[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.

[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.

[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 occurred with a strong ejection of debris and ash, which corresponds to the usual phase of the Plinian type, during which there was a series of prolonged emissions under high pressure of fragmented lava and pumice in the form of a gas-ash mixture.

It was a volumetric pyroclastic flow as a final stage, which partially spread along the seabed and released into the atmosphere in the form of an eruptive column (ash, fragments of pumice, small crystals and tephra).

Scientists had conducted a detailed study of the spread of volcanic material over an area of about 4,500 square kilometers around the center of the eruption and mapped the thickness of the underwater pyroclastic sediment.

After analyzing the textures and nature of the fragments of the underwater volcanic strata, the authors concluded that it was formed from a suspended stream, which can cover long distances even up the slope, as it turned out.

Having built a model of the Kikai-Akahoya eruption, researchers have found that in addition to the underwater pyroclastic flow and the powerful release of the tephra cloud into the atmosphere, there was also a third stream of thin volcanic material that spread along the surface of the water to the nearest islands.