The Japanese volcano whose 1792 eruption caused a tsunami that killed over 15,000 people was Mount Unzen. The disaster occurred on the Shimabara Peninsula in Kyushu, where volcanic activity at Fugen-dake was followed by the collapse of the eastern flank of the Mayuyama lava dome.
The eruption began in February 1792 after months of earthquakes. Lava flows continued for nearly two months, but the greatest destruction came later, on 21 May, when a powerful earthquake helped trigger the flank collapse. Millions of tonnes of rock rushed into Ariake Bay, generating a tsunami that struck both sides of the bay. About 15,000 people died in total, making it Japan’s deadliest volcanic disaster.
Mount Unzen is a volcanic complex with several peaks, including Fugen-dake and Heisei-shinzan. It became internationally known again during its 1990–1995 eruption, when pyroclastic flows killed 43 people, including volcanologists. That modern tragedy can cause confusion with the 1792 event, but both disasters are associated with Mount Unzen. Mount Fuji, Mount Asama, and Mount Ontake are separate Japanese volcanoes with different eruptive histories.