Naruko

Geography & Climate

Naruko is located in Japan, within the Northeast Japan Volcanic Arc of the broader Northwestern Pacific Volcanic Regions. Situated at 38.73° N, 140.73° E in the Northern Hemisphere, the volcano lies within a temperate climate zone. At just 470 meters above sea level, Naruko 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 cluster, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Naruko 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 Naruko, 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 rhyolite, a silica-rich volcanic rock associated with highly viscous magma. Rhyolitic eruptions can be extremely explosive and are responsible for some of the largest volcanic events in Earth's history, including supervolcanic caldera-forming eruptions. The high silica content traps dissolved gases, building enormous pressure that can lead to catastrophic explosive releases.

Eruption History Summary

Naruko has 5 recorded eruptions in the geological database, spanning from 4400 BCE to 837 CE. The most powerful recorded event was a gentle, effusive event in 837 CE, reaching VEI 1 on the Volcanic Explosivity Index. This eruption frequency indicates a moderately active volcanic system with periodic reawakenings.

Significance

With 5 recorded eruptions on file, Naruko has enough documented activity to help scientists identify patterns in its eruptive behavior.

GVP Reference Summary

Naruko is a poorly defined, 5.5 x 7 km caldera NW of the city of Sendai. Formed during eruptions about 73,000 and 45,000 years ago, it contains a cluster of four dacitic lava domes of Holocene age surrounding the 400-m-wide lake-filled Katanuma crater. The highest of the low, but steep-sided lava domes, Ogadake, lies SE of the lake and reaches only 470 m above sea level. Ogadake and Kurumigadake domes are capped by conglomerates and mudstones uplifted during dome growth. The only recorded eruption in occurred in 837 CE. Water vapor and sulfur-dioxide gas emission occurs from Shurado crater on Toyagamori lava dome west of the lake and from the bottom of the crater lake, which is one of the most acidic in Japan, with a pH of 1.6. Solfataras are found on the western shore of Katanuma, and sulfur is mined from sediments on the lake floor.

— Smithsonian Institution, Global Volcanism Program