To understand the structure and growth history of Unzen Volcano in Japan and to clarify the eruption mechanisms of SiO 2-rich viscous magmas, the Unzen Scientific Drilling Project (USDP), a six-year program consisting of two phases, began in April 1999. In the first phase, two holes were drilled into the volcano's flank (USDP-1 and -2 wells). In the second phase, drilling penetrated the magma conduit that fed a lava dome at the summit during the 1991-95 eruption. Through directional drilling, samples of the lava dike believed to have fed the 1991-95 eruption were recovered. The lava dike sample was unexpectedly altered, suggesting that circulation of hydrothermal fluids rapidly cools the conduit region of even very active volcanoes. It is likely that seismic signals monitored before the emergence of lava dome reflected fracturing of the country rocks, caused by veining as volatiles escaped predominantly upward, not outward, from the rising magma.
|出版ステータス||出版済み - 3月 1 2006|
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