Structural and Hydrothermal Inferences from a Magnetotelluric Survey Across Mt. Ruapehu, New Zealand

Abstract

Magnetotelluric measurements made at 27 sites on and around Mt. Ruapehu, analysed using the phase tensor technique of Caldwell et al. (2004), clearly show that the electrical conductivity structure associated with the volcano is 3-dimensional. Limited 1 and 2-D modelling of the high frequency data show a shallow conductor beneath the eastern part of the volcanic massif which is probably the result of wet volcanic debris rather than from the existence of Tertiary sediments beneath the Tongariro Volcanic Centre. A near surface conductor identified at a single site on the summit plateau is inferred to be connected with the hydrothermal system associated with the Crater Lake. No traces of subsurface outflow from the hydrothermal system were detected within the limited cover provided by this survey.