Terrestrial and Submarine Characterization of Whakaari / White Island for Flank Stability Assessment
Presentation
Authors: Miller, C.A., Bertrand E.A., Caratori Tontini, F., Constable, S., de Ronde, C.E.J. King, R.
Event: AGU 2024
Summary: To assess the likelihood of flank collapse we undertook extensive submarine and airborne geophysical imaging to map volcanic structure, and infer hydrothermal alteration, fluid seepage and degree of saturation.
https://agu.confex.com/agu/agu24/meetingapp.cgi/Paper/1638640(external link)
Abstract:
Numerical simulations of tsunami induced by flank collapse of Whakaari/White Island, New Zealand, suggest inundation of parts of a densely populated coast could occur within 20 minutes. To fully assess the likelihood of flank collapse we undertook extensive submarine and airborne geophysical imaging to map volcanic structure, and infer hydrothermal alteration, fluid seepage and degree of saturation.
Terrestrial edifice assessment utilized time domain electromagnetic and magnetic data from helicopter borne SkyTEM, while submarine edifice assessment utilized magnetic data from AUV Sentry and frequency domain controlled-source electromagnetic data from a surface-towed CSEM system. Deep-towed self-potential data were collected along CSEM lines.
Detailed magnetic vector inversion modelling of SkyTEM magnetic data over the terrestrial edifice shows volumes of low magnetic susceptibility interpreted as alteration from past and present hydrothermal activity. A large low susceptibility volume is located on the north flank while high susceptibility underlies the high standing parts of the crater rim.
Similar inversion of AUV magnetic data from the submarine portion shows typically higher magnetic susceptibilities associated with high bathymetric relief interpreted as unaltered lava flows.
Three-dimensional inversion of the SkyTEM electromagnetic data identifies areas of low resistivity (<5 Ωm) coincident with the low magnetic susceptibility volume on the north flank. Very low resistivities (1 Ωm) are associated with the crater floor infill saturated with hydrothermal fluids. Higher resistivities (50-100 Ωm) are coincident with higher magnetic susceptibilities on the northeast flank.
The identified areas of coincident low magnetic susceptibility and low electrical resistivity mark potentially unstable rock volumes that will be used for future flank stability assessment and tsunami propagation modelling.