Three-dimensional magnetotelluric modeling of Vulcano Island (Eolie, Italy) and its implications for understanding recent volcanic unrest

Abstract

This paper presents the results of an original short-period magnetotelluric survey performed on Vulcano Island (Italy). The obtained three-dimensional resistivity model details structures up to 2.5 km depth, hitherto unexplored. The La Fossa caldera area corresponds to a moderate resistive anomaly, which extends down to the resolved depth and likely represents a “conduit-like” structure along which magmatic fluids stall and ascend. Other resistive anomalies characterize volcanic edifices, craters, volcanic conduits, and/or eruptive fissures. In addition, the shallower hydrothermal system is detected as a conductive anomaly. Sharp resistivity contrasts generally characterize caldera faults. A main N‒S alignment characterizes the island sector, where considerable amounts of deep subsurface fluids accumulate and mix with the ascending magmas related to the most recent volcanic dynamics. The volcanological interpretation of such findings significantly contributes to understanding the geophysical and geochemical anomalies detected in the last year, which involved the Vulcano shallow hydrothermal system, highlighting the potential for possible hydrothermal/phreatic eruptive events.

Multi‐Temporal InSAR, GNSS and Seismic Measurements Reveal the Origin of the 2021 Vulcano Island (Italy) Unrest

“…Di Giuseppe et al. (2023) have identified a conduit‐like structure saturated with magma‐derived fluids in good agreement with our modeled source. This finding is consistent with the interpretation of an elongated rock volume that facilitates the upward movement of fluids to the surface (Montanaro et al., 2020).…”

“…We further note that our results allow us to identify the temporal evolution of the occurred phenomena, which can be summarized as follows (Figure 4f): the La Fossa Caldera hydrothermal system went under pressure between late July and early September 2021; from 5 September 2021 (when the first VLP was recorded) to early November 2021, the pressurization of the hydrothermal system increases (peak reached in mid‐October 2021); the occurrence of VLP, suggesting the gas transfer from the hydrothermal system, is coherent with the arrival of hydrothermal fluids at the surface (Federico et al., 2023); the alignment between the location of the VLP source and the fumarole areas inside the caldera (La Fossa cone, Faraglione) suggests the role of an N‐S structure in the transfer of hydrothermal fluids (Bonaccorso et al., 2010; Di Giuseppe et al., 2023; Fulignati et al., 1998; Ruch et al., 2016); from the beginning of November onwards, the deformation does not increase, while a series of phenomena coherent with the northward shift begin to occur (increase of gas flux in the fumarolic field between the Faraglione and Vulcanello; Federico et al., 2023). …”

“…the alignment between the location of the VLP source and the fumarole areas inside the caldera (La Fossa cone, Faraglione) suggests the role of an N‐S structure in the transfer of hydrothermal fluids (Bonaccorso et al., 2010; Di Giuseppe et al., 2023; Fulignati et al., 1998; Ruch et al., 2016);…”

“…Notably, Very Long Period (VLP; frequency peak ∼ 0.3 Hz) seismic events were recorded for the first time, with the source area located at 950 ± 270 m below sea level, North of La Fossa cone (Federico et al., 2023). VLP events were attributed to fluid release within La Fossa Caldera's fracture network, and the source's consistent location suggests a connection between pressurized fluids and geological structures (Di Giuseppe et al., 2023; Federico et al., 2023).…”

Imaging volcanoes during unrest: Ambient Noise Tomography of a transient plumbing system, Vulcano, Italy.

“…However, its hydrothermal system has been intermittently affected by episodes of magmatic intrusions and volcanic degassing unrest over the past four decades 4,5 . Given the densely populated center of Vulcano Porto during summer season and the island's touristic significance, the exposure to volcanic hazards remains exceedingly high, even for minor eruptive or degassing events 6,7 .…”