Deformation at Stromboli volcano (Italy) revealed by rock mechanics and structural geology

We approach the reconstruction of the recent structural evolution of Stromboli volcano (Italy) and the analysis of the interplay between tectonics, gravity and volcanic deformation. By tying together structural, lithostratigraphic and rock mechanics data, we establish that since 100 ka BP, the edifice has faulted and jointed mainly along NE-striking planes. Faults mostly dip to the NW with normal displacement. Taking also into account the presence of a NW-trending regional least principal stress and of tectonic earthquake hypocenters inside the cone, we suggest that this fracturing can be related to the transmission of tectonic forces from the basement to the cone. Dyking concentrated along a main NE-trending weakness zone (NEZ) across the volcano summit, resembling a volcanic rift, whose geometry is governed by the tectonic field. In the past 13 ka, Stromboli experienced a reorganisation of the strain field, which was linked with the development of four sector collapses affecting the NW flank, alternating with growth phases. The tectonic strain field interplayed with dyking and fracturing related to unbuttressing along the collapse shoulders. We propose that tectonics control the geometry of dykes inside the cone and that these, in turn, contribute to destabilise the cone flanks.     

Hydrogeochemistry of Roccamonfina volcano (Southern Italy)

This is the first hydro-geochemical investigation carried out on the Roccamonfina Volcanic Complex groundwaters. The chemistry of Roccamonfina waters is defined by water–rock and water–rock–gas interactions. In fact, interactions between rocks of the first eruptive high-K formations and circulating groundwaters are recognized by high K concentrations. On the other hand, inverse concentration of calcium versus alkali metals is related to two different rock interactions occurring in different areas of the volcano: (a) within the caldera where groundwaters flow within latite and pyroclastic formations releasing calcium, and (b) similarly at the base of the volcano where groundwaters flowing from surrounding carbonates got strongly enriched in Ca. These geochemical processes are also associated with K (SE of caldera) and Mg/Ca (in sites located at the NE base of the volcano) decrease. Completely different dynamics occurs at Riardo groundwaters (SE). Here waters are the result of a mix between the Roccamonfina deep aquifer and the carbonate aquifer of the Riardo plain. Rich-CO₂ emissions make these waters strongly mineralized. Minor elements show a similar geochemical behavior of major ions and are crucial defining interactions processes. The evolution of Roccamonfina groundwaters is also evident along the simultaneous enrichment of Ba, Sr, and Ca. Ba increase is the result of deep local carbonate alteration enhanced by CO₂ emissions and, the lower Sr/Ca ratio, from 10 to 2 (ppb/ppm), is also due to the same process. In the light of our results the Roccamonfina aquifer can be schematically divided into two main reservoirs: (a) a superficial aquifer which basically follows the volcanic structure morphology and tectonics and (b) a deeper reservoir, originating within the oldest Roccamonfina volcano ultra potassic lavas and then flowing into the carbonate aquifers of the neighboring plain. Eventually, the chemistry of the Roccamonfina aquifer does not show any specific and visible pollution, contrary to what happens in the volcano surrounding plains. In fact, only 14% of the samples we collected (206) show a NO₃ content >30 mg/l. These sites are all located at the base of the volcano, near the plain.     

Numerical model of the Stromboli volcano (Italy) including the effect of magma pressure in the dyke system

Summary  The Stromboli island, in the Aeolian archipelago (Italy), is one of the most active volcanoes in Europe. In the last 13,000 years, its growth has been complicated by four sector collapses affecting the NW flank, the latest of which resulting in the formation of Sciara del Fuoco (SdF) horseshoe-shaped depression. Slope instability phenomena are represented not only by giant deep-seated gravitational slope deformations, but also by more frequent large landslides, such as occurred in December 2002–January 2003, and shallow landslides, involving loose or weakly cemented deposits, that constitute a natural hazard and affect residential and tourists safety. It is noteworthy that in volcanic environment the instability factors are manifold and much more complex than in other non-volcanic contexts. This paper deals with the Stromboli NW flank instability, and focuses on the effects of magma pressure in the feeding system. Two main objectives have been pursued: (1) to test a methodological approach, in order to evaluate a complex instability process; (2) to contribute to the understanding of volcano deformation and collapse mechanisms and associated hazard. A numerical model was developed by the Finite Difference Method and the FLAC 4.0 code, considering a cross-section of the entire volcano, orthogonal to the SdF and including both subaerial and submerged slopes. The stability of the volcano was analysed under gravity alone, and by introducing the magma pressure effect, both related to magmastatic and overpressure components. The results indicate that gravity alone is not sufficient to affect the stability of the volcano slopes, nor is the magmastatic pressure component. If an excess magma pressure component is introduced, instability is produced in accordance with field evidences and recent slope dynamics. Correspondence: Tiziana Apuani, Dipartimento di Scienze della Terra “A. Desio”, via Mangiagalli 34, 20133 Milano, Italy     

Subaqueous density flow processes and deposits of an island volcano landslide (Stromboli Island, Italy)

Stromboli is a 3000 m high island volcano, rising to 900 m above sea-level. It is the most active volcano of the Aeolian Archipelago in the Tyrrhenian Sea (Italy). Major, large volume (1 km³) sector collapses, four occurring in the last 13 kyr, have played an important role in shaping the north-western flank (Sciara del Fuoco) of the volcano, potentially generating a high-risk tsunami hazard for the Aeolian Islands and the Italian coast. However, smaller volume, partial collapses of the Sciara del Fuoco have been shown to be more frequent tsunami-generating events. One such event occurred on 30 December 2002, when a partial collapse of the north-western flank of the island took place. The resulting landslide generated 10 m high tsunami waves that impacted the island. Multibeam bathymetry, side-scan sonar imaging and visual observations reveal that the landslide deposited 25 to 30 × 10⁶ m³ of sediment on the submerged slope offshore from the Sciara del Fuoco. Two contiguous main deposit facies are recognized: (i) a chaotic, coarse-grained (metre-sized to centimetre-sized clasts) deposit; and (ii) a sand deposit containing a lower, cross-bedded sand layer and an upper structureless pebbly sand bed capped by sea floor ripple bedforms. The sand facies develops adjacent to and partially overlying the coarse deposits. Characteristics of the deposits suggest that they were derived from cohesionless, sandy matrix density flows. Flow rheology and dynamics led to the segregation of the density flow into sand-rich and clast-rich regions. A range of density flow transitions, both in space and in time, caused principally by particle concentration and grain-size partitioning within cohesionless parent flows was identified in the deposits of this relatively small-scale submarine landslide event.     

Application of large-scale ring shear tests to the analysis of tsunamigenic landslides at the Stromboli volcano, Italy

The island of Stromboli (Southern Italy) is a 4,000-m-high volcanic edifice about 900 m above sea level. Most of the NW flank is formed by a wide scar (Sciara del Fuoco) filled by irregular alternations of volcaniclastic layers and thin lava flows. Between 29 and 30 December 2002, a submarine and a subaerial landslide involved the northernmost part of the Sciara del Fuoco slope and caused two tsunami waves with a maximum run-up of 10 m. Mechanisms of the rapid submarine landslide and the preceding deformation of the subaerial and submarine slope were investigated using large-scale ring shear tests on the saturated and dry volcaniclastic material. The shear behaviour of the material under different drainage conditions was analysed during tests conducted at DPRI, Kyoto University. Pore pressure generation, mobilised shear strength and grain crushing, within a range of displacements encompassing the different stages of evolution of the slope, were considered. Experimental results suggest that even at larger displacements, shear strength of the dry material explains the virtual stability of the slope. Conversely, full or partial liquefaction can be invoked to explain the submarine failure and the subsequent long runout (more than 1,000 m) of the failed materials.     

Evidence of a partial melt zone beneath Stromboli volcano (Italy) from inversion of teleseismic receiver functions

Teleseismic body waves from broadband seismic stations are used to investigate the crustal and uppermost mantle structure of Stromboli volcano through inversion of the receiver functions (RFs). First, we computed RFs in the frequency domain using a multiple-taper spectral correlation technique. Then, the non-linear neighbourhood algorithm was applied to estimate the seismic shear wave velocity of the crust and uppermost mantle and to define the main seismic velocity discontinuities. The stability of the inversion solution was tested using a range of initial random seeds and model parameterizations. A shallow Moho, present at depth of 14.8 km, is evidence of a thinned crust beneath Stromboli volcano. However, the most intriguing and innovative result is a low S velocity layer in the uppermost mantle, below 32 km. The low S velocity layer suggests a possible partial melt region associated with the volcanism, as also recently supported by tomographic studies and petrological estimations.     

Earthquake dynamics during unrest episodes at Campi Flegrei Caldera (Italy): A comparison with Rabaul (New Guinea)

We have analysed the earthquake sequence occurred at Campi Flegrei during an unrest episode of strong ground uplift and seismicity, occurred in the period 1982–1984. The maximum magnitude of these events was about 4. Both earthquake occurrence and ground deformation have been interpreted in terms of the role played by a ring fault system, inward dipping, related to phenomena of caldera collapse and resurgence. Earthquakes are of mixed strike-slip and normal fault type. They show a dip movement opposite to the static ground deformation. The rising of the internal block with respect to the zone external to the ring fault, as observed by ground deformation, should cause thrust fault slip on the fracture system, whereas a normal fault dip component is observed. The simulation of the stress field generated by overpressure in a magma chamber in presence of lateral discontinuities, as performed by a boundary element method, allows to hypothesise that reverse fault slip on the ring fault is mainly aseismic, and such aseismic movement is able to focus normal fault shear stress along the lateral discontinuities. Aseismic slip on the ring fault in response to static deformation is also supported by the low amount of seismic moment released (M₀ ≅ 10¹⁵ Nm), about two orders of magnitude lower than expected from the shear slip on the discontinuities needed to accomplish the total static surface deformation (1.8 m). Such results have been compared with observations at Rabaul caldera, during a similar unrest episode. In such area, the seismic moment release is in good agreement with shear slip produced on a system of outward dipping ring faults, and seismicity is much more focused on the fault structures. The comparison between the two areas shed new light about the dynamics of earthquakes in calderas, as due to the role of bordering ring fault systems.     

Dynamics of magma mixing and degassing recorded in plagioclase at Stromboli (Aeolian Archipelago,Italy)

Crystal-rich materials (scoriae and lava flows) emitted during the 1985–2000 activity of Stromboli were taken into consideration for systematic study of bulk rock/matrix glass chemistry and in particular for the study of chemical and textural zoning of plagioclase, the most abundant mineral phase. Over the considered time period, bulk rock composition remained fairly constant in both major (SiO₂ 49.2–50.9 wt% and K₂O 1.96–2.18 wt%) and trace elements. The quite constant chemistry of matrix glasses also indicates that the degree of crystallization of magma was maintained at around 50 vol%. Plagioclase ranges in composition between An₆₂ and An₈₈ and is characterized by alternating, <10–100 m thick, bytownitic and labradoritic concentric layers, although the dominant and representative plagioclase of scoriae is An_68. The labradoritic layers (An_62–70) show small-scale (1–5 µm), oscillatory zoning, are free of inclusions, and appear to record episodes of slow crystal growth in equilibrium with a degassed liquid having the composition of the matrix glass. In contrast the bytownitic layers (An₇₀-An₈₈) are patchy zoned, show sieve structure with abundant micrometric glass inclusions and voids, and are attributed to rapid crystal growth.A key to understanding the origin of bytownitic layers can be retrieved from the texture and composition of the coronas of plagioclase xenocrysts, inherited from crystal-rich magma, in nearly aphyric pumice which are erupted during more energetic events and represent a deep, volatile-rich, HK-basaltic magma. They show a continuum from fine-sieve to evident skeletal texture from the inner to the outer part of the corona associated with normal compositional zoning from An₉₀ to An₇₅. In the light of these observations, we propose that input of H₂O-rich melt blobs, and their mixing with the residing magma, causes partial dissolution of the labradoritic layers followed by the growth of bytownitic composition whose sieve texture attests of rapid crystallization occurring under undercooling conditions mainly induced by degassing. As a whole, the zoning of plagioclase in the scoriae records successive and discrete intrusions of volatile-rich magma blobs, its degassing and mixing with the resident degassed magma at shallow level.Editorial responsibility: T.L. GroveAn erratum to this article can be found at     

New data on the paleogeography of Southern Tuscany (Italy) since Late Miocene time

In order to add new data to the knowledge of the paleogeography of Southern Tuscany and the Tuscan shelf, a multidisciplinary study on the petrology and distribution of magmatic clasts of the widely exposed Messinian, Pliocene, and Quaternary sediments in Southern Tuscany was carried out. The magmatic clasts consist of porphyric aplites and subordinate granite porphyries, which derive from eroded subvolcanic acidic bodies. The porphyric aplite clasts were analyzed in detail to define their textural, petrographic, and chemical (major and trace elements, Sr and Nd isotopic composition) features. The porphyric aplite clasts show strong affinities with the 8.4–7.9 Ma old Capo Bianco aplite, whereas the granite porphyry clasts have affinities with the Portoferraio porphyry (ca. 8 Ma) which intruded the Cretaceous and Paleogene Flysch Units and the Ophiolitic Unit in central-western Elba Island (Northern Tyrrhenian Sea). The present outcrops of the Capo Bianco aplite in central Elba Island cannot be considered as the source rock for the Late Messinian gravels, because at that time such Capo Bianco aplite (located at the lower portion of the laccolitic stack) was there buried at several kilometers depth. However, other Capo Bianco-like aplitic bodies outcropped during the latest Miocene in the host rocks above and also around the 6.8 Ma M. Capanne Pluton in the western Elba areas. The exposure of such bodies was made possible by the activation of the central Elba detachment fault (=CEF), due to the uplift of the M. Capanne pluton. This uplift displaced a significant portion of the cover (including the upper portion of the laccolithic stack) of the granitoid body at about 6, 7 Ma, thus allowing the erosion of the lower part of the laccolith complex made up of the Capo Bianco aplite and of the Portoferraio porphyry and leaving still buried the M. Capanne pluton. The paleogeographic picture of Southern Tuscany arising from the collected evidences is the following: during Late Messinian, the clasts were dispersed by a SSW/NNE-trending complex fluvial system in the Colline Metallifere area. The Early Pliocene extensional tectonics cut off the detrital inputs from the Messinian source areas, because of the onset of the Piombino Channel and of the Campiglia–Gavorrano Ridge. During the Pliocene, the clasts were cannibalized from the previous sedimentary units and reached the easternmost areas due the eastward progressive uplift of the Colline Metallifere, likely connected with the coeval magmatic intrusions. Finally, the Quaternary regional uplift allowed a drainage reversal and a backward displacement of the aplitic clasts toward the Tyrrhenian coast. These data point to a rapidly evolving drainage pattern in Southern Tuscany during the considered time interval, which was mostly driven by the intrusion and uplift of the Messinian to Quaternary plutons. The morpho-tectonic evolution is well framed also within the models since long accepted for the Northern Apennine geodynamics, characterized by an overall eastward shift of the orogenic front.     

Gas hazard assessment at the Monticchio crater lakes of Mt. Vulture, a volcano in Southern Italy

Geochemical investigations have shown that there is a considerable inflow of gas into both crater lakes of Monticchio, Southern Italy. These lakes are located in two maars that formed 140 000 years ago during Mt. Vulture volcano's last eruptive activity. Isotopic analyses suggest that CO₂ and helium are of magmatic origin; the latter displays ³He/⁴He isotope ratios similar to those measured in olivines of the maar ejecta. In spite of the fact that the amount of dissolved gases in the water is less than that found in Lake Nyos (Cameroon), both the results obtained and the historical reports studied indicate that these crater lakes could be highly hazardous sites, even though they are located in a region currently considered inactive. This could be of special significance in very popular tourist areas such as the Monticchio lakes, which are visited by about 30 000 people throughout the summer, for the most part on Sundays.     

Geodetic techniques applied to the study of the Etna volcano area (Italy)

Volcanic behaviour of Mt. Etna is due to the complex interaction between both the local and the regional stress field involving the eastern Sicily. Eruptions could trigger (be triggered?) during crust extension and/or compression, which are strictly linked with the dynamics of the lower mantle. In this study, very long baseline interferometry (VLBI) space geodesy technique has been used in order to study Etna volcano’s activity by means of the crustal deformations between Noto and Matera (located on the African and the Eurasian Plates, respectively). By analysing VLBI data, we obtained the behaviour of the baseline which crosses the Etnean area, from 1990 December to 2003 March, representing the time variations of the distance between the two geodetic stations; the linear trend of the baseline shows a general increasing, pointing out an extension of the crust between them. A detailed analysis of the Noto-Matera baseline allows the identification of three parts of the VLBI curve in the considered period. In the first part of the curve (from 20/12/90 to 09/02/94), VLBI data are rather poor and therefore no reliable consideration about correlation between crust movements and volcanic and seismicity activity has been made. In the second part of the curve (from 09/02/94 to 04/09/00), VLBI data are more frequent and show slightly fluctuations in the distance. Increasing in the extension and compression were observed in the central and in the final part of this period. In the third period (from 04/09/00 to 25/03/03), VLBI data are very sparse even if the time series was quite long; therefore, to fill gaps in the information, we analysed global positioning system (GPS) data. GPS technique performs continuous observations, and we were able to highlight both extensions and compressions in detail. Comparisons between the trend of Noto-Matera baseline length variations, volcanic activity and seismicity in the Etna area show the complexity of the development over time and space of the phenomenology determined by a deep cause which can be traced, in our opinion, to the interaction between the asthenospheric mantle, deep crust and surface crust. Therefore, we state that crustal distension and compression are determined by the lower pulsating mantle.     

A novel displacement prediction method using gated recurrent unit model with time series analysis in the Erdaohe landslide

Natural Hazards - Landslides are natural phenomena, causing serious fatalities and negative impacts on socioeconomic. The Three Gorges Reservoir (TGR) area of China is characterized by more prone...     

Intra-Grain Sr Isotope Evidence for Crystal Recycling and Multiple Magma Reservoirs in the Recent Activity of Stromboli Volcano, Southern Italy

Over the last several hundred years, Stromboli has been characterizedby steady-state Strombolian activity. The volcanic productsare dominated by degassed and highly porphyritic (HP-magma)black scoria bombs, lapilli and lava flows of basaltic shoshoniticcomposition. Periodically (about one to three events per year),more energetic explosive eruptions also eject light colouredvolatile-rich pumices with low phenocryst content (LP-magma)that have more mafic compositions than the HP-magma. An in situmajor and trace element and Sr isotope microanalysis study ispresented on four samples chosen to characterize the differentmodes of activity at Stromboli: a lava flow (1985–1986effusive event), a scoria bomb from the ‘normal’present-day activity of Stromboli (April 1984), and a scoriaand coeval pumice sample from a recent more explosive eruption(September 1996). Plagioclase (An_62–90) and clinopyroxene(Mg-number between 0·69 and 0·91) phenocrystsin all samples record marked major element variations. Largeand comparable Sr isotope variations have been detected in plagioclaseand clinopyroxene. HP-magma crystals have resorbed cores, witheither high ⁸⁷Sr/⁸⁶Sr (0·70635–0·70630)or low ⁸⁷Sr/⁸⁶Sr (0·70614–0·70608); thelatter values are similar to the values of the outer cores.Mineral rims and glassy groundmasses generally have intermediate⁸⁷Sr/⁸⁶Sr (0·70628–0·70613). Similarly,mineral growth zones with three groups of ⁸⁷Sr/⁸⁶Sr values characterizeminerals from the LP-pumice, with the lowest values presentin mineral rims and groundmass glass. These results define amixing process between HP- and LP-magmas, plus crystallizationof clinopyroxene, plagioclase and olivine, occurring in a shallowmagma reservoir that feeds the present-day magmatic activityof Stromboli. An important observation is the presence of athird component (high ⁸⁷Sr/⁸⁶Sr in mineral cores) consideredto represent a pre-AD 1900 cumulus crystal mush reservoir situatedjust below the shallow magma chamber. These cumulus phases areincorporated by the LP-magma arriving from depth and transportedinto the shallow reservoir. A rapid decrease of ⁸⁷Sr/⁸⁶Sr inthe replenishing LP-magma immediately prior to eruption of theAD 1985 lava flow is associated with an increased volume ofLP-magma in the shallow magma chamber. The HP-magma in the shallowreservoir is not fully degassed when it interacts with the LP-magma,making efficient mixing possible that ultimately produces awell overturned homogeneous magma. Further degassing and crystallizationoccur at shallower levels as the HP-magma moves through a conduitto the surface. KEY WORDS: isotopic microsampling; mineral recycling; mixing; Sr isotope disequilibria; Stromboli     

Experimental Crystallization of a High-K Arc Basalt: the Golden Pumice, Stromboli Volcano (Italy)

The near-liquidus crystallization of a high-K basalt (PST-9golden pumice, 49·4 wt % SiO₂, 1·85 wt % K₂O,7·96 wt % MgO) from the present-day activity of Stromboli(Aeolian Islands, Italy) has been experimentally investigatedbetween 1050 and 1175°C, at pressures from 50 to 400 MPa,for melt H₂O concentrations between 1·2 and 5·5wt % and NNO ranging from –0·07 to +2·32.A drop-quench device was systematically used. AuPd alloys wereused as containers in most cases, resulting in an average Feloss of 13% for the 34 charges studied. Major crystallizingphases include clinopyroxene, olivine and plagioclase. Fe–Tioxide was encountered in a few charges. Clinopyroxene is theliquidus phase at 400 MPa down to at least 200 MPa, followedby olivine and plagioclase. The compositions of all major phasesand glass vary systematically with the proportion of crystals.Ca in clinopyroxene sensitively depends on the H₂O concentrationof the coexisting melt, and clinopyroxene Mg-number shows aweak negative correlation with NNO. The experimental data allowthe liquidus surface of PST-9 to be defined. When used in combinationwith melt inclusion data, a consistent set of pre-eruptive pressures(100–270 MPa), temperatures (1140–1160°C) andmelt H₂O concentrations is obtained. Near-liquidus phase equilibriaand clinopyroxene Ca contents require melt H₂O concentrations<2·7–3·6 and 3 ± 1 wt %, respectively,overlapping with the maximum frequency of glass inclusion data(2·5–2·7 wt % H₂O). For olivine to crystallizeclose to the liquidus, pressures close to 200 MPa are needed.Redox conditions around NNO = +0·5 are inferred fromclinopyroxene compositions. The determined pre-eruptive parametersrefer to the storage region of golden pumice melts, which islocated at a depth of around 7·5 km, within the metamorphicarc crust. Golden pumice melts ascending from their storagezone along an adiabat will not experience crystallization ontheir way to the surface. KEY WORDS: basalt; pumice; experiment; phase equilibria; Stromboli     

Analysis of the Maierato landslide (Calabria,Southern Italy)

On 15 February 2010, a landslide of great dimensions occurred at Maierato (Calabria, Southern Italy) after a long rainy period. Although the zone was continuously affected by ground movements especially during the wet seasons, no monitoring system was installed before the occurrence of the landslide. However, many photos and two videos were taken during the failure process of the slope. In the present study, the available images are used to reconstruct the kinematics of the landslide. In addition, a finite element analysis is performed to define the main factors of triggering and to interpret the failure mechanism of the slope. This analysis is also based on the data from a site investigation carried out after the landslide to characterise the involved soils from a geotechnical viewpoint. The analysis also accounts for the strain-softening behaviour of some soils. The results have shown that the Maierato landslide was the reactivation of a pre-existing landslide body, which was caused by a significant increase in groundwater level.     

Contamination risk of the Alburni Karst System (Southern Italy)

The Alburni massif (1742m a.s.l.) stretches NW–SE, about 23km long and 9–10km wide, covering 246km² with an average elevation of about 940m a.s.l. This massif, with more than 500 caves, is the most important karst area in southern Italy. The karst channel network is hierarchically organized: some channels feed a major spring (1m³/s) with a very short transit time while others communicate directly with the basal water table related to other springs (Q > 3m³/s).There are several dolines and swallow holes just above the basal water table and in the urbanized areas; for years a swallow hole directly transferred pollutants into the aquifer. The contamination vulnerability map shows that the prevalent vulnerability degree ranges from high to very high, due to the widespread karstification of the area and to the presence, on the plateau, of large vegetated areas with gentle slopes favouring fast infiltration.Hence it is important to ascertain the human impact on the area and the consequent contamination risk of the aquifer of the Alburni karst area. Three main layers were created to assess groundwater contamination risk: the vulnerability map, the hazard map, and the value map.The groundwater contamination risk map stresses the importance in a park area of aquifer vulnerability, which strongly influences the risk: indeed, the prevalent moderate degree of risk in the final map depends on the high vulnerability and the low hazard degree. However, in the future it is crucial to take into account the nature of the agricultural land use allowed in the park, which could increase the hazard degree and consequently the risk degree.     

H2S fluxes from Mt. Etna, Stromboli, and Vulcano (Italy) and implications for the sulfur budget at volcanoes

We present here new measurements of sulfur dioxide and hydrogen sulfide emissions from Vulcano, Etna, and Stromboli (Italy), made by direct sampling at vents and by filter pack and ultraviolet spectroscopy in downwind plumes. Measurements at the F0 and FA fumaroles on Vulcano yielded SO₂/H₂S molar ratios of ≈0.38 and ≈1.4, respectively, from which we estimate an H₂S flux of 6 to 9 t · d⁻¹ for the summit crater. For Mt. Etna and Stromboli, we found SO₂/H₂S molar ratios of ≈20 and ≈15, respectively, which combined with SO₂ flux measurements, suggest H₂S emission rates of 50 to 113 t · d⁻¹ and 4 to 8 t · d⁻¹, respectively. We observe that “source” and plume SO₂/H₂S ratios at Vulcano are similar, suggesting that hydrogen sulfide is essentially inert on timescales of seconds to minutes. This finding has important implications for estimates of volcanic total sulfur budget at volcanoes since most existing measurements do not account for H₂S emission.