With this feature, Agate kicks off an occasional series by Jeff Broberg on the Driftless Region in southeastern Minnesota and surrounding states. With the enduring curiosity and patience of a geologist, Broberg takes us through the process of scientific discovery that has built an understanding of this region’s early origins. It’s a dramatic, complex and still-unfolding story with the capacity to change how we all look at this landscape.
The Driftless Area in the Upper Mississippi Valley is distinct and unforgettable. In contrast to much of the Midwest where glacial drift buries the bedrock in clay, sand, pebbles, cobbles and boulders, the Driftless features exposed bedrock bluffs, ridges and coulees. Steep hillsides still display remarkable biodiversity. It is a land of caves, sinkholes, and spring-fed, blue-ribbon trout streams. Dramatic bluffs, hardwood forests, and valleys offer beautiful vistas.
As a geologist and resident of the Whitewater Valley, I have often been asked by friends who are more accustomed to going “up north” why this area is different from the rest of the Midwest.
The extraordinary narrative of the origins of the Driftless’s geologic history starts in the exposed sedimentary rocks and the fossil record from 500 to 450 million years ago. Cambrian sandstone shows a geologic record of ancient tropical beaches and tidal flats, and limestone and dolomite show a history of shallow tropical seas. Long-extinct fossil trilobites and brachiopods illuminate global extinctions and the ensuing explosion of new life forms. Yet, it is the Driftless regions’ Pleistocene history and karst at the edge of the great glaciers that continue to fuel our wonder.
During the Pleistocene (which began roughly 2.58 millions years before present), the weight of thousands of feet of glacial ice bulldozed over large parts of Minnesota and neighboring states. Not that conditions in the Driftless were calm: here, the landscape was transformed by raging meltwater, howling wind, and melting of deep, resistant permafrost, not by glacial ice.
What do we know? We know that glacial ice sheets rarely covered the Driftless area. We know that deep permafrost melted, creating pock-marked “thermokarst” topography of hummocks and marshy hollows as it thawed, over time eroding deep, dendritic (finely branched) valleys. We know that the permafrost meltwater flowing through fractured bedrock and an underground network of conduits and caves dissolved the underlying Ordovician limestone into a karst landscape. We know that frigid, gale-force winds formed as cold air coursed off the mile-thick ice sheet: fierce winds that blew 60-80 miles per hour, day and night, for thousands of years and could be felt hundreds of miles from the edge of the ice. These “katabatic” winds from glacial margins sculpted the exposed rock, and clouds of windblown silt (loess) covered the permafrost uplands with a dune-like blanket of frozen dust.
As the glaciers melted and retreated farther away from the Driftless, the meltwaters vanished, the winds died down, and the permafrost thawed. The deep loess sprouted boggy wetlands and tall-grass prairies. Oak forests covered the rocky valley walls, and giant cottonwoods and willows shaded springs that fed thousands of miles of streams. These streams, which stayed cold in summer and never froze in winter, have since become home to over ten thousand successive generations of native brook trout and the invertebrates that have thrived in the nutrient-rich, limestone-steeped waters.
The Driftless Area Age of Geologic Discovery 1872-1880
The Upper Mississippi Valley below Mendota was the subject of scientific debate and was first called the Driftless Area just before the Civil War. Early geologists in the Midwest first recognized the general absence of glacial deposits beyond the edge of the ice. Then they discovered the Driftless region that was devoid of drift but completely surrounded by glacial deposits. Newton Horace Winchell, Minnesota’s first geologist, was appointed the head of the Minnesota Geological Survey in 1872. Winchell was called on by the Legislature to “make a complete account of the state’s mineral kingdom.”[2]
At the time of Winchell’s first report to the Legislature at the end of his 1872 field season, the prevailing Biblical version of creation assumed that the earth was just 6,000 years old. Winchell told the Legislature, “Time is long”…(and) “geologists…may read in the rocks the grand changes the earth has undergone since the beginning.”[3] He argued that the rock formations he described took millions of years to form. He put forth to the Minnesota legislature, and to his University colleagues, the scale of geologic time: a concept that is still challenging to many non-geologists.
For 32 years, Newton Winchell passionately continued to document his geologic surveys as he traveled by horseback, oxcart, canoe, and rail across Minnesota. He helped coin the “Driftless” title in SE Minnesota by describing the weathered bedrock and the general lack of glacial deposits. He noted the dominance of ancient sandstone, limestone, and dolomite bedrock, and karst features such as springs, sinkholes, and caves in the bluffs and valley walls. His reports on Houston, Fillmore, and Winona counties remarked on the area’s pristine groundwater and spring-fed streams, highlighting the streams as an economic resource of water-power for local grist mills and sawmills.
In 1883, T.C. Chamberlin, neighboring Wisconsin’s first geologist, cited Winchell’s early work and then expanded the Driftless definition to Southwestern Wisconsin, Northeastern Illinois, and Northeastern Iowa. In his first report, Geology of Wisconsin 1873-1879, he published two color plates titled “Hypothetical Map of Wisconsin during the First Glacial Epoch” and “Theoretical Map of Wisconsin During the Second Glacial Epoch.” Chamberlin’s maps—which still hold among geologists today—delineated a 24,000 square mile area that was mostly untouched by glacial ice.
More clues, modern views
As geologists moved toward greater consensus on the existence and extent of the Driftless, there remained the question of why the glaciers largely missed the area.
Chamberlin refined his theories on the origins of the Driftless in 1885, decades before Louis Agassiz and polar explorers began to observe the process of glacial movement. Based on his field studies, he hypothesized that Precambrian highlands to the northeast and structural troughs to the east and west created highlands that obstructed the ice sheet’s southern movement and channeled the grinding ice past the Driftless Area [4]. These theories dominated the geologic literature for almost one hundred years.
Geologists continued to map the clues to the area’s origins, collecting well data and field observations of new excavations and road cuts. They began to understand the role of profoundly weathered and fractured carbonate bedrock and sandstone in the Driftless, mapped areas of the Driftless that had older glacial drift, and recognized that four different glaciations surrounded the Driftless and retreated during warmer interglacial periods.
With satellite imagery and high definition topography, it became possible to synthesize the field data. In the 1980s, geologists delineated the overlapping glacial lobes, prehistoric meltwater flow paths, and surface water and groundwater interactions in the Driftless Area watersheds. They proved that only a small area of the Driftless Area in Western Wisconsin escaped glacial coverage.
Still, the question of why? For 135 years, the dominant theory followed Chamberlin’s view that the Midcontinent uplift repelled the glaciers. But the arch and trough theory did not hold up. First, the Driftless area did not coincide with the ancient uplift’s topographic boundary; second, there were no modern analogs where glaciers flowed past large regions due to topography. Finally, detailed fieldwork showed that earlier glaciers had advanced across most of what we call the Driftless Area.
With a view similar to Chamberlin, some geologists later postulated that the Driftless coincided with the Paleozoic Plateau’s old erosion surface where shallow, preglacial valleys blocked the advance of Pleistocene glaciers. But this theory also failed to hold up, because field work had proven that older glaciers had covered most of the Driftless Area in Minnesota.
In 1999, Howard Hobbs of the Minnesota Geological Survey reviewed the data and proposed a new theory based on the influence of the underlying karst. He hypothesized that the ice sheet stopped because the porous limestone karst acted as a giant sieve that dewatered the base of the advancing ice. The rapid drainage of glacial water through the karst allowed the ice to grind directly on the bedrock; the meltwater couldn’t lubricate the moving ice. The friction between the ice and the karst may have stopped the ice’s eastern flow.
Hobbs’ karst drainage model explained that wherever glaciers were underlain by the impervious bedrock like the Decorah Shale, the ice would flow. Still, karst drainage farther east created too much friction and stopped the ice. Hobbs admitted in his publication that this theory did not correlate very well to Wisconsin’s geology. The bedrock on the Wisconsin side of the Driftless was mostly sandstone, siltstone, and older metamorphic and igneous rock that were less porous. Hobbs could not explain why the eastern advance of the Labradorian and Keewatin ice sheets would grind to a halt and miss the Driftless Area.
In 2010 in the Open Geology Journal [5], geologist Michael Iannicelli took each of the peer-reviewed Driftless theories and viewed them through the lens of new data on the paleo-climate of the region and of Uniformatarism. This doctrine assumes that the same natural laws govern processes in the past and present. Iannicelli believed that there should be a modern example of all geologic events and sought to develop a model that mimicked tundra and arctic areas still covered by permafrost, snow, and ice. He was the first geologist to publish ideas that incorporated climate changes that must have occurred during the Pleistocene.
Modern paleobotanists used pollen from ancient lake sediments to conclude that parts of the Midwest had an arid climate compared to areas farther north. Using this data, Iannicelli drew new conclusions about how the combination of low snowfall, permafrost resistance, and strong paleo winds can create driftless regions.
Iannicelli’s Driftless Area model considers modern climate models, has a modern analog in the Arctic and accounts for drift placed by older glaciations formed during wetter climate conditions. His model meets all the hypothetical criteria for a 24,000 square mile Driftless Area.
Bringing it all together
Since the 1870’s, each of these geologists tried to define the Driftless Area origins using the most current geologic observations and reasoning. Geologists had mapped the Mid-Continent Arch, and it made sense that the highlands might repel the ice, but in 1885 Chamberlin had little information about how continental glaciers moved and buried everything. Hobbs uses the most current knowledge of the karst and the massive underground drainage that robbed the glaciers of their lubrication, but he did not consider a drier climate. Most recently, Iannicelli has incorporated new knowledge about paleoclimates and applied a more strict adherence to the principle of Uniformatarism, and he found modern examples of driftless landscapes in the high arctic. The collective story developed since the 1870s now makes sense.
In sum, the area was glaciated earlier in history, but more recent ice sheets (in the past 35,000 years) avoided the region due to bedrock’s karst nature and topography. At the same time, the area became arid. The glacial ice accumulation centers where heavy snow formed the mile-thick ice was hundreds of miles away. The ice was fluid enough to flow past, but there was too much friction on the karst and locally there was not enough snow to form glacial ice.
So where do we stand today on the origins of the Driftless Area? I think we know the storyline, but we are missing the finer details. Fortunately, new work is in progress. In Greenland and the Arctic, melting ice shows new areas once covered by glaciers where the permafrost is rapidly melting. In the local karst, geochemists are now using isotopes that accurately define temperature changes over time. Geochronologists are age-dating the limestone that forms stalactites and stalagmites in caves. These new data might reveal the climate changes, the melting of the permafrost, and the exact timing of glacial retreat and advance. In my mind, there is no doubt that scientists have much more to teach us about the origins of the Driftless.
My farm is near the top of the Whitewater Watershed south of Elba on the Driftless Area’s western edge. Every part of my land evolved from rock, soil, water, and ice. A new sinkhole on my farm continues to dissolve the Ordovician bedrock with percolating water. That percolating surface water recharges the groundwater in my well and feeds the local springs that sustain the Whitewater River and local trout streams.
I love the Driftless bluffs, ridges, and valleys and spend much of my time fishing, hunting, gardening, and foraging near the three branches of the Whitewater. I love the fact that I have found scrapers and broken spear points, and the knowledge that a neighboring farmer has discovered Paleo-Indian artifacts. I’m thrilled that the Driftless Area is a region where the confluence of waters is a unique, even sacred gathering place.
As I look out the window at the frozen ground on my ridge above the Whitewater as November passes to December, I’m grateful to understand my surroundings as a scientist. But nowadays, I wonder about all the Driftless knowledge lost over twelve millennia of continuous human occupation. I reflect on the ageless words of Native American Chief Oren Lyons, and I’m humbled at thinking I know about the land.
“We have seen the sun come up in the same place for thousands of years.”
Chief Oren Lyons
About the Author
Jeff Broberg is a Minnesota Licensed Professional Geologist who grew up in Minneapolis and graduated from the Newton Winchell Department of Geology and Geophysics at the University of Minnesota in 1977. He worked for four years as a Student Research Assistant at the Minnesota Geological Survey. He retired from corporate life as an Environmental Consultant in 2017 when he returned to college to earn a Masters Degree in Philanthropy and Development from Saint Mary’s University of Minnesota in Winona. He served on the Legislative Citizen Commission of Minnesota Resources for ten years, has been the President of the Minnesota Trout Association, the National Trout Center in Preston, MN and serves as a Director for Fresh Energy. Jeff currently runs the Minnesota Well Owners Organization (MNWOO), a non-profit serving the interests of people who rely on private wells for their drinking water.
Source Notes
[1] Platypus, 2018, The Driftless Area, posted on Reddit.com
[2,3] Leaf, S. 2020, Minnesota’s Geologist – The Life of Newton Horace Winchell, University of Minnesota Press, Minneapolis and London, pp 46 & 49.
[4] T.C. Chamberlin and R.D. Salisbury, “On the Driftless Area of the Upper Mississippi Valley”, U.S. Geological Survey, 6th Annual Report, 1885, pp. 199-322
[5] Iannicelli, M., 2010, Evolution of the Driftless Area and Contiguous Regions of Midwestern USA Through Pleistocene Periglacial Processes, The open Geology Journal, v 4, p 35-54
Next in Agate’s Driftless Series by Jeff Broberg: Fragile Lands & Waters
