy in ski goggles to record the erosional brawn of the winds and waves. The sand-laced 50-mile-per-hour gusts scoured the numbers off her surveying rod. But now, as park brass arrived to coordinate an emergency response, Argyilan kept a cool distance. She scanned Baldy’s taupe slopes, sure the boy was just hiding somewhere. At 6 p.m., almost two hours after his disappearance, she packed up her wind meter and drove home.
He’ll turn up, she told herself.
For dinner that night, Argyilan, her fiancé and her father went to a nearby Applebee’s. As they finished their meal, the restaurant’s TV screens flashed with news from Baldy: After a three-and-a-half hour search involving 50 rescuers and a pair of construction-site excavators, the boy was found a dozen feet beneath the dune’s surface. He had no pulse or breath at first, and his sand-encrusted body was ice-cold.
“I felt absolutely shattered,” Argyilan remembers. Everything she knew about geology—all the courses she’d taken, all the papers she’d read over years of study—told her this couldn’t happen. But her science had led her astray.
She sobbed on the way home, and spent a sleepless night on the couch, hunting online for any reports of similar cases. She scolded herself for not digging alongside the father. As a mom-to-be, she wished she’d tried to comfort the boy’s mother. Worst of all, though, was a recurring thought: “If they had listened to me, they wouldn’t have kept looking.”
We live in an era when the robotic arms of unmanned spaceships can scoop sand on Mars, then phone home across millions of miles to tell us its chemistry. Yet here, in the well-traveled regions of Earth, on the very ground we walk, we are still being surprised by geologic mystery.
In California’s Death Valley, “sailing stones” cruise the desert floor under a locomotion that science struggled for decades to explain. In Siberia’s Yamal Peninsula, a patch of permafrost snapped earlier this year into a gaping crater, a previously unrecorded phenomenon.
Mount Baldy stands out even in this rogues’ gallery. It lazes not in some far-flung badlands, but in the temperate Midwest, on a popular beach an hour’s drive from Chicago.
People have turned a scientific eye on minerals since at least the fourth century B.C., when Theophrastus, a disciple of Aristotle, wrote his treatise “On Stones.” But because deserts are inhospitable and sand has scant commercial value, the subdiscipline of dunes had to wait until the 20th century to find a champion. Ralph Bagnold, a Cambridge-educated engineer in the British Army, explored the Sinai and Sahara on leave before drafting his 1941 masterwork The Physics of Blown Sand and Desert Dunes, which is still routinely cited in scientific journals.
Today a great deal is known about dunes: how wind launches individual grains of sand and piles them into parabolas, ridges and other distinctive shapes; how plants steady dunes, and how waves weather them; how a dune’s history and age can be deduced from certain properties of buried sand and soil. Riddles remain (the movement of small particles is a complicated, chaotic business), but one thing about dunes has never been in doubt: their solidity.
“For sand to accumulate in a way that would leave holes or caverns in the subsurface doesn’t at first glance make a whole lot of sense,” says Alan Arbogast, a Michigan State University geographer who is the leading authority on the region’s dunes.
Jeff Lee, a physical geographer at Texas Tech University who co-edits Aeolian Research, the field’s pre-eminent journal, told me that “dunes just don’t do that. They don’t swallow people, except in Lawrence of Arabia.” In the movie, a Bedouin boy drowns in Sinai quicksand—a scene ridiculed by scientists because dunes, both desert and coastal, are almost always too high above the water table for quicksand to form.
Mount Baldy began to take shape 4,500 years ago, when the water level in Lake Michigan dropped about 20 feet, exposing vast fields of sand to the will of the wind. Before last year’s incident, the dune had intrigued scientists not because it defied any principles of windblown sand, but because it followed them all too enthusiastically. Most dunes on the Indiana lakeshore are forested. But Baldy is a “blowout”: a victim of some ancient force—a violent storm, a dramatic change in wind direction—that scalped the dune of the plants and trees whose roots once held it in place. And like an animal freed from its cage, Baldy began to roam.
Combining painstaking physical measurements with an analysis of aerial photographs, Zoran Kilibarda, a colleague of Argyilan’s at IU Northwest, discovered that the dune had rolled nearly 440 feet inland between 1938 and 2007. It had buried trails and a staircase, and stands of black oak, 60- to 80-feet tall, that had long stood between Baldy’s bottom edge and the parking lot. In March 2007, as the first of Kilibarda’s figures came in, stunned park officials called Baldy’s pace “alarming,” warning that it could bury its own parking lot within seven years. They banned the public from its steep inland side, or slipface; footfalls were thought to be accelerating its advance. But Baldy refused to be tamed.
Argyilan wasn’t a Baldy expert, per se; for her dissertation at the University of Illinois at Chicago, she’d analyzed buried beach sand to chart water level shifts in the Great Lakes. But as a specialist in coastal geology at a nearby university, she, like Kilibarda, soon found herself under Baldy’s spell.
With park service funding in 2011, she began a multifaceted study of changes in the dune’s overall shape. The results confirmed what many people could see with their own eyes. “It’s flattening, it’s pancaking in the middle,” she told me. The sand fueling Baldy’s migration was coming not from the beach, where erosion left little to spare anyway, but from the middle of its lakeward slope, the side still open to the public.
But none of these revelations prepared Argyilan for that long summer day. The idea of a void opening in a dune was so beyond the ken of geologists that in the days and weeks afterward one question in particular haunted her: In a place with so many tourists, rangers and scientists, why did no one notice holes before now? When she asked Todd Thompson, an expert on the Indiana lakeshore who’d been a grad school mentor, he paraphrased a quote from the French philosopher Henri Bergson: “The eye sees only what the mind is prepared to comprehend.”
Nathan Woessner, a cherubic 6-year-old from the cornfields of northwestern Illinois, had been looking forward to the trip all summer. Normally for vacation, the family stayed close to home, venturing across the nearby Iowa line to a Best Western with a nice swimming pool and a Medieval castle theme. Nathan’s father, Greg, sold tractor tires for a living, and his mother, Faith, quit her nursing job to focus on their four kids.
Neither had heard of the Indiana Dunes National Lakeshore until some church friends suggested a weekend camping trip there. So after breakfast on July 12, 2013, Nathan and his three siblings piled into a Chevy Tahoe that Greg had borrowed from his parents and drove east for nearly three hours to a campsite near the dunes.
Among the siblings, Nathan, the third-born, was “the lover” of the family, says his mother. More than the others, he liked to cuddle, and to help his teacher in the morning by taking chairs off tables and passing out papers. Though shy around new people, he was adventurous outdoors, an ace frog hunter who liked casting for catfish in the river behind his house.
At the beach in front of Baldy that July afternoon, Nathan and his best friend, Colin, a son of their church friends, splashed in the waves for a couple of hours before deciding they were ready for something new. Someone suggested a race up the lakefront side of the dune, and off they went. Greg and Keith, Colin’s dad, were in the lead, halfway up the dune, when they heard Colin cry out.
“Nathan fell,” Colin said. (According to park investigators, Colin, the only witness to the moment of Nathan’s disappearance, later reported that Nathan saw an open hole and lowered himself in to see where it went.) When the fathers turned around, there was no sign of Nathan—just a round, 12-inch-diameter hole in the sand. Keith, tall and beanpole thin, lay across the sand and reached into the hole.
“I’m scared,” came the boy’s voice from somewhere in the darkness.
“We’ll get you out,” his father said.
The men dug furiously, confident they’d soon feel Nathan’s hand or head. But within minutes, sand was sloughing into the hole from every direction.
Over the next three and a half hours, rescuers with flexible probes, shovels and heavy machinery would excavate a pit a dozen feet deep and at least 50 feet across. At about eight feet down, they began noticing odd features in the sand: pipe-like cylinders, eight inches in diameter and a foot or two long, of what looked like old bark. Brad Kreighbaum, 36, a third-generation firefighter, soon came across a six-inch diameter hole that shot deep into the sand: “You could shine a flashlight and see 20 feet down.” Almost as soon as the holes were uncovered, sand rushed in to fill them. “Just like an hourglass.”
When he scooped Nathan’s body out of the sand at 8:05 p.m., Kreighbaum noticed other patterns, in the cavity cocooning the boy. Its inside wall was sandy and soft, but bore the imprint of bark, almost like a fossil. It was as if the boy had wound up at the bottom of a hollowed-out tree trunk, except not a bit of tree was there.
Most people buried in sand suffocate within ten minutes. But Nathan walked out of the hospital two weeks later—the sand mostly removed from his lungs, the scrapes on his head mostly healed. Local officials called it “The Miracle on Mount Baldy.” Indiana Gov. Mike Pence came to Michigan City to meet the boy and award a plaque to 140 people who participated in his rescue. Doctors said he must have had an air pocket, or that he’d been saved by some version of the mammalian diving reflex, a slowdown of the vital organs in cold water that conserves oxygen.
Nathan recalls nothing of his ordeal. His parents, deeply religious Christians, believe that divine grace is the only reason for their son’s survival and full recovery. “There are a lot of things science can’t explain,” Faith told me, cradling a mug of coffee in the living room of the family’s rustic home, in Sterling, Illinois. “I have God, and that’s enough for me. I don’t need a how and a why for why those holes are there.”
But Argyilan did. When she learned that on the way to the hospital the boy had begun to show vital signs, it annealed her shame into resolve. “It was like a switch,” her fiancé, DeWet Le-Roux, told me. “She wanted to get to the bottom of it and maybe save others” from a similar—or worse—fate.
As the public deluged park headquarters with wild theories (lightning did it!), Argyilan spent late nights emailing prominent geologists and badgering park officials for new leads. When she asked Kilibarda, the resident Baldy expert, he told her someone must have dug a hole. “That’s still my leading explanation,” he said when we met. Just about everything else “simply disobeys physics.”
A month to the day after the accident, another hole was discovered: a saw-toothed maw a few hundred feet east of Nathan’s. Park officials called Argyilan, but by the time she arrived, the hole had refilled. Undeterred, she pounded in a coring tube. But the sand she extracted was perfectly ordinary. Investigators with the U.S. Environmental Protection Agency fared scarcely better. Their survey with ground-penetrating radar picked up 66 faint “anomalies”—irregularities inside the dune. What they were, the technology couldn’t say.
As news of the mystery spread, Argyilan began hearing from scientists around the world. Could the thawing of winter snow and ice, which can infiltrate sand, trigger a collapse? It wasn’t a terrible hypothesis, except that the accident happened in July. Another thought was that sections of clay undergirding the dune had eroded, allowing groundwater to pipe away columns of sand. Locals reminded Argyilan that there had once been beach shacks, wells and other structures behind Baldy. Might their roofs be caving, sucking down sand?
When Argyilan returned to Baldy last spring with a trowel and brush, she found a growing number of clues pointing in another direction: the black oaks buried decades ago by the dune’s inland march. Their crooked upper limbs still pierced the dune surface, like the arms of drowning men. If the trees were rotting from the inside out, would they leave tunnels? If so, how would those tunnels withstand the pressure of all that surrounding sand? They couldn’t—unless, Argyilan thought, the bark or maybe a decay fungus was releasing chemicals that somehow cemented the sand into a cast. She has sent samples to labs, but the tests hinge on the schedules of scientists with other priorities.
As she waits, she has had to hang on to just one, lonely parallel—on Facebook. Dina Pavlis, a U.S. Forest Service volunteer who leads tours and ranger training at the Oregon Dunes National Recreation Area, on the Pacific Coast, had posted photos she’d taken of deep, funnel-like openings in off-trail areas there. Pavlis told me she calls them “tree holes.” As in Indiana, wandering dunes are burying old forests. But no scientists have studied the Oregon holes, and their origins remain an enigma.
The park’s decision to close all of Baldy to the public after the accident turned out to be a shrewd one. Workers have discovered half a dozen new holes since, a sign that Baldy is not through with its mischief. Investigators now have to work in pairs and radio in on arrival and departure.
One bright and windy morning this past August, I followed a ranger up a chute of slippery sand onto Baldy’s western shoulder. I was there to see Argyilan and two of her colleagues, who were in the first days of what is expected to be an intensive yearlong investigation. Argyilan had pressed the National Park Service to enlist Thompson, her grad school mentor, who was now assistant research director at the Indiana Geological Survey. Thompson, in turn, brought in G. William Monaghan, a veteran geoarchaeologist with a lab at Indiana University’s flagship campus, in Bloomington.
Ducking under a strip of yellow tape, Thompson, in cargo shorts, aviator sunglasses and a reflective vest, spoke about the devices scattered behind him. The ones that looked like luggage carts bore ground-penetrating radar that would capture images of deformations up to 75 feet beneath the surface. The one that evoked a dentistry nightmare was a hydraulic coring drill called a GeoProbe that would pluck samples from deep within. The scientists’ goal: a navigable 3-D map of Baldy’s interior, a first-of-its-kind undertaking that might finally unlock the dune’s secrets.
“As the guy in the lab described it, you’ll put on glasses and take a walk through the inside of the dune,” Argyilan told me.
Dunes are the backdrop to beach vacations the world over, marvels of slippery geometry that mirror the shifting swells of the sea. Will dunes elsewhere sprout holes, too? Or is Baldy a kind of perfect storm, where the peculiarities of mineralogy, microbiology and climate have produced a singular freak of nature?
Either way, says dune expert Alan Arbogast, “if they are able to document a legitimate geological process, that would be news.”
I met Argyilan again later in the week at Shoreline Brewery, a restaurant a short drive from Baldy. Her father, Don, had joined us, to look after her daughter, Charlotte, now a cheerful 11-month-old.
I asked Argyilan what Thompson had meant when he said the eye sees only what the mind can comprehend. She said it had come up in a meeting, when he was asked why so many holes were suddenly appearing now. “His basic answer was, ‘Because we’re looking for them.’
“Mount Baldy is a great reminder that geological processes are still happening that are unrecorded,” Argyilan said. She nursed a pint of Singing Sands Oatmeal Stout as Charlotte toddled precariously around us, clutching her mother’s knee for balance. “You could have holes developing all through time and no one cares”—“no one notices,” she corrected herself—“until a boy falls in.”