The work of John Bluemle PhD

Climate

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

 

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

 

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