Study of the eruptive products from three volcanoes in Kamchatka: Insights into shallow magma evolution and dynamics.

摘要

The Kamchatka Peninsula is a natural volcanological laboratory hosting some 29 active volcanoes which restlessly exhibit the entire range of eruptive processes. Three of these volcanoes, Stubel Cone of Ksudach Caldera in 1907, Shiveluch in 1964, and Tolbachik in 1975-1976 produced some of the most voluminous and powerful eruptions of this century. The main focus of this study is to interpret mechanisms and dynamics of these eruptions through field-scale and microscopic-scale observations of the eruptive products. This dissertation consists of three independent chapters, each of which deals with a specific problem.;Chapter 2 discusses some aspects of one of the classic basaltic fissure eruption that occurred at Tolbachik volcano in 1975-1976. This eruption produced an alignment of cinder cones (Northern and Southern Breakout) along the 28-km-long Tolbachik fault zone and exhibited broad range of eruptive mechanisms and styles (from magmatic to hydromagmatic, and from explosive to effusive). A broad spectrum of compositions of erupted materials (ranging from high-;Chapter 3 addresses shallow andesitic magma crystallization and degassing and its effects on eruptive processes, exemplified by recent eruptions at Shiveluch volcano. Its two consecutive eruptions, the November 12, 1964 event which produced debris deposits and Plinian fall and flow deposits, and 1980-1994 extrusive cycle, provide a good case study. As a result of the 1964 eruption the feeding system was replenished by fresh low-crystalline andesitic magma. This magma experienced active crystallization during 16-20 years of repose which produced a 2 to 3-fold crystallinity increase. Broad limits on the storage zone are imposed by seismological data (0-5 km); the upper limit is constrained by a pressure of ;Chapter 1 is devoted to interpretation of magmatic processes responsible for diversity of eruptive styles and materials which originated from Stubel Cone volcano. Two main eruptive phases can be distinguished during the growth of the volcano. The lower part of the edifice consists mainly of short lava flows with a few local tephra units which are related to the dominantly effusive eruptions. Magmas erupted during the effusive phase are high crystalline basaltic andesites and andesites (55-62 wt%. SiO