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New insights into the spatiotemporal evolution of the Y5 phase of the Taupō 232 ± 10 CE eruption, New Zealand

Sarah Tapscott1, Gert Lube2 , Colin Wilson3

  • Affiliations: 1 Geoscience and Exploration, RSC, Wellington, New Zealand  2 School of Agriculture and Environment, Massey University, Palmerston North, New Zealand  3 School of Geography, Environment and Earth Sciences, Victoria University of Wellington, Wellington, New Zealand. 

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 95

  • Programme No: 3.12.21

  • Theme 3 > Session 12

Abstract

The Plinian Y5 phase of the Taupō 232 ± 10 CE eruption generated a widespread and well-preserved deposit incorporating fall and coeval PDC deposits. Despite extensive study, there remain conflicting views around the deposits regarding eruption and sedimentation processes. To reconstruct the spatiotemporal evolution of the Y5 and address Plinian eruption dynamics and sedimentation, a detailed dataset of the Y5 deposit characteristics is presented. Analyses for grain size distributions, componentry, and juvenile textural characteristics demonstrate that foreign lithic lithologies and their time-relative abundance can be used to inform vent location, conduit evolution and the balance between PDC and fall activity. Vertical variations in the abundance and relative proportions of different juvenile and lithic pyroclasts, juvenile textures and pumice densities, following the initial development of the vent, define three successive stages within a continuous, relatively steady, eruption: 1) conduit excavation; 2) increasing mass eruption rate towards a climax; and 3) a decrease in mass eruption rate and the acceleration of conduit erosion prior to the Y6 ignimbrite. Vertical bedding features previously documented in the Y5 fall deposit can be demonstrated to be laterally discontinuous and pinch out over length scales of 101-103 m. We interpret these features in the Y5 deposit to result from gravitational instabilities in the umbrella cloud, sedimenting as tephra swathes. Using quantitative analysis such as this provides a field-based foundation for the reconstruction of the spatiotemporal evolution of such eruptions, ultimately providing a pathway for the amalgamation of field data and computational eruption models.