Morris Run: An East Branch Perkiomen Creek Barbed Tributary

Authors

Morris Run is an East Branch Perkiomen Creek tributary located between Perkasie and Dublin in Bucks County and originates as a northeast oriented stream before turning in north, west, north, and northwest directions to join southwest oriented East Branch Perkiomen Creek. Most Morris Run tributaries flow in southwest directions to join north oriented Morris Run segments while the Morris Run valley appears to have beheaded a southwest oriented East Branch Perkiomen Creek tributary. Of further interest southwest oriented Morris Run tributaries originate in valleys parallel to a northeast oriented Tohickon Creek tributary while a northeast oriented Tohickon Creek tributary flows in a valley parallel to the southwest oriented East Branch Perkiomen Creek headwaters valley. Southwest oriented East Branch Perkiomen Creek eventually reaches the Schuylkill River while northeast oriented Tohickon Creek turns in a southeast and east direction to reach the south oriented Delaware River. Morris Run is flowing adjacent and roughly parallel to the Delaware-Schuylkill River drainage divide.

MorrisRun

Figure 1: Morris Run drainage basin area between Perkasie and Dublin. See text for detailed description. United States Geological Survey map digitally presented using National Geographic TOPO software. 

Figure 1 illustrates the Morris Run drainage basin area between Perkasie and Dublin. Location 1 identifies northeast oriented Threemile Run, which north of figure 1 flows to northeast oriented Tohickon Creek with water eventually flowing to the south oriented Delaware River. Location 2 identifies southwest oriented East Branch Perkiomen Creek with water eventually reaching the southeast oriented Schuylkill River. The stream identified with the number 3 is a southwest oriented East Branch Perkiomen Creek tributary. The number 4 is used to identify the northeast, north, west, north, and northwest oriented Morris Run drainage route and headwaters of three southwest oriented Morris Run tributaries. Note how Morris Run originates south of figure 1 as a northeast oriented stream and then turns to flow in a north, west, north, and northwest direction to reach southwest oriented East Branch Perkiomen Creek. Note also how the northern southwest oriented Morris Run tributary appears to be a northeast extension of the southwest oriented valley used by the stream identified by the number 3. Finally the number 5 identifies a northeast oriented Tohickon Creek tributary.

Several linear northeast-to-southwest oriented valleys and ridges cross the figure 1 map and suggest the ridges are composed of erosion resistant rock while the valleys are underlain by more easily eroded bedrock. The Pennsylvania Geologic Survey web applications map shows the Lockatong Formation underlies the ridges while the Brunswick Formation underlies the valleys. The Lockatong Formation is described as an argillite with zones of shale and some thin layers of limestone and impure calcareous shale. The Brunswick Formation is described as shale, mudstone, and siltstone. Apparently differences between these two formations were great enough to result in the ridge and valley pattern seen in figure 1. What makes Morris Run interesting is the fact that Morris Run after originating along a northeast oriented ridge crest ignores the underlying geology and flows in a north direction across northeast-to-southwest oriented ridges and valleys to reach the southwest oriented East Branch Perkiomen Creek valley. Further the north-oriented Morris Run drainage course is located almost adjacent to and parallel to the drainage divide between the Delaware River and the Schuylkill River. How does a drainage route transverse to the underlying geologic structure develop adjacent to and parallel to the drainage divide between two major river drainage basins?

To understand the Morris Run drainage route we need to first visualize the region before erosion of present day valleys began. At that time the entire region was at least as high, if not higher, than the highest points in figure 1 today and there was no deep Delaware River east of figure 1. Instead the high upland surface continued in a northeast direction into present day New Jersey and massive and prolonged southwest oriented floods were moving from New Jersey across the present day Bucks County region (including the figure 1 map region). The flood source cannot be determined from southeast Pennsylvania evidence, although continental ice sheet melt water would be a likely and logical possibility. Whatever the flood source the floodwaters were flowing in anastomosing complexes of shallow southwest oriented diverging and converging channels. Initially no deep valleys provided a nearby lower base level and as a result floodwaters were unable to deeply erode the figure 1 area upland surface.

Deep erosion of the figure 1 map area began when headward erosion of the deep south oriented Perkiomen Creek valley (west and south of figure 1) from the actively southeast oriented Schuylkill River valley captured the southwest oriented flood flow moving across the figure 1 map area. With a lower base level to the southwest the southwest oriented flood flow was able to erode valleys headward along the easily eroded bedrock units between the more erosion resistant bedrock units, which gradually emerged as ridges. The deepest southwest oriented valley eroded headward along the present day East Branch Perkiomen Creek drainage route. The north oriented Morris Run valley eroded headward from the deep East Branch Perkiomen Creek valley and captured flood flow moving in shallower southwest oriented flood flow channels to the southeast. The northeast oriented Morris Run headwaters drainage route was created by a reversal of flood flow on the northeast end of a beheaded southwest oriented flood flow channel.

At the same time that the deep southwest oriented East Branch Perkiomen Creek valley was eroding headward into the figure 1 map area the much deeper south-oriented Delaware River valley was eroding headward across the region east of figure 1 and the present day southeast and east oriented lower Tohickon Creek valley eroded headward from the actively eroding Delaware River valley head. Headward erosion of the southeast-oriented Tohickon Creek valley segment east of figure 1 progressively captured in sequence from south to north the southwest oriented flood flow channels crossing figure 1. When the flood flow channels were beheaded floodwaters on northeast ends of shallower channels reversed direction to flow to the deeper Tohickon Creek valley. However, not all floodwaters reversed direction. The actively eroding southwest oriented East Branch Perkiomen Creek valley in the figure 1 map region was as deep (or deeper) than the actively eroding Tohickon Creek valley and as a result there was no reversal of flow in the East Branch Perkioment Creek valley seen in figure 1 (there was a reversal of flow east and north of figure 1 to create a northeast oriented Tohickon Creek tributary).

 

 

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: