Examples of Philadelphia Area Water Gaps

· barbed tributary, Chester Valley, Delaware-Susquehanna drainage divide, Gulph Creek, Octoraro Creek, Piedmont Province, Schuylkill River, Valley Forge National Historical Park, water gap, Wissahickon Creek
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  • Eric Clausen Website: http://geomorphology… At present I am a professor emeritus having taught geology at Minot State University (North Dakota, USA) from 1968 until 1997. I was trained in geology at Columbia University and the University of Wyoming where my studies emphasized regional geomorphology. For many years I have pursued a research interest that developed when as result of geologic field work and interpretation of large mosaics of detailed North American topographic maps I discovered significant evidence previous investigators had ignored. Over a period of many years, after studying such anomalous evidence, I was forced to develop a fundamentally different interpretation of North American geomorphic history than that which is generally accepted. Geomorphology is the study of landforms and my interest as a geomorphology researcher is in determining the origin of large drainage systems, such as the Missouri River drainage basin in North America. The Missouri River drainage basin consists of thousands of smaller drainage basins, each of which has a history my essays (website posts) are trying to unravel. What I try to do is reconstruct the landscape the way it looked prior to the present day drainage system. I then try to determine how the present day drainage system evolved. While conducting my Missouri River drainage basin landform origins study I also developed an interest in scientific paradigms, especially in how scientific paradigms develop and how they are replaced. The Missouri River drainage basin landform origins project at geomorphologyresearch.com has been completed and I am currently creating a catalog of Philadelphia, PA area erosional landforms, which can be found at phillylandforms.info For off site questions and discussions about either project I can be contacted at eric2clausen@gmail.com

Water gaps are formed where a stream or river has cut a valley across some type of ridge. Pennsylvania’s water gaps are often associated with where streams and rivers have cut what are sometimes spectacular water gaps in the state’s Valley and Ridge Province. Often overlooked are numerous, but somewhat less specular water gaps found near Philadelphia in the southeast Pennsylvania Piedmont Province. This blog will use detailed topographic maps from the United States Geological Survey National Map website (sometimes supplemented with Google Earth images) to illustrate some of the many different types of water gaps found within a 50 mile radius of Philadelphia. Contour intervals for the topographic maps are not given but are generally 10 or 20 feet.

To start the figure 1 topographic map (below) shows where south-oriented Schuylkill River and Wissahickon Creek leave the Chester Valley floor to enter separate 250-to-300-foot-deep gorges carved across an upland of erosion resistant metamorphic and sedimentary rocks before finally reaching Philadelphia and the Coastal Plain (Wissahickon Creek joins the Schuylkill River near thee Schuylkill River gorge southeast end). While perhaps different from water gaps seen in the Ridge and Valley Province the Schulylkill River and Wissahickon Creek gorges qualify as water gaps because they are a river valley and stream valley eroded completely across an erosion resistant upland.

Figure 1: Topographic map from the United States Geological Survey (USGS) National Map website showing where the Schulykill River and Wissahickon Creek leave the Chester Valley floor to enter 250-300-foot-deep gorges carved completely across a highland composed of erosion resistant metamorphic and sedimentary rocks.

The Delaware River as it flows along what is now the Pennsylvania-New Jersey border has eroded several significant water gaps the most famous of which is in northeast Pennsylvania (and New Jersey) near Stroudsburg, Pennsylvania. Further to the south and much closer to Philadelphia is a somewhat less spectacular, but still significant water gap located just to the south of New Hope, Pennsylvania and Lambertsville, New Jersey which is seen in the figure 2a topographic map and in the figure 2b Google Earth image. The water gap is formed where the Delaware River has cut a 300-400-foot-deep valley across the diabase intrusion which now forms the Solebury Mountain and Goat Hill erosional remnants. The rapids seen in the Google Earth image are known as Wells Falls

Figure 2a. Topographic map from the USGS National Map website showing a Delaware River water gap to the south of New Hope (PA) and Lambertsville (NJ) between Solebury Mountain and Goat Hill.

Figure 2b. Google Earth image looking in a north direction showing the Delaware River water gap carved across the erosion resistant diabase intrusion which forms Pennsylvania’s Solebury Mountain (west) and New Jersey’s Goat Hill (east).

Another Philadelphia area water gap can be seen at the Valley Forge National Historical Park as illustrated in the figure 3a topographic map and the figure 3b Google Earth image. Today Valley Creek after flowing on the Chester Valley floor turns in a north direction to flow through the water gap located between Mount Joy and Mount Misery to reach the Schuylkill River as a barbed tributary, Note how the Schuylkill River turns at the point where Valley Creek joins it from flowing in a southeast direction to flow in a northeast direction.

Figure 3a. Topographic map from the USGS National Map website showing the Valley Creek water gap located in the Valley Forge National Historical Park.

Figure 3b. Google Earth image showing the Valley Creek water located at the Valley Forge National Historical Park.

One of the Philadelphia area’s most interesting water gaps is seen in figure 4 and is where Gulp Creek turns from a northeast-oriented valley leading to the Schuylkill River to flow through a water gap which is cut across a narrow, but high northeast-trending ridge before turning to flow in a parallel northeast-trending valley to reach the southeast-oriented Schuylkill River. What on the map look like wind gaps are deep cuts where Interstate 76 and Interstate 476 now cross the ridge (the Interstate 76 cut took advantage of a preexisting wind gap). Today one can travel through and get a good view of the narrow and tree covered Gulph Creek water gap by driving on a narrow road or by riding SEPTA’s Norristown High Speed Line between the Matsonford and Gulph Mills Stations.

Figure 4. Topographic map from the USGS National Map website showing the Gulph Creek water gap which is located near West Conshocken and just a few miles from Philadelphia.

In figure 5a two different major highways and two railroads converge to pass through the Sandy Run water gap near Fort Washington. Sandy Run is today a local stream which originates near the Chester Valley eastern end and which flows along the Chester Valley floor in a west direction until almost reaching south-oriented Wissahickon Creek. Instead of continuing to flow in a west direction to reach Wissahickon Creek Sandy Run turns in a north direction to flow through a water gap across the sandstone ridge which makes up the Chester Valley north wall and then joins south-oriented Wissahickon Creek as a barbed tributary. Note in figure 4a how Wissahickon Creek cut its own water gap across the sandstone ridge so as to enter the Chester Valley and how Loraine Run (which is today a very minor stream) has also cut a water gap across the same sandstone ridge. Figure 5b is a Google Earth image showing how the transportation routes converge at the Sandy Run water gap.

Figure 5a. Topographic map from the USGS National Map website showing how major transportation routes converge at the Sandy Run water gap and how Sandy Run turns in a north direction to leave the Chester Valley and to join south-oriented Wissahickon Creek as a barbed tributary.

Figure 5b. Google Earth image showing how major highways and two different railroads converge so as to take advantage of the Sandy Run water gap.

The Chester Valley is narrow structural valley extending for almost 100 miles from north of Philadelphia in a west-southwest direction and is bounded by erosion resistant ridges on either side and is crossed by at least seven different major drainage routes including Wissahickon Creek seen in figures 1 and 5a. Further to the southwest is the Valley Forge water gap which crosses the Chester Valley north wall seen in figures 3a and 3b and then further to the west-southwest are water gaps formed where East and West Brandywine Creeks and their tributaries enter and then leave the structural lowland. The greatest concentration of water gaps can be found near the Chester Valley’s west-southwest end and is shown in figure 6 which also shows how the Delaware River-Susquehanna River drainage divide crosses the Chester Valley floor. Note how Buck Run and Octoraro Creeks flow from the area to the north of the Chester Valley through water gaps to enter the Chester Valley and then to leave the Chester Valley. Also note how local north- and south-oriented Buck Run and Octoraro Creek tributaries have eroded water gaps as they flow in either north or south directions to enter the Chester Valley.

Figure 6. Topographic map from the USGS National Map website showing the Chester Valley’s west-southwest end area and at least nine different water gaps eroded across the erosion resistant ridges which form the Chester Valley’s north and south walls.

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