HR: 0800h
AN: V31E-0711    [Abstracts]
TI: Large Scale Failures on Volcanoes of Kurile Islands: the First Data
AU: * Belousov, A
EM: belousov@mail.ru
AF: Inst. Volcanol. Seismol., Petropavlovsk, Petropavlovsk, 683980, Russian Federation
AU: Belousova, M
EM: belousov@mail.ru
AF: Inst. Volcanol. Seismol., Petropavlovsk, Petropavlovsk, 683980, Russian Federation
AB: Investigations of air and space images of volcanoes of the Kurile arc, supplemented by observations from a vessel as well as by on-land field work on several islands, have allowed us to identify 23 active volcanoes with well-preserved horseshoe-shaped scars formed by large-scale edifice failures. Breaches of most of the scars (14 cases) range from 0.5 to 2 km wide, indicating moderate failure volumes – around 1 km3. The two largest scars were 4 km-across (which were formed by failures with volumes about 5 km3) belong to Milne and Sinarka volcanoes. Most of the failures occurred on andesitic volcanoes which dominate in the region. At least 3 volcanoes (Harimkotan, Sinarka and Mendeleev) experienced multiple (3 or more) failures. Only two failures occurred on dominantly basaltic stratovolcanoes (Alaid and Atsonupuri). Most of the collapsed volcanoes of the Kurile arc exhibit strong hydrothermal alteration of rocks inside their horseshoe-shaped scars, and their debris avalanche deposits contain a large proportion of clayey material. This suggests that weakening of rocks composing volcanic edifices caused by hydrothermal alteration played a leading role in gravitational destabilization of the volcanoes. In 50% of the cases, failures were followed by magmatic activity; the horseshoe- shaped craters are partially filled by younger volcanic cones. This indicates that the failure surfaces intersected upper parts of feeding channels of active volcanoes, and the failures may have been triggered by magma intruding into the volcanic edifices. Apart from failures on active volcanoes there are multiple rather large scale (>0,01 km3) failures along sea cliffs of the islands which involved volcanic rocks. These cases are transitional to non-volcanic failures. Debris avalanches of all of the studied failures traveled far beyond the shore line of Okhotskoye Sea or the Pacific Ocean and thus their exact lengths and drop heights are unknown. The debris avalanches obviously generated tsunamis upon entering the sea. The studied failures have Late Pleistocene-Holocene ages; and one historical case failure of Harimkotan volcano on January 8, 1933 with the volume 0.4 km3. The failure generated a tsunami up to 20 m high with 2 reported victims on nearby Onekotan Island. The failure was followed by a strong, 5-day-long Plinian eruption with deposition of pyroclastic flows and subsequent dome growth over several months.
DE: 8400 VOLCANOLOGY
DE: 8428 Explosive volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting