Abstract
A crucial feature to manage a volcanic crisis is the ability of volcanologists to promptly detect an impending eruption. This is often affected by significant uncertainty, mainly for the difficulty in interpreting the monitoring signals in terms of the exact timing of a possible eruption. Here we contribute to this problem, focusing on the states of active volcanoes with closed conduit, as deduced from monitoring data. Four main states can be identified. In the quiescence state 1) the monitoring data lie on a baseline, suggesting the lack of shallow magma/fluid movement. The unrest state is highlighted by minor 2) to major 3) variations in the intensity and rate of monitoring data; in both cases, radial ground deformation pattern and non-migrating seismicity imply shallow magma and/or fluid accumulation. The state of impending eruption 4) is characterised by non-radial, asymmetric ground deformation pattern and migrating seismicity, which suggest that magma approaches the surface through a propagating dyke. As early recognition of this distinctive state is crucial for timely eruption forecast, monitoring activity should be aimed at its prompt detection. The application of this rationale to two types of active volcanoes in densely inhabited areas, a restless caldera (Campi Flegrei) and a quiescent stratovolcano (Vesuvio), highlights its feasibility and importance in eruption forecasting. This rationale may foster a general reference framework to be adopted in case of unrest, supporting in interpreting the monitoring data, as well as more effective: 1) operationally-oriented, monitoring system; 2) probabilistic forecast; 3) use of volcanic alert levels.
Highlights
With the increase of global population, human settlements near active volcanoes have increased dramatically, and nowadays about 800 million people live within 100 km from a volcano that has the potential to erupt (Papale and Marzocchi, 2019)
The conceptual model takes into account for a few evidence-based, key elements widely accepted by most of the scientific community. These include volcanological, structural and petrological-geochemical data, as well as information on the current state of the volcano derived from the monitoring system. To build these simplified conceptual models, we have evaluated all available literature related to Campi Flegrei and Vesuvio and possible analogues, and openly discussed to find the combination of the key-elements that delineate a working reference model for each volcano, in terms of magma supply, shallow magmatic storage and mode of final magma rise to surface
We suggest that the proposed approach, in which the states of a volcano are defined in terms of expected changes in the magma dynamics on the basis of the conceptual model, could represent an important contribution for those approaches aimed at establishing procedures of eruption forecasting, as BET_EF (Marzocchi et al, 2008)
Summary
With the increase of global population, human settlements near active volcanoes have increased dramatically, and nowadays about 800 million people live within 100 km from a volcano that has the potential to erupt (Papale and Marzocchi, 2019). These include volcanological, structural (geological-geophysical) and petrological-geochemical data, as well as information on the current state of the volcano derived from the monitoring system To build these simplified conceptual models, we have evaluated all available literature related to Campi Flegrei and Vesuvio and possible analogues (i.e., volcanoes with similar behaviour), and openly discussed to find the combination of the key-elements that delineate a working reference model for each volcano, in terms of magma supply, shallow magmatic storage and mode of final magma rise to surface. We would like to stress that, despite the adoption of a preferred conceptual model, any dogmatic use should be avoided and, wherever possible, during a volcanic crisis alternative conceptual models should be considered (e.g., Newhall et al, 2021)
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