The work of John Bluemle PhD

Erosion and Deposition

14-KILLDEER MOUNTAINS

 

Pembina mountain, geology, North Dakota

Fig. 14-A. View to the east from Pembina Mountain over the Red River Valley of the North. The town of Mountain is about three miles in the distance. The town’s name may have alluded to the view of the “mountain” to the west as the town itself was on the relatively flat shore of Glacial Lake Agassiz. Photo June, 2009.

Several years ago, billboards were posted around North Dakota in an effort to entertain and catch motorists’ attention. One of them, outside of Mandan, read “North Dakota Mountain Removal Project Completed.” The billboard referred to the image many people have of North Dakota as a flat and featureless land, but the sign ignored the fact that, within our borders are at least half-a-dozen features bearing the name “mountain.” Was the removal project a failure?

Fig. 14-B. Tracy Mountain, 8 miles southwest of Fryburg in Billings County. The caprock is probably Sentinel Butte Formation.

Fig. 14-B. Tracy Mountain, 8 miles southwest of Fryburg in Billings County. The caprock is probably Sentinel Butte Formation. Photo September 9, 2009.

 

 

 

 

 

One of our mountainous areas is the Killdeer Mountains in western North Dakota, about 40 miles due north of Dickinson. Another is Turtle Mountain, home of the International Peace Garden on the North Dakota-Manitoba border. (Turtle Mountain is singular, not plural; I’ll explain later). It may seem odd that the Killdeer Mountains, Turtle Mountain, and several other features in North Dakota are called “mountains.” The idea may be related somewhat to scale. When viewed by a person who has recently traveled over eastern North Dakota, the features may be  impressive, but I wonder what they might have been named if more of our settlers had come via Wyoming or Montana.

Killdeer Mountains, North Dakota, geology

Fig. 14-C. View of North Killdeer Mountain in Dunn County. Photo August 5, 2009.

We have several more places in North Dakota that bear the name “mountain.” The town of Mountain in Pembina County was settled by Icelanders in 1873. Mountain is situated on the former shoreline of glacial Lake Agassiz, and the view from there, over the Red River Valley, is impressive. Just north of Mountain, the hilly area along the Pembina River Valley in northeastern North Dakota is sometimes referred to as “Pembina Mountain,” but the term “Pembina Hills” is commonly used as well. The steep escarpment is also referred to as the “Pembina Escarpment” or “Manitoba Escarpment.” Pioneer geologist David Dale Owen, when he traveled through the Red River Valley in 1848, commented on Pembina Mountain thus: it is “in fact no mountain at all, nor yet a hill. It is the terrace of table land – the ancient shore of a great body of water that once filled the Red River Valley.” People have been critical of the kind of mountains we have in North Dakota ever since! (Owen was from Indiana).

Killdeer Mountains, North Dakota, geology

Fig. 14-D. View toward the east of South Killdeer Mountain. Photo August 5, 2009.

Other named “mountains” in North Dakota include Devils Lake Mountain in southeastern Ramsey County, Blue Mountain in western Nelson county, Lookout Mountain in northeastern Eddy County, and the Prophets Mountains in western Sheridan County. All of these features are ice-thrust hills or complexes of ice-thrust topography that stand as high as a few hundred feet above the surrounding areas. Near Medora, in Billings County, we have Tracy Mountain, but we don’t have many “mountains” in southwestern North Dakota – in that area the term “butte” is used more often. Several hundred formally named features called “hills” or “buttes” are found in North Dakota, as well as a few “points” and “ridges.” Many of these are at least as impressive as some of our mountains. We also have many features that fit the formal definition of a mesa, but very few of them have been referred to as mesas. I won’t dwell any longer on the vagaries of naming topographic features. The names don’t necessarily make much sense. We do manage to communicate, at least if we stay close to home. This article will deal mainly with the Killdeer Mountains and I will follow it with an article on Turtle Mountain. Both features are of considerable scenic beauty no matter what you want to call them and both have interesting stories to tell. The Killdeer Mountains 

Arikaree Formation, wormy marker bed, North Dakota, geology, Killdeers

Fig. 14-E. Arikaree Formation, a highly resistant, freshwater limestone that forms a caprock on the Killdeer Mountains. This formation is known also as the Wormy Marker Bed. The rock has holes caused by burrowing mollusks (clam-like animals similar to modern shipworms) before the sediment solidified. Photo September 25, 2009.

        The Killdeer Mountains consist of two large, flat-topped buttes in Dunn County. They cover an area of 115 square miles and rise from 700 to 1,000 feet above the surrounding plains. The entire elevated Killdeer Mountain region is about nine miles long and six miles wide. The highest elevation in the area is 3,314 feet, which is 192 feet lower than the highest point in the state (White Butte). The term “Killdeer” is presumably a translation of a Sioux phrase: “Tah-kah-p-kuty” (the place where they kill the deer).

Arikaree boulders, geology, North Dakota, Killdeer

Fig. 14-F. The slopes of the Killdeer Mountains are littered with large numbers of boulders that have broken away from the Arikaree Formation caprock and rolled down the slopes around the buttes. They are especially numerous on the south slope of South Killdeer Mountain. Photo September 25, 2009.

 

 

 

 

 

The caprock on the Killdeer Mountains consists of a 300-foot-thick sequence of siltstone, sandstone and carbonate beds that belong to the Miocene-age Arikaree Formation. One of the most conspicuous, ledge-forming units within the Arikaree Formation is found about 150 feet below the caprock. Known as the “burrowed marker unit” or “wormy marker bed,” it is a sequence of hard, erosion-resistant interbedded siltstone and sandstone with some carbonate lenses (the burrows in the bed were dug by clams living in the sediment before it hardened; the organisms that did the digging were similar to modern “shipworms”). The Arikaree Formation lies on top of the Eocene-age Chadron Formation, a sequence of yellow to green sandy mudstone, clayey sandstone, and pebbly sandstone. The tree-covered, slopes around the flanks of the Killdeer Mountains are mainly landslide topography, consisting of materials that have fallen or slid from higher up. A little farther away, the grassy or farmed, less-hilly areas are underlain mostly by the Golden Valley Formation, a Paleocene to Eocene-age rock unit. The Paleocene Sentinel Butte Formation, which underlies the Golden Valley Formation beneath the Killdeer Mountains, occurs at the surface in a broad area surrounding the Killdeer Mountain upland.

caprock, Arikaree formation, North Dakota, geology, Killdeer

Fig. 14-G. This boulder on a south slope of the Killdeer Mountains has broken off of the Arikaree Formation caprock (Wormy Marker Bed) near the top of the butte and rolled down the butte. Photo September 25, 2009.

The two main buttes that make up the Killdeer Mountains coincide with areas that were once lakes in which sandy and limy sediments, along with some stream deposits, accumulated during Miocene time. Repeated volcanic eruptions in the Rocky Mountains to the west produced large amounts of ash, which blew eastward, fell to the ground, and washed into the lakes, forming tuffaceous (meaning they contain volcanic ash) sandstones.

Battle of Killdeer Mountain, geology, North Dakota

Fig. 14-H. This sign overlooks the site of the Battle of Killdeer Mountain, at the south end of the Killdeer Mountains. The site is 8 ½ miles northwest of the town of Killdeer. Photo August 5, 2009.

 

 

 

 

 

A new erosion cycle began about five million years ago, long after the lakes had filled with sediment, and dried up. The relatively hard tuffs and freshwater limestone and sandstone beds that had been deposited in the Miocene lakes were much more resistant to erosion than were the surrounding sediments. Because of their resistance to erosion, these hard materials remained standing above the surrounding area as the softer Golden Valley and Sentinel Butte sediments were eroded away by streams and rivers. The Killdeer Mountains, with their resistant caprock, are the result of that erosion; they are the modern manifestation of ancient lake beds. The topography has undergone a complete reversal; areas that were once low are now high due to their resistance to erosion.

medicine hole, killdeer mountain, geology, North Dakota

Fig. 14-I. This is the opening in the rocks that serves as the entrance to Medicine Hole, on top of South Killdeer Mountain. Photoscan 1970s photo.

Two sites in the Killdeer Mountains are of particular interest. The Killdeer Mountain Battle State Historic Site is located on the southeast edge of the Killdeer Mountains, seven miles northwest of the town of Killdeer (Section 34, T. 146 N., R. 96 W.). The Battle of the Killdeer Mountains took place on July 28, 1864 when General Sully and 2,200 troops used artillery on 6,000 Teton and Yanktonai Sioux in revenge for the uprising of Santee Sioux in southern Minnesota. Sully decimated the Sioux, killing many of them and destroying their camp and equipment. Less than a year earlier, on September 3, 1863, Sully had accomplished a similar feat at the Battle of Whitestone Hill, where his troops killed, captured or wounded 300 to 400 Sioux Indians. Medicine Hole is, indeed, a hole in the ground, but it is not a cave in the traditional sense because it did not form as most caves do. No solution of carbonates was involved, and there are no stalactites or stalagmites. It is, rather, a crack in the ground, where a large block of material has begun to fall away from the main body of the southern butte of the Killdeer Mountain. Medicine Hole is located on private land and, as I write this, in 2015, the area is not open to public access. Please respect the wishes of the land owner. The Killdeer Mountains support the largest deciduous forest in southwestern North Dakota, except for the forests on the floodplains bordering the major rivers. The Killdeer Mountain forest consists largely of aspen and oak, with some ash, elm, birch, and juniper, along with shrubs such as chokecherry, willow, plum and buffaloberry. The forest is interesting in that it contains species that tend to be found in more boreal settings, areas that may be 200 miles or more to the northeast.

frost wedge, glaciation, Killdeers, North Dakota, geology

Fig.-14-J. Photo of a frost wedge in pediment sediments along the west side of Killdeer Mountain. The geologist’s finger is pointing to the wedge formed when the frost forced sand and gravel apart during the Ice Age when the area was a tundra environment.* Photoscan, JPB photo, 1970s.

In summary, the Killdeer Mountains are an erosional feature, preserved because of their resistant caprock of tuffaceous sandstone and limestone. Erosion of the area began in late Miocene time, and continued into Pleistocene time, resulting in gravel-covered, flat, sloping surfaces (pediments) around the flanks of the Killdeer Mountain uplands. These gravel deposits, up to ten feet thick, were derived from the sandstone and limestone beds higher up in the Killdeers. The gravels are themselves resistant to further erosion and they help to retard the rate of the ongoing, modern erosion cycle. The current erosion cycle began when the nearby Little Missouri River was diverted by a glacier from its northerly route so that it flowed (flows) eastward to its modern confluence with the Missouri River. As a result of the diversion, and the resulting steeper gradient over which it flows, the Little Missouri River began to erode vigorously, carving the badlands through which the modern river flows today. Although the Killdeer Mountains show no evidence of ever having been glaciated, their modern topography dates largely to the Pleistocene. Old ice wedges can be seen in the pediment gravels in places, testimony to the time when the area was subjected to tundra conditions during one or more of the glacial epochs. There were no glaciers over the Killdeers, but continuous frigid conditions provided a tundra ecosystem. *Frost WedgesFrost wedges are common,  but many areas of patterned ground that have been interpreted to be frost polygons are really dessication cracks developed in silcrete. These are much older than frost wedges, such as this one, which formed in loose materials.

11-GLACIERS IN NORTH DAKOTA – PART TWO

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.

till, fluvial deposits, North Dakota, geology

Fig. 11-A. This photo shows till (on top) overlying banded gravel (the materials at the bottom of the photo have fallen from above). The tan till at the top was deposited by a glacier flowing over fluvial (water-lain) deposits, which were likely deposited by water flowing from the glacial ice. The contact between the base of the till and the top of the gravel, the bedding of which is truncated, is remarkably sharp. These materials are old; deposited by a pre-Wisconsinan glacier. The till contains abundant pieces of lignite coal, so we know that the glacier that deposited it flowed over lignite-bearing Tertiary rocks to the northwest. Till deposited by glaciers flowing from the east or northeast contain little or no lignite. McLean County. Photo-scan. 1978.

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.

Wisconsinan till, till on bedrock, North Dakota, geology

Fig. 11-B. The darker material on top, with numerous vertical iron-stained fractures is glacial material (till), likely Early Wisconsinan age (about 70,000 years old). Notice the pebbles in the glacial sediment, an easy way of identifying till. The till lies directly on top of bedrock of the Sentinel Butte Formation, fine-grained siltstone, about 57 million years old. The contact between the bedrock and the overlying till is known as an “unconformity,” meaning there is a substantial break in the geologic record, both in time and manner of deposition. In this case, the bedrock beneath the till is about 800 times older than the till on top. McLean County. Photoscan. 1965.

 

 

 

 

 

 

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.

glacial lake sediments, North Dakota, geology

Fig. 11-C. Evenly bedded sediments of Glacial Lake Agassiz, south side of Mayville, Traill County. The light-colored beds of silt are about 5 inches thick. They are separated by thinner dark bands. The light-colored bands were deposited on the floor of the lake during a single summer season, the dark bands during a winter. During the summer, steams flowing into the lake carried large amounts of silt, which accumulated in thicker layers on the lake floor. In the winters, the amount of incoming sediment was much less. The layers shown here record about 15 years of Lake Agassiz’s history. Photoscan. 1978.

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.

gravel deposit, North Dakota, Griggs Co.

Fig. 11-D. Gravel exposed in a pit four miles west of Hannaford, Griggs County. This gravel is part of an esker deposit. Most esker gravels tend to be less well-sorted than this one, with inclusions of till, boulders, etc. Layers of coarser materials were deposited by fast-moving water; finer materials by slower moving water. Photoscan. 1969.

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.

geology, North Dakota, paleosols

Fig. 11-E. The two horizontal black lines are buried soils—paleosols—in alluvium along the Cannonball River in Sioux County. These two buried soils are unusually level and therefore easy to recognize. The soils formed on river alluvium at times the river was not depositing sediment in that area, when the river was not building its bed. I am unsure how much time is represented by each of the two paleosols – perhaps it took a few thousand years for each soil to develop (the soils have not been dated). Nor do I know how long it took for the river to deposit the alluvial sediment during the three periods of deposition shown (the light-colored silty sediment below the lower paleosol and above each of the paleosols). Deposition of the sediment might have been much quicker than the time it took for the soils to form. This area was probably not glaciated during the most-recent glaciation. Photoscan. 1978

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.

glacial ice, geology, North Dakota

Fig. 11-F. Debris-covered glacial ice in Alaska. When thick, debris-laden glacier melts, the material that was within the ice becomes concentrated on the surface of the remaining ice. As the debris cover becomes thicker, it becomes an increasingly effective cover of insulation, causing the remaining ice to melt more and more slowly. During Late Wisconsinan time, about 14,000 years ago, debris-covered glacial ice like that shown here covered the Missouri Coteau and Turtle Mountain. It may have taken as long as 3,000 years for the insulated ice to melt. During that time, forests grew on top of the slowly melting glacier. The resulting topography is referred to as “dead-ice-moraine.”
In the distance (top of this photo), forest can be seen growing on the debris-covered glacial ice. Photoscan UND Geology Dept. 1962.

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.

 

paleolsol; McLean County, Deadman Till, geology

Fig. 11-G. This exposure of glacial deposits is along Lake Sakakawea near Riverdale. Two tills are being eroded and exhumed by wave action at the lake shore. The upper till (farthest back and more brown in color) is early Wisconsinan in age. The lower till, which is pre-Wisconsinan in age, is much older and harder than the upper one. For this reason, the upper till is being removed much faster than the lower ones. This leaves the older till surface stripped of its former covering of younger till. Photoscan. 1978

 

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).

8-THE BADLANDS – PART TWO

Badlands erosion,North Unit of Theodore Roosevelt National Park,

Fig. 8-A. Erosion in the Sentinel Butte Formation, North Unit of Theodore Roosevelt National Park, McKenzie County. Some beds have eroded into a “rilled” micro-topography (center of photo), with vertical grooves, while other beds retain their horizontal layering, which forms tabular concretions in places. A lag covering of reddish nodules covers the surface at the base of slopes. Photo: 7-27-11

Rain and melting snow, wind, frost, and other forces of erosion have carved our badlands into intricate shapes. Since the Little Missouri River began to form the badlands, it has removed an enormous amount of sediment from the area. In the southern part of the badlands, near the river’s headwaters and close to Devils Tower in northeastern Wyoming and adjacent Montana, the river has cut down about 80 feet below the level at which it had been flowing before it was diverted by a glacier farther north. Near Medora, the valley floor is 250 feet lower than the pre-diversion level. Still farther downstream, in the North Unit of Theodore Roosevelt National Park and near the confluence of the Missouri and Little Missouri rivers, and nearer to where the glacier diverted it, the east-trending portion of the Little Missouri River flows at a level that is 650 feet deeper than when it was diverted.

The average rates of erosion in the badlands, assuming they started to form about 640,000 years ago, can be calculated as follows:

Headwaters area in Wyoming: 0.15-inch/100 years;

Medora area: 0.5-inch/100 years;

badlands, Bully Pulpit, North Dakota, geology

Fig. 8-B. This view is from the Bully Pulpit golf course near Medora, east of the Little Missouri River. The golden beds exposed in the cliff belong to the Bullion Creek Formation, which is the main geologic formation seen in the South Unit of Theodore Roosevelt National Park. Photo: 9-9-2009.

Confluence area near Mandaree – Missouri and Little Missouri rivers: 1.25 inch/100 years.

These rates may seem tiny but, over time, erosion has removed a huge amount of sediment. Approximately 40 cubic miles of sediment have been eroded and carried away by the Little Missouri River from the area that is now the badlands. Most of that sediment now lies beneath the water of the Gulf of Mexico.

The rates of erosion I’ve noted are long-term averages, but erosion goes on at highly irregular rates. Locally, considering only the past few hundred years, the badlands have undergone four separate periods of erosion and three periods of deposition. Since about 1936, new gullies have been cut to their present depths. It may seem a paradox that, although running water is the main agent of erosion, badlands formation tends to be most intense when water is in short supply. Why? Because erosion tends to be more vigorous during times of drought when the vegetative cover is too sparse to protect the soil from the occasional rain storm or spring snow melt. When precipitation is sufficient for the growth of heavy vegetation, the soil is better protected from severe erosion.

 

Fig. 8-C. Concretion pedestals (“hoodoos”) in badlands topography. The concretions act as caprock, and keep the underlying softer sediments from eroding, resulting in table-like configurations. These examples are in the South Unit, Theodore Roosevelt National Park, Billings County. Photo: 9-10-2009.

Fig. 8-C. Concretion pedestals (“hoodoos”) in badlands topography. The concretions act as caprock, and keep the underlying softer sediments from eroding, resulting in table-like configurations. These examples are in the South Unit, Theodore Roosevelt National Park, Billings County. Photo: 9-10-2009.

Streams and rivers carry sediment away from the area of the badlands, but most of the actual “on-the-spot” erosion is a result of slopewash. In places where vegetation is sparse, the soil and rock materials are easily weathered, forming loose surfaces that slide downslope easily, slumping and sliding during showers or when the snow cover melts.

The Badlands Landscape

The shapes, sizes, and configurations of the hills, buttes, valleys, and other landforms in the badlands are not entirely happenstance. Differences in hardness of the materials result in differences in resistance to erosion. Nodules and concretions help to shape a landscape ranging from beautiful, to desolate – even grotesque. Hard beds of sandstone or clinker cap many of the small buttes. Variations in permeability (permeability is a measure of the ease with which water can move through porous rock) have similar effects; rain and melted snow soak into the more open and permeable sands, resulting in only minimal erosion. When water flows over the surface of tighter, less permeable sediment, such as clay, it abrades and erodes the material, carrying some of it away. The presence or absence and the character of the vegetation also play important roles in governing the rate of erosion. Grass usually helps to control erosion more effectively than does forest vegetation.

The irregular placement of hard nodules and concretions may result in the development of rock-capped pillars, known as “hoodoos,” mushroom-like shapes perched on stalks of clay. In places, slopes are covered by nodules of siderite (iron carbonate). As they weather out of the surrounding materials, becoming concentrated on the surface, the copper-colored nodules form an erosion-resistant armor, which temporarily slows the rate of erosion. Clinker beds are also much more resistant to erosion than are the softer surrounding beds. We commonly see buttes capped by red clinker beds.

Limestone concretion, hoodoo

Fig. 8-D. Pedestal, a small “hoodoo” with a limestone concretion caprock, located about a half mile south of Lake Sakakawea in northern McKenzie County. Pods of such freshwater limestone are common in several of the Tertiary formations found in the badlands. They may occur sporadically or as semi-connected layers and they often form small caprocks, such as this one. Photo: 7-23-2010.

Badlands "Pipes"

Fig. 8-E. Badlands “pipes,” vertical cavities measuring about 15 feet top to bottom. These pipes are located in northeastern McKenzie County, about a half mile south of Lake Sakakawea. A cross-sectional view of a pipe, as shown here, is rare. More often, they are concealed with the only opening at the top (but notice that the tops of these pipes are partially sealed by a concretion. Photo 7-23-2010.

 

 

 

 

 

 

 

 

 

 

 

Erosional “pipes” sometimes form in gullies and ravines where surface runoff is focused. “Piping” results where runoff can flow downward into small cracks and joints.  Pipes are common in places where surface runoff erodes cavities vertically downward through the soft rock. With time, the initial pathways may widen at depth into caves the size of small rooms. The average depth of vertical pipes is about 10 to 15 feet, but some are much deeper. The tops of pipes may be partially concealed making hiking treacherous. I have seen the bones of animals, such as rabbits and deer, at the bottoms of pipes (so far I haven’t seen any human bones). The animals fell into the holes and could not get out.

Conclusion

The geology is only part of the badlands story. The weather and climate, vegetation, animals, birds, insects, sounds and aromas–all of these, along with the human history and the ranching heritage, work together to complete the story of the badlands.

I think the North Dakota badlands are particularly beautiful because of their parklands; wooded areas that occur in draws and on north-facing slopes. Heavy vegetation in the badlands in places like Little Missouri State Park adds to the scenery. Evergreens, such as the Rocky Mountain juniper, ponderosa, and creeping juniper are interspersed with quaking aspen, cottonwood, and poplar. Limber pines are found in the badlands in the southwest corner of the state, near Marmarth.

I’ve hiked and camped in the badlands many times. Evening summer showers accentuate the colors and the clinker beds assume intense shades of red and orange. The fresh, pungent aroma of wet sage and cedar enhance the experience. At night, the stark, intricately eroded pinnacles can seem unreal. In the moonlight or in a night lightning storm, it is easy to imagine the strange shapes as ruins of a magical city, rather than structures of mere sand and clay. Blend in the sound of coyotes conversing and the badlands environment is complete.

Little Missouri River, badlands

Fig. 8-F, Panoramic view of the bend in the Little Missouri River from North Unit of Theodore Roosevelt Park. Materials exposed in cliffs are Sentinel Butte Formation. Photo: 7-27-2011

 

7-THE BADLANDS – PART ONE

If asked what he or she knows about North Dakota’s geology, an average resident will likely mention the badlands first. That’s true too of visitors, many of whom come to the state to see our best-known natural feature, the scenic badlands along the Little Missouri River.

Little Missouri River

Fig. 7-A. View upstream (to the south) of the Little Missouri River in Billings and Golden Valley counties about three miles north of Bullion Butte. Photo: 7-8-2010.

The badlands landscape is a rugged and hilly one, best viewed from above, looking down on the hills, not up at them, as we usually view buttes. From the rim of the “breaks,” the point where we descend into the badlands, an intricately eroded landscape of sparsely wooded ridges, bluffs, buttes, and pinnacles lies before us. Black veins of lignite coal may be seen eroding out of the steep badlands slopes. Reddish bands of clinker add vivid colors to the area. Pieces of petrified wood, as well as fossil stumps and logs, litter the surface. Behind us stretch rolling plains, interrupted only by occasional buttes.

Bullion Creek Badlands, Golden Valley County

Fig. 7-B. Bullion Creek Formation badlands, four miles north of Bullion Butte in Golden Valley County. Castellated sandstone structures, resulting in towering or battlement shapes, can be seen at the top of the butte. Such structures are examples of one of many kinds of badlands erosion. Photo: 8-7-2011.

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The American Indians, who inhabited the area when the European settlers arrived, referred to badlands as “mako sica,” (“land bad”). Early French explorers translated and added to this, referring to “les mauvais terrers a’ traverser” (“bad land to travel across”).

Bullion Creek badlands, Billings County

Fig. 7-C. Tertiary Bullion Creek Formation badlands along the Little Missouri River, Billings County. This view is to the north, along the East River Road about five miles north of the South Unit of Theodore Roosevelt National Park. The snow shows the erosion patterns in the south-facing bluffs in the distance beyond the river, which is at the base of the bluffs. Photo :1-15-2010.

 

 

 

 

General Alfred Sully, preparing to cross the badlands in August of 1864, described them as “hell with the fires burned out.” Theodore Roosevelt, who lived for a while in the Little Missouri Badlands in the 1880s, described them as “fantastically beautiful.” I prefer TR’s description.

Age of the Badlands Materials

Badlands topography is found in several places on the plains of the U.S. and Canada. The best-known badlands in the United States are the extensive “Big Badlands,” along the White River in western South Dakota. Near Dickinson we have the “South Heart Badlands” (known also as the “Little Badlands”) where we find layers of sedimentary rock, equivalent (same materials, same geologic age) in part to those in South Dakota’s Big Badlands. The South Heart Badlands are an erosional remnant of what was once a large butte or group of buttes. The South Heart Badlands are carved mainly from strata of Eocene and Oligocene age, ranging between 55 and 25 million years old. The youngest beds belong to the Miocene Arikaree Formation sandstone (22 million years old), which caps some badlands buttes.

South Heart Badlands

Fig. 7-D. South Heart Badlands about six miles south of South Heart, Stark County. Photo 9-24-2009..

North Dakota’s Little Missouri Badlands extend from near the Little Missouri River’s headwaters in Wyoming near Devils Tower to the point where the Little Missouri River joins the Missouri River in western North Dakota. The materials being eroded in these, our most extensive area of badlands, are much older than those in the South Heart Badlands.

The oldest materials in the badlands are in the southwest corner of the state, near Marmarth, where Cretaceous-age Hell Creek Formation beds (about 65 million years old) have been carved into badlands. The dark and somber, gray and purple beds of the Hell Creek Formation contain dinosaur fossils. Small patches of badlands, carved from the Hell Creek formation can also be seen along State Highway 1806 between Huff and Fort Rice in Morton County.

badlands

Fig. 7-E. This badlands topography is located about three miles northeast of Marmarth in Slope County. The materials are Cretaceous in age, about 65 million years old. In contrast to the badlands farther north, which are shades of light brown, these older beds are darker, tending to be purple and gray. They contain dinosaur fossils. Photo 10-22-2009.

However, the main area of  the Little Missouri Badlands is that which has been carved largely from the Paleocene Bullion Creek and Sentinel Butte formations, which were deposited  between 58 and 56 million years ago. The beds that have been eroded into these badlands are too young for dinosaur fossils; the dinosaurs were already extinct when they were deposited.

Between 70 and 40 million years ago, a major mountain-building event known as the Laramide Orogeny (orogeny = “mountain forming”) formed the Rocky Mountains in Montana and Wyoming. As the mountains rose, they were attacked by intense erosion, providing sediment to eastward-flowing rivers and streams. The rivers delivered the eroded sediment to western North Dakota’s coastal plain, an area that could be likened to today’s Mississippi River Delta (central North Dakota was an inland sea at that time). Sediment from the eroding mountains accumulated into thick layers of soft, poorly lithified siltstone, claystone, and sandstone: materials that were deposited on river floodplains and in swamps in what is now western North Dakota. These are the sediments we see exposed today in the Little Missouri Badlands.

In addition to the stream-transported sediments, clouds of volcanic ash, blown eastward from the rising Rocky Mountains during the Laramide Orogeny, collected in layers that were later weathered to clays ( “bentonite”). When wet, the clay absorbs water and swells, and it can become slippery when wet so don’t try walking or driving on it. When the beds dry, they assume a surface  texture, similar in appearance and consistency to popcorn, with colors ranging from white to bluish-gray or black.

Why the Badlands Formed

South Heart Badlands

Fig. 7-F. The dark-gray to black mound-like hills are examples of topography of the South Heart Member of the Eocene Chadron Formation in the South Heart Badlands south of the town of South Heart, Stark County. The material is a clay that forms a popcorn-like surface when it is dry. When wet, it is sticky and slippery. The clay is a weathering product of volcanic ash. Photo 9-24-2009

Even though the layers of sedimentary rock exposed in North Dakota’s Little Missouri Badlands range from Cretaceous through Eocene in age (65 to 50 million years old), the badlands themselves–the hills and valleys we see today–are not nearly that old. Before a glacier diverted it, the Little Missouri River flowed northward through a broad, smooth valley, joining the early Yellowstone River in northern Williams County. The Little Missouri and Yellowstone rivers came together near Alamo (about 30 miles north of Williston) in a place now buried beneath 400 feet of glacial deposits. From there, the combined Yellowstone-Little Missouri River flowed northeastward into Canada.

The diversion of the Little Missouri River, away from its route to the north, probably happened sometime prior to the deposition of a volcanic ash bed on the glacial sediment blocking the channel (the ash was deposited as a result of a volcanic eruption in the area of Yellowstone Park 640,000 years ago). It is possible, though, that an earlier glacier might have diverted the river – the 640,000-year figure is a minimum date; erosion of the badlands may have begun as early as 3.5 million years ago.

Since it was diverted by glacial ice, the Little Missouri River has flowed over a shorter and steeper route than it did prior to its diversion. That part of the river’s route today, from the point where it makes its sharp turn toward the east in the area of the North Unit of Theodore Roosevelt National Park, is east rather than north as it had been before a glacier diverted it. When the river assumed its new, shorter route toward the Gulf of Mexico, it began a vigorous erosion cycle, cutting down more rapidly and deeply and sculpting badlands topography. The badlands then, are an indirect result of glacial activity, even though the only conspicuous direct evidence of glaciation remaining in the area is an occasional glacial erratic on the upland in northern McKenzie County.

Sentinel Butte badlands; Theodore Roosevelt Park

Fig. 7-G. Badlands carved from the Tertiary-age Sentinel Butte Formation in the North Unit of Theodore Roosevelt National Park. Notice that certain beds can be followed across the entire vista, although they may be discontinuous, eroded away in places. An example is the bluish gray layer that forms the surface of many table-like pedestals. This layer is a bentonitic clay, a weathered volcanic ash deposit. The layers shown here are slightly younger than are those exposed in the South Unit of the park. Total relief here, from valley floor to upland surface, is about 500 feet. Photo: 10-24-2009

 

5-ESKERS AND KAMES

Dahlen Esker

Fig. 5-A. Dahlen Esker, junction of Grand Forks, Walsh, and Nelson counties. This view is to the south, in the direction the stream that deposited the esker was flowing. The esker has a generally accordant crest level, which, however, appears irregular because of numerous minor gaps. The esker consists of a mixture of sand, gravel, till, and boulders, a mixture that resulted from a combination of materials deposited by running water, and debris in the glacier sliding from the ice walls into the esker stream. Photo: 6-26-2009.

Eskers and kames are among the best-known of the various features formed by glaciers and by the running water associated with melting glaciers. Eskers come in all sizes: ridges snaking across the countryside ranging from a few hundred feet to several miles long, and up to 50 or 100 feet high. Kames may be cone or pyramidal-shaped hills as high as a hundred feet, or they may be simply small mounds of material. Kames and eskers are found in most parts of North Dakota that were covered by the Late Wisconsinan glacier.

Eskers were deposited by streams and rivers flowing 1)  on the surface of a glacier, 2) in cracks in the glacial ice or, sometimes, 3) in tunnels beneath the ice. Imagine a river flowing in a valley or crack in the glacier. The banks of the river were formed of ice and, in some places, the river floor might also have been on ice. These Ice-Age rivers and streams deposited gravel and sand in their ice-walled valleys, just as a modern stream deposits sediment in its earthen valley. However, the ice banks of esker rivers eventually melted away, leaving the gravel deposits that had been deposited in the ice-walled valleys, standing as ridges above the surrounding countryside.

 

North Dakota has thousands of esker ridges. Most are small and non-descript, apparent only from a height (air view) or on air photos, but some eskers are impressive.

esker, North Dakota, glaciation, geology

Fig. 5-B. This diagram shows how an esker forms when a stream of meltwater carrying sediment develops beneath a glacier or, in some instances, in an open crack in the glacier. Such a stream may meander a little as it winds its way underneath the glacier, making its way to the front of the ice. The sand and gravel are eventually deposited when the ice melts, and the meltwater flow gradually slows and it drops its sediment load. When the ice melts away, the fluvial sediment is left as a long, narrow, winding ridge, which marks the course of the former subglacial, ice-walled stream.
The stream may be in a crack so that it does not flow in a tunnel, and it may flow on both solid ground in places beneath the glacier and over ice in other places. In places where the stream flowed over ice, the esker ridge may have a gap or dip in its crest because, when the ice beneath the stream bed melted, the overlying stream deposits collapsed.
1-30-2015

One of the best examples of an esker in the U.S. is the Dahlen Esker, located midway between Fordville and Dahlen in the northeastern part of the state. It can be seen as a prominent ridge off to the west where State Highway 32 crosses the Grand Forks-Walsh County line. If the weather is dry, you can drive about a mile on a section-line trail to the crest of the Dahlen Esker (if the fields on either side of the trail are being farmed, be careful not to drive on the crops).

Kame, Jack Lake

Fig. 5-C. The Jack Lake kame in eastern Foster County, a mile west of the James River and eight miles east of the town of Bordulac. This is a scan of a photo I took in 1962. Notice that much of the kame (the hill in the center of the photo) has been removed for gravel. Photo scan: 1962.

 

 

 

 

 

 

 

 

 

 

The Dahlen Esker was deposited by a meltwater stream flowing in an ice-walled channel, or possibly through a tunnel in the ice,  near the edge of the glacier. The stream flowed mainly southward, toward the margin of the glacier. The esker is about four miles long, 400 feet wide, and as high as 50 to 80 feet. In some places, native prairie covers the surface. The Dahlen Esker has been described in various geologic reports dating to the late 19th century, but the best description and discussion of the feature was provided by Jack Kume for the North Dakota Geological Survey (“The Dahlen Esker of Grand Forks and Walsh Counties, North Dakota,” Miscellaneous Series 32, 1966).

Other large eskers include ones near Benedict in northeastern McLean County;  another about ten miles southwest of Carrington in Foster County; one immediately west of Hannaford in Griggs  and Barnes counties; one near Dazey in Barnes and Stutsman counties; and an unusual one in Frankhauser Lake in northern Sheridan County. The Frankhauser esker is particularly interesting because it winds its way through a lake, which floods a depression that was formed by ice-thrusting. The esker formed during the ice-thrusting process.

Kames are similar in many ways to eskers. Like eskers, they consist largely of gravel and sand, but they are conical or irregularly shaped hills, rather than long ridges.

Pierce County Kame

Fig. 5-D. The hill in the middle of this photo is a kame two miles southeast of Orrin in Pierce County. Photo 8-20-2010.

Water flowing on the surface of the glacier, or in esker valleys, plunged into holes in the ice, filling the  holes with a mixture of materials. When the ice eventually melted, the water-deposited materials slumped down, resulting in mounds and conical hills. Kames occur in several places, mainly on the Glaciated Plains, usually in association with ground moraine, but they are sometimes found in areas of dead-ice moraine. A few examples include one in southwestern Richland County, one south of Lidgerwood, and one west of Cayuga in Sargent County. A prominent kame, visible from miles away, is located four miles south of State Highway 200 in eastern Foster County along the west side of the James River. About half of the 60-foot-high feature has been mined for sand and gravel.

Most eskers and kames are composed of coarse, poorly sorted materials, a mixture of sedimentary textures ranging from silt and sand, up to large cobbles or boulders. As they were forming, flowing water deposited flat-lying beds of sand and gravel. Later though, when the ice-walls melted and the bedding collapsed, the bedding became contorted. While a stream was flowing in an ice-walled tunnel or valley, or water was flowing into a hole in the glacier (a “moulin”), cobbles and boulders fell from the melting ice into the water-lain deposits, into the stream or down the moulin. Some eskers have a nearly complete covering of boulders on their surfaces. Most kame or esker deposits contain so many cobbles they are not suitable for construction purposes. Some of them consist of materials suitable for rough fill work.

Frankhauser Esker, Sheridan County

Fig. 5-E. This is an air view of the Frankhauser Esker in northern Sheridan County, about eight miles southwest of the Town of Drake. The esker lies in a lowland that is largely flooded by a lake. The lowland is the result of ice thrusting. The glacier excavated material from what is now the lowland and deposited it a short distance to the southeast, forming a prominent hill. The esker formed when large amounts of groundwater were released as the glacier removed material overlying a large aquifer. The water flowed in a tunnel at the base of the glacier, depositing the gravel and sand in the esker ridge. Photo scan: 1979.

3-GLACIAL ERRATICS: NORTH DAKOTA’S WANDERING ROCKS

Fountain at Crystal Springs

Fig. 3-A. Fountain at Crystal Springs, Kidder County. This field-stone monument was constructed in 1935 by stonemason Art Geisler. It was a Works Progress Administration project intended to replace an old iron pipe from which travelers used to obtain a cool drink of spring water while motoring on U.S. Highway 10. The fountain was listed on the National Register of Historic Places in 2010. The spring was flowing when I took this picture. The water flows from an ice-thrust hole, which intersected a preglacial river valley. Photo: 8-30-2010.

Field stones are common in parts of North Dakota that have been glaciated. Early settlers used the stones for the foundations of their homes and farm buildings and some people built entire structures with them. Today, field stones are used in landscaping, as rip rap along the faces of dams and shorelines, or as decorations in front yards in towns like Bismarck and Minot (less so in places like Fargo and Grand Forks, where they are much less common).

North Dakota, geology, erratics, Forbes, Schulstad House

Fig. 3-B. House built of field stones in Forbes, in Dickey County on the ND-SD state line. An inscription reads “Schulstad House: 1907.” Photo: 7-8-2010.

 

 

 

 

 

 

 

Geologists use the term “erratic” to refer to field stones left behind by glacial ice. The term “erratic,” with reference to rocks, dates to 1779, when Horace de Saussure, a Swiss geologist, described granite boulders lying on top of limestone in the Jura Mountains in Switzerland. He recognized that the boulders were out of place. His term, “terrain erratique,” comes from the Latin erratus, “to wander,” and means, literally, “ground that has wandered.”

In some instances, the source-area of an erratic can be pinpointed. North of Winnipeg, for example, several Paleozoic carbonate limestone formations are quarried. We can determine from which area and formation a North Dakota boulder was derived by matching it to the Manitoba limestone exposures.  Several years ago, Bob Biek, then a North Dakota Geological Survey geologist, found a number of unusual erratics along Lake Sakakawea — dark-colored stones known as “omars.” The name “”omar” is short for the Omarolluk Formation, a 1.76 billion-year-old greywacke formation. The rocks are found in-place (where they originally formed) today only in the Belcher Islands in southeastern Hudson Bay, so it is possible that the Lake Sakakawea omars originated in the Belcher Islands, or near there. The Belcher Islands are located nearly 1,000 miles northeast of Lake Sakakawea.

granite erratic, field stone

Fig. 3-C. Large granitic erratic about ten miles west of Mandan, Morton County. This is one of the largest erratics in North Dakota. Several pieces of granite, some of them rising ten feet above the ground surface, are all part of what was once a single erratic, which weighed at least 350 tons (but I don’t know how much additional rock may be buried beneath the ground surface). Numerous large granite erratics occur in this part of eastern Morton County. They are all that remains of materials deposited during an old (pre-Wisconsinan) glacial advance.
Old Highway 10 can be seen on the right. My wife, Mary (5’7”) shows the scale. Photo: 6-5-09

Erratics have been used as exploration tools in the search for ore deposits. Copper mines were opened in Finland after copper-bearing erratics were traced back to their source. Analysis of gold-bearing erratics in Maine resulted in the discovery of gold ore deposits in Quebec. I have found occasional erratic boulders in North Dakota containing traces of gold. Such erratics were probably transported to North Dakota from the metal mining districts of Manitoba and Saskatchewan, about 700 miles to the north.

riprap, Devils Lake

Fig. 3-D. Riprap of erratics along a Devils Lake levee built to protect the town of Minnewaukan, Benson County. Photo: 9-13-2011

 

 

 

 

 

 

 

 

 

Glacial erratics represent the oldest geologic materials found on the surface in North Dakota. Those composed of limestone or dolomite are mainly from 300 to 500 million years old, while some of the igneous or metamorphic erratics may be three or four billion years old. In contrast, the land surface they are lying on could be as young as 12,000 years old in places where erratics lie directly on glacial deposits.

In contrast to the long-distance travelers, boulders of sandstone were moved no more than a few miles by a glacier from nearby locations within the State. Sandstone is less well consolidated than granite or limestone and any extensive glacial transport of sandstone boulders would break them down into smaller fragments, or reduce them to sand. Occasionally, boulders of shale are included in layers of glacial sediment. Most such boulders are quite fragile and have probably been moved only a few tens or hundreds of feet from their original source.

erratics, boulders

Fig. 3-E. Field with abundant erratics, about six miles east of Wing, northeastern Burleigh County. Photo: 9-4-10.

The larger erratics, those three feet or more in diameter, tend to be igneous or metamorphic rocks, such as granite or gneiss. Such rocks are hard and much more resistant to abrasion and fracturing than are sedimentary rocks such as limestone. In some places, especially large granite or quartzite erratics, ten feet or more in diameter are numerous (some are car-sized, measuring up to 20 feet across). A few examples include the walls of the Sheyenne River Valley near Fort Ransom; many of the high bluffs along the Missouri River; along the White Earth River Valley in Mountrail County; and in the valley walls along the Souris River in and near Minot and Velva. Both large and small erratics are particularly abundant near Venturia and Zeeland in McIntosh County. The largest erratic I have seen is located eleven miles south of Calgary, Alberta. Composed of quartzite, and known as the Okotoks Erratic (aka “Big Rock”), it weighs 16,500 tons, stands 30 feet above the surrounding area and is billed as the world’s largest glacial erratic.

Erratics tend to be abundant in places where the ground surface has been washed by the winnowing action of waves along the shores of glacial lakes and modern reservoirs. Wave action removes the finer materials, leaving a lag of cobbles and boulders behind. Examples include areas along the wave-worn shore of glacial Lake Agassiz, near Pisek in Walsh County and Hankinson in Richland County. Erratics are sometimes concentrated along the shores of modern lakes, such as Lakes Addie and Sibley, near Binford in Griggs County and along Devils Lake in Benson County (but many of the erratics along Devils Lake are now submerged). A good place to see erratics is along the levees and causeway roads that have been constructed in response to Devils Lake flooding. Great numbers of erratics have been brought to the area to serve as rip rap along shorelines subject to wave erosion.

boulder pavement

Fig. 3-F. Road cut along State Highway 32 north of Niagara, Grand Forks County, exposing a boulder pavement lying on Cretaceous Pierre Formation shale (dark gray beneath the stones) and overlain by till deposits. Scanned photo: 1968

Most erratics are rounded and worn, but some of them have beveled or faceted surfaces. During the course of their journey, the rocks were jostled against one another while in the glacial ice, or against the rock over which the glacier was flowing. As a result of this rubbing, the surfaces were planed smooth. Glacial transport fractured some boulders, producing fresh, angular edges. Some erratics are grooved or polished, a result of abrasion by the moving ice. Coarse sand and gravel within the ice scraped against the boulders, scratching or “striating” them, sometimes as the boulder moved along with the advancing glacial ice or when the glacier flowed over a hard, stationary rock.

In some places where the more-easily eroded glacial deposits have been largely eroded away, erratics may be concentrated on the land surface (eastern Burleigh and western Kidder counties are examples), resulting in a very bouldery landscape. If such a landscape was then glaciated again, and covered by fresh glacial deposits (Late Wisconsinan glacial deposits lying over Early Wisconsinan glacial deposits, for example), the erratics may occur as a buried boulder zone, known as a “boulder pavement.” Boulder pavements are common, but not often discovered, unless an excavation cuts though the boulder zone. This is most likely to happen during road construction. Striated boulders with straight grooves are sometimes found in such “boulder pavements.” If the boulders have not moved, the striations can sometimes be used to determine the direction of glacial flow.

buffalo boulder

Fig. 3-G. “Buffalo boulder” rubbing stone, about five miles southeast of Napoleon, Logan County. This boulder is about four feet in diameter. Photo: 5-30-2010

Single large, isolated erratics are sometimes surrounded by depressions, a result of animals such as bison or cattle using them as rubbing stones. Such “buffalo boulders” form as animals rub against the stone, loosening the soil with their hooves. The wind blows the loose soil away, leaving a depression surrounding the rock. Many buffalo boulders are polished from repeated rubbing by the animals.

Erratics aren’t restricted to the surface. They occur throughout the entire thickness of glacial sediments, which averages between 150 and 250 feet thick throughout the northern and eastern parts of North Dakota. Seasonal freezing and thawing causes rocks to work their way upward to the surface from below the plow zone. Every farmer knows that, each spring, a new “crop” of stones has to be removed from the fields. The smaller rocks can be picked up with rock-picking equipment and carried away. Larger erratics are sometimes blasted with explosives and the pieces hauled away. Some of the very largest are simply left in place and avoided.

Standing Rock monument

Fig. 3-H. Standing Rock monument along State Highway 46 in Ransom County. The monument is placed on top of Standing Rock Hill, a prominent ice-thrust hill. Photo: 7-17-2009.

Some erratics are famous. Everyone has heard of Plymouth Rock where the Pilgrims first set foot in the New World on December 21, 1620. In North Dakota we have the Standing Rock, where Highway 46 crosses the Sheyenne River Valley near Fort Ransom. The explorers Nicollet and Fremont, in 1839, noted Standing Rock Hill  on their maps. In northwestern North Dakota, near Alkabo in Divide County, is Writing Rock, which was known by the Sioux as Hoi-waukon or Spirit Rock.

In his book, Blue Highways, a Backroads Tour of Rural America, William Least Heat Moon captured the resignation of farmers to a continual crop of boulders:

East of Fortuna, North Dakota, just eight miles south of Saskatchewan, the high moraine wheat fields took up the whole landscape. There was nothing else, except piles of stones like Viking burial mounds at the verges of tracts and big rock pickers running steely fingers through the glacial soil to glean stone that freezes had heaved to the surface; behind the machines, the fields looked vacuumed. At a filling station, a man who long had farmed the moraine said the great ice sheets had gone away only to get more rock. “They’ll be back. They always come back. What’s to stop them?”

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