INGV Osservatorio Etneo

The 2002 effusive flank eruption at Stromboli volcano started on December 28, after several months of strong explosive activity at the summit craters. On December 30, the seismic network recorded two large flank failures and associated tsunami waves. This is the first time that a flank collapse and tsunami, and their associated phenomena, have been recorded by a multi‐disciplinary monitoring system. Volcanological and geophysical monitoring, as well as thermal surveys performed immediately before and after the failure, allowed us to define and interpret the sequence of events. The still on‐going eruption has provided, for the first time, the opportunity to look into the dynamics of Stromboli's effusive eruptions, flank failure and landslide formation, and their potential hazard.

SO 2 flux is widely monitored on active volcanoes as it gives a window into the hidden, subsurface magma dynamics. We present here a new approach to SO 2 flux monitoring using ultraviolet imaging of the volcanic plume through carefully chosen filters to produce images of SO 2 column amount. The SO 2 camera heralds a breakthrough in both our ability to measure SO 2 flux at unprecedented frequencies (2 Hz) and at unprecedented accuracy, thanks to the application of correlation techniques to determine wind speed directly from the images and the ability to measure the whole profile simultaneously. In this paper we detail the commercially available pieces required to construct the SO 2 camera, introduce a retrieval scheme to determine SO 2 amounts from the images and present results from a field campaign in November 2005 on Sakurajima volcano, Japan.

The persistent explosive activity of Stromboli volcano (Italy) ceased in December 2002 and correlated with the onset of a seven-month-long effusive eruption on the volcano flank from new vents that opened just below the summit craters. We intensively monitored this effusive event, collecting and interpreting, in real time, an extensive multiparametric geophysical data set. The resulting data synergy allowed detailed insights into the conduit dynamics that drove the eruption and the transition back to the typical Strombolian activity. We present a direct link between gas flux, magma volume flux, and seismicity, supporting a gas driven model whereby the balance between gas flux and gas overpressure determines whether the system will support effusive or explosive activity. This insight enabled us to monitor the migration of the magma column up the conduit and to explain the onset of explosive activity.

Volcano deformation may occur under different conditions. To understand how a volcano deforms, as well as relations with magmatic activity, we studied Mt. Etna in detail using interferometric synthetic aperture radar (InSAR) data from 1994 to 2008. From 1994 to 2000, the volcano inflated with a linear behavior. The inflation was accompanied by eastward and westward slip on the eastern and western flanks, respectively. The portions proximal to the summit showed higher inflation rates, whereas the distal portions showed several sectors bounded by faults, in some cases behaving as rigid blocks. From 2000 to 2003, the deformation became nonlinear, especially on the proximal eastern and western flanks, showing marked eastward and westward displacements, respectively. This behavior resulted from the deformation induced by the emplacement of feeder dikes during the 2001 and 2002–2003 eruptions. From 2003 to 2008, the deformation approached linearity again, even though the overall pattern continued to be influenced by the emplacement of the dikes from 2001 to 2002. The eastward velocity on the eastern flank showed a marked asymmetry between the faster sectors to the north and those (largely inactive) to the south. In addition, from 1994 to 2008 part of the volcano base (south, west, and north lower slopes) experienced a consistent trend of uplift on the order of ∼0.5 cm/yr. This study reveals that the flanks of Etna have undergone a complex instability resulting from three main processes. In the long term (10 3 –10 4 years), the load of the volcano is responsible for the development of a peripheral bulge. In the intermediate term (≤10 1 years, observed from 1994 to 2000), inflation due to the accumulation of magma induces a moderate and linear uplift and outward slip of the flanks. In the short term (≤1 year, observed from 2001 to 2002), the emplacement of feeder dikes along the NE and south rifts results in a nonlinear, focused, and asymmetric deformation on the eastern and western flanks. Deformation due to flank instability is widespread at Mt. Etna, regardless of volcanic activity, and remains by far the predominant type of deformation on the volcano.

The 2001 Etna eruption was characterized by a complex temporal evolution with the opening of seven eruptive fissures, each feeding different lava flows. This work describes a method adopted to obtain the three‐dimensional geometry of the whole lava flow field and for the reconstruction, based on topographic data, of the temporal evolution of the largest lava flow emitted from a vent located at 2100 m a.s.l. Preeruption and posteruption Digital Elevation Models (DEM) were extracted from vector contour maps. Comparison of the two DEMs and analysis of posteruption orthophotos allowed us to estimate flow area, thickness, and bulk volume. Additionally, the two‐dimensional temporal evolution of the 2100 flow was precisely reconstructed by means of maps compiled during the eruption. These data, together with estimates of flow thickness, allowed us to evaluate emitted lava volumes and in turn the average volumetric flow rates The analysis performed in this paper provided, a total lava bulk volume of 40.1 × 10 6 m 3 for the whole lava flow field, most of which emitted from the 2100 vent (21.4 × 10 6 m 3 ). The derived effusion rate trend shows an initial period of waxing flow followed by a longer period of waning flow. This is in agreement not only with the few available effusion rate measurements performed during the eruption, but also with the theoretical model of Wadge (1981) for the temporal variation in discharge during the tapping of a pressurized source.

Using thermal infrared images recorded by a permanent thermal camera network maintained on Stromboli volcano (Italy), together with satellite and helicopter‐based thermal image surveys, we have compiled a chronology of the events and processes occurring before and during Stromboli's 2007 effusive eruption. These digital data also allow us to calculate the effusion rates and lava volumes erupted during the effusive episode. At the onset of the 2007 eruption, two parallel eruptive fissures developed within the northeast crater, eventually breaching the NE flank of the summit cone and extending along the eastern margin of the Sciara del Fuoco. These fed a main effusive vent at 400 m above sea level to feed lava flows that extended to the sea. The effusive eruption was punctuated, on 15 March, by a paroxysm with features similar to those of the 5 April paroxysm that occurred during the 2002–2003 effusive eruption. A total of between 3.2 × 10 6 and 11 × 10 6 m 3 of lava was erupted during the 2007 eruption, over 34 days of effusive activity. More than half of this volume was emplaced during the first 5.5 days of the eruption. Although the 2007 effusive eruption had an erupted volume comparable to that of the previous (2002–2003) effusive eruption, it had a shorter duration and thus a mean output rate (=total volume divided by eruption duration) that was 1 order of magnitude higher than that of the 2002–2003 event (∼2.4 versus 0.32 ± 0.28 m 3 s −1 ). In this paper, we discuss similarities and differences between these two effusive events and interpret the processes occurring in 2007 in terms of the recent dynamics witnessed at Stromboli.

Seismic, deformation, and volcanic gas observations offer independent and complementary information on the activity state and dynamics of quiescent and eruptive volcanoes and thus all contribute to volcanic risk assessment. In spite of their wide use, there have been only a few efforts to systematically integrate and compare the results of these different monitoring techniques. Here we combine seismic (volcanic tremor and long‐period seismicity), deformation (GPS), and geochemical (volcanic gas plume CO 2 /SO 2 ratios) measurements in an attempt to interpret trends in the recent (2007–2008) activity of Etna volcano. We show that each eruptive episode occurring at the Southeast Crater (SEC) was preceded by a cyclic phase of increase‐decrease of plume CO 2 /SO 2 ratios and by inflation of the volcano's summit captured by the GPS network. These observations are interpreted as reflecting the persistent supply of CO 2 ‐rich gas bubbles (and eventually more primitive magmas) to a shallow (depth of 1–2.8 km asl) magma storage zone below the volcano's central craters (CCs). Overpressuring of the resident magma stored in the upper CCs' conduit triggers further magma ascent and finally eruption at SEC, a process which we capture as an abrupt increase in tremor amplitude, an upward (>2800 m asl) and eastward migration of the source location of seismic tremor, and a rapid contraction of the volcano's summit. Resumption of volcanic activity at SEC was also systematically anticipated by declining plume CO 2 /SO 2 ratios, consistent with magma degassing being diverted from the central conduit area (toward SEC).

A lava emission started at Mt. Etna, Italy, on 7 September, 2004. Neither earthquake seismicity heralded or accompanied the opening of the fracture field from which the lava poured out, nor volcanic tremor changed in amplitude and frequency content at the onset of the effusive activity. To highlight long‐term changes, we propose a method for the location of the tremor source based on a 3D grid search, using the amplitude decay of the seismic signal, from January to November 2004. We find the centroid of the tremor source within a zone close to and partially overlapped with the summit craters (pre‐effusive phase), which extended up to 2 km south of them (effusive phase). The depths are of between 1698 and 2387 m a.s.l. We hypothesize the lava effusion stemmed from a degassed magma body, although we find evidence of temporary magma overpressure conditions, such as those documented on 25 September.

We present results from a campaign in March 2009 to assess the current state of emissions from Masaya Volcano, Nicaragua. These results constitute one of the most comprehensive inventories to date of emissions from an active volcano and update the exceptional record of emissions from Masaya. Results from open‐path Fourier transform infrared spectroscopy and filter packs demonstrate that, in terms of H 2 O, SO 2 , CO 2 , HCl, and HF (molar H 2 O/SO 2 = 63, CO 2 /SO 2 = 2.7, SO 2 /HCl = 1.7, SO 2 /HF = 8.8), the 2009 gas composition was highly comparable to that from the 1998 to 2000 period, indicating stability of the shallow magma system. This continuity extends to certain aerosol species (molar SO 2 /SO 4 2− = 190, Na + /SO 4 2− = 0.68, K + /SO 4 2− = 0.71, Ca 2+ /SO 4 2− = 1.6 × 10 −2 , Mg 2+ /SO 4 2− = 3.6 × 10 −3 ) and, to a lesser extent, the heavy halogens (i.e., molar HCl/HBr = 2.4 × 10 3 , HCl/HI = 5.0 × 10 4 ). In contrast to an earlier study at Masaya, we did not detect HNO 3 . SO 2 fluxes were low (690 Mg d −1 ), suggesting that Masaya was close to the minimum of its degassing cycle. By combining compositional results with the SO 2 flux, we estimate a total volatile flux of 14,000 Mg d −1 . This rate is consistent with 1−4 wt% volatile loss from a convective magma flux of 17,000–4000 kg s −1 . These results will allow for a better understanding of degassing processes at Masaya and other basaltic volcanoes.

Understanding Etnean flank instability is hampered by uncertainties over its western boundary. Accordingly, we combine soil radon emission, interferometric synthetic aperture radar (InSAR), and electronic distance measurement (EDM) data to study the Ragalna fault system (RFS) on the SW flank of the volcano. Valuable synergy developed between our differing techniques, producing consistent results and serving as a model for other studies of partly obscured active faults. The RFS, limited in its surface expression, is revealed as a complex interlinked structure ∼14 km long that extends from the edifice base toward the area of summit rifting, possibly linking northeastward to the Pernicana fault system (PFS) to define the unstable sector. Short‐term deformation rates on the RFS from InSAR data reach ∼7 mm yr −1 in the satellite line of sight on the upslope segment and ∼5 mm yr −1 on the prominent central segment. Combining this with EDM data confirms the central segment of the RFS as a dextral transtensive structure, with strike‐slip and dip‐slip components of ∼3.4 and ∼3.7 mm yr −1 , respectively. We measured thoron ( 220 Rn, half‐life 56 s) as well as radon, and probably because of its limited diffusion range, this appears to be a more sensitive but previously unexploited isotope for pinpointing active near‐surface faults. Contrasting activity of the PFS and RFS reinforces proposals that the instability they bound is divided into at least three subsectors by intervening faults, while, in section, fault‐associated basal detachments also form a nested pattern. Complex temporal and spatial movement interactions are expected between these structural components of the unstable sector.

Late on the night of 26 October 2002, a dike intrusion started suddenly at Mount Etna, producing intense explosive activity and lava effusion on the southern flank. Five to six hours afterward, a long field of eruptive fractures propagated radially along the northeastern flank of the volcano, producing marked variations at the permanent tilt network. The dike propagation velocity was inferred by the associated seismicity. We modeled the temporal evolution of the continuously recorded tilt data, both during the vertical dike propagation on the high south flank on 26 October and during the radial propagation along the northeast flank, between 27 and 28 October. The reproduction of the recorded tilt signal allowed us to describe the geometry and characteristics of the two dikes in greater detail than the previous static inversion. We deduced that the eruption was characterized by an unusual composite mechanism, clearly showing a transition from a nearly pure opening mode displacement to a mechanism characterized by an equally strong normal dip‐slip component and a smaller left lateral strike‐slip component. In this study we demonstrate the interaction between the final segment of the dike and a preexisting structure that was reactivated in response to the intrusion. We show that tilt and its modeling represent a powerful tool to verify and constrain dike intrusions in detail.

We applied an automatic pattern recognition technique, known as Support Vector Machine (SVM), to classify volcanic tremor data recorded during different states of activity at Etna volcano, Italy. The seismic signal was recorded at a station deployed 6 km southeast of the summit craters from 1 July to 15 August, 2001, a time span encompassing episodes of lava fountains and a 23 day‐long effusive activity. Trained by a supervised learning algorithm, the classifier learned to recognize patterns belonging to four classes, i.e., pre‐eruptive, lava fountains, eruptive, and post‐eruptive. Training and test of the classifier were carried out using 425 spectrogram‐based feature vectors. Following cross‐validation with a random subsampling strategy, SVM correctly classified 94.7 ± 2.4% of the data. The performance was confirmed by a leave‐one‐out strategy, with 401 matches out of 425 patterns. Misclassifications highlighted intrinsic fuzziness of class memberships of the signals, particularly during transitional phases.

Abstract Following the Hunga Tonga eruption (20.6°S, 175.4°W, mid‐January 2022), we present a balloon‐borne characterization of the stratospheric aerosol plume one week after its injection (on 23 and 26 January 2022, La Réunion island at 21.1°S, 55.3°E). Satellite observations show that flight (a) took place during the overpass of a denser plume of sulfate aerosols (SA) compared to a more diluted plume during flight. (b) Observations show that the sampled plumes (at around 22, 25 and 19 km altitude, respectively) consist exclusively of very small particles (with radius <1 µm). Particles with radii between 0.5 and 1.0 µm show optically transparent features pointing to predominant SA. Particles with radii below 0.5 µm are partly absorbing, which could point to small sulfate coated ash particles, a feature not identified with space‐borne observations. This shows that in situ observations are necessary to fully characterize the microphysical properties of the plumes tracked by space‐borne instruments.

On the night of October 26, 2002, intense explosive activity and lava effusion began suddenly on the southern flank of Mt. Etna at an altitude of 2750 m. During the 27 and 28 October, a long field of eruptive fractures propagated radially along the north‐eastern flank of the volcano. Ground deformation changes recorded between 26 and 27 October from GPS and tilt data collected at the permanent geodetic network of Mt. Etna, were modeled to infer the positions and dimensions of the two dikes. The observed deformation pattern was consistent with a response of the edifice to a composite mechanism consisting of a vertical uprising dike in the upper Southern flank and a lateral intrusion propagating along the north‐eastern sector. The first dike, which triggered the eruption, crossed the volcano edifice in a few hours and was located in the same area as the 2001 eruption, while the second lateral dike, which crossed the NE flank, was the primary cause of the recorded deformation pattern.

Abstract Over the last four decades Etna has shown a high output rate through numerous eruptions. The volcano has displayed two eruptive behaviors. The first is characterized by effusive eruptions that efficiently drained the storage system and emitted large volumes of magma; the second behavior is related to lava fountains, erupting small magma batches, which are normally with high frequency and have been considered as precursors of major effusive eruptions. In this paper, we present an updated estimation of emitted volumes from Etna eruptions, which include the 38 lava fountain episodes that occurred from January 2011 to April 2013. These recent explosive episodes have been frequent, discharging significant magma volumes. Observing the steady trend of magma output over time, we present insights on expected erupted volumes. We highlight that the January 2011 to April 2013 lava fountains efficiently drained the intermediate‐shallow storage system and favored a balance between the incoming and outgoing magma.

We investigated the banded tremor activity occurring at Mt. Etna volcano between August–October 2008 during the 2008–2009 eruption. The banded tremor occurred in episodes lasting 25–30 min with intervals in between the episodes of about 25 min. Seismic signal analyses showed that the banded tremor was characterized by spectral contents, wavefields, and source locations that differed from the “ordinary” volcanic tremor. The infrasound recordings exhibited an intermittent infrasonic tremor alternating with the banded tremor episodes. Finally, nonlinear analyses suggested that a banded tremor system can be considered chaotic, implying (1) sensitive dependence on initial conditions, suggesting not only that a banded tremor system requires particular conditions to generate but also that slight variations of these conditions are able to greatly change the features of the banded tremor or even to stop it; and (2) long‐term unpredictability, that is, the impossibility to forecast the long‐term evolution of the banded tremor. On the basis of all these results and analogies with geyser models, we suggest a model of banded tremor that invokes alternating recharge‐discharge phases. Banded tremor is due to “perturbations” in shallow aquifers, such as fluid movement and bubble growth or collapse due to hydrothermal boiling, triggered by the heat and hot fluid transfer from the underlying magma bodies. This heat‐fluid transfer also causes an increasing pressure in the aquifer, leading to fluid discharge. During this process, the seismic radiation decreases, and, if the fluid discharge is well coupled with the atmosphere, acoustic signals are generated.

Three eruptive episodes during the 2006 summit eruptions of Mount Etna were exceptionally well documented by visual, seismic, and thermal monitoring. The first (16 November) was strongly explosive, with vigorous Strombolian activity and ash emission from multiple vents, lava emission, and phreatomagmatic explosions generating pyroclastic density currents (PDCs). The second episode (19 November) had a rather weakly explosive component, with mild Strombolian activity but more voluminous lava emission. The third (24 November) was a moderately explosive paroxysm, with intermittent lava fountaining and generation of a tephra column as well as lava emission and PDCs. Data recorded by a thermal monitoring camera clearly document the different phases of each paroxysm, weather clouds occasionally hampering thermal monitoring. The images show a rapid onset of the volcanic activity, which during each of the paroxysms reached a peak in eruptive and thermal intensity and then decreased gradually. The stronger phreatomagmatic explosions and PDCs on 16 and 24 November did not yield any seismic signature linked to the opening of new vents nor were they associated with peculiar characteristics of the seismic signal. Nevertheless, eruptive styles (Strombolian activity, lava emission) and different levels in the intensity of explosive activity were generally well reflected in the amplitude and frequency content of the seismic signal and in the source location of the volcanic tremor centroid throughout the three eruptive episodes. This multidisciplinary study, therefore, not only provides a key to distinguish between endogenous and exogenous origins of the phenomena observed but also documents the complex magma dynamics within the volcano.

Soil radon emissions have been proved as a useful tool for predicting earthquakes and volcanic eruptions and furthermore aided in determining the location of active faults. Continuous radon monitoring was carried out near Southeast Crater of Mt. Etna in September–November 1998, during a period of frequent eruptive episodes at that crater. Radon anomalies were detected when eruptive episodes and the accompanying volcanic tremor became increasingly intense: no anomalies in radon activity were observed during the first five, and weaker, eruptive episodes, whereas significant spikes in radon activity preceded the latter five episodes by ≥46 hours. This probably reflects increased gas leakage through fractures intersecting the shallow plumbing system, as gas pressure in the Southeast Crater conduit became higher with time. Radon monitoring thus might serve to better understand eruptive mechanisms and possible precursors, making further studies in this field a promising perspective.

Structural observations carried out on the volcanic Island of Pantelleria show that the tectonic setting is dominated by NNE trending normal faults and by NW-striking right-lateral strike-slip faults with normal component of motion controlled by a ≈N 100°E oriented extension. This mode of deformation also controls the development of the eruptive fissures, dykes and eruptive centres along NNE–SSW belts that may thus represent the surface response to crustal cracking with associated magma intrusions. Magmatic intrusions are also responsible for the impressive vertical deformations that affect during the Late Quaternary the south-eastern segment of the island and producing a large dome within the Pantelleria caldera complex. The results of the structural analysis carried out on the Island of Pantelleria also improves the general knowledge on the Late Quaternary tectonics of the entire Sicily Channel. ESE–WNW directed extension, responsible for both the tectonic and volcano-tectonic features of the Pantelleria Island, also characterizes, at a greater scale, the entire channel as shown by available geodetic and seismological data. This mode of extension reactivates the older NW–SE trending fault segments bounding the tectonic troughs of the Channel as right-lateral strike-slip faults and produces new NNE trending pure extensional features (normal faulting and cracking) that preferentially develop at the tip of the major strike-slip fault zones. We thus relate the Late Quaternary volcanism of the Pelagian Block magmatism to dilatational strain on the NNE-striking extensional features that develop on the pre-existing stretched area and propagate throughout the entire continental crust linking the already up-welled mantle with the surface.

Abstract Magmatic intrusions, eruptions and flank collapses are frequent processes of volcano dynamics, inter-connected at different space and time scales. The December 2018 recrudescent episode at Mt. Etna is an exemplary case where a sudden intrusive event culminated with a short eruption, intense seismicity and a shallow large strike-slip earthquake at the edge of the eastern sliding flank. Here, we show that high resolution velocity models and transient changes of V P and V P /V S resolve the magma intrusion through a dyke and local stress increase at the base of the unstable flank, inducing the collapse. Episodic brittle faulting occurs at the edge of the sliding sector, locally contributed by high fluid pressure. The feedback between magma ascent, stress changes and flank collapse is driving the volcano dynamics, with processes ranging from long term to transient episodes.