The eruptive history of Aira caldera in southern Kyushu during 100-30 ka is revealed by tephrostratigraphical studies. In this period, seven explosive eruptions of the caldera are identified. These tephra formations are as follows : 1) Hikiyama scoria fall at 103-95 ka, 2) Kongoji pyroclastic surge at 95-86 ka, 3) Fukuyama pumice fall at 95-86 ka, 4) Iwato tephra formation at ca. 60 ka consisting of three pumice falls, five pyroclastic flows and one pyroclastic surge, 5) Otsuka pumice fall at 32.5 ka, 6) Fukaminato tephra formation at 31 ka consisting of a pumice fall and a pyroclastic flow, and 7) Kenashino tephra formation at 30 ka consisting of ash falls and pyroclastic surges. These eruptive ages are estimated by stratigraphic relation with widespread tephras, as well as
14C dating. Three lava flows also effused during this period. Among them, the Shikine andesites between the Fukuyama pumice fall and Iwato tephra formation dammed up a river and formed a local small lake. The eruptive centers during 100-30 ka are located on the eastern half of the caldera.After 0.1 Ma (=100 ka) is an active period of many explosive and effusive eruptions. The Aira pyroclastic eruption at 27 ka (more than 411 km
3 in bulk volume) separates this active period. Total mass of erupted magma during 100-30 ka is 63.3×10
12 kg. And the average rate is 0.9×10
12 kg/ky. The Aira caldera had repeated its magmatic eruptions at intervals of ca. 7500 years. However, the interval during 32.5-30 ka just before the Aira pyroclastic eruption is 1000 years.
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