The 1792 Unzen earthquake and tsunami resulted from the volcanic activities of Mount Unzen (in the Shimabara Peninsula of Nagasaki Prefecture, Japan) on 21 May. This caused the collapse of the southern flank of the Mayuyama dome in front of Mount Unzen, resulting in a tremendous megatsunami, killing 15,000 people altogether. It was also called Shimabara erupted, Higo affected, (Shimabara means the central mountain of the Shimabara Peninsula) since many people were killed by this tsunami in Higo (Kumamoto Prefecture, situated 20 km (12 mi) away across the Ariake Sea). Source