Abstract:
There have been three episodes of lava dome growth at Shiveluch volcano, Kamchatka since the Plinian explosive eruption in 1964. The episodes in 1980-1981, 1993-1995 and 2001-2004 have discharged at least 0.27 km3 of silicic andesite magma. A time-averaged mean extrusion rate of 0.2 m3/s is thus estimated for the last 40 years. Here the 2001-2004 activity is described and compared with the earlier episodes. The recent activity involved three pulses in extrusion rate and a transition to ongoing lava extrusion. Estimated magma temperatures are in the range 830 to 900 °C, with 850 °C as the best estimate, using the plagioclase-amphibole phenocryst assemblage and Fe-Ti oxides. Melt inclusions in amphibole and plagioclase have maximum water contents of 5.1 wt.%, implying a minimum pressure of ~ 155 MPa for water-saturated conditions. The magma chamber depth is estimated to be about 5-6 km or more, a result consistent with geophysical data. The thicknesses of opx-mt-amph reaction rims on olivine xenocrysts are used to estimate the residence time of olivine crystals in the shallow chamber in the range 2 months to 4 years, suggesting replenishment of deeper magma into the shallow chamber contemporaneous with eruption. The absence of decompression-driven breakdown rims around amphiboles indicates ascent times of less than 7 days. Volcanological observations of the start of the 2001-2004 episode suggest approximately 16 days for the ascent time and a conduit equivalent to a cylinder of diameter approximately 53-71 m. Application of a conduit flow model indicates that the magma chamber was replenished during the 2001-2004 eruption, consistent with the results of olivine reaction rims, and that the chamber has an estimated volume of order 7 km3. © 2006 Elsevier B.V. All rights reserved.
