SILICIC EXPLOSIVE VOLCANISM: Understanding the Conditions of Steady and Unsteady Eruptive Behavior in Silicic Magmas - The Kaharoa 1314 Eruption

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The Taupo Volcanic Zone in New Zealand has had 3 intense sustained eruptions in the last 2000 years with the two most recent events from the host volcano Tarawera (Kaharoa 1314 and Tarawera 1886). The Kaharoa eruption was a devastating and long-lived event that featured multiple highly unsteady explosive phases with rapid and reversible shifts in eruptive intensity. As the youngest rhyolitic eruption in New Zealand it has served as the bench mark scenario to train emergency managers in response and recovery to a large volume explosive eruption. The host volcano, Tarawera, is also a major tourist resource visited by thousands of visitors and school children.In detail, the Kaharoa 1314 eruption had explosive phases that are an intriguing combination of features of high intensity 'Plinian' and short-lived transient 'Vulcanian' explosivity. These characteristics are currently not compatible with end-member numerical models for either rapid and sustained Plinian, or short-lived, low intensity Vulcanian explosions. This proposed study will therefore address a fundamental issue in explosive volcanism - the transition from unsteady to steady flow processes in the conduit. The study plan is to combine microtextural, geochemical and modeling approaches in order to permit examination of the factors that modulate open versus closed system degassing, which are first-order controls on the explosivity of magma in the conduits of silicic volcanoes. This study includes the use of two synchrotron beamlines, continued development of numerical fluid flow codes using HRXRT reconstructed pumice images, and also the application of 1D modeling codes to determine vesiculation and degassing histories of magmas erupted in the spectrum exhibited by the 1314 eruption.