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Hydrothermal Alteration on Composite Volcanoes -Mineralogy, Hyperspectral Imaging and Aeromagnetic Study of Mt Ruapehu, New Zealand
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  • Gabor Kereszturi,
  • Lauren N Schaefer,
  • Craig Andrew Miller,
  • Stuart Mead
Gabor Kereszturi
Volcanic Risk Solutions, School of Agriculture and Environment, Massey University

Corresponding Author:[email protected]

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Lauren N Schaefer
U.S. Geological Survey
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Craig Andrew Miller
GNS Science
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Stuart Mead
Soil and Earth Sciences, School of Agriculture and Environment, Massey University
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Prolonged volcanic activity can induce surface weathering and hydrothermal alteration that is a primary control on edifice instability, posing a complex hazard with its challenges to accurately forecast and mitigate. This study uses a frequently active composite volcano, Mt Ruapehu, New Zealand, to develop a conceptual model of surface weathering and hydrothermal alteration applicable to long-lived composite volcanoes. The rock samples were classified as non-altered, supergene argillic alteration, intermediate argillic alteration, and advanced argillic alteration. The first two classes have a paragenesis that is consistent with surficial infiltration and circulation of the low-temperature (40 degree C) neutral to mildly acidic fluids, inducing chemical weathering and formation of weathering rims on rock surfaces. The intermediate and advanced argillic alterations are formed from hotter (100 degree C) hydrothermal fluids with lower pH, interacting with the andesitic to dacitic host rocks. The distribution of weathering and hydrothermal alteration has been mapped with airborne hyperspectral imaging through image classification, while aeromagnetic data inversion was used to map alteration to several hundred meters depth. The joint use of hyperspectral imaging complements the geophysical methods since it can numerically identify hydrothermal alteration style. This study established a conceptual model of hydrothermal alteration history of Mt Ruapehu, exemplifying a long-lived and nested active and ancient hydrothermal system. This study highlights the need to combine mineralogical information, geophysical techniques and remote sensing to distinguish between current and ancient hydrothermal and supergene alteration systems, to indicate the most likely areas of future debris avalanche initiation.
Sep 2020Published in Geochemistry, Geophysics, Geosystems volume 21 issue 9. 10.1029/2020GC009270