Abstract:
The microbarographs installed at distances of 45 and 113 km from Shiveluch Volcano recorded acoustic signals during the powerful explosive eruption of November 12, 1964. The signals were produced by the formation of a convection column and provided information of the dynamics of the eruption and of the amount of ash ejected to the atmosphere. Correlation of seismic and acoustic signals indicated that the eruption began with an enormous rockslide avalanche (1.5 km3), which produced a dust-air cloud whose origin was recorded as a first-arriving acoustic signal. Twelve minutes after the collapse, volcanic tremor was recorded as the second acoustic signal, which marked the beginning of Plinian-type activity and the eruption of pyroclastic flows. The change from one eruptive phase to another was accompanied by the intensification of tremor, the arrival of > 0.05-Hz acoustic signal, and the generation of a long-wave (>10min) disturbance with 50-Pa excess pressure at a distance of 113 km. Based on the energy of the long-wave disturbances, the volume of the ash ejected to the atmosphere has been estimated at 0.35-0.45 km3, the value compatible with a volume of 0.3 km3 indicated by geological evidence.