March 11 marked the 10th anniversary of the Tohoku Earthquake and accompanying tsunami which took the lives of almost 16,000. While Kumamoto does not face the threat of a plate-thrust induced tsunami, it does face a threat from a different cause: the Mt. Fugen volcano on Shimabara Peninsula in Nagasaki Prefecture.
On May 21, 1792, volcanic activity on Mt. Fugen caused a massive landslide of 340 million cubic meters to tumble into Ariake Sea, resulting in a tsunami reaching 22 meters in Kumamoto; a “bathtub effect” of energy reflected back at Shimabara, which, due to its more abrupt shoreline inclination, created a tsunami as massive as 57 meters. These killed some 5,000 in Kumamoto and 10,000 in Shimabara. Remnants of this disaster can be seen in the numerous islets off Shimabara known as Tsukumojima (九十九島). The disaster is known as the “Shimabara Taihen Higo Meiwaku” (島原大変肥後迷惑), which can be translated as “Disastrous for Shimabara, Troublesome for Higo,” somewhat downplaying the latter - waters would have ebbed up Kamitori.
Such an event is unlikely to reoccur in our lifetimes, but don’t turn your back on Mt. Fugen - its last major eruption, pictured below, was as recent as 1991. - William