, containing the Ata North Caldera,

Mount Kaimon , or Mount Kaimon, is an undissected volcano – consisting of a basal stratovolcano and a small complex central lava dome – which rises to a height of 924 metres above sea level near the city of Ibusuki in southern Kyūshū, Japan. The last er ...

and

Ikeda Caldera , is a volcanic caldera filled now with Lake Ikeda and associated with the older Ata Caldera on the Satsuma Peninsula. Geology The Ikeda volcano produced about 20,000 years before present the Iwamoto tephra layer found right around the region o ...

amongst other volcanos, is a massive, ill defined, mostly submerged volcanic

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

associated with the southern portions of

Kagoshima Bay also known as Kinkō Bay, is a deep inlet of the East China Sea on the coast of Japan.''Merriam Webster's Geographical Dictionary, Third Edition'', p. 562. Kagoshima Bay is on the south coast of the island of Kyūshū. The port city of Kagoshi ...

Geology

The earliest tephra assigned to the volcano, is the widespread on regional sea bed cores, Ata–Torihama tephra (Ata-Th) at 240,000 years before the present. The caldera contributed to an eruption which has been dated to about 100,000 years before present (range by various techniques mostly fall 100,000 to 109,000) that generated the Ata tephra in southern Japan. This eruption has been assigned a VEI of 7.5 and generated over of tephra. This is overlaid in some places in Japan by the more recent Mitake No. 1 (On-Pm1) tephra from an eruption in the

Mount Ontake , also referred to as , is the 14th highest mountain and second highest volcano in Japan (after Mount Fuji) at . It is included in ''100 Famous Japanese Mountains''. Description Mt. Ontake is located around northeast of Nagoya, and around 200& ...

area and K-Tz tephra from the

Kikai Caldera (alternatively Kikaiga-shima, Kikai Caldera Complex) is a massive, mostly submerged caldera up to in diameter in the Ōsumi Islands of Kagoshima Prefecture, Japan. Geology Caldera formation has been dated from about 95,000 years ago and has in ...

. There have been many more lesser eruptions.

Structure

Some of the recent literature separates the caldera into a northern almost completely submerged caldera that generated the Ata tephra and Ata ignimbrite, and a southern caldera which includes the recently active

and the Kaimondake stratovolcano in the Ibusuki Volcanic Field. This southern caldera first had the Ata name but is not believed now to be associated with the vents of the major eruption of 100,000 years ago. High resolution Bouguer gravity imaging of Kyushu is consistent with the larger caldera being the Ata North Caldera but suggests it may be centred near the island of

Chiringashima is an island in Ibusuki, Kagoshima, Japan. Geography Chiringashima is the biggest island in Kagoshima Bay. It is uninhabited and lies about 800m off Tarahama. Its circumference is about 3 km and the area is about 60 ha, with a highest poi ...

, and that the Ata South Caldera is the smaller in size, overlaps it being centred near Yamagawafukumoto district. The National Catalogue of the Active Volcanoes of Japan (JMA, 2013) included features of the Ibusuki Volcanic Field as part of the Ata post-caldera system. By this definition the single caldera may be a rounded triangle about 30km in length and up to 25km in width, although the usual quoted size is smaller.

Relationships

Immediately adjacent to the north of the caldera is the

Sakurajima Sakurajima ( ja, 桜島, literally "Cherry Blossom Island") is an active stratovolcano, formerly an island and now a peninsula, in Kagoshima Prefecture in Kyushu, Japan. The lava flows of the 1914 eruption connected it with the Ōsumi Peninsula ...

volcano in the

Aira Caldera Aira Caldera is a gigantic volcanic caldera that is located on the southern end of Kyushu, Japan. It is believed to have been formed about 30,000 years ago with a succession of pyroclastic surges. It is currently the place of residence to over 9 ...

and further away to the south along what has been termed the Kagoshima Graben is the

. This alignment was first described by Tadaiti Matumoto in the 1940s. The alignment extends all the way north past

Mount Kirishima are a 1700 meter high active volcano group in Kagoshima Prefecture and Miyazaki Prefecture, Kyushu, Japan. Numerous eruptions have been recorded since 742. Very strong eruptions happened in 788, 1716 and 1717. Augite-hypersthene andesite is t ...

to intersect the

Aso Caldera Aso caldera (also known as Asosan, the Aso Volcano or Mount Aso, although the later term usually is used related to its currently active vents) is a geographical feature of Kumamoto Prefecture, Japan. It stretches 25 kilometers north to south ...

by gravitational anomaly. The tectonic processes are rather complex in this region where the

Okinawa Plate The Okinawa Plate, or Okinawa Platelet, is a minor continental tectonic plate in the northern and eastern hemispheres stretching from the northern end of Taiwan to the southern tip of the island of Kyūshū. The Okinawa Plate hosts typical earthq ...

is colliding with the

Amur Plate The Amurian Plate (or Amur Plate; also occasionally referred to as the China Plate, not to be confused with the South China Subplate) is a minor tectonic plate in the northern and eastern hemispheres. It covers Manchuria, the Korean Peninsula, ...

and the

Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate. The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...

is subducting under both.

References

{{Reflist Volcanoes of Kyushu VEI-7 volcanoes Calderas of Kyushu Submarine calderas Pleistocene calderas Active volcanoes Supervolcanoes Volcanoes of Kagoshima Prefecture Paleolithic Japan