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Hydrothermal Seal Systematics Giving Rise to Gas-driven Eruptions

Bruce Christenson1 , Agnes Reyes2, Ben Kennedy3 and Richard Henley4

  • Affiliations: 1National Isotope Centre, GNS Science, Lower Hutt 5010, New Zealand  2Geological Sciences, University of Canterbury, Private Bag 4800, 8140 Christchurch, New Zealand 3GNS Science, Lower Hutt 5010, New Zealand 4Department of Applied Mathematics, Research School of Physics, The Australian National University, ACT 0200, Australia

  • Presentation type: Poster

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

  • Poster Board Number: 76

  • Programme No: 3.14.10

  • Theme 3 > Session 14

Abstract

Whakaari, Ruapehu and Raoul are three "wet" volcanoes that are prone to recurring gas-driven eruption events.  Studies of ejecta produced by these eruptions, along with emissions data and monitoring observables, provide constraints for the development of conceptual and numerical models of the systems.  All have lakes over their respective vent regions, with those at Ruapehu and Whakaari being hyper-acidic, wherein the circulating pore fluids are demonstrably in near-equilibrium with sulphate mineral phases.  Here fracture permeability gives rise to fumarolic emissions which are typified mainly by CO2, SO2, H2S and HCl gases.  Elemental S is ubiquitous in the zones where rising fumarolic vapors encounter pore-resident fluids, whereas convective flow regimes induced by the fumarolic emissions draw cool lake water downward into deeper hot environments.  This leads to precipitation of sulfate mineral phases, thereby reducing lateral permeability, and leading to the development of vertical zones of gas accumulation.  Pressures in these compressible gas columns are predominantly governed by local hydrostatic pressure, and presence of CO2 clathrates in fluid inclusions points to the occurrence of pressures in excess of 40 b attained.  Such pressures can exceed rock strength, leading to eruption.  Raoul Island (Kermadecs), on the other hand, has a convective flow regime situated over a deeper heat source, from which the more aggressive hydrolysis-promoting agents are scrubbed during ascent. Here, permeability is governed by carbonate mineralization, and lesser amounts of anhydrite, wherein focused deposition of these phases occurs in zones of boiling as the altered seawater fluids rise to the surface.