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Open conduit volcanoes like Stromboli can display elusive changes in activity before major eruptive events. Starting on December 2020, Stromboli volcano displayed an increasing eruptive activity, that on 19 May 2021 led to a crater-rim collapse, with pyroclastic density currents (PDCs) that spread along the barren NW flank, entered the sea and ran across it for more than 1 km. This episode was followed by lava flow output from the crater rim lasting a few hours, followed by another phase of lava flow in June 2021. These episodes are potentially very dangerous on island volcanoes since a landslide of hot material that turns into a pyroclastic density current and spreads on the sea surface can threaten mariners and coastal communities, as happened at Stromboli on 3 July and 28 August 2019. In addition, on entering the sea, if their volume is large enough, landslides may trigger tsunamis, as occurred at Stromboli on 30 December 2002. In this paper, we present an integration of multidisciplinary monitoring data, including thermal and visible camera images, ground deformation data gathered from GNSS, tilt, strainmeter and GBInSAR, seismicity, SO2 plume and CO2 ground fluxes and thermal data from the ground and satellite imagery, together with petrological analyses of the erupted products compared with samples from previous similar events. We aim at characterizing the preparatory phase of the volcano that began on December 2020 and led to the May–June 2021 eruptive activity, distinguishing this small intrusion of magma from the much greater 2019 eruptive phase, which was fed by gas-rich magma responsible for the paroxysmal explosive and effusive phases of July–August 2019. These complex eruption scenarios have important implications for hazard assessment and the lessons learned at Stromboli volcano may prove useful for other open conduit active basaltic volcanoes.

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 show hydrothermal 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., Journal of Volcanology and Geothermal Research, 414, ISSN:0377-0273

Studies concerning

This is a seven-year study (1/7/2011-31/12/2017) of radon monitoring at two sites of Campi Flegrei caldera (Neaples, Southern Italy) that in the last 70 years experienced repeated phases of volcanic unrest. The sites are equipped with devices for radon detection, based on the spectrometry analysis of the α-particles of radon daughters. A hybrid method, as combination of three known methods, is applied for the identification of residuals (anomalies) and trends of the time series of Radon. The results are compared with the following indicators of current caldera unrest: the tremor caused by the major fumarolic vent registered by a seismic station; the cumulative of background seismicity; the maximum vertical deformation acquired by GPS networks during the current phase of uplift; the temperature-pressure of the hydrothermal system estimated based on gas geo-indicators. The comparisons show strong correlation among independent signals and suggest that the extension of the area affected by current Campi Flegrei crisis is larger than the area of seismicity and of intense hydrothermal activity from which the radon stations are 1–4 km away. These results represent an absolute novelty in the study of a such calderic area and mark a significant step forward in the use and interpretation of the radon signal.

Studies concerning 222Rn emission from soils are growing interest in the Earth Sciences, due to the gas potential as a tracer of natural phenomena. This paper presents a study of radon monitoring in two sites of Campi Flegrei caldera (Neaples, Italy) during the period July 1, 2011–December 31, 2017. This area was characterized by several phases of volcanic unrest. A hybrid method based on Multiple Linear Regression + Remote Radon Estimation method + Singular Spectrum Analysis (MLR + RRE + SSA) is developed for the trend extraction and the identification of anomalies in the time series of 222Rn. The results are compared with several routinely used geo-indicators of the caldera unrest. The comparisons show strong correlation among the signals. The present study proves the 222Rn is a potential indicator of the evolution of a volcanic crisis.

Radon is considered one of the short- and immediate-term earthquake precursors by International Association of Seismology and Physics of the Earth’s Interior. For this reason, the accurate and reliable measurement of its specific activity in soil gas is mandatory. Since its presence is influenced by many environmental factors, in order to eliminate this influence on the radon activity measurement a multi-parametric and multi-site analysis is necessary. Following this approach, a continuous radon monitoring was carried out in two sites of the Phlegrean Fields caldera (Campania, Italy) using the RaMonA system, which also allows for the measurement of temperature, relative humidity and pressure. In particular, the dependence of measured radon specific activity on the meteorological conditions was studied using the multiple linear regression method. The analysis was implemented also by testing data averages on different timescales. In this paper, the results of a preliminary analysis performed on data collected throughout 2012 are presented; the outcomes obtained allow to emphasize site-specific behavior and to discriminate apparent radon “anomalies” of climatic origin from those tied to the phenomena occurring in the earth’s crust. The method employed showed its usefulness by removing the effects of meteorological conditions and thus to better identify the possible radon anomalies caused by seismo-volcanic activity. The peculiarities of the different sites and some correlations with earthquakes are discussed.

Fumaroles are known to generate seismic and infrasonic tremor, but this fumarolic tremor has so far received little attention. Seismic records taken near the Pisciarelli fumarole, a vigorously degassing vent of the restless Campi Flegrei volcano in Italy, reveal a fumarolesourced tremor whose amplitude has recently intensified. We use independent geochemical evidence to interpret this fumarolic tremor for the first time quantitatively. We find that the temporal increase in fumarolic tremor RSAM (real-time seismic-amplitude measurement) quantitatively correlates with increases in independent proxies of fumarole activity, including the CO2concentrations in the fumarole's atmospheric plume, the fumarole composition (CO/CO2and H2/H2O ratios), and temperature (T) and pressure (P) conditions of the source hydrothermal system. This association between RSAM and geochemical data suggests that the current escalation in fumarolic tremor is driven by increased gas transport and venting from a hydrothermal system that evolves toward higher T-P conditions. More widely, our results suggest that monitoring the tremor generated by fumaroles can pave the way to real-time tracking and interpreting the evolution of an ongoing hydrothermal-magmatic unrest, thus complementing information from periodic gas surveys. Our novel method of fumarole monitoring, based on well-established seismic techniques, is potentially suitable for capturing signals of unrest at any active volcano, including those in remote regions.

A detailed analysis of a time-series of the Radon (222Rn) specific activity is carried out to identify anomalies that can be correlated with earthquakes occurrence in the monitored area. New hybrid methods are developed for this purpose and the advantages of each single component method are exploited. These methods are applied to two-years data series recorded continuously in the soils of a site within the seismo-volcanic area of Phlegrean Fields (Naples-Italy). Since the measurement system distinguishes and separately measures the 222Rn and 220Rn, an alternative estimation of the remote fraction of the gas and its anomalies has been also performed using the 220Rn trend. The results of different methods are compared to recognize and to highlight Radon anomalies. Clear relationships have been found between anomalies and earthquakes of local origin and selected according to a specific formula of the earthquake preparation zone. The effectiveness of the methods and the goodness of the results are established by the high values of the cross correlation factors between the anomalies and the occurrence of the earthquakes.

Aim of this paper is to identify variations in Very-Long-Period (VLP) source associated with eruptive style changes at Stromboli volcano (Italy) and to retrieve information about the shallow plumbing system that sustains the eruptive activity. We have considered a dataset of 74493 VLP events recorded during the period from January through August 2007, when an effusive eruption occurred (February 27–April 2). We performed a polarization analysis of the entire dataset and divided the considered period into four sub-periods on the basis of polarization characteristics. We then located the events and selected a subset of these events by applying a location quality threshold. The high quality locations demonstrate that during the effusive eruption the VLP sources first moved downward and then moved southwestward. To retrieve information about the geometry of the structures where the source processes take place, we further consider a subset of events and estimate their source mechanisms by using a moment tensor source function (MTSF) inversion technique. Inversion of the waveforms of the VLP events that occurred on February 27 allows us to obtain information about the dynamics of different source centroids distributed along different portions of the shallow magmatic conduits. The structure defined by the locations and source mechanisms shows a greater complexity compared with previous studies and their time variations give an insight into the kinematics of the eruption.

An important research facility for subnuclear particle physics and astrophysics has been operating in central Italy since 1986. These laboratories (Laboratori Nazionali del Gran Sasso: LNGS), promoted by the Italian National Institute of Nuclear Physics, are located in an underground tunnel about 120 km east of Rome, alongside a motorway tunnel 10.5 km long. The tunnel is shielded by 1,400 m of limestone rocks (Gran Sasso massif). The LNGS are located very close to one of the major seismic faults of the central Apennines. The seismic activity of the central Apennines and in particular in the region of the Gran Sasso massif is presently relatively low compared to seismically active areas of Europe, such as central Greece. In the last decade three seismic swarms occurred: August 1992, June 1994, and October 1996, with the largest earthquake having ML 4.2. These swarms constituted the largest events in this region since 1985. The area has, however, experienced destructive earthquakes in the past, including a magnitude ∼7 earthquake in 1703. The 1915 ( Ms 6.8) Avezzano earthquake occurred close to the region, causing more than 15,000 deaths (Amoruso et al. , 1998). On average, about one microearthquake per day above ML 1 occurs within a 20-km radius of LNGS. The laboratory facilities, in addition to the seismotectonic features, make them an excellent site for studies related to the physics of earthquake sources and wave propagation in a complex medium, and to development of high-sensitivity techniques to search for earthquake precursors. In this paper we describe a dense small-aperture seismic array, or seismic antenna, designed to study wave-propagation phenomena and source processes of microearthquakes occurring in this region. A seismic array is a set of seismographs distributed over an area of the Earth's surface with sufficiently small spacing that the signal …

The main purpose of this work is the design and implementation of an integrated wireless network as support to the multiparametric geophysical monitoring network of the Campi Flegrei volcanic area, in view of the increased need for seismic monitoring, which is a consequence of the drilling of an exploration well for scientific purposes. The goal is to increase the performance of the transmission system in terms of speed, real-time availability and reliability, given the high seismic risk and hazard associated with the experiment. The drilling is part of the international research project called “Campi Flegrei Deep Drilling Project” (CFDDP). For this purpose, in the first half of 2012, it was necessary to enhance the multiparametric monitoring network of Campi Flegrei, creating a subnet of seismic sensors, with limited geographical extension, but concentrated around the area of the well realization. The data acquisition from the monitoring center “Osservatorio Vesuviano”, section of Naples of the INGV, is guaranteed by a system of radio links in the 5 GHz band, due to the high interference in the typical band 802.11 and the highly urbanized area of interest. The subnet has shown a good cost/benefit ratio as regards the transmission, and it has proved to be useful for the monitoring purposes in order to detect in real time possible anomalies related to the drilling.

We present an overview of the volcanic seismicity recorded at Stromboli from January to September 2003. The data set starts a few weeks after the onset of the eruption and covers most of the effusive phase and the subsequent recovery of the explosive activity. The most important variations occurred between May and July coinciding with the waning of the lava flow and the reappearance of Strombolian activity at the summit craters. All the parameters indicate that the shallow magmatic system has not undergone permanent changes during this period. The only significant variation related to the shallow conduit is the increase in volcanic tremor amplitude and the change in the spectral content of long-period events during the transition between effusive and explosive activity. A slight increase in the very long period (VLP) events source elevation seems to mark the rise of the magma at the end of the effusive phase. The variations in the VLP events occurrence rate are more likely to be attributed to changes in the gas flow rate and the bubble coalescence mechanism, therefore, to a deeper portion of the magmatic system. The 5 April paroxysm is associated only with a small increase of the activity in the following days.

On February 27, 2007, the Stromboli volcano, which has usually been characterized by moderate explosive activity, started an effusive eruption with a small lava flow down the NW flank. The permanent broadband network installed on the island allowed the revealing of anomalies in the seismicity before the effusive eruption and for the phenomena to be followed over time, thus obtaining meaningful information about the eruption dynamics. During the effusive phase, a major explosion occurred on March 15, 2007. On that occasion, two strainmeters deployed on the volcano in the previous year recorded a strain increment before the blast. After this explosion, which further destabilized the upper part of the edifice, swarms of Long-Period (LP) and hybrid events were recorded. The characteristics and locations of these events suggest that they were associated with the fracturing processes that affected the summit area of the cone. During the effusive phase, changes in the Very Long Period (VLP) event location were recorded. This type of events accompanied the change in the eruptive style, providing information about the magmatic conduit involved in their seismogenetic processes. The effusive phase stopped on April 2, 2007, and the typical Strombolian activity restarted some months later.

A very compact 32-channel digital delay module has been designed to fit in a single VME 6 U unit. It is equipped with both VME and Fast Intercrate Readout (FAIR) interfaces. Furthermore, a local manual programmability was implemented to use the module also in a stand-alone mode. A variety of NIM and ECL output have been implemented. A special ECL input allows the selection of different output regimes. The thermal stabilization is controlled via a PLL based circuit. The main features of the module are the wide range for the delay and the width of the output pulse: from 25 ns up to 6400 ns, in 25 ns steps; and the low jitter: values of the order of 27 ps (11 ppm) were measured in several bench tests.

Optimization of in soil air radon monitoring using thoron and radon and thoron parents