Factors Causing Sinkhole Development In Northhampton County, Pennsylvania

Abstract

Stratigraphic and structural analyses combined with electrical resistivity soundings and drilling were used to investigate factors causing the development of sinkholes at a site in Northampton County, Northeastern Pennsylvania. By compiling and contrasting data obtained from these investigative techniques, it was possible to hypothesize the manner in which local carbonate geology determines the development of sinkholes in the area. Bedrock at the site is comprised mostly of the Epler Formation, which contains both dolomite and limestone, and is covered by glacial till which varies in thickness between meters and tens of meters. It seems, however, that sinkholes in the study area occur only in the limestone units. In areas underlain primarily by dolomite no sinkholes were detected. Sinkhole development appears to be related to the greater solubility of limestone relative to dolomite. This solubility difference produces pinnacled bedrock topography in areas underlain by limestone, in contrast to the low relief subsurface topography in areas underlain by dolomite. Electrical resistivity measurements, while not capable of distinguishing limestone from dolomite directly, can distinguish the two types of bedrock topography. Although resistivity was not able to conclusively detect clay and water filled voids directly, it was able to detect air-filled features within the bedrock. I conclude that resistivity can be used to ascertain whether the subsurface geology is characteristic of bedrock prone to the development of voids, and to decide where to drill when searching for direct evidence of voids, but only with a thorough understanding of the local geology.