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| Akan Caldera | |
|---|---|
| Name | Akan Caldera |
| Elevation m | 821 |
| Location | Kushiro Subprefecture, Hokkaido, Japan |
| Type | Caldera |
| Last eruption | Historical records (rare) |
Akan Caldera is a large volcanic caldera complex in eastern Hokkaido, Japan, forming part of the volcanic chain within Akan Mashu National Park. It hosts multiple nested volcanic cones, hydrothermal systems, and crater lakes, situated on the island of Hokkaidō near the cities of Kushiro and Akan. The caldera lies within a regional tectonic and volcanic setting influenced by the Pacific Plate, the Okhotsk Plate, and the Kuril Trench.
Akan Caldera is located in eastern Hokkaidō within Akan Mashu National Park, near Lake Akan and Lake Mashū, and is part of the Kurile arc volcanic front associated with the Pacific Plate subduction beneath the Okhotsk Plate. The caldera occupies terrain drained by the Akan River and sits upstream of the port city of Kushiro. Geologically, the complex includes Quaternary silicic and intermediate volcanics related to the regional magmatism that produced the Shiretoko Peninsula volcanic systems and the Daisetsuzan Volcanic Group. The local lithology shows trachyte, andesite, and dacite sequences comparable to deposits in the Izu-Bonin-Mariana Arc and the Kuril Islands. The caldera rim and nested cones are bounded by faults related to the Yubetsu Fault Zone and basin structures that influence geothermal circulation and hydrothermal alteration.
Akan Caldera formed through multiple explosive eruptions during the late Pleistocene to Holocene, with major caldera-forming events producing extensive pyroclastic flows and ignimbrites similar in scale to eruptions cataloged at Towada Volcano and Aso Caldera. Tephrochronology links distal ash layers to eruptions recorded in lacustrine and peat sequences in the Kushiro Plain and correlative tephras used in regional stratigraphy by researchers from institutions such as Hokkaido University and the Japan Meteorological Agency. Post-caldera volcanism built lava domes and stratocones, including the active cones that host hydrothermal activity analogous to those on Satsuma Iwo-jima and Unzen. Paleomagnetic and radiocarbon dating constrain the main collapse phases and subsequent eruptive pulses; volcanic hazards assessments reference events comparable to prehistoric eruptions at Towada and documented historic activity at Usu Volcano.
The caldera contains a complex of nested craters, fumarolic fields, solfataras, and geothermal springs that feed scenic lakes such as Lake Akan with its celebrated marimo algal mats, and smaller crater lakes. Prominent intracaldera cones include those comparable in morphology to cones on Mount Meakan and Mount O-akan, which rise from the caldera floor and influence lake hydrology. Hydrothermal alteration has produced acid sulfate environments similar to those at Iwo Jima and Nishinoshima, with sinter and sulfur deposits observed around fumaroles used as analogues in studies by the Geological Survey of Japan. The interplay of collapse structures, ring faults, and resurgent doming controls vent distribution, as seen in other calderas like Kikai Caldera and Aira Caldera.
Akan Caldera lies within Akan Mashu National Park, designated to protect boreal and temperate ecosystems including old-growth forest stands of Sakhalin fir and Ezo spruce, wetlands important for birdlife such as species recorded by the Japanese Ministry of the Environment and conservation groups like WWF Japan. The lakes and surrounding forests support endemic and migratory fauna comparable to assemblages found in Shiretoko National Park, including populations of blakiston's fish owl and salmonids in the Akan watershed. Protected status under national park legislation enables management cooperation with organizations like Hokkaido Prefecture and local municipalities such as the Town of Kushiro (Akan area), and interfaces with UNESCO biosphere program priorities and Ramsar wetland criteria applied regionally.
Human presence around the caldera is tied to the indigenous Ainu people, who have traditional cultural landscapes and spiritual associations with lakes such as those containing marimo, and with peaks referenced in Ainu oral traditions. The caldera and its lakes feature in regional histories involving Meiji period development of Hokkaidō, infrastructural expansion tied to the Hokkaido Development Commission (Kaitakushi), and later conservation actions culminating in the establishment of national park status during the Showa era. Scientific exploration has engaged institutions such as Hokkaido University, the National Institute of Advanced Industrial Science and Technology (AIST), and the Japan Meteorological Agency, while cultural tourism has been promoted by local tourism bureaus and municipalities including the Akan Town Office.
The Akan region is accessed via road networks from Kushiro Station and Obihiro Station with bus links and seasonal services promoted by the Hokkaido Tourism Organization. Visitor facilities include interpretive centers operated by Akan Mashu National Park authorities, museums highlighting Ainu culture such as the Akan Ainu Kotan, and accommodations in the towns of Akan and Teshikaga. Outdoor activities mirror those at comparable volcanic parks like Daisetsuzan National Park and Towada-Hachimantai National Park, offering boat tours on Lake Akan, hiking to viewpoints on cones analogous to Mount Meakan trails, and guided natural-history excursions coordinated with local tourism associations and conservation NGOs.
Category:Calderas of Japan Category:Volcanoes of Hokkaido