A geomorphic history based on topographic map evidence

This essay provides an overview of more detailed essays illustrating and discussing the northeast Montana Big Dry Creek drainage basin drainage history. The detailed essays can be under Big Dry Creek on this website’s sidebar category list. All interpretations in this essay and in the more detailed essays are based entirely on topographic map evidence. Big Dry Creek drains in a northeast, east, and north direction to the east-oriented Missouri River in northeast Montana. Big Dry Creek tributaries include northeast oriented Sand Creek and northeast and northwest-oriented Little Dry Creek. This overview essay provides highlights from more detailed essays describing drainage divides between Big Dry Creek and its tributaries and with adjacent drainage basins provide evidence the Big Dry Creek valley and its tributary valleys eroded headward to capture an immense southeast-oriented flood moving across the present day Big Dry Creek drainage basin. The immense flood was derived from a rapidly melting North American ice sheet and was flowing in a southeast direction along the ice sheet’s southwest margin. Late during the ice sheet’s melt down history supra-glacial melt water rivers carved giant ice-walled and bedrock-floored canyons into the ice sheet surface. The deep east-northeast oriented Missouri River valley eroded headward (across the ice sheet’s detached and decaying southwest margin) from one of those huge ice-walled canyons and the north-oriented Big Dry Creek valley eroded headward from the actively eroding Missouri River valley. Evidence supporting this flood origin interpretation includes the positions and orientations of the Big Dry Creek, Little Dry Creek and tributary valleys and through valleys eroded across present day drainage divides. Northwest-oriented Big Dry Creek tributary valleys, including the Little Dry Creek valley segment, were eroded by reversals of flood flow on beheaded southeast-oriented flood flow channels. Headward erosion of the northeast-oriented Little Dry Creek valley segment occurred before headward erosion of the northeast-oriented Sand Creek valley, which occurred before headward erosion of the northeast-oriented Big Dry Creek valley segment. Flood flow to the Big Dry Creek drainage basin ended when headward erosion of the Missouri River-Musselshell River valley captured the southeast-oriented flood flow.

Figure 1: Northeast Montana Big Dry Creek drainage basin location map. National Geographic Society map digitally presented using National Geographic Society TOPO software

Big Dry Creek drainage basin drainage history

The Big Dry Creek drainage basin is located in eastern Montana and is a northeast, east, and north-oriented Missouri River tributary. Major Big Dry Creek tributaries are northeast oriented Sand Creek and northeast, east, northeast, and northwest-oriented Little Dry Creek. To the south of the Big Dry Creek drainage basin are headwaters of southeast-oriented tributaries flowing to the east and northeast oriented Yellowstone River. To the west of the Big Dry Creek drainage basin are northwest-oriented tributaries to the north-oriented Musselshell River and to a northeast oriented Missouri River segment.  To the east of the Big Dry Creek drainage basin are the north-oriented Prairie Creek drainage basin and the northeast and north-oriented Redwater River drainage basin. To the north and the northwest of the Big Dry Creek drainage basin is the Missouri River valley and its associated drainage basin. The Missouri River valley north of the Big Dry Creek drainage basin (and also the Big Dry Creek valley north end) are today flooded by Fort Peck Lake, which is a large reservoir impounded behind Fort Peck Dam. Big Dry Creek tributaries from the southeast and east tend to be oriented in a northwest direction and tributaries from the northwest and west are often oriented in a southeast direction (see figure 2 below). The northwest-southeast orientation of Big Dry Creek tributary valleys suggests the deep northeast and north oriented Big Dry Creek valley (and northeast-oriented Sand Creek valley and east-and east-northeast oriented Little Dry Creek valley segments) were eroded headward across multiple southeast-oriented flood flow channels, such as might be found in a large southeast-oriented anastomosing channel complex. This interpretation requires the east-northeast oriented Little Dry Creek valleys segment to have been eroded before the northeast oriented Sand Creek valley and the Sand Creek valley to have been eroded before the northeast oriented Big Dry Creek valley to the northwest of the Sand Creek valley. The southeast-oriented tributary valleys to the present day east-northeast, northeast and north oriented Big Dry, Little Dry, and Sand Creek valleys were eroded headward along captured southeast-oriented flood flow channels. The northwest oriented tributary valleys were eroded by reversals of flood flow on northwest ends of beheaded flood flow channels. The flood flow channels were beheaded in sequence from the north to south and from east to west. Because the flood flow channels were captured and beheaded in sequence, one at a time, and also because the flood flow channels were anastomosing (or interconnected) reversed flood flow in a newly beheaded flood flow channel could capture yet to be beheaded flood flow from adjacent flood flow channels located south and/or west of the actively eroding Big Dry Creek valley head. Such captures of yet to be beheaded flood water helped erode the northwest-oriented tributary valleys.

Figure 2: Big Dry Creek drainage basin area showing southeast and northwest-oriented tributaries. North-oriented Musselshell River is located near west edge and flows to east-northeast oriented Missouri River. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

The Big Dry Creek drainage basin history began with development of a North American ice sheet comparable in size to the present day Antarctic Ice Sheet, if not larger. The ice sheet was thick, probably several kilometers thick, and was located in a deep “hole”, which the ice sheet had formed by a combination of deep glacial erosion and crustal warping caused by the ice sheet weight. When at its maximum size the ice sheet stood high above the pre-glacial surface, but also had roots that extended well below the pre-glacial surface, which no longer exists. The Big Dry Creek drainage basin location was probably located south and west of ice sheet’s southwest margin, although evidence for the ice sheet’s southwest margin has probably been removed by deep melt water flood erosion. The pre-glacial surface under the ice sheet was completely destroyed by deep glacial erosion and the pre-glacial surface adjacent to the ice sheet and elsewhere on the North American continent was deeply eroded by deep melt water flood erosion and was also probably significantly altered by crustal warping caused by the thick North American ice sheet presence. Highest points in the present day Big Dry Creek drainage basin are probably well below the level of the pre-glacial surface.

• Events important to Big Dry Creek drainage basin history began as the ice sheet was rapidly melting and had melted to the point it no longer stood high above the surrounding non-glaciated surface, which had probably already been significantly lowered by deep melt water erosion. Immense melt water floods were flowing in a southeast direction along the ice sheet’s southwest margin and were deeply eroding the region between the present day Pine Ridge Escarpment in South Dakota and the ice sheet’s southwest margin, which at that time was located north and east of today’s Big Dry Creek drainage basin. Also at that time immense southeast and south-oriented supra-glacial melt water rivers were flowing across the ice sheet’s surface to the ice sheet’s southern margin and carving giant ice-walled and bedrock-floored canyons. A huge southeast and south-oriented ice-walled and bedrock-floored canyon was carved east of the present day Missouri River valley in North and South Dakota and the Missouri Escarpment is what remains of that giant canyon’s west and southwest wall. The floor of that huge ice-walled and bedrock-floored canyon was significantly lower in elevation than the bedrock surface south and west of the decaying ice sheet, and separating the immense southeast-oriented ice marginal floods from the much deeper ice-walled and bedrock floored canyon floor was the decaying and detached ice sheet southwest margin or ice barrier.

• As the ice sheet’s detached southwest margin continued to decay the southeast-oriented ice marginal floods, which were flowing at a higher elevation than deep ice-walled and bedrock-floored canyon floor to the northeast and east, began to breach the ice barrier and to flow into the giant ice-walled and bedrock-floored canyon. The northeast and east-facing Missouri Escarpment is located north and east of the Big Dry Creek drainage basin, meaning the deep southeast-oriented ice-walled and bedrock-floored canyon was located north and east of the present day Big Dry Creek drainage basin location. The deep east-northeast oriented Missouri River valley eroded headward from a major ice sheet margin breach. Prior to Missouri River valley headward erosion the deep northeast oriented Yellowstone River valley had eroded headward from a different ice sheet margin breach. The north-oriented Big Dry Creek valley eroded headward (or south) from the actively eroding deep east-northeast oriented Missouri River valley and was able to capture southeast-oriented flood flow routes before Missouri River valley headward erosion beheaded those flood flow routes. Many of the southeast-oriented flood flow routes captured by Big Dry Creek and tributary valley headward erosion were supplying flood waters to actively eroding southeast-oriented tributary valleys eroding headward from what was then the newly eroded Yellowstone River valley and to actively eroding southeast-oriented tributary valleys eroding headward from newly eroded north-oriented Missouri River tributary valleys (located east of the Big Dry Creek drainage basin, such as the northeast and north-oriented Prairie Elk Creek valley and the Redwater River valley). Flood waters on northwest ends of beheaded flood flow channels reversed flow direction to erode northwest-oriented tributary valleys.

Figure 3: Hungry Pass area located east of the Big Dry Creek drainage basin illustrates on a small-scale how headward erosion of the deep Missouri River valley captured southeast-oriented flood flow. United States Geological Survey map digitally presented using National Geographic Society TOPO software.

The figure 3 map area is located a short distance east of the Big Dry Creek drainage basin and illustrates on a small-scale how headward erosion of the north-oriented Big Dry Creek valley and tributary valleys captured southeast-oriented flood flow channels prior to those flood flow channels being beheaded by Missouri River valley headward erosion. The northwest and north-northeast oriented Missouri River tributary in the figure 3 east half is Hungry Creek. The West Fork Hungry Creek flows in an east-northeast direction from the figure 3 southwest corner area and a road is located in its valley. The north-northeast oriented Missouri River tributary originating in the figure 3 southwest corner area and located in the figure 3 west half is Lost Creek. Note Hungry Creek Pass, which is located in sections 29 and 32 between a north-northwest oriented Lost Creek tributary valley and a southeast-oriented West Fork Hungry Creek tributary valley. Also note Sids Flat in sections 3 and 4 near the figure 3 south edge. Sis Flat is also a through valley linking a north-oriented West Fork Hungry Creek tributary valley with a north-northeast oriented Hungry Creek tributary valley (Cheer Creek). Hungry Creek Pass and Sids Flat are especially well-developed examples of through valleys found crossing all drainage divides in the Big Dry Creek drainage basin (and throughout the entire Missouri River drainage basin). While many of the Big Dry Creek drainage basin through valleys are not as deep or as easy to recognize as Hungry Creek pass and Sids Flat, all of the through valleys provide evidence of former flood flow channels.

• In the case of figure 3 the north-northeast oriented Hungry Creek valley eroded headward from what was at that time the deep and actively eroding east-oriented Missouri River valley head, which was eroding headward across an immense southeast-oriented flood. The northwest-oriented Hungry Creek valley segment was eroded by a reversal of flood flow on a southeast-oriented flood flow route beheaded by headward erosion of the deep north-northeast oriented Hungry Creek valley. The north-northeast oriented Cheer Creek valley (which is really an extension of the north-northeast oriented Hungry Creek valley segment) captured a major southeast-oriented flood flow route which was moving flood waters across the present day Hungry Creek Pass and Sids Flat through valley locations and the flood waters were diverted north to the newly eroded Missouri River valley (at that time Missouri River valley headward erosion had not beheaded the southeast-oriented flood flow route and flood waters were probably flowing on a topographic surface at least as high as the highest figure 3 elevations today). Shortly after the Cheer Creek valley capture of the southeast-oriented flood flow route headward erosion of the deep east-northeast oriented West Fork Hungry Creek valley captured the same southeast-oriented flood flow route and beheaded the newly eroded and deep flood flow channel which had been eroded across Sids Flat to the newly eroded north-northeast oriented Cheer Creek and Hungry Creek valleys. Shortly after the West Fork Hungry Creek valley capture of the southeast-oriented flood flow route headward erosion of the north-oriented Lost Creek valley (from what was then the actively eroding Missouri River valley head) captured the southeast-oriented flood flow route and beheaded the newly eroded and deep flood flow channel which had been eroded across Hungry Creek Pass. Flood waters on the northwest end of the beheaded flood flow route reversed flow direction to erode the northwest-oriented Lost Creek valley.

• Through valleys in the Big Dry Creek drainage basin are not as well-defined as the Hungry Creek Pass and Sids Flat through valleys, however the through valleys exist and the Big Dry Creek drainage basin detailed essays illustrate and describe numerous through valleys crossing drainage divides within the Big Dry Creek drainage basin and also crossing drainage divides with adjacent drainage basins. Each of the detailed essays includes one or more location maps and eight or more detailed topographic maps. One or more paragraphs of text associated with each map point out and interpret landforms located on the maps. Evidence illustrated and described in these Big Dry Creek drainage basin detailed essays documents Big Dry Creek valley headward erosion from what was at that time the actively eroding and deep east-oriented Missouri River valley head, which was eroding headward across an immense southeast-oriented flood. Big Dry Creek (and Sand Creek and Little Dry Creek) valley headward erosion captured yet to be beheaded southeast-oriented flood flow routes (yet to be beheaded by headward erosion of the deep Missouri River valley). Flood waters on northwest ends of southeast-oriented flood flow routes beheaded by Big Dry Creek (and Sand Creek and Little Dry Creek) valley headward erosion reversed flow direction to erode northwest-oriented Big Dry Creek (and Sand Creek and Little Dry Creek) tributary valleys. Headward erosion of the deep east-northeast oriented Missouri River valley and its north-oriented Musselshell River tributary valley beheaded southeast-oriented flood flow routes to what had been the actively eroding Big Dry Creek drainage basin and the Big Dry Creek drainage basin landscape has changed little since.

• Detailed essays describing all drainage divides surrounding the present day Big Dry Creek drainage basin can be found under Big Dry Creek on the sidebar category list. Evidence presented in the detailed essays demonstrates the Big Dry Creek valley eroded headward to capture an immense southeast-oriented flood and to divert the flood waters north and northeast. This evidence strongly supports a geomorphology research paradigm defined by (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, and (5) deep flood water erosion of the North American continent surface.

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.