火山体掘削の科学的成果と今後の展望

Abstract

Drilling into volcanoes is important to obtain an understanding of subterranean three-dimensional geometrical and thermal structures. Even shallow drilling in volcanic areas provides various information including the eruption histories of the volcanoes. The magmatic system and conditions at eruption sites together with eruption and development histories are important to understand magma processes in the upper crust, forecast future eruptions, and mitigate volcanic disasters. Using the holes drilled as observation wells is an additional advantage for monitoring the volcanic activity in-situ. Volcano and magma development histories have been revealed by deep drilling at Mauna Kea volcano (Hawaii), Unzen volcano, Fuji volcano, etc. Drillings was carried out into a hot basalt lava lake and a volcanic conduit of a recently erupted Kilauea volcano (Hawaii) and Unzen volcano, respectively. During geothermal drilling at Kakkonda and in Iceland, a solidifying magma chamber and rhyolite magma, respectively, were accidentally drilled. Three-D subsurface structures under caldera volcanoes have been understood by carrying out geothermal drillings at Long Valley, Aso, and Nigorikawa calderas. In addition, some projects to drill at caldera volcanoes have been undertaken or are being prepared as ICDP projects. Recently, national economic problems have made it difficult for researchers to propose deep drilling projects at volcanoes and calderas as an ICDP project. Under this situation, close international cooperation among researchers related to these projects or participation in geothermal exploration drilling projects may be better solutions.