Characterizing lithological, weathering, and hydrothermal alteration influences on volcanic rock properties via spectroscopy and laboratory testing: a case study of Mount Ruapehu volcano, New Zealand

Lauren N. Schaefer, Gabor Kereszturi, Ben Kennedy, Marlene Villeneuve

Publikation: Beitrag in FachzeitschriftArtikelForschungBegutachtung

30 Downloads (Pure)

Abstract

The geomechanical characterization of volcanic material has important implications for geothermal and mineral exploration, engineering design, geophysical signals of volcano unrest, and models of instability and mass flows. Chemical weathering and hydrothermal systems can alter the host rock, leading to changes in mechanical behavior and failure mode. Here, we compare the physical and mechanical properties of lava, autoclastic breccia, and pyroclastic (scoria) rocks from Mount Ruapehu volcano (Ruapehu) in New Zealand to mineralogical composition determined via infrared spectroscopy and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). We use correlation matrices, principal component analysis, and parametric analysis to determine which parameters can be used to predict physical and mechanical properties and form the basis for transfer functions. Laboratory-based spectroscopy shows that the samples contain absorption features indicative of Al- and Mg-rich hydrous phyllosilicates (e.g., kaolinite, halloysite, montmorillonite), Fe- oxides (e.g., goethite), and sulfates attributed to surface weathering, supergene, and steam-heated alteration. We find that porosity and primary lithology are the predominant control on physical and mechanical properties, followed by the pervasiveness of weathering/alteration, and then mineralogical composition. Several properties, such as porosity, uniaxial compressive strength, P-wave seismic velocity, density, and Young’s modulus, show strong correlations with other properties, indicating the potential for transfer functions between these properties. Hydrothermally altered rocks near the vent complex (up to ~ 400 m depth beneath the crater lake) with high-intensity hydrothermal alteration do not follow typical physical and mechanical property trends due to high clay content, low permeability, and low strength. The presence of these rocks within the edifice at Ruapehu implies local barriers to fluid flow and subsequent pore pressure variations. Additionally, they may have less than half the strength than would be dictated by typical porosity-strength trends for surface rocks, increasing the likelihood of structural failure. Trends in the pervasiveness of weathering with physical and mechanical properties, along with shifts in the position of spectral absorption peaks as hydrothermal/weathering alteration increases, suggest that it may be possible to extrapolate properties from imaging spectroscopy.
OriginalspracheEnglisch
Aufsatznummer43
Seitenumfang29
FachzeitschriftBulletin of volcanology
Jahrgang85
Ausgabenummer8
DOIs
PublikationsstatusVeröffentlicht - 13 Juli 2023

Bibliographische Notiz

Funding Information:
The Authors are grateful for Department of Conservation and Iwi around the Tongariro National Park for providing sampling permits (Authorization Number: 63618-GEO), and to all student and staff who joined in fieldwork and sampling campaigns throughout this project. Thank you to Stan Mordensky and an anonymous reviewer for helping to improve this manuscript. This research was supported by the New Zealand Ministry of Business, Innovation & Employment’s Natural Hazards Research Platform for the project “Too big to fail? – A multidisciplinary approach to predict collapse and debris flow hazards from Mt. Ruapehu”.

Funding Information:
The Authors are grateful for Department of Conservation and Iwi around the Tongariro National Park for providing sampling permits (Authorization Number: 63618-GEO), and to all student and staff who joined in fieldwork and sampling campaigns throughout this project. Thank you to Stan Mordensky and an anonymous reviewer for helping to improve this manuscript. This research was supported by the New Zealand Ministry of Business, Innovation & Employment’s Natural Hazards Research Platform for the project “Too big to fail? – A multidisciplinary approach to predict collapse and debris flow hazards from Mt. Ruapehu”.

Publisher Copyright:
© 2023, This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.

Dieses zitieren