Stony Creek flows in a southwest and south direction in Montgomery County to join the southeast oriented Schuylkill River at Norristown. Southwest oriented Stony Creek headwaters and headwaters tributaries are linked by shallow through valleys with the south oriented Wissahickon Creek valley to the east. Other Stony Creek tributaries flow in south, southwest, and northeast directions to join the south and southwest oriented Stony Creek valley. Stony Creek and Stony Creek tributaries show an interesting pattern of aligned drainage with elbows of capture, barbed tributaries, through valleys, and small-scale water gaps. The question needing an answer is, what conditions were created and the remarkable pattern of aligned valleys, barbed tributaries, through valleys, elbows of capture, and water gaps seen today?
The aligned valleys, elbows of capture, barbed tributaries, through valleys, and water gaps are consistent with the hypothesis that the Stony Creek valley eroded headward across massive and prolonged southwest oriented floods prior to headward erosion of the adjacent Wissahickon Creek valley to the east. Floodwaters flowed in an anastomosing complex of shallow diverging and converging channels that were probably being eroded into easily eroded bedrock units located between erosion resistant materials and in this manner the underlying geology helped shaped the flood flow direction. However, until deep valleys eroded headward into the region all floodwaters moved on a surface at least as high as the highest regional ridge crests today and no present day valleys existed.
South oriented valley segments eroded headward across the southwest oriented flood flow channels and the pattern of aligned valleys, elbow of captures, barbed tributaries, through valleys, and water gaps suggests the Stony Creek valley eroded headward across diverging and converging southwest oriented flood flow channels. The evidence for this interpretation can be seen in figure 1 where Stony Creek today flows in a southwest direction at location 1 and then turns to flow in south direction before turning to flow in a southwest direction at location 2. After flowing by location 2 in a southwest direction Stony Creek turns to flow in a south direction between the Norristown Farm Park and the Norris City Cemetery to the figure 1 south edge and into the City of Norristown.
Figure 1: Stony Creek drainage basin just north of Norristown, Pa. See text for detailed description. United States Geological Survey map digitally presented using National Geographic TOPO software.
Note the southwest oriented Stony Creek tributary at location 4 and the ridge separating that tributary valley from the southwest oriented Stony Creek valley at location 2. Also note the southwest oriented Stony Creek tributary at location 3 and how that tributary makes a U-turn to flow in a northeast direction to location 6 and then makes another U-turn to flow in a south direction to join the southwest oriented Stony Creek valley and then to flow in a south direction to the figure 1 south edge. What happened here was a deep south-oriented valley eroded headward from the newly eroded Schuylkill River valley across a southwest oriented anastomosing channel complex.
Southwest-oriented flow in the captured flood flow channels eroded deeper tributary valleys headward from the newly eroded and much deeper south-oriented valley. The tributary at location 4 would an example of such a southwest oriented valley and the southwest oriented Stony Creek valley at location 2 would be another example. The south oriented valley between the Farm Park and the Cemetery continued to erode headward and captured the southwest oriented flood flow channel that eroded the shallow through valley seen at location 7. A southwest oriented valley began to erode headward toward location 7 along that channel. But, headward erosion of a deep south-oriented valley along the present day south oriented Stony Creek segment to the east beheaded the southwest oriented flood flow moving in the through valley at location 7 and headward erosion of a southwest oriented valley toward location 7 ceased.
The northeast oriented Stony Creek tributary segment at location 6 is on the same alignment as the through valley at location 7. In other words headward erosion of the south-oriented valley east of the Norristown Farm Park not only captured a southwest oriented flood flow channel, but flood flow on the northeast end of the beheaded channel reversed flow direction to move in a northeast direction to the newly eroded and much deeper south oriented valley. Because the flood flow channels were diverging and converging the reversed flow in that channel was able to capture southwest oriented flow from the yet to be beheaded channel to the northwest and that captured water made a U-turn seen in the present day tributary valley that drains from location 3 to location 6.
Headward erosion of the Stony Creek valley next captured the southwest oriented flood flow channel that extended from location 1 to locations 5, 8, and 3 and beheaded flow to locations 5, 8, and 3. Flow on the northeast end of the beheaded flood flow channel reversed flow direction to create the northeast oriented and barbed Stony Creek tributary seen at location 5. South oriented tributaries to that northeast oriented tributary suggest water from channels further to the north moved in a south direction into the newly reversed valley and this spillage helped erode the northeast oriented valley. Similar spillage from further to the north also moved to the southwest oriented channel at location 3 and helped erode that valley deeper. The present day through valley at location 8 provides evidence that southwest oriented flow once moved from location 1 to locations 5, 8, 3, and then made a U-turn to go to location 6 before flowing in a south direction to join the newly eroded south-oriented Stony Creek valley. Headward erosion of the deep south-oriented Wissahickon Creek valley to the east (see figure 2) captured all southwest flood flow channels leading to newly eroded Stony Creek valley and tributary valleys and rapid erosion of the Stony Creek drainage ended.
Figure 2: Stony Creek headwaters flow in southwest direction through location 3. Wissahickon Creek flows from location 1 to location 4 and headward erosion of the Wissahickon Creek valley beheaded southwest oriented flood flow moving in the through valley at location to the actively eroding Stony Creek valley. Note the southwest oriented Wissahickon Creek tributary flowing on the same alignment as the southwest oriented Stony Creek valley at location 3. United States Geological Survey map digitally presented using National Geographic TOPO software.
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