Tarawera Volcanic Complex

Abstract

The Tarawera Volcanic Complex is situated on the south eastern side of the Okataina Volcanic Centre, and is an association of rhyolite domes, flows and tephra, and basalt scoria. Twelve rhyolite domes are described, and using evidence obtained from the good internal sections available, the general structure of volcanic domes is discussed. Tephra stratigraphy of the Tarawera-Rerewhakaaitu region is described and by relating stratigraphy on the mountain to this tephra, four major eruptions can be recognized. A sequence of events for the Kaharoa eruption about 1020 A.D. can be postulated. The Tarawera eruption in 1886, however, was observed, and from the eye witness accounts, together with present day field evidence, a detailed account can be written. All the rocks of the Complex are described petrographically, mineralogically, and in some cases petrochemically. Twelve new full analyses; nine partial analyses of plagioclase, and eight partial analyses of residual glass are given, and the relationship of these is illustrated by variation diagrams. Finally, the origins of the acid and basic rocks of the Complex are discussed, and a hypothesis for the occurrence of the two lava types is given.