Identifying Sinkholes with LiDAR
Sinkholes are depressions in the surface of the earth that form when bedrock dissolves over geologic time, causing a void to develop. Areas underlain by soluble rock such as limestone can develop multiple sinkholes – sinkholes are one part of a landscape that geologists call “karst terrain”. Most sinkholes, when present, are clearly visible on LiDAR derived data.
The image below shows numerous sinkholes in a narrow zone along a low ridge within the Catawba Valley in Roanoke County. The sinkholes are developing in limestone layers along the contact between the Beekmantown Formation and the Conococheague Formation. While a great deal of carbonate rock is present in the area shown, sinkhole development is obviously much more active within this specific set of layers.
Sinkholes in the center of this image are along the
Beekmantown-Conococheague Formation contact in Roanoke County
When carbonate rocks are exposed over a large area, sinkhole development can be widespread. The image below looks across U.S. Highway 460 in Giles County to show the “cratered” appearance of the land surface above soluable Middle Ordovician-aged limestone beds. Sinkhole development of this density can present challenges to building construction and engineering projects.
Sinkholes in Knox Group near Highway 460 Giles County
Sinkholes come in all shapes and sizes, depending on the size of the underground collapse. The large sinkhole near the top of the image below has formed in an area underlain by Middle Ordovician limestone in Bland County, and may represent the combined effects of several smaller collapse events. It is approximately 500 feet across. Note the road that curves around its lower edge.
Huge sinkhole in Bland County
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