A shallow (20-40 foot deep) through valley at location 1 (in figure 1) and shown in more detail in figure 2 (at end of text) links the south and south-southeast oriented Ironworks Creek valley head with a northeast oriented valley (Potter Run) draining through Northampton Country Club and Tyler State Park to southeast and south oriented Neshaminy Creek at location 2 (in figure 1). This relatively minor landscape feature is one of several other easily-missed through valleys linking the southeast and south oriented Neshaminy Creek valley with the south and south-southeast oriented Ironworks Creek valley. What is the significance of these shallow through valleys?
Figure 1: Reduced size topographic map of Neshaminy Creek-Ironworks Creek through valley and region. See text for description and figure 2 for a more detailed map of the shallow Neshaminy creek-Ironworks Creek through valley. . United States Geological Survey map digitally presented using National Geographic TOPO software.
Today Ironworks Creek flows from near location 1 through Churchville Park to Springfield Lake (a manmade reservoir) and then joins east-northeast Mill Creek at the figure 1 location 3, which then joins Neshaminy Creek at its Playwick Park elbow of capture (figure 1 location 5) as a barbed tributary. The Playwick Park elbow of capture in interesting because after flowing in a southeast and south direction Neshaminy Creek turns at the figure 1 location 4 to flow in west-southwest direction to location 5 and then turns to flow in a narrow south and southeast oriented valley and eventually reach the southwest oriented Delaware River valley found south of figure 1.
What is particularly puzzling about this Neshaminy Creek route is the east-northeast oriented Mill Creek valley alignment continues not only from the figure 1 location 5 to location 4, but also to the figure 1 map east edge and then to the present day south oriented Delaware River valley (the Delaware River flows in a south direction east of figure 1 and then turns to flow in a southwest direction south of figure 1)). The ridge through which the Neshaminy Creek valley south of the figure 1 location 5 has been cut is 60-80 feet higher than the Neshaminy Creek-Delaware River drainage divide elevation east of the figure 1 location 4. Why does Neshaminy Creek turn in a west-southwest direction at the figure 1 location 4 rather than flow in an east-northeast direction across the lower elevation drainage divide to reach the Delaware River valley?
To reconstruct how valleys seen in figure 1 were eroded it is necessary to go back to a time when those valleys did not exist. At that time all elevations in the figure 1 map area were at least as high or higher than the highest elevations today and massive and prolonged southwest oriented floods moved across the region. Flood erosion was probably deepest to the south and east of figure 1 and the deep southwest oriented Delaware River valley (south of figure 1) eroded headward along what was probably a major southwest oriented flood flow channel. The south oriented Delaware River valley east of figure 1 had not yet been eroded and southwest oriented floodwaters were moving in anastomosing complexes of diverging and converging flood flow channels from present day New Jersey to and across the entire figure 1 map region.
A west-southwest oriented flood flow channel formed along the present day route defined by locations 4, 5, and 3 in figure 1, although that channel was at an elevation at least as high as the highest elevations surrounding the valley today. The valley straightness suggests an underlying linear geologic feature may have been responsible for the west-southwest oriented flood flow channel location. The deep south-oriented Neshaminy Creek valley then eroded headward from the newly eroded and deep southwest-oriented Delaware River valley and captured flood flow in the west-southwest oriented channel at the figure 1 location 5 to create the Playwick Park elbow of capture.
Flood flow on the east-northeast end of the beheaded flood flow channel then reversed direction to flow in an east-northeast direction to the much deeper south oriented Neshaminy Creek valley at figure 1 location 5 and created the east-northeast oriented Mill Creek drainage route. Reversed flow on the newly created Mill Creek drainage route was able to erode a valley headward in a west-southwest direction (along the present day Mill Creek alignment) and then in a north and north-northwest direction (along the present day Ironworks Creek alignment) to capture southwest oriented flood flow channels north of the Neshaminy Creek valley head, which was eroding headward along the present day southwest oriented Neshaminy Creek segment between locations 4 and 5.
Location 1 (on figures 1 and 2) shows the location of one northern southwest oriented flood flow channels captured by headward erosion of the deep Ironworks Creek valley. When Ironworks Creek valley headward erosion captured that southwest oriented flood flow channel at location 2 (in figure 2) the deep Neshaminy Creek valley to the northeast and east had yet to be eroded. Water from that southwest oriented flood flow channel helped erode the deep Ironworks Creek and Mill Creek valleys seen today, although headward erosion of the deep south-southeast oriented Ironworks Creek valley ended when headward erosion of the deep southeast and south oriented Neshaminy Creek valley captured the southwest oriented flow at location 3 (in figure 2) and then eroded headward for a short distance along that southwest oriented flow channel.
Again water on the northeast end of the beheaded flood flow channel reversed flow to create northeast Potter Run (the unnamed northeast oriented Neshaminy Creek tributary flowing through Tyler State Park). And again the reversed flow was able to capture southwest oriented flood flow from north and west of the actively eroding Neshaminy Creek valley head and that captured flood flow helped erode the northeast oriented Potter Run valley seen today.
Figure 2: Detailed map of Neshaminy Creek-Ironworks Creek through valley at location 1. Ironworks Creek originates at location 2 and Potter Run is the unnamed northeast oriented tributary joining southwest, southeast, south, and southeast oriented Neshaminy Creek at location 3. United States Geological Survey map digitally presented using National Geographic TOPO software.