The 1792 Unzen earthquake and tsunami resulted from the volcanic activities of

Mount Unzen is an active volcanic group of several overlapping stratovolcanoes, near the city of Shimabara, Nagasaki on the island of Kyushu, Japan's southernmost main island. In 1792, the collapse of one of its several lava domes triggered a megatsunam ...

(in the

Shimabara Peninsula is a peninsula located in Nagasaki Prefecture on the island of Kyushu, Japan. The peninsula incorporates the cities of Shimabara, Minamishimabara, Unzen. It was also the site of the Shimabara Rebellion, a 1637-1638 peasant and rōnin revolt, led ...

Nagasaki Prefecture is a Prefectures of Japan, prefecture of Japan located on the island of Kyūshū. Nagasaki Prefecture has a population of 1,314,078 (1 June 2020) and has a geographic area of 4,130 Square kilometre, km2 (1,594 sq mi). Nagasaki Prefecture borders ...

, 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 A megatsunami is a very large wave created by a large, sudden displacement of material into a body of water. Megatsunamis have quite different features from ordinary tsunamis. Ordinary tsunamis are caused by underwater tectonic activity (movemen ...

, killing 15,000 people altogether. It was also called , (Shimabara means the central mountain of the Shimabara Peninsula) since many people were killed by this tsunami in Higo (

Kumamoto Prefecture is a Prefectures of Japan, prefecture of Japan located on the island of Kyūshū. Kumamoto Prefecture has a population of 1,748,134 () and has a geographic area of . Kumamoto Prefecture borders Fukuoka Prefecture to the north, Ōita Prefecture to ...

, situated across the

Ariake Sea The is a body of salt water surrounded by Fukuoka, Saga, Nagasaki, and Kumamoto Prefectures, all of which lie on the island of Kyūshū in Japan. It is the largest bay in Kyūshū. Its deepest point is only about 50 meters (165 ft) deep, and ...

Volcanic activities

Towards the end of 1791, a series of earthquakes occurred on the western flank of Mount Unzen which gradually moved towards Fugen-dake (one of Mount Unzen's peaks). In February 1792, Fugen-dake started to erupt, triggering a lava flow which continued for two months. Meanwhile, the earthquakes continued, shifting nearer to the city of Shimabara. On the night of 21 May, two large earthquakes were followed by a collapse of the eastern flank of Mount Unzen's Mayuyama dome, causing a landslide which swept through the city of Shimabara and into Ariake Bay, triggering a great tsunami. File:Unzen pyroclastic and lahar deposits.jpg, Mount Unzen (center) and Mayuyama (right) showing the destruction, recent photo File:Shimabara Mayuyama.jpg, Mayuyama of Shimabara Peninsula, from the sea of Shimabara City

Megatsunami

It is not known whether the collapse occurred as a result of an eruption of the dome or as a result of the earthquakes. The tsunami struck Higo Province on the other side of Ariake Bay before bouncing back and hitting Shimabara again. Out of an estimated total of 15,000 fatalities, around 5,000 are thought to have been killed by the landslide, around 5,000 by the tsunami across the bay in Higo Province, and a further 5,000 by the tsunami returning to strike Shimabara. The initial wave once reached a height of , classing this tsunami as a

. At the Osaki-bana point Futsu town, the waves locally grew to a height of due to the effect of sea bottom topography.

Monuments

As of July, 1991, the following monuments have been found:''200 Years after the Kansei Great Tsunami, Symposium and Exhibition of Unzen Disaster'' Booklet published by Newspaper Museum, Yoyasu Machi, Kumamoto-shi, 1991

Lake Shirachi

Lake Shirachi is a pond in Shimabara city, Nagasaki Prefecture which was created after the landslide at Mayuyama created by the inpouring of underground water. Its size was first 1 km (south-north) and 300m 400m (east to west), but the production of a water exit river made it smaller and it is now 200 m by 70 m.

Tsukumojima (99 Islets)

As a result of the destruction, Tsukumojima or 99 islets or rocks were distributed near Shimabara city. In the same

, there are 99 islands or Kujūkushima distributed from

Sasebo is a core city located in Nagasaki Prefecture, Japan. It is also the second largest city in Nagasaki Prefecture, after its capital, Nagasaki. On 1 June 2019, the city had an estimated population of 247,739 and a population density of 581 persons p ...

city to

Hirado is a city located in Nagasaki Prefecture, Japan. The part historically named Hirado is located on Hirado Island. With recent mergers, the city's boundaries have expanded, and Hirado now occupies parts of the main island of Kyushu. The component ...

city. These islands are different from Tsukumojima.

References