GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.2 GNGTS 2023 NNW-SSE, while the northern vent of the 1969 eruptive fissure corresponds to Aa1 in the Pendulum Cove area. These geographical correspondences show high-absorption anomalies that can represent: (a) the magmatic residues of past eruptions; (b) newly formed shallow magma storage zones; (c) or, more likely, high-temperature fluids rising through the pathways formed during the previous eruptions. The NNW-SSE elongated low-attenuation strip Ba1 located south of the high attenuation zone Aa1 follows the trace of a cooled dike responsible for the 1969 eruption, opening several vents across its path. We infer that Aa1, which is located at the northern tip of the eruptive fractures where the eruption originated, represents the shallowest feature of the volcanic conduit, still hot today. The high-absorption areas in our maps generally correspond to areas of higher thermal potential (Paredes et al., 2006). Low-absorption anomalies appear instead as the seismological signature of cooled erupted material due to the local cold weather conditions. Similar processes could affect materials under the ice-capped Mt. Kirkwood, corresponding to the second low-absorption anomaly (Ba2), which corresponds to the 1842 eruption vents at Mt. Kirkwood (De Rosa et al., 1995). The ability of coda waves to detect shallow, unconsolidated, and cooled systems has been proven when targeting debris avalanches, like the one at Mount St. Helens volcano in 1980 (De Siena et al., 2016; Gabrielli et al., 2020), and shallow dike intrusions (De Siena et al., 2017). The assessment of the Ba1 and Ba2 anomalies as rapidly-cooled erupted materials (Figure 3, white-contoured gray lines, right) is supported by their spatial correspondence with historical vents. The vent distribution allowed Bartolini et al. (2014) to define the spatial arrangement of the highest susceptibility values (probability of vent opening) in the hazard map of Deception Island. The hotter zones coincide with the high-absorption anomaly Aa2 in the Fumarole Bay area (Figure 3, black-contoured gray circle) where the hydrothermal emissions and sub-surface hot zones occur. This implies that the hazard maps or, more in general, hazard evaluations should include the results of attenuation studies in addition to volcanological, geochemical, and other geophysical data (Berrocoso et al., 2006). At Deception, hazard maps are essential to establish escape routes for scientists and tourists in the case of an impending eruption. The connection we infer between temperature and seismic absorption could be a central ingredient for a better hazard assessment of the island. In particular, we focus attention on Aa2 and the Aa3 anomaly located at the island entrance. Both anomalies coincide with areas suggested for landing and take-off of rescue helicopters (Smellie et al., 2002). Our analysis identifies these anomalies as potential reservoirs from which hazardous materials could rise to the surface.