K. Kataoka et al., An extremely large magnitude eruption close to the Plio-Pleistocene boundary: reconstruction of eruptive style and history of the Ebisutoge-Fukuda tephra, central Japan, J VOLCANOL, 107(1-3), 2001, pp. 47-69
An extremely large magnitude eruption of the Ebisutoge-Fukuda tephra, close
to the Plio-Pleistocene boundary, central Japan. spread volcanic materials
widely more than 290,000 km(2) reaching more than 300 km from the probable
source. Characteristics of the distal air-fall ash (> 150 km away from the
vent) and proximal pyroclastic deposits are clarified to constrain the eru
ptive style, history, and magnitude of the Ebisutoge-Fukuda eruption.
Eruptive history had five phases. Phase 1 is phreatoplinian eruption produc
ing > 105 km(3) of volcanic materials. Phases 2 and 3 are plinian eruption
and transition to pyroclastic how. Plinian activity also occurred in phase
3, which ejected conspicuous obsidian fragments to the distal locations. In
phase 5, collapse of eruption column triggered by phase 4. generated large
pyroclastic how in all directions and resulted in more than 250-350 km(3)
of deposits. Thus, the total volume of this tephra amounts over 380-390 km(
3). This indicates that the Volcanic Explosivity Index (VEI) of the Ebisuto
ge-Fukuda tephra is greater than 7. The huge thickness of reworked volcanic
lastic deposits overlying the fall units also attests to the tremendous vol
ume of eruptive materials of this tephra.
Numerous ancient tephra layers with large volume have been reported worldwi
de, but sources and eruptive history are often unknown and difficult to det
ermine. Comparison of distal air-fall ashes with proximal pyroclastic depos
its revealed eruption style, history and magnitude of the Ebisutoge-Fukuda
tephra. Hence, recognition of the Ebisutoge-Fukuda tephra, is useful for un
derstanding the volcanic activity during the Pliocene to Pleistocene, is im
portant as a boundary marker bed, and can be used to interpret the global e
nvironmental and climatic impact of large magnitude eruptions in the past.
(C) 2001 Elsevier Science B.V, All rights reserved.