Edge Hill Wind Gap

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The SEPTA Lansdale line between Glenside and North Hills and Limekiln Pike cross Edge Hill Ridge at the Edge Hill Wind Gap. The Edge Hill Wind Gap is one of three wind gaps cut into the Wissahickon Creek-Tacony Creek drainage divide along the northeast oriented Edge Hill Ridge with the other two wind gaps being the Ardsley Wind Gap to the northeast and the Seminary Wind Gap to the southwest. The Edge Hill Wind Gap floor elevation was probably about 350 feet before being altered by railroad and highway construction. Edge Hill Ridge crest elevations vary but exceed 400 feet at numerous points. The region north of the Edge Hill Wind Gap is drained today by west oriented Wissahickon Creek tributaries with Wissahickon Creek being a Schuylkill River tributary. South of the Edge Hill Wind Gap water today drains to south oriented Tacony Creek, which flows to the Delaware River and the Edge Hill Wind Gap is located on the Schuylkill River-Delaware River drainage divide. While not as spectacular as wind gaps elsewhere in Pennsylvania the Edge Hill Wind Gap provides important scientific information related to the Delaware River and Schuylkill River drainage basin origins.

Figure 1. Ardsley Wind Gap.

Figure 1. The Edge Hill Wind Gap is found at location 2 where the SEPTA Lansdale Regional Rail line and Limekiln Pike cross the southwest-to-northeast oriented Edge Hill Ridge. Edge Hill Ridge today forms the Wissahickon-Tacony Creek drainage divide and extends from the Seminary Wind Gap (location 5) to the Ardsley Wind Gap (location 1). Tacony Creek (sometimes known in this region as Tookany Creek) flows from location 3 to the Jenkintown Elbow of Capture, where it turns to flow in a south-southeast direction and eventually reach the southwest oriented Delaware River. Location 6 shows headwaters of a west oriented stream flowing to Wissahickon Creek, which then flows through the deep Wissahickon Creek Gorge to reach the southeast oriented Schuylkill River. United States Geological Survey map digitally presented using National Geographic TOPO software. 

The Edge Hill Wind Gap is oriented in a northwest to southeast direction suggesting it was eroded by southeast oriented flow moving across what are today west oriented Wissahickon Creek tributary drainage basins to reach what at that time was the actively eroding and deeper Tacony Creek drainage basin to the south. Water would have flowed through the wind gap and then in a southeast direction along the route used by the SEPTA Lansdale Regional Rail line and would have joined Tacony Creek near the Jenkintown Elbow of Capture. This route suggests the deep south-oriented Tacony Creek valley eroded headward from what was probably a newly eroded southwest oriented Delaware River valley to capture southwest oriented flow until it encountered erosion resistant bedrock in the northeast oriented Edge Hill Ridge. Headward erosion of the south oriented Tacony Creek valley up until it encountered the Edge Hill Ridge obstacle was probably across multiple southwest-oriented flow channels such as might be found in a southwest oriented anastomosing channel complex.

When the south oriented Tacony Creek valley eroded headward to the Edge Hill Ridge region the area north of the Edge Hill Ridge was higher in elevation than present day Edge Hill Ridge crest elevations and southwest oriented flow moved across that high-level surface. The Edge Hill Ridge is composed of erosion resistant rock and limited the ability of the south-oriented Tacony Creek valley to erode headward into less erosion resistant bedrock located north and west of the ridge. Tacony Creek valley headward erosion did erode the Edge Hill Wind Gap notch as it eroded headward into the area north and west of the Edge Hill Ridge and started to capture southwest oriented flow on that higher-level surfae. However, once the deep south oriented Wissahickon Creek valley eroded its gorge across northwest Philadelphia, southwest oriented flow to the Wissahickon Creek valley was able to erode the less erosion resistant rocks north of the Edge Hill Ridge much faster than the captured flow eroding the Edge Hill Wind Gap valley floor. As a result flow to the Tacony Creek valley moving across the Edge Hill Wind Gap floor was beheaded as southwest oriented flow to the Wissahickon Creek valley deeply eroded the less erosion resistant material north of the Edge Hill Ridge.

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