ALBERT

Description: Probabilistic hazard assessments of volcanic gases need to account for the natural variability associated to aspects such as weather conditions, source location, emission rate, and gas species. In order to quantitatively carry out these assessments, computational tools for gas dispersal need to be validated to demon- strate the reliability of the model results. Here we provide an exemplificative gas dispersal model validation at La Solfatara (a maar crater within Campi Flegrei caldera) which hosts one of the largest and hazardous fumarolic sites of the world, by using a workflow designed for automating the simulation strategy for probabilis- tic gas hazard assessments. This represents the first fundamental step towards gas hazard quantification in the area.

Description: Published

Description: 186

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: Caldeiras da Ribeira Grande is one of the degassing areas of Fogo, a trachytic central volcano located at Sa ̃o Miguel Island (Azores archipelago). Recently, new steam emissions, soil CO2 and temperature anomalies developed towards the inhabited area, causing high indoor CO2 values and affecting the vegetation and several small animals that were found dead in depressions and low-ventilated zones. During July–August 2021, a soil CO2 flux survey was carried out on the north flank of the volcano, estimating a soil gas release of at least 40 t d− 1 (excluding the contribution of the fumaroles) over an area of ~0.27 km2. Two populations for the CO2 released were found, highlighting the biogenic and volcanic-hydrothermal origins. General NW-SE diffuse degassing structures (DDS) were identified, in agreement with the tectonic lineaments previously recognized in the area. In this regard, we investigated the passive gas dispersion in the atmosphere at Caldeiras da Ribeira Grande per- forming a model validation aimed to estimate the fumarolic gas flux at source and the potential hazard for human and animal lives posed by CO2. Numerical simulations were carried out with the DISGAS-2.3, a 3D Eulerian advection-diffusion model, and the relative outputs processed through the VIGIL-1.3 workflow able to provide probabilistic long-term CO2 concentration maps, considering a meteorological variability over the last 30 years (1991–2020) taken from the ECMWF ERA5 reanalysis dataset. A best-fit between observed and simulated CO2 concentrations allowed us to estimate the total gas flux of the area (~209 t d− 1) obtained by scaling the soil CO2 gas flux by a factor 30. Such an estimate is composed of ~174 t d− 1 as unknown fumarolic and ~ 35 td− 1 as diffuse contribution, in a good agreement with measurements. Although the present-day CO2 concentration at 0.3 m height cannot be considered to raise serious concerns for human health, we reasonably infer that the death of small animals may be due to local conditions of CO2 accumulation or to the presence of H2S. The current study highlights the relevance of coupling gas flux maps, concentration data, and gas dispersion modeling to obtain robust estimation of gas fluxes, including the fuma- rolic contribution, and identify zones potentially impacted by dangerous concentrations of volcanic gases, which are relevant for land-use planning and hazard assessment in case of renewed escalations of volcanic activity.

Description: Published

Description: 107807

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: Nowadays, modeling of tephra fallout hazard is coupled with probabilistic analysis that takes into account the natural variability of the volcanic phenomena in terms of eruption probability, eruption sizes, vent position, and meteorological conditions. In this framework, we present a prototypal methodology to carry out the long-term tephra fallout hazard assessment in southern Italy from the active Neapolitan volcanoes: Somma–Vesuvius, Campi Flegrei, and Ischia. The FALL3D model (v.8.0) has been used to run thousands of numerical simulations (1500 per eruption size class), considering the ECMWF ERA5 meteorological dataset over the last 30 years. The output in terms of tephra ground load has been processed within a new workflow for large-scale, high resolution volcanic hazard assessment, relying on a Bayesian procedure, in order to provide the mean annual frequency with which the tephra load at the ground exceeds given critical thresholds at a target site within a 50-year exposure time. Our results are expressed in terms of absolute mean hazard maps considering different levels of aggregation, from the impact of each volcanic source and eruption size class to the quantification of the total hazard. This work provides for the first time, a multi-volcano probabilistic hazard assessment posed by tephra fallout, comparable with those used for seismic phenomena and other natural disasters. This methodology can be applied to any other volcanic areas or over different exposure times, allowing researchers to account for the eruptive history of the target volcanoes that, when available, could include the occurrence of less frequent large eruptions, representing critical elements for risk evaluations.

Description: Published

Description: 2289–2311

Description: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Description: JCR Journal

Description: Risk mitigation in long-dormant volcanic provinces is a challenge due to the absence of collective memory of past disasters as well as the scarcity, and subtlety, of unrest signals that can be monitored. In this study, the impact of a potential limnic eruption is assessed at the 92-m-deep lake Pavin (French Massif Central). The lake is hosted in a maar crater formed during the last eruptive event in metropolitan France (∼7 ka) and contains dissolved CO2 in the deepest water layer, below 60 m. Carbon dioxide (CO2) emissions measured at the lake surface (0.44 km2) reach up to 10.1 tons/day during the winter. Beyond this (limited) continuous degassing of the lake, the current CO2 budget in the monimolimnion layer (at a depth of 60 m to 92 m) was estimated at 1750 tons, of which about 450 tons are available for release in case of overturn of the lake. Scenarios for CO2 dispersion in the lower atmosphere were simulated with the DISGAS and TWODEE-2 models by varying (i) meteorological conditions, (ii) the amount of CO2 released, (iii) and the mechanisms of degassing during a potential limnic eruption. The simulations allowed identification and delimitation of areas potentially impacted by hazardous CO2 levels in the air down-valley from the lake and directly around the lake. The spatio-temporal evolution of the potential CO2 cloud raises issues regarding the impacts of such a hypothetical event in the close vicinity of the lake and, given the area is populated and highly visited, needs to be considered in future risk mitigation strategies.

Description: Published

Description: 108024

Description: OSV1: Verso la previsione dei fenomeni vulcanici pericolosi

Description: JCR Journal