A geomorphic history based on topographic map evidence

The Missouri River-Souris River drainage divide area east of Shell Creek discussed here is primarily located in Ward and McLean Counties, North Dakota, USA. Major landforms present besides the river valleys include the Missouri Escarpment and the Missouri Coteau. Landforms in the drainage divide area formed during a thick North American ice sheet’s rapid melt down. Thick ice sheet rapid melting produced immense floods, which late during the ice sheet melt down history reversed direction and flowed north instead of south. This melt water flood flow direction change significantly altered the Northern Hemisphere climate, which not only halted the rapid melt down, but also forced remaining flood waters to again flow south.

• The purpose of this essay is to use topographic map interpretation methods to explore Missouri River-Souris River drainage divide area landform origins east of Shell Creek in Ward and McLean Counties, North Dakota, USA. Map interpretation methods can be used to unravel many geomorphic events leading up to formation of present-day drainage routes and development of other landform features. While each detailed topographic map feature provides detailed evidence to be explained, the solution must be consistent with explanations for adjacent area map evidence as well as solutions to big picture map evidence puzzles. I invite readers to improve upon my solutions and/or to propose alternate solutions that better explain evidence and are also consistent with adjacent map area and big picture evidence. Readers may do so either by making comments here or by writing and publishing their own essays and then by leaving a link to those essays in a comment here.

• This essay is also exploring a new geomorphology paradigm in which erosional landforms are interpreted as evidence left by immense glacial melt water floods. Implied in that interpretation is the immense floods were derived from a thick North American ice sheet that created a deep “hole” in the North American continent and also melted fast. The previously unexplored paradigm being tested in this and other Missouri River drainage basin landform origins research project essays is a thick North American ice sheet, comparable in thickness to the Antarctic ice sheet, occupied the North American region usually recognized to have been glaciated, and through its weight and erosive actions created a deep North American “hole”. The southwestern rim of that deep “hole” is today preserved in the high Rocky Mountains. The ice sheet through its weight and deep erosion (and perhaps deposition along major south-oriented melt water flow routes) caused significant crustal warping and tectonic change, through its action of melting fast produced immense floods that flowed across the continent, and through its action of melting fast systematically opened up space in the ice sheet created “hole” so headward erosion of newly developed north-oriented drainage systems captured immense south-oriented melt water floods and diverted immense melt water floods north into space the ice sheet had once occupied.

• If this previously unexplored paradigm is correct the geographic region explored by this essay should contain evidence of immense floods that were captured by headward erosion of new valley systems so as to cause the floods to flow in a different direction. Ability of this previously unexplored paradigm to explain Missouri River-Souris River drainage divide area landform evidence east of Shell Creek will be regarded as evidence supporting the “thick ice sheet that melted fast” paradigm. This essay is included  in the Missouri River drainage basin landform origins research project essay collection.

Missouri River-Souris River drainage divide area location map

Figure 1: Missouri River-Souris River drainage divide area location map (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

Figure 1 provides a Missouri River-Souris River drainage divide area east of Shell Creek location map. The Canada-United States border is located along the figure 1 north edge. Saskatchewan is the western Canadian province and Manitoba is the eastern Canadian province. North Dakota is the state located south of the Canadian border. The Missouri River flows from near Williston in the figure 1 west center edge area to near Bismarck in the figure 1 south center edge area. Lake Sakakawea is a large reservoir flooding the Missouri River valley upstream from Garrison Dam. Note how the Missouri River segment immediately upstream from Garrison Dam is east-oriented and the segment downstream from Garrison Dam is south-southeast oriented. The unnamed (in figure 1) north and east-oriented river in the figure 1 southwest quadrant flowing through Theodore Roosevelt National Park and then east to the east-oriented Missouri River valley segment is the Little Missouri River. Shell Creek is a south- and southwest-oriented stream flowing to one of the large Lake Sakakawea bays near Parshall, North Dakota. The Souris (or Mouse) River originates in Canada and flows southeast to Estevan, Saskatchewan (located in figure 1 northwest corner) and then flows east, with a northeast jog to Oxbow, Saskatchewan before turning to flow southeast to Minot and Velva, North Dakota. At Velva the Souris River turns to flow northeast and then northwest to the Canadian border. Souris River water eventually reaches Hudson Bay. The Des Lacs River is located west of the Souris River in North Dakota and flows southeast to join the Souris River near Burlington, North Dakota. The Missouri River-Des Lacs River drainage divide area essay discusses the region north and west of this essay’s study region and can be found under ND Missouri River on the sidebar category list. Other essays describing North Dakota drainage divide areas can be under Southwest North Dakota and Little Missouri River on the sidebar category list.

• This essay uses topographic maps to illustrate and describe how the Missouri River and Souris River are related to the Missouri Coteau and Missouri Escarpment, which are two prominent landforms not identified in figure 1, but which can be identified on detailed topographic maps below. The interpretation provided by this Missouri River drainage basin research project  series is fundamentally different from interpretations provided by previous researchers and is based almost entirely on topographic map evidence (previous workers used other types of evidence). The Missouri Coteau briefly is a region of hummocky topography and numerous small lakes and depressions located between the Missouri River and the southeast oriented Des Lacs and Souris Rivers. Missouri Coteau area drainage is often to local depressions or small lakes, although southwest areas of the Missouri Coteau region drain to the Missouri River. The Missouri Escarpment is a northeast-facing escarpment located immediately northeast of the Missouri Coteau, which drains to the Des Lacs and Souris Rivers. The Missouri Coteau is interpreted as being covered by glacial deposits left by decaying remnants of what had been a rapidly melting thick North American ice sheet that had occupied a deep “hole”. The lowland at the Missouri Escarpment base (into which the Des Lacs River valley has been eroded) is referred to as the Midcontinent Trench, which was eroded by an immense southeast and south-oriented glacial melt water river. The immense river, which originated on the thick ice sheet’s surface, is named the Midcontinent River. The Missouri Escarpment is interpreted to have been formed as the Midcontinent Trench’s southwest wall or the southwest wall of what at one time was the Midcontinent River’s ice-walled and bedrock-floored valley.

Missouri River-Souris River drainage divide area location map

Figure 2: Missouri River-Souris River drainage divide area location map. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 2 provides a more detailed map of the Missouri River-Souris River drainage divide area. Mountrail, McHenry, McLean, and Ward Counties are located in North Dakota. Burke County is the unnamed county north of Mountrail County. The red shading identifies Fort Berthold Indian Reservation lands. Lake Sakakawea, is a large reservoir impounded behind Garrison Dam (located in the figure 2 south center edge area). Shell Creek originates northwest of the Shell Lake National Wildlife Refuge (located south of Blaisdell in the figure 2 northwest quadrant) and after flowing southeast turns to flow southwest to the flooded Missouri River valley. The Des Lacs River flows south and southeast and joins the south-southeast oriented Souris River near Burlington, which is located northwest of Minot. The Souris River flows southeast to Minot, makes a short jog east at Minot and then continues to flow southeast to Velva. At Velva the Souris River turns to flow northeast and northeast of figure 2 turns to flow northwest and north to Canada. Souris River water eventually reaches Hudson Bay. Note numerous short northeast-oriented Des Lacs River and Souris River tributaries. Those northeast-oriented tributaries are draining the northeast-facing Missouri Escarpment slope. The region in southern Ward County and northeast McLean County with numerous small lakes is the Missouri Coteau. The Missouri Coteau extends in a northwest-southeast direction across the figure 2 map area and is located north and east of the Missouri River and south and west of the Missouri Escarpment (which is located southwest of the Des Lacs and Souris Rivers). Note how the southern and southwestern margin of the Missouri Coteau has drainage routes to the Missouri River valley, but how further to the north and east Missouri Coteau areas lack an integrated drainage pattern. This essay attempts to explain the Missouri Escarpment and Missouri Coteau origins and their relationships to the present day Missouri River and Souris River valleys. Detailed maps below begin with a look at the Missouri Escarpment and Souris River valley in the figure 2 north center area and proceed south across the Missouri Coteau to the Missouri River valley near Garrison Dam. Detailed maps then follow the Missouri River valley upstream to the Shell Creek and the New Town, North Dakota area.

Missouri Coteau and Missouri Escarpment southwest of Minot, North Dakota

Figure 3: Missouri Coteau and Missouri Escarpment southwest of Minot, North Dakota. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 3 illustrates the Missouri Escarpment and the Missouri Coteau southwest of Minot, North Dakota. The southeast oriented Des Lacs River and south-southeast oriented Souris River meet at Burlington (located northwest of Minot near the figure 3 north center edge). The Souris River flows southeast from Burlington to Minot, where it makes an eastward jog and then flows southeast to the figure 3 east center edge. Note the numerous northeast oriented tributaries flowing to the southeast oriented Souris River (and Des Lacs River). These northeast-oriented tributaries are locally known as coulees and are draining the northeast-facing Missouri Escarpment slope. The hummocky topography with many small lakes located south and west of the Missouri Escarpment is the Missouri Coteau. Note the lack of any integrated in the Missouri Coteau region of figure 3. The hummocky topography, numerous small lakes and depressions, and the lack of an integrated drainage pattern suggest the Missouri Coteau region is underlain by glacial moraines and the Coteau is interpreted here to be covered by moraine materials deposited by a decaying ice sheet remnant. The Missouri Coteau and Missouri Escarpment extend far beyond the figure 3 map area in both directions. To the southeast and south the Missouri Coteau and Missouri Escarpment roughly parallel the southeast and south oriented Missouri River across North Dakota and southward through South Dakota to southern South Dakota. For that entire distance there is a lowland northeast or east of the northeast- or east-facing Missouri Escarpment slope and at the Missouri Escarpment crest the area of glacial moraine materials or the Missouri Coteau begins. The Missouri Coteau varies in width, although generally evidence of the thickest glacial moraines (where integrated drainage patterns are absent) is found closest to the Missouri Escarpment crest. Integrated drainage patterns are found further to the southwest and west in the Missouri Coteau region, where evidence of glacial moraines is not as obvious (on topographic maps). The Missouri River represents the Missouri Coteau’s southwest and west margin and is a narrow valley carved into an upland surface, which is considerably higher than the Souris River valley and adjacent lowland region (e.g. figure 3 northeast corner area). Southwest and west of the Missouri River glaciation evidence (with a few exceptions) cannot be identified using topographic maps alone (see Knife River drainage basin essay under Southwest North Dakota on sidebar category list). The Missouri Coteau and Missouri Escarpment continue northwest of the figure 3 map area into Canada, although the Missouri River is no longer located along the Missouri Coteau southwest margin. In total the Missouri Escarpment and Missouri Coteau represent two of the most remarkable landscape features in the Northern Great Plains region and extend from Alberta to southern South Dakota. The Missouri Coteau could be explained as an end moraine deposited at the southwest margin of a continental ice sheet. However, such an explanation does not explain the Missouri Escarpment origin nor does it explain why Missouri Coteau type glacial moraine material are not present on the Missouri Escarpment slope or in the lowland area northeast of the Missouri Escarpment. If the Missouri Coteau in figure 3 is not an end moraine then what is it and how did the Missouri Escarpment form?

Missouri Coteau and Missouri Escarpment southwest of Velva, North Dakota

Figure 4: Missouri Coteau and Missouri Escarpment southwest of Velva, North Dakota. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 4 illustrates the Missouri Coteau and Missouri Escarpment south and east of the figure 3 map area and includes overlap areas with figure 3. Red shaded areas located on the Missouri Escarpment slope (figure 4 south center) represent strip mine areas, where lignite coal was once mined. The Souris River flows southeast to Sawyer and Velva in a valley eroded into the lowland located at the Missouri Escarpment base. At Velva the Souris River turns to flow northeast and northeast of the figure 4 map area turns again to flow northwest and north to Canada. Souris River water eventually reaches Hudson Bay. Northeast-oriented Souris River tributaries drain the northeast-facing Missouri Escarpment slope. Note how the northwest-southeast oriented Missouri Escarpment continues southeast of where the Souris River turns at Velva to flow northeast. Also note in figure 4 southeast-oriented channels, which once were used by southeast-oriented flood routes, which were beheaded by headward erosion of the deeper northeast-oriented Souris River valley. This figure 4 map area provides evidence a southeast-oriented flood was captured and diverted to flow north. Water flowing southeast from the figure 4 map area could have been moving to the present day Sheyenne River and/or James River valleys. In the case of the Sheyenne River that river also makes a remarkable U-turn in southeast North Dakota, where it turns from flowing south to flowing northeast (with water eventually reaching Hudson Bay). Prior to being diverted north water in the Sheyenne River valley would have moved south to the south-oriented James River, which flows to the Missouri River in southern South Dakota. The Missouri Coteau is the area of hummocky topography and small lakes located in the figure 4 southwest section.

• In the figure 3 discussion the question was asked, what is the Missouri Coteau and how did the Missouri Escarpment form? The Missouri Escarpment and Missouri Coteau history are closely related to the history of a thick North American ice sheet (comparable in thickness to the present day Antarctic Ice Sheet) that rapidly melted. The thick North American ice sheet developed on a topographic surface now represented by high level Rocky Mountain erosion surfaces (if the topographic surface on which the thick North American ice sheet developed has been preserved at all). A deep North American “hole” was created by the thick ice sheet weight, which caused crustal down warping. In addition, deep glacial erosion probably further deepened ice sheet’s deep “hole”. Over time a considerable per cent of the ice sheet came to be located at elevations significantly below the ice sheet rim elevation, although a significant per cent of the ice sheet mass probably stood high above the ice sheet rim elevation. In terms of modern-day landscape features the ice sheet’s original rim elevation was probably comparable in elevation to present day high level Rocky Mountain erosion surfaces, if not higher. However, evidence to support that interpretation cannot be found in North Dakota (essay describing Missouri River drainage basin drainage divides in the high Rocky Mountains of Montana, Wyoming, and Colorado provide evidence for that interpretation). Exactly where this ice sheet’s southwest rim was located probably cannot be determined, because the rim has since been deeply eroded by melt water flood erosion. At some point in the ice sheet’s history the thick ice sheet began to melt faster than new ice was being formed. The figure 5 discussion continues the discussion of what happened in this Missouri River-Souris River drainage divide when the thick ice sheet, which was located in a deep “hole”, began to rapidly melt.

Missouri Coteau area near Max, North Dakota

Figure 5: Missouri Coteau area near Max, North Dakota. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 5 illustrates the Missouri Coteau and Missouri Escarpment south and west of the figure 4 map area (and includes overlap areas with figure 4). Max, North Dakota is the town located at the railroad junction located on the north-south red highway. The northeast-facing Missouri Escarpment slope is located in the figure 5 northeast corner (note the two small strip mine areas marked with red shading-they can be matched with the same location on figure 4). The remainder of figure 5 illustrates typical Missouri Coteau topography. Note the northeast-oriented streams draining the Missouri Escarpment slope in the figure 5 northeast corner. These streams provide the only integrated drainage pattern seen on figure 5 and are unusual in that they extend headward into the Missouri Coteau area. Figure 6 below provides a more detailed map of these drainage routes and discusses reasons why they may have been eroded headward into the Missouri Coteau region. But before addressing why the streams eroded headward into the Missouri Coteau region it is necessary to answer the question, what happened when the thick ice sheet began to rapidly melt?

• When the thick ice sheet rapid melt down began melt water rivers developed on the ice sheet surface. These supra-glacial rivers carved ice-walled and ice-floored valleys into the ice sheet surface, which eroded headward just as small gullies erode headward into unconsolidated clays. Over time some ice-walled and ice-floored river valleys developed extensive supra-glacial drainage networks. During periods of intense melting these supra-glacial rivers became immense melt water flood routes. Such melt water floods flowing to the ice sheet’s southern margin eventually flowed to the Gulf of Mexico and significantly eroded the landscape between the thick ice sheet’s southern margin and the Gulf of Mexico. In time melting progressed to the point where some ice-walled and ice-floored valleys became ice-walled and bedrock-floored valleys. One such giant ice-walled and bedrock-floored valley was carved by an immense southeast and south-oriented melt water river, named here as the Midcontinent River, which at its peak flowed from east central Alberta southeast through Saskatchewan to central North Dakota, where it turned to flow south to southern South Dakota. The Midcontinent River ice-walled and bedrock-floored valley (or canyon) is here named the Midcontinent Trench, and the Missouri Escarpment was formed as the Midcontinent Trench’s southwest and west wall.

• The Midcontinent Trench detached the thick ice sheet’s southwest margin in South Dakota, North Dakota and Saskatchewan. The detached ice sheet margin is named as the Southwest Ice Sheet and its northeast edge was located at the Missouri Escarpment crest. The Southwest Ice Sheet was an immense ice wall between melt water floods moving along the Southwest Ice Sheet’s southwest margin and on the Midcontinent Trench valley floor to the east and northeast. In time the Southwest Ice Sheet melted and whatever debris contained within that detached ice mass was deposited forming the present day Missouri Coteau. Melt water flood erosion along the Southwest Ice Sheet’s southwest and west margin removed much of that debris, although closer to the Missouri Escarpment, where that ice marginal melt water flood erosion was not as intense, debris deposited by the melting Southwest Ice Sheet still remains and the landscape looks what is seen in figure 5.

Oak Creek valley in Missouri Coteau

Figure 6: Oak Creek valley in Missouri Coteau. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 6 provides a more detailed map of the Oak Creek valley, which heads in the Missouri Coteau and then drains northeast down the Missouri Escarpment slope (the figure 6 map area is shown in less detail in figure 4 and 5. Oak Creek flows north and northwest from the figure 6 south center edge area into Newman Township and then turns to flow in a northeast direction down the Missouri Escarpment Slope (to the figure 6 north center edge area). Bonnes Coulee is the north and northeast-oriented drainage route flowing to the figure 6 northeast corner area (with red shaded strip mine areas located adjacent to its valley). The presence of the strip mine areas along the Missouri Escarpment slope is evidence glacial deposits are thin and bedrock containing lignite coal seams are located close to the surface. Note how typical Missouri Coteau topography (with numerous small hills and lakes) is located in the figure 6 southeast corner area and also in the western third of figure 6. Between the two areas of typical Missouri Coteau topography is an area drained by north and northeast-oriented Oak Creek and Bonness Coulee headwaters. A close look at the Oak Creek and Bonness Coulee headwaters are reveals an anastomosing complex of channels, such as might be expected to develop during a north or northeast-oriented flood event. What happened in the figure 6 map area that was different from what happened to the northwest and southeast (see figures 3 and 4 to make a comparison)?

• As previously mentioned the Missouri Escarpment developed as the southwest wall of the large southeast-oriented Midcontinent Trench when the southeast-oriented Midcontinent River sliced a deep ice-walled and bedrock-floored valley into the rapidly melting thick ice sheet surface. The Midcontinent Trench detached the ice sheet’s southwest margin, which then served as a massive ice wall between ice marginal melt water floods and the Midcontinent Trench floor. Also, as previously mentioned the thick ice sheet was located in a deep “hole”, which meant the ice sheet floor elevation was considerably lower than elevations along the ice sheet rim. Deep melt water flood erosion along the ice sheet’s rim did significantly lower the ice sheet’s rim elevation, especially close to the melting ice sheet’s southwest margin. However, even with that rim lowering the area immediately southwest of the ice sheet’s detached southwest margin was still higher in elevation than the Midcontinent Trench floor. Wherever possible ice marginal melt water floods broke through the Southwest Ice sheet ice wall barrier to flow to the deeper Midcontinent Trench floor. Breaches ranged in size from large rivers that cut deep ice-walled and bedrock-floored valleys to flow through narrow ice-walled and ice-floored valleys (and/or tunnels). This indentation in the Missouri Coteau at the headwaters of Oak Creek and Bonness Coulee was probably developed by flood water moving north and northeast to the deeper Midcontinent Trench floor from southwest of the Southwest Ice Sheet southwest margin.

Missouri Coteau area north and east of Garrison Dam, North Dakota

Figure 7: Missouri Coteau area north and east of Garrison Dam, North Dakota. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 7 illustrates the Missouri Coteau area north and east of Garrison Dam and south of the figure 5 map area (and includes overlap areas with figure 5). Garrison Dam is located in the figure 7 southwest corner and the former Missouri River channel upstream from Garrison Dam is shown. Note how the Missouri River changes from being east-oriented to being south oriented in the figure 7 southwest corner. The flooded Missouri River valley west of the north-south red highway is Lake Sakakawea and the flooded valley east of the highway is Lake Audubon. Note how Lake Audubon has two arms, with one arm extending to the northeast and the other larger arm extending in an east-southeast direction. The northeast-oriented arm is flooding the valley of south and southwest-oriented Snake Creek. The south-oriented Snake Creek headwaters valley if extended north leads to the Oak Creek and Bonnes Coulee headwaters area seen in figure 6 above. There may be a relationship between the two, although topographic map evidence alone probably is not adequate to say for sure. The east-southeast oriented Lake Audubon arm leads to an east-southeast lowland now occupied by several lakes. Note how today the McClusky Canal extends from the Lake Audubon southwest arm to the figure 7 southeast corner area. The McClusky Canal is a major irrigation canal constructed to move water from Lake Audubon across the Missouri Coteau to the lower Midcontinent Trench area to the east. A pumping plant can lift water from Lake Sakakawea to Lake Audubon, although when Lake Sakakawea is full no pumping is needed. Once in Lake Audubon the water can flow without further pumping through the McClusky Canal to the James River valley, which is located in the Midcontinent Trench southeast and south of figure 5. The low sag in the Missouri Coteau area (used today by the McClusky Cana)l once was a major east-oriented breach (probably an ice-walled and bedrock-floored valley), which had been eroded across the Southwest Ice Sheet massive ice wall. The east-oriented Missouri River upstream from Garrison Dam probably eroded headward from the east-oriented breach and probably eroded west to capture the north-oriented Little Missouri River (see figure 1). At that time the Little Missouri River valley had eroded south and southwest to capture immense southeast-oriented melt water floods and to divert the flood waters north and northeast to the lower elevation thick ice sheet margin area and then across the Southwest Ice Sheet surface and/or through Southwest Ice Sheet breaches to the lower elevation Midcontinent River initially moving south and southeast on the thick ice sheet floor. Later, when the Midcontinent River was dismembered the flood waters were diverted north.

Missouri Coteau area north and west of Douglas Creek Bay

Figure 8: Missouri Coteau area north and west of Douglas Creek Bay.United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 8 illustrates the Missouri Coteau area north of Lake Sakakawea (or the Missouri River valley) and is located west of the figure 7 map area. Unlike Missouri Coteau areas seen in earlier figures the figure 8 map area does have some semblance of an integrated drainage pattern, especially close to the flooded Missouri River valley. Garrison, North Dakota is the town located along the figure 8 east center edge. South of Garrison is Garrison Bay, which is the flooded valley of Garrison Creek, which flows south, southeast, and south to the Missouri River valley. West of Garrison Bay is the much larger Douglas Creek Bay, which floods the valleys of the south-southwest oriented East Branch Douglas Creek, south-oriented Middle Branch of Douglas Creek, and southeast-oriented West Branch Douglas Creek. In the Fort Berthold Indian Reservation area in the figure 8 southwest quadrant southeast-oriented Nishu Bay is the flooded valley of southeast-oriented Sixmile Creek.The presence of an integrated drainage pattern in figure 8 is a change from the Missouri Coteau area further north and east (where no integrated drainage pattern is present). The figure 8 map area is located on the Missouri Coteau, but is located on the southwest margin where there is drainage to the Missouri River valley.

• Why is there an integrated drainage pattern on the Missouri River side of the Missouri Coteau and not on the Souris River side? Melt water floods flowed southeast along the ice sheet’s southwest margin because the thick ice sheet was located in a deep “hole”. As melting lowered the thick ice sheet’s surface elevation deep northeast-oriented valleys eroded headward from the deep “hole” (in which the rapidly melting ice sheet was located) to capture the southeast-oriented ice-marginal floods and divert flood waters northeast into space the thick ice sheet had once occupied. As previously mentioned the Southwest Ice Sheet southwest margin was deeply eroded by immense ice marginal floods that at times broke through the Southwest Ice Sheet ice wall barrier and flowed northeast to the lower Midcontinent Trench floor to the northeast. Probably some of that flood flow moved over Southwest Ice Sheet margin areas still covered with decaying ice sheet remnants. When headward erosion of the deep southeast-oriented Missouri River valley reached the figure 8 it captured the southeast-oriented ice-marginal flood flow and also beheaded and reversed flood flow routes leading to narrow Southwest Ice Sheet breaches. The southeast-oriented West Branch Douglas Creek and Sixmile Creek valleys were probably initiated as southeast-oriented flood flow channels in a southeast-oriented ice-marginal anastomosing channel complex, which the deep Missouri River valley eroded headward into and captured.

Missouri Coteau area north and east of Deepwater Creek Bay

Figure 9: Missouri Coteau area north and east of Deepwater Creek Bay. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Figure 9 illustrates the Missouri Coteau area north and east of Deepwater Bay and west and slightly north of figure 8 (and includes overlap areas with figure 8). Southeast-oriented Sixmile Creek and Nishu Bay are located near the figure 9 south center edge area. Southeast-oriented West Branch Douglas Creek is located in the figure 9 southeast quadrant and headwaters flow northwest and northeast to White Shield before turning to flow southeast to Douglas Creek Bay (as seen in figure 8). Deepwater Bay is the large bay located in the figure 9 west center area and is the flooded valley of Deepwater Creek. Deepwater Creek flows south-southeast from the figure 9 north center edge area and then turns to flow southwest to Deepwater Bay. The southwest-oriented Deepwater Creek segment has northwest-oriented tributaries, some of which are aligned with southeast-oriented West Branch Douglas Creek. A broad northwest-southeast oriented through valley links the southwest-oriented Deepwater Creek valley with the southeast-oriented West Branch Douglas Creek valley. The through valley provides evidence of a large southeast-oriented flood flow channel parallel to the southeast-oriented flood flow channel the deep Missouri River valley eroded headward along. Note how the Missouri River valley changes direction in the figure 9 southwest quadrant. The direction change is related to the Little Missouri River, which enters the Missouri River just west of the figure 9 southwest corner. East of the Little Missouri River mouth the Missouri River valley is east-southeast and east oriented to the figure 7 map area. Immediately upstream from the Little Missouri River mouth the Missouri River valley is almost south-oriented, although it becomes much more complex northwest of the Deepwater Bay area (see figure 10 below). Just prior to headward erosion of the Missouri River valley between the Little Missouri River mouth area and the Deepwater Bay area there were at least two major southeast-oriented flood flow routes across the figure 9 map area. One flood flow route was carrying flood waters from the Little Missouri River valley east and east-southeast along the present day Missouri River valley route. The other flood flow route was carrying southeast-oriented ice-marginal flood waters to the Deepwater Bay area and then southeast to the West Branch Douglas Creek valley. Headward erosion of the deep Missouri River valley then beheaded the southeast-oriented flood flow route to the West Branch Douglas Creek valley. Flood flow reversals on northwest ends of the beheaded flood flow routes were responsible for creating the present day northwest-oriented Deepwater Creek tributary valleys.

Missouri Coteau area east and south of Shell Creek

Figure 10 illustrates the Missouri Coteau area east and south of Shell Creek and is located north and west of the figure 9 map area (and includes overlap areas with figure 9). The Missouri River is southeast oriented in the figure 10 northwest corner, but turns to flow south-southwest and then southeast to the figure 10 south center area, where it makes a jog to the northeast before flow south-southeast to the Deepwater Bay area along the figure 10 south edge. New Town is the largest town located in the figure 10 northwest quadrant and Sanish is located west of New Town. New Town is located in a northwest-southeast oriented through valley linking west-oriented Sanish Bay with south-southeast oriented Van Hook Arm. Note another prominent northwest-southeast oriented through valley crossing the peninsula separating the Missouri River valley from Van Hook Arm. These multiple northwest-southeast oriented through valleys are evidence of multiple southeast oriented (and probably anastomosing) flood flow channels that existed prior to headward erosion of the deep Missouri River valley.  Parshall, North Dakota is the town located in the figure 10 northeast quadrant. The west-southwest oriented stream flowing through Parshall is the East Fork Shell Creek, which flows to Shell Creek Bay, which has flooded the southwest-oriented Shell Creek valley. The stream flowing to the north end of Van Hook Arm is southeast and south oriented Crane Creek. Van Hook Arm provides evidence of broad south-southeast oriented valley extending headward from the Missouri River valley to the northwest-southeast oriented through valley at New Town. These multiple “parallel” valleys were probably eroded during an immense ice-marginal southeast-oriented flood event, with headward erosion of the Missouri River valley beheading flood flow moving to the Van Hook Arm channel.

• Why would an immense melt water flood move southeast along the Southwest Ice Sheet southwest margin when there were northeast-oriented ice-walled and bedrock-floored valleys both upstream and downstream that could move the flood waters northeast to the deeper Midcontinent Trench floor? The thick ice sheet rapid melt down ended when a sudden climate change froze flood waters on the thick ice sheet floor and reinvigorated thick ice sheet remnants (such as the detached Southwest Ice Sheet ice masses). Freezing of flood waters to the north and reinvigorating the Southwest Ice Sheet effectively blocked flood waters still south and west of the Southwest Ice Sheet from moving northeast to the Midcontinent Trench floor. Flood waters instead had to flow southeast along the Southwest Ice Sheet southwest margin (i. e. where that southwest margin was located at that time). This change in flood water flow direction from northeast to southeast resulted in the erosion of the present day Missouri River valley along the Southwest Ice Sheet southwest margin.

• Why did the climate suddenly change during final stages of the thick ice sheet’s rapid melt down? Evidence to answer the question is not found in the Missouri River-Souris River drainage divide area. However, some evidence is located nearby and can be seen in figure 10a below. The Midcontinent River began as an immense southeast and south-oriented supra-glacial melt water river flowing to the ice sheet’s south margin. Over time as the thick ice sheet melted the Midcontinent River carved a deep ice-walled and bedrock-floored valley into the thick ice sheet mass (the Midcontinent Trench). At the same time as south-oriented melt water rivers were eroding headward into the decaying ice sheet, north-oriented melt water rivers were doing the same along the ice sheet’s north margins. When headward erosion of the south-oriented ice-walled and bedrock-floored valleys intersected with the headward erosion of the north-oriented ice-walled and bedrock-floored valleys there were rapid and massive flood flow reversals. North-oriented melt water rivers had shorter routes to the ocean and captured south-oriented melt water rivers and diverted the water north. The Midcontinent River was captured in southeast North Dakota, north central North Dakota, and again further to the northwest. The Souris River elbow of capture in figure 10a below provides evidence of the north central North Dakota capture (where the immense southeast-oriented Midcontinent River was captured and diverted to flow north). These captures over a very short time interval diverted melt water floods from flowing south to the Gulf of Mexico to flowing north to Hudson Bay. The result was a rapid change in Atlantic Ocean currents, which caused a sudden Northern Hemisphere cooling event. That cooling event froze north-oriented melt water floods on the former ice sheet floor and reinvigorated the Southwest Ice Sheet ice wall, which in turn blocked northeast-oriented flood waters from moving to the Midcontinent Trench floor and forced flood waters southwest of the Southwest Ice Sheet to flow southeast along the Southwest Ice Sheet southwest margin (and to erode the Missouri River valley).

Figure 10a: Souris River loop illustrates capture of southeast-oriented melt water flood waters by a north-oriented flood flow route to Hudson Bay (the figure 10a north edge is the Canada-United States border). Note how the Souris River flows south-southeast in Renville and Ward Counties and then at Velva (near the figure 10a south edge) turns northeast to Towner and then northwest and northwest to the Canadian border. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

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.