The Shiveluch volcanic eruption of 12 November 1964—explosive eruption provoked by failure of the edifice

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 took 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.