A geomorphic history based on topographic map evidence

This essay provides an overview of more detailed Elkhorn River drainage basin essays, which can be found under Elkhorn River on this website’s sidebar category list. All essays use topographic map evidence to interpret Elkhorn River drainage basin landform origins. The Elkhorn River drainage basin is located in northeast Nebraska. The Elkhorn River originates near Bassett and flows in a southeast and northeast direction to Stuart and then flows in a generally southeast direction through O’Neill, Neligh, Norfolk, and Wisner before turning to flow in a south-southeast direction through West Point and Scribner to join a south-southeast oriented Platte River segment near Elkhorn (located a short distance west of Omaha, Nebraska). Approximately 100 topographic maps are included in detailed essays and are used to illustrate and interpret drainage history along numerous drainage divide areas within the Elkhorn River drainage basin and between the Elkhorn River drainage basin and adjacent drainage basins. The Elkhorn River valley and its tributary valleys eroded headward from what was then a newly eroded Missouri River-Platte River valley to capture two immense floods converging in what is today the Elkhorn River drainage basin. One of the immense floods was oriented in southeast direction and moving across the entire present day Elkhorn River drainage basin area. The other flood was moving in a south direction and was flowing across what is today the eastern Elkhorn River drainage basin. Flood waters were derived from a rapidly melting thick North American ice sheet and the southeast oriented flood waters were flowing along what was then the ice sheet’s southwest margin while the south-oriented flood waters were emerging from giant ice-walled and bedrock-floored canyons carved into the decaying ice sheet surface. Headward erosion of the south-southeast oriented Elkhorn River valley and parallel south-southeast oriented Missouri River valley (to the east) probably occurred at about the same time. Headward erosion of the deeper Missouri River valley in time beheaded south-oriented flood flow routes to the south-southeast oriented Elkhorn River valley and its south-southeast oriented Logan Creek tributary valley while southeast oriented flood water continued to flow into the Elkhorn River drainage basin from the northwest and what is today the southeast and east oriented Elkhorn River valley segments eroded headward along and across those flood flow routes and beheaded flood flow routes to what had been actively eroding southeast-oriented Platte River and Loup River tributary valleys. Subsequently Niobrara River valley headward erosion beheaded all southeast-oriented flood flow routes to what had been the actively eroding southeast-oriented Elkhorn River valley and its tributary valleys and created the present day Niobrara River-Elkhorn River drainage divide.

Figure 1: Northeast Nebraska Elkhorn River drainage basin location map (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.

Elkhorn River drainage basin history

This northeast Nebraska Elkhorn River drainage basin landform origins overview essay and its related detailed essays is one of a series of Missouri River drainage basin landform origins research project overview essays and related detailed essays. The research project goal is to use topographic map evidence to interpret the evolution of drainage divides separating each significant present day Missouri River tributary valley and also to determine the evolution of drainage divides separating the present day Missouri River drainage basin from adjacent drainage basins. Each overview essay and its related detailed essays pertains to a specific Missouri River tributary, tributary to a present day Missouri River tributary, or a present day Missouri River valley segment. Each detailed essay illustrates and discusses detailed topographic map evidence describing the evolution of a secondary drainage divide separating specified Missouri River tributary valleys. The Missouri River drainage basin research project series is being developed one essay at a time and overview essays are added as significant tributaries are reached.

• The Elkhorn River is a northeast Nebraska River and flows for much of its distance in a southeast or east direction before turning to flow in a south-southeast direction to join a south-southeast oriented Platte River segment, which then turns to flow in an east direction to the south-southeast oriented Missouri River. Logan Creek is a south-southeast and south oriented Elkhorn River tributary (shown, but unlabeled in figure 1) located between the south-southeast oriented Elkhorn River segment and the south-southeast oriented Missouri River. The Logan Creek-Missouri River drainage divide area is narrow and figures 1 and 2 show no east-oriented Missouri River tributaries. The east-oriented Missouri River along the South Dakota-Nebraska border also provides a northern boundary for the Elkhorn River drainage basin where the Missouri River flows in an east and southeast direction along the South Dakota-Nebraska border. Figure 2 below shows north-oriented tributaries to this east-oriented Missouri River segment. One of the north-oriented tributaries is the Niobrara River, which for most of its distance is primarily an east-oriented river, but which in northeast Nebraska joins a north-oriented tributary and then turns to flow in a north direction to join a northeast-oriented segment of the east-oriented Missouri River segment. North of the Missouri River in South Dakota are south-oriented Missouri River tributaries including the south and south-southeast oriented James River, which is important to the interpretation provided here. South of the Elkhorn River drainage basin is the Platte River drainage basin, which includes the Loup River tributary drainage basin. Figures 1 and 2 illustrate several southeast oriented Platte River and Loup River tributaries originating south of the southeast and east-oriented Elkhorn River.

• Elkhorn River drainage basin history, at least the history that can be determined from topographic map evidence, begins at a time when immense southeast and south-oriented floods were converging in northeast Nebraska. Flood waters were derived from a rapidly melting North American ice sheet and at the time the two immense floods converged in northeast Nebraska the decaying ice sheet’s southwest margin was located north and east of the present day Missouri River in South Dakota, although at that time the Missouri River valley did not exist. The southeast-oriented floods were flowing along the decaying ice sheet’s southwest margin while the south-oriented floods were emerging from the mouths of a giant ice-walled and bedrock-floored canyons carved into the decaying ice sheet’s surface. The largest of these ice-walled canyons was located along the alignment of the present day James River lowland in North and South Dakota. The east-facing Missouri Escarpment and the west-facing Prairie Coteau Escarpment in South Dakota are what remain of that giant south-oriented ice-walled and bedrock-floored canyon’s walls. The large ice-walled canyons were carved into the ice sheet’s surface very late during the ice sheet’s melt down history.

• The ice sheet had been large, probably as large if not larger than the present day Antarctic Ice Sheet. At one time the ice sheet may have stood as much two kilometers or more above the surrounding non-glaciated surface and probably had “roots” that may have extended as much as one kilometer or more below the surrounding non-glaciated surface. The deep “hole” in which the ice sheet “roots” were located, had been eroded by deep glacial erosion of underlying bedrock and had also been formed by crustal warping caused by ice sheet’s tremendous weight. To what extent the ice sheet once extended south and west of the present day Missouri River valley is difficult to determine because immense melt water floods destroyed much if not all of the ice sheet’s original southwest margin evidence. South Dakota and Nebraska were located near the southern margin of the deep “hole” and the ice sheet “roots” may not have been as deep in the figure 1 and 2 map areas. As the ice sheet melted so it no longer stood above the surrounding non-glaciated surface the surrounding non-glaciated surface was also lowered in elevation due to deep melt water flood erosion. Today there are no markers (non eroded high points) remaining which can be used to determine how deeply melt water floods eroded northeast Nebraska prior to Elkhorn River drainage basin development, although it is possible melt water floods stripped many hundreds of meters of easily eroded bedrock material from the region. Elkhorn River drainage history determinable from topographic maps probably began very late in the ice sheet’s melt down history after gigantic melt water floods had deeply eroded ice sheet marginal areas to the point the ice sheet’s exposed and decaying “roots” were all that was left.

Figure 2: More detailed regional drainage map for northeast Nebraska. National Geographic Society map digitally presented using National Geographic Society TOPO software.

At the time determinable Elkhorn River drainage basin history began giant melt water rivers were flowing on the decaying ice sheet surface and carving huge ice-walled and ice-walled canyons (later bedrock-floored canyons) into the ice sheet surface. One south-oriented ice-walled and bedrock-floored canyon was located directly north of northeast Nebraska along the alignment of what is today the south-oriented James River lowland in North and South Dakota. The east-facing Missouri Escarpment is the lowland’s western boundary and the west-facing Prairie Coteau Escarpment is the lowland’s eastern boundary and provide evidence of this once giant ice-walled and bedrock-floored canyon. The Missouri Escarpment can be traced in a north direction into central North Dakota and then in a northwest direction into southwest Saskatchewan and east central Alberta suggesting the ice-walled and bedrock-floored canyon once drained melt water from a large area of the decaying ice sheet’s surface. For a time another large south-oriented melt water river also flowed from the mouth of another ice-walled canyon located along the present day Big Sioux River alignment, however most melt water flood flow to this Big Sioux River ice-walled canyon was beheaded and diverted to adjacent ice-walled canyons. Evidence related to these giant southeast and south-oriented ice-walled and bedrock-floored canyons can be found in essays under James River and Big Sioux River on the sidebar category list. What is important to Elkhorn River drainage basin history is prior to Missouri River valley headward erosion massive south-oriented melt water floods emerging from the mouths of giant ice-walled and bedrock-floored canyons flowed across northeast Nebraska to what at that time were deep and actively eroding Missouri River-Platte River valley heads, which at that time were eroding headward in the present day Omaha, Nebraska region.

• While this immense south-oriented flood was flowing across northeast Nebraska massive southeast-oriented ice-marginal melt water floods were also flowing into northeast Nebraska from the northwest. At that time the Pine Ridge Escarpment did not exist and the northern plains were just as high, if not higher, than the present day high plains south of the Pine Ridge Escarpment crest. The Pine Ridge Escarpment was formed as the south wall of a 300-meter deep White River valley which subsequently eroded headward to the Black Hills south end. Flood waters from the northwest then completely removed the deep White River valley’s north wall and lowered elevations across the entire northern plains region. Headward erosion of the deep east-oriented White River valley did not occur until after Missouri River valley headward erosion had captured south-oriented melt water floods emerging from the mouth of the south-oriented James River ice-walled and bedrock-floored canyon. White River drainage basin history is described in essays related to that river basin. The southeast-oriented ice-marginal floods eroded the entire region between the Rocky Mountains and the decaying ice sheet’s southwest margin so southeast-oriented flood waters at one time were flowing across the entire state of Nebraska. At the same time immense southeast-oriented melt water floods were also flowing across and through the Rocky Mountain region and then in an east direction across Nebraska, although those east-oriented floods probably did not play a major role in Elkhorn River drainage basin history.  Convergence of southeast-oriented ice marginal flood waters with south-oriented melt water floods in northeast Nebraska probably resulted in the ponding of flood waters, which combined with the east-oriented melt water floods resulted in further ponding of flood waters in much of central and western Nebraska. Southeast-oriented ice-marginal floods flowing into the resulting temporary lakes probably deposited significant quantities of flood transported sediments. The present day Nebraska Sand Hills region, which is located directly south and west of the Elkhorn River headwaters, was probably developed on these deltaic deposits.

• The Elkhorn River valley and its tributary valleys eroded headward along and across immense south and southeast-oriented floods, which were eroding south and southeast-oriented anastomosing channel complexes into the northeast Nebraska landscape. The anastomosing channels were developing as flood waters flowed to what were then actively eroding Missouri River and Platte River valleys and to actively eroding southeast-oriented Platte River and Loup River tributary valleys. Note how south-southeast and south oriented Elkhorn River segments and tributaries are generally located near the south-southeast oriented Missouri River while southeast and east-southeast Elkhorn River segments and tributaries are generally located further to the west. The south and south-southeast oriented valley segments were probably eroded headward in regions where south-oriented flood flow dominated. The southeast and east-southeast oriented valley segments probably eroded headward across south- and southeast-oriented flood flow routes to the actively eroding southeast-oriented Platte River and Loup River tributary valleys and beheaded flood flow moving to those actively eroding tributary valleys. Headward erosion of the Platte River, Loup River, and Elkhorn River valleys and their tributary valleys probably drained most ponded flood water from the region while headward erosion of the deep Missouri River valley and its tributary Niobrara River valley captured all south- and southeast-oriented melt water flood flow moving into the what is now the Elkhorn River drainage basin.

Figure 3: Regional drainage map for Logan Creek-Missouri River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 3 provides an even more detailed map of regional drainage routes in northeast Nebraska. The Missouri River flows in a southeast direction to Sioux City, Iowa in the figure 3 northeast corner and then in a south-southeast direction to the figure 3 east edge (south half). The Elkhorn River flows in an east direction to Norfolk, Nebraska in the figure 3 southwest corner and then in a southeast and northeast direction in Stanton County before turning to flow in a southeast direction in Cuming County. Logan Creek is the southeast-oriented stream flowing across the Dixon and Thurston County southwest corners and then turning to flow in a south direction in the figure 3 southeast quadrant. East of Logan Creek in Thurston County note Cow Creek and Omaha Creek, which flow in a southeast directions to join north-oriented South Omaha Creek and then to flow in a north direction into southern Dakota County before turning to flow in an east direction to the south-southeast oriented Missouri River. Also in Dakota County note north-northeast, southeast, and east oriented Pigeon Creek, which joins the south-southeast oriented Missouri River just north of Omaha Creek. Elk Creek, north of Pigeon Creek, has interesting southeast, north, southeast, and northeast oriented route to south-southeast oriented Missouri River. East of Omaha Creek in Thurston County are North and South Blackbird Creeks, which join to form east-oriented Blackbird Creek, which flows to the south-southeast oriented Missouri River. North Blackbird Creek flows in a south direction to join east-oriented Blackbird Creek, but South Blackbird Creek originates as a southeast-oriented stream and then turns to flow in a north direction to join east-oriented Blackbird Creek. The north-oriented Missouri River tributaries (or north-oriented segments of Missouri River tributaries) provide evidence of reversals of flood flow in what were once beheaded south-oriented anastomosing flood flow channels. Detailed Elkhorn River drainage basin essays provide topographic maps illustrating through valleys linking these north-oriented Missouri River tributary valley segments with south oriented Logan Creek tributary valleys. Headward erosion of the deep Missouri River valley beheaded the south oriented flood flow channels and flood waters on north ends of the beheaded flood flow routes reversed flow direction to erode north oriented Missouri River tributary valleys.

Figure 4: Regional  drainage map for Missouri River-Elkhorn River drainage divide area. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

Figure 4 provides a similar more detailed regional drainage map for the Missouri River-Elkhorn River drainage divide area north and west of the figure 3 map area. The Elkhorn River flows in a southeast and east-southeast direction from the figure 4 west center edge area to Norfolk (near the figure 4 south edge). The North Fork Elkhorn River flows in a southeast direction in Pierce County to join the Elkhorn River near Norfolk. The Missouri River flows in a southeast direction from near the figure 4 northwest corner to Niobrara, Nebraska and then turns to flow in a northeast and east direction to Yankton, South Dakota. From Yankton the Missouri River flows in a southeast direction to the figure 4 east edge. The east-southeast oriented Niobrara River is located a short distance south of the Missouri River in the figure 4 northwest corner area and flows into Knox County where it joins north oriented Verdigre Creek and then flows in a north direction to join the Missouri River near Niobrara, Nebraska. Verdigre Creek is a north-northeast and north oriented Niobrara River tributary with northwest-oriented tributaries from the east. East of Verdigre Creek in Knox County is north and north-northwest oriented Bazille Creek. Little Bazille Creek is an interesting Bazille Creek tributary from the east and flows in a south and west direction to reach north and north-northwest oriented Bazille Creek, which then joins a northeast-oriented Missouri River segment. Continuing east there are other north- and northeast-oriented Missouri River tributaries some of which have northwest-oriented tributaries. The numerous barbed tributaries seen in this figure 4 map region are again the result of flood flow reversals on north and northwest ends of beheaded south and southeast-oriented flood flow channels. Flood waters on north and northwest ends of beheaded flood flow channels reversed flow direction to erode north- and northwest-oriented tributary valleys.

• Topographic maps included in the detailed Elkhorn River drainage basin essays provide much better evidence of the former flood flow channels. The topographic maps illustrate many more barbed tributaries and through valleys linking present day north and northwest-oriented valleys with present day south and southeast-oriented valleys. The through valleys were initiated as south and/or southeast-oriented channels in the large-scale maze of south and southeast-oriented anastomosing channels which were being carved into the northeast Nebraska landscape just prior to headward erosion of the deep Missouri River valley. As previously described at that time the decaying ice sheet margin was located just north of the present day Missouri River valley located in figure 4. Immense south-oriented floods were flowing across the figure 4 map area from the mouth of the giant south-oriented James River ice-walled and bedrock-floored canyon, which had been carved into the decaying ice sheet’s surface just north of the figure 4 map area. At the same time  immense southeast-oriented ice-marginal floods were flowing into the figure 4 map area from the northwest. Headward erosion of the deep Missouri River valley first captured the south-oriented floods while southeast-oriented flood waters continued to flow into the figure 4 map area. However, soon after Missouri River valley capture of the south-oriented floods Niobrara River valley (and a short time later Missouri River-White River valley) headward erosion captured all southeast-oriented flood flow moving into the figure 4 map area.

Figure 5: Reduced size topographic map of Elkhorn River headwaters area. Bassett is the town in the northwest corner and Stuart is the town in the northeast quadrant. United States Geological Survey map digitally presented using National Geographic Society TOPO software. 

Convergence of the southeast-oriented floods with the south-oriented floods in northeast Nebraska almost certainly resulted in the temporary ponding (or at least slowing) of flood waters until headward erosion of the deep valleys could drain the massive flood flow from the region. South-oriented flood waters were derived directly from the melting ice mass, and while they contained debris that had been contained in the ice sheet, they contained much less sediment than the ice-marginal floods which were flowing across easily eroded bedrock materials. Southeast-oriented ice-marginal flood waters flowing into northeast and eastern Nebraska probably were significantly slowed in velocity as they approached the region. The slower moving flood waters almost certainly deposited significant amounts of sediments in deltaic deposits. Figure 5 uses a reduced size topographic map to illustrate the Elkhorn River headwaters area. Low hills in the figure 5 southwest quadrant and south center area are probably sand dunes. The sand dune region extends for a considerable distance west and southwest from the figure 5 map area suggesting the region covered by the flood deposited deltaic sediments was large (see region labeled “Sand Hills” in figure 6 below). Deltaic deposits in the northeast and eastern Sand Hills region can be explained in part by southeast-oriented ice-marginal floods converging with south-oriented melt water floods emerging from the giant ice-walled and bedrock-floored canyons to the north. Deltaic deposits further west in the Sand Hills region are better explained by southeast-oriented floods converging with east-oriented floods moving across Nebraska. The east-oriented floods were coming from the Platte River headwaters areas in the Rocky Mountains. Essays describing melt water flood flow routes in the Rocky Mountains have not yet been published, but when published will illustrate routes flood waters used to reach the Platte River headwaters areas and then to flow in an east direction across Nebraska.

Figure 6: Regional map shoeing relationship of Nebraska Sand Hills region to Elkhorn River headwaters area. National Geographic Society map digitally presented using National Geographic Society TOPO software.

All drainage divides surrounding the Nebraska Elkhorn River drainage basin have been illustrated and described in the detailed Elkhorn River drainage basin essays. Topographic map evidence presented builds a strong case for headward erosion of the Elkhorn River valley along and across massive southeast and south oriented floods. Southeast-oriented flood water apparently converged with massive south oriented floods moving across eastern Nebraska and with massive east-oriented floods moving across Nebraska along the present day Platte River valley alignment. Southeast-oriented flood waters converging with the large east-oriented floods and southeast-oriented flood water moving into northeast Nebraska were ponded as they converged with south oriented flood waters in what is today the Elkhorn River drainage basin. Present day sand dunes have developed on deltaic sediments deposited as flood waters entered these ponded areas. Headward erosion of the Elkhorn River valley and Elkhorn River tributary valleys beheaded southeast-oriented flood flow to what were at that time actively eroding Platte River and Loup River valleys and tributary valleys. Subsequently, headward erosion of the Missouri River-Niobrara River valley beheaded south and southeast oriented flood flow routes to what were then actively eroding Elkhorn River valley and tributary valleys.

Introduction to Missouri River drainage basin research project essay series

• The Missouri River drainage basin research project introduces a new regional geomorphology paradigm. An essay titled “About the ‘thick ice sheet that melted fast’ geomorphology paradigm” provides a brief introduction to the new paradigm and how the new paradigm emerged. Detailed evidence illustrated and discussed in the Missouri River drainage basin research project builds a strong case for (1) deep glacial erosion of the North American continent by a thick North American ice sheet that created and occupied a deep “hole”, (2) rapid melting of that thick North American ice sheet, (3) immense floods of south-oriented melt water, (4) headward erosion of deep east, northeast and north-oriented valley systems to capture the south-oriented melt water floods and to divert the melt water further and further northeast into space the ice sheet had once occupied, (5) deep flood water erosion of the North American continent surface, and (6) crustal warping that resulted in uplift of mountain ranges as flood waters were deeply eroding what are now high mountain regions. This interpretation is fundamentally different from most previous interpretations. The Nebraska Elkhorn River drainage basin evidence in this overview essay and its related detailed essays is presented for review and discussion by qualified research geomorphologists and geologists.

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.