Collaborative Research: Structure, Conditions and Magmatic Processes Within an Active Volcano: Analysis of Samples From Boreholes Drilled into the Conduit of Unzen Volcano, Interna

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This project will allow the PIs to participate in internationally collaborative investigations of boreholes and samples now being drilled by the Unzen Scientific Drilling Project (USDP), Japan. The USDP is part of the International Continental Drilling Program (ICDP), which seeks to use drilling as a tool to advance understanding of fundamental processes of Earth's crust. The goal of the USDP is to understand the eruptive behavior of Unzen as representative of an important class of andesitic arc volcanoes. In the now-completed first phase of the drilling project, flank holes of 750 m and 1500 m were drilled to the base of the volcanic edifice in order to obtain a complete physical and chemical record of the volcano's activity. This proposal aims to continue a one-year pilot project that have shown that the present Unzen magma system, which is characterized by frequent injection of fractionated mafic magma into a crust-resident slush of remarkably constant composition, has persisted for 500,000 years. The intellectual targets for the next phase of the drilling project will be: 1.) to understand how viscous magma behaves mechanically, chemically, and thermally as it approaches Earth.s surface; 2.) to determine why Unzen is such an exemplary case of non-explosive eruption of initially wet magma, and 3.) to improve techniques to forecast eruptions by providing direct subsurface observations that inform interpretation of precursory seismicity, deformation, and degassing. The investigators propose to use optical, SEM, electron microprobe, XRF, and LA-ICPMS techniques to examine the samples. In particular, proximal units will be correlated to units encountered in flank drilling, zones of hydrothermal alteration will be mapped, and intrusive features identified. Most importantly, the conduit that fed the 1991-1994 eruption will be delineated. In order to constrain degassing behavior, special attention will be paid to occurrence of intrusive glass on the margin of the conduit and residual melt in the central portion. Comparison of glassy dome lava with partially crystalline conduit material (if residual melt remains) and with crystalline conduit material will serve to define the complete crystallization path of Unzen magma. Conduit width, textural variations within the conduit related to degassing and cooling, plausible rheologies of the magma and wallrock, and effects of conduit flow and degassing on the wallrock will be determined. In terms of broader impacts, the work should improve the understanding and predictability of this dangerous type of volcanic activity, which has afflicted not only Shimabara, Japan but also towns near Pinatubo Volcano in the Philippines and Soufriere Hills Volcano in Montserrat in recent years. The project has attracted much public interest in Japan, and will likely do so worldwide once drilling to the conduit has begun. Accordingly, the USDP team plans to make results available to the public in near-real time in English, Japanese, and German over the Worldwide Web. As representatives of the US scientific community on the team, the investigators will make appropriate use of this opportunity to acquaint their American colleagues with research opportunities as they arise. This will serve to increase the breadth of expertise engaged in the Unzen enterprise, while at the same time acquainting Americans with the very substantial resources, experience, and ideas of the volcanological community of Japan.