Kikai Caldera | |
---|---|
Highest point | |
Peak | Mount Iō (Iōjima), Iōjima, Ōsumi Islands, Japan |
Elevation | 704 m (2,310 ft) |
Coordinates | 30°47′N 130°19′E / 30.79°N 130.31°E [1] |
Dimensions | |
Length | 17 km (11 mi) NS |
Width | 20 km (12 mi) EW |
Naming | |
Native name | 鬼界カルデラ ( Japanese) |
Geography | |
Country | Japan |
State | Kagoshima Prefecture |
Region | Ōsumi Islands |
District | Kagoshima District |
Subdivisions | Mount Yahazu, Mount Iō (Iōjima), Mount Inamura (Iōjima), Iōjima, Shin Iōjima, Takeshima, Mount Nakasone, Mount Asase, Mount Shitakisone, Iō Tai and Takeshima Tai |
Municipality | Mishima |
Geology | |
Age of rock | 6,300 to 95,000 years ago |
Kikai Caldera (鬼界カルデラ, Kikai karudera) (alternatively Kikaiga-shima, Kikai Caldera Complex) is a massive, mostly submerged caldera up to 19 kilometres (12 mi) in diameter in the Ōsumi Islands of Kagoshima Prefecture, Japan. [2]
The Kikai Caldera Complex has twin ovoid caldera 20 km (12 mi) by 17 km (11 mi) in diameter. [2] Yahazu-dake (north west part of Satsuma Io-jima) and Takeshima, located on the caldera rim, are pre-caldera volcanoes. [2] The pre-caldera stage of volcanic activity involved rhyolite, basalt, and andesite phases. [2] [3] The earliest definitive caldera formation has been dated back to at least 140,000 years ago, resulting from the eruption of Koabiyama pyroclastic flows. [2] [4] [3] The formation of caldera has been associated with at least three catastrophic ignimbrite eruptions. [2] [4] [3] Additionally, there are two older deposits (Koseda pyroclastic flows and Anbo tephra) of large caldera-forming eruptions in the vicinity, although their attribution to the Kikai caldera remains controversial. [5] [6] [7]
The Kikai-Koabiyama (K-Kob) pyroclastic flows are rhyolitic and are distributed across most of Takeshima and the plateau-like area on the northwest side of the caldera rim of Satsuma Iwo-Jima. They consist of numerous thin flow units and fill the basins in the basement, exhibiting significant variation in thickness. In Takeshima, the pyroclastic flows are thick, ranging from 20–100 m (66–328 ft), whereas in Iwo Jima, they are relatively thin, measuring a few to 30 m (98 ft). [2] [3]
The eruption of the K-Kob pyroclastic flows has been dated using K-Ar dating to be 140,000±20,000 years before present. [2] While no distal tephra from this eruption has been reported, a tephra layer with potential geochemical and age correlation has been discovered in Lake Suigetsu. [8]
Kikai-Tozurahara (K-Tz) tephra is a widespread rhyolitic tephra layer of Late Pleistocene age, attributed to a large VEI-7 eruption from the Kikai caldera. [9] This layer is confirmed to have a wide distribution, extending from south Kyushu to eastern Honshu and reaching the Pacific Ocean, [10] and possibly including the Shandong Peninsula. [11] The proximal equivalents of K-Tz are the Nagase pyroclastic flow and the Nishinoomote pyroclastic surges. [9] [12] The combined bulk volume of both distal and proximal deposits is estimated to exceed 150 km3 (36 cu mi). [10]
In marine isotope stratigraphy (MIS), K-Tz is located between MIS 5.2 and 5.3, providing a loosely constrained preliminary eruption age of approximately 95,000 years before present. [10] More reliable age constraints were imposed by the high-resolution chronology derived from the Lake Suigetsu sediment sequence, which yielded an age of 94,500±4,800 years before present for this eruption. [13]
The caldera was the source of the Kikai-Akahoya eruption, one of the largest eruptions during the Holocene (10,000 years ago to present) that produced the Kikai-Akahoya (K-Ah) tephra. [14] Between 7,200 and 7,300 years ago, [14] [15] [16] pyroclastic flows producing Koya ignimbrite from that eruption reached the coast of southern Kyūshū up to 100 km (62 mi) away, and ash fell as far as Hokkaidō. The eruption produced about 133–183 km3 (32–44 cu mi) DRE, most of it tephra. [17] [18] giving it a Volcanic Explosivity Index of 7, [18] so making it one of the most explosive in the last 10,000 years, ranking alongside the eruptions of Santorini, Paektu, Crater Lake, Kurile Lake, Samalas and Tambora. [19]
The eruption had a major impact on the Jōmon culture in southern Kyūshū although the impact was not as great as some commentary had suggested with Nishinozono sub-type pottery tradition, that had started prior to the eruption, maintained in Kyūshū. [20]
Kikai is still an active volcano. Io-dake(Mount Iō), Inamura-dake (south coast of Satsuma-Io-jima), Tokara-Iwo-Jima (north east coast of Satsuma-Io-jima) and Shōwa Iōjima (Shin-Io-jima) are post-caldera volcanoes within it. [2] Minor eruptions occur frequently on Mount Iō, one of the post-caldera subaerial volcanic peaks on Iōjima. Iōjima is one of three volcanic islands, two of which lie on the caldera rim. On June 4, 2013, weak tremors were recorded. Shortly after, eruptions began and continued off-and-on for several hours. [18] Iwo-dake now is monitored for earthquake, gas and steam plume activity so that between the 2020 and 2023 eruptions it is known to have had continuous low grade activity. [18]
Kikai Caldera | |
---|---|
Highest point | |
Peak | Mount Iō (Iōjima), Iōjima, Ōsumi Islands, Japan |
Elevation | 704 m (2,310 ft) |
Coordinates | 30°47′N 130°19′E / 30.79°N 130.31°E [1] |
Dimensions | |
Length | 17 km (11 mi) NS |
Width | 20 km (12 mi) EW |
Naming | |
Native name | 鬼界カルデラ ( Japanese) |
Geography | |
Country | Japan |
State | Kagoshima Prefecture |
Region | Ōsumi Islands |
District | Kagoshima District |
Subdivisions | Mount Yahazu, Mount Iō (Iōjima), Mount Inamura (Iōjima), Iōjima, Shin Iōjima, Takeshima, Mount Nakasone, Mount Asase, Mount Shitakisone, Iō Tai and Takeshima Tai |
Municipality | Mishima |
Geology | |
Age of rock | 6,300 to 95,000 years ago |
Kikai Caldera (鬼界カルデラ, Kikai karudera) (alternatively Kikaiga-shima, Kikai Caldera Complex) is a massive, mostly submerged caldera up to 19 kilometres (12 mi) in diameter in the Ōsumi Islands of Kagoshima Prefecture, Japan. [2]
The Kikai Caldera Complex has twin ovoid caldera 20 km (12 mi) by 17 km (11 mi) in diameter. [2] Yahazu-dake (north west part of Satsuma Io-jima) and Takeshima, located on the caldera rim, are pre-caldera volcanoes. [2] The pre-caldera stage of volcanic activity involved rhyolite, basalt, and andesite phases. [2] [3] The earliest definitive caldera formation has been dated back to at least 140,000 years ago, resulting from the eruption of Koabiyama pyroclastic flows. [2] [4] [3] The formation of caldera has been associated with at least three catastrophic ignimbrite eruptions. [2] [4] [3] Additionally, there are two older deposits (Koseda pyroclastic flows and Anbo tephra) of large caldera-forming eruptions in the vicinity, although their attribution to the Kikai caldera remains controversial. [5] [6] [7]
The Kikai-Koabiyama (K-Kob) pyroclastic flows are rhyolitic and are distributed across most of Takeshima and the plateau-like area on the northwest side of the caldera rim of Satsuma Iwo-Jima. They consist of numerous thin flow units and fill the basins in the basement, exhibiting significant variation in thickness. In Takeshima, the pyroclastic flows are thick, ranging from 20–100 m (66–328 ft), whereas in Iwo Jima, they are relatively thin, measuring a few to 30 m (98 ft). [2] [3]
The eruption of the K-Kob pyroclastic flows has been dated using K-Ar dating to be 140,000±20,000 years before present. [2] While no distal tephra from this eruption has been reported, a tephra layer with potential geochemical and age correlation has been discovered in Lake Suigetsu. [8]
Kikai-Tozurahara (K-Tz) tephra is a widespread rhyolitic tephra layer of Late Pleistocene age, attributed to a large VEI-7 eruption from the Kikai caldera. [9] This layer is confirmed to have a wide distribution, extending from south Kyushu to eastern Honshu and reaching the Pacific Ocean, [10] and possibly including the Shandong Peninsula. [11] The proximal equivalents of K-Tz are the Nagase pyroclastic flow and the Nishinoomote pyroclastic surges. [9] [12] The combined bulk volume of both distal and proximal deposits is estimated to exceed 150 km3 (36 cu mi). [10]
In marine isotope stratigraphy (MIS), K-Tz is located between MIS 5.2 and 5.3, providing a loosely constrained preliminary eruption age of approximately 95,000 years before present. [10] More reliable age constraints were imposed by the high-resolution chronology derived from the Lake Suigetsu sediment sequence, which yielded an age of 94,500±4,800 years before present for this eruption. [13]
The caldera was the source of the Kikai-Akahoya eruption, one of the largest eruptions during the Holocene (10,000 years ago to present) that produced the Kikai-Akahoya (K-Ah) tephra. [14] Between 7,200 and 7,300 years ago, [14] [15] [16] pyroclastic flows producing Koya ignimbrite from that eruption reached the coast of southern Kyūshū up to 100 km (62 mi) away, and ash fell as far as Hokkaidō. The eruption produced about 133–183 km3 (32–44 cu mi) DRE, most of it tephra. [17] [18] giving it a Volcanic Explosivity Index of 7, [18] so making it one of the most explosive in the last 10,000 years, ranking alongside the eruptions of Santorini, Paektu, Crater Lake, Kurile Lake, Samalas and Tambora. [19]
The eruption had a major impact on the Jōmon culture in southern Kyūshū although the impact was not as great as some commentary had suggested with Nishinozono sub-type pottery tradition, that had started prior to the eruption, maintained in Kyūshū. [20]
Kikai is still an active volcano. Io-dake(Mount Iō), Inamura-dake (south coast of Satsuma-Io-jima), Tokara-Iwo-Jima (north east coast of Satsuma-Io-jima) and Shōwa Iōjima (Shin-Io-jima) are post-caldera volcanoes within it. [2] Minor eruptions occur frequently on Mount Iō, one of the post-caldera subaerial volcanic peaks on Iōjima. Iōjima is one of three volcanic islands, two of which lie on the caldera rim. On June 4, 2013, weak tremors were recorded. Shortly after, eruptions began and continued off-and-on for several hours. [18] Iwo-dake now is monitored for earthquake, gas and steam plume activity so that between the 2020 and 2023 eruptions it is known to have had continuous low grade activity. [18]