, is a 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 ...

filled now with

Lake Ikeda is a caldera lake located 40 km south of Kagoshima city; Kyūshū island, Japan. It is perhaps best known to tourists as the location of the purported sightings of a monster named Issie, and as the largest lake on Kyūshū island with a s ...

and associated with the older

Ata Caldera , containing the Ata North Caldera, Mount Kaimon and Ikeda Caldera amongst other volcanos, is a massive, ill defined, mostly submerged volcanic caldera associated with the southern portions of Kagoshima Bay. Geology The earliest tephra assigned ...

on the Satsuma Peninsula.

Geology

The Ikeda volcano produced about 20,000 years before present the Iwamoto

tephra Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size, or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts. Once clasts have fallen to the ground, they re ...

layer found right around the region 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 Kag ...

but not further. It later erupted Senta

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

before about 7300 years ago erupting the Kikai-Akahoya tephra. The caldera-forming eruptions began 6400 years ago involving by the time they had finished about of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

and produced local pyroclastic deposits and the Ikezaki tephra. In subsequent magmatic eruptions fall deposits were created of Osagari and Mizusako

scoria Scoria is a pyroclastic, highly vesicular, dark-colored volcanic rock that was ejected from a volcano as a molten blob and cooled in the air to form discrete grains or clasts.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. Jackson, eds. (2005) '' ...

and Ikeda

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...

. The present caldera was formed 4800 years ago when the Ikeda

ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surro ...

erupted that reached the eastern and western sides and southern tip of the Satsuma Peninsula. The north western wall of this caldera aligns with the Onkadobira fault scarp. This was followed by later eruptions including the Ikedako tephra and those from a fissure vent line southeast of the caldera that produced the pumiceous Yamagawa base surge. A central lava dome was formed within the caldera during the late stage of these eruptions. About 2,800 years ago on part of the margin of the caldera rim the

andesitic Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomin ...

Nabeshimadake lava dome was formed. During the caldera forming events, and after, about of ignimbrite and of tephra was erupted with each of the tephra deposits reaching into the

Ōsumi Peninsula 261x261px, Satellite image of Ōsumi Peninsula The projects south from the Japanese island of Kyūshū and includes the southernmost point on the island, Cape Sata. Its east coast lies on the Pacific Ocean, while to the west it faces the Satsuma ...

due to the prevailing winds. Ikeda Caldera is associated in the Ibusuki volcanic field with the more recently active Kaimondake stratovolcano. The National Catalogue of the Active Volcanoes of Japan (JMA, 2013) includes features of the Ibusuki volcanic field as part of the Ata post-caldera system.

References

Volcanoes of Kyushu VEI-5 volcanoes Calderas of Kyushu Pleistocene calderas Active volcanoes Volcanoes of Kagoshima Prefecture Paleolithic Japan {{Kagoshima-geo-stub