I can tell you very definitely that Lake Waccamaw, a Carolina Bay lake in southeastern North Carolina, is NOT an impact crater or basin formed by a tsunami. The lake is not more than 10,000 years old, is extremely shallow for its size (max depth ~ 12 feet), and is underlain by marine clay only 2-3 feet below the bottom. I know, I cored the lake in 1986 with my paleolimnologist colleague, Dr. Curt Stager. We published the results of that study in the Journal of the Elisha Mitchell Scientific Society in 1987. Our best guess on the formation of the Carolina bays is that they are wind ablation basins, much like playa lakes in west Texas and elsewhere. Impact craters have very different morphologies and tsunamis do not make elliptical basins.