Mount Unzen's 1792 collapse caused a tsunami that killed about 15,000 people in Japan.
Mount Unzen is a volcanic complex on the Shimabara Peninsula of Kyushu. During the 1792 eruption, lava domes and unstable volcanic slopes developed on its Mayuyama area. On 21 May, part of the flank collapsed into Ariake Bay, displacing water and generating a devastating tsunami.
The combined effects of the landslide and waves killed roughly 15,000 people, making the disaster Japan's deadliest volcanic event. The tsunami caused most of the fatalities, rather than direct burial by lava. This is why the 1792 event is often discussed as a volcano-related landslide disaster as well as an eruption.
Unzen also erupted dramatically from 1990 to 1995, when lava domes and pyroclastic flows threatened communities. It should not be confused with Mount Aso, another large volcanic complex on Kyushu.