Southwest North Dakota Missouri Slope region landform origins, USA

Authors

A geomorphic history based on topographic map evidence

Abstract:

The southwest North Dakota Missouri Slope region is located south and west of the Missouri River and east and south of the Little Missouri River in North Dakota and includes the Knife, Heart, Cannonball River drainage basins and their drainage divides with the Little Missouri River. Also included are the Deep and Sand Creek drainage basins, which drain to the Little Missouri River, and the northwest end of the North Fork Grand River drainage basin, which drains to the Grand River in South Dakota. The Knife, Heart, Cannonball Rivers begin as southeast oriented rivers and at pronounced elbows of capture turn to flow in northeast directions to join the south-oriented Missouri River as barbed tributaries. The overview essay provides highlights from more detailed essay which describe the Knife River, Heart River, Cannonball River, North Fork Grand River, and Deep and Sand Creek drainage basins and drainage divides between those drainage basins and also drainage divides with the adjacent Little Missouri River and Missouri River drainage basins. Detailed essays can be found under North Dakota Missouri Slope on this website’s sidebar category list. Detailed essays provide evidence immense southeast oriented floods flowed across the southwest North Dakota Missouri Slope region and were captured by headward erosion of deep northeast-oriented valleys, which originated east and north of the present day Missouri River valley. Flood waters were derived from a rapidly melting North American ice sheet and were flowing along the ice sheet’s detached southwest margin. The ice sheet’s southwest margin had become detached when a large supra-glacial melt water river carved an immense southeast and south-oriented ice-walled and bedrock floored canyon into the rapidly melting ice sheet’s surface. The floor of the large ice-walled and bedrock floored valley was lower in elevation than elevations along the ice sheet southwest margin and as the detached ice sheet southwest margin decayed ice marginal floods breached the ice barrier and began to flow into the lower elevation ice-walled and bedrock-floored canyon. Headward erosion of a deep southeast and east-oriented valley along the ice sheet’s southwest margin next enabled the deep north oriented Little Missouri River valley to erode headward across the southeast-oriented flood flow routes and to capture all southeast-oriented ice marginal flood waters to what had been actively eroding Knife River, Heart, Cannonball River, and North Fork Grand River valleys and tributary valleys. The deep north oriented Little Missouri River valley eroded headward at approximately the same time the deep south-oriented Missouri River valley eroded headward further to the east and captured in sequence the east-oriented Grand River in South Dakota and the northeast-oriented Cannonball, Heart, Knife Rivers in North Dakota and also the north and east oriented Little Missouri River in North Dakota to create the southwest North Dakota Missouri Slope Region drainage network seen today.

Figure 1: Location map for southwest North Dakota Missouri Slope Region showing the Cannonball, Heart, Knife, North Fork Grand and Little Missouri Rivers. National Geographic Society map digitally presented using National Geographic Society TOPO software.

Southwest North Dakota Missouri Slope Region Drainage History

The Southwest North Dakota Missouri Slope Region is located in southwestern North Dakota, west and south of the south-oriented Missouri River and east and south of the north-oriented Little Missouri River, which is a tributary to the Missouri River. Included in the Southwest North Dakota Missouri Slope Region are the Knife River drainage basin, the Heart River drainage basin, the Cannonball River drainage basin, the northwest end of the North Fork Grand River drainage basin, and the Deep and Sand Creek drainage basins, where Deep and Sand Creek are north-oriented Little Missouri River tributaries. The Knife, Heart, Cannonball, and North Fork Grand Rivers and/or their major tributaries begin near the edge of the deep north-oriented Little Missouri River valley and flow in southeast directions. The Knife, Heart, and Cannonball River all turn from flowing in southeast directions to flow in northeast directions to join the south-oriented Missouri River as barbed tributaries. The north-oriented Little Missouri River, at the northwest end of the Knife River drainage basin, turns to flow in a northeast, north, southeast, and northeast direction to reach an east-oriented Missouri River valley segment. While the present day Missouri River turns to flow in a south-southeast direction at the Garrison Dam location, map evidence suggests the east-oriented Missouri River valley continues eastward.

  • Looking at the figure 1 location map it is tempting to suggest the deep Missouri River valley eroded headward along the southwest margin of a North American ice sheet, which had blocked north-oriented streams and rivers, and in this manner created a south-oriented drainage system, where prior to glaciation the drainage system had been oriented in a north direction. Evidence for valleys extending north and east of the present day Missouri River valley can be found and it is also tempting to say at least some of those valleys represent routes used by the pre-glacial north-oriented drainage system. While this pre-glacial drainage system hypothesis has been proposed it does not explain why the Knife, Heart, and Cannonball Rivers and their major tributaries begin as southeast-oriented drainage routes and then turn to become northeast-oriented drainage routes. Nor does the pre-glacial north-oriented drainage system hypothesis explain how the Knife, Heart, and Cannonball River elbows of capture were formed. Further, the pre-glacial drainage system hypothesis does not explain how the asymmetric drainage divide between the deep north-oriented Little Missouri River valley and the southeast-oriented headwaters of the Knife, Heart, Cannonball, and North Fork Grand Rivers was formed. In addition, the pre-glacial drainage system hypothesis fails to address numerous other landform features illustrated on maps shown in the detailed essays, all of which argue for a fundamentally different hypothesis.

Figure 2: Reduced size topographic maps illustrating the Little Missouri River-Knife River, Little Missouri River-Green River (Heart River), and the Knife River-Green River drainage divides. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

What topographic map evidence argues for a fundamentally different interpretation of Southwest North Dakota Missouri Slope drainage history than the pre-glacial north-oriented drainage system hypothesis? Figure 2 illustrates the Little Missouri River-Knife River, Little Missouri River-Green River (Heart River), and Knife River-Heart River drainage divides north of Belfield. The north-oriented Little Missouri River is located west of the figure 2 map area and the northwest-oriented streams flowing to the figure 2 west edge are Little Missouri River tributaries. The southeast-oriented streams in the figure 2 south center area are Green River headwaters and tributaries. South and east of the figure 2 map area the Green River is a southeast-oriented tributary to the southeast-oriented Heart River, which still further east turns to flow in a northeast direction. Note how the north-south oriented highway is located on an upland surface and east of the highway in the figure 2 northeast quadrant there is an escarpment-surrounded basin where an east-oriented river begins. The east-oriented river is the Knife River and east of the figure 2 map area the Knife River turns to flow in a southeast direction before turning to flow in a northeast direction. South and east of the Knife River escarpment-surrounded basin is a second escarpment-surrounded basin, which is drained by Crooked Creek. East of the figure 2 map area Crooked Creek joins the Knife River. Note how the Crooked Creek escarpment-surrounded basin has also been eroded into the upland surface where the Green River headwaters originate.

  • What is the upland surface upon which the highway is located and the Green River headwaters originate? And what are the Knife River and Crooked Creek escarpment-surrounded basins? The upland surface was eroded by an immense southeast-oriented flood or floods. Note how Green River headwaters streams are predominately southeast-oriented, many Knife River headwaters streams are southeast-oriented, and most Little Missouri River tributaries are northwest-oriented. Flood waters were moving in southeast direction along the southwest margin of a rapidly melting North American ice sheet located north and east of the figure 2 map area. At the time flood waters flowed across the figure 2 map area the deep north-oriented Little Missouri River valley did not exist and flood waters were first flowing to the actively eroding southeast-oriented Green River valley and its tributary valleys. Headward erosion of a deeper east- and southeast-oriented valley complex north of the actively eroding Green River valley began to capture flood flow east of the figure 2 map area and to behead flood flow routes to what were then actively eroding Green River tributary valleys. Escarpments surrounding the Knife River and Crooked Creek escarpment-surrounded basins are large abandoned headcuts, eroded by massive flood water sheets which flowed into the deep east-and southeast-oriented valley. Headward erosion of the north-oriented Little Missouri River valley next captured the southeast-oriented flood flow. Flood waters on northwest ends of southeast-oriented flood flow routes reversed flow direction to erode northwest-oriented Little Missouri River tributary valleys and the landscape has changed little since.

Figure 3: Reduced size topographic maps showing northwest-southeast oriented through valleys eroded across the Killdeer Mountain upland surface, north and east of the figure 2 map area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Did the immense southeast-oriented melt water floods erode the Southwest North Dakota Missouri Slope Region and if so how much erosion occurred? The Killdeer Mountains seen in figure 3 are composed of erosion resistant rock and, while not the highest points in North Dakota, are among the highest points. Note how the Killdeer Mountain upland surface is crossed by several northwest-southeast oriented through valleys. Southeast-oriented streams in the figure 3 northeast quadrant flow to east and north-oriented Jim Creek, which is a Little Missouri River tributary. Southeast-oriented streams in the figure 3 south center flow to east-oriented Spring Creek, which flows to Killdeer (the town) and east of the figure 3 map area joins the Knife River. The north-oriented stream along the figure 3 west edge is Crosby Creek, which flows to a north-oriented Little Missouri River valley segment. West of that north-oriented valley segment the Little Missouri River flows in an east direction and east of that north-oriented valley segment the Little Missouri River flows in a southeast direction (see figure 1). Note how Crosby Creek tributaries from the east are almost all northwest-oriented.

  • The northwest-southeast oriented through valleys across the Killdeer Mountain upland surface provide evidence flood waters at one time flowed across the Killdeer Mountains upland surface, which means flood water erosion removed all surrounding material. The Killdeer Mountains are among the highest points in North Dakota, which means there are no significantly higher elevations to check. How much material was removed from the region before flood waters flowed across the Killdeer Mountains upland surface is impossible to determine, although it is possible flood waters stripped hundreds (maybe more) of meters of sedimentary rock from the Southwest North Dakota Missouri Slope Region. At the time flood waters flowed across the Killdeer Mountains upland surface (the upland we see today), flood waters first flowed to what was then the actively eroding east-oriented Spring Creek valley, which eroded headward into the region. Next headward erosion of the deep southeast-oriented Little Missouri River valley (north and east figure 3) beheaded south-oriented flood flow routes to the actively eroding Spring Creek valley. Flood waters on north ends of beheaded south-oriented flood flow routes reversed flow direction to erode the north-oriented Jim Creek valley, which captured southeast-oriented flood flow routes in the figure 3 northeast quadrant. Finally, headward erosion of the deep southeast-oriented Little Missouri River valley beheaded a south-oriented flood flow channel which was developing along the Killdeer Mountain resistant rock mass western flank. Flood waters on the north end of the beheaded flood flow channel reversed flow direction to erode the north-oriented Little Missouri River valley segment and the north-oriented Crosby Creek valley. Northwest-oriented Crosby Creek tributary valleys were eroded by reversals of flood flow on northwest ends of beheaded southeast-oriented flood flow routes.

Figure 4: Cannonball River and Cedar Creek elbows of capture. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

If the flood waters were flowing in a southeast direction why were the Cannonball, Heart, and Knife River captured by northeast-oriented valleys and why was the north-oriented Little Missouri River valley able to erode headward and capture an immense southeast-oriented flood? The flood water was flowing in a southeast direction along the southwest margin of a rapidly melting North American ice sheet. The ice sheet had been thick and had been located in a deep hole, which had been formed by a combination of deep glacial erosion and crustal warping caused by the ice sheet weight. At one time this thick ice sheet stood high above the surrounding surface while the ice sheet roots extended far below the surrounding surface. As this thick ice sheet melted immense volumes of melt water poured off its surface and flowed in any direction the landscape at that time permitted and the landscape at that time did not look at all like the landscape today. Flood water erosion deeply eroded the pre-existing landscape while crustal warping caused by ice sheet weight continued to uplift regions elsewhere on the continent.

  • In time the ice sheet melted to the point that its surface, at least in the North and South Dakota region was not significantly higher than the surrounding landscape and the southeast-oriented ice-marginal floods still flowing along the ice sheet’s southwest margin. At the same time immense melt water rivers flowing across the ice sheet surface had carved deep ice-walled and ice-floored canyons into the ice sheet surface and in time these giant ice-walled and ice-floored canyons became giant ice-walled and bedrock-floored valleys. One of the largest of these huge ice-walled and bedrock-floored canyons was located north and east of the present day Missouri Escarpment, which is located north and east of the present day Missouri River in North and South Dakota (the Missouri Escarpment is what remains of that ice-walled and bedrock-floored canyon’s west and southwest wall). The floor of that giant southeast and south-oriented ice-walled and bedrock-floored canyon was lower in elevation than the landscape south and west of the ice sheet margin and in time flood waters moving along the ice sheet’s southwest margin were able to breach the northwest-southeast and north-south oriented ice barrier (the ice sheet’s detached southwest margin) to reach the deeper Ice-walled and bedrock floored canyon floor. Deep northeast-oriented valleys eroded headward from those ice sheet margin breaches.
  • Evidence describing breaches through the rapidly melting ice sheet’s detached southwest margin ice barrier is provided in essays listed under ND Missouri River and James River on the sidebar category list and is not contained in the Southwest North Dakota Missouri Slope detailed essays. Flood waters flowing across the Southwest North Dakota Missouri Slope Region were probably flowing in large anastomosing channel complexes and the southeast oriented Knife, Heart, Cannonball, and North Fork Grand River valleys were probably eroded headward along ever evolving southeast oriented anastomosing channels. Evidence illustrated and described in the Missouri Slope Region detailed essays is similar to that seen in figure 4 above, where the southeast oriented Cannonball River (flowing from the figure 4 northwest corner) has been captured by headward erosion of a deep northeast-oriented valley. Headward erosion of that deep northeast-oriented valley also captured southeast- and east-oriented Cedar Creek (seen in the figure 4 southwest quadrant). The southeast-oriented Heart River and Knife River exhibit similar elbows of capture where they also were captured by deep northeast-oriented valleys, which had eroded headward from ice sheet margin breaches. Northeast-oriented valleys eroding headward from breaches through the decaying ice sheet southwest margin captured flood waters flowing in a large-scale southeast-oriented anastomosing channel complex.

Figure 5: Little Missouri River and Missouri River routes north of the Knife River drainage basin. National Geographic Society map digitally presented using National Geographic Society TOPO software.

Headward erosion of the deep Little Missouri River valley is somewhat more complex and is described more fully in essays found under Little Missouri River and ND Missouri River on the sidebar category list. However, figure 5 illustrates evidence needed to understand Little Missouri River valley headward erosion. Note how in figure 5 the Missouri River flows from Williston in the northwest corner to Garrison Dam (Lake Sakakawea is the reservoir impounded by Garrison Dam) and then in a southeast direction to the figure 5 east edge. Note how Lake Sakakawea has flooded a valley east of the Garrison Dam area. That flooded valley provides evidence of what was once an east oriented valley, which had eroded headward from a major breach in the detached and decaying ice sheet southwest margin. The east oriented valley eroded headward along what is now the east oriented Missouri River valley segment and captured multiple southeast-oriented anastomosing flood flow channels along the ice sheet southwest margin. Deep valleys eroded headward along some of those captured flood flow channels, including along the southeast-oriented Missouri River valley segment and along the present day Little Missouri River valley route. Headward erosion of the deeper east and southeast-oriented valleys captured flood flow moving to a shallower north-oriented breach and flood waters on north ends of that beheaded north-oriented flood flow route began to erode a deep north oriented valley. The actively eroding deep north oriented valley was able to capture southeast-oriented flood flow more rapidly than the deep east and southeast oriented valleys and rapidly eroded headward in a south direction across the southeast-oriented flood flow routes. In this manner headward erosion of the deep Little Missouri River valley was able to behead all southeast oriented flood flow routes to what had been the actively eroding Knife River, Heart River, Cannonball River, and North Fork Grand River valleys and the Missouri Slope landscape has changed little since. Subsequently north, northeast, and east oriented flood flow on the former ice sheet floor froze to form a wet based thin ice sheet, which surrounded rejuvenated thick ice sheet remnants. This thin ice sheet blocked the breaches that had permitted floodwaters to flow across what had been the thick ice sheet’s detached southwest margin and forced the north, northeast, and east oriented drainage routes leading to those blocked breaches to again move along the ice sheet margin, resulting in the present day Missouri River route.

Additional information and sources of maps studied

This essay has provided only a sample of the detailed topographic map evidence supporting the flood erosion interpretation. Many additional illustrations could be provided. Readers are encouraged to look at mosaics of detailed topographic maps to see the abundance of available data. Maps used in this study were created and published by the United States Geologic Survey and can be obtained directly from the United States Geological Survey and/or from dealers offering United States Geological Survey maps. Hard copy maps can also be observed at United States Geological Survey map depositories which are located throughout the United States and elsewhere. Illustrations used here were created using National Geographic Society TOPO software and digital map data. TOPO software and map data can be obtained from the National Geographic Society and/or dealers offering National Geographic Society digital map data.

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