DETAILS OF THE EXTENT AND ORIGIN OF THE JACKSVILLE ESKER/DELTA COMPLEX, AND ASSOCIATED DRAINAGE DIVERSIONS REVEALED BY LIDAR, BUTLER COUNTY, PENNSYLVANIA

The existence of the Jacksville Esker in Butler County, Pennsylvania has long been known. Leverett noted its existence in his 1902 USGS Monograph XLI. He also noted a gravel plain at the end of the esker at the glacial margin. Sitler (1957) mapped the esker, but didn’t notice the extensive delta form beyond it on his 15’ quadrangle topographic base map. He mapped several patches of sand and gravel beyond the esker only where it was exposed in small pits.

With the advent of LiDAR bare earth images, both hillshade and shaded slope maps, as well as the DEM, the details of the complex of esker, delta, lake plain, and 3 drainage diversions can be identified. Much of this detail was not obvious from the 15’ nor 7½’ topographic maps, because of the 20-foot contour interval, nor in the field because of extensive vegetative cover. Additional esker segments along the same trend in an upstream direction were identified using LiDAR images (Durco, 2009). These segments were probably once continuous with the downstream 3 miles of the esker, extending the length of the original esker to at least 9 miles, and possibly longer if it connects with the Schollard Run esker.

Recognition of the details of the delta allowed the determination of the drainage history resulting from the esker and delta deposition. In addition to the main diversion of Black Run into the adjacent Hogue Run valley, apparent on topographic maps, a sequence of 2 additional minor diversions emerged from the LiDAR images.

Recent mining of the delta deposits revealed a much more complex depositional history than a simple delta built into an ice-dammed lake by the subglacial stream that also deposited the esker. Even with the greater detail of the external landforms revealed on LiDAR images, the entire history cannot be determined without internal study of the deposit. Internal study reveals a complicated sequence of multiple delta lobes from multiple sources. LiDAR is still limited in what it can reveal but has allowed the geomorphic recognition of the entire depositional complex, and determination of the drainage diversion history.