カルデラの構造に関する考察

概要

論文の詳細を見る
This paper is only concerned with the calderas of low gravity anomaly type (or Krakatoan type). As an example of the subsurface structure of the calderas of this type, that of Hakone Caldera is discussed on the bases of gravity anomalies and the results of the drillings there. It is proved that there is the Tertiary basement at rather shallow depth under the deposits of ejecta from the post-caldera volcanoes at some parts of the caldera. Therefore, the caldera would not have collapsed as a whole into "magma reservoir" if any. As general problems, mass deficiency on the Japanese calderas are compared with those on the Canadian meteorite craters. Caldera formation consists of the two actions, i.e. explosion and outflow of the ejecta : The former is the main factor of meteorite craters while the latter is a characteristic of volcanic calderas and becomes dominant with the increase of their diameters. A hypothesis saying that enlargement of caldera openings would occur between the stages of pumice fall and pumice flow, is proposed. This may explain the pressure drop of pumice flow eruptions and also a large amount of pumice flow compared with that of pumice fall.
特定非営利活動法人日本火山学会の論文
1969-08-01