Yonemaru-Sumiyoshiike

Geography & Climate

Yonemaru-Sumiyoshiike is located in Japan, within the Ryukyu Volcanic Arc of the broader Western Pacific Volcanic Regions. Situated at 31.77° N, 130.59° E in the Northern Hemisphere, the volcano lies within a subtropical climate zone. At just 40 meters above sea level, Yonemaru-Sumiyoshiike is a relatively low-elevation volcanic feature. Despite its modest height, it remains an active geological formation with the same underlying magmatic processes as its taller counterparts. The volcanic landform is characterized as a minor (basaltic), which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Yonemaru-Sumiyoshiike 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 Yonemaru-Sumiyoshiike, 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 basalt / picro-basalt, 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

Yonemaru-Sumiyoshiike has 2 recorded eruptions in the geological database, spanning from 6250 BCE to 6200 BCE. The most powerful recorded event was a severe eruption capable of regional ash fall and pyroclastic flows in 6200 BCE, reaching VEI 3 on the Volcanic Explosivity Index. These eruptions span roughly 50 years of volcanic history.

Significance

With a maximum recorded VEI of 3, Yonemaru-Sumiyoshiike 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.

GVP Reference Summary

Yonemaru and Sumiyoshiike are basaltic maars formed in coastal lowland deposits north of the Aira caldera, on the SW and SE flanks of the small Pleistocene Aojiki cone. The three features are also known as the Kamo Volcanic Field. The maar eruptions occurred during a period of rising sea level at the beginning of the Holocene. The 500-m-wide Sumiyoshiike was created about 7,000 years ago. The larger, 1.2-km-wide Yonemaru erupted about 2 km W of Sumiyoshiike about 6,500 years ago and produced pyroclastic surges that traveled 4 km from the vent.

— Smithsonian Institution, Global Volcanism Program