Drilling and logging results of USDP-4 - Penetration into the volcanic conduit of Unzen Volcano, Japan

Sumio Sakuma, Tatsuya Kajiwara, Setsuya Nakada, Kozo Uto, Hiroshi Shimizu

Research output: Contribution to journalArticle

25 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)1-12
Number of pages12
JournalJournal of Volcanology and Geothermal Research
Volume175
Issue number1-2
DOIs
Publication statusPublished - Jul 30 2008

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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