The work of John Bluemle PhD

McLean

12-DEAD-ICE MORAINE

North Dakota, physiographic map, geology

Fig. 12-A. Physiographic map showing the distribution of the landform regions in North Dakota. The main areas of dead-ice moraine are the Missouri Coteau, Turtle Mountain, and the Prairie Coteau. Diagram: 1-29-2015

Geologists tend to concoct unusual names for the things they study. “Dead-ice moraine” may sound odd to some of you. It’s a name for a kind of landform found in parts of North Dakota. Dead-ice moraine sounds odd enough, but can you believe it is found along with things called “doughnuts” and “puckered lips”? First of all, the word “moraine” is an 18th century French word. It was coined by Horace de Saussure to refer to “a heap of earth or stony debris” (de Saussure did not initially realize he was referring to glacial deposits).  I’ll explain the “dead” part of dead-ice moraine later.

North Dakota, geology, Mountrail Co., dead ice topography

Fig. 12-B. Photo of dead-ice moraine topography on the Missouri Coteau in Mountrail County, about five miles north of Palermo. The view is to the west. The road helps to show the irregularity in the landscape. Photo: 7 – 2 – 2010.

 

 

 

Dead-ice moraine is also referred to as “hummocky collapsed glacial topography” or “stagnation moraine.” It has irregular topography,  formed as the last glaciers were melting at the end of the Ice Age, between about 12,000 and 9,000 years ago. The most extensive area of dead-ice moraine in North Dakota is found on the Missouri Coteau, which extends from the northwest corner to the south-central part of the state (coteau is French for “little hill”) Other extensive areas of dead-ice moraine are Turtle Mountain in north-central North Dakota and the Prairie Coteau in the southeast corner of the state near Lidgerwood. All three areas are uplands that stand above the nearby lower land. The landforms on Turtle Mountain are identical to those on the Missouri Coteau and Prairie Coteau, but Turtle Mountain has a woodland cover, the result of several inches more annual precipitation than the other areas.

dead-ice moraine, Wells Co., geology, North Dakota

Fig. 12-C. Dead-ice moraine on the Missouri Coteau near Otis about three miles southeast of Ruso in McLean County. Photo: 6-20-2009.

North Dakota’s areas of dead-ice moraine generally make for poor farmland as they are rough and bouldery. They do, however, include a lot of excellent rangeland and thousands of depressions, which may contain lakes, ponds, and sloughs known as prairie potholes . The dead-ice moraine of the Missouri Coteau is known as the prairie-pothole region (the so-called North Dakota “duck factory”). The dead-ice moraine is essentially undrained, except locally. No rivers or streams flow  for any appreciable distance in any of the three dead-ice regions – Turtle Mountain, the Missouri Coteau, or the Prairie Coteau. Dead-ice moraine formed when glaciers advanced against and over steep escarpments as they flowed onto the three upland areas. The land rises as much as 650 feet in little more than a mile along parts of the Missouri Escarpment, which marks the eastern and northeastern edge of the Missouri Coteau. Similar prominent escarpments border the Prairie Coteau and Turtle Mountain in North Dakota and Manitoba, especially the west side of Turtle Mountain near Carbury. When the glaciers advanced over these escarpments, the internal stress resulted in shearing in the ice. The shearing brought large amounts of rock and sediment from beneath the glacier into the ice and to its surface.

Bottineau Co., Turtle Mountain, North Dakota, geology

Fig. 12-D. Dead-ice moraine, about four miles west of Lake Metigoshe, Turtle Mountain, Bottineau County. The topography here is essentially the same as that on the Missouri Coteau, but because the area receives several more inches annual precipitation, it is wooded. Photo: 6-30-2010.

geology, North Dakota, Hurdsfield, dead-ice moraine

Fig. 12-E. Dead-ice moraine on the Missouri Coteau, six miles south of Hurdsfield, Wells County. The crop-duster airplane is spraying for weeds. Photo: 8/25/2009.

 

 

 

 

 

 

 

 

 

 

Eventually, as the Ice Age climate moderated, the glaciers became thinner and could no longer flow over higher land, although they kept flowing through lower areas. When the ice on the uplands became detached from still-flowing ice, the glaciers on the uplands stopped advancing and stagnated (or “died”). As the stagnant glacial ice melted, large amounts of sediment that had been dispersed through the ice gradually accumulated on top of the ice, which was several hundred feet thick. The thick covering of sediment on the stagnant glacier helped to insulate the underlying ice, helping to preserve it and prolonging the time it took to melt. As a result, it took several thousand years for the ice to melt. Geologists have determined that insulated, stagnant glacial ice continued to exist on the Turtle Mountain and Missouri Coteau uplands until about 9,000 years ago, nearly 3,000 years after actively moving glaciers had disappeared from North Dakota.

Fig. 12-F. When glaciers advanced onto upland areas such as the Missouri Coteau, the resistance to ice flow that resulted when the glacier edge was forced upward as it pushed onto the upland barrier caused large amounts of subglacial material to be forced into the moving ice. After the glacier on the uplands stopped moving (stagnated), and the ice began to melt, the debris that had been incorporated in the ice remained there. As the ice melted, the debris it contained gradually built up top of the melting stagnant glacier. This resulted in an effective layer of insulation, which greatly slowed the rate at which the remaining ice melted. Diagram: 1-29-2015

Fig. 12-F. When glaciers advanced onto upland areas such as the Missouri Coteau, the resistance to ice flow that resulted when the glacier edge was forced upward as it pushed onto the upland barrier caused large amounts of subglacial material to be forced into the moving ice. After the glacier on the uplands stopped moving (stagnated), and the ice began to melt, the debris that had been incorporated in the ice remained there. As the ice melted, the debris it contained gradually built up top of the melting stagnant glacier. This resulted in an effective layer of insulation, which greatly slowed the rate at which the remaining ice melted. Diagram: 1-29-2015

In places where the debris on top of the ice was thickest, the glacier was slowest to melt. If little or no insulating debris covered the glacial ice, melting was quicker and the ice had entirely melted away by 12,000 years ago.

glacial "donut" formation, North Dakota, geology

Fig. 12-HA. Formation of a “doughnut.” Three stages in the development of a “doughnut” in dead-ice moraine. Sediment fills a hole in the low ice (but ice exists beneath the hole). As the glacier melts, the sediment that had filled the hole slumps down, on top of the ice beneath it (which had not melted, because it is insulated by the material on top). Eventually when the remaining ice finally melts, what was an ice-cored mound of sediment now has a depression in the center, where the ice had been. 1-20-2015

As the stagnant ice on the uplands slowly melted, the glacier surface became more and more irregular. The soupy debris on top of the ice continually slumped and slid, flowing into lower areas, eventually shaping the hummocky, collapsed glacial topography – dead-ice moraine – found today over the uplands. As the stagnant glacial ice melted, and debris slid from higher to lower places, a variety of unusual features resulted. Long ridges formed when sediment slid into cracks in the ice. Such ridges may be straight or irregular, depending on the shape of the cracks. Often, cracks that formed in a rectilinear pattern when the glacial ice was disintegrating, became partly filled with debris that slid into them. Today, we see nearly straight, intersecting ridges, where the ice cracks had been. These ridges are called “disintegration ridges.” Mounds of material collected in holes and depressions in the ice.  If the mounds were cored by ice, when the ice cores melted, the centers of the mounds collapsed, forming circular-shaped ridges – “doughnuts.” Some of the doughnuts are breached on two sides because the debris cover on a mound of ice slid off two sides of the mound. Some geologists have referred to such features as “puckered lips.” Wherever part of the covering of debris slid off an area of ice to a lower place, the newly exposed ice then melted more quickly transforming what had been a hill into a hole or depression. Such reversals of topography continued until all the ice had eventually melted.

Dead-ice moraine, Stutsman Co., North Dakota, geology

Fig. 12-G. Air view of dead-ice moraine, near Woodworth, Stutsman County. This photo was taken in early spring when the snow was mainly melted, but ice still covered most of the pot-hole lakes. Photo scan of University of North Dakota air photo. 1962.

The insulating blanket of debris on top of a stagnant glacier was so thick in places that the cold temperatures of the ice had little or no effect on the surface of the ground. Trees, grasses, and animals lived on the land surface overlying the stagnant glacial ice. As conditions gradually stabilized, water collected in lakes in depressions on the debris-covered glacial ice. Most of the water in the lakes was probably the result of local precipitation rather than from melting ice. Precipitation at the time was greater than it is today, probably 50 or 75 or more inches of rainfall a year. The mean annual temperature was only a few degrees cooler than it is today.

Surrounding the ponds and lakes, the debris on top of a stagnant glacier was forested by spruce, tamarack, birch, and poplar, as well as aquatic mosses and other vegetation, much like parts of northern Minnesota today. This stagnant-ice environment in North Dakota, 10,000 years ago, was in many ways similar to stagnant, sediment-covered glaciers in parts of Alaska today. Fish, clams, and other animals and plants thrived in the numerous lakes. Wooly mammoths, bear, caribou, wapiti, and other large game roamed the broad areas of forested, debris-covered ice.

Dead-ice topography; North Dakota, geology

Fig. 12-I. The two circular ridges shown on this air photo are known as “doughnuts,” landforms characteristic of dead-ice moraine. The three-step diagram (Figure 12-H) shows how doughnuts form.

During the years I was mapping North Dakota geology, I occasionally came across Ice Age fossils in North Dakota’s dead-ice moraine: caribou bones, mammoth teeth, fossil fish (mainly perch), and various kinds of snails, but paleontologists studying the Ice Age fauna and flora in detail have found many more kinds of Ice Age fossils than I noticed.

Modern dead ice; geology, North Dakota

Fig. 12-J. This is a pile of melting snow on the State Capitol grounds, spring of 2013. The discontinuous covering of grass and dirt on top of the snow tends to retard the rate at which it melts. Notice how sediment forms covers on pedestals of melting snow. This behavior is analogous to melting glacial ice, which had a covering of sediment (much thicker than the small amount of covering shown here – the insulating cover on melting stagnant ice may have been hundreds of feet thick, and retarded melting by thousands of years. Photo: 4-27-2013.

 

 

 

 

 

 

Prehistoric people probably lived on the insulated glaciers in North Dakota 10,000 years ago without realizing the ice lay only a few feet below. Or, if they did realize it, they likely accepted it as a normal situation (and I suppose it was normal for that time). Eventually, all the buried ice melted, and all the materials on top of the glacier were lowered to their present position, resulting in the hilly areas of dead-ice moraine we see today.

 

 

 

North Dakota geology, stagnant ice and soil, Alaska glacial debris

Fig. 12-K. This is a glacier in Alaska, covered with debris. In the distance, a forest is growing on the debris, which provides insulation from the ice, which is melting, very slowly. This scene might approximate the stagnant glacial ice on Turtle Mountain, as it was melting, about 12,000 years ago. Photoscan UND Geology Dept. 1962

10-GLACIERS IN NORTH DAKOTA – PART ONE

Glaciers in North Dakota: Part One

 

Glaciers are giant bodies of ice, formed from snow that survives from year to year. Accumulations of snowfall from past years compact into a substance called firn, a recrystallized residue of snow left over from past seasons. During the summers, when temperatures are warm enough for rain instead of snow, the rainfall adds to the mass of a glacier, eventually freezing and becoming part of the glacier. With time and additional snow cover, the whole mass gradually solidifies into hard ice: a glacier.

The color of pure glacial ice, if it is clear and lacking the various rocks and sediments often found in glaciers, is ice-blue. Drop a piece of glacial ice into a glass of warm water and it may literally “explode.” Any air trapped in the ice, thousands of years ago, and pressurized by the great overlying weight of the glacier, escapes with force from the piece of ice as it melts in the glass. By analyzing these trapped pockets of air, scientists can learn what our atmosphere consisted of in the past.

glacial ice, North Dakota, geolog

Fig. 10-A. This block diagram shows how glacial ice, as it flows over the surface of the ground, picks up debris from the underlying rock and sediment. These materials become part of the moving mass of the glacier. The bottom part of a glacier may consist of more entrained debris than ice. When the glacier eventually melts, all of the debris it contained is deposited on the ground. Diagram: 1-29-2015

When an ice mass becomes thick enough and heavy enough to flow, it “officially” becomes a true glacier. A glacier flows slowly away from the place where it is thickest. It may flow at a few feet a year although, in some circumstances, the flow rate may be much faster. In the northern hemisphere, glaciers expand mainly southward, away from polar regions because the temperatures to the south are warmer than to the north. A glacier flows most easily when it is warmer and less brittle. It will move much faster at 30 degrees F. than at minus 30 degrees F.

A glacier doesn’t glide placidly over the land. It scratches and grinds the underlying bedrock surface, picking up pieces of rock and soil, dragging them along and using them as tools to scour the ground beneath the ice.

glacial till; Dead Man Coulee

Fig. 10-B. This exposure, along Lake Sakakawea near Riverdale, shows a light-colored till in the foreground that is pre=Wisconsinan in age (more than 100,000 years old). Above, and in the background, is a younger till, probably Early Wisconsinan in age (about 70,000 years old). A quartzite erratic is encased in the till in the foreground. Photo: 10-09-2012.

Glaciers don’t normally flow uphill, but they do fill lowlands and overtop them, much like flood water.

Glaciers in mountainous areas, unlike broad ice sheets in places like Greenland and Antarctica, come with a sense of “scale.” The mountain peaks in the distance and the valley walls that hold the glacier help you to orient yourself. But suppose you are standing on a snow-covered, continental-size glacier (dressed in a heavy parka). You see nothing but frozen wasteland, nothing but whiteness. No buildings, no fences, no trees, no landmarks. Only emptiness. No sound but the wind. On a cloudy day, sky and ice blend; making it nearly impossible to distinguish the horizon marking their boundary.

The most-recent major glacial episode in North Dakota is referred to as the Wisconsinan glaciation. It began approximately 90,000 years ago and ended 11,500 years ago, but glacial conditions were not continuous during that entire time. An initial pulse of glaciation (the Early Wisconsinan, 90,000 to 70,000 years ago), was followed by withdrawal of the ice, which was probably complete by 65,000 years ago. Between 65,000 and 35,000 years ago, North Dakota’s climate alternated between combinations of warmer, wetter, cooler, and drier periods, much as it does today. Then, about 30,000 years ago, a second major pulse of glaciation, the Late Wisconsinan, began. The Late Wisconsinan glacier reached its maximum extent between 18,000 and 16,000 years ago when it covered all but the southwestern part of the state. The position of the Missouri River approximates the maximum extent of the Late Wisconsinan glacier. Active glaciers melted completely from the state by 11,500 years ago.          

baked till

Fig. 10-C. Baked till exposure in Ward County. When a lignite seam just beneath this till burned, it baked the overlying materials, including this till, to a reddish-hued material. Baked till is uncommon in North Dakota but, in this case, the baking helps to accentuate the larger particles (pebbles and cobbles) from the finer-grained groundmass. The till is probably Late Wisconsinan in age; it was probably baked sometime during the past 10,000 years. Photo scan 1965.

  By the time each glacier advanced, the land ahead of it may have become deeply frozen permafrost and, as the ice moved over the frozen rock and soil, it picked up chunks of these materials, incorporating them into the glacier itself. In the areas where it formed, west of Hudson Bay, the materials beneath the thickening ice were mainly crystalline igneous and metamorphic rocks such as granite and gneiss. Farther south, the glaciers flowed over layers of sedimentary rock.  Whatever the ice flowed over, it picked up some of it and carried it along.

A moving glacier may be likened to a huge excavation and grading machine that does its job of eroding by plucking and abrasion. Plucking, the more important of the two, is based on a freeze-thaw cycle. The cycle begins when downward pressure melts the ice at the base of a glacier. Water seeps into cracks in the rock beneath the glacier. When the water freezes, the expanding ice plucks rock fragments and incorporates them into the debris near the base of the glacial ice.

After a glacier covers an area for a while, and a considerable thickness of ice lies on the land, the materials beneath a glacier gradually thaw, a combined result of the pressure of the overlying ice and the natural upward flow of heat from the Earth’s interior. The ground surface beneath the North Dakota glaciers was not frozen, and the base of a glacier may have been a muddy mass. This facilitated even more sediment being incorporated into the base of the moving ice.

In some places ground water in the saturated sediments beneath the heavy weight of the glacier built up great pressures due to the weight of the overlying ice.

Besides transforming materials beneath the ice into a mud-like mixture, the water, because it was pressurized, tended to force — squeeze–the sub-glacial sediments upward, into the base of the moving glacier. Sediments beneath the ice were smeared out as they were carried along with the advancing mass of ice.

Dead Man Coulee, geology, glacial till,

Fig. 10-D. This cliff of till is located along the shore of Lake Sakakawea near Riverdale. When the lake was flooded, waves attacked the shore of what was previously a smooth, grassy valley (Dead Man Coulee). The waves quickly eroded the steep exposure of till. The age of this till is probably Early Wisconsinan (lower part) and Late Wisconsinan (upper part). Photo: 6-20-2009

A glacier seldom behaves like a bulldozer, pushing debris ahead of it. It does, however, incorporate debris as it moves by freezing it onto its base. In whatever way the boulders, gravel, sand, silt, and clay beneath a glacier became part of the moving glacier mass, both ice and sediment flowed forward and the farther the glacier traveled, the more material it accumulates. Glaciers advanced over North Dakota several times, and each time, when they melted, they dropped their entire load of rock and sediment, material gathered from places previously overridden. Some of the material carried by the glacier ended up far from where it had originated. We find rocks in North Dakota that came from northern Saskatchewan, Manitoba, and Ontario. We also find chunks of shale that came from only a few dozen feet away. The sediment a glacier was carrying finally came to rest when the last ice melted.

During the active life of a glacier, every crystal of ice, every boulder, sand grain and fragment of rock within the ice, is moving, slowly making its way away from the center of snow and ice accumulation.

In North Dakota, the movement was generally southward, away from the Keewatin center of ice accumulation west of Hudson Bay. Apart from its overall southward progress, variations in the topography over which the glacier advanced locally affected the direction of flow.

When the glaciers that covered much of North Dakota eventually melted, all of the material they had been carrying was laid down on the land surface where the glacier had been. This included everything from large boulders (erratics) to fine-grained material: sand, silt, and clay. This “glacial sediment,” deposited directly from the melting ice, is known as “till.” Till was deposited as a kind of stony mud that eventually dried out after the glacier melted away. Usually, the till amounted to a few tens of feet of material, but after several glaciations, it might have accrued to several hundred feet: the materials from several glaciations, stacked one on top of another.

glaciers, North America, glacial map

Fig. 10-F. This map of North America shows the extent of the major continental-scale glaciers during the Pliocene/Pleistocene glaciation. North Dakota was glaciated by ice flowing from the Keewatin Center, located west of Hudson Bay. This map shows the maximum extent of Early and/or pre- Wisconsinan glaciers (“Maximum southern extent of Pleistocene glaciation”) and also the maximum extent of the Late Wisconsinan glaciation, which did not cover as much area as previous glaciations had. The maximum extent of the Late Wisconsinan glaciation may have been about 18 to 20 thousand years ago.
Glaciers flowing from the several centers grew large enough to coalesce. Thus, the Keewatin and Cordilleran centers merged in Alberta and Montana. When the ice eventually withdrew, opening an ice-free corridor between the Cordilleran and Keewatin ice sheets, it is theorized that the earliest Americans (Canadians?), who had migrated from Asia by way of the Beringia Land Bridge (which had been drained due to the low sea level), were able to migrate southward.
Note too, the minimum sea level reached during the glacial epochs (Minimum sea level line). Great amounts of sea water were tied up as ice so sea level was lower. Sea level was about 400 feet lower than it is today, exposing much more area on the continents.
(I don’t recall where I found this map, but I used it in a talk I gave in 2013. Dozens of similar examples exist on the internet).

2-INTRODUCTION TO NORTH DAKOTA GEOLOGY – PART TWO

Turtle Mountain erratics

Fig. 2-A. Slopes on the south side of Turtle Mountain in Bottineau County, in an area where glacial erratic boulders are abundant. Erosion by running water, flowing on the surface along the slope of the Turtle Mountain upland has removed much of the fine materials, leaving erratics concentrated on the surface. Photo: 8-31- 2010.

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.”

Little Missouri River, wind canyon

Fig. 2-B. Badlands along the Little Missouri River in Billings County. Rapid erosion by the river causes the poorly consolidated sandstone and siltstone layers of the Bullion Creek Formation to slide downward, resulting in steep, freshly exposed slopes. The water carries these materials away when they fall into river, starting them on their way to the Gulf of Mexico. Photo: Photo: 9-16- 2009.

 

 

 

 

 

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.

Blue Buttes, near Keene ND.

Fig. 2-C. Blue Buttes area of McKenzie County, near Keene. This butte, and others near the south end of a grouping known as the “Blue Buttes,” is capped by a sandstone layer of the Eocene Golden Valley Formation (the caprock is barely visible, along the top of the butte). Many of the larger buttes in this part of the State are capped by the same sandstone bed. The view is toward the west, with a thunderstorm approaching. Photo: 7-27- 2010.

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.

Lake Sakakawea till, glacial deposits

Fig. 2-D. Glacial deposits (till) exposed in bluffs along Lake Sakakawea near Riverdale. This 40-foot-high cliff exposes boulders incorporated in a mass of finer material – the overall mixture is referred to as “till” by geologists. Most of the till shown here – the part that is characterized by vertical partings – was deposited by a glacier during Early Wisconsinan time, about 70,000 years ago. Younger, Late Wisconsinan till, about 16,000 years old, lies on top lighter color, lacking vertical partings and immediately beneath the grass cover. Photo: 6-27-2009.

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.

Dead-ice moraine on Missouri Coteau

Fig. 2-E. Dead-ice moraine topography on the Missouri Coteau, about five miles north of Palermo, Mountrail County. The road helps to show the relief. Photo: 7-2-2010.

 

 

 

 

 

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.

Baldhilll Creek, glacial meltwater channel

Fig. 2-F. Baldhill Creek in its meltwater valley about three miles south-southeast of Hannaford in southern Griggs County. This is an example of a very small stream flowing in a valley that is much too large for the size of the stream (an “underfit stream”). The valley was formed by a much larger flow of water from melting glacial ice. Photo: 6-29-2011.

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.

Sheyenne River; meltwater channel, erratics

Fig. 2-G. Sheyenne River meltwater channel (a small part of the valley) about six miles southeast of Cooperstown in southern Griggs County. Notice the large number of glacial erratic boulders on the slopes of the valley wall. Erratics remain behind when erosion by the running water removes the finer materials (silt, clay, etc.). Photo: 6-29- 2011.

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