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| Shikotsu-Tōya Volcanic Group | |
|---|---|
| Name | Shikotsu-Tōya Volcanic Group |
| Location | Hokkaido, Japan |
| Type | Complex volcano |
| Last eruption | ongoing fumarolic activity |
Shikotsu-Tōya Volcanic Group is a cluster of calderas, stratovolcanoes, lava domes and monogenetic cones in western Hokkaido on the island of Japan. The complex lies within the Northeast Honshu Arc region associated with the Pacific Plate subduction beneath the Okhotsk Plate and sits near national parks and protected areas including Shikotsu-Tōya National Park and Shikotsu-Toya National Park. The group is notable for large calderas, persistent geothermal activity, and a record of Holocene eruptions that have influenced regional Ainu people settlements and modern infrastructure in Sapporo, Otaru, and Hakodate.
The volcanic group occupies central-western Hokkaido between the Ishikari Mountains and the Oshima Peninsula, bordered by bodies of water such as Lake Shikotsu and Lake Tōya and proximate to coastal cities including Tomakomai and Muroran. Geologically it is situated along the convergent margin where the Pacific Plate dives beneath the Okhotsk Plate, producing a volcanic front tied to the wider Kuril arc and Northeast Japan Arc. Regional tectonics involve interactions with the Japan Trench, the Ou Backbone Range extension, and transform segments near the Soya Fault and Fossa Magna influence. The basement comprises Paleogene and Neogene sedimentary and volcanic strata correlated with surveys by the Geological Survey of Japan and mapping by the Japanese Meteorological Agency.
The complex contains nested calderas including the Lake Shikotsu caldera and the Lake Tōya caldera, classic examples of phreatomagmatic collapse structures comparable to Kikai Caldera and Aira Caldera. Major edifices include stratovolcanoes such as Mount Tarumae, Mount Yotei (nearby but distinct), Mount Usu, and lava domes like Mount Eniwa, with monogenetic cones and fissure vents dispersed across the field similar to formations in Aso Caldera and Zao. Stratigraphic sequences show Pleistocene to Holocene pyroclastic-flow deposits, ignimbrites, block-and-ash flows, and tephra layers correlated with regional markers identified in cores by researchers from Hokkaido University and the University of Tokyo. Petrology ranges from basaltic to dacitic compositions, with mineral assemblages studied by teams at the National Institute of Advanced Industrial Science and Technology.
Holocene activity includes notable historical eruptions at prominent centers such as Mount Usu (eruptions in 1663, 1910, 1944–45, 1977–78, 2000) and Mount Tarumae (eruption episodes in 1719, 1739, 1874, 1926, 1982), with tephrochronology linked to ash layers found as far as Honshu and the Kurile Islands. Eruption styles span explosive phreatomagmatic events, Plinian activity, and effusive lava flows analogous to events at Sakurajima and Mount Aso. Historical records from the Edo period and modern instrumental catalogs maintained by the Japan Meteorological Agency and the Volcanological Society of Japan document ashfall impact on settlements like Sobetsu and Date. Volcanoes in the group pose hazards including pyroclastic density currents, lahars affecting river systems such as the Toyohira River, and ballistic hazards observed in recent centuries during Mount Usu eruptions.
Seismicity in the region is monitored by the Japan Meteorological Agency, networks operated by Hokkaido University, and national arrays such as the Hi-net and JMA seismic network, which detect volcano-tectonic earthquakes, long-period events, and volcanic tremor preceding episodes like the 1977 Mount Usu crisis and the 2000 eruption. Geodetic measurements using GPS and InSAR by the Geospatial Information Authority of Japan and researchers at Tohoku University have documented inflation–deflation cycles, caldera subsidence, and dike intrusions comparable to observations at Izu–Bonin–Mariana Arc volcanoes. Gas monitoring of sulfur dioxide and carbon dioxide fluxes is performed by teams from the National Research Institute for Earth Science and Disaster Resilience and international collaborators, and geothermal exploration has been conducted by corporations such as Hokkaido Electric Power Company under regulation from the Ministry of Economy, Trade and Industry.
Vegetation around the calderas and volcanic slopes includes boreal and cool-temperate flora studied by ecologists at Hokkaido University and National Institute for Environmental Studies, with subalpine forests and peatlands that provide habitat for species like the Ezo red fox and Sika deer monitored by the Ministry of the Environment (Japan). Volcanic soils enriched by tephra support productive forests and agricultural zones around Chitose and Shiraoi, similar to fertility patterns near Mount Fuji and Mount Bandai. Large eruptions have influenced paleoclimate records preserved in lake sediments analyzed by teams at Kyoto University and the University of Tsukuba, showing links between explosive tephra deposition and short-term regional cooling documented in dendrochronology and ice-core correlates from the Greenland ice sheet studies.
Geothermal resources beneath the group sustain onsen resorts at Noboribetsu, Jozankei, Usu, and lakeside facilities on Lake Tōya and Lake Shikotsu, developed with guidance from the Japan Tourism Agency and operated by local municipalities and private ryokan chains. Recreational activities include hiking on routes to Mount Tarumae and Mount Eniwa, boating on caldera lakes, and winter sports in the nearby Sapporo Teine and Niseko regions, with visitor safety coordinated by the Japan Self-Defense Forces and municipal disaster management offices. Geothermal power prospects have been explored by energy firms and academic consortia, balancing conservation within Shikotsu-Toya National Park and cultural preservation for the Ainu people.
The volcanic landscape figures in Ainu oral traditions and place names studied by scholars at Hokkaido University and the National Museum of Ethnology, and appears in Edo-period cartography archived by the National Diet Library. Modern cultural responses include literature and art depicting eruptions, local festivals in Sōbetsu and Toyako commemorating resilience, and educational exhibits at institutions such as the Volcano Museum (Sapporo), reflecting intersections with municipal planning by Sapporo City and regional development initiatives by the Hokkaido Prefectural Government.
Category:Volcanoes of Hokkaido