ALBERT

Description: Campi Flegrei caldera (Southern Italy) is among the areas with the highest volcanic risk in the world. The megacity of Naples, hosting more than 1 million inhabitants, lies across the caldera borders. In recent years Campi Flegrei caldera has experienced an accelerating uplift rate of the ground deformation. In particular, during the April 2012 - January 2013 time interval the caldera has shown a rapid uplift of about 6 cm with a peak rate of about 3 cm/month in December 2012. This event led the Italian Civil Protection to raise the alert level of the volcano from green to yellow. We exploited the displacement time series obtained by processing 90 SAR images acquired from the COSMO-SkyMed sensor constellation along ascending orbits via the well-known DInSAR algorithm referred to as SBAS algorithm, and the measurements provided by 14 continuous GPS stations deployed within the caldera and belonging to the permanent INGV-OV monitoring network. To study the detail of the intrusion process we have applied novel geodetic imaging technique to determine the spatial and temporal kinematics of the ground deformation source in the selected period. The retrieved temporal pattern of the source geometry reflects that of a growing sill which, at the end of the considered period, has a roughly elliptical geometry with an extension of about 6 km in the EW direction and about 4 km in the NS one. The maximum aperture of the sill is of about 30 cm at its center. To understand the dynamics of this phenomenon we used a recently developed numerical model of the emplacement of a magmatic sill, to fit the retrieved geometry. The parameters to be determined are: the average magma viscosity, the amount of magma already present in the sill before the 2012-2013 episode and the magma injection rate. Results show that the most likely value for the viscosity is between 103 − 104Pa · s and that to justify the observed deformation pattern it is required that the reservoir should have contained at least 1010kg of liquid magma before 2012. The injection rate has two main peaks on September and December 2012, and a smaller one on March 2013. The first two peaks have a value of about 400 kg/s and duration of 3-4 months. The total amount of injected magma is of about 8.2 · 1010kg. The magma viscosity value is compatible with that of the most common magmas erupted in the past 40 ky: phonolites, while the total inferred amount of liquid magma is of the same order of magnitude of small-size eruptions (VEI 2-3) occurred in the caldera during the last 15 ky. The first injection peak is associated with a seismic swarm, located beneath the town of Pozzuoli. The swarm consisted in about 200 earthquakes (maximum magnitude 1.8) occurring within an interval of about 1.5 hours. The hypocenters were located outside the area usually affected by microearthquakes in the previous years. Using finite element structural mechanical modeling we show that the inferred source caused a marked increase in the maximum shear stress along the rim of the sill. In fact hypocenters were located very close to the northern edge of the growing magmatic reservoir. Our findings suggest a key to interpret the caldera unrest that, started about 60 years ago, has led to a maximum uplift in the area of more than 3 m. Consequently, the observed uplift phenomenon could be interpreted in terms of injection of limited magma batches feeding the growth of a shallow magmatic reservoir. Similar mechanisms have been inferred for other calderas, where the repeated emplacement of magmatic sills has been recognized having an important role in the evolution of the volcano. Accordingly, the observation of short evolution of volcanic precursory phenomena as well as the development of innovative real- time analysis techniques should be taken into account for an effective surveillance of the Campi Flegrei caldera. This work has been supported by the Italian Department of Civil Protection and by the Italian Space Agency under theSAR4Volcanoes project (agreement n. I/034/11/0) and by MED-SUV project (European Union’s Seventh Programme for research, technological development and demonstration under grant agreement No 308665).

Description: Published

Description: Vienna

Description: 2V. Dinamiche di unrest e scenari pre-eruttivi

Description: open

Description: Volcanic processes operate over a wide range of time scale that requires different instruments and techniques to be monitored. The best approach to survey a volcanic unrest is to jointly monitor all the geophysical quantities that could vary before an eruption. The monitoring techniques are sometimes peculiar for each volcano, which has its own behavior. The simultaneous investigation of all the geophysical and geochemical parameters improves the sensibility and the understanding of any variation in the volcanic system. The Osservatorio Vesuviano is the INGV division charged of the Campi Flegrei and Vesuvius monitoring, two of the highest risk volcanic complexes in the world due to the large number of people living on or close to them. Each of them have peculiarities that increase the monitoring challenge: Campi Flegrei has high anthropic noise due to people living within its numerous craters; Vesuvius has a sharp topography that complicates the data transmission and analysis. The real time monitoring of the two areas involves several geophysical fields and the data are transmitted by a wide data-communication wired or radio infrastructure to the Monitoring Centre of Osservatorio Vesuviano: - The seismic network counts of 20 station sites in Campi Flegrei and 23 in Vesuvius equipped with velocimetric, accelerometric and infrasonic sensors. Some of them are borehole stations. - The GPS network counts of 25 stations operating at Campi Flegrei caldera and 9 stations at Vesuvius volcano. All the procedures for remote stations managing (raw data downloading, data quality control and data processing) take place automatically and the computed data are shown in the Monitoring Centre. - The mareographic network counts of 4 stations in the Campi Flegrei caldera coast and 3 close to the Vesuvius that transmit to the Monitoring Centre where the data are elaborated. - The tiltmetric network consist of 10 stations distributed around Pozzuoli harbor, the area of maximum ground uplift of Campi Flegrei, evidenced since 2005, and 7 stations distributed around the Vesuvius crater. Each tiltmetric station is also equipped with a temperature and magnetic sensor. The signals recorded are sent to the Monitoring Centre. - The 4 marine multiparametric stations installed in the Pozzuoli gulf send accelerometric, broad band, hydrophonic and GPS data to the Monitoring Centre. - The geochemical network counts of 4 multiparametric stations in the fumarolic areas of Campi Flegrei and 2 stations in the Vesuvius crater (rim and bottom) with data transmission to the Monitoring Centre. They collect soil CO2 flux, temperature gradient and environmental and meteorological parameters and transmit them directly to the Monitoring Centre. - The permanent thermal infrared surveillance network (TIRNet) is composed of 6 stations distributed among Campi Flegrei and Vesuvius. The stations acquire IR scenes at night-time of highly diffuse degassing areas. IR data are processed by an automated system of IR analysis and the temperatures values are sent to the Monitoring Centre

Description: Published

Description: Vienna, Austria

Description: 1IT. Reti di monitoraggio e sorveglianza

Description: The study concerns the analysis of 220Rn (thoron) recorded in the surface soil in two sites of the Campi Flegrei caldera (Naples, Southern Italy) characterized by phases of volcanic unrest in the seven-year period 1 July 2011–31 December 2017. Thoron comes only from the most surface layer, so the characteristics of its time series are strictly connected to the shallow phenomena, which can also act at a distance from the measuring point in these particular areas. Since we measured 220Rn in parallel with 222Rn (radon), we found that by using the same analysis applied to radon, we obtained interesting information. While knowing the limits of this radioisotope well, we highlight only the particular characteristics of the emissions of thoron in the surface soil. Here, we show that it also shows some clear features found in the radon signal, such as anomalies and signal trends. Consequently, we provide good evidence that, in spite of the very short life of 220Rn compared to 222Rn, both are related to the carrier effect of CO2, which has significantly increased in the last few years within the caldera. The hydrothermal alterations, induced by the increase in temperature and pressure of the caldera system, occur in the surface soils and significantly influence thoron’s power of exhalation from the surface layer. The effects on the surface thoron are reflected in both sites, but with less intensity, the same behavior of 222Rn following the increasing movements and fluctuations of the geophysical and geochemical parameters (CO2 flux, fumarolic tremor, background seismicity, soil deformation). An overall linear correlation was found between the 222−220Rn signals, indicating the effect of the CO2 vector. The overall results represent a significant step forward in the use and interpretation of the thoron signal.

Description: Published

Description: 5809

Description: 4V. Processi pre-eruttivi

Description: JCR Journal

Description: The analogue experiments that produce seismo-acoustic events are relevant for understanding the degassing processes of a volcanic system. The aimof thiswork is to design an unsupervised neural network for clustering experimental seismo-acoustic events in order to investigate the possible cause-effect relationships between the obtained signals and the processes. We focused on two tasks: 1) identify an appropriate strategy for parameterizing experimental seismo-acoustic events recorded during analogue experiments devoted to the study of degassing behavior at basaltic volcanoes; 2) define the set up of the selected neural network, the Self-Organizing Map (SOM), suitable for clustering the features extracted from the experimental events. The seismo-acoustic events were generated using an ad hoc experimental setup under different physical conditions of the analogue magma (variable viscosity), injected gas flux (variable flux velocity) and conduit surface (variable surface roughness). We tested the SOMs ability to group the experimental seismo-acoustic events generated under controlled conditions and conduit geometry of the analogue volcanic system. We used 616 seismo-acoustic events characterized by different analogue magma viscosity (10, 100, 1000 Pa s), gas flux (5, 10, 30, 60, 90, 120, 150, 180 × 10−3 l/s) and conduit roughness (i.e. different fractal dimension corresponding to 2, 2.18, 2.99). We parameterized the seismoacoustic events in the frequency domain by applying the Linear Predictive Coding to both accelerometric and acoustic signals generated by the dynamics of various degassing regimes, and in the time domain, applying a waveform function. Then we applied the SOM algorithm to cluster the feature vectors extracted fromthe seismo-acoustic data through the parameterization phase, and identified four main clusters. The results were consistent with the experimental findings on the role of viscosity, flux velocity and conduit roughness on the degassing regime. The neural network is capable to separate events generated under different experimental conditions. This suggests that the SOM is appropriate for clustering natural events such as the seismo-acoustic transients accompanying Strombolian explosions and that the adopted parameterization strategy may be suitable to extract the significant features of the seismoacoustic (and/or infrasound) signals linked to the physical conditions of the volcanic system.

Description: Published

Description: 581742

Description: 5V. Processi eruttivi e post-eruttivi

Description: JCR Journal

Description: One of the most effective approaches to identifying possible precursors of eruptions is the analysis of seismicity patterns recorded at volcanoes. Accurate locations of the seismicity and the estimate of source mechanisms can resolve fault systems and track fluid migrations through volcanoes. We analysed the six main swarms recorded at Campi Flegrei since 2000, using them as a proxy of the processes involved in the long-term-unrest of this densely populated caldera. We re-located the earthquakes comprised in these swarms and estimated the focal mechanisms, which appear in agreement with the fault systems of the caldera and with tomographic images. The focal mechanisms are in agreement with the tensional stress induced by the caldera uplift. Most of the swarms and remaining seismicity delineate a highly fractured volume extending vertically below the Solfatara/ Pisciarelli vents, where gases find preferential paths to the surface triggering earthquakes. The main swarms are located below this volume where the presence of a rigid caprock is still debated. We interpreted the current unrest in term of a gradual increment in the activity of a wide hydrothermal system whose most evident manifestation is the enlargement of the fumarolic-field of Pisciarelli and the increment of the earthquakes occurrence rate.

Description: Published

Description: 2900

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: JCR Journal

Description: Fluids supplied by stored magma at depth are causal factors of volcanic unrest, as they can cause pressurization/ heating of hydrothermal systems. However, evidence for links between hydrothermal pressurization, CO2 emission and volcano seismicity have remained elusive. Here, we use recent (2010−2020) observations at Campi Flegrei caldera (CFc) to show hydrothermal pressure, gas emission and seismicity at CFc share common source areas and well-matching temporal evolutions. We interpret the recent escalation in seismicity and surface gas emissions as caused by pressure-temperature increase at the top of a vertically elongated (0.3–2 km deep) gas front. Using mass (steam) balance considerations,we showhydrothermal pressurization is causing energy transfer from the fluids to the host rocks, ultimately triggering low magnitude earthquakes within a seismogenetic volume containing the hydrothermal system. This mechanism is probably common to other worldwide calderas in similar hydrothermal activity state.

Description: MIUR project n. PRIN2017-2017LMNLAW“Connect4Carbon”

Description: Published

Description: 107245

Description: 4V. Processi pre-eruttivi

Description: JCR Journal

Description: Two paroxysmal explosions occurred at Stromboli on July 3 and August 28, 2019, the first of which caused the death of a young tourist. After the first paroxysm an effusive activity began from the summit vents and affected the NW flank of the island for the entire period between the two paroxysms. We carried out an unsupervised analysis of seismic and infrasonic data of Strombolian explosions over 10 months (15 November 2018–15 September 2019) using a Self- Organizing Map (SOM) neural network to recognize changes in the eruptive patterns of Stromboli that preceded the paroxysms. We used a dataset of 14,289 events. The SOM analysis identified three main clusters that showed different occurrences with time indicating a clear change in Stromboli’s eruptive style before the paroxysm of 3 July 2019. We compared the main clusters with the recordings of the fixed monitoring cameras and with the Ground-Based Interferometric Synthetic Aperture Radar measurements, and found that the clusters are associated with different types of Strombolian explosions and different deformation patterns of the summit area. Our findings provide new insights into Strombolian eruptive mechanisms and new perspectives to improve the monitoring of Stromboli and other open conduit volcanoes.

Description: This work was supported by the project Progetto Strategico Dipartimentale INGV 2019 “Forecasting eruptive activity at Stromboli volcano: timing, eruptive style, size, intensity and duration” (FIRST). This work is also supported by a Marie Sklodowska-Curie Innovative Training Network Fellowship of the European Commission’s Horizon 2020 Programme under Contract Number 765710 INSIGHTS. This work benefited from the EU (DG ECHO) Project EVE n. 826292. This work has been partially supported by the “Presidenza del Consiglio dei Ministri–Dipartimento della Protezione Civile” (Presidency of the Council of Ministers–Department of Civil Protection; Scientific Responsibility: N.C.). However, this publication does not necessarily represent the official opinion and policies of the department.

Description: Published

Description: 1287

Description: 4V. Processi pre-eruttivi

Description: JCR Journal