Every summer, even during the coldest part of the Ice Age, some melting took place on a glacier’s surface and along its margin. Melting occurred during each summer season – even more when the climate warmed for periods of several years at a time – 20 or 30 years – periods of time comparable to the kinds of swings we see in North Dakota’s climate today. The farther south the glacier advanced, into more temperate zones, the more the amount of melting challenged the health of the glacier in those areas until a balance was finally struck between 1) the rate at which the glacial was ice advancing, 2) warmer climates to the south, and 3) overall climate warming due to the approaching end of the Ice Age. Gradually, the balance among these three factors shifted farther north (and east) and ice began to disappear in those parts of North Dakota that were glaciated.
The position of the edge of an ice sheet at any given time was determined by the balance between melting and the rate at which the glacier was flowing. While the climate remained cold (at average annual temperatures below freezing), a continental ice mass became thicker and the edge of a glacier advanced. When it warmed a little, perhaps with average temperatures a bit cooler than those we have now, the glacier margin melted back about as fast as new ice could be supplied. Even though the glacier was moving, its edge neither advanced nor receded (but melting was taking place on the glacier surface). Given still warmer conditions, the surface of a glacier melted more rapidly; the ice thinned, and the glacier’s edge melted back faster than new ice was being supplied. Areas the ice had covered gradually became deglaciated.
As the margin of a glacier melted, debris that had been frozen into the ice many miles to the north was freed and deposited on the ground. This “glacial sediment” consisted of a blended sampling of the various kinds of rock and sediment over which the glacier had flowed. Glaciers advancing into North Dakota from the northeast deposited mainly sandy, granite-rich materials they had picked up as they flowed over the Precambrian rocks of northwest Ontario. Ice coming from the northwest brought a mixture of sandy and clayey materials it had accumulated as it flowed over broad expanses of Cretaceous shale and Tertiary sands of southern Alberta and Saskatchewan. Ice advancing straight southward from Manitoba, up the Red River Valley, deposited carbonate-rich sediment it had picked up north of Winnipeg where Paleozoic limestone and dolostone are exposed today. If you travel north of Winnipeg to Stony Mountain or Stonewall, Manitoba, be sure to notice the quarries, now producing some of the same materials that glaciers brought to North Dakota, perhaps 17,000 years ago. Studying the composition of the glacial sediment is one way that geologists can determine the direction from which the ice came, and the kind of land it flowed over.
Eventually, as each glacier melted (North Dakota was probably glaciated between 10 and 20 times during the past three million years), the land gradually became free of ice. No reversal of ice flow is involved when the glacier recedes; I emphasize that “retreat” of a glacier refers to the melting of the ice. Three different kinds of ice wasting occurred, at different times and places in North Dakota. The first occurred when the glacier margin may have been far to the south, in Iowa and South Dakota. The result of melting, perhaps over a period of relative warmth of hundreds or thousands of years, resulted in the loss of much of the ice mass off the glacier’s surface. The “view from above” in North Dakota would not have changed much – everything was still all ice – but the thickness of glacial ice covering the land was diminished in thickness by hundreds or thousands of feet, even before the glacier margin had receded into North Dakota.
The second way a glacier wasted (at least from our North Dakota perspective) was when the ice margin was nearby. When that happened, wasting involved frequent change in the position of the edge of the active glacier. As a glacier melted, and after it had become thinner, its active margin gradually receded because the volume of ice arriving was insufficient to replace the ice lost at the edge due to melting. Shrinkage of this kind caused the ice margin to melt back, sometimes in a step-like fashion, the flow of ice pausing long enough at times for the forward movement of the glacier to deliver piles of sediment (moraines) to the receding ice margin. A year of glacial activity might involve the margin moving forward a short distance during a winter; then, during the following summer, the margin receding a slightly greater distance. During this phase, one of the most important things taking place, at least during summer seasons, was the deposition of large amounts of gravel and sand being deposited in front of the glacier by water flowing from the melting, sediment-laden ice. The net effect of this second phase of glacial melting was deglaciation; land that had been covered by ice saw the light of day again, after about 20,000 years.
The third way a glacier wasted involved large-scale stoppage of ice movement, leaving large parts of the glacier stranded, sometimes over broad, mainly upland areas, detached from the main body of still-actively-flowing ice on surrounding lowlands (the plains surrounding Turtle Mountain, for example). In North Dakota, this was important over upland places like the Missouri Coteau and Turtle Mountain. Areas of “stagnant,” or “dead” ice on the uplands then continued to melt slowly. Landforms resulting from the melting of such stagnant ice are distinctive and much different from those that were constructed during the step-wise retreat of active glacial ice I described earlier.
Much of North Dakota’s modern landscape reflects its latest encounter with glaciers during the Ice Age. While glaciers flowed into and over the state, carrying the pulverized rock and soil debris they had picked up along their routes, they sheared off old bedrock landforms, smeared on new layers of sediment, and built new landforms. They filled old river valleys with sediment at the same time rivers of meltwater were flowing from the glaciers carving new valleys. In some places, the glacial ice forced existing rivers to follow different routes; in other places it completely obliterated and concealed what had been rivers and valleys. Cold winds blowing over sand that had earlier been deposited on floodplains and in lakes built dunes and spread a veneer of silt (loess) over much of the state.
Most of the sediment associated with the action of glaciers of the most-recent glaciation is soft. It is “unconsolidated,” and does not hold together well (you can dig it with a shovel). An exception: earlier glaciers also deposited sediment. Nearly all of this earlier sediment has eroded away, but in those places where we have found it exposed, or drilled into it, it may be cemented. A jackhammer may be more appropriate than a shovel for digging in such cemented deposits. However, the softer, looser materials that form most North Dakota glacial deposits are much more common. Sediments related to glaciation in North Dakota can be grouped into three main types: till, lake sediment, and outwash.
1. Till was deposited directly from the ice, mostly in the form of mud flows, which slumped or flowed into their current position as the ice melted. Till consists of silty, sandy, pebbly clay, as well as cobbles, or even large boulders.
2. Lake sediment is layered material that was deposited in lakes, which formed on and near the glacier. Such sediment consists mainly of layers of fine-grained silt and clay, deposited on lake floors, along with some sand and gravel, which collected as beaches along the shores of lakes , many of which were dammed by glaciers.
3. Outwash consists of material deposited by running water. Some outwash may be cemented into a kind of stony concrete, but most of it is loose sand and gravel that was washed out of the melting glacier (hence the name “outwash”). Outwash was deposited by streams and rivers flowing through meltwater valleys or as broad, often nearly level sheets of sand ahead of a melting glacier.
Where they are present, sediments deposited directly by glaciers, and by wind and water associated with glaciation, form a thick covering on top of much of the preglacial (bedrock) surface. In central North Dakota, in Sheridan County, the glacial sediment is over 700 feet thick in places. Ten miles northwest of Tolley in northwestern Renville County, it is at least 800 feet thick, the thickest I can document in the state. The amount and thickness of glacial sediment can vary considerably over short distances so it is likely that even thicker deposits than I mentioned exist in places. Over much of the glaciated part of the state, the glacial materials average 150 feet thick.
At any given location, the glacial deposits may consist of two or more layers of till, interbedded with lake beds, alluvial sediments or other materials. In some places, soils, which had developed on the surface of an earlier glacial, river, lake, or wind-blown deposit, were buried when a new layer of glacial material was deposited. These old, buried soils (paleosols) were formed during long intervals of weathering and exposure, like the one we are enjoying now. Paleosols are among the best indicators in the geological record for multiple episodes of glaciation during the Ice Age. The characteristics of a paleosol also help us understand the climatic conditions (forest or grassland, wet or dry, cool or warm, etc.) at the time it formed.
The best places to see several multiple layers of glacial deposits in North Dakota are near Riverdale, at the Wolf Creek inlet to Lake Sakakawea in McLean County and in Beulah Bay, about 15 miles north of the town of Beulah in Mercer County. In both locations, two and, in some places, three discrete till units, separated by cemented gravel layers or paleosols, are being eroded by waves along the lake.
Drill-hole data in eastern and southeastern North Dakota provide evidence that at least a half dozen glacial advances have occurred there since the Ice Age began. Parts of southwestern North Dakota were glaciated during some of the earlier glaciations, but (apart from some rare exceptions) glacial landforms are not found there today because they were eroded away long ago. Glacial lake sediments and river gravels containing glacially derived materials can be found as far southwest as Dickinson and near the Killdeer Mountains, and I have tentatively identified patches of hard, cemented till and glacial river gravels near Bowman and Rhame, places usually considered never to have been glaciated.
Modern soils are an important link to our geologic past. Fresh glacial deposits consist of a mixture of materials, and, because their sources are so varied, they provide the combination of nutrients necessary for fertile soil. In the glaciated part of the state, North Dakota’s soils consist of the weathered exterior of materials left by glacial action. In the thousands of years that have elapsed since the ice sheets disappeared, constantly changing climate, physical and chemical weathering, accumulation of prairie and woodland plant litter, development of root systems, and burrowing activity by organisms have all contributed to the transformation of glacial deposits into the rich soils that form the basis for much of our agricultural wealth.
Glaciation was the main geologic influence on much of North Dakota’s landscape. The Ice Age, a time geologists also refer to as the Pleistocene Epoch, includes most of the past three million years of geologic time. Glaciers advanced over the northern plains several times during the Ice Age, reaching northern and eastern North Dakota. When it wasn’t glaciated, the state had a climate much like the one we enjoy today or possibly even milder at times. the Ice Age wasn’t one long “deep-freeze.”
During their studies of the geology of the state, geologists have found evidence for at least seven separate glaciations, but there may have been more. The most recent of these glaciations is known as the Wisconsinan (because deposits typical of that glaciation are widespread in Wisconsin). The Wisconsinan glaciation began about 100,000 years ago and ended about 11,000 years ago. Some geologists debate whether the Ice Age has really ended yet. After all, large areas of the earth’s surface are still covered by extensive glaciers (Greenland, Antarctica, etc.). It’s likely that we are currently enjoying a lull between major glaciations.
Even though North Dakota was glaciated many times during the Ice Age, it is the Wisconsinan glacial deposits, the most recent ones, that are most obvious to us. These are the ones that form the hills and valleys in eastern and northern North Dakota and they are the ones in which our prairie potholes and wetlands are developed. Most of our richest farmland is developed on the Wisconsinan glacial surface.
Early glaciers, which advanced into North Dakota before the Wisconsinan glacier, also had a profound effect on the state. The materials they deposited have been largely eroded away, and about all that remains of them are occasional boulders — “erratics.” I will discuss erratics elsewhere. It was an early glacier that diverted the course of the Little Missouri River eastward more than 640,000 years ago (possibly earlier). Before that time, the Little Missouri River flowed northward into Canada. In fact, all of North Dakota used to be drained by rivers that flowed into Canada. When it was diverted, the Little Missouri River began to carve the badlands we see today.
All of us who have traveled around North Dakota know that the landscape varies considerably from place to place. Southwestern North Dakota, with its badlands, buttes, and broad vistas is largely the result of hundreds of thousands of years of erosion. The landscape there is not glacial. It has been carved from layers of flat-lying sandstone and other materials.
The Missouri River marks an approximate boundary between the eroded landscape of southwestern North Dakota and the entirely different glacial landscape north and east of the river, where we see small hills – small at least compared to large buttes like Sentinel Butte and Bullion Butte found in southwestern North Dakota. Eastern North Dakota is characterized by thousands of potholes, poorly developed drainage in places, and remarkably fertile farmland.
When the glaciers advanced over the state, they picked up some of the materials over which they flowed. The glaciers contained a variety of kinds of soil and rock, which they eventually deposited as thick layers of sediment. The exposed surface of these sediments has been weathered for the past several thousand years (since the glaciers melted) and it forms the rich soils our farmers work today.
Over much of eastern North Dakota, the glacial sediments were laid down as an undulating plain (think of the Carrington, Finley or Kenmare areas, for example). In other places, a more hilly landscape resulted (think of Turtle Mountain or the Missouri Coteau — places like Belcourt, Hurdsfield, Max, Ryder and countless others). In still other places, water from the melting glacier became ponded, forming huge lakes. Today, most of these areas are flat. Examples of the flat topography may be seen in places like Fargo, Hillsboro, Grand Forks or Grafton. The old floor of Glacial Lake Agassiz (the Red River Valley) is the classic example of flat. Hundreds of smaller glacial lake plains are found in North Dakota too.
As the glaciers flowed over North Dakota, they tended to smooth off and wear down the hill tops and fill in the lower areas with sediment. The overall result is a fairly level landscape. The layers of glacial sediment underlying that landscape are extremely complex, containing buried river channels, blocks of sandstone and shale, old landscapes that were covered many times by fresh glacial sediments. Buried layers of gravel and sand, deposited by water flowing from the melting glacial ice, constitute aquifers. They contain some of our best sources of fresh water.
As the ice flowed, in some places it picked up large chunks of material and moved them short distances before setting them down again. A good example of this is at Devils Lake, where a large amount of material was picked up and moved southward a few miles. Today, Devils Lake lies in a broad lowland. South of the lake is a high range of hills, including Sully’s Hill. The hills consist of materials that were once in the lowland where Devils Lake is now.
In some places, huge floods of water from melting glaciers carved deep river channels. Countless small meltwater valleys, along with some large ones too, are found throughout eastern and northern North Dakota. The Sheyenne, Souris, and James River valleys are good examples of large meltwater valleys. Valley City, Minot, and Jamestown are nestled in meltwater valleys. The Missouri River valley is another example of a glacial river channel, but it had such a complicated history that I’ll plan on writing a special article about it.
How thick were the glaciers that covered North Dakota? Certainly, they were more than a thousand feet thick in the east and north, so thick that the Earth’s crust beneath the ice buckled and sagged downward, eventually rebounding when the ice melted.
Who or what lived in North Dakota during the Ice Age? Mastodons and wooly mammoths lived along the edge of the glacier. Elk, caribou, and horses were common. Horses became extinct in North Dakota and in North America at the end of the Ice Age, They survived, worldwide, because they had migrated to Asia via the land bridge between North America and Asia prior to then. During my field work over the years, I’ve found mastodon teeth, caribou bones and, in the Lake Agassiz deposits, fossil fish bones, mainly perch. It’s likely that early humans also lived here while the most recent glacier was still melting.
I’ve mainly been discussing North Dakota’s glacial landscape. Part of the state, the southwest quarter, was not glaciated, but the glaciers also left their mark there. The badlands along the Little Missouri River owe their existence to early glaciers that diverted the river eastward from its northerly route into Canada. This diversion triggered greatly increased erosion by the Little Missouri River, which resulted in the formation of badlands. Some places that were not glaciated are marked by polygons, formed when permafrost froze the land beyond the limit of the glaciers.
During my 42 years with the Geological Survey (1962 – 2004), I worked on nearly every facet of North Dakota geology: the rocks that produce oil, gas, coal, gravel, ground water and our other mineral resources. My studies of the glacial sediments near Devils Lake helped me to gain detailed insights into North Dakota’s past climate changes. However, I was always most interested in the origin of the hills and valleys I saw every day as I traveled around the state. I’ve spent a lifetime trying to understand how the land that is North Dakota came to be the way it is. My wife, Mary, and our three children as they came along, lived with me in about 25 North Dakota towns over the years. Our oldest son, Bill, was born in Park River while I was mapping Walsh County, and our daughter, Irene, arrived in Lisbon while I was mapping Ransom County. Paul, the youngest, was born in Grand Forks on the first day of January, when it was too cold to map anywhere. Over the years, we lived, up to six months each, in places like Carrington, Cooperstown, Harvey, Hazen, Mayville, McClusky, Washburn, White Shield, Fort Totten, Fort Yates, Rock Lake, and Turtle Lake. Our summer homes were in towns in about 30 counties, and on four Indian Reservations. We enjoyed every one of them.
Each place was special in some way. North Dakota people are open and friendly, and often interested in geology. When we arrived at a new place, we asked locally if anyone had an apartment for rent and, usually, someone did. In Harvey we rented from the owner of the town bakery—a great choice! In Enderlin, our landlady’s son, a hunter, kept us supplied with pheasants and geese that autumn. In another town, our landlady’s son provided us with wild turkeys (some of them may have been poached—we didn’t ask). In another place, we shared a rental house with some bats. In Fort Yates, the brand-new nursing home was not yet filled and still had room, so that became our home. Our little kids were a hit with the elderly residents. I worked in every part of the state. A “field season” for me usually lasted from sometime in May, beginning when it was dry enough to get around, and ending in November, when the ground was frozen too hard to auger a hole. Just before Thanksgiving, we would move back to our own home in Grand Forks. The day after we got home one year, I raked the yard and put up the storm windows. The next day a blizzard blew, and the snow stayed until spring. Our neighbor, an elderly Norwegian man, commented, in his wonderful accent, “that Bluemle, he always times things right.” Well, I don’t “always time things right,” but I was glad I had that year. For the nearly 25 years that we spent our summers “in the field,” throughout North Dakota, we tended to visualize Grand Forks as a white and snowy “winter wonderland” because we weren’t around much to enjoy it in the summer time. Mary and I claim some important knowledge and understanding of North Dakota, apart from the geology. While mapping, I noted stands of chokecherries, wild plums, buffalo berries and juneberries. That valuable information went on my field maps, right along with the geology, as did the locations of the best places to buy sausage and kuchen.
Most of the photos I will post on this website will illustrate landforms. I hope they will help readers appreciate and understand the geologic processes that shaped our modern landscape. I took most of them during the summers of 2009, 2010, and 2011 while we traveled throughout the state. The notion to travel around the state in the summer as kind of a “post-retirement” project turned out to be a great decision. To provide purpose, I took photos of geologic features. During some of our trips around the state we got a little more “off the beaten path” than I intended. One day, I drove along a road on the Missouri Coteau that became a trail, and eventually a narrow, mostly washed-out path with no place to turn around easily, so I kept going. Finally, we came to a barricade, so I stopped and walked around it to read the hand-printed sign: “Do Not Enter: Road Impassible.” The seven miles I had just driven were impassible! I dug out a couple of the steel fence posts, drove to the “good” side of the barricade, and replaced the posts and sign. Another day, I walked over to a fence line, took a picture, and stepped in a badger hole and broke my foot. Still another time, we stopped to admire a herd of longhorn cattle, standing on the road, surrounding us. I thought one was particularly handsome so I took his picture through the open window on the passenger side of our van. I felt something cold, turned around, and found myself nose to nose with a cow that had gotten her head in through the open window as far as her horns allowed. I presumed she probably wanted her picture taken too, so I snapped her as well.
Many geologists move from country to country around the world; we moved from county to county around the state of North Dakota. Unspoiled prairies and buttes, rivers and lakes, wildflowers and wild fruit are everywhere. Wildlife abounds. Gravel trails lead to broad horizons. Late afternoon summer
showers are followed by spectacular sunsets. The prairie landscapes are multi-dimensional. Their breadths, elevations and depths reflect geologic events and processes I’ll explore on this website. And the geology is always there. Geology opens the door to another world just beneath the familiar scenes of our everyday lives. It takes us outdoors as we explore the intricacies of our Earth’s history. Mary and I have traveled beyond North Dakota–to most of the states and Canadian provinces and about 20 other countries. Much of our travel has been to enjoy geology. We’ve seen a lot of spectacular geology in places like Montana, Alberta, and Sweden. Scotland is my favorite destination for geology and for the history of the science of geology. Our geology, here in North Dakota, may be more subtle than the places I just mentioned, but it is just as interesting. My career has been satisfying, my work interesting and rewarding. Every day on the job was different for me. Whether it was the glorious summer days in the field, mapping geology, or wintry days I spent in my office, piecing together and trying to understand what I had mapped the previous summer, it was always fascinating.