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Tyatya Volcano, southwestern Kuril arc: Recent eruptive activity inferred from widespread tephra
Authors:MITSUHIRO  NAKAGAWA  YOSHIHIRO  ISHIZUKA †  TAKASHI  KUDO  MITSUHIRO  YOSHIMOTO ‡  WATARU  HIROSE  YOSHIO  ISHIZAKI  NOBUO  GOUCHI  YOSHIO  KATSUI  ALEXANDER W  SOLOVYOW  GENRIKH S  STEINBERG and ARSLAN I  ABDURAKHMANOV
Institution:Division of Earth and Planetary Sciences, Graduate School of Sciences, Hokkaido University, Sapporo, Japan (email: ),;
Geological Survey of Hokkaido, Sapporo, Japan,;
Department of Earth Sciences, Toyama University, Toyama, Japan,;
Shari Town Library, Shari, Japan and;
Institute of Volcanology and Geodynamics, Russian Academy of Natural Sciences, Yuzhno-Sakhalinsk, Russia
Abstract:Abstract Tyatya Volcano, situated in Kunashir Island at the southwestern end of Kuril Islands, is a large composite stratovolcano and one of the most active volcanoes in the Kuril arc. The volcanic edifice can be divided into the old and the young ones, which are composed of rocks of distinct magma types, low‐ and medium‐K series, respectively. The young volcano has a summit caldera with a central cone. Recent eruptions have occurred at the central cone and at the flank vents of the young volcano. We found several distal ash layers at the volcano and identified their ages and sources, that is, tephras of ad 1856, ad 1739, ad 1694 and ca 1 Ka derived from three volcanoes of Hokkaido, Japan, and caad 969 from Baitoushan Volcano of China/North Korea. These could provide good time markers to reveal the eruptive history of the central cone, which had continued intermittently with Strombolian eruptions and lava flow effusions since before 1 Ka. Relatively explosive eruptions have occurred three times at the cone during the past 1000 years. We revealed that, topographically, the youngest lava flows from the cone are covered not by the tephra of ad 1739 but by that of ad 1856. This evidence, together with a report of dense smoke rising from the summit in ad 1812, suggests that the latest major eruption with lava effusion from the central cone occurred in this year. In 1973, after a long period of dormancy, short‐lived phreatomagmatic eruptions began to occur from fissure vents at the northern flank of the young volcano. This was followed by large eruptions of Strombolian to sub‐Plinian types occurring from several craters at the southern flank. The 1973 activity is evaluated as Volcanic Explosivity Index = 4 (approximately 0.2 km3), the largest eruption during the 20th century in the southwestern Kuril arc. The rocks of the central cone are strongly porphyritic basalt and basaltic andesite, whereas the 1973 scoria is aphyric basalt, suggesting that magma feeding systems are definitely different between the summit and flank eruptions.
Keywords:Kunashir Island  Kuril arc  recent eruption  Tyatya Volcano  widespread tephra
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