The tsunami washed over Fire Island and, to the west, waves perhaps as high as 20 feet spilled into Lower Manhattan. The furious onrush of water left sediment a foot and a half deep on the Jersey Shore, and debris cascaded far up the Hudson River. No, there’s no need to rush to higher ground, commandeer a rowboat in Central Park or empty the closet to grab the rubber boots. This disaster occurred about 2,300 years ago, though how bad it was, or even if it was a tsunami, remains in dispute. But several geologists have collected evidence indicating that...