ELSEVIER Journal of Volcanology and Geothermal Research 66 (1995) 357-365 Journal of volcanology and geothermal research The Shiveluch volcanic eruption of 12 November 1964— explosive eruption provoked by failure of the edifice A.B. Belousov Institute of Volcanic Geology and Geochemistry, Petropavlovsk-Kamchatsky, Russia Received 20 March 1994; accepted 7 July 1994 Abstract Restudy of deposits at Shiveluch in comparison with other data has shown that the sequence of eruptive events at Shiveluch volcano on 12 November 1964 was the following: edifice failure involving 1.154 km 3 of material at 07:07 a.m.; phreatic explosion with ejection of resurgent ash with a volume of 0.01 km 3 ; Plinian activity between 07:20 and 07:47 a.m., during which andesitic juvenile tephra with a volume of 0.3 km 3 erupted. During the final stage of the eruption between 07:47 and 08:22 a.m., pyroclastic flows with a volume of 0.3-0.5 km 3 were erupted. In this sequence, there was no catastrophic directed blast with generation of a destructive pyroclastic density current like those that look place at Bezymianny volcano in 1956 and at Mount St. Helens in 1980. The absence of a directed blast is attributed to the fact that the 1964 eruption occurred before magma had enough time to intrude into the edifice and build a cryptodome. The failure of the edifice depressurized only a hydrothermal system that existed around the old domes. This appears to have been insufficient for the generation of a catastrophic directed blast. The case history of volcanic activity at Shiveluch before 1964 suggests that if the edifice of the Young Shiveluch had been stronger and had not failed by landsliding, the eruption of 1964 might have consisted of prolonged dome extrusion with relatively weak explosive activity. 1. Introduction The eruption of Shiveluch on 12 November 1964 is regarded as one of the great historical explosive erup- tions of Kamchatka with respect to the volume of juve- nile pyroclastic material thrown out (about 0.8 km 3 ). The eruption was of short duration and occurred during the hours of darkness, so the main conclusions about its character have been based on studies of the deposits, seismograms and barograms (Gorshkov and Dubik, 1970). The main factor in the interpretation of the sequence of events for this eruption was the identification of the so-called "directed blast agglomerate": coarse- grained resurgent deposits with a particular hummocky surface, which formed a thick deposit covering an area of 98 km 2 at the southern foot of the volcano. This type of deposit was identified for the first time in the work of Gorshkov and Bogoyavlenskaya (1965), who inves- tigated the results of the catastrophic eruption of Bezymianny volcano that occurred on 30 March 1956. Gorshkov and Bogoyavlenskaya thought that the directed expulsion of several cubic kilometers of the old volcanic edifice could occur as a result of a powerful volcanic explosion with the materials being thrown on ballistic trajectories over distances exceeding 10 km. Simultaneously with the "directed blast agglomerate" at Bezymianny, the deposits of "directed blast sand" were described as thin, relatively fine-grained juvenile deposits, distributed around the "agglomerate" cov- ering an area of about 500 km 3 . The areal pattern of the "sand" deposits coincided with the area with fallen 0377-0273/95/S09.50 © 1995 Elsevier Science B.V. All rights reserved SSDl 0377-0273 ( 9 4 ) 0 0 0 7 2 - 7