The Meadow Bank: A Nontectonic Linear Feature in the Wabash Valley Seismic Zone

The Meadow Bank (MB) is a 10-km-long and 5- to 7-m-high linear scarp in glacial sediments, trending north-northeast along the west edge of the Wabash River Valley in southeast Illinois. The MB is within the Wabash Valley seismic zone and closely parallels the trace of the Herald–Phillipstown fault zone, which lies 1 km west of the MB. Previous geophysical studies found no underlying faulting but did not provide a conclusive explanation for how such a long straight feature could have been formed. Recently available mine maps in the area demonstrate that there has been no post-Pennsylvanian faulting below the MB. We used closely spaced boreholes to develop evidence that the MB is the result of erosion, not tectonics. Most likely, the MB is an erosional scarp formed by a late-glacial outburst flood.