Geologists have evidence that 32,000 years ago, on the western edge of the Hawaiian Island of Oahu, a relatively small volcano whose west-facing wall lay alongside the Atlantic Ocean, experienced a major underwater fissure along an undersea flank. Perhaps caused by a minor magmatic tremor, it allowed countless thousands of gallons of cool seawater to suddenly pour into a complex labyrinthine network of volcanic lava tubes already heated to hundreds of degrees by the underground chambers of liquid rock. The sudden flash of steam in the enclosed geologic formation exploded with such violence that the entire western wall of the…