Most subaerial eruptions are associated with subduction zones, places where oceanic plates are forced under overriding, less dense plates. In this setting, heat and water in the mantle cause rocks to melt. If the melt (magma) makes it to the surface there is an eruption. There are no active subduction zones on the east coast (or the Great Plains).
I don't know of any place in the Central Plains that has experienced volcanic activity directly. Ashfall State Historical in Nebraska has some fantastic features that are the result of an ashfall from a vent near Yellowstone.
Steve Mattox
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