Adatarayama

Geography & Climate

Adatarayama is located in Japan, within the Northeast Japan Volcanic Arc of the broader Northwestern Pacific Volcanic Regions. Situated at 37.65° N, 140.28° E in the Northern Hemisphere, the volcano lies within a temperate climate zone. With a summit elevation of 1,728 meters above sea level, Adatarayama is a moderately sized peak that remains accessible to hikers and researchers for much of the year. The volcanic landform is characterized as a composite, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Adatarayama sits in a subduction zone, where one tectonic plate dives beneath another, creating intense heat and pressure that generates magma. Subduction zones are responsible for many of the world's most explosive volcanoes and deadliest eruptions. For communities in Japan near Adatarayama, this tectonic setting means the volcano is capable of producing powerful explosive eruptions, pyroclastic flows, and lahars that can threaten populated areas within tens of kilometers of the summit. The dominant rock type is andesite / basaltic andesite, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Adatarayama has 13 recorded eruptions in the geological database, spanning from 8050 BCE to 1996 CE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 590 BCE, reaching VEI 3 on the Volcanic Explosivity Index. Notable eruptions include 590 BCE (VEI 3), 2600 BCE (VEI 3), 4300 BCE (VEI 3). This level of eruptive frequency indicates a persistently active volcanic system that warrants ongoing monitoring. The most recent eruption in 1996 CE places this volcano within the modern era of volcanological observation.

Significance

With a maximum recorded VEI of 3, Adatarayama has produced eruptions capable of generating pyroclastic flows and significant ash fall in the surrounding area. While not among the largest eruptions globally, VEI 3 events pose serious hazards to local populations and can disrupt regional air travel. With 13 recorded eruptions, Adatarayama has a substantial eruptive history that provides valuable data for understanding volcanic behavior and assessing future hazards in the Northwestern Pacific Volcanic Regions region. Given its recent activity, Adatarayama is closely monitored by geological survey organizations to provide early warning of future unrest.

GVP Reference Summary

The broad forested massif of Adatarayama volcano is located E of Bandai volcano, about 15 km SW of Fukushima city. It consists of a group of dominantly andesitic stratovolcanoes and lava domes that rise above Tertiary rocks on the south and abut Azumayama volcano on the north. Construction took place in three main stages that began about 550,000, 350,000, and 200,000 years ago. The high point of the complex is 1728-m-high Minowasan, a dome-shaped stratovolcano north of Tetsuzan, the currently active stratovolcano. Numanotaira, the active summit crater, is surrounded by hot springs and fumaroles and is breached by the Iogawa river ("Sulfur River") on the west. Seventy-two workers of a sulfur mine in the summit crater were killed during an eruption in 1900. Historical eruptions have been restricted to the 1.2-km-wide, 350-m-deep Numonotaira crater.

— Smithsonian Institution, Global Volcanism Program