Abstract:

Introduction:

• The purpose of this essay is to use topographic map interpretation methods to explore Missouri River-Des Lacs River drainage divide area landform origins between Little Knife River and Shell Creek in Mountrail County, 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-Des Lacs River drainage divide area landform evidence between Little Knife River and 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-Des Lacs River drainage divide area location map

Figure 1: Missouri River-Des Lacs River drainage divide area between Little Knife River and Shell Creek 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-Des Lacs River drainage divide area between Little Knife River and 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 Canadian province in the figure 1 northeast corner. The state south of the Canadian border is North Dakota. Lake Sakakawea is a large reservoir flooding the Missouri River valley upstream from Garrison Dam, which is located just south of the figure 1 south center edge (south of Garrison, 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. The Des Lacs River is located immediately west of the southeast-oriented Souris River in North Dakota and flows from near Portal, North Dakota to Kenmare and then to join the Souris River near Burlington, North Dakota. The White Earth River is a south-oriented Missouri River tributary located southwest of the Des Lacs River and as shown in figure 1 flows south from near Powers Lake through the town of White Earth to the Missouri River. The Little Knife River on figure 1 is the unnamed southwest-oriented Missouri River tributary located between the White Earth River and southwest-oriented Shell Creek, which is located south of Blaisdell and which flows south and southwest to the flooded Missouri River valley. The Little Knife River on figure 1 flows southwest from Stanley, North Dakota to join the Missouri River near New Town, North Dakota. This knol illustrates and discusses the Missouri River-Des Lacs River drainage divide area between the Little Knife River and Shell Creek.

• This essay uses topographic maps to illustrate how the Missouri River and Des Lacs 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 in detailed topographic maps below. The Missouri Coteau briefly is a region of hummocky topography 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 and which drains to the Des Lacs and Souris Rivers. Essays describing the region west of the Little Knife River are the White Earth River-Little Knife River drainage divide area essay and the Little Muddy River-White Earth River drainage divide area essay and can be found under ND Missouri River on the sidebar category list. Detailed maps illustrated below begin with the Des Lacs River valley and Missouri Escarpment located at the northeast margin of the Missouri Coteau. The Missouri Coteau is interpreted here as being 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) in is referred to in other essays as the Midcontinent Trench, which was eroded by an immense southeast and south-oriented glacial melt water river. The immense river, which originated as a melt water flow route on a 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-Des Lacs River drainage divide area detailed location map

Figure 2: Missouri River-Des Lacs River drainage divide area detailed 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-Des Lacs River drainage divide area. Mountrail, Renville, 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. The flooded Missouri River valley is located in the figure 2 southwest quadrant. The Missouri River valley is today flooded by Lake Sakakawea, which is a large reservoir impounded behind Garrison Dam (not shown in figure 2). The Little Knife River originates near Stanley (in north central Mountrail County) and flows southwest and south-southwest to join the southeast-oriented Missouri River near New Town (located on the figure 2 south center edge). Shell Creek originates northwest of the Shell Lake National Wildlife Refuge (located south of Blaisdell) and after flowing southeast turns to flow southwest to the flooded Missouri River valley. The Des Lacs River flows south and southeast through the Des Lacs National Wildlife Refuge near Kenmare in the figure 2 north center edge area and then flows southeast to join the south-southeast oriented Souris River near the figure 2 east edge. Note numerous short northeast-oriented Des Lacs River tributaries. Those northeast-oriented tributaries are draining the northeast-facing Missouri Escarpment slope. This essay attempts to explain the origin of Little Knife River and Shell Creek valleys and their relationship to the present day Missouri River and Des Lacs River valleys as well as their relationship to the Missouri Coteau and Missouri Escarpment. Detailed maps below begin with a look at the Missouri Escarpment and Des Lacs River valley in the figure 2 north center area and proceed south across the Missouri Coteau to the Little Knife River and Shell Creek headwaters area. Detailed maps then follow the Little Knife River-Shell Creek drainage divide to the Missouri River valley and proceed south along the present day peninsula south of New Town, North Dakota.

Missouri Coteau and Missouri Escarpment southwest of Kenmare

Figure 3: Missouri Coteau and Missouri Escarpment southwest of Kenmare. 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 Kenmare, North Dakota. The Des Lacs River flows from Middle Des Lacs Lake to Lower Des Lacs Lake and to the figure 3 southeast corner area. Many areas in the figure 3 Des Lacs River valley are included in the Des Lacs National Wildlife Refuge. The hummocky topography with many small lakes in the figure 3 southwest section is the Missouri Coteau. Missouri Coteau landscape is typical of glacial moraine regions and in figure 3 is interpreted to be covered by moraine materials deposited by a decaying ice sheet remnant. The northeast facing slope from the lowland in the figure 3 northeast section (into which the Des Lacs River valley has been eroded) to the higher elevation Missouri Coteau is the Missouri Escarpment. 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 southeast South Dakota. The relationship for that entire distance is similar to the relationship seen in this essay. There is a lowland northeast or east of the northeast or east-facing Missouri Escarpment and at the crest of the Missouri Escarpment 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 near the Missouri Escarpment crest. Southwest of those thickest glacial moraines there is some evidence of integrated drainage patterns leading to the Missouri River and the glacial moraine evidence is less obvious, although still may be present. The Missouri River represents the Missouri Coteau southwest and west margin and is generally a narrow valley eroded into an upland surface, which is considerably higher than the lowland northeast and east of the Missouri Escarpment. Southwest and west of the Missouri River any evidence of glaciation with a few exceptions cannot be identified using topographic maps alone. The Missouri Coteau and Missouri Escarpment continue northwest of the figure 3 map area into Saskatchewan and east central Alberta, 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 east central Alberta to south central South Dakota. It is tempting to interpret the Missouri Coteau 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 evidence of Missouri Coteau type glacial moraine material appear to be missing from the Missouri Escarpment slope and from the lowland northeast of the Missouri Escarpment. If the Missouri Coteau is not an end moraine then what is it and how did the Missouri Escarpment form?

Missouri Coteau and Missouri Escarpment southwest of Des Lacs River

Figure 4: Missouri Coteau and Missouri Escarpment southwest of Des Lacs River. 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. The Des Lacs River flows southeast in a valley eroded into the lowland located at the Missouri Escarpment base. The Missouri Coteau is the area of hummocky topography and small lakes located in the figure 4 southwest section. The northeast-facing Missouri Escarpment rises from the lowland into which the Des Lacs River valley has been eroded to the Missouri Coteau edge. The Missouri Escarpment slope is well-drained  by northeast-oriented streams referred to as coulees. Continuing with the figure 3 discussion, what is the Missouri Coteau and how did the Missouri Escarpment form? To answer the question it is necessary to describe a thick North American ice sheet (comparable in thickness to the present day Antarctic Ice Sheet). 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). The weight of the thick ice sheet caused crustal warping, which combined with deep glacial erosion created a deep “hole” in the North American continent. As a result 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. The ice sheet rim elevation probably was equivalent to the elevation of present day high level Rocky Mountain erosion surfaces (although drainage divide in the high Rocky Mountains need to be studied to make 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 described in this Missouri River drainage basin research project essay series. At some point in the ice sheet’s history the thick ice sheet began to melt faster than new ice was being formed. Figure 5 below illustrates the region south of figure 4 and the figure 5 discussion continues the discussion of what happened in this Des Lacs River-Missouri River drainage divide area when the thick North American ice sheet, which was located in a deep “hole”, began to rapidly melt.

Missouri Coteau and Missouri Escarpment east of Blaisdell

Figure 5: Missouri Coteau and Missouri Escarpment east of Blaisdell. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 5 illustrates the Missouri Coteau and Missouri Escarpment east of Blaisdell and south of the figure 4 map area (and includes overlap areas with figure 4). The northeast-facing Missouri Escarpment slope is located in the figure 5 northeast section. The remainder of figure 5 illustrates typical Missouri Coteau topography. Continuing with the discussion, what happened when the thick ice sheet began to rapidly melt? Melt water moving to the ice sheet margins developed drainage systems or rivers on the ice sheet surface. These supra-glacial rivers flowed across the ice sheet surface to ice sheet margins and in doing so carved ice-walled and ice-floored valleys into the ice sheet surface. These ice-walled and ice-floored valleys eroded headward into the ice sheet surface, just as gullies erode headward into easily eroded sedimentary rock today. And, just as some gullies erode more successfully than others, some of these ice-walled and ice-floored valleys were more successful than others and in time captured extensive drainage networks on the ice sheet surface. During periods of intense melting these supra-glacial rivers became immense melt water flood routes across the ice sheet surface to the ice sheet margin and eventually to the Gulf of Mexico. These immense melt water floods eroded the landscape between the Gulf of Mexico and the ice sheet margin and later as melting lowered the ice sheet surface below the deep “hole” rim elevation also deeply eroded the ice sheet rim. In time melting progressed to the point where the largest of the ice-walled and ice-floored valleys became ice-walled and bedrock-floored valleys. The Missouri Escarpment represents the west and southwest wall of a giant ice-walled and bedrock-floored valley carved by an immense melt water river (which is named in this essay series as the Midcontinent River and the immense southeast and south-oriented valley is here named as the Midcontinent Trench). Headward erosion of the deep ice-walled and bedrock-floored Midcontinent Trench into the rapidly melting thick ice sheet mass for all practical purposes detached the ice sheet’s southwest margin. 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 gradually became a northwest-southeast and north-south oriented thick ice sheet remnant or an immense ice wall between melt water floods moving along the Southwest Ice Sheet’s southwest margin (wherever that southwest margin was located at that time) and the much lower elevation 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 as glacial moraine material. Melt water flood erosion along the Southwest Ice Sheet’s southwest and west margin removed much of that debris, although close to the Missouri Escarpment, where that ice marginal melt water flood erosion was not intense the thick debris deposited by the Southwest Ice Sheet still remains and forms the Missouri Coteau.

Little Knife River and Shell Creek headwaters area

Figure 6: Little Knife River and Shell Creek headwaters area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 6 illustrates the Little Knife River and Shell Creek headwaters area west and south of the figure 5 map area and includes overlap areas with figure 5. The Little Knife River originates in the figure 6 northwest quadrant and drains northwest before turning to flow southwest to the figure 6 west edge. Shell Creek originates in the figure 6 southeast quadrant as a south-southeast oriented stream, but has both northeast and southwest tributaries. The presence of an integrated drainage pattern in the figure 6 northwest and southeast quadrants is a change from the Missouri Coteau area further to the north and east (where no integrated drainage pattern is present). The figure 6 map area is located on the Missouri Coteau, but is located on the southwest side of the Missouri Coteau 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 Des Lacs River side? Melt water floods resulting from the thick ice sheet’s rapid melt down not only flowed across the thick ice sheet’s surface in immense melt water rivers like the Midcontinent River, but also flowed southeast along the ice sheet’s southwest margin. Some of the immense southeast oriented floods probably reached the ice sheet’s margin in western Alberta and may have flowed southeast in the present day Rocky Mountain Trench (located in western British Columbia) to reach western Montana. 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 floods and to divert the flood waters northeast into space the thick ice sheet had once occupied. While routes the immense melt water floods took evolved as the thick ice sheet melted, immense melt water floods flowed northeast toward the ice sheet’s southwest margin and, once the ice sheet’s surface elevation had been lowered, also flowed onto the ice sheet’s surface to what was then the deep southeast and south oriented Midcontinent Trench. To reach the Midcontinent Trench flood waters eroded ice-walled and ice-floored valleys and in some locations ice-walled and bedrock-floored valleys. After the Southwest Ice Sheet became detached northeast-oriented ice-walled and bedrock-floored valleys further segmented the Southwest Ice Sheet into a northwest-southeast and north-south oriented chain of smaller ice sheet masses. No such ice-walled and bedrock-floored valleys existed in the Des Lacs River-Missouri River drainage divide area being illustrated and discussed in this essay. However, there were probably narrow ice-walled and ice-floored valleys that did permit northeast-oriented flood waters from southwest of the Southwest Ice Sheet ice wall to reach the much deeper Midcontinent Trench floor to the northeast. These northeast-oriented flood flow routes were captured by headward erosion of tributary valleys when the deep Missouri River valley eroded headward into the region and for that reason the Missouri Coteau southwest margin was more intensely eroded by flood water than the northeast margin.

Little Knife River-Shell Creek drainage divide area near Epworth

Figure 7: Little Knife River-Shell Creek drainage divide area near Epworth. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 7 illustrates the Little Knife River-Shell Creek drainage divide area near Epworth and is located south of the figure 6 map area (and includes overlap areas with figure 6). The southeast and southwest-oriented Little Knife River is located in the figure 7 northwest quadrant. South-southeast and south-southwest oriented Shell Creek is located along the figure 7 east edge. Southwest-oriented Crane Creek originates in the figure 7 center area. The southwest-oriented stream at Epworth is West Shell Creek, which near the figure 7 south edge turns to flow southeast to join Shell Creek. Note how several of the present day valleys, such as the Little Knife River valley and the West Shell Creek valley, have incised meanders.These incised meanders may be evidence the valleys were initiated at a time when ice still covered the region. If so, the valleys were initiated as ice-walled and bedrock-floored valleys. This figure 7 map area illustrates a region on the southwest side of the Missouri Coteau. The presence of small lakes and the poorly integrated drainage pattern in significant areas of the figure 7 map area suggest glacial moraine materials are present, although probably not as thick as in the Missouri Coteau regions further to the north and east. As previously mentioned the southwest margin of the detached Southwest Ice Sheet was deeply eroded by immense ice marginal floods that at times were able to break through the Southwest Ice Sheet ice wall barrier and flow northeast to the lower Midcontinent Trench to the northeast. Some of the present day southwest-oriented Missouri River tributary valleys may have been initiated as northeast-oriented valleys to such Southwest Ice Sheet breaches. However, breaches in the drainage divide illustrated and discussed in this essay were not large enough to handle all of the flood flow and considerable flood flow also moved southeast along the Southwest Ice Sheet southwest margin. 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 region south of figure 7 it captured the southeast-oriented ice-marginal flood flow and also beheaded and reversed northeast-oriented flood flow routes leading to narrow Southwest Ice Sheet breaches. Flood waters on the southwest ends of the beheaded northeast-oriented flood flow routes reversed flow direction to flow southwest to the newly eroded and deep Missouri River valley. These reversed flood flow routes eroded the present day southwest-oriented Missouri River tributary valleys into the Southwest Ice Sheet southwest margin area.

Little Knife River-Shell Creek drainage divide area northeast of New Town

Figure 8: Little Knife River-Shell Creek drainage divide area northeast of New Town.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 8 illustrates the Little Knife River-Shell Creek drainage divide area south and west of figure 7 and includes overlap areas with figure 7. The Little Knife River meanders south along the figure 8 west edge to Little Knife Bay, which is the flooded Little Knife River valley. Little Knife Bay has been flooded by Lake Sakakawea, which has flooded the Missouri River valley upstream from Garrison Dam. Shell Creek flows southwest from Epworth (in the figure 8 northeast corner) and then turns southeast, south, and southwest to enter Shell Creek Bay (the bay by the Van Hook State Wildlife Management Area in the figure 8 southeast quadrant). Crane Creek flows southwest and south through the figure 8 center area to Van Hook Arm, which is the large bay located along the figure 8 south center edge. Note the southeast-oriented Crane Creek and Shell Creek tributaries, which provide evidence the Crane Creek valley and Shell Creek valley eroded headward across multiple southeast-oriented flood flow routes. Further evidence of southeast-oriented flood flow routes can be seen in the figure 8 southwest quadrant where New Town is located in a large northwest-southeast oriented through valley linking northwest- and west-oriented Sanish Bay with southwest-oriented Van Hook Arm (see figure 9 for a better illustration). The through valley combined with additional through valleys seen in figures 9 and 10 below (including the present day Missouri River valley) provides evidence of multiple southeast-oriented flood flow routes such as might be expected in a southeast-oriented anastomosing channel complex. In other words, the southeast-oriented Missouri River valley did not erode headward into the region as a single deep channel, but as a series of roughly parallel and probably constantly changing anastomosing channels, with the deep Missouri River valley eroding headward along those ever-changing anastomosing channels. Headward erosion of the deep Missouri River valley channel (located just west of Sanish Bay and Little Knife Bay-see figure 9) beheaded southeast-oriented flood flow across the New Town through valley to the southeast-oriented Van Hook Arm channel, although it is possible factors not visible on topographic maps also played a role in this capture event. However the capture event occurred headward erosion of the deep Missouri River valley captured southeast-oriented flood from the adjacent channels.

Missouri River-Van Hook Arm drainage divide area south of New Town

Figure 9: Missouri River-Van Hook Arm drainage divide area south of New Town.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 9 illustrates the Missouri River-Van Hook Arm drainage divide area south and west of the figure 8 map area and includes overlap areas with figure 8. The Missouri River flows southeast from the figure 9 northwest corner before turning southwest to flow to the figure 8 west center edge (figure 10 below illustrates the Missouri River course west and south of figure 9). Van Hook Arm is a large south-southeast oriented bay in Lake Sakakawea (the reservoir impounded behind Garrison Dam). Van Hook Arm is the flooded south-southeast oriented Little Knife River valley. Shell Creek is the flooded Shell Creek valley. The land mass between the Missouri River and Van Hook Arm is today a large peninsula almost completely surrounded by Lake Sakakawea, although prior to Garrison Dam it was the drainage divide between the north-oriented Missouri River to the west and the south-southeast oriented Little Knife River to the east. The northwest-southeast oriented through valley linking Sanish Bay with Van Hook Arm has already been mentioned. Another northwest-southeast oriented through valley eroded across this present day peninsula is located in the figure 9 southwest quadrant (extending southeast from Reunion Bay and better seen in figure 10). In addition to the through valleys there is additional evidence the drainage divide was once crossed by multiple southeast-oriented flood flow routes (or channels). Near Sanish are southeast-oriented streams that turn to flow northeast and then northwest to Sanish Bay. The southeast-oriented headwaters of those streams provide evidence of multiple southeast-oriented flood flow routes across the drainage divide in the Sanish area. The northeast-oriented stream probably captured the southeast-oriented flood flow when the deeper northwest-southeast oriented through valley from Van Hook Arm to Sanish Bay was eroded. The northwest-oriented valley segment developed as a reversal of southeast-oriented flood flow when headward erosion of the deep Missouri River valley beheaded and reversed flood flow moving southeast from the Sanish Bay area to the Van Hook Arm area. Proceeding south along the peninsula there is additional evidence of southeast-oriented drainage routes which were captured and diverted to flow north-northeast to what at one time was the deep southeast-oriented through valley from Sanish Bay to Van Hook Arm.

Missouri River-Van Hook Arm drainage area north of Missouri River

Figure 10: Missouri River-Van Hook Arm drainage area north of Missouri River.United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 10 illustrates the south end of the Missouri River-Van Hook Arm drainage divide area south of the figure 9 map area and includes overlap areas with figure 9. The Mountrail -Dunn County boundary is located along the Missouri River channel (before flooding by Lake Sakakawea). The northwest-southeast oriented through valley extending southeast from Reunion Bay is better illustrated here than in figure 9. Note how the northwest end of that through valley is drained by a northwest-oriented stream to Reunion Bay and the southeast end is drained by a southeast-oriented stream to Muskrat Lake. Note the prevalence of southeast-oriented drainage on the peninsula’s south end. Northwest-oriented Missouri River tributaries at Reunion Bay and elsewhere in figures 9 and 10 were developed by reversals of flood flow on the northwest ends of beheaded southeast-oriented flood flow routes. Evidence for multiple southeast-oriented channels suggests the deep Missouri River valley eroded headward to capture southeast-oriented flood flow moving in multiple southeast-oriented anastomosing channels. Why would melt water floods move southeast along the Southwest Ice Sheet southwest margin when there were northeast-oriented ice-walled and bedrock-floored valleys 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 ice masses 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 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 Des Lacs River-Missouri River drainage divide area illustrated and discussed in this knol. However, some evidence is located nearby and can be seen in figure 10a below. The Midcontinent River as previously described began as an immense southeast and south-oriented supra-glacial melt water river flowing to the thick ice sheet 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 they captured south-oriented melt water rivers and diverted the flood water north. The Midcontinent River was captured in southeast North Dakota, north central North Dakota, and also 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 (and perhaps the Arctic Ocean). The result was a rapid change in Atlantic Ocean currents, which caused a sudden Northern Hemisphere cooling event. It was that cooling event that 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.

Figure 10a: Souris River loop illustrates capture of southeast-oriented melt water flood by opening up of 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 to northeast to Towner and then to 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.