Porosity, strength, and alteration – Towards a new volcano stability assessment tool using VNIR-SWIR reflectance spectroscopy

Abstract

Volcano slope stability analysis is a critical component of volcanic hazard assessments and monitoring. However, traditional methods for assessing rock strength require physical samples of rock which may be difficult to obtain or characterize in bulk. This study uses visible to shortwave infrared reflected light spectroscopy to estimate and compare rock strength and porosity data for laboratory-tested rock samples from Ruapehu, Ohakuri, Whakaari, and Banks Peninsula (New Zealand), Merapi (Indonesia), Chaos Crags (USA), Styrian Basin (Austria) and La Soufrière de Guadeloupe (Eastern Caribbean) volcanoes.

While spectroscopy provided moderately accurate estimations of both rock strength and porosity, using laboratory-measured porosity to inform calculations significantly improved the accuracy of rock strength estimations. Our models also showed that observed changes in rock strength are coupled with subtle mineralogical changes due to hydrothermal alteration, including mineral replacement, precipitation, and/or silicification.

Our approach highlights that spectroscopy can provide a first order, non-destructive assessment of rock strength and/or porosity, and alteration mineralogy, or be used to complement laboratory porosity-based predictive models.