A geomorphic history based on topographic map evidence
This Niobrara River drainage basin landform origins overview essay provides highlights from more detailed essays which illustrate and interpret detailed topographic map evidence. The detailed essays can be found under Niobrara River on this website’s sidebar category list. All interpretations in this overview essay and the related detailed essays are based on topographic map evidence illustrated in the detailed essays. The Niobrara River originates in eastern Wyoming and flows in an east and southeast direction into western Nebraska. Once in Nebraska the Niobrara River flows in a northeast direction and then in a generally east direction until reaching northeast Nebraska, where it turns to flow in a north direction to join the southeast-oriented Missouri River. North of the Niobrara River drainage basin in Wyoming is the north-facing Hat Creek Breaks Escarpment and Cheyenne River drainage basin and in western Nebraska and South Dakota the northwest and north-facing Pine Ridge Escarpment and White River drainage basin. This overview essay and its related detailed essays describing landform origins along drainage divides between Niobrara River tributaries and between the Niobrara River drainage basin and adjacent drainage basins provides evidence the Niobrara River valley eroded headward to capture immense southeast-oriented floods moving across the present day Niobrara River drainage basin. At the time of Niobrara River valley headward erosion the north-facing Pine Ridge and Hat Creek Breaks Escarpments to the north did not exist and topography north of the present day Niobrara River drainage basin was at least as high if not higher than the present day escarpment crests. Flood waters were derived from a rapidly melting thick North American ice sheet, which was located in a deep “hole”, and flood waters were flowing in a southeast direction along the decaying ice sheet’s southwest margin. Deep east and northeast oriented valleys eroded headward from space in the deep “hole” being opened up as the ice sheet melted, with the east and northeast oriented valleys being eroded headward in sequence from south to north as space in the deep “hole” opened up. Headward erosion of the deep Niobrara River valley beheaded southeast-oriented flood flow to what at that time were the newly eroded Platte River valley and its tributary valleys. Headward erosion of the deep White River valley beheaded southeast-oriented flood flow to the eastern Niobrara River drainage basin and eroded the north-facing Pine Ridge Escarpment, while headward erosion of the deep Cheyenne River valley beheaded southeast-oriented flood flow to the western Niobrara River drainage basin and eroded the north-facing Hat Creek Breaks Escarpment.
Figure 1: Northern Nebraska and eastern Wyoming Niobrara River drainage basin location map (select and click on maps to enlarge). National Geographic Society map digitally presented using National Geographic Society TOPO software.
Northern Nebraska and eastern Wyoming Niobrara River drainage basin drainage history
This essay provides an overview of topographic map evidence illustrated and discussed in more detailed essays, which can be found under Niobrara River on this website’s sidebar category list. Each of the detailed essays includes location maps and at least 8 topographic maps illustrating drainage divide evidence in various Niobrara River drainage basin regions. The purpose of the overview essay and related detailed essays is to interpret the topographic map evidence so as to determine Niobrara River drainage basin landform origins. Maps and discussion in this overview essay provide only a sample of evidence available in the more detailed essays and maps and discussions in the more detailed essays provide only a sample of the total Niobrara River drainage basin topographic map evidence available. All interpretations in this essay and in the detailed essays are based entirely on the topographic map evidence and no effort has been made to introduce evidence from other sources. Evidence presented in this essay and in detailed essays has been interpreted in the context of a previously ignored “thick ice sheet that melted fast” paradigm, in which the thick ice sheet was located in a deep “hole” created by deep glacial erosion and by crustal warping caused by the ice sheet weight. In addition, the paradigm assumes massive melt water floods, which at first flowed south along the ice sheet margin and later were captured in sequence from south to north by headward erosion of deep east and northeast-oriented valleys which eroded headward from space in the deep “hole” being opened up as the thick ice sheet melted. This paradigm is fundamentally different from most previously published interpretations, but is being used in all Missouri River drainage basin landform origins research project essays (which are published on this website), because the paradigm better explains topographic map evidence than any previously published paradigm.
- The Niobrara River originates in eastern Wyoming near Manville (see figure 2 below) and flows in a southeast direction into northwest Nebraska where it turns to flow in an east and northeast direction into north central Nebraska (near the South Dakota border). From north central Nebraska the Niobrara River flows in an east-southeast direction until it turns to flow in a north direction to join the Missouri River near Niobrara, Nebraska (see figures 1 and 3). North of the Niobrara River drainage basin in Wyoming and extreme northwest Nebraska is the Cheyenne River drainage basin, with the Cheyenne River flowing in a southeast and northeast direction around the Black Hills south end and then flowing in a northeast direction to join the southeast oriented Missouri River in central South Dakota (see figure 1). East of Harrison, Nebraska the southeast, northeast, and east-oriented White River drainage basin is located north of the Niobrara River drainage basin, with the White River flowing to the southeast-oriented Missouri River in south central South Dakota. Between the Niobrara River drainage basin and the Cheyenne River drainage basin is the north-facing Hat Creek Breaks Escarpment, with the Escarpment slope being drained by Cheyenne River tributaries. Between the Niobrara River drainage basin and the White River drainage basin is the north-facing Pine Ridge Escarpment with the Escarpment slope again being drained primarily by White River tributaries. These north-facing escarpments mark the boundary between high plains to south, on which the Niobrara River drainage basin is located, and low plains to the north, on which the northeast-oriented Cheyenne River and White River valleys are located. The elevation difference between the low plains to the north and high plains to the south varies although is often as much as 300 meters and sometimes even more. The origins of these escarpments is an important question any regional drainage history must address.
Figure 2: Niobrara River route and tributaries and adjacent rivers and tributaries in eastern Wyoming, northwestern Nebraska, and southwest South Dakota. National Geographic Society map digitally presented using National Geographic Society TOPO software.
Figure 2 provides a somewhat more detailed map of the Niobrara River route and tributaries and adjacent rivers and tributaries in eastern Wyoming and northwest Nebraska and southwest South Dakota than figure 1. Note how in the figure 2 northwest quadrant (west of the Black Hills) the Cheyenne River has an extensive drainage network with both southeast and northeast-oriented tributaries all of which converge near the Black Hills south end and then flow in a northeast direction between the Black Hills and the adjacent and somewhat parallel White River. While figure 2 does not show the north-facing Hat Creek Breaks Escarpment, the Escarpment is located along the Cheyenne River-Niobrara River drainage divide and elevations between the Escarpment base and the Black Hills south end are generally 200-300 meters or lower than elevations in the Niobrara River drainage basin to the south. The southeast-oriented White River headwaters originate on the high plains, but soon flow in a deep valley to the lower elevations at the north-facing Escarpment base and then turn to flow in a northeast direction along the base of the northwest-facing Pine Ridge Escarpment which further east becomes the north-facing Pine Ridge Escarpment. Northwest-oriented White River tributaries such as Wounded Knee Creek originate near the Pine Ridge Escarpment crest and flow down the Escarpment slope. Further east in the figure 2 northeast quadrant area the east and east-southeast headwaters of what becomes the north-northeast oriented Little White River flow along the Escarpment crest and the north-northeast oriented Little White River segment flows down the Escarpment slope. Again the White River valley today is often 300 meters or lower in elevation than elevations along the Escarpment crest.
- To understand Niobrara River drainage basin drainage history it is necessary to understand Cheyenne River and White River drainage basin drainage history. Essays found under White River on the sidebar category list provide overviews and detailed essays describing how headward erosion of a 200-300 meter or more deep White River valley first captured massive southeast-oriented floods and diverted flood waters in an east direction to the southwest margin of a decaying ice sheet, which had been located in a deep “hole”. The southeast-oriented floods were flowing between the ice sheet’s southwest margin and what may have been emerging Rocky Mountains (to the southwest) and at least initially flowed across what were probably the emerging Black Hills. The ice marginal surface on which the southeast-oriented floods were flowing was significantly higher than the floor of the deep “hole” in which the decaying ice sheet was located. The Black Hills emerged as an upland region probably due to a combination of deep flood water erosion of the surrounding region and also due to delayed crustal warping triggered by the thick ice sheet’s tremendous weight. As the Black Hills emerged flood waters were diverted around the Black Hills with significant flood flow being concentrated around the Black Hills’ south end. At first the concentrated flood flow moved east along the alignment of what is now the east oriented White River valley. As the ice sheet melted deep ice-walled and bedrock-floored canyons were carved in the ice sheet surface and provided a significantly lower base level than the ice margin surface elevation. Deep east and northeast-oriented valleys eroded headward across the ice sheet detached southwest margin and into the adjacent region from these deep ice-walled and bedrock-floored canyons in sequence from south to north and captured the immense southeast-oriented melt water floods. The deep White River valley was first of these large valleys to erode headward across the region, although the deep northeast-oriented Cheyenne River eroded headward soon thereafter and beheaded all flood flow routes to the White River valley.
- Evidence for capture of southeast oriented flood flow as the deep east and northeast-oriented valleys eroded headward across South Dakota and Nebraska can be seen in the numerous southeast oriented tributaries and also in northwest-oriented tributaries. The northwest-oriented tributary valleys were eroded by reversals of flood flow on northwest ends of newly beheaded flood flow channels. Flood flow channels were beheaded in sequence from east or northeast to the west or southwest. Also flood flow channels were anastomosing (or interconnected) and reversed flood flow in a newly beheaded flood flow channel could easily capture flood flow from channels west or southwest of the actively eroding east or northeast-oriented valley head. Note how these southeast and northwest oriented tributaries can be seen both north and south of the Pine Ridge Escarpment, providing evidence flood waters initially flowed into and across Nebraska. In addition to tributary orientations through valleys cross many drainage divides and provide further evidence of southeast-oriented flood flow channels such as might be found in a southeast-oriented anastomosing channel complex. The Nebraska Sand Hills region, which is identified on figures 2 and 3, is located immediately south of the Niobrara River in much of western Nebraska and provides evidence of probable flood deposited deltaic sediments. Evidence presented in essays found under Platte River (NE) on the sidebar category list suggests southeast-oriented ice-marginal floods converged with east-oriented flood waters in western Nebraska and it is possible this convergence of floods resulted in a ponding of flood waters, which would have caused flood carried sediments to settle out. Routes the east-oriented melt water floods used to reach western Nebraska were through the present day Rocky Mountain region in Wyoming and Colorado before turning to reach western Nebraska.
Figure 3: Niobrara River route and tributaries and adjacent rivers and tributaries in northeastern Nebraska and southeastern South Dakota. National Geographic Society map digitally presented using National Geographic Society TOPO software.
Figure 3 illustrates the Niobrara River route and tributaries and adjacent rivers and tributaries in northeastern Nebraska and southeast South Dakota. Note how the Niobrara River flows in an east-southeast, east-northeast, and east-southeast direction from Valentine, Nebraska to join a north-oriented stream (Verdigre Creek) and then to flow in a north direction to join the Missouri River near Niobrara, Nebraska. Further note how the north-oriented Verdigre Creek alignment is similar to the alignment of south-oriented Missouri River tributaries in South Dakota. North of the figure 2 map area the south-oriented James River flows on a similar alignment. The south-oriented James River today flows in a broad lowland bounded on the west by the east-facing Missouri Escarpment and on the east by the west-facing Prairie Coteau Escarpment. The two opposite facing escarpments are what remain of what was once a gigantic south-oriented ice-walled and bedrock-floored canyon carved by an immense supra-glacial melt water river into the decaying ice sheet surface. Prior to Missouri River valley headward erosion the immense south-oriented river flowing in that south-oriented canyon flowed in south direction across northeast Nebraska. Headward erosion of the deep Missouri River valley captured the south-oriented river and diverted the water east and southeast in the deep Missouri River valley. Flood waters on the north end of the beheaded south-oriented flood flow route in northeast Nebraska reversed flow direction to erode the north-oriented Verdigre Creek and Niobrara River valley segments. The Niobrara River valley may have begun to erode headward across Nebraska to capture southeast-oriented ice-marginal flood flow prior to beheading and reversal of south-oriented northeast Nebraska flood flow. However, the deep Niobrara River eroded headward after deep Missouri River valley headward beheaded and reversed the south-oriented northeast Nebraska flood flow.
- Also of interest in figure 3 are the numerous southeast-oriented Platte River tributaries south of the east-oriented Niobrara River (southeast-oriented streams flowing to the figure 3 south edge). The southeast-oriented Platte River tributary valleys eroded headward along southeast-oriented flood flow routes, which were subsequently beheaded by Niobrara River valley headward erosion. Note how the east-oriented Niobrara River has some major southeast-oriented tributaries including the Keya Paha River and unlabeled Ponca Creek, which is located between the southeast-oriented Missouri River and the southeast Keya Paha River (the southeast-oriented Missouri River valley alignment may have been initiated as a southeast-oriented valley, similar to the Ponca Creek and Keya Paha River valleys, which eroded headward from the large south-oriented melt water river flowing across northeast Nebraska). What is particularly interesting about the southeast-oriented Keya Paha River and Ponca Creek valleys is the valleys are truncated by the north-facing Pine Ridge Escarpment. These parallel truncated southeast-oriented valleys provide further evidence of southeast-oriented flood flow channels which were captured by Niobrara River valley headward erosion. Truncation of those parallel southeast-oriented valleys is evidence southeast-oriented flood flow captured by Niobrara River valley headward erosion came from north and west of the present day Pine Ridge Escarpment and flowed on a surface as high or almost as high as the present day high plains in Nebraska. Niobrara River drainage basin landform origins detailed essays provide topographic maps illustrating much better evidence for the Keya Paha River and Ponca Creek valley truncation than can be seen in figure 3.
- Niobrara River drainage basin drainage history is best understood when viewed as one of many east and northeast-oriented river valleys which eroded headward in sequence (from south to north) to capture immense south and southeast-oriented ice-marginal melt water floods and to divert the flood waters in an east or northeast direction to the deep “hole” the melting ice sheet was opening up. To best understand these east and northeast-oriented valleys one needs to understand the magnitude of the thick North American ice sheet and the deep “hole” in which it was located and also the magnitude of melt water produced as the thick ice sheet rapidly melted. The Missouri River drainage basin needs to be viewed as a complete unit eroded by these immense melt water floods and no Missouri River tributary valley was eroded in isolation of the others.
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.