Unravelling the role of hydrothermal alteration in volcanic flank and sector collapses using combined mineralogical, experimental, and numerical modelling studies
(2016)
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- Volcanic flank and sector collapses have been observed at several hundred volcanic edifices worldwide and pose one of the most sudden, destructive and life-threatening volcanic hazards. The study of debris avalanche deposits sourced to volcanic edifice collapses suggests that hydrothermal rock alteration plays a key role in promoting failure but the exact effect of such alteration on the mechanisms leading to edifice instability has yet to be elucidated. The present thesis aims to unravel this issue through combined field works, laboratory analyses and experiments, and numerical modelling studies. Results from field works and laboratory analyses of volcanic debris deposits from Cayambe and Tutupaca volcanoes emphasise the importance of careful mineralogical analyses for correctly interpreting the origin triggering factor of debris flows and debris avalanches in volcanic terrains. Findings from a series of geotechnical measurements performed on variably altered volcanic rocks show that the nature of secondary minerals contained in an altered edifice is a critical factor to take into account when evaluating its stability. Further, numerical modelling studies revealed that mechanical properties of altered rocks are more critical for stability when alteration is situated in the edifice compared to when it is situated within the basement. The low permeability and high water retention capacity of clay-bearing altered rocks have also been found to impact volcanic flank stability by influencing groundwater dynamics and pore pressure distribution within the edifice.
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Detienne, M. (2016). Unravelling the role of hydrothermal alteration in volcanic flank and sector collapses using combined mineralogical, experimental, and numerical modelling studies. https://hdl.handle.net/2078.5/75242