Tarawera Volcanic Complex

<p>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.</p>

Tarawera Volcanic Complex

<p>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.</p>

Holocene tephra stratigraphy in four lakes in southeastern Oregon and northwestern Nevada, USA

To better understand the regional tephra stratigraphy and chronology of northern Nevada and southern Oregon, tephras in archived cores, taken as part of the Steens Mountain Prehistory Project from four lakes, Diamond Pond, Fish and Wildhorse lakes in southeastern Oregon and Blue Lake in northwestern Nevada, were reexamined using more advanced electron microprobe analytical technology. The best preserved and most complete core from Fish Lake along with Wildhorse Lake hosted two tephras from Mt. Mazama (Llao Rock and the Climactic Mazama), a mid-Holocene basaltic tephra from Diamond Craters, Oregon, two Medicine Lake tephras and an unexpected late Holocene Chaos Crags (Mt. Lassen volcanic center) tephra which was also found in the other lakes. Blue Lake was the only lake that hosted a Devils Hill tephra from the Three Sisters volcano in west central Oregon. Another tephra from the Three Sisters Volcano previously reported in sediments of Twin Lakes in NE Oregon, has now been confirmed as Rock Mesa tephra. The Chaos Crags, Devils Hill and Rock Mesa tephras are important late Holocene stratigraphic markers for central and eastern Oregon and northwestern Nevada.