火山噴出物は何を語るのか

Abstract

The concept of vesiculation and gas loss of magma during ascent in a conduit, and the results of analytical studies of natural eruptive materials are reviewed in comparison with theoretical and experimental studies. Vesiculation of magma is a complex interplay of nucleation, growth, and coalescence of bubbles. In the recent two decades, theoretical and experimental studies on nucleation and growth of bubbles brought us a lot of information about the vesiculation mechanism by applying simplified models to natural samples. However, there are few works on coalescence and gas loss, which is believed to be the most dominant effect on the diversity in eruption style. In fact, most natural pyroclasts and some experimental products seem to be suffered from bubble coalescence. Thus, we should bear in mind when applying theoretical models to natural samples that estimations for bubble nucleation rate and growth rate without considering bubble coalescence may lead to misunderstanding. However, if we analyze natural samples systematically in terms of volatile content, some physical properties and texture, as well as geological information, it would be possible to reconstruct many processes recorded in the eruptive materials.