The 1792 Unzen landslide 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 megatsuna ...

(in the Shimabara Peninsula of

Nagasaki Prefecture is a Prefectures of Japan, prefecture of Japan, mainly located on the island of Kyūshū, although it also includes a number of islands off Kyūshū's northwest coast - including Tsushima and Iki. Nagasaki Prefecture has a population of 1,246,4 ...

, 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

tsunami A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...

, 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 t ...

, 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 ext ...

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 the

, 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 was an old province of Japan in the area that is today Kumamoto Prefecture on the island of Kyūshū. It was sometimes called , with Hizen Province. Higo bordered on Chikugo, Bungo, Hyūga, Ōsumi, and Satsuma Provinces. History The cas ...

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

megatsunami A megatsunami is an incredibly large wave created by a substantial and sudden displacement of material into a body of water. Megatsunamis have different features from ordinary tsunamis. Ordinary tsunamis are caused by underwater tectonic activi ...

. 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 the second-largest city in Nagasaki Prefecture, after its capital, Nagasaki. , the city had an estimated population of 230,873 in 102,670 households, and a population density of 540 per ...

city to

Hirado is a city located in Nagasaki Prefecture, Japan. , the city had an estimated population of 28,172, and a population density of 120 people per km2. The total area of the city is Geography Hirado City occupies the northern part of Nagasaki P ...

city. These islands are different from Tsukumojima.

References