カルデラ学説に関するいくつかの問題

抄録

Since the papers by WILLIAMS (1941, 1942), the definition of caldera has changed little. Most important discovery has been the recognition of the Valles-type calderas and resurgent cauldrons closely related to them (SMITH and BAILEY, 1962, 1968). Most important varieties of the collapse calderas are ; 1) Kilauea-type, 2) Crater Lake-type or Krakatoa-type, and 3) Valles-type calderas. Very small varieties of the Crater Lake-type calderas, transitional to craters, are frequently met with throughout the Japanese volcanic field (tentatively named the Haruna-type). A shallow, inverted cone-shaped structure has been strongly proposed by YOKOYAMA based on his recent geophysical investigations of Japanese Crater Lake-type calderas. Similar funnel-shaped structure is compatible with the recent geological findings : 1) Occurrence of the basement rocks at shallow depths within caldera floor, 2) very high rate (one caldera per 3, 000 years) of caldera formation in the Japanese islands in late Quaternary, 3) findings of funnel-shaped volcanic structures related to large-scale pyroclastic eruptions.