Postglacial wedges cutting stratified late Quaternary glacial deposits have been widely reported throughout the northeastern United States. Previous interpretations of these features as periglacial ice-wedge casts have proved untenable for at least several of the reported localities. This conclusion is also reached in our detailed study of 29 such wedges at a gravel quarry in eastern Connecticut. The wedges there are found to be planar vertical zones that widen upward from a few centimetres to as much as 150 cm, and that contain material injected from below as well as collapsed from the sides. These zones are interpreted as extension and collapse fissures that served as conduits for water and liquefied sediment during one or more prehistoric liquefaction events. Seismic excitation seems the most likely cause for the episode(s) of liquefaction and violent dewatering. Similar phenomena were reported to accompany large eighteenth-century earthquakes in New England. If the relation between large earthquakes and wedges is substantiated at our study locality and other localities, these possibly contemporaneous features may provide an opportunity to determine the felt-area magnitude of prehistoric earthquakes in the northeastern United States.

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