Thermal monitoring to infer possible interactions between shallow hydrothermal system and slope-scale gravitational deformation of Mt. Epomeo (Ischia Island, Italy)

Posted on 05.07.2021 - 11:16
Geothermal and volcanic systems are prone to gravity-induced slope instability at different scales. Endogenous magmatic, hydrothermal, and seismic forcings can significantly modify mechanical properties and perturb the local stress field and gravitational equilibrium inducing shallow or slope-scale instabilities. The island of Ischia, which is part of the Phlegrean Volcanic District (Italy), is a remarkable example of this kind of complex interacting system. This study focuses on monitoring the hydrothermal system located beneath the ongoing slope-scale deformation, which involves Mt. Nuovo (the western part of Mt. Epomeo) and is a complementary effect of the resurgence of an ancient caldera. Debris and rock avalanches have affected the slopes of this volcanic island, in response to the renewal of volcanic activity and caldera resurgence. Large parts of the corresponding mass-wasting deposits overlay the most active areas of the Ischia hydrothermal system, where ongoing slope-scale gravity-driven deformation due to a mass rock creep (MRC) process is still evolving. To investigate possible relations between the perturbing shallow hydrothermal system and the MRC process, thermal monitoring of selected groups of fumarolic emissions located in several portions of the deforming sector has been carried out since 2008 on a monthly basis by means of direct (thermal probes) and remote sensing (IR-thermography) techniques. Thermal monitoring of specific fumaroles shows a peculiar seasonal trend characterised by a delayed inverse correlation with rainy periods and a short-term pulsating response to dry stages. The fumaroles also appear spatially correlated to the presence of MRC-related structures involving volcanic slopes. According to the measured thermal data, a conceptual model of the thermal interactions within the Mt. Nuovo slope is provided, framing the potential role of thermal actions in accelerating the deformation process. In this view, possible hazard scenarios, due to magmatic or hydrothermal renovation are depicted, delineating the interconnected multi-hazard worst scenario consisting of an accelerating evolution of the MRC process towards paroxysmal collapse.

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Della Seta, M; Esposito, C; Fiorucci, M; Marmoni, G M; Martino, S; Sottili, G; et al. (2021): Thermal monitoring to infer possible interactions between shallow hydrothermal system and slope-scale gravitational deformation of Mt. Epomeo (Ischia Island, Italy). Geological Society of London. Collection. https://doi.org/10.6084/m9.figshare.c.5497819.v1
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