volatile induced magma differentiation in the plumbing system of mt etna volcano italy evidence from glass in tephra of the 2001 eruption mount etna volcano was shaken during the summer 2001 by one of the most singular eruptive episodes of the last centuries for about 3 weeks several eruptive fractures developed emitting lava flows and tephra that significantly modified the landscape of the southern flank of the volcano this event stimulated the attention of the scientific community especially for the simultaneous emission of petrologically distinct magmas recognized as coming from different segments of the plumbing system a stratigraphically controlled sampling of tephra layers was performed at the most active vents of the eruption in particular at the 2 100 m cal and at the 2 550 m lag scoria cones detailed scanning electron microscope and energy dispersive x ray spectrometer sem eds analyses performed on glasses found in tephra and comparison with lava whole rock compositions indicate an anomalous increase in ti fe p and particularly of k and cl in the upper layers of the lag sequence mass balance and thermodynamic calculations have shown that this enrichment cannot be accounted for by classical differentiation processes such as crystal fractionation and magma mixing the analysis of petrological features of the magmas involved in the event integrated with the volcanological evolution has evidenced the role played by volatiles in controlling the magmatic evolution within the crustal portion of the plumbing system volatiles constituted of h2o co2 and cl complexes originated from a deeply seated magma body dbm their upward migration occurred through a fracture network possibly developed by the seismic swarms during the period preceding the event in the upper portion of the plumbing system a shallower residing magma body abt had chemical and physical conditions to receive migrating volatiles which hence dissolved the mobilized elements producing the observed selective enrichment this volatile induced differentiation involved exclusively the lowest erupted portion of the abt magma due to the low velocity of volatiles diffusion within a crystallizing magma body and or to the short time between volatiles migration and the onset of the eruption furthermore the increased amount of volatiles in this level of the chamber strongly affected the eruptive behavior in fact the emission of these products at the lag vent towards the end of the eruption modified the eruptive style from classical strombolian to strongly explosive

crustal xenoliths in recent hawaiites from mount etna italy evidence for alkali exchanges during magma wall rock interaction abstract detailed mineralogical and geochemical systematics were carried out on crustal xenoliths the host hawaiite lavas erupted from mount etna sicily italy in 1892 1986 and 1989 as well as the flyschs from the volcano basement the xenoliths suffered morphological structural mineralogical and geochemical alteration induced by thermal and chemical exchange with the enclosing lava high temperature reactions and partial or complete melting as well as different mechanisms of elemental interdiffusion took place their exact nature depending on the type of xenolith an early and strong mobility of k rb and cs and their selective migration towards the anatectic melts the lava envelope was observed at both mineral phase and whole rock scales this is closely connected to a release of h 2 o cl s and co 2 associated with the dehydration and the decarbonation of the sediments thus the selective migration of the k rb and cs towards the enclosing lava as well as contamination of the host lava observed seems to be induced by a selective diffusion of alkalis away from the anatectic melts and especially by their selective transfer through the action of complex interstitial and chemically active fluids such processes might be connected to the strong enrichment in k rb and cs of the recent hawaiites from mount etna they might also substantiate the hypothesis that these enrichments result from selective contamination of the magma as a consequence of the percolation or circulation of a carrier fluid phase through the upper parts of the magmatic feeding system

a multidisciplinary approach to detect active pathways for magma migration and eruption at mt etna sicily italy before the 2001 and 2002 2003 eruptions two strong flank eruptions occurred in july august 2001 and from late october 2002 to late january 2003 at mt etna volcano the two eruptions mainly involved the upper southern flank of the volcano a particularly active area during the last 30 years damaging several tourist facilities and threatening some villages the composite eruptive activity on the upper southern flank of mt etna during 2001 2003 has confirmed a posteriori the results of a multidisciplinary study started well before its occurrence by combining geological seismic and geochemical data gathered in this part of the volcano we were able in fact to highlight fractured zones likely to be re activated in the near future in this area where the largest majority of eruptive fissures in the recent past opened along n120 to n180 ranging directions the spatial distribution of earthquake epicentres during the period june 30th 2000 june 30th 2001 showed the greatest frequency in a sector compatible with both the direction of the main fissures of the pre 2001 period and that of the 2001 and 2002 lateral eruptions soil co2 and soil temperature surveys carried out in the studied area during the last 3 years have revealed anomalous release of magmatic fluids mainly co2 and water vapour along some nnw sse trending volcano tectonic structures of the area even during inter eruptive periods indicating persistent convective hydrothermal systems at shallow depth connected with the main feeder conduits of etna the temporal changes in both seismic and geochemical data from june 30th 2000 to june 30th 2001 were compared with the evolution of volcanic activity the comparison allowed to recognize at least two sequences of anomalous signals august to december 2000 and april to june 2001 likely related to episodes of step like magma ascent towards the surface as indicated by the following eruptive episodes the n120 to n180 structural directions are in accord with one of the main structural lines affecting eastern sicily they would be important pathways for magma uprise to the surface that will keep on feeding the eruptive activity of etna in the near future this study also pointed out the high instability of the southern slope of etna a sector where the potential hazard by lava flow invasion will remain high also in the near future

long and short term magma differentiation at mt etna as revealed by sr nd isotopes and geochemical data abstract mt etna in sicily italy produces effusive and explosive eruptions from summit craters and flanks petrology of erupted products has proved fundamental to explore the relationship between magma dynamics within the plumbing system and eruptive styles data of sr nd isotopes are quite scarce if compared with the great number of chemical analyses carried out in products of last decades we measure sr nd isotopes major and trace elements in products emitted from 2001 to 2012 and consider also published analyses of the 1995 2001 eruptions because carried out in the same laboratories of 2001 2012 ones furthermore we take into account other published analyses extending back to the 14th century even if performed by different facilities based on this dataset magma dynamics operating at different timescales inside the volcano s plumbing system have been explored our analyses evidence that from 2001 2012 three magma types are present in the volcano s plumbing system i a deep and poorly evolved basaltic and k trachybasaltic magma enriched in radiogenic sr and lile erupted during the 2001 and 2002 03 flank activity ii a shallower more evolved k trachybasaltic magma less enriched in radiogenic sr feeding both summit and flank eruptions and iii an uncommon and scarcely radiogenic hawaiitic magma lile poor emitted exclusively from a small sector of the 2002 03 eruptive fissures by considering a broader time scale from 14th to 21st century we conclude that i different magmatic components are present in the deep volcano s plumbing system at about 10 12 km b s l ii a decoupling of geochemical and isotopic features in magmas stored at different depths is observed after the 1974 flank eruption up to date iii mixing between different magmas is an efficient magmatic process to produce magma differentiation at mt etna regardless of the investigated temporal scale

variations in lava composition during the march 1981 eruption of mount etna and the implications of a compositional comparison with earlier historic eruptions the march 1981 eruption of mount etna occurred on the northern slopes of the volcano in an area previously inactive for more than 400 a a radial fissure system extending 7 5 km and producing 20 2 106 m3 of basic hawaiite lava opened at 2600 m a s l on 17th march and migrated downslope to 1125 m a s l where activity ceased on 23rd march gravity evidence points to the draining of a radial storage dyke located between sea level and 1 km a s l whole rock chemistry and petrography suggests that the magma in the dyke was a hybrid supporting crystal and compositional gradients developed as a result of progressively greater mixing of residual 1979 basic hawaiite magma with fresh basic hawaiite magma during permissive filling of the dyke around september 1980 these mixing gradients caused the eruption to display a significant contrast in the concentrations of al2o3 sr cao mgo and fe2o3 total between early high altitude and later low altitude products the fresh magma which entered the high level system around september 1980 ascended rapidly from a deep storage region at 16 24 km depth

isotopic evolution of lavas from haleakala crater hawaii pb and sr isotopic ratios have been determined for tholeiitic shield building alkalic cap and post erosional stage lavas from haleakala crater pb isotopic compositions of the tholeiites overlap those of the alkalic cap lavas although87sr 86sr ratios of these two suites are distinct alkalic cap and post erosional lavas appear to be indistinguishable on the basis of sr and pb isotopic composition sr and pb isotopic ratios of haleakala post shield building lavas are positively correlated such a trend is previously undocumented for any suite of hawaiian lavas and contrasts with the general negative correlation observed for data from hawaiian tholeiites these relations are consistent with a three component petrogenetic mixing model specifically it is proposed that magma batches at individual hawaiian volcanoes formed by 1 mixing of melts generated from mantle plumes containing two isotopically distinct mantle components primitive vs enriched and 2 subsequent variable degrees of interaction between these plume melts and a third morb signature mantle reservoir prior to their emplacement in a crustal magma chamber these observations and inferences provide new constraints on physical models of hawaiian magmatism based on observed temporal isotopic variations of haleakala lavas it is suggested that the ratio of enriched primitive mantle components in the hawaiian plume source decreases during the waning stages of alkalic volcanism over the same time interval both decreasing melt production and protracted residence of ascending melts within the upper mantle contribute to a systematic increase in the ratio of depleted vs plume component

the march 1981 mount etna eruption inferred through ground deformation modelling abstract the march 1981 eruption of mt etna was characterised by the fast propagation of a long eruptive fissure approximately 7 km and by an unusually high eruption rate the continuous tilt recorded by a bore hole station located on the southern flank showed a small inflation 3 4 months before the eruption followed by a rapid deflation during the fissure opening the discrete deformation measurements electroptical distance measurements edm and levelling showed large horizontal changes in the volcano flanks and smaller vertical ones close to the eruptive fissure we modelled the deformation pattern associated with the 1981 eruption using horizontal 57 data and vertical 50 data measurements two geometric constraints were considered for the eruptive fissure the dislocation theory was used to model the intrusion by characterising it in two parts as a double tensile crack which represents the initial deeper intrusion first crack and then the final shallower part associated with the eruptive fissure second crack an analytic inversion was performed obtaining a very good solution and then the robustness of this result was verified through an accurate trial and error search the first deeper crack extends vertically from about 300 to 1700 m above sea level a s l it was widely opened opening 5 m dipping w and radiating from the summit of the volcanic edifice in the nnw direction for approximately 3 km in the shallowest part last 500 m the intrusion propagated radially in the northern sector along the nnw direction second crack matching the surface location of the observed eruptive fissure we interpret that the deeper crack formed during the 3 4 months preceding the eruption

petrological notes on the 1983 lavas at mount etna sicily with reference to their ree and sr nd isotope composition the 1983 hawaiite of mount etna was sampled and analyzed for groundmass and mineral compositions rare earth element concentrations and sr nd isotope ratios microprobe data for coexisting mineral phases and glass show crystallization temperatures of around 1100 c from a rather differentiated hawaiite magma at rather highfo2 10 8 at 1100 c well above the qfm buffer the hawaiites are characterized by a marked enrichment in the light ree similar to other alkaline magmas the ce n yb n is greater than 10 a feature these hawaiites have in common with alkaline magmas erupted earlier on mount etna since the ce yb ratio cannot be affected by fractionation of clinopyroxene and plagioclase it is taken as an accurate reflection of the lree enriched nature of the hawaiites from this point of view the etnean hawaiites are identical to within plate alkaline magmas erupted on the hawaiian islands this similarity extends to the nd sr isotope features two hawaiites have87sr 86sr 0 70346 and 0 70352 and143nd 144nd 0 51286 and 0 51284 these data indicate a source similar to oceanic island basalts a source depleted in rb sr and nd sm for some period of time the sr isotope data are identical to that previously reported for mount etna extraction of hawaiites from depleted source regions requires either recent enrichment events mixing of asthenospheric and lithospheric melts or variable degrees of melting at present the data do not allow a clear decision the peculiar tectonic setting of mount etna between the relatively undeformed african foreland and the active aeolian volcanic islands may suggest contributions to the source region from subduction and within plate processes etnean lavas have a geochemical imprint of subduction related enrichment processes and they also share petrological and chemical features identical to oceanic island basalts whose source region has been affected by within palte enrichment processes

geochemical evolution of kohala volcano hawaii kohala volcano the oldest of five shield volcanoes comprising the island of hawaii consists of a basalt shield dominated by tholeiitic basalt pololu volcanics overlain by alkalic lavas hawi volcanics in the upper pololu volcanics the lavas become more enriched in incompatible elements and there is a transition from tholeiitic to alkalic basalt in contrast the hawi volcanics consist of hawaiites mugearites and trachytes 87sr 86sr ratios of 14 pololu basalts and 5 hawi lavas range from 0 70366 to 0 70392 and 0 70350 to 0 70355 respectively this small but distinct difference in sr isotopic composition of different lava types especially the lower 87sr 86sr in the younger lavas with higher rb sr has been found at other hawaiian volcanoes our data do not confirm previous data indicating sr isotopic homogeneity among lavas from kohala volcano also some abundance trends such as mgo p2o5 are not consistent with a simple genetic relationship between pololu and hawi lavas we conclude that all kohala lavas were not produced by equilibrium partial melting of a compositionally homogeneous source

the etnean lavas 1977 1983 petrology and mineralogy the products emitted by mount etna in the 1977 1983 period are porphyric sodic trachybasalts etnaites that though substantially higher in k2o resemble most of the historic lavas

the tectonic significance of italian magmatism an alternative view to the popular interpretation the tyrrhenian rift zone has been the site of widespread magmatism since late tortonian times a pronounced asymmetrical distribution reflecting the tectonic structure characterizes italian magmatism sodic basalts occur on the western tyrrhenian flank and transitional morb basalts occur in the tyrhenian sea the eastern flank however is characterized by k alkaline and hk to ultra alkaline e g carbonatites and melilitites rocks major trace elements and isotopic compositions allow two major magmatic lineages to be identified one relating to a non radiogenic basaltic end member and the other to a mantle end member enriched in ca with high lile hfse ratio and high sr isotopic ratios their mantle sources are located within the lithosphere thermal boundary layer tbl and the metasomatized phlogopite carbonate asthenosphere at the base of the tbl respectively the composition and spatial distribution of volcanism and relative mantle sources tend to map the geometry of the lithospheric mantle and to define a pronounced increase in depth from less than 60 km to about 100 km across the boundary between the thinned tyrrhenian lithosphere and the adriatic lithosphere a mechanism of intra continental passive rifting which drives mantle upwelling is sufficient to satisfy the petrological and geochemical constraints and the observed tectonic environment without requiring a subduction plane

compositional variation in the 1983 and other recent etnean lavas insights on the shallow feeding system a systematic petrographic and chemical study of chronologically ordered lava samples collected during the 1983 etna eruption has shown minor fluctuating variations in crystallinity and chemistry apparently correlated with variations in the rate of effusion comparison with the compositional variations observed in the lavas emitted during the 1971 1983 period has revealed a repeated evolutional tendency suggesting a small size shallow storage system periodically refilled as in 1983 by more primitive magma

the role of selective alkali contamination in the evolution of recent historic lavas of mt etna abstract the recent and abrupt encounter of magma bodies with the phreatic system beneath the sedimentary basement of mt etna is considered to be responsible for the alkali anomaly detected in lavas emitted since 1970 geochemical work on the inclusions and the rocks of the sedimentary basement indicates that the piedimonte and the capo d orlando flysch units are the possible sources of contamination

new insights on volcanic and tectonic structures of the southern tyrrhenian italy from marine and land seismic data 1 we present results from the first crustal seismic tomography for the southern tyrrhenian area which includes ocean bottom seismometer obs data and a bathymetry correction this area comprises mt etna the aeolian islands and many volcanic seamounts including the marsili seamount the seismicity distribution in the area depends on the complex interaction between tectonics and volcanism the 3 d velocity model presented in this study is obtained by the inversion of p wave arrival times from crustal earthquakes we integrate travel time data recorded by an obs network tyrrhenian deep sea experiment the sn 1 seafloor observatory and the land network our model shows a high correlation between the p wave anomaly distribution and seismic and volcanic structures two main low velocity anomalies underlie the central aeolian islands and mt etna the two volumes which are related to the well known active volcanism are separated and located at different depths this finding in agreement with structural petrography and gps data from literature confirms the independence of the two systems the strongest negative anomaly is found below mt etna at the base of the crust and we associate it with the deep feeding system of the volcano we infer that most of the seismicity is generated in brittle rock volumes that are affected by the action of hot fluids under high pressure due to the active volcanism in the area lateral changes of velocity are related to a transition from the western to the central aeolian islands and to the passage from continental crust to the tyrrhenian oceanic uppermost mantle

thermal survey of mount etna volcano from space surveys of ground thermal anomalies and the monitoring of their evolution are of great importance in the study of volcanoes thermal monitoring techniques could be used in conjunction with classical monitoring tools i e seismological and deformation networks to give better predictions of the onset of a volcanic event in order to detect and emphasize small anomalies in the surface temperature of the ground we have developed a new method based on the joint use of two satellite radiometers the noaa advanced very high resolution radiometer avhrr for the quality of its thermal band calibration and the landsat thematic mapper tm for its high spatial resolution this method is applied to the mount etna volcano sicily and reveals several thermal anomalies one anomaly is already known and is associated with the permanently active craters of the summit zone the second is a larger area where an eruption occurred one week after the data acquisition 10 23 86 the general trend of the thermal anomalies leads to recognition of a large semi circular intrusive zone corresponding to the borders of the well known valle del bove

recovery of spectral emissivity from thermal infrared multispectral scanner imagery acquired over a mountainous terrain a case study from mount etna sicily the estimation of ground radiance and emissivity from thermal infrared multispectral scanner tims data is strongly dependent on the atmospheric correction applied to these data since such corrections are a function of the atmospheric path between the sensor and ground correction techniques that do not consider the topographic variations within a scene can introduce appreciable error in the estimation of the atmosphere effects in this paper we describe the development and application of a variable elevation atmospheric correction procedure our objective was to incorporate changes in target altitude into a general atmosphere correction strategy this procedure was tested on a tims data set acquired over mt etna italy in july 1986 the methodology adopted in this study is based on the use of the lowtran radiative transfer code and a digital elevation model dem registered to the image data the image data are divided into a series of layers based on elevation and a separate atmosphere correction is applied to each layer maps of emissivity estimates derived with the variable elevation approach were compared with geologic maps of the etna flow fields prior to the variable elevation correction the emissivity spectra of long lava flows appeared to vary with elevation following the variable elevation correction many of these spectral artifacts were removed from the emissivity maps in addition the variable elevation correction increased our ability to discriminate individual lava flows

the dyke swarm of mount calanna etna italy an example of the uppermost portion of a volcanic plumbing system a new multidisciplinary study combining geology petrography and geochemistry on the rocks of the isolated hill of mount calanna mount etna italy has provided evidence for the existence of a dyke swarm formed by more than 200 dykes distributed over an area of 0 7 km2 with an intensity of intrusion up to 40 all bodies are deeply altered and the geological and mesostructural surveying of 132 dykes revealed that they intruded in e w direction with an average dip of 60 the faults affecting the outcrop have in general an e w strike and dip of 55 these have all normal motion and have been interpreted as coeval with the dykes this interpretation contrasts with the previous hypothesis that considered mount calanna as a thrust resulting from compressive deformation resulting from the gravitational spreading of the volcanic edifice mount calanna is here interpreted as the uppermost portion of a vertically extensive magmatic plexus that fed the eruptive activity of one or more eruptive center s sited in the valle del bove area measurements of the apparent densities on 23 dykes and host rock samples give an average value of 2 420 kg m3 for the entire complex 15 lower than the density expected for hawaiitic magma placing an important constraint on the geophysical identification of similar structures considering that mount etna is not an old eroded edifice but an active and growing volcano the exposure of this subvolcanic structure can be regarded as exceptional its geometry and physical characteristics can be thus regarded as an interesting example of the present day shallow plumbing system of mount etna as well as of other basaltic volcanoes

he ar o sr and nd isotope constraints on the origin and evolution of mount etna magmatism abstract the 0 5 ma history of the origin and evolution of mount etna sicily has been investigated by analysing the isotopic composition of he ar o sr and nd in 21 selected lava samples the near constancy of the isotopic compositions of oxygen 18 o 5 4 0 3 and of helium trapped in olivine phenocrysts 6 7 0 4 ra is interpreted as evidence of a single mantle source despite drastic petrological changes during the volcano s history he analyses performed by crushing cogenetic pyroxene and olivine phenocrysts show a tendency to lower 3 he 4 he ratios in pyroxenes this is best explained by crystallization of pyroxenes at a depth shallower than that of olivines and or by exchange of helium trapped in pyroxenes with atmospheric or radiogenic he before eruption 87 sr 86 sr ratios of recent lavas tend to increase with time and to correlate with rb th ratios and for historical lavas these variations are tentatively attributed to shallow selective contamination from underlying sediments based on the similarity of the 3 he 4 he ratios at etna to those of european mantle xenoliths 1 we propose that the baseline geochemical signature of isotopic tracers at etna reflects the composition of the subcontinental mantle comparison to other southern italian active volcanoes etna vulcano ischia campi flegrei vesuvius shows gradual dilution of the predominantly mantle etnean end member by more radiogenic sr and he and material with higher 18o and c 3 he which is reasonably explained by the progressively important influence of subducted continental crust

boron sr o and h isotope geochemistry of groundwaters from mt etna sicily hydrologic implications combined b o h and sr isotopic studies of groundwaters from mt etna provide new constraints on their origin and the consequences of fluid rock interaction within this hydrologic system variations in d 18 o 29 7 to 27 2 and d d 262 to 223 mainly lie along the regional meteoric water line and suggest that most waters originated as local precipitation however small shifts in d 18 o and variable 87 sr 86 sr 0 70355 to 0 70879 and d 11 b 25 2 to 125 8 indicate that subsequent interactions occurred between the fluids and local rocks high b cl ratios in all samples seemingly preclude direct involvement of seawater in the hydrologic system despite the proximity to the coast and in some samples elevated 87 sr 86 sr and d 11 b two general end member water types are recognized on the basis of their chemistry these apparently are produced by interactions of local meteoric waters with the dominant reservoir rocks either basaltic lavas of etna or the underlying sediments respectively high d 11 b in the sediment hosted end member points to a significant marine carbonate contribution subsequent mixing between these or similar end members produced a range of intermediate composition groundwaters certain anomalous water compositions require the presence locally of a distinct component with high b and moderate d 11 b ca 110 but relatively low 87 sr 86 sr an anthropogenic source for this component is plausible one unusual sample has b and sr isotopic compositions similar to the other volcanic rock hosted waters but anomalously high cl content that likely reflects local magmatic outgassing near this sampling locality in general this study indicates that groundwater b and sr isotopic compositions are rock dominated these data provide useful constraints on the origin and evolution of groundwaters copyright 2000 elsevier science ltd

dynamics of mount etna before during and after the july august 2001 eruption inferred from gps and differential synthetic aperture radar interferometry data we acknowledge the istituto nazionale di geofisica e vulcanologia the italian dipartimento per la protezione civile and the european community contract ingv dpc ur v3 6 36 and volume project for their economic contribution to this research the sar data are provided by esa esrin

effects of magma storage and ascent on the kinetics of crystal growth the size distributions of crystals of olivine plagioclase and oxides of the 1991 93 eruption at mt etna italy are analyzed the simultaneous collection of this information for different minerals gives precious insight into the cooling history of lavas three distinct episodes are detectable a storage of the magma in a deep reservoir characterized by nearly constant and low nucleation and growth rates near to equilibrium an ascent phase with an ever increasing nucleation rate related to volatile exsolution and finally a quenching phase in addition to geochemical and geophysical evidence the similarity of the crystal size distributions of the present eruption with those of previous ones of this century makes it possible to exclude that crystal size distributions of etnean lavas are due to mixing of different populations this strongly suggests that the main features of the volcano feeding system have not changed despite observed variations in the magma output rates

relationships between crustal contamination and crystallisation in continental flood basalt magmas with special reference to the deccan traps of the western ghats india the upper part of the deccan traps sequence bushe to mahabaleshwar formations shows a statistically significant tendency for the most mafic lavas to be the most contaminated by crustal materials this is the reverse of the relationship shown by suites evolving by contamination accompanied by fractional crystallisation afc the observed correlations e g between mg number and sr isotope initial ratios are partly an accidental consequence of the fact that the most mafic lavas are more abundant in the lower part of the sequence while contaminant availability declines in the upper part it is probable however that the correlations are augmented by increased contamination of hotter magma batches during ascent through dykes a process during which fractional crystallisation is suppressed by magmatic turbulence the absence of afc relationships suggests that most of the contamination took place during the ascent stage rather than in a magma chamber other continental flood basalt provinces such as the parana and etendeka do show afc relationships and it is speculated that this may be a result of magma chamber contamination coupled with flow rates which prevent contamination during ascent

roots of etna volcano in faults of great earthquakes abstract results from several seismic methods allow us to sketch the deep structure of etna and its ionian margin under etna a volume of high velocity material is found in a structurally high position the emplacement of this suggests spreading of the surrounding medium just offshore down to the east normal faults penetrate through the upper crust the deeper crustal structure beneath appears upwarped from the basin towards etna juxtaposed with the crust of sicily a thinner crust reaches from the ionian basin under etna and the mantle is upwarped in such a structure magma can then be viewed as a melted lens capping a mantle upwarp at shallow depth rather than in an intracrustal chamber this reduces the conflict between estimates of its volume from excess output of volatiles and short residence times a link in time is indicated between volcanic and seismic activity at a large scale over the millennium the reported ends of episodes of high output rates of magma are followed by the reported occurrences of magnitude 7 earthquakes which caused destruction in southeastern sicily several steep active normal fault have been imaged to a depth of 10 km the crust up to 30 km offshore of the cities of catania and augusta which may be fault planes for such large earthquakes they expand and prolongate the system of the timpe faults on the eastern flank of etna thus linking large scale tectonics offshore with the volcano etna developed together with normal faulting upwarp and spreading during the recent evolution of the former ionian subduction activation of the material at depth at the lateral edge of the slab by vertical motion with extension above could produce the peculiar type of etna magmatism

geochemical and sr isotope data on historic lavas of mount etna abstract the concentration of trace elements la nb rb zr sr ni co cr and cu have been determined in 46 samples from 14 historical eruptions of mt etna 1444 to 1983 as well as their sr isotope compositions the measured values show significant variations that are explained in terms of magma generation differentiation and mixing processes the contamination by diffusion of volatile enriched fluids suggested by earlier authors might be confirmed here with reference to rb behaviour and the same process is also invoked in order to explain variation of sr isotope compositions nevertheless the hypothesis of source heterogeneity stated by other authors cannot be ruled out

the 1669 eruption at mount etna chronology petrology and geochemistry with inferences on the magma sources and ascent mechanisms analysis of the petrochemical characters of the 1669 etnean lavas shows that they can be grouped into two sets set1 lavas were erupted from 11 to 20 march and are more primitive in composition than set2 erupted later until the end of activity both sets may be interpreted as the result of crystallization under different conditions of two primary magmas which are compositionally slightly distinct and which fractionate different volumetric proportions of minerals to explain why more mafic lavas set1 were erupted earlier than more acid ones set2 we argue that new deeper magma rose up into a reservoir where residing magma was fractionating density calculations demonstrate that new magma is less dense and may originate a plume rapidly rising through the residing magma which is cooler and more volatile depleted than the new magma calculations of uprise velocity assuming laminar flow are consistent with this hypothesis

morb type neon in an enriched mantle beneath etna sicily abstract noble gas elemental and isotopic compositions were determined for five co 2 ch 4 samples collected around etna sicily to investigate the geochemical features of the mantle beneath the volcano the samples contain mantle derived noble gases the measured helium isotopic ratios 3 he 4 he vary between 5 9 and 6 4 times atmospheric ratio r a 1 4 10 6 which are comparable to the ratios of olivines 6 1 8 2 r a in the lavas of the same volcano 1 neon in the samples is enriched in both 20 ne and 21 ne 20 ne 22 ne 9 95 10 7 21 ne 22 ne 0 030 0 037 indicating derivation from the mantle the 20 ne 22 ne 21 ne 22 ne values are identical with that of mid ocean ridge basalts morb indicating a similarity in the time integrated u ne ratio between the etnean magma source and the depleted upper mantle morb source argon in the samples has 40 ar 36 ar ratios up to of 1800 which are higher than in atmosphere these ratios are positively correlated with the 20 ne 22 ne ratios indicating a mantle origin of the radiogenic argon compared with olivines from the etnean lavas 1 the argon in our natural gas samples is less contaminated by atmospheric argon two samples from a co 2 well show small but resolvable excess of 129 xe and 134 136 xe the volcanic rocks of etna ranging from tholeiites to alkaline are enriched in incompatible elements nd sr and pb isotopes of the volcanic rocks indicate that the magma source is isotopically heterogeneous and contain a component with high sr pb and low nd isotopic ratios derived from a mantle region which has been enriched in incompatible elements for a few million years 2 3 4 relative to the depleted upper mantle the helium isotopic ratios of the gas samples are lower than those of morb and are consistent with geochemical signatures of the solid elements in the etnean volcanic rocks however the observed morb type neon is on a morb correlation array without accumulation of nucleogenic 21 ne this apparent decoupling may be explained by a recent mixing of the depleted upper mantle morb source with fluid enriched in both incompatible elements and radiogenic 4 he when the fluid was formed with a small degree of partial melting fractionation of radiogenic 4 he from nucleogenic 21 ne could have occurred because of smaller partition coefficient of he than ne

tectonic stresses and volcanism in situ stress measurements and neotectonic investigations in the etna area italy abstract mt etna has been building up for about 500 000 years on the eastern margin of sicily at the external border of the apenninic maghrebian mountain chain and at the crossing of several important regional fault systems the tholeiitic and alkaline magmatism of mt etna represents the northernmost manifestation of present day volcanism which was continuous in space and time from the upper miocene to the lower pleistocene in central eastern sicily in situ stress measurements and neotectonic investigations have been carried out on mt etna on its periphery and on the hyblean mountains to obtain a better understanding of the stress field which is connected to the present day activity of the volcano and a clearer picture of the regional geodynamical evolution the investigations allow a comparison of the present stress field with that acting during the quaternary the neotectonic analysis has given evidence of strong compressional stresses exerted on the pleistocene sediments overlying the substratum of the volcano and its immediate surroundings in addition to evidencing the already known extensional deformation the compressional forces were oriented approximately n s at the beginning of the volcanic activity the in situ stress measurements show now that this n s compression is today active only in the northernmost part of the etna area whereas in the remaining area extensional stresses oriented approximately wnw ese prevail it is concluded that the compressional stresses near the surface today limited to the northernmost part of the etna area had a much more widespread distribution at the beginning of the volcanic activity this conclusion is important for understanding the deep seated magmatic process focal mechanisms of earthquakes indicate a complex tectonic situation with normal faulting down to a depth of 5 km and reverse faulting at deeper levels

2001 flank eruption of the alkali and volatile rich primitive basalt responsible for mount etna s evolution in the last three decades abstract since the early 1970s enhanced eruptive activity of mount etna has been accompanied by selective geochemical changes in erupted lavas among which a gradual increase of alkalis whose origin is still debated here we provide further insight into the origin of this recent evolution based on a detailed study of the chemistry and dissolved volatile content of melt inclusions trapped in olivine crystals of unusual plagioclase poor primitive basalt that was extruded during a highly explosive flank eruption in july august 2001 two types of lava were erupted simultaneously along a n s fracture system trachybasalts from the upper vents 2950 2700 m were simply drained out by fracturing of the central volcanic conduit they are identical to summit crater lavas and contain mg poor olivines fo 70 72 with evolved and volatile poor melt inclusions that represent late stage crystallisation during shallow open conduit degassing in contrast plagioclase poor basalt 80 of total extruded through the lower vents 2550 2100 m derived from lateral dyke intrusion of a more primitive and volatile rich magma across the sedimentary basement this primitive melt is best preserved in rare fo 82 4 80 5 skeletal olivines present in lapilli deposits from the most powerful activities at the 2550 m vent its high dissolved contents of h 2 o 3 4 wt co 2 0 11 to 0 41 wt s 0 32 wt cl 0 16 wt and f 0 094 wt point to its closed system ascent from 400 to 250 mpa 12 to 6 5 km depth b s l however the predominance of euhedral olivine phenocrysts with common reverse zoning cores fo 76 78 and rims fo 78 80 and decrepited inclusions shows that most of the erupted basalt derived from a slightly more evolved crystallizing body of the same magma that was invaded by the uprising primitive melt prior to erupting the few preserved inclusions in these olivines indicate pre eruptive storage of that magma body at about 5 km depth b s l in coherence with seismic data we propose that the 2001 flank eruption resulted from gradual overpressuring of etna s shallow plumbing system due to the influx of volatile rich primitive basalt that may have begun several months in advance we find that this basalt is much richer in alkalis 2 0 wt k 2 o and has higher s cl 2 0 but lower cl k and cl f ratios than all pre 1970s etnean lavas 1 4 wt k 2 o s cl 1 5 as further exemplified by melt inclusions in entrained olivine xenocrysts combining these new observations with previously published data we argue that the 2001 basalt represents a new alkali rich basic end member feeding mt etna only few amount of which had previously been extruded during a 1974 peripheral eruption and more recently during brief paroxysmal summit events over the last three decades this new magma has progressively mixed with and replaced the former k poorer trachybasalts filling the plumbing system leading to extrusion of gradually more primitive and alkali richer lavas its geochemical singularities cannot result from shallow crustal contaminations instead they suggest the involvement of an alkali richer but cl poorer arc type component during recent magma genesis beneath etna

recent deep earthquake occurrence at mt etna sicily italy abstract the seismic activity of mt etna from april 1988 until the december 1991 eruption was monitored by means of permanent and temporary seismic networks volcanic activity that occurred during this period tremor increase with lava fountains at the summit craters and eruptions was preceded and accompanied by the occurrence of deep z 15 km seismicity this deep seismic activity occurring a few days up to some weeks before the volcanic phases was characterized by typical mainshock aftershocks sequences focal mechanisms of the more energetic events which preceded the eruptions show that the compression axis was nearly north south parallel to the direction of the compressive stress field acting in the area at regional scale both the observation of deep seismicity occurrence also before or during previous eruptions and the role played by tectonics as controller of the magma uprise suggest the hypothesis of a relation between the seismic energy released in the volcanic basement and the recharge mechanisms of the volcanic system in this hypothesis the deep seismicity located in the etnean area could be considered as a possible forerunner of volcanic activity

the control of lava flow during the 1991 1992 eruption of mt etna abstract all the actions carried out in 1992 to protect the village of zafferana etnea from being invaded by lava are described an earthen barrier 234 m long and 21 m high was firstly built in january 1992 by accumulating with mechanical escavators 370 000 m 3 of earth scoriae and stones this embankment contained the lava for about one month and was overflowed by april 9 1992 three additional smaller earthen barriers lenght 90 160 m height 6 12 m were built in april to gain time while the lava front was descending towards zafferana from the overflowed first embankment the major effort of the 1992 operation consisted of several attempts at stopping the lava front advance by diverting the flow out from the natural and extensively tunnelled channel through a skylight near the vent the main intervention point was located in valle del bove at an elevation of 2000 m at 8 km from zafferana in a zone almost unaccessible from land helicopters were hence extensively used during the whole operation initial interventions called for attempts at plugging a tunnel by dumping into it linked concrete blocks hedgehogs and blasted portions of the solid levee each intervention caused the partial obstruction of the tunnelled channel which determined major increases of lava overflow in valle del bove and the consequent halt of the most advanced fronts however benefits were of brief duration at the most two weeks of respite before new lava fronts approached again and again the outskirts of zafferana the final successful intervention was carried out on may 27 29 an artificial channel was dug departing from the natural one the solid separation levee was thinned to 3 m and blasted by 7000 kg of explosives after the explosion 2 3 of the lava flowed spontaneously in the artificial channel and then the total diversion was obtained the tunnel being plugged by dumping into the natural flow 230 m 3 of lava boulders as a consequence of the intervention the active natural lava front that on may 27 was only 850 m from zafferana came to an halt as did the entire flow downhill from the diversion point bringing back the situation as it was five months earlier a few days after the beginning of the eruption with the new front of the diverted flow at 6 7 km from zafferana in june 1992 the effusion rate halved from 30 to 15 m 3 s and with this reduced thrust the lava was no longer capable of covering long distances five months after the conclusive intervention the diverted lava continues to flow over its initial natural field but remaining confined in the upper valle del bove without any new threat to zafferana

petrology and sr nd isotope geochemistry of recent lavas from mt etna bearing on the volcano feeding system abstract the volcanic activity of mt etna during the period 1971 1987 has been investigated based on new volcanological petrographic geochemical and isotopic data the magma output rate since 1971 is much higher than that of the last 200 years marking a significant change in the feeding regime of mt etna the highest output rate has been observed for the 1981 eruption sub aphyric lavas emitted during the excentric activity of 1974 are the most primitive of those studied mg 57 55 the major and trace element chemistry of the lavas indicates limited differentiation by crystal fractionation mainly involving mafic phases nevertheless the observed variability of some ratios between highly incompatible elements suggests possible source heterogeneities the sr nd isotopic compositions range between 0 70362 0 70377 and 0 512829 0 512892 respectively with the lowest and highest 87sr 86sr ratios measured in the 1981 and 1974 lavas the observed isotopic variability is not due to late contamination processes but probably to the mantle source variations in sr and nd isotopic composition could indicate the lack of large magma chambers at any level in mt etna feeding system suggesting a model in which magma reaches the surface through a network of dikes where complete homogenization of different batches cannot be attained

activity of mount etna 1977 1983 volcanic phenomena and accompanying seismic tremor a period of exceptional eruptive activity for both size and frequency of lateral eruptions and violence of paroxysms at the summit craters characterized etna from 1977 to 1983 the complex fissure eruption of 1971 and the eccentric eruption of 1974 on the w flank appear to be precursors of the present activity which began in july 1977 with the change in style of summit eruptions from moderate persistent activity to intermittent paroxysms the ne crater produced a score of such unusual eruptions up to march 1978 lasting a few days or even a few hours with powerful lava fountaining and flows up to 7 km long with high effusion rates other solely explosive paroxysms occurred in april 1980 in the chasm central crater and later at the se crater a return to a period of gentle persistent activity may august 1980 at the latter vent was interrupted by the recommencement of violent explosive and effusive events at the ne crater in september 1980 and february 1981 particularly remarkable lateral flank eruptions occurred in april june 1978 fracturing of the se slope from 3000 to 2600 m altitude august 1978 se ene 3000 2300 m november 1978 se 3000 1650 m august 1979 se e ne 3000 1600 m march 1981 nnw 2600 1120 m and march august 1983 s 2700 2260 m the first four of these eruptions were preceded and accompanied by violent lava fountaining at the se crater all were accompanied and or followed by phreatic explosions principally from the bocca nuova or w central crater the flow emitted on 4th august 1979 from the eastern flank reached next to the village of fornazzo in half a day that of 17 march 1981 the most destructive cut all communications roads and railways round the northern foot of the mountain in the 14 hours following its appearance it was in places 800 m wide and in less than 5 days 18 106 m3 of lava had been emitted covering 6 km2 of largely agricultural land from 28th march to 6th august 1983 the slow but sustained emission of lava gradually covered and destroyed several tourist installations between 2300 and 1100 m altitude each of these eruptive paroxysms was marked by a substantial increase in the trace amplitude of harmonic seismic tremor the intensity of which being not directly proportional to the observed activity it is likely that turbulence caused by the rising of magma in the main conduits had an important effect in the energy of the tremor this is considerably reduced after the initial paroxysmal phase e g in 1983 yet the lava effusion may continue tremor energy attains relatively high levels from 1 to 5 months before eruptions this may be caused by the recharging of the system of dykes and fissures leading up to an eruptive event after a variable period several distinct periods of recharging may precede one eruption there were three before the 1983 eruption in the few days preceding the start of some of the eruptions aug 1979 sep 1980 feb and mar 1981 a rapid diminution in the amplitude of tremor occurred this may be associated with changes in the stress field caused by the opening of new fractures or the closing opening of pre existing ones

geochemical and isotopic monitoring of mt etna 1989 1993 eruptive activity bearing on the shallow feeding system two flank eruptions took place at mt etna during 1989 1993 the former september october 1989 produced lavas among the most primitive of this century while the latter december 1991 march 1993 was unusually long lasting and the largest of the last three centuries alkali basalts of 1989 displayed initial enrichments of rb and k accompanied by an higher value of radiogenic sr and isotopic disequilibrium between host rock and clinopyroxene 0 70364 and 0 70356 respectively subsequently within one week k rb and 87sr86sr ratio decreased to constant values 87sr86sr 0 70355 nd isotopic ratio did not show significant variations these features can be explained by a selective contamination process involving essentially rb k and radiogenic sr the bulk from the 1991 1993 eruption hawaiites were erupted between january and may 1992 in this period lavas here called jml were characterised by uniform geochemical and isotopic compositions and sr isotopic equilibrium between whole rock and pyroxene 0 70355 in other periods december 1991 and june 1992 we observed lower and variable sr isotopic compositions coupled with disequilibria between lavas and their clinopyroxenes 0 70351 in the w r and 0 70345 in the cpx of the sample of 15 december 1991 starting from june 1992 the products seem to reveal fractionation effects as suggested by the continuous rise in concentrations of incompatible elements when the observed variability cannot be ascribed to fractionation effects we are not able to discriminate mixing from selective contamination however lavas erupted during december 1991 evolved towards the isotope composition of jml that was never exceeded moreover the regular behaviour of rb k and radiogenic sr of 1989 lavas was not observed during the 1991 1993 eruption thus we prefer to interpret these variations as mainly due to mixing processes between an end member of jml composition and another one having the same or lower isotopic composition of the clinopyroxene found in the sample of december 1991 several petrogenetic processes are contemporaneously active at mt etna they encompass magma mixing selective contamination and fractional crystallization their relative importance varies according to the original volume of each magma batch and to the status of the shallow feeding system the complexity of these processes acting in the short time span of a few months claims caution about the geochemical representativity of a single lava sample for each eruption

petrologic evidence of a complex plumbing system feeding the july august 2001 eruption of mt etna sicily italy after the major 1991 1993 eruption mt etna resumed flank activity in july 2001 through a complex system of eruptive fissures cutting the ne and the s flanks of the volcano and feeding effusive activity fire fountains strombolian and minor phreatomagmatic explosions throughout the eruption magmas with different petrography and composition were erupted the vents higher than 2 600 m a s l hereafter upper vents uv erupted porphyritic plagioclase rich trachybasalt typical of present day summit and flank activity differently the vents located at 2 550 and 2 100 m a s l hereafter lower vents lv produced slightly more primitive trachybasalt dominated by large clinopyroxene olivine and uncommon minerals for etna such as amphibole apatite and orthopyroxene and containing siliceous and cognate xenoliths petrologic investigations carried out on samples collected throughout the eruption provided insights into one of the most intriguing aspects of the 2001 activity namely the coeval occurrence of distinct magmas we interpret this evidence as the result of a complex plumbing system it consists in two separate magma storage systems a shallow one feeding the activity of the uv and a deeper and more complex storage related to the activity of lv in this deep storage zone which is thermally and compositionally zoned the favourable conditions allow the crystallization of amphibole and the occurrence of cognate xenoliths representing wall cumulates throughout 2001 eruption uv and lv magmas remain clearly distinct and ascended following different paths ruling out the occurrence of mixing processes between them furthermore integrating the 2001 eruption in the framework of summit activity occurring since 1995 we propose that the 2001 magma feeding the vents lower than 2 600 m a s l is a precursor of a refilling event which reached its peak during the 2002 2003 etna flank eruption

bayesian inversion of 1994 1998 vertical displacements at mt etna evidence for magma intrusion summary we have developed a bayesian method for the inversion of static ground deformations at volcanic areas the method allows inference of the conditional probability density on the location and mechanism of point sources representing volcanic phenomena isotropic strain nuclei tensile faults embedded in homogeneous elastic media the method has been tested with simulated and real data from volcanic areas we have then analysed vertical displacements recorded at mt etna southern italy from 1994 to 1998 by high precision levelling measurements in this period had been carried out yearly so resulting displacements have been analysed both in consecutive periods and in the cumulative one measurement periods 1994 1995 and 1997 1998 show significant uplift of several centimetres the maximum cumulative displacement amounts to 6 5 cm with a trend similar to each of the two periods 1994 1995 and 1997 1998 the shape of displacement is well approximated by a circular symmetry thus allowing one to hypothesize an isotropic overpressure model as the source simulating magma intrusion at shallow depth the application of the inverse method gives the most probable location at about 4 5 km of depth b s l at about 1 5 km north of the central craters the 95 per cent of probability density is concentrated within a radius of about 0 5 km on the horizontal 1 km on depth the obtained results give important insight on the interpretation of recent eruptive episodes

high precision relocation of microearthquakes at mt etna 1991 1993 eruption onset a tool for better understanding the volcano seismicity abstract the beginning of the 1991 1993 large eruption at mt etna was marked by a seismic swarm and a sudden increase of volcanic tremor amplitude several earthquakes were recognized as clusters of shallow events with nearly identical waveforms multiplets we have analyzed these signals with a cross spectral technique that allows us to locate the relative position of the events within a multiplet obtaining a precision higher than with traditional routines the relocated shocks occurred some kilometers away from the propagating eruptive fracture east of both the summit craters and the modeled eruptive dykes they clustered in a relatively small volume elongated in the nnw sse direction the depth of which ranged from about 1100 to 2000 m below sea level these earthquakes are interpreted as the passive brittle response of the volcanic basement to the intrusion of the eruptive dyke rather than being directly linked to the magma transport

petrology and geochemistry of rodrigues island indian ocean rodrigues island is composed of a differentiated series of transitional mildly alkaline olivine basalts the lavas contain phenocrysts of olivine fo88 68 plagioclase an73 50 together with a megacryst suite involving olivine plagioclase kaersutite clinopyroxene apatite magnetite and hercynite rich spinels troctolitic anorthositic gabbro xenoliths are widely dispersed throughout the lavas and are probably derived from the upper parts of an underlying layered complex the megacrysts may originate from coarse easily disaggregated differentiates near the top of this body modelling of major and trace element data suggests that the majority of chemical variation in the lavas results from up to 45 fractionation of olivine clinopyroxene plagioclase and magnetite at low pressures in the ratio 20 35 39 6 the clinopyroxene rich nature of this extract assemblage is significantly different to that of the xenoliths and suggests that clinopyroxene rich gabbros and or ultrabasic rocks may lie at greater depth sr and nd isotopic data 87sr 86sr 0 70357 070406 143nd 144nd 0 51283 0 51289 indicate a mantle source with relative lree depletion and emphasise an unusual degree of uniformity in indian ocean island sources a small group of lavas with strong hree enrichment suggest a garnet poor source for these while high overall al2o3 cao ratios imply high clinopyroxene garnet ratios in refractory residua

magma dynamics in the shallow plumbing system of mt etna as recorded by compositional variations in volcanics of recent summit activity 1995 1999 describe the reactivation and the successive evolution of the shallow plumbing system of mt etna between the end of the largest flank eruption of the last three centuries 1991 1993 and the subterminal eruption from south east crater sec which occurred between february and mid november 1999 our analysis is based on observations of the volcanic activity and petrological studies of the erupted volcanics bulk rock mineral and glass compositions have been determined for more than 80 samples erupted from the four summit craters between october 1995 and february 1999 these data allow us to recognise significant compositional variations among the products of different craters in particular volcanics produced between 1995 and 1999 by bocca nuova bn voragine vor and north east crater nec show limited compositional variations and are similar to those observed during recent eruptions e g 1991 93 more primitive magmas have been produced during the more vigorous fire fountains episodes on the contrary the south east crater produced slightly more differentiated volcanics than those of the other summit craters following its reactivation november 1996 until the end of 1998 whole rock compositions of products from this crater show low cao al 2 o 3 whereas interstitial glasses have lower mgo and higher alkali contents than those from the other craters however since the beginning of 1999 and just before the start of the subterminal eruption from sec the volcanics erupted from this crater progressively changed in composition becoming similar to those of the other craters this trend indicates that within the conduits of the summit craters distinct thermal and fluid dynamical regimes can evolve controlling the cooling and crystallisation of etna magmas

seismogenic stress field beneath mt etna south italy and possible relationships with volcano tectonic features abstract shallow shear type seismic activity occurring beneath the etna volcano during 1990 1995 has been analysed for hypocenter locations focal mechanisms and stress tensor inversion the results have been examined jointly with electronic distance measurements and tiltmeter data collected in the same period and reported in the literature significant seismicity located in the upper 10 km was found to be confined to the time intervals in which ground deformation data indicated inflation of the volcano edifice e g the periods preceding the december 1991 march 1993 and august 1995 march 1996 eruptive phases the shocks mostly occurred in a sector approximately centered on the crater area and elongated in the east west direction the causative seismogenic stress shows a low dip east west orientation of 1 in agreement with existing knowledge on relationships between local fault systems and magma uprise processes the shallow seismicity in question is tentatively explained as being due to lateral compression by magma inside a nearly north south system the volcano deflation phase revealed by electronic distance measurements and tilt data during the 1991 1993 major eruption was not accompanied by any significant shear type shallow event below the depth of 10 km the north south prevailing orientation of 1 reflects the dominant role of the regional stress

response to the comment by w h schwarz et al on joint determination of 40k decay constants and 40ar 40k for the fish canyon sanidine standard and improved accuracy for 40ar 39ar geochronology by p r renne et al 2010

upwards migration of seismic focii a forerunner of the 1989 eruption of mt etna italy data from a portable array of three component digital stations run at mt etna from 1988 to early 1990 highlight the seismic behaviour of the volcano before the 1989 eruption one of the most significant in terms of energy of the last two decades after a two year period of weak and discotinuous seismicity the depth of the seismically active volumes was observed to become shallower a few months before the volcanic event the overall migration of the events inferred by hypocentral locations and decreases of s p time differences at two stations agrees with other geophysical forerunners and allows further insights into the changes in the stress field leading to the eruption

dynamics of mount etna volcano inferred from static and kinematic gps measurements 1 ground deformations measured on mount etna from late 1995 to mid 1998 using gps observations are analyzed four gps surveys were carried out during the considered period in 1995 the gps network consisted of 18 stations on the volcanic edifice and 6 stations around it during the 1996 survey 22 new monuments were added along a n s profile crossing the summit craters area this profile was surveyed by a semikinematic method allowing greater spatial detail to be achieved on the uppermost part of the volcano the comparisons between the gps surveys are reported here in terms of horizontal and vertical displacements for each station and also in terms of areal dilatation and strain distribution this last parameter continues its ascending trend at a rate of 5 strain yr 1 already shown in the previous period after the end of the 1991 1993 flank eruption inversion of the ground deformation patterns permits investigation of the evolution of both the position and dynamics of magma reservoirs beneath the volcano consistently associated with a general eastward sliding of its eastern sector this study allows us to define the nonuniqueness of ground deformation sources through the investigated period suggesting that the plumbing system of the volcano is made up of a complex system of single intrusions occurring at different times

global patterns in opal deposition from late cretaceous to late miocene biogenic silica accumulation rates were calculated at deep sea drilling project dsdp sites from legs 1 44 and were plotted on global reconstructions at seven 10 m y intervals these data were then contoured because of the correlation between opaline sediments and upwelling these maps may be used to trace paleocirculation patterns through time they demonstrate a gradual transition from the cretaceous circum global equatorial current to the modern circum antarctic divergence as tethys closed and australia and south america separated from antarctica modern bottom water circulation tends to concentrate opaline sediments in the pacific and carbonate sediments in the atlantic basinal opal fluxes were measured for each interval and in combination with carbonate compensation depth ccd histories reveal four lagoonal versus estuarine exchange reversals from the late cretaceous to the present these reversals can be directly related to the development of new bottom water sources with changing climatic and tectonic conditions

magma ascent and the pressurization of mount etna s volcanic system after a period of deflation during the 1991 1993 flank eruption mount etna underwent a rapid inflation seismicity and ground deformation show that since 1994 a huge volume of magma intruded beneath the volcano producing from 1998 onward a series of eruptions at the summit and on the flank of the volcano the last of these started on 27 october 2002 is still in progress and can be considered one of the most explosive eruptions of the volcano in recent times here we show how geodetic data and seismic deformation between 1994 and 2001 indicate a radial compression around an axial intrusion consistent with a repressurization of mount etna s plumbing system at a depth of 6 to 15 kilometers which triggered most of the seismicity and provoked the dilatation of the volcano and the recent explosive eruptive activity

subduction like fluids in the genesis of mt etna magmas evidence from boron isotopes and fluid mobile elements abstract new whole rock b sr nd isotope ratios and 87sr 86sr on clinopyroxenes have been collected to study the enrichment of fluid mobile elements fmes observed in mt etna volcanics etna volcano one of the most active in the world is located in an extremely complex tectonic context at the boundary between colliding african and european plates the analytical work focuses on current 1974 1998 and historic 1851 1971 eruptive activity including some key prehistoric lavas in order to interpret the secular shift of its geochemical signature to more alkaline compositions boron is used as a tool to unravel the role of fluids in the genesis of magmas revealing far reaching consequences beyond the case study of mt etna small variations are observed in 11b 3 5 to 8 0 87sr 86sr 0 70323 0 70370 and 143nd 144nd 0 51293 0 51287 moreover temporal evolution to higher 11b and 87sr 86sr and to lower 143nd 144nd is observed in the current activity defining a regular trend sr isotopic equilibrium between whole rock and clinopyroxene pairs indicates the successive introduction of three distinct magma types into the etna plumbing system over time these are characterized by differing degrees of fme enrichment in addition certain lavas exhibit evidence for country rock assimilation magma fluid interaction or magma mixing in the shallow feeding system at times these processes apparently lowered magmatic 11b and or induced sr isotopic disequilibrium between whole rock and clinopyroxene the regular increase of 11b values is correlated with nb fme and 87sr 86sr ratios these correlations are consistent with simple mixing between the mantle source and aqueous fluids derived from nearby ionian slab the best fit of mt etna data is obtained using an enriched morb mantle source and a fluid phase with 11b of about 2 and 87sr 86sr of 0 708 we argue that the slab window generated by differential roll back of subducting ionian lithosphere with respect to sicily allows the upwelling of asthenosphere from below the subduction system and provides a suitable path of rise for subduction related fluids the increasing geochemical signature of fluid mobile elements enrichment to mt etna lavas is considered a consequence of the progressive opening of slab window through time

mt etna volcano modelling of ground deformation patterns of recent eruptions and considerations on the associated precursors abstract the study of the ground deformation associated with the recent eruptions of the etna volcano 1981 1989 1991 93 furnished the opportunity to observe different behaviour relating to the eruptive activity and suggested different feeding and penetration mechanisms inside the volcano edifice in particular the analytical modelling of geodetic data was applied to study the strain sources of these eruptions by the application of single and multiple source models i e composed of two single sources in particular a single tensile dislocation was used to model the se fracture associated with the 1989 eruption a double tensile dislocation was adopted to interpret and model the deformation pattern of the 1981 eruption a double source composed of a tensile dislocation for the final eruptive fracture and a depressuring body for the deflation during the eruption course was considered for the 1991 93 eruption the results of this modelling show that however the final uprising system i e the tensile mechanisms inside the volcano edifice involved the same structure oriented approximately nnw sse this structure was activated by different eruption mechanisms with associated different deformation patterns during these three recent eruptions a review of the methodologies applied and main results obtained in modelling of different sources and mechanisms is presented here the analysis of the deformation data and the performed modelling evidence that the associated precursors can strongly change for the different eruptions in addition the implications both in terms of how the volcano works and in terms of ground deformation precursors are discussed

the role of supercritical fluids in the potassium enrichment of magmas at mount etna volcano italy abstract the enrichment in potassium shown by the basic lavas erupted at mount etna volcano after 1971 k2o max 2 2 wt has been considered by previous researchers to be too high to be related to simple crystal fractionation and instead linked this high k2o content to either crustal assimilation or changes in the magma source unfortunately all existing models for the post 1971 k2o enrichment fail to explain the phenomenon satisfactorily leaving the question still open we present a critical re examination of published data for major elements 633 whole rock analyses trace elements 376 whole rock analyses and isotopic ratios 136 87sr 86sr analyses for historical and pre historical lavas potassium enrichment is not limited to the products of the last 35 years a comparable increase in potassium is noticed in lavas erupted during the pre historic phase of the recent mongibello k2o max 2 5 wt and in lavas related to the early phase of the ancient mongibello k2o max 3 wt moreover data from melt inclusions in olivines from the 2001 and 2002 eruptions reveal that potassium contents remain constant for melts with entrapment pressure between 490 to 100 mpa and increase significantly in melts entrapped at pressures below 100 mpa we propose that supercritical fluids coming from deeper magmas and carrying alkali cl complexes migrate through basic to intermediate magmas residing in the shallow feeding system as chlorine exsolves and leaves the system alkalis are released contributing to the observed potassium enrichment of the shallow magma fluctuations of the volatiles influx throughout time are likely related to the magma supply rate considering that the amount of magma entering a plumbing system is determined by the rate of regional extension the flux of alkali cl complexes entering the melt might be related to an extensional regime acting in the etnean area

magma mixing during the 2001 event at mount etna italy effects on the eruptive dynamics abstract during the 2001 eruptive episode three different magmas were erupted on the southern flank of mount etna volcano from distinct vent systems major and minor element chemistry of rocks and minerals shows that mixing occurred and that the mixed magma was erupted during the last eruptive phases the space time integrated analysis of the eruption supported by geophysical data together with major and trace element bulk chemistry xrf icp ms and major and trace mineral chemistry epma lam icp ms support the following model 1 trachybasaltic magma rises through a nnw sse trending structure connected to the main open conduit system 2 ascent of an amphibole bearing trachybasaltic magma from a 6 km deep eccentric reservoir through newly open n s trending fractures 3 just a few days following the eruption onset the two tectonic systems intersect at the laghetto area 4 at the laghetto vent a mixed magma is erupted mixing occurred between the amphibole bearing trachybasaltic magma and an inferred deep more basic end member the most relevant aspect in the eruptive dynamics is that the eruption of the mixed magma at the laghetto vent was highly explosive due to volatile content in the magma the gas phase formed mainly because of the decreased volatile solubility due to rapid fractures opening and increased t related to mixing and partially because of the amphibole breakdown

buoyancy controlled eruption of magmas at mt etna buoyancy controls the ability of magma to rise its ascent rate and the style of the eruptions geophysical geological and petrological data have been integrated to evaluate the buoyancy of magmas at mt etna the density difference between host rocks and magmas is mainly related to the amount of h2o dissolved in the magma and to the bubble liquid separation processes in the depth interval 22 2 km b s l highly hydrated h2o 3 basaltic magmas or mixtures of bubbles liquid have positive buoyancy and rise rapidly conversely bubble depleted liquids with an intermediate h2o content 1 5 having neutral buoyancy will spread out and form magmatic reservoirs at different depths until cooling crystallization further modify composition and density these different processes account for the magma compositions location of magmatic reservoirs as determined by geophysical methods and the complex eruptive cycles slow effusions fire fountains and plinian eruptions that have been observed in the history of the volcano