Bull Volcanol (1999) 61 : 324–342 Q Springer-Verlag 1999 ORIGINAL PAPER A. Belousov 7 M. Belousova 7 B. Voight Multiple edifice failures, debris avalanches and associated eruptions in the Holocene history of Shiveluch volcano, Kamchatka, Russia Received: 28 June 1998 / Accepted: 28 March 1999 Editorial responsibility: D. A. Swanson Alexander Belousov (Y) 7 Marina Belousova Institute of Volcanic Geology and Geochemistry, Petropavlovsk-Kamchatsky, 683006, Russia e-mail: A.Belousov6g23.relcom.ru Fax: c095-7193776 Barry Voight Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA Present address: Alexander Belousov, Vavilova str, 31/1–28, Moscow, 117312, Russia Abstract Investigation of well-exposed volcaniclastic deposits of Shiveluch volcano indicates that large-scale failures have occurred at least eight times in its history: approximately 10,000, 5700, 3700, 2600, 1600, 1000, 600 14 C BP and 1964 AD. The volcano was stable during the Late Pleistocene, when a large cone was formed (Old Shiveluch), and became unstable in the Holocene when repetitive collapses of a portion of the edifice (Young Shiveluch) generated debris avalanches. The transition in stability was connected with a change in composition of the erupting magma (increased SiO 2 from ca. 55–56% to 60–62%) that resulted in an abrupt increase of viscosity and the production of lava domes. Each failure was triggered by a disturbance of the vol- canic edifice related to the ascent of a new batch of vis- cous magma. The failures occurred before magma in- truded into the upper part of the edifice, suggesting that the trigger mechanism was indirectly associated with magma and involved shaking by a moderate to large volcanic earthquake and/or enhancement of edif- ice pore pressure due to pressurised juvenile gas. The failures typically included: (a) a retrogressive landslide involving backward rotation of slide blocks; (b) frag- mentation of the leading blocks and their transforma- tion into a debris avalanche, while the trailing slide blocks decelerate and soon come to rest; and (c) long- distance runout of the avalanche as a transient wave of debris with yield strength that glides on a thin weak layer of mixed facies developed at the avalanche base. All the failures of Young Shiveluch were immediately followed by explosive eruptions that developed along a similar pattern. The slope failure was the first event, followed by a plinian eruption accompanied by partial fountain collapse and the emplacement of pumice flows. In several cases the slope failure depressurised the hydrothermal system to cause phreatic explosions that preceded the magmatic eruption. The collapse-in- duced plinian eruptions were moderate-sized and ordi- nary events in the history of the volcano. No evidence for directed blasts was found associated with any of the slope failures. Key words Failure of volcanic edifice 7 Debris avalanche 7 Lava dome 7 Plinian eruption 7 Shiveluch volcano 7 Kamchatka Introduction The 1980 eruption of Mount St. Helens clearly demon- strated that a volcanic edifice can be destroyed in a large-scale slope failure, resulting in a destructive, fast- moving debris avalanche that travels a long distance (Voight et al. 1981; Glicken 1986, 1998). The Mount St. Helens avalanche deposit displays a hummocky land- scape and distinctive features that enabled old debris- avalanche deposits to be recognised in volcanic regions worldwide (Ui 1983; Siebert 1984). Thus, it was discov- ered that large-scale slope failures were common events in the history of many volcanoes, and that some volca- noes experience multiple failures (Inokuchi 1988; Beget and Kienle 1992; Komorowski et al. 1993; Siebert et al. 1995; Belousov and Belousova 1996; Belousova 1994, 1996). Most of the newly discovered old debris-avalanche deposits had been earlier misinterpreted, usually as moraines or lahar deposits. In the Kurile-Kamchatka region of Russia, some debris-avalanche deposits, in- cluding several at Shiveluch volcano, had been de-