EXPLORING THE WANDERING DUNES OF LAKE MICHIGAN

BY HANNAH WAGIE

Myattraction to nature has gotten stronger as I have gotten older. Trained in the lab as a chemist, I have slowly emerged from that carefully controlled environment, drawn to wilder places with more variables, like the well-worn paths in Kohler-Andrae State Park, south of Sheboygan on Lake Michigan’s western shore, where I seek solitude. Yet I realize that I am not really alone there, because under my feet, the path itself journeys with me. Sand is under, around, and on top of me.

Technically, sand is defined as loose, granular rock fragments that are 0.05 to 2.0 millimeters in diameter. Any fragments smaller are silt or clay; larger ones are gravel or cobbles. Sand can be of any mineral composition: fragments of coral, or garnet, or pure quartz, for example. Sand grains can be rough and angular, or uniformly rounded, or of mixed shapes.

The sand found in the Wisconsin dunes that I’m walking, and especially in the high dunes of Michigan’s western shore, is composed largely of silicon dioxide (SiO2). It is a molecule that is rather boring and chemically unremarkable at first glance. Yet its inert and non-polar individual SiO 2 units are exactly what make them so useful when they are melted into glass. Flasks and beakers in medical, biology, and chemistry labs are made of glass because the material rarely interferes with the processes, tests, and analyses conducted inside of them.

Silicon dioxide is, in fact, a social creature, mostly sticking to what it knows and occasionally fraternizing with more exotic guests. In a group, it is more familiarly called silica. A grain of sand consists of many SiO 2 units holding hands with other identical units. If these friendships are allowed to form slowly, a neat network is formed. The straight, stiff geometry of a single molecule bends and aligns with another SiO 2 molecule to form a pyramid shape, which, in turn, bonds with another and another and another until an extended lattice forms. This is the careful process of making a crystal. A crystal made of silica is known as quartz, and the hints of sparkle you see on ideal white sand beaches owe their dazzle to tiny gems of quartz.

As a Midwesterner, I take long walks on the beach, but they don’t typically include a bikini, an ocean sunset, or white sand beaches. Rather these walks mean shoes tossed aside and pant legs rolled up to let Lake Michigan’s frigid water lap at my feet. Sand dunes rise rather unexpectedly in Kohler-Andrae State Park, part of the mix of rocky ledges, clay bluffs, and dunes that form Lake Michigan’s Wisconsin shoreline. The sudden glimpse of Lake Michigan during a country drive through eastern Wisconsin is a surprise that never fails to delight my young children and me. A couple of summers ago, some scrubby areas of the dunes were stable enough to host common milkweed plants along with the monarch caterpillars they attract. My seven-year-old daughter and I had been hunting for them all summer and pointed them out to each other with joyful shouts.

Those monarch migrants found their stopover at a place that itself migrates season after season. Sand dunes travel, moving at the whim of driving winds and waves. Waves throw sand grains onto the beach, and wind picks up the dry grains and carries them along. On the eastern shore of Lake Michigan, which receives the full-on effect of prevailing westerly winds, the sand dunes reach dramatic heights as they steadily creep east. The state of Michigan has the largest accumulation of freshwater coastal dunes in the world. “Walking dunes,” such as those in Silver Lake, Michigan, are areas where the landscape can change dramatically during stormy weather, causing tsunamis of both water and sand. Permanent construction in these zones is extremely risky. Amazing views from bluffs still tempt lake-loving residents into foolishness: a house built on such an unstable foundation can go the way of the proverbial sandcastle overnight.

Much of this sand was created during the last Ice Age by glaciers pushing south out of Canada scraping and crushing bedrock, such as quartz-rich granite, into fine fragments. This debris was carried into Glacial Lake Michigan where it was further broken, abraded, and chemically weathered over thousands of years. As the lake level rose and fell with the waxing and waning of the glacier, quartz sand was sorted by wave action and deposited on the beach to be picked up by the wind, a force that continues today to sift and sort the grains. While the wind leaves heavier fragments on the beach, it carries silt and clay dust far inland, and deposits sand-size grains in near shore dunes. Over a long time, repeated winnowing produces the kind of dunes seen in Michigan that are almost entirely fine silica sand of uniform size, a valuable resource.

The seemingly endless deposits of this silicon-dioxide mineral on Lake Michigan’s western shore have resulted in a booming sand mining industry, whose economic value rivals those states with ocean coastlines. The state of Michigan began regulating sand dune mining in 1994, and dozens of sand quarry sites have closed since then.

What kind of career options does a grain of sand have? Hailing from such a pure source as lake dunes, those sparkling, fine-sized grains are prime candidates for making glass, which is primarily silicon dioxide that has been melted out of an orderly crystalline form into a mixed-up tangle known as an amorphous form. Once removed from the beach and processed into window glass, this disorderly arrangement of silica has a new relationship with the sun. Its polished surface still reflects the sun’s rays, and it appears to remain transparent like a quartz crystal, but this is true only as far as the human eye can see. Amorphous glass does not transmit the near ultraviolet rays that penetrate our skin. In other words, I can sit on top of the sand watching the lake as I get a tan, but viewing the same serene scene behind that sand—in its form as a window— dramatically attenuates those tanning effects.

Humans are not the only organisms that harvest silica for their own uses. Although the friction from glaciers, waves, and currents are largely responsible for the production of silica pebbles and sand from bedrock, there is evidence that cyanobacteria mine silicon dioxide from volcanic rock. This mining happens molecule by molecule, rather than in large chunks. The biogenic process is many times faster than waiting for sand to simply dissolve, which surprisingly does occur, though extremely slowly. In situ, pits and channels in lava flows (which have a high composition of silica) contain traces of nucleic acids, a tell-tale sign that something biological is happening. These microscopic miners may be after the iron and manganese trapped in the sand. The cyanobacteria “micro-miners” grab these essential nutrients for themselves and cast off the silicon dioxide molecules as waste. The silica enters the water as wild, unconstrained silicic acid. This material, it turns out, is scavenged and used by yet other types of microbes.

This took me by surprise. In biochemistry, the elements carbon, nitrogen, oxygen, hydrogen, and phosphorus comprise most atoms in living organisms. Carbon in particular is considered the terrestrial marker of life. Silicon (Si), which sits directly below carbon (C) on the periodic table in Group IV, is decidedly inorganic (even though a powerhouse in industry and technology). But as I take a closer look at microscopic photographs of sand, I find that silicon does in fact weave itself quite beautifully into life on Planet Earth. I expected to see jagged grains of silica in many colors mixed in with tiny shells and exoskeleton fragments (typically made of calcium carbonate from zooplankton, snails, and clams). However, I marveled at the sight of symmetrical sunbursts and intricate webs made entirely of glass.

These gems are the spicules (spines) and skeletons of sponges and of diatoms, a type of algae. These tiny armor trappings are made of opal, a form of silica that incorporates water molecules into its structure. Rather than constructing an opaque, white calci- um-based shell like much of microscopic marine life, diatoms build a house of glass that weathers better than much softer calcium compounds. Diatoms create cell walls with lacey patterns that form a cage around themselves. What results is a variety of three-dimensional shapes from disks to rods to rounded triangles that are reminiscent of the gears in my childhood Spirograph set. The diatoms leave a beautiful boneyard in the Great Lakes sand between my toes, one that I wish I could collect and display.

The ancient, enigmatic agate, a gemstone that can be found on the shores of the Great Lakes, is also the result of dissolved silica. The colorful bands of agate nodules are crystalline deposits of silica that have found a home in pea- to baseball-sized empty cavities within volcanic rock. These cavities are formed by bubbles of sulfur gas during an initial lava flow. Layer by layer, dissolved silica deposits and builds up on the inside of the bubbles, bringing along metals picked up on its journey. Lake Superior’s western beaches are littered with rusty red agates, if you know where to look. The rich iron content of Superior provides the reddish pigment along with highlights of yellow, brown, and orange that are iron’s various oxide forms. This process requires no mediation by lifeforms. Rather, agate formation is a work of art crafted secretly inside dead rock, although it seems like a sentient creation with no purpose other than to delight. Our great freshwater sea slowly sculpts these gems in a mysterious way that has never been reproduced in a lab and then nonchalantly breaks up the encasing rock and tosses the agates ashore for some lucky treasure hunter. I have learned to tune my vision to the subtle glow that is characteristic of the microcrystalline silica of agates on a sunny beach.

The rules about collecting anything from a natural area vary from place to place (municipal beaches are generally more amenable to rockhounds than state or national parks or nature preserves). However, collecting beach glass (or “sea glass”) is usually allowed and even encouraged. Although beach glass often appears to be colorful pebbles in the sand, it is actually fragments of glass from industrially produced bottles, decanters, and other packaging that made its way into the water through shipwrecks, meandering landfill waste, and intentional dumping. Entering the lake as broken shards, the castoff glass is buffed and abraded by waves and currents in the lake until it emerges after months and years, smooth and frosted. Beach glass still retains the striking man-made colors created by adding metals, similar to the naturally created agates: cobalt for blue, chromium for green, manganese for purple. Industrial cities around the Great Lakes have rich deposits of beach glass, including coveted glass marbles (ironically, marbles were made of agate in ancient times). Beach glass is now collected and marketed as material for crafts and jewelry. The sand provides raw material to make colored glass, humans thoughtlessly return the glass from whence it came, and the lake spits out the trash as treasure.

Visiting my land-locked beaches these last few years has been complicated. Increasing precipitation over the Great Lakes watershed over the past decade significantly raised water levels in 2020 and 2021 in all of the Great Lakes. The shore erosion that followed has implications all over the region. My beach exploration is now confined to a narrow strip. One of my favorite Lake Michigan spots, Port Washington, experienced a major landslide from the reddish clay bluff facing its North Beach in 2022, which prompted the city to close the beach. The cycle of waves sweeping sand away from the beach into the water, and the re-deposit farther along the shore of sand from those same waves or from the adjacent bluffs, is a natural, ongoing process called littoral transport. Human activity, like sand mining and the development of harbors, can speed up the loss part of the cycle. Beach nourishment is an active remediation used by the DNR to complete the gain part of the cycle. It is an intervention that delivers sand and silt dredged from the bottom of the lake to an eroded part of the coastline to try to restore what was lost.

After gaping at the fallen earth from the top of the bluff overlooking North Beach, my children and I visit the much busier South Beach to find relief on a sweltering summer day. My children are old enough now to dig in the sand and hunt for rocks and fossils on their own while I take in the solitude of the beach a little farther down the shoreline. My daughter makes an acute observation: “No one has ever looked at these rocks before! The waves push new ones onto the beach all of the time!” She intuitively understands that the beach constantly comes and goes. Cyclical migration has happened throughout the history of the Great Lakes but seems to be rather one-sided lately. I wonder, as the beach wanders through this century, how much will be left for them to explore.

Hannah E. Wagie earned a Ph.D. in physical chemistry at UW–Milwaukee in 2015. She is interested in making science accessible in the classroom and through creative nonfiction. She is currently an assistant professor at Wisconsin Lutheran College in Wauwatosa.

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