Geophysical investigations of the plumbing system of Stromboli volcano (Aeolian Islands,Italy)

In this work, we report the results of an integrated approach using both seismological and geodetic data provided by the INGV-CT (Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania) Stromboli volcano monitoring systems, in order to improve the knowledge of its plumbing system. In particular, we investigated the relationships between the June 1999 seismic swarm, occurring in the area of Stromboli, and the possible activation of the NE–SW oriented volcano-tectonic structure. We analyzed this seismic swarm proposing new locations and a morphological analysis of the waveforms. This approach allowed us to demonstrate that there are relationships between the tectonic activity near Stromboli and the rising of magma. This evidence supports the hypothesis that during the 1999 swarm an intrusive process started from a crustal level where earthquakes were located (about 10–15 km b.s.l.).     

Coeval strombolian and vulcanian-type explosive eruptions at Panarea (Aeolian Islands,Southern Italy)

In this paper, we document the evolution of the emergent Panarea dome in the Aeolian islands (Southern Italy), placing particular emphasis on the reconstruction of the explosive events that occurred during the final stage of its evolution. Two main pyroclastic successions exposing fall deposits with different compositions have been studied into detail: the andesitic Palisi succession and the basaltic Punta Falcone succession. The close-in-time deposition of the two successions, the dispersal area and grain-size distribution of the deposits account for their attribution to vents located in the western sector of the present island and erupting almost contemporaneously. Vents could have been aligned along NNE-trending regional fracture systems controlling the western flank of the dome and possibly its collapse. Laboratory analyses have been devoted to the characterization of the products of the two successions that have been ascribed to vulcanian- and to strombolian-type eruptions respectively. The vulcanian eruption started with a vent-clearing phase that occurred by sudden decompression of a pressurized magma producing ballistic bombs and a surge blast and the development of a vulcanian plume. Vulcanian activity was almost contemporaneous to strombolian-type fall-out eruptions. The coeval occurrence of basaltic and andesitic eruptions from close vents and the presence of magmatic basaltic enclaves in the final dacitic lava lobe of the dome allow us to speculate that the intrusion of a basaltic dyke played a major role in triggering explosive eruptions. The final explosive episodes may have been caused by extensional tectonics fracturing the roof of a zoned shallow magma chamber or by the intrusion of a new basaltic magma into a more acidic and shallow reservoir. Intrusion most likely occurred through the injection of dykes along the western cliff of the present Panarea Island inducing the collapse of the western sector of the dome.     

Fluid circulation at Stromboli volcano (Aeolian Islands, Italy) from self-potential and CO2 surveys

This work addresses the study of fluid circulation of the Stromboli island using a dense coverage of self-potential (SP) and soil CO₂ data. A marked difference exists between the northern flank and the other flanks of the island. The northern flank exhibits (1) a typical negative SP/altitude gradient not observed on the other flanks, and (2) higher levels of CO₂. The general SP pattern suggests that the northern flank is composed of porous layers through which vadose water flows down to a basal water table, in contrast to the other flanks where impermeable layers impede the vertical flow of vadose water. In the Sciara del Fuoco and Rina Grande–Le Schicciole landslide complexes, breccias of shallow gliding planes may constitute such impermeable layers whereas elsewhere, poorly permeable, fine-grained pyroclastites or altered lava flows may be present. This general model of the flanks also explains the main CO₂ patterns: concentration of CO₂ at the surface is high on the porous north flank and lower on the other flanks where impermeable layers can block the upward CO₂ flux. The active upper part of the island is underlain by a well-defined hydrothermal system bounded by short-wavelength negative SP anomalies and high peaks of CO₂. These boundaries coincide with faults limiting ancient collapses of calderas, craters and flank landslides. The hydrothermal system is not homogeneous but composed of three main subsystems and of a fourth minor one and is not centered on the active craters. The latter are located near its border. This divergence between the location of the active craters and the extent of the hydrothermal system suggests that the internal heat sources may not be limited to sources below the active craters. If the heat source strictly corresponds to intrusions at depth around the active conduits, the geometry of the hydrothermal subsystems must be strongly controlled by heterogeneities within the edifice such as craters, caldera walls or gliding planes of flank collapse, as suggested by the correspondence between SP–CO₂ anomalies and structural limits. The inner zone of the hydrothermal subsystems is characterized by positive SP anomalies, indicating upward movements of fluids, and by very low values of CO₂ emanation. This pattern suggests that the hydrothermal zone becomes self-sealed at depth, thus creating a barrier to the CO₂ flux. In this hypothesis, the observed hydrothermal system is a shallow one and it involves mostly convection of infiltrated meteoric water above the sealed zone. Finally, on the base of CO₂ degassing measurements, we present evidence for the presence of two regional faults, oriented N41° and N64°, and decoupled from the volcanic structures.     

Geochemical investigations of submarine volcanic exhalations to the east of Panarea, Aeolian Islands, Italy

Results are presented on scubadiving investigations carried out on thermal manifestations in the area of Panarea (Aeolian Islands). The area investigated falls inside a caldera which extends from the main island to the group of islets located to the northeast. The distribution of the gaseous manifestations is regulated by the NE-SW, NW-SE and N-S regional tectonic directrices, through which the more recent basic magma intruded, giving rise to dikes and pillow lavas. f_O2-temperature relation of the gases sampled in the investigated area was calculated to be: logf_O2 = 11−24,593/T which indicates that a buffering mechanism acted on the gases as they cooled down during their ascent. The high ³He/⁴He ratio (6 × 10⁻⁶) and the δ¹³C = −3.2%. (PDB), suggest the presence of a magmatic component in the gas feeding the investigated manifestations. The above relations and the almost constant high He/N₂ ratio suggest that all the fumaroles are fed by the same deep hot fluids. On the basis of both the chemical characters of the fluids and the geothermo-barometric data, a deep geothermal body, having a temperature of about 240°C, is recognized. Two other shallower thermal aquifers, with a temperature of 170–210°C, are identified. A circulation pattern of the geothermal fluids is also proposed. On the basis of calculations regarding the convective energy released by the geothermal system of Panarea, and the magmatic mass responsible for the positive gravimetric anomaly of the area, it was estimated that the last volcanic activity took place less then 10,000 years ago.     

Evolution of Br/Cl ratios in fumarolic salammoniac from Vulcano (Aeolian Islands,Italy)

 Bromine/chlorine ratios in salammoniac samples, collected from 1983 to 1994 at the Fossa crater fumaroles of Vulcano (Aeolian Islands), were determined. The data obtained in this work have been compared to those obtained by Coradossi et al. (1985) in order to carry out a systematic study of the Br/Cl ratio variations since 1977. Br/Cl ratios range from 0.04 to 0.29. The Br/Cl ratio variations observed have been interpreted as the result of different contributions among deep and shallow components feeding the fumarolic fluids of Vulcano. The Br/Cl increases, which occurred from 1977 to 1979, in 1983–1984 and in 1992–1993, have been connected to an increased input of magmatic gases. Received: 10 November 1995 / Accepted: 12 July 1996     

Pyroclastic density currents at Stromboli volcano (Aeolian Islands,Italy): a case study of the 1930 eruption

Pyroclastic density currents (PDC) related to paroxysmal eruptions have caused a large number of casualties in the recent history of Stromboli. We combine here a critical review of historical chronicles with detailed stratigraphic, textural, and petrographic analyses of PDC deposits emplaced at Stromboli over the last century to unravel the origin of currents, their flow mechanism and the depositional dynamics. We focus on the 1930 PDC as they are well described in historical accounts and because the 1930 eruption stands as the most voluminous and destructive paroxysm of the last 13 centuries. Stromboli PDC deposits are recognizable from their architecture and the great abundance of fresh, well-preserved juvenile material. General deposit features indicate that Stromboli PDC formed due to the syn-eruptive gravitational collapse of hot pyroclasts rapidly accumulated over steep slopes. Flow channelization within the several small valleys cut on the flanks of the volcano can enhance the mobility of PDC, as well as the production of fine particles by abrasion and comminution of hot juvenile fragments, thereby increasing the degree of fluidization. Textural analyses and historical accounts also indicate that PDC can be fast (15–20 m/s) and relatively hot (360–700 °C). PDC can thus flow right down the slopes of the volcano, representing a major hazard. For this reason, they must be adequately taken into account when compiling risk maps and evaluating volcanic hazard on the Island of Stromboli.     

Geochemical surveillance of active volcanoes: data on the fumaroles of Vulcano (Aeolian Islands,Italy)

Temperature and chemical composition of condensates of higher temperature fumaroles, located on the rim of the crater of Vulcano, were studied over a period of one year. Maximum temperature changed from 216°C (June 1977) to 291°C (May 1978). HCl is the main constituent of condensates which, in comparison with data from fumaroles of other volcanoes, contain also noteworthy quantities of boron and bromine. Since these chemical characteristics suggested the possible inflow of water of marine origin into the volcanic conduit, experimental data on seawater-rock reactions at high temperatures and pressures were taken into account. A model is drafted for the volcanic system, in which the occurrence of an aquifer interposed between the magma chamber and the surface is considered. The vaporization of this aquifer would feed the fumaroles giving rise, through different mixing processes with surface waters, to the observed differences in temperature and chemical composition. However, data available at present are not sufficient to support the proposed model, which must be mainly considered as a working hypothesis.     

Geochemistry of the Submarine Gaseous Emissions of Panarea (Aeolian Islands, Southern Italy): Magmatic vs. Hydrothermal Origin and Implications for Volcanic Surveillance

The marine sector surrounding Panarea Island (Aeolian Islands, South Italy) is affected by widespread submarine emissions of CO₂ -rich gases and thermal water discharges which have been known since the Roman Age. On November 3^rd, 2002 an anomalous degassing event affected the area, probably in response to a submarine explosion. The concentrations of minor reactive gases (CO, CH₄ and H₂) of samples collected in November and December, 2002 show drastic compositional changes when compared to previous samples collected from the same area in the 1980s. In particular the samples collected after the November 3^rd phenomenon display relative increases in H₂ and CO and a strong decrease in the CH₄ contents, while other gas species show no significant change. The interaction of the original gas with seawater explains the variable contents of CO₂, H₂S, N₂, Ar and He which characterize the different samples, but cannot explain the large variations of CO, CH₄ and H₂ which are instead compatible with changes in the redox, temperature and pressure conditions of the system. Two models, both implying an increasing input of magmatic fluids are compatible with the observed variations of minor reactive species. In the first one, the input of magmatic fluids drives the hydrothermal system towards atypical (more oxidizing) redox conditions, slowly pressurizing the system up to a critical state. In the second one, the hydrothermal system is flashed by the rising high-T volcanic fluid, suddenly released by a magmatic body at depth. The two models have different implications for volcanic surveillance and risk assessment: In the first case, the November 3^rd event may represent both the culmination of a relatively slow process which caused the overpressurization of the hydrothermal system and the beginning of a new phase of quiescence. The possible evolution of the second model is unforeseeable because it is mainly related to the thermal, baric and compositional state of the deep magmatic system that is poorly known.     

Occurrence of Somma-Vesuvio fine ashes in the tephrostratigraphic record of Panarea,Aeolian Islands

Ash-rich tephra layers interbedded in the pyroclastic successions of Panarea island (Aeolian archipelago, Southern Italy) have been analyzed and related to their original volcanic sources. One of these tephra layers is particularly important as it can be correlated by its chemical and morphoscopic characteristics to the explosive activity of Somma-Vesuvio. Correlation with the Pomici di Base eruption, that is considered one of the largest explosive events causing the demolition of the Somma stratovolcano, seems the most probable. The occurrence on Panarea island of fine ashes related to this eruption is of great importance for several reasons: 1) it allows to better constrain the time stratigraphy of the Panarea volcano; 2) it provides a useful tool for tephrochronological studies in southern Italy and finally 3) it allows to improve our knowledge on the distribution of the products of the Pomici di Base eruption giving new insights on the dispersion trajectories of fine ashes from plinian plumes. Other exotic tephra layers interbedded in the Panarea pyroclastic successions have also been found. Chemical and sedimentological characteristics of these layers allow their correlation with local vents from the Aeolian Islands thus constraining the late explosive activity of Panarea dome.     

Structural features of Panarea volcano in the frame of the Aeolian Arc (Italy): Implications for the 2002–2003 unrest

Panarea, characterized by gas unrest in 2002–2003, is the volcanic island with the least constrained structure in the eastern-central Aeolian Arc (Italy). Based on structural measurements, we define here its deformation pattern relative to the Arc. The main deformations are subvertical extension fractures (63% of data), normal faults (25%) and dikes (12%). The mean orientation of the extension fractures and faults is N38°E, with a mean opening direction of N135° ± 8°, implying extension with a moderate component of dextral shear. These data, matched with those available for Stromboli volcano (pure opening) and Vulcano, Lipari and Salina volcanoes (predominant dextral motions) along the eastern-central Arc, suggest a progressive westward rotation of the extension direction and an increase in the dextral shear. The dextral shear turns into compression in the western arc. The recent unrest at Panarea, coeval to that of nearby Stromboli, may also be explained by the structural context, as both volcanoes lie along the portion of the Arc subject to extension.     

Time-space variation of volcano-seismic events at La Fossa (Vulcano, Aeolian Islands, Italy): new insights into seismic sources in a hydrothermal system

We investigated the relationship between volcano-seismic events, recorded at La Fossa crater of Vulcano (Aeolian Islands, Italy) during 2004-2006, and the dynamics of the hydrothermal system. During the period of study, three episodes of increasing numbers of volcano-seismic events took place at the same time as geothermal and geochemical anomalies were observed. These geothermal and geochemical anomalies have been interpreted as resulting from an increasing deep magmatic component of the hydrothermal fluids. Three classes of seismic events (long period, high frequency and monochromatic events), characterised by different spectral content and various similarity of the waveforms, have been recognised. These events, clustered mainly below La Fossa crater area at depths of 0.5–1.1 km b.s.l., were space-distributed according to the classes. Based on their features, we can infer that such events at Vulcano are related to two different source mechanisms: (1) fracturing processes of rocks and (2) resonance of cracks (or conduits) filled with hydrothermal fluid. In the light of these source mechanisms, the increase in the number of events, at the same time as geochemical and geothermal anomalies were observed, was interpreted as the result of an increasing magmatic component of the hydrothermal fluids, implying an increase of their flux. Indeed, such variation caused an increase of both the pore pressure within the rocks of the volcanic system and the amount of ascending fluids. Increased pore pressures gave rise to fracturing processes, while the increased fluid flux favoured resonance and vibration processes in cracks and conduits. Finally, a gradual temporal variation of the waveform of the hybrid events (one of the subclasses of long period events) was observed, likely caused by heating and drying of the hydrothermal system.     

Geochemical survey on the phreatic waters of Vulcano (Aeolian Islands,Italy)

In the frame of a geochemical surveillance survey of Vulcano, the phreatic waters, mainly from wells located at the Northern basis of the active volcanic centre, were studied over a time span of sixteen months. On the basis of fundamental chemical composition, contamination by a shallow aquifer of brackish water and hydrothermal alteration of rocks seem the main processes to which the observed chemical picture can be attributed. An R-mode factor analysis procedure allowed to distinguish a principal factor associated to sodium, magnesium, chloride, possibly representing the contribution of the brackish aquifer, and three minor but distinct factors. These are respectively associated to calcium and sulfate, hydrogencarbonate, boric acid, and are considered as reflecting the influence of gaseous compounds from volcanic emanations. The variation in time of this influence appears in correlation with the variation of the observed temperature at the hottest fumaroies of the crater.     

Late Quaternary deformation history of the volcanic edifice of Panarea,Aeolian Arc,Italy

A series of raised palaeoshorelines is documented along the emergent coastal slopes of Panarea and surrounding islets at elevations of 115 (palaeoshoreline Ia) and 100 m a.s.l. (Ib), 62.5 m (II), 35 m (III), 12 m (IV), 10–12 (Va) and 5 m (Vb). According to stratigraphic constraints and cross-cutting relationships, these palaeoshorelines are correlated with discrete high sea-level stillstands during marine oxygen-isotope stages (MIS) 5e, 5c, 5a and 3. Coastal elevation changes suggest the occurrence of a long-term, sustained uplift trend of the volcanic edifice since the last interglacial (last 124 ka). The uplift rates are not constant but display a progressive deceleration from maximum values of 1.5–1.58 m/ka, in the period between 124 and 100 ka, down to the lowest values of 0.66–0.69 m/ka, which tend to be constant starting from 81 ka BP. The long-term deformation pattern of Panarea suggests that a transitory, volcano-related component of uplift interplayed with the regional tectonic component affecting the sub-volcanic basement, which has undergone a persistent and widespread uplift since the mid-Pleistocene. The volcano-related component of uplift, prevailing between 124 and 100–81 ka, is interpreted as the result of visco-elastic deformation mechanisms which characterize the progressive re-equilibration of the shallow magmatic system following the incoming quiescence of the volcanic edifice. The long-term uplift values at Panarea are higher than in the main portion of the western-central Aeolian Arc, where a mean uplift rate of 0.34 m/ka was estimated since the last interglacial (last 124 ka). Such a pattern of deformation on a regional scale may be a response to active deformation processes connected with the southeastward rollback of the subducting Ionian slab which is still active only in correspondence with the eastern sector of the Aeolian Arc (including Panarea). In the short-term, a localized submergence trend has been documented at the nearby islet of Basiluzzo for the last 2,000 years, likely connected to neo-tectonic movements along main NE–SW trending faults.     

Fluids in early stage hydrothermal alteration of high-sulfidation epithermal systems: A view from the Vulcano active hydrothermal system (Aeolian Island,Italy)

High-sulfidation (HS) epithermal systems have elements in common with passively degassing volcanoes associated with high T, acid fumarole fields or acid crater lakes. They are considered to form in two stages, the first of which involves advanced argillic alteration resulting from intense, strongly acidic fluid–rock interaction. The La Fossa hydrothermal system (Vulcano Island) represents a classic example of such an active HS system and can be considered as a modern analogue of this early stage of alteration, resulting in a core of intense silicic (90–95% pure SiO₂) alteration surrounded by alunitic alteration zones.     

Imaging and modelling the subsurface structure of volcanic calderas with high-resolution aeromagnetic data at Vulcano (Aeolian Islands,Italy)

In this paper, we present a magnetic model of the subsurface structure of Vulcano island based on high-resolution aeromagnetic data. Three profiles across the most intense magnetic anomalies over the Piano and Fossa calderas were selected for the magnetic modelling, which was constrained by structural and volcanological data, previous geophysical models, paleomagnetic data, and borehole stratigraphy obtained from two deep wells. The interpretation of the magnetic sources represents a significant contribution to the understanding of the Piano and Fossa calderas’ underlying structure, providing us with evidence of the lateral discontinuity between them at depth. We propose that the positive magnetic anomalies in the Piano caldera area are caused by: (a) the remnants of an early submarine volcano; (b) an outcropping dyke swarm related to the feeding system of the Primordial Vulcano phase (beneath Mt. Saraceno); and (c) the presence of a non-outcropping dyke system intruded along a NE–SW-oriented intra-caldera fault (beneath the eastern part of the Piano caldera). Offshore, to the west, the magnetic anomaly map suggests the presence of a submarine volcanic structure, not revealed by bathymetric data, which could represent the eruptive centre, the presence of which has been indirectly deduced from the outcrop of eastern-dipping lavas on the western seashore. Magnetic modelling of the Fossa caldera points to the presence of a highly magnetized cone-like body inside the Fossa cone, centred beneath the oldest crater rims. We interpret this body as a pile of tephritic lavas emplaced in an early phase of activity of the Fossa cone, suggesting that the volume of mafic lavas that erupted at the beginning of the construction of the Fossa edifice was more significant than has previously been deduced. Furthermore, the presence of a magnetized body inside the Fossa cone implies that high temperatures are contained in very limited spaces, do not affect its bulk inner structure, and are restricted to fumarolic conduits and vents. In addition, structures beneath the western and northern part of the Fossa caldera are revealed to have null or low magnetization, which can be ascribed to the presence of pyroclasts and hyaloclastites in this area as well as to a large volume of hydrothermally altered materials. This suggests that the hydrothermal system, with a very limited extension at present, affected a larger area in the past, especially beneath the western part of the caldera.     

Stratigraphy and significance of Brown Tuffs on the Aeolian Islands (southern Italy)

Brown Tuffs (BT) are volcaniclastic ash deposits prominently represented in the stratigraphic profiles of all the Aeolian Islands (and Capo Milazzo on the northern coast of Sicily). Detailed stratigraphy and tephrochronology together with available radiometric ages suggest that they were emplaced over a long time interval spanning from the end of the last interglacial period (ca. 80 ka BP) up to 4–5 ka BP (age of the overlying Punte Nere pyroclastic products on Vulcano). The most complete BT succession is documented on Lipari where 14 distinct and successive units are subdivided by the interbedding of widespread tephra layers, local volcanic products, paleosols and epiclastic deposits and the occurrence of local erosive surfaces. Inter-island occurrence of Ischia-Tephra (a widely known tephra layer in the Aeolian archipelago dated at 56 ka BP) and Monte Guardia pyroclastics from Lipari (dated at 22–20 ka BP) subdivides the BT succession in Upper (UBT), Intermediate (IBT) and Lower BT units (LBT), which can be correlated at regional level: the LBT was emplaced between 80 and 56 ka BP, the IBT between 56 and 22 ka BP and the UBT between 20 and 4–5 ka BP. On the basis of stratigraphy, similarity in lithology and textural features, morphology of glass fragments, composition and consistency of thickness and grain-size variations, UBT units correlate with Piano Grotte dei Rossi tuffs on Vulcano island. They were generated by pulsating hydromagmatic explosive activity giving rise to pyroclastic density currents spreading laterally from a source located inside the La Fossa caldera on Vulcano island. Composition is in agreement with this hypothesis since UBT compositional features match those of Vulcano magmas erupted in that period. The effect of co-ignimbrite ash clouds (or associated fallout processes from sustained eruptive columns) is seen to explain the presence of UBT in areas further away from the suggested source (e.g. Salina and Lipari islands and Capo Milazzo). The origin of UBT exposed on Panarea island is still a matter of debate, due to contrasting compositional data. Due to large uniformity of lithological, textural and componentry characters with respect to the UBT, the lower portions of the BT succession (LBT-IBT) are considered to be the result of recurrent, large scale hydromagmatic eruptions of similar type. Moreover, for the IBT units, the correlation with Monte Molineddo 3 pyroclastics of Vulcano island (on the basis of lithological, compositional and stratigraphic matching) again suggests source(s) related to the Vulcano plumbing system and located within the La Fossa Caldera.     

Varicolored and vesiculated tuffs from La Fossa volcano,Vulcano Island (Aeolian Archipelago,Italy): evidence of syndepositional alteration processes

Chemical and mineralogical data for samples collected from a surge sequence from La Fossa cone (Vulcano Island, Italy) show a wide variety of alteration states between adjoining beds, the macroscopic features of which are expressed by various degrees of reddening. The effects of the alteration processes on pyroclastic rocks are as follows: hydration and oxidation of each component of the pyroclastic rocks to varying degrees; formation of authigenic smectite; precipitation of a large variety of soluble salts; and corrosion on the surface of glass fragments (pitting). Dry surge beds, emplaced from a two-phase, dry steam + solid, suspension do not show significant alteration. By contrast, wet surge deposits, suggesting an emplacement from free water-bearing turbulent flows, show an increasing degree of alteration, passing from grey to red coloured beds. The strict relationship between the present alteration state and the depositional unit rules out any post-depositional processes. The occurrence of alteration in wet surge beds and the lack of alteration in dry beds shows that the main controlling agent was water condensed from the eruptive cloud and suggests a syn-depositional character to the alteration itself. These observed differences can be ascribed to the different chemical reactivities of the water, probably related to the amounts of acidic species carried by the eruptive cloud and/or by the efficiency of their capture during the condensation of the water vapour.     

Ash erupted during normal activity at Stromboli (Aeolian Islands,Italy) raises questions on how the feeding system works

Ash fallout collected during 4 days of sampling at Stromboli confirms that a crystal-rich (HP) degassed magma erupts during the Strombolian explosions that are characteristic of the normal activity of this volcano. We identified 3 different types of juvenile ash fragments (fluidal, spongy and dense), which formed through different mechanisms of fragmentation of the low-viscosity, physically heterogeneous (in terms of the size and spatial distribution of bubbles) shoshonitic magma. A small amount (less than 3 vol%) of volatile-rich magma with low porphyricity (LP), erupted as highly vesicular ash fragments, has been collected, together with the HP magma, during normal strombolian explosions. Laboratory experiments and the morphological, textural and compositional investigations of ash fragments reveal that the LP ash is fresh and not recycled from the last paroxysm (15 March 2007). We suggest that small droplets of LP magma are dragged to the surface by the time-variable but persistent supply of deep derived CO₂-rich gas bubbles. This coupled ascent of bubbles and LP melts is transient and does not perturb the dynamics of the HP magma within the shallow reservoir. This finding provides a new perspective on how the Stromboli volcano works and has important implications for monitoring strategies.