Drilling into the magmatic path was carried out at Unzen Volcano during the period 2002-2004 to understand the eruption mechanisms of the volcanic eruption during the period 1990-1995. This project was sponsored partially by the International Continental Scientific Drilling Program (ICDP).
(Upper left) Rig site of Unzen Scientific Drilling Project (USDP-4 site), about 1 km north of the summit at an altitude of 840 m. The mountain with bared rocks in the background is the lava dome (altitude of about 1400 m) formed at the summit during the 1990-1995 eruption. Directional drilling was carried out toward the area below the summit from this site. The photograph was taken in June 2004.
(Lower left) USDP-4 rig site on the northern middle slope of Mount Unzen. The height of the rig is about 55 m. Taken from the dome in November 2003.
(Upper right) Drilled core taken from conduit zone, which is a composite dyke. This is pyroclastic dyke (tuffisite) in volcanic breccia, which formed during magma ascent. Drilled depth is 1748 m (about 100 m below sea level). The diameter is about 13 cm.
(Middle right) Conduit dacite lava from the 1990-1995 eruption, taken from a drilled depth of 1977 m (about 150 m below sea level). The rock has already been altered hydrothermally. The diameter is about 4 cm.
(Lower right) Photomicrograph of the conduit dacite lava with corroded quartz phenocryst. The diameter is about 2.5 mm.
(Photograph and explanation: Setsuya NAKADA)
