V010-02
Shallow Conduit and Vent Processes in the 1886 Basaltic Plinian Eruption at Tarawera, New Zealand

Tuesday, 8 December 2020: 19:07
Virtual
Hannah Clare Moore, University of Tasmania, Hobart, TAS, Australia, Rebecca Carey, University of Tasmania, Centre of Ore Deposits and Earth Sciences, Hobart, TAS, Australia, Bruce F Houghton, University of Hawaii at Manoa, Geology & Geophysics, Honolulu, HI, United States and Martin Jutzeler, University of Tasmania, School of Natural Sciences and Centre for Ore Deposit and Earth Sciences (CODES), Hobart, TAS, Australia; University of Otago, National Oceanography Centre, Southampton, United Kingdom
Recorded Presentation
Abstract:
The 1886 eruption of Tarawera, New Zealand, is one of four known examples of basaltic Plinian eruptions in geological history. During the climactic phase, high Plinian eruption columns were produced at four vents along an 8-km-long fissure and were simultaneously accompanied by numerous low-intensity phases at separate vents along the same fissure.

We present a detailed re-examination of microtextures from proximal and medial suites of clasts. Clasts erupted from the margins of the high plumes are deposited in beds with wide spread dispersal (t1/2 of 100s m), whereas clasts erupted from low-intensity eruptions are deposited in beds with localized dispersal (t1/2 10s m). Although clast vesicle number densities are similar between all sample locations (in the order of 106–107 cm-3), we find that (i) microlite abundances in clasts from localized proximal units are greater and with little to no groundmass glass compared to clasts from medial units, (ii) clasts from widespread proximal units have a wide range of crystal and glass abundances, encompassing ranges seen in widespread medial units, iii) xenolith abundances in clasts from localized proximal units are greater than clasts from medial units, and (iv) clasts from widespread proximal units have a wide range of xenolith abundances, encompassing ranges seen in widespread medial units.

Microlite contents suggest contrasting magma ascent histories. Xenoliths in clasts were included into the magma either at the conduit walls or in the vent between explosions and could highlight an external influence on eruption intensity and dynamics.

This research furthers our understanding of a poorly understood and hazardous end-member of basaltic volcanism. Improved knowledge of the conditions that promote powerful eruption of basaltic magma is crucial for volcanologists and to provide better short-term forecasts of eruption onset to emergency managers and hence mitigate hazardous situations.

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