UP-SQUEEZING OF MAGMA UNDER TECTONIC STRESS

Abstract

That some volume of magma could be squeezed up from the magma reservoir triggering a volcanic eruption when compressional tectonic stress is strengthened by plate motion has been proposed as a possible explanation of successive occurrences of volcanic eruption and large earthquake. This idea, called the "flask model, " has been put forward in attempting to account for the relationship between the activities of Izu-Oshima volcano and the occurrences of great inter-plate earthquake associated with the Sagami trough off the Pacific coast of Central Japan. It is intended in this paper to examine whether such a model really works or not by taking the detailed configuration of magma reservoir into account. When a combination of parameter values usually accepted is assumed, it turns out that the volume of magma squeezed up by compressional tectonic stress may not be enough for triggering an eruption. It is therefore doubtful that a flask-model mechanism is actually working. Occasional eruptive activities of the volcano may rather be due to an increase in internal gas pressure in association with development of chemical reaction in the magma reservoir.