阿武火山群 - Abu Volcanic Group - 3/4/2025

My Experience: I meandered through and visited multiple geologic sites related to the Abu Volcano field. (All of which will also be condensed into upcoming Youtube video)

Ryuringo 龍鱗郷  - Is a site that shows basalt columnar joints, a rock surface with magnificent rows of hexagonal stone pillars, were discovered by chance during construction of a farm road in the Ogawa area. It has been designated a natural monument of Yamaguchi Prefecture. https://www.hagishi.com/search/detail.php?d=1100254

Saruya Falls 猿屋の滝 - another site moving south from Ryuringo that you can also views hexogonal basalt joints

Tatamigafuchi 畳ヶ淵 - A neatly arranged hexagonal rock formation. One of Yamaguchi Prefecture's Top 100 Natural Sites. The tortoiseshell-shaped rocks that line the riverbed like paving stones and the 70cm-long hexagonal columnar jointed pillars that stand vertically on the riverbank create a magnificent natural beauty. These rocks were formed when the lava that flowed from a volcanic eruption cooled and hardened into regular hexagons. https://www.hagishi.com/search/detail.php?d=1100201

Irao Volcanic Ash Observation Facility イラオ火山灰層観察施設 - which shows the history (in ash layers) of the Irao volcano

Finally, pulled into the town of Hagi. For the most part it was raining heavily all day so visited the Mt. Kasayama Observatory 笠山山頂展望台 which also provides views to the many other "Abu" eruptive sites (islands), from the observatory

Kasumayama does itself have a crater (see directly below but very small). So, all that said, I am sure there are a variety of small hikes, mostly visiting the "Abu Volcanoes" is spread across a vast area with many sites to visit that tell the story of history and eruptions. The town of Hagi itself is known for Fugu (Blowfish) and earthenware specifically so you can also pick up a variety of Fugu items from the local stores. I visited JF Yamaguchi Hagi District MarketＪＦやまぐち（山口県漁協）萩地方卸売市場

Walking down into crated of Kasumayama, literally a 5 minute walk.

Demographics

• Volcano No.- H26
• Volcano name - Abu Volcano Group
• Geologic code **Q3b
• Main activity period - Gelasian (first half of Early Pleistocene) - HoloceneActivity period / recent activity ***From 1.9 Ma.
• Latest eruption: 8,800 yBP (Kasayama Scoria Cone)
• Volcano type - Pyroclastic cone, Lava flow, Lava dome
• Representative rock type - Mafic
• Main rock type ****Basalt, Andesite
• Height above sea level - 571 m (Nishidai), 626 m (Monomidake), 641 m (Iraoyama)
• Location (Prefecture)YAMAGUCHI
• Active volcano name by JMA - Abu Volcanoes
• Record of eruption & disaster: Not indicated by GSJ although Global Volcanism Program indicates the group dates from 800,000 years ago and was active into the Holocene era with the last eruption occurred around 8800 years ago
• Additional comments : None
• Source: GSJ

About

Abu (阿武火山群, Abu Kazan-gun) is the name of a group of shield volcanoes located on the coast of Japan on the southwest end of the island of Honshū. It is primarily based in the city of Hagi, Yamaguchi Prefecture.

The group dates from 800,000 years ago and was active into the Holocene era. The last eruption occurred around 9000 years ago.

The group of volcanoes consists of basalt and dacitic lava flows, small shield volcanoes, cinder cones, and lava domes. Altogether, there are about 40 volcanoes, with the highest peak being Irao-yama.

Volcanic activity in the region is related to subduction of the Philippine Sea Plate.

The erupted magmas of Abu are mainly alkaline basalt and calc-alkaline andesite - dacite in composition.

Geological Summary

The dominantly Pleistocene Abu volcano group, located along northern coast near the SW end of Honshu, consists of basaltic-to-dacitic lava flows, small shield volcanoes (some with associated cinder cones), and lava domes. More than 40 monogenetic volcanoes are located in an area of 400 km2. Iraoyama forms the high point of this group of edifices, some of which form offshore islands or submarine vents. Volcanism here is considered to be related to subduction of the Philippine Sea Plate. An earlier phase of activity during the late-Pliocene to early Pleistocene was followed by renewed activity about 800,000 years ago that continued into the Holocene. The latest known activity was determined by thermoluminescence to be about 8,800 years ago, when the Kasayama scoria cone was formed. Source: Global Volcanism Program

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