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| Kikai Caldera | |
|---|---|
| Name | Kikai Caldera |
| Elevation m | 214 |
| Location | Kagoshima Prefecture, Japan |
| Range | Ryukyu Islands |
| Type | Caldera |
| Last eruption | 1934 |
Kikai Caldera is a large submarine and partially subaerial caldera located south of Kyushu in the Kagoshima Prefecture of Japan. The feature lies near populated islands such as Kagoshima (city), Amami Ōshima, and Tanegashima, and forms part of the volcanic arc associated with the Izu–Bonin–Mariana Arc and the Ryukyu Arc. Its history includes one or more explosive eruptions during the late Pleistocene and Holocene that produced widespread tephra layers correlated with records from Honshu, Hokkaido, and Sakhalin.
The caldera occupies a region between Kyushu and the Ryukyu Islands, situated within the tectonic setting influenced by the subduction of the Philippine Sea Plate beneath the Eurasian Plate and proximity to the Nankai Trough. Bathymetric mapping shows a complex sea-floor morphology with a basin bounded by high rims adjacent to islands including Iōjima and Kakeromajima. Regional geology links the feature to the broader magmatic system that also includes volcanic centers such as Sakurajima, Aira Caldera, and Kirishima (volcano), and to seismic activity recorded by agencies like the Japan Meteorological Agency and the US Geological Survey.
Morphologically, the caldera is a roughly circular depression with dimensions inferred from bathymetric surveys comparable to other large calderas like Aira Caldera and Kikai Peninsula features. Remnant volcanic islands form parts of the rim, with Mount Iō and submarine cones inside the depression resembling features at Taal, Santorini, and Campi Flegrei. Submarine volcanic cones and hydrothermal areas have been identified, analogous to sites investigated by institutions such as the Ocean Research Institute, University of Tokyo and the Japan Agency for Marine-Earth Science and Technology.
The eruptive chronology includes a major caldera-forming eruption in the late Pleistocene commonly correlated with widespread "Kikai-A" tephra identified in cores and outcrops across Kyushu, Shikoku, and Honshu. Tephrostratigraphic correlations tie this event to markers found in records associated with Jomon period layers and paleoclimate proxies used by researchers from institutions like Kyoto University and the National Museum of Nature and Science (Japan). Holocene activity includes smaller explosive and effusive events, with documented historic eruptions recorded by the Japan Meteorological Agency and local historical chronicles recording ashfall episodes in the Edo and Meiji periods. The 1934 event was minor compared with the late Pleistocene eruption but demonstrates ongoing magmatic unrest similar to episodic activity at Sakurajima.
Petrographic and geochemical studies of pumices, scoria, and lavas show a compositional range from high-silica rhyolite to andesite, with rare dacitic compositions that resemble products of other large caldera systems such as Krakatoa and Taupō. Geochemical fingerprints—including major and trace elements and isotopic ratios—have been used to distinguish tephra layers in distal sites studied by researchers at Tohoku University and the Geological Survey of Japan. Magmatic evolution models invoke crustal assimilation, fractional crystallization, and magma recharge processes analogous to mechanisms proposed for Yellowstone and Long Valley Caldera.
Hazards include explosive eruption, widespread tephra dispersal impacting islands and Kyushu, pyroclastic density currents, tsunamis triggered by caldera collapse or flank failure, and submarine explosive activity that could affect shipping lanes near Osumi Strait and air routes to Kagoshima Airport. Monitoring is undertaken by the Japan Meteorological Agency, national universities, and marine agencies using seismic networks, infrasound, GPS, tide gauges, and bathymetric repeat surveys similar to monitoring at Aira Caldera and Sakurajima. Tsunami hazard assessments reference paleotsunami evidence from coastal deposits studied by teams from University of Tokyo and Hokkaido University.
Archaeological and paleoenvironmental studies link major tephra layers to cultural changes in the Jomon period and to prehistoric settlement abandonment on islands in the Ryukyu Islands chain, with research conducted by archaeologists at Kyushu University and Kagoshima University. Historical documents from the Edo period and local gazetteers note ashfall and maritime disturbances, which are cross-referenced with geological records by scholars at the National Institute of Advanced Industrial Science and Technology and regional museums such as the Amami City Museum.
The caldera region and adjacent islands host marine ecosystems influenced by hydrothermal inputs and volcanic substrates, supporting benthic communities studied by marine biologists from the Japan Agency for Marine-Earth Science and Technology and the National Research Institute of Fisheries Science. Terrestrial environments on rim islands harbor endemic flora and fauna similar to those cataloged in the Ryukyu Islands biodiversity assessments by the Ministry of the Environment (Japan). Conservation initiatives involve local governments, the Kagoshima Prefectural Government, and conservation NGOs focusing on habitat protection, invasive species control, and sustainable tourism development modeled after programs on Yakushima and Amami Ōshima.
Category:Volcanoes of Japan Category:Calderas