On August 18, 1741, the remote volcanic island of Oshima-Ōshima in the Sea of Japan began a catastrophic eruption that would trigger one of history's most devastating tsunamis. Eleven days into the eruption, on August 29, a massive sector collapse sent an estimated 2.4 cubic kilometers of the volcano—comparable to Mount St. Helens—plunging into the sea, generating the Kampo tsunami with wave heights reaching a staggering 90 meters (300 feet). The collapse reduced the volcanic peak from 850 meter