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A large basaltic tuff ring associated with the Ambrym Caldera, Vanuatu, SW Pacific

Abstract:

A thick basaltic pyroclastic series surrounding the Ambrym Caldera is presented. The gradual evolution from pyroclastic flow deposits and typical phreatomagmatic deposits at the base of the series to surtseyan type hyaloclastites, and then to ash flow deposits, indicates the role of water in the triggering and the evolution of the eruption. The volume and the petrology of these products suggest the emptying of a basaltic reservoir in which incipient differentiation by fractional crystallization was occurring. There is an abridged English version. -from English summary