雲仙岳 (平成新山) - Unzen (Heisei Shinzan) - 10/26/2023

About: Mount Unzen (雲仙岳, Unzen-dake) 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 megatsunami that killed 14,524 people in Japan's worst volcanic-related disaster. The volcano was most recently active from 1990 to 1995, and a large eruption in 1991 generated a pyroclastic flow that killed 43 people, including three volcanologists.

Its highest peaks are Fugen-dake (普賢岳) at 1,359 meters (4,459 ft) and Heisei-shinzan (平成新山) at 1,486 meters (4,875 ft). The latter emerged during the eruptions of the early, eponymous Heisei era (1989–2019).

Mount Unzen (or Unzen-dake) rises in the central part of the Shimabara Peninsula, Nagasaki Prefecture. It is located on the outer ring of the Chijiwa Caldera centering on Tachibana Bay in the west of the peninsula. It consists of a total of more than 20 mountains, however, the complexity in the shape of Unzen-dake was expressed by various numbers (such as Mitake Goho/Mimine Godake as "24th peak", or Yatsuha as "36th peak"). As a result, the usage of only eight mountains (sometimes three mountains) was coined in a narrow sense, but historically it is a name that refers to the entire mountain range towering over the sea. It is often confused with the name of the oldest peak, Fugen-dake.

Surrounding the highest peak of Heisei-shinzan (1,483 m (4,865 ft)), are Fugen-dake (1,359 m (4,459 ft)), Kunimi-dake (1,347 m (4,419 ft)), Myoken-dake (1,333 m (4,373 ft)), Nodake (1,142 m (3,747 ft)), Kusenbedake (1,062 m (3,484 ft)), and Yadake (943 m (3,094 ft)). Fugen-dake and Heisei-shinzan derive magma from the Chijiwa Caldera. In other words, it is supplied from a magma chamber beneath Tachibana Bay off Obama Onsen. The main peak is Fugen-dake, but the volcanic activity from 1990 (Heisei 2) to 1995 (Heisei 7) made Heisei-shinzan, which was higher in elevation. Heisei-shinzan is also the highest peak in Nagasaki Prefecture.

Unzen originally read "onsen" in the notation of a hot spring, but it was changed to the current notation when it was designated as a national park. An army radar base was built near the summit of Fugen-dake during the Pacific War, where about 100 people were stationed. (Source: Wikipedia)

Geological Summary: The massive Unzendake volcanic complex comprises much of the Shimabara Peninsula east of the city of Nagasaki. An E-W graben, 30-40 km long, extends across the peninsula. Three large stratovolcanoes with complex structures, Kinugasa on the north, Fugen-dake at the east-center, and Kusenbu on the south, form topographic highs on the broad peninsula. Fugendake and Mayuyama volcanoes in the east-central portion of the andesitic-to-dacitic volcanic complex have been active during the Holocene. The Mayuyama lava dome complex, located along the eastern coast west of Shimabara City, formed about 4000 years ago and was the source of a devastating 1792 CE debris avalanche and tsunami. Historical eruptive activity has been restricted to the summit and flanks of Fugendake. The latest activity during 1990-95 formed a lava dome at the summit, accompanied by pyroclastic flows that caused fatalities and damaged populated areas near Shimabara City.

This volcano is located within the Unzen, a UNESCO Global Geopark property. (Source: Global Volcanism Program)