TY - JOUR
T1 - Drilling and logging results of USDP-4 - Penetration into the volcanic conduit of Unzen Volcano, Japan
AU - Sakuma, Sumio
AU - Kajiwara, Tatsuya
AU - Nakada, Setsuya
AU - Uto, Kozo
AU - Shimizu, Hiroshi
N1 - Funding Information:
The Six-year Unzen Scientific Drilling Project (USDP) has been funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. Following a one-year feasibility study in 1998, a project consisting of two phases was started in 1999. The first phase of this project aimed at clarifying the growth history and magmatic evolution of Unzen, by drilling two 1000 m coring boreholes on the flank of the volcano (USDP-1 and 2). In addition, a 350 m section of core was drilled on the northern slope of Unzen (USDP-3) as part of the preparation for drilling the conduit. The purpose of the second phase was to understand the eruption processes of the last eruption and to model the eruption mechanisms of dacite magma by drilling to the conduit area of the last eruption and taking cores. In particular, we hoped to gain a better understanding of degassing processes in the upper part of the conduit, ( Uto et al., 2001; Nakada and Eichelberger, 2004 ). The conduit drilling of the second phase, USDP-4, was carried out as a joint research project with International Continental Scientific Program (ICDP).
PY - 2008/7/30
Y1 - 2008/7/30
N2 - Borehole USDP-4 was drilled into the Unzen volcanic conduit 9 years after its last eruption. The sub-surface mechanism of eruption at Unzen Volcano was investigated by taking cores and by geophysical logging. The drilling operations were carried out in 2003-04, as a joint research program sponsored by the Japanese Government and the International Continental Scientific Drilling Program (ICDP). Borehole USDP-4 was a directional 6-1/4 in. (158.8 mm) borehole drilled from a site located on the northern slope of the volcano at 840 m above sea level, and was designed to penetrate into the conduit at sea level with a final deviation angle of over 70° from vertical and a borehole depth of 1800 m. An igneous dyke with a high likelihood of being the Unzen conduit was encountered at 1996 m depth and core samples were taken from that location. Chemical analysis of drill cores confirmed the identification of the conduit. Geophysical logging, including recording of gamma ray, resistivity, self-potential, density, neutron porosity, sonic velocity, and temperature suggested an alternation of dykes and flows in rock penetrated during the drilling, and in-hole pictures confirmed the lithologic identifications. Although borehole collapse and high temperature had been expected in the conduit, the actual drilling and logging into the conduit experienced no gas or fluid kick, and the measured temperatures within the dyke were below 200 °C.
AB - Borehole USDP-4 was drilled into the Unzen volcanic conduit 9 years after its last eruption. The sub-surface mechanism of eruption at Unzen Volcano was investigated by taking cores and by geophysical logging. The drilling operations were carried out in 2003-04, as a joint research program sponsored by the Japanese Government and the International Continental Scientific Drilling Program (ICDP). Borehole USDP-4 was a directional 6-1/4 in. (158.8 mm) borehole drilled from a site located on the northern slope of the volcano at 840 m above sea level, and was designed to penetrate into the conduit at sea level with a final deviation angle of over 70° from vertical and a borehole depth of 1800 m. An igneous dyke with a high likelihood of being the Unzen conduit was encountered at 1996 m depth and core samples were taken from that location. Chemical analysis of drill cores confirmed the identification of the conduit. Geophysical logging, including recording of gamma ray, resistivity, self-potential, density, neutron porosity, sonic velocity, and temperature suggested an alternation of dykes and flows in rock penetrated during the drilling, and in-hole pictures confirmed the lithologic identifications. Although borehole collapse and high temperature had been expected in the conduit, the actual drilling and logging into the conduit experienced no gas or fluid kick, and the measured temperatures within the dyke were below 200 °C.
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U2 - 10.1016/j.jvolgeores.2008.03.039
DO - 10.1016/j.jvolgeores.2008.03.039
M3 - Article
AN - SCOPUS:50049107821
SN - 0377-0273
VL - 175
SP - 1
EP - 12
JO - Journal of Volcanology and Geothermal Research
JF - Journal of Volcanology and Geothermal Research
IS - 1-2
ER -