Mill Creek-Pidcock Creek drainage divide and Pidcock Creek drainage basin origin

Authors

The Pidcock Creek drainage basin is located east of Doylestown in Bucks County and is bounded on the southwest by the southeast and south oriented Mill Creek drainage basin, the northwest by Buckingham Mountain, the north by Solebury Mountain, the northeast by the southeast oriented Delaware River, and the south and southeast by Bowman Hill and Jericho Mountain. Buckingham Mountain is a southwest-to-northeast oriented ridge shown on the Pennsylvania Geological Survey web applications map as being composed of quartzite, sandstone, and quartz-pebble conglomerate. The same map shows Solebury Mountain, Bowman Hill, and Jericho Mountain as being composed of diabase that was intruded into more easily eroded sedimentary rocks, which underlie most of the Pidcock Creek drainage basin and which are primarily composed of shale and mudstone.

PidcockMill

Figure 1: Pidcock Creek drainage basin with southeast oriented Mill Creek in the map southwest corner and the southeast oriented Delaware River in the map northeast corner. See text for detailed description. United States Geological Survey map digitally presented using National Geographic TOPO software. 

Figure 1llustrates how Buckingham Mountain, Solebury Mountain, Bowman Hill, and Jericho Mountain surround the Pidcock Creek drainage basin. Pidcock Creek originates near location 1 and flows in a northeast direction to location 2 where it turns to flow in a southeast direction to location 3. From location 3 Pidcock Creek flows in a northeast direction to location 4, makes a jog to location 5, and then flows in a northeast direction to join the Delaware River as a barbed tributary at location 6. Interesting Pidcock Creek tributaries flow from near location 7 to near location 3, from location 8 to location 9, and from location 10 to location 11. Jericho Creek is a Delaware River tributary located south of Jericho Mountain and can be seen flowing between locations 10 and 11. Mill Creek flows in a southeast direction between locations 13 and 14 (southwest corner of map) and south of figure 1 joins southeast and south oriented Neshaminy Creek, which eventually joins the southwest oriented Delaware River segment located south and east of figure 1.

The Mill Creek-Pidcock Creek drainage divide is asymmetric with northeast oriented Pidcock Creek headwaters being located much closer to the southeast oriented Mill Creek valley than they are to the southeast oriented Delaware River valley. Also, Pidcock Creek today flows in a northeast direction toward Solebury Mountain and then in a southeast direction toward Jericho Mountain and still later in a south direction toward Bowman Hill before reaching the Delaware River. And in addition, Pidcock Creek flows in a northeast direction to join the southeast Delaware River as a barbed tributary. Random processes operating over long periods of time do not create landform features like the asymmetric Mill Creek-Pidcock Creek drainage divide and barbed tributaries and to understand the Delaware River valley origin it is important to understand how the asymmetric Mill Creek-Pidcock Creek drainage divide developed and why Pidcock Creek flows in a northeast direction to join a southeast oriented river.

The present day figure 1 region landscape was shaped during an erosion event that began with a regional surface at least as high or higher than the highest points seen in figure 1 (i.e. tops of Bowman Hill and of Buckingham, Solebury, and Jericho Mountains). At that time the Delaware River valley did not exist and there was no Delaware River, nor did Pidcock Creek, Jericho Creek, Mill Creek, or Neshaminy Creek exist. Instead massive and prolonged southwest oriented floods were moving across the entire region. The flood flow direction was probably shaped as floodwaters eroded shallow channels into the underlying bedrock in which southwest-to-northeast oriented structures are common throughout southeast Pennsylvania. Floodwaters were flowing in complexes of shallow anastomosing channels (diverging and converging channels) with water also moving freely between the channels. The deep Delaware River valley then began to erode headward into this high-level surface to capture the southwest oriented flood flow.

Before eroding the southeast oriented valley seen in figure 1 the Delaware River valley first eroded headward (from present day Philadelphia) almost to present day Trenton, NJ along what must have been a major southwest oriented flood flow channel. South of Trenton the actively eroding Delaware River valley ceased to erode headward along that southwest oriented flood flow channel and began to erode headward in a north and northwest direction across the southwest oriented flood flow channels. Immense volumes of water were required to erode the deep Delaware River valley headward and comparable volumes of water were required to erode deep Delaware River tributary valleys headward from the newly eroded and deep Delaware River valley .

The deep east, southeast, and south oriented Neshaminy Creek valley (not seen in figure 1 and located south and west of the figure 1) eroded headward from the actively eroding southwest oriented Delaware River valley at a time when the deep south-oriented Delaware River valley seen in figure 1 had yet to be eroded. Headward erosion of the deep Neshaminy Creek valley and its south oriented tributary valleys (e.g. Mill Creek valley seen in the southwest corner of figure 1) captured the southwest oriented flood flow moving across the figure 1 map region. These captured floodwaters then eroded deep southwest-oriented valleys headward into the figure 1 map region. Erosion of the present day Pidcock Creek drainage basin began at this time with massive southwest oriented flood flow moving to the actively eroding Neshaminy Creek and tributary valleys (Mill Creek) significantly lowering the region between Buckingham, Solebury, and Jericho Mountains (with regions north of Solebury and Buckingham Mountains still being as high as those mountain tops are today).

Before the deep Neshaminy Creek valley could become the dominant regional drainage route the deep southeast and south-oriented Delaware River valley eroded headward across the southwest oriented flood flow channels that were supplying floodwaters to the actively eroding Neshaminy Creek drainage basin. Headward erosion of the deep Delaware River valley beheaded the southwest oriented flood flow channels in sequence from south to north. Floodwaters on northeast ends of the beheaded flood flow channels reversed direction to flow in a northeast direction to the newly eroded and much deeper Delaware River valley. In figure 1 the east oriented Jericho Creek drainage route was first created by such a flood flow reversal. The reversal of flow affecting the Pidcock Creek drainage basin first occurred between Bowman Hill and the north end of Jericho Mountain, and because the flood flow channels diverged and converged and because floodwaters were moving freely between the flood flow channels the reversed flow on newly beheaded flood flow channels could capture floodwaters from yet to be beheaded flood flow channels that first reversal of flood flow was able to erode the northeast oriented seen today.

Delaware River valley headward erosion next beheaded and reversed what must have been a deeper southwest oriented flood flow channel on the Pidcock Creek alignment between locations 5 and 6. Again because floodwaters could move freely between flood flow channels that reversed flow channel captured a yet to be beheaded (by Delaware River valley headward erosion) southwest oriented flood flow channel on the Pidcock Creek alignment between locations 3 and 4. Delaware River valley headward erosion beheaded that southwest oriented flood flow channel, but the reversed flow on the beheaded flood flow  channel ended up moving between locations 4 and 5 to the previously reversed flood flow channel. Again because floodwaters could move freely between flood flow channels the reversed flow on the Pidcock Creek alignment between locations 3 and 4 was able to behead and reverse flood flow on what had been southwest oriented channels between locations 10 and 11 and between locations 1 and 2. Again Delaware River valley headward erosion ended southwest flood flow on those newly captured flood flow channels and the reversed flood flow on those beheaded channels then used the present day Pidcock Creek route between locations 3, 4, 5, and 6 to reach the newly eroded and much deeper Delaware River valley.

For a time yet to be beheaded southwest oriented flood flow moving north of Solebury Mountain eroded the valley between Buckingham Mountain and Solebury Mountain at location 8. Such yet to be beheaded (by Delaware River valley headward erosion) southwest oriented flood flow was helping to erode the region north of Solebury and Buckingham Mountains at the time flood flow in the present day Pidcock Creek drainage basin was still being reversed. Note how the Pidcock Creek tributary originating at location 8 first flows in a southwest direction before turning to flow in a south direction to join northeast oriented Pidcock Creek at location 9. The southwest oriented Pidcock Creek tributary segment just downstream from location 8 illustrates how reversed flood flow in the Pidcock Creek drainage basin was able to progressively capture and reverse all southwest oriented flood flow channels in the region between Buckingham, Solebury, and Jericho Mountains while the much deeper southeast oriented Delaware River valley was still eroding headward to behead and reverse southwest oriented flood flow channels north of Solebury and Buckingham Mountains.

 

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