combined discrete and continuous gravity observations at mount etna systematic investigation of discrete gravity measurements has continued at mount etna since 1986 the network now covers an area of 400 km2 with about 70 stations 0 5 3 km apart mass redistributions occurring at depths ranging between about 8 km below sea level and a few hundred metres below the surface magma level changes within the shallower parts of the feeding conduits have been identified from these data conventional discrete microgravity monitoring on a network of stations furnishes only instantaneous states of the mass distribution at continuously active systems in order to obtain information on the rate at which the volcanic processes and thus mass transfers occur three stations for continuously recording gravity where installed on mount etna in 1998 a 16 month long sequence from one of the continuously running stations pdn located 2 km from the active northeast crater at the summit of etna volcano is presented after removing the effects of earth tide and tilt the correlation of the residual gravity sequence with simultaneous recordings of meteorological parameters acquired at the same station was analysed once the meteorological effects have also been removed continuous gravity changes are within 10 gal of gravity changes measured using conventional microgravity observations at sites very close to the continuous station this example shows how discrete and continuous gravity observations can be used together at active volcanoes to get a fuller and more accurate picture of the spatial and temporal characteristics of volcanic processes

monitoring ash emission episodes at mt etna the 16 november 2006 case study abstract mt etna in sicily italy is one of the best monitored basaltic volcanoes in the world due to the frequent eruptions from its summit and flanks routine monitoring carried out by istituto nazionale di geofisica e vulcanologia sezione di catania for surveillance purposes permits following the evolution of volcanic events in this paper a description of the ash monitoring system as occurred during the august december 2006 summit eruption at the southeast crater sec is shown this eruption was characterized by lava flow effusions and vigorous strombolian activity eighteen paroxysmal episodes occurred up to the end of november forming weak ash plumes accompanied by moderate tephra fallout over etna s slopes during these events we applied a multidisciplinary approach to promptly monitor the paroxysmal activity and the associated tephra fallout through analysis from seismic tremor and observation from live cameras sampling operations mapping and analysis of the deposit during the most significant episodes we carried out textural and grain size analysis on tephra samples and evaluated the total grain size deposit and the erupted volume while numerical simulations of tephra dispersal allowed better understanding eruptive dynamics an example of this methodology is applied to the 16 november episode during which seismic tremor furnished important constraints on the chronology this paroxysmal eruption produced light fallout on the north east sector of the volcano for about ten hours and a number of debris avalanches over the slopes of the sec cone the erupted deposit was composed for the most part of lithic components and characterized by a total size distribution centered on 2 2 while its total mass was evaluated 7 10 6 kg on the whole such integrated studies help to obtain information on magma fragmentation and eruptive mechanisms to characterize the explosive styles shown by etna and finally to better approach the monitoring of imminent eruptions

time resolved seismic tomography detects magma intrusions at mount etna the continuous volcanic and seismic activity at mount etna makes this volcano an important laboratory for seismological and geophysical studies we used repeated three dimensional tomography to detect variations in elastic parameters during different volcanic cycles before and during the october 2002 january 2003 flank eruption well defined anomalous low p to s wave velocity ratio volumes were revealed absent during the pre eruptive period the anomalies trace the intrusion of volatile rich 4 weight percent basaltic magma most of which rose up only a few months before the onset of eruption the observed time changes of velocity anomalies suggest that four dimensional tomography provides a basis for more efficient volcano monitoring and short and midterm eruption forecasting of explosive activity

silicic volcanism at an off axis geothermal field in the mariana trough back arc basin an abyssal hill site with localized high heat flow on the 3 m y old west flank of the active ridge in the mariana trough has sets of oblique fault scarps mapped by multi beam transits and clusters of 50 to 1 000 m diameter domes examined with a deep tow survey some of the domes including small 20 to 30 m high rocky knobs encrusted with manganese oxide crop out through the sediment cover but despite heat flow evidence that they are sites of hydrothermal discharge these bedrock features are fundamentally different from the hydrothermal mounds found on some mid ocean ridges dredging one dome recovered a rhyodacite pumice that we believe erupted at a depth of 2 600 3 600 m within the basin the siliceous rock may be an extreme differentiate of a tholeiitic magma but a more likely origin is partial melting of the basin s sedimentary fill

the 16 november 2006 flank collapse of the south east crater at mount etna italy study of the deposit and hazard assessment 1 on 16 november 2006 a flank collapse affected the unstable eastern slope of the south east crater sec of mount etna the collapse occurred during one of the paroxysmal events with sustained strombolian activity that characterized the august december 2006 eruption and was triggered by erosion of loose hydrothermally altered material of the steep south east sector of sec from the outpour of lava the collapse produced a debris avalanche that involved both lithic and juvenile material and resulted in a deposit emplaced on the eastern flank of the volcano up to 1 2 km away from the source the total volume of the deposit was estimated to be in the order of 330 000 413 000 m3 the reconstruction of the collapse event was simulated using titan2d software designed to model granular avalanches and landslides this approach can be used to estimate areas that may be affected by similar collapse events in the future the area affected by the 16 november 2006 lateral collapse of sec was a small portion of the mount etna summit area but the fact that no one was killed or injured should be considered fortuitous the summit and adjacent areas of the volcano in fact are usually visited by many tourists who are not prepared to face this type of danger the 16 november 2006 collapse points to the need to be prepared for similar events through scientific investigation analysis of flank instability numerical simulation of flows and development of specific civil protection plans

petrology of the axial ridge of the mariana trough backarc spreading center abstract the axial ridge of the mariana trough backarc basin between 17 40 n and 18 30 n rises as much as 1 km above the floor of a 10 15 km wide rift valley physiographic segmentation with minor ridge offsets and overlaps coincides with a petrologic segmentation seen in trace element and isotope chemistry analyses of 239 glass and 40 aphyric basalt samples collected with alvin and by dredging show that the axial ridge is formed largely of olivine hypersthene normative tholeiitic basalt about half of these are enriched in both lil elements and volatiles but are depleted in hfs elements like other rocks found throughout much of the mariana trough the lil enrichments distinguish these rocks from n morb even though nd and sr isotope ratios indicate that much of the crust formed from a source similar to that for n morb in addition to lil enriched basalt there is lil depleted basalts even more closely resembling n morb in major and trace elements as well as sr nd and pb isotopes both basalt varieties have higher al and lower total fe than morb at equivalent mg level mg ranges from relatively primitive e g mg 65 70 to more highly fractionated e g mg 45 50 highest parts of the axial ridge are capped by pinnacles with elongated pillows of basaltic andesite e g 52 56 sio 2 these are due to extreme fractional crystallization of basalts forming the axial ridge active hydrothermal vents with chimneys and mats of opaline silica barite sphalerite and lesser amounts of pyrite chalcopyrite and galena formed near these silicic rocks the vents are surrounded by distinctive vent animals polychaete worms crabs and barnacles isotope data indicate that the mariana trough crust was derived from a heterogeneous source including mantle resembling the morb source and an arc source component the latter was depleted in hfs elements in previous melting events and later modified by addition of h 2 o and lil elements

volcanic tremor at mt etna italy preceding and accompanying the eruption of july august 2001 the july 17 august 9 2001 flank eruption of mt etna was preceded and accompanied by remarkable changes in volcanic tremor based on the records of stations belonging to the permanent seismic network deployed on the volcano we analyze amplitude and frequency content of the seismic signal we find considerable changes in the volcanic tremor which mark the transition to different styles of eruptive activity e g lava fountains phreatomagmatic activity strombolian explosions in particular the frequency content of the signal decreases from 5 hz to 3 hz at our reference station etf during episodes of lava fountains and further decreases at about 2 hz throughout phases of intense lava emission the frequency content and the ratios of the signal amplitude allow us to distinguish three seismic sources i e the peripheral dike which fed the eruption the reservoir which fed the lava fountains and the central conduit based on the analysis of the amplitude decay of the signal we highlight the migration of the dike from a depth of ca 5 km to about 1 km between july 10 and 12 after the onset of the effusive phase the distribution of the amplitude decay at our stations can be interpreted as the overall result of sources located within the first half kilometer from the surface although on a qualitative basis our findings shed some light on the complex feeding system of mt etna and integrate other volcanological and geophysical studies which tackle the problem of magma replenishment for the july august 2001 flank eruption we conclude that volcanic tremor is fundamental in monitoring mt etna not only as a marker of the different sources which act within the volcano edifice but also of the diverse styles of eruptive activity

paroxysmal summit activity at mt etna italy monitored through continuous soil radon measurements 1 soil radon emissions have been proved as a useful tool for predicting earthquakes and volcanic eruptions and furthermore aided in determining the location of active faults continuous radon monitoring was carried out near southeast crater of mt etna in september november 1998 during a period of frequent eruptive episodes at that crater radon anomalies were detected when eruptive episodes and the accompanying volcanic tremor became increasingly intense no anomalies in radon activity were observed during the first five and weaker eruptive episodes whereas significant spikes in radon activity preceded the latter five episodes by 46 hours this probably reflects increased gas leakage through fractures intersecting the shallow plumbing system as gas pressure in the southeast crater conduit became higher with time radon monitoring thus might serve to better understand eruptive mechanisms and possible precursors making further studies in this field a promising perspective

unzipping of the volcano arc japan abstract a working hypothesis for the recent evolution of the southern volcano arc japan is presented which calls upon a northward progressing sundering of the arc in response to a northward propagating back arc basin extensional regime this model appears to explain several localized and recent changes in the tectonic and magrnatic evolution of the volcano arc most important among these changes is the unusual composition of iwo jima volcanic rocks this contrasts with normal arc tholeiites typical of the rest of the izu volcano mariana and other primitive arcs in having alkaline tendencies high concentrations of light ree and other incompatible elements and relatively high silica contents in spite of such fractionated characteristics these lavas appear to be very early manifestations of a new volcanic and tectonic cycle in the southern volcano arc these alkaline characteristics and indications of strong regional uplift are consistent with the recent development of an early stage of inter arc basin rifting in the southern volcano arc new bathymetric data are presented in support of this model which indicate 1 1 structural elements of the mariana trough extend north to the southern volcano arc 2 2 both the mariana trough and frontal arc shoal rapidly northwards as the volcano arc is approached 3 3 rugged bathymetry associated with the rifted mariana trough is replaced just south of iwo jima by the development of a huge dome 50 75 km diameter centered around iwo jima such uplifted domes are the immediate precursors of rifts in other environments and it appears that a similar situation may now exist in the southern volcano arc the present distribution of unrifted volcano arc to the north and rifted mariana arc to the south is interpreted not as a stable tectonic configuration but as representing a tectonic snapshot of an arc in the process of being rifted to form a back arc basin

petrology of mariana trough and lau basin basalts the crust of actively opening back arc basins has close chemical and mineralogic similarities to normal mid ocean ridge basalts n morb but some subtle but distinctive differences exist these are largely due to differences in volatiles fe oxidation ratio abundances of large ion lithophile elements lil and some high field strength hfs elements isotope data for sr pb nd he and o are variable but broadly are morb like we present data contrasting mariana trough mtb and lau basin basalts lbb showing how they differ in certain trace element and isotopic signatures and compare both to n morb relative to n morb and lbb the mtb are enriched in alkalis alkaline earths light rare earth elements ree h2o and fe fe even for primitive samples while having morb type he 3 4 7 8 to 8 4 ra sr 87 86 mean 0 70293 and nd e 10 2 the lau basin is zoned with a central area having n morb characteristics for h2o lil ree nd e 8 1 to 9 0 and o but a depletion in hfs elements sr is more radiogenic mean 87 86 0 70347 and 3he 4he 3 4 7 2 to 11 0 ra is high relative to n morb the lau basin has a zone bordering the adjacent island arcs which is like mtb in both back arc basins relatively primitive unfractionated basalts with mg 100 mg fe 62 are found which resemble postulated primitive n morb calculated parental magmas obtained by adding xenocrystic olivine plot near or on 3 and 4 phase boundaries at 1 1 5 gpa for the ol di si system low p fractional crystallization and magma mixing explain most of the observed rock types possible explanations for differences between mtb and lbb include differences in the extent of previous melting episodes of their mantle sources and effects of source metasomatism through dehydration and partial melting of subducted lithosphere the long and complex history of mariana trough mantle sources led to a metasomatized mantle which gives rise to the distinctive mtb in contrast the lau basin is dominated by basalts derived from a source depleted in volatiles lil and hfs elements a previous melting history is implied mixing with a mantle component enriched in 87sr and 3he may be due to mantle counterflow driven by the subduction process

eruption dynamics and tephra dispersal from the 24 november 2006 paroxysm at south east crater mt etna italy abstract between 30 august and 15 december 2006 mt etna italy underwent both effusive and explosive activity which took place from the south east crater one of its summit craters several paroxysmal episodes followed in succession separated by a few days of minor activity and characterised by dissimilar explosive style and intensity here we report one of the most studied and powerful episodes which started early in the morning on 24 november 2006 and lasted about 13 h excellent weather conditions enabled reconstructing in detail the onset and evolution of the eruptive phenomena both by live camera recordings and direct observations the explosive activity consisted of powerful strombolian activity alternating with short periods of lava fountains a weak volcanic plume rose up to 2 km above the volcanic vent followed by tephra fallout which covered the se and s flanks of etna campaigns allowed collecting about 40 tephra samples and mapping the fallout deposit the clockwise shifting of the volcanic plume during the eruption caused the different timing of the fallout on the ground thus widening the dispersal area voronoi s method was used to evaluate i the total grain size distribution indicating that the fallout deposit peaked at 1 and for the first time at etna ii the total componentry distribution finding that most of the particles were lithics with a low proportion of juvenile vs lithics 34 65 the total erupted mass was estimated 1 9 108 kg corresponding to a mass eruption rate of 5 103 kg s 1 physical parameters and textural features of the erupted products suggest that the 24 november 2006 explosive event may be classified as small sized in the recent history of etna and that the eruptive dynamic was mainly governed by magma gas decoupling which produced relatively fine grained fallout deposits containing unusual elongated sideromelane ash particles

geochemical monitoring system ii prototype gms ii installation at the acqua difesa well within the etna region first data during the 1999 volcanic crisis abstract the geochemical monitoring system ii gms ii prototype was designed assembled tested and installed at the acqua difesa test site near belpasso ct within the etna region in the frame of an ec funded program named automatic geochemical monitoring of volcanoes the easily changeable and versatile configuration of the remote station provides actual data every 10 min recording groundwater temperature electrical conductivity ph redox potential dissolved co 2 he atmospheric pressure and air temperature the radon sensor was assembled despite no jet added to the remote station an automatic sampler collects every 72 h 3 days two bottles of water acidified and not for further laboratory analyses the choice of the acqua difesa test site arises from preliminary volcanological studies deserving special interest i e for the high co 2 degassing for the high he isotopic values exhibiting a direct mantle signature of the volcanic gases and for the peculiar sensitivity to volcanic activity as tested by discrete monitoring in the past and confirmed by the present study during the discussed monitoring period october 1998 june 1999 an enhanced volcanic activity of etna was observed it started on july 1998 with enhanced plume degassing and since september 1998 with periodical lava fountains as well as with episodic low energy earthquakes and seismic swarms m max 3 1 till june 1999 the activity culminated with a summit crater fracture involving a sub terminal eruption on 04 02 1999 the summit crater fracture was not accompanied by enhanced seismicity despite moderate seismic energy release occurring in the succeeding months in that monitoring period the acqua difesa gms ii station recorded a few geochemical anomalies mostly in temperature ph co 2 electrical conductivity and eh as well as in the concentration of some major elements trend mostly in mg and hco 3 the geochemical continuous and discrete data set is discussed in comparison with the available information on the ongoing volcanic and seismic activity tentatively enhancing the comprehension of the aquifers mass heat transport properties of the volcano during crises the experimental observations may be defined at present the forerunners of the etna eruptions affecting the single out acqua difesa well it is nowadays a self consistent site with its own response to the pre eruptive processes defined sensitive to the etna aquifer modifications induced by the volcanic activity in a recurrent way thus we defined the typical answer of this specific test site to the pre eruptive processes and to the associated seismicity further data may modify this statement the station prototype configuration and the results may give hints for future volcanic eruption and seismic activity forecasting

three dimensional volcanic aerosol dispersal a comparison between multiangle imaging spectroradiometer misr data and numerical simulations 1 the three dimensional reconstruction of volcanic plumes is a central goal to enhance our understanding on dispersal processes in this paper we use data from the multiangle imaging spectroradiometer misr on board nasa s terra spacecraft combined with a stereo matching retrieval procedure we show the potential of misr in capturing important features of volcanic plumes like column height optical depth type and shape of the finest particles of two highly explosive eruptions occurring on mount etna in 2001 and 2002 this work tests how tephra dispersal models reconstruct the 3 d shape of volcanic clouds we compare misr data with fall3d an eulerian model for the transport and deposition of volcanic ash and aerosols coupled with the weather research and forecasting mesoscale meteorological model agreement between simulations and misr data is good regarding both events although it could be improved by increasing the accuracy of the meteorological data a better constraint on volcanological input parameters like the height of the eruptive column and improving our understanding of processes such as aggregation phenomena and volcanic cloud microphysics

petrologic consequences of rift propagation on oceanic spreading ridges abstract the production of anomalously differentiated lava compositions at several mid ocean spreading centers can be attributed to magmatic processes associated with propagating rifts the degree of differentiation attained by magmas beneath oceanic spreading ridges depends mainly on the balance between cooling rate and the supply rate of new magma to shallow chambers low supply rates and moderate cooling rates allow advanced degrees of closed system fractionation to occur high supply rates result in open systems in which magma compositions are buffered by frequent replenishment with new hot magma propagating rift tips are a special class of ridge transform intersection in which the balance between cooling and supply rates is conducive to the development of advanced degrees of differentiation over an expanded length of ridge this balance is affected by the spreading rate the propagation rate of the rift the length of the bounding transform and proximity to hotspots maximum compositional variability and maximum degree of differentiation occur within 50 km of propagating rift tips and subsequently diminish with increasing distance rifts that propagate through plates in directions approximating their absolute motion relative to the lower mantle are characterized by the presence of anomalously differentiated lavas over longer ridge segments than are rifts that propagate against their absolute motion geochemical anomalies may persist though changing in degree and extent for several million years on ridge segments that stop propagating the concept of magnetic telechemistry is generally supported by our study but in the vicinity of hotspots magnetic anomaly amplitude may be controlled more by bathymetric and or thickened magnetic layer effects than by geochemistry

shoshonitic magmas in nascent arcs new evidence from submarine volcanoes in the northern marianas volcanoes in the northern mariana arc between uracas lat 20 n and minami iwo jima 24 n are very active yet entirely submarine in contrast to the predominantly low k basaltic magmas of the central mariana arc the northern mariana arc is dominated by more siliceous melts in the south and by shoshonites in the north the northern arc melts have enrichments in ba 800 ppm rb 70 ppm sr 1000 ppm ce 50 ppm and ce yb n 24 which increase to the north as far as iwo jima lavas from volcanoes north of iwo jima lack these enrichments and are indistinguishable from those of the central maranas the shoshonites are unusual in occurring along the magmatic front of a primitive intra oceanic arc we hypothesize that they represent the reconstruction of a magmatic arc following melting of enriched mantle due to the propagation of the mariana trough spreading center northward through the volcano arc shoshonites thus may characterize the initial stages of arc construction after an episode of back arc rifting and need not be restricted to the mature stages of arc evolution this situation contrasts with subduction zone initiation where first melts may be boninites or low k tholeiites these differing initial melts converge toward tholeiitic and calc alkaline compositions as arcs evolve

role of ridge jumps and ridge propagation in the tectonic evolution of the lau back arc basin southwest pacific gloria sidescan imagery of the central lau basin reveals a complex neotectonic framework in which the central lau spreading center is actively propagating southward at the expense of the eastern lau spreading center the latter is located about 75 km closer to the active tofua arc and the transfer of spreading motion across this distance is achieved via a relay spreading ridge segment new magnetic and bathymetric interpretations suggest that the majority of the central and southern basin was formed by the eastern lau spreading center between 5 ma and the present day the processes of arcward ridge migration ridge propagation and basinward arc migration may reflect the complex interplay of the subduction zone and regional tectonics in driving back arc spreading and may be a common feature of this tectonic environment

modeling tephra sedimentation from a ruapehu weak plume eruption 1 we present a two dimensional model for sedimentation of well mixed weak plumes accounting for lateral spreading of the cloud downwind advection increase of volumetric flux in the rising stage and particle transport during fallout the 17 june 1996 subplinian eruption of ruapehu produced a bent over plume that rose to a height of 8 5 km in a wind field with an average velocity of 24 m s 1 and generated a narrow deposit on land extending up to 200 km from vent the sedimentation from the ruapehu plume was dominated by coarse ash with all the blocks and most of the lapilli falling while the plume was still rising particles with diameter 125 m show three accumulation maxima one coincident with a secondary maximum in the total tephra deposit about 150 km from the vent numerical modeling shows that the plume started spreading horizontally beyond about 30 km from vent investigations also show that fickian diffusion can be a good approximation to the crosswind spreading of both vigorous and low energy weak plumes but a wide range of diffusion coefficients is to be expected with the largest values necessary to describe the most vigorous weak plumes such as ruapehu one dimensional and two dimensional simulations show that tephra sedimentation must have been subvertical this feature also supported by direct observations can be the result of the turbulence structure of the local wind field and convective instabilities which could also have played an important role in the generation of the pronounced sinuosity shown by the ruapehu deposit

new insights into magma dynamics during last two eruptions of mount etna as inferred by geochemical monitoring from 2002 to 2005 two distinct eruptive events characterize the volcanic activity at mount etna during the 2002 to 2005 period we identified signals of magma ascent preceding these eruptions by geochemical monitoring of both chemical composition and he isotope ratio of gas emissions from five locations in the peripheral area of the volcano the geochemical signals are interpreted using the models proposed by caracausi et al 2003a 2003b and allow identification of episodes of magma ascent and estimation of the pressures of degassing magma as observed for the 2001 eruption caracausi et al 2003b magma ascent probably triggered the onset of the 2002 2003 eruption and minor events of magma ascent were observed between may and december 2003 in contrast to the previous two eruptions the 2004 2005 eruption was not preceded by significant geochemical signals of volcanic unrest suggesting that this eruption was mainly triggered by the failure of the upper portion of the volcanic edifice under the magmatic hydrostatic pressure in the conduits high 3he 4he ratio revealed new volatile rich magma accumulation the 2002 2003 eruption was preceded by a much shorter period of new magma accumulation from deep levels of the feeding system few minor signals of magma migration were detected at some of the sites during the months preceding the 2004 2005 eruption suggesting that the degassed 3he depleted magma resident in the volcanic conduits was not replaced by new volatile rich magma this is in agreement with the lack of explosive activity during the 2004 2005 eruption and with petrologic observations that the parent magma probably erupted in 2000 and 2001 new geochemical signals of magma ascent from the deep reservoir have been identified since june 2005 indicating that the volcanic activity of mount etna is evolving toward new pre eruptive conditions

a statistical approach to evaluate the tephra deposit and ash concentration from puff model forecasts abstract in this paper we present a new statistical approach which provides tephra deposit load and ash concentration using puff a lagrangian model widely used to forecast volcanic ash dispersal during volcanic crisis we perform a parametric study in order to analyze the influence of each input parameter on model outputs for this test we simulate two eruptive scenarios similar to the 2001 scenario 1 and 1998 scenario 2 etna eruptions using high resolution weather data and a domain of 170 170 km results show that for both scenarios we are able to calculate the tephra deposit load and ash concentration but the use of millions of particles is required specifically up to 33 and 220 millions of particles were necessary to accurately predict the tephra deposit and ash concentration in air respectively this is approximately two orders of magnitude larger than the values typically considered running puff the parametric study shows that the horizontal diffusion coefficient the time step of the simulations the topography and the standard deviation of the particle distribution greatly affect the model outputs we also validate the model by best fit procedures results show a good comparison between field data of the 2001 etna eruption and puff simulations being inside 5 and 1 5 times the observed data comparable with results of eulerian models this work will allow to reliably outline the areas of contaminated airspace using puff or any other lagrangian model in order to define the no fly zone and ensure the safety aviation operations as required after the eyjafjallajokull eruption

geophysical characteristics of the southern mariana trough 11 50 n 13 40 n despite slow opening rates generally inferred for the mariana trough the southernmost part of the basin has fast spreading geophysical and morphologic characteristics that are unlike the features of the basin to the north a side scan sonar and geophysical survey maps the eastern part of the basin and the seafloor spreading center between 11 50 n and 13 40 n and identifies the following characteristics the ridge across axis profile forms a triangular to rounded high with relief of 100 to 500 m and cross sectional area variations of 1 to 7 km2 the along axis mantle bouguer gravity gradient is 0 2 mgal km axial segmentation occurs as overlapping axes and small deviation in trend no transform fault offsets exist despite significant changes in the trend of the spreading center characteristics of the surrounding basin include shallower overall depth than in the north no well developed frontal arc high in the southernmost trough the close proximity of submarine arc type volcanoes to the spreading center and tectonic fabric that is at a high angle to the trend of the spreading center on the eastern flank but is concordant on the western flank these characteristics imply different tectonic and magmatic conditions in the southern trough from the rest of the basin we propose that these effects are related to 1 the geometry of trench rollback in the southern trough leading to trench parallel extension generating inward radiating extensional faults 2 decoupling of the trench parallel extensional strain by the spreading center so that it primarily affects the eastern flank of the basin and 3 augmentation of the spreading center s magmatic budget by arc magmatic sources contributing to its fast spreading character although these effects may be accentuated in the southern mariana trough by the geometry of trench rollback and position of the slab which here underlies the spreading center they reflect distinct volcanic and tectonic processes which are varyingly expressed in back arc systems but are not normally found at mid ocean ridges

the gas content and buoyancy of strombolian ash plumes plinian plumes erupt with a bulk density greater than that of air and depend upon air entrainment during their gas thrust phase to become buoyant if entrainment is insufficient the column collapses into a potentially deadly pyroclastic flow this study shows that strombolian ash plumes can be erupted in an initially buoyant state due to their extremely high initial gas content and in such cases are thus impervious to column collapse the high gas content is a consequence of decoupled gas rise in the conduit in which particles are ultimately incidental the relations between conduit gas flow eruption style and plume density are explored here for strombolian scenarios and contrasted with conventional wisdom derived from plinian eruptions considering the inherent relation between gas content and initial plume density together with detailed measurements of plume velocities can help unravel ambiguities surrounding conduit processes eruption styles and hazards at poorly understood volcanoes analysis of plume dynamics at santiaguito volcano guatemala adds further support for a model involving decoupled gas rise in the conduit

mt etna sulfur dioxide flux monitoring using aster tir data and atmospheric observations this work is aimed at estimating the sulfur dioxide emission of mt etna volcano sicily italy using the thermal infrared images remotely sensed by the advanced spaceborne thermal emission and reflection radiometer aster a new procedure named fun is presented based on approximating functions which represent the atmospheric terms of the radiative transfer equation transmittance up welling and down welling radiances the parameters of the approximating functions have been computed through the modtran simulations performed using atmospheric monthly mean profiles measured at trapani 1989 2003 trapani wmo station 16429 is located at the western tip of sicily and is the closest station to mt etna volcano with these functions modtran is no longer necessary to compute the so2 abundance in the plume emitted from mt etna and seen by aster only an atmospheric radiosounding and a digital elevation model dem registered to the aster image are required this new procedure is compared with the known look up tables lut procedure proposed by other authors an interesting aspect of the fun procedure derives from its combined use with a split window sw algorithm in this case only radiosounding is required to compute the so2 map the fun procedure presented in this paper is a rapid simple and accurate means of generating so2 map estimates from the aster view of mt etna the proposed scheme can easily be adapted to another sensor and another volcano in this paper the results from two aster images 19 july 2003 and 29 july 2001 are presented in

shifting styles of basaltic explosive activity during the 2002 03 eruption of mt etna italy abstract the 2002 03 flank eruption of etna was characterized by two months of explosive activity that produced copious ash fallout constituting a major source of hazard and damage over all eastern sicily most of the tephra were erupted from vents at 2750 and 2800 m elevation on the s flank of the volcano where different eruptive styles alternated the dominant style of explosive activity consisted of discrete to pulsing magma jets mounted by wide ash plumes which we refer to as ash rich jets and plumes similarly ash rich explosive activity was also briefly observed during the 2001 flank eruption of etna but is otherwise fairly uncommon in the recent history of etna here we describe the features of the 2002 03 explosive activity and compare it with the 2001 eruption in order to characterize ash rich jets and plumes and their transition with other eruptive styles including strombolian and ash explosions mainly through chemical componentry and morphology investigations of erupted ash past models explain the transition between different styles of basaltic explosive activity only in terms of flow conditions of gas and liquid our findings suggest that the abundant presence of a solid phase microlites may also control vent degassing and consequent magma fragmentation and eruptive style in fact in contrast with the strombolian or hawaiian microlite poor fluidal sideromelane clasts ash rich jets and plumes produce crystal rich tachylite clasts with evidence of brittle fragmentation suggesting that high groundmass crystallinity of the very top part of the magma column may reduce bubble movement while increasing fragmentation efficiency

continuous soil radon monitoring during the july 2006 etna eruption 1 continuous soil radon monitoring was carried out near the southeast crater sec of mt etna during the 10 day july 2006 strombolian effusive eruption this signal was compared with simultaneously acquired volcanic tremor and thermal radiance data the onset of explosive activity and a lava fountaining episode were preceded by some hours with increases in radon soil emission by 4 5 orders of magnitude which we interpret as precursors minor changes in eruptive behavior did not produce significant variations in the monitored parameters the remarkably high radon concentrations we observed are unprecedented in the literature we interpret peaks in radon activity as due primarily to microfracturing of uranium bearing rock these observations suggest that radon measurements in the summit area of etna are strongly controlled by the state of stress within the volcano and demonstrate the usefulness of radon data acquisition before and during eruptions citation neri m b behncke m burton g galli s giammanco e pecora e privitera and d reitano 2006 continuous soil radon monitoring during the july 2006 etna eruption geophys res lett 33 l24316 doi 10 1029 2006gl028394

multivariate time series clustering on geophysical data recorded at mt etna from 1996 to 2003 abstract time series clustering is an important task in data analysis issues in order to extract implicit previously unknown and potentially useful information from a large collection of data finding useful similar trends in multivariate time series represents a challenge in several areas including geophysics environment research while traditional time series analysis methods deal only with univariate time series multivariate time series analysis is a more suitable approach in the field of research where different kinds of data are available moreover the conventional time series clustering techniques do not provide desired results for geophysical datasets due to the huge amount of data whose sampling rate is different according to the nature of signal in this paper a novel approach concerning geophysical multivariate time series clustering is proposed using dynamic time series segmentation and self organizing maps techniques this method allows finding coupling among trends of different geophysical data recorded from monitoring networks at mt etna spanning from 1996 to 2003 when the transition from summit eruptions to flank eruptions occurred this information can be used to carry out a more careful evaluation of the state of volcano and to define potential hazard assessment at mt etna

thermal observations of gas pistoning at kilauea volcano 1 data acquired by three continuously recording thermal infrared thermometers situated on the north rim of pu u o o crater at kilauea volcano during 2002 revealed episodes of periodic thermal pulses originating from a degassing vent on the crater floor these thermal pulses are interpreted as gas release jetting events associated with gas pistoning a mechanism observed previously at both mauna ulu and pu u o o during a 35 day long period spanning june and july 2002 gas pistoning was frequently the dominant mode of gas release with as many as several hundred pulses occurring in uninterrupted series on other days degassing alternated between periods of quasi continuous gas jetting and intervals of gas pistoning that contained a few to a few dozen pulses characteristic time intervals between pistoning events ranged from 2 up to 7 min we identify three types of pistoning type 1 involves emission of lava followed by gas jetting and drain back type 2 is the same but the elevated position of the vent does not allow postjet drain back and type 3 involves gas jetting only with no precursory lava flow to explain gas pistoning we apply a model whereby a stagnant cap of degassed magma develops in the conduit below the vent gas bubbles rise through the magma column and collect under the cap the collective buoyancy of these bubbles pushes the cap upward when the cap reaches the surface it erupts from the vent as a lava flow unloading of the conduit magma in this way results in an abrupt pressure drop i e the overburden felt by the bubbles is reduced causing explosive gas expansion in the form of gas jetting from the vent this terminates the event and lava drains back into the conduit to start the cycle anew in the case where there is no surface lava emission or drain back the cap instead pushes into and spreads out within a subsurface cavity again this unloads the conduit magma and terminates in explosive gas release once gas is expelled lava in the cavity is free to drain back we hypothesize that pistoning is a stable mode of degassing for low viscosity basaltic magmas with appropriate conduit geometries and volatile supply rates

petrology chemistry and isotopic composition of submarine volcanoes in the southern mariana arc four submarine volcanoes in the southern and central mariana arc were dredge sampled the recovered lavas were analyzed for major and trace element abundances including rare earth elements ree mineral compositions and sr and nd isotopic ratios the samples exhibit a great range of chemical and mineral compositions relative to subaerial exposures in the central arc zealandia bank produces high magnesium basalts mgo 8 9 wt enriched in ni and with forsteritic olivine as much as fo 88 this lava composition is probably parental to more fractionated basalts and basaltic andesites exposed on the adjacent islands of guguan and sarigan the southernmost seamounts in the mariana arc south of lat 15 n produce dacitic pumice a composition that is not common in the active arc ree data preclude their derivation from a basaltic parent by fractional crystallization they may be derived by direct partial mantle melting under water saturated conditions at low pressure nd and sr isotopic data 143 nd 144 nd 0 5130 0 5131 87 sr 86 sr 0 7032 0 7035 indicate a mantle source for the mariana arc lavas similar in isotopic characteristics to sources for ocean islands significant contributions to these arc magmas from subducted oceanic crust or sediment are not evident a spatial distribution in magmatic characteristics coincides with a structural break in the arc near 16 n south of this submarine seamounts produce incompatible element enriched lavas with relatively high 87 sr 86 sr 0 7034 0 7035 these lavas were produced by a relatively low degree of partial melting 5 15 of a shallow spinel bearing mantle to the north zealandia bank and the central arc islands are characterized by lower incompatible element abundances and lower 87 sr 86 sr 0 7032 0 7033 these lavas were produced by higher degrees of partial melting 15 25 of a deeper garnet bearing mantle

seamarc ii evidence for the locus of seafloor spreading in the southern mariana trough abstract two surveys near 13 45 n across the mariana trough identify the axis of backarc seafloor spreading at 143 53 e the spreading center is identified on the basis of its high acoustic backscatter in seamarc ii side scan images and by the presence of young volcanic features neither asymmetric spreading nor discrete jumps in the spreading center location are required to explain the observed morphology and backscatter characteristics changes in the orientation of the seafloor spreading fabric suggest that an early phase of arc rifting may have been followed by northward propagation of the backarc spreading center to widen this portion of the basin this could have produced the current situation with the rift axis offset about 35 km east of the center of the mariana trough the off center position of the spreading axis may also the result of overgrowth of backarc crust by the volcanic arc

plume chemistry provides insights into mechanisms of sulfur and halogen degassing in basaltic volcanoes abstract this paper deals with sulfur chlorine and fluorine abundances in the eruptive volcanic plume of the huge october 2002 january 2003 eruption of mount etna aiming at relating the relevant compositional variations observed throughout with changes in eruption dynamics and degassing mechanisms the recurrent sampling of plume acidic volatiles by filter pack methodology revealed that during the study period s cl and cl f ratios ranged from 0 1 6 8 and 0 9 5 6 respectively plume s cl ratios increased by a factor of 10 as volcanic activity drifted from paroxysmal lava fountaining mid and late november to passive degassing and minor effusion early january and then decreased to the low values s cl 0 1 typical of the final stages of the eruption parallel variations in chlorine to fluorine ratios were also observed a theoretical model is proposed for quantitative interpretation of these changes in plume composition the model calculates the composition of a volatile phase exsolving from an ascending etna magma based on knowledge of solubilities and abundances in the undegassed melt of sulfur and halogens t m gerlach eos 72 1991 249 254 255 according to this model degassing of etnean basaltic melt at high pressures and depths 100 mpa 3 km is likely to release a co2 h2o rich vapor phase with s cl molar ratios 1 extensive sulfur and chlorine degassing from the melt would take place at shallower depth p

ground deformation modeling of flank dynamics prior to the 2002 eruption of mt etna on 22 september 2002 1 month before the beginning of the flank eruption on the ne rift an m 3 7 earthquake struck the northeastern part of mt etna on the westernmost part of the pernicana fault in order to investigate the ground deformation pattern associated with this event a multi disciplinary approach is presented here just after the earthquake specific gps surveys were carried out on two small sub networks aimed at monitoring the eastern part of the pernicana fault and some baselines belonging to the northeastern edm monitoring network of mt etna were measured the leveling route on the northeastern flank of the volcano was also surveyed furthermore an investigation using sar interferometry was performed and also the continuous tilt data recorded at a high precision sensor close to the epicenter were analyzed to constrain the coseismic deformation the results of the geodetic surveys show a ground deformation pattern that affects the entire northeastern flank of the volcano clearly shaped by the pernicana fault but too strong and wide to be related only to an m 3 7 earthquake leveling and dinsar data highlight a local strong subsidence up to 7 cm close to the pernicana fault significant displacements up to 2 cm were also detected on the upper part of the ne rift and in the summit craters area while the displacements decrease at lower altitude suggesting that the dislocation did not continue further eastward three dimensional gps data inversions have been attempted in order to model the ground deformation source and its relationship with the volcano plumbing system the model has also been constrained by vertical displacements measured by the leveling survey and by the deformation map obtained by sar interferometry

characteristics of seismic waves composing hawaiian volcanic tremor and gas piston events observed by a near source array a correlation method specifically designed for describing the characteristics of a complex wave field is applied to volcanic tremor and gas piston events recorded by a semicircular array of geos instruments set at the foot of the puu oo crater on the east rift of kilauea volcano hawaii the spatial patterns of correlation coefficients obtained as functions of frequency for the three components of motion over the entire array are similar for gas piston events and tremor and clearly depict dispersive waves propagating across the array from the direction of puu oo the wave fields are composed of comparable amounts of rayleigh and love waves propagating with similar and extremely slow phase velocities ranging from 700 m s at 2 hz to 300 m s at 8 hz the highly cracked solidified lava flow on which the array was deployed and subjacent structure of alternating lava and ash layers formed during repeated eruptions of puu oo since 1983 appear to be responsible for the low velocities observed the results from puu oo stand in sharp contrast to those obtained in an experiment conducted in 1976 on the partially solidified lava lake of kilauea iki rayleigh waves were not observed in kilauea iki but well developed trains of love waves were seen to propagate there with velocities twice as high as those observed near puu oo these differences in the propagation characteristics of surface waves at the two sites may be attributed to the presence of a soft horizontal layer of molten rock in kilauea iki which may have lowered the phase velocity of rayleigh waves more drastically than that of love waves resulting in severe scattering of the rayleigh wave mode on the other hand the thin superficial pahoehoe flow under our array at puu oo may have favored the development of vertical columnar joints more extensively at this location than at kilauea iki which may have reduced the shear moduli controlling the love wave mode the average phase velocities in the frequency band from 2 to 5 hz found at puu oo are roughly similar to those determined for tremor at klyuchevskoy volcano kamchatka but the frequency dependence appears much stronger at puu oo

syneruptive sequential fragmentation of pyroclasts from fractal modeling of grain size distributions of fall deposits the cretaio tephra eruption ischia island italy abstract in this work we use fractal statistics in order to decipher the mechanisms acting during explosive volcanic eruptions by studying the grain size distribution gsd of natural pyroclastic fall deposits the method was applied to lithic rich proximal deposits from a stratigraphic section of the cretaio tephra eruption ischia island italy analyses were performed separately on bulk material juvenile and lithic fraction from each pyroclastic layer results highlight that the bulk material is characterized by a single scaling regime whereas two scaling regimes with contrasting power law exponents are observed for the juvenile and the lithic fractions on the basis of these results we infer that the bulk material cannot be considered as a good proxy for deducing eruption dynamics because it is the result of mixing of fragments belonging to the lithic and juvenile fraction both of which underwent different events of fragmentation governed by different mechanisms in addition results from fractal analyses of the lithic fraction suggest that it likely experienced a fragmentation event in which the efficiency of fragmentation was larger for the coarser fragments relative to the finer ones on the contrary we interpret the different scaling regimes observed for the juvenile fraction to be due to sequential events of fragmentation in the conduit possibly enhanced by the presence of lithic fragments in the eruptive mixture in particular collisional events generated increasing amounts of finer particles modifying the original juvenile gsds and determining the development of two scaling regimes in which the finer fragments record a higher efficiency of fragmentation relative to the coarser ones we further suggest that in lithic rich proximal fall deposits possible indications about the original gsds of the juvenile fraction might still reside in the coarser particles fraction

volcanomagnetic changes accompanying the onset of the 2002 2003 eruption of mt etna italy abstract remarkable changes in the local magnetic field were associated with the onset of the 2002 2003 flank eruption at mt etna after differential magnetic field measurements were filtered from the external noise by using adaptive filters we recognized two stages in the total intensity changes which are closely related to different volcanic events a rapid variations of about 4 5 nt associated with october 26 seismic swarm recorded beneath the summit craters b step like variations of 9 10 nt coincident with october 27 eruptive fissures opening up in the north flank these observations are generally consistent with those calculated from simple magnetic models of these volcanic processes in which the magnetic changes are generated by stress redistribution due to magmatic intrusions at different depth the magnetic data not only allow the timing of the intrusive event to be described in greater detail but also together with other volcanological and geophysical evidences permit some constraints to be set on the characteristics of propagation of a shallow dike firstly at around midnight on 26 october magma was rapidly injected to a depth of 3 4 km just below the summit craters secondly after 1 00 on 27 october continued intrusion magma occurred upward and culminated a few hundred meters below the free surface fractured along a n e direction thirdly at about 2 28 magma gave rise to an explosive fissural vent at the northern base of the ne crater near 3000 m a s l finally at about 5 00 the first eruptive fissure became active along the eastern border of the ne rift at 2500 m a s l the rate of growth of the magnetic anomalies moreover leads to the interpretation that the magmatic intrusion travelled northward from base of the ne crater to the ne rift at approximately 14 m min

continuous soil co2 and discrete plume so2 measurements at mt etna italy during 1997 2000 a contribution to volcano monitoring continuous monitoring of soil co2 dynamic concentration which is proportional to the co2 flux through the soil was carried out at a peripheral site of mt etna during the period november 1997 september 2000 using an automated station the acquired data were compared with so2 flux from the summit craters measured two to three times a week during the same period the high frequency of data acquisition with both methods allowed us to analyze in detail the time variations of both parameters anomalous high values of soil co2 dynamic concentration always preceded periods of increased flux of plume so2 and these in turn were followed by periods of summit eruptions the variations were modeled in terms of gas efflux increase due to magma ascent to shallow depth and its consequent depressurization and degassing this model is supported by data from other geophysical and volcanological parameters the rates of increase both of soil co2 dynamic concentration and of plume so2 flux are interpreted to be positively correlated both to the velocity of magma ascent within the volcano and to lava effusion rate once magma is erupted at the surface low rates of the increase were recorded before the nine month long 1999 subterminal eruption higher rates of increase were observed before the violent summit eruption of september november 1999 and the highest rates were observed during shorter and very frequent spike like anomalies that preceded the sequence of short lived but very violent summit eruptions that started in late january 2000 and continued until late june of the same year furthermore the time interval between the peaks of co2 and so2 in a single sequence of gas anomalies is likely to be controlled by magma ascent velocity

potential application of the scintrex cg 3m gravimeter for monitoring volcanic activity results of field trials on mt etna sicily abstract a series of field trials have been conducted for 11 months on and around mt etna sicily to test the performance of the new automated scintrex cg 3m gravimeter on active volcanoes the results show that the data from the cg 3m compare favourably with those from the traditionally employed lacoste and romberg l r model d gravimeter under severe field conditions the scintrex meter because of its greater ruggedness and fully automated capabilities yields results superior to those from the l r d models repeated measurements 568 in a wide range of field conditions yielded errors in g between stations of 3 5 to 4 4 gal our tests also showed that both the strong drift in stationary conditions 1 mgald 1 and changes of the instrumental calibration factor with time whose rate decreased from 6 to 1 ppmd 1 during the 11 month study can be reduced by regular checks to acceptable standards thus a using experimental data the instrumental drift was forecasted and corrected by the real time automatical compensator of the instrument to within about 20 gald 1 and b using the measurements along an 18 station profile on mt etna total gravity range 300 mgal and an 80 km long calibration line away from the volcano six stations total gravity range 365 mgal the changes of the calibration factor were determined and corrected to within about 30 ppm

observations of mt etna volcanic ash plumes in 2006 an integrated approach from ground based and polar satellite noaa avhrr monitoring system abstract mt etna in sicily italy is one of the world s most frequent emitters of volcanic plumes during the last ten years etna has produced copious tephra emission and fallout that have damaged the inhabited and cultivated areas on its slopes and created serious hazards to air traffic recurrent closures of the catania international airport have often been necessary causing great losses to the local economy recently frequent episodes of ash emission lasting from a few hours to days occurred from july to december 2006 necessitating a look at additional monitoring techniques such as remote sensing the combination of a ground monitoring system with polar satellite data represents a novel approach to monitor etna s eruptive activity and makes etna one of the few volcanoes for which this surveillance combination is routinely available in this work ash emission information derived from an integrated approach based on comparing ground and noaa avhrr polar satellite observations is presented this approach permits us to define the utility of real time satellite monitoring systems for both sporadic and continuous ash emissions using field data visible observations collection of tephra samples and accounts by local inhabitants the duration and intensity of most of the tephra fallout events were evaluated in detail and in some cases the order of magnitude of the erupted volume was estimated the ground data vs satellite data comparison allowed us to define five different categories of etna volcanic plumes according to their dimensions and plume height taking into account wind intensity using frequent and good quality satellite data in real time this classification scheme could prove helpful for investigations into a possible correlation between eruptive intensity and the presence and concentration of ash in the volcanic plume the development and improvement of this approach may constitute a powerful warning system for civil protection thus preventing unnecessary airport closures

relationship between tremor and volcanic activity during the southeast crater eruption on mount etna in early 2000 1 the southeast crater of mount etna italy was characterized by a violent eruptive activity between 26 january and 24 june 2000 this activity produced 64 lava fountain episodes with repose periods from 3 hours to 10 days we estimated a volume of about 15 20 106 m3 lava and at least 2 3 106 m3 of tephra we compared the paroxysmal volcanic activity to its associated seismic signature the high number of events highlighted a strict correlation between tremor and volcanic activity seismic and volcanic characteristics such as the frequency of occurrence the duration of lava fountains and the associated tremor energy suggested the subdivision of the studied period into two stages separated by the 20 february event combining volcanic with seismic data we observed some useful relationships among lava fountain height sustained column height and reduced displacement in addition we found that the entire episode was well correlated with the duration of the amplitude increase computing the tremor energy linked to each event the total energy associated with lava fountains episodes results in 76 of the energy released during the whole period finally the different ratios among the overall spectral amplitude of the seismic signals of the stations located at different altitudes suggested to us the elaboration of a simple qualitative model to explain the dynamic behavior of the tremor source during the whole episode

total grain size distribution and volume of tephra fall deposits on 17 june 1996 ruapehu volcano new zealand produced a sustained andesitic sub plinian eruption which generated a narrow tephra fall deposit extending more than 200 km from the volcano the extremely detailed data set from this eruption allowed methods for the determination of total grain size distribution and volume of tephra fall deposits to be critically investigated calculated total grain size distributions of tephra fall deposits depend strongly on the method used and on the availability of data across the entire dispersal area the voronoi tessellation method was tested for the ruapehu deposit and gave the best results when applied to a data set extending out to isomass values of 1 g m 2 the total grain size distribution of a deposit is also strongly influenced by the very proximal samples and this can be shown by artificially constructing subsets from the ruapehu database unless the available data set is large all existing techniques for calculations of total grain size distribution give only apparent distributions the tephra fall deposit from ruapehu does not show a simple exponential thinning but can be approximated well by at least three straight line segments or by a power law fit on semi log plots of thickness vs area 1 2 integrations of both fits give similar volumes of about 4 106 m3 integration of at least three exponential segments and of a power law fit with at least ten isopach contours available can be considered as a good estimate of the actual volume of tephra fall integrations of smaller data sets are more problematic

explosive activity at mt etna summit craters and source modeling by using high precision continuous tilt we investigated the relationships between modelled strain produced by explosive activity through a volcanic conduit observed paroxystic episodes on mt etna and high precision continuous tilt signals recorded during such events from the tilt monitoring network the tilt changes detected during two different explosive episodes were compared with those calculated from analytical models of ground deformation in order to constrain source properties the july 22 1998 subplinian explosion from voragine crater produced small tilt changes order of 0 5 1 5 rad recorded over the entire volcano edifice implying a small storage at nearly 2 5 km below sea level the 1998 2000 period was characterized by tens of spectacular lava fountains from the south east crater very small tilt change 0 1 rad was recorded by a single station on the high north eastern flank of mt etna and indicated the action of a limited and shallow conduit with 1 5 1 9 km depth these results provide a contribution to better infer the shallow plumbing system beneath mt etna

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

the initial phases of the 2008 2009 mount etna eruption a multidisciplinary approach for hazard assessment accepted for publication in journal of geophysical research copyright 2010 american geophysical union

lava effusion rate definition and measurement a review measurement of effusion rate is a primary objective for studies that model lava flow and magma system dynamics as well as for monitoring efforts during on going eruptions however its exact definition remains a source of confusion and problems occur when comparing volume flux values that are averaged over different time periods or spatial scales or measured using different approaches thus our aims are to 1 define effusion rate terminology and 2 assess the various measurement methods and their results we first distinguish between instantaneous effusion rate and time averaged discharge rate eruption rate is next defined as the total volume of lava emplaced since the beginning of the eruption divided by the time since the eruption began the ultimate extension of this is mean output rate this being the final volume of erupted lava divided by total eruption duration whether these values are total values i e the flux feeding all flow units across the entire flow field or local i e the flux feeding a single active unit within a flow field across which many units are active also needs to be specified no approach is without its problems and all can have large error up to 50 however good agreement between diverse approaches shows that reliable estimates can be made if each approach is applied carefully and takes into account the caveats we detail here there are three important factors to consider and state when measuring giving or using an effusion rate first the time period over which the value was averaged second whether the measurement applies to the entire active flow field or a single lava flow within that field and third the measurement technique and its accompanying assumptions

ontong java plateau and late neogene changes in pacific plate motion aided by a new geometrical technique called hot spotting we recently proposed a new model for the absolute motion of the pacific plate this model called wk97 assumed the hawaiian hotspot is under loihi and that there was a change in plate motion at 3 6 ma the model located the louisville hotspot close to the hollister ridge a shallow volcanic ridge associated with a geoid high seismicity and recent volcanism most of the tectonic implications of wk97 however were not addressed furthermore although several recent studies suggest that the geochemistry of hollister lavas may indicate a mixture between louisville melt material and pacific antarctic ridge mid ocean ridge basalt these studies strongly disagree with wk97 and consider it seriously flawed here we discuss numerous tectonic predictions of wk97 and present a large amount of observational evidence in support of it we find that a late neogene collision between the ontong java plateau and the northern margin of the australia plate appears to have altered the motion of the pacific plate as inferred from hotspot volcanism by forcing it to rotate counter clockwise this rotation about a low latitude pole appears to have induced right lateral shear stress along the entire pacific plate divergent boundary which resulted in the formation of extensional transform faults microplates and propagating ridges this change in motion also appears to have triggered concomitant circum pacific tectonism including trench migration and back arc rifting the wk97 suggests that long lived plume fed volcanism on the pacific plate appears very limited perhaps only to five to six hotspots hawaii louisville cobb caroline and perhaps marquesas and bowie the geometry of these chains are consistent with our model despite some evidence for volcanic age progressions most other pacific neogene hotspots are most likely crack spots i e sites of extensional volcanism at preexisting zones of weakness reactivated by plate stresses indeed several volcanic ridges such as hollister ridge near the louisville hotspot appear to have formed in response to stresses following the change in absolute plate motion wk97 also obviates the need for simultaneous different directions of mantle flow in the south central pacific transpression at the san andreas and alpine strike slip faults and aleutian arc explosivity since 6 ma also appear to be consequences of the changes in pacific plate motion furthermore both the wk97 model and observed relative plate motions suggest that adjoining plates have changed their absolute motions as well and that large changes in absolute plate motion do not necessarily imply large changes in relative plate motion our findings support slab pull as the dominant plate tectonic driving force highlight the rheological difference between strong oceanic lithosphere and weak continental crust and suggest that wk97 presently provides a unifying albeit preliminary framework for relating both intraplate and circum pacific tectonism and volcanism in the late neogene

ten years of soil co2 continuous monitoring on mt etna exploring the relationship between processes of soil degassing and volcanic activity 1 the measurement of soil co2 flux variations is a well established practice in many volcanic areas around the world until recently however most of these were made using direct sampling methods these days a variety of automatic devices providing real time data now make the continuous monitoring of volcanic areas possible a network of automatic geochemical monitoring stations etnagas network was developed by ingv palermo and installed at various sites on the flanks of mt etna here we present a large set of soil co2 flux data recorded by the network dating back 10 years a period in which several noteworthy eruptive phenomena occurred our statistical analysis strongly suggests that anomalous measurements of soil co2 flux are attributable to volcanic origin and in almost all cases precede volcanic activity here we present the actual data series recorded by etnagas and an interpretative model of the expected behavior of soil co2 flux in terms of increase decrease cycles which corresponded well with the volcanic activity during this period through the use of a comparative approach incorporating both volcanological and geochemical data the global soil co2 flux trends are put into a coherent framework highlighting close links between the time flux variations and volcanic activities these insights made possible from 10 years of uninterrupted data confirm the importance of continuous monitoring of volcanic soil degassing and may contribute in the forecasting of imminent eruptive activity or the temporal evolution of an in progress eruption therefore facilitating civil defense planning in volcanic areas under high hazard conditions

estimating rates of decompression from textures of erupted ash particles produced by 1999 2006 eruptions of tungurahua volcano ecuador persistent low to moderate level eruptive activity of andesitic volcanoes is difficult to monitor because small changes in magma supply rates may cause abrupt transitions in eruptive style as direct measurement of magma supply is not possible robust techniques for indirect measurements must be developed here we demonstrate that crystal textures of ash particles from 1999 to 2006 vulcanian and strombolian eruptions of tungurahua volcano ecuador provide quantitative information about the dynamics of magma ascent and eruption that is difficult to obtain from other monitoring approaches we show that the crystallinity of erupted ash particles is controlled by the magma supply rate msr ash erupted during periods of high magma supply is substantially less crystalline than during periods of low magma supply this correlation is most easily explained by efficient degassing at very low pressures 50 mpa and degassing driven crystallization controlled by the time available prior to eruption our data also suggest that the observed transition from intermittent vulcanian explosions at low msr to more continuous periods of strombolian eruptions and lava fountains at high msr can be explained by the rise of bubbles through strombolian or trapping of bubbles beneath vulcanian vent capping variably viscous and crystalline magma

reconstruction of so2 flux emission chronology from space based measurements abstract infrared satellite images measured with the modis instrument of the volcanic plume produced during the 2006 eruption of mt etna were analysed to produce maps of so 2 amount we used these maps to reconstruct time series of so 2 fluxes by integrating profiles of so 2 orthogonal to the plume advection direction and multiplying with wind speeds from a meteorological model these data were then compared with a reconstructed time series of so 2 fluxes measured with the flame ground based network of ultraviolet doas systems surrounding the volcano we found weak agreement on 3rd december when little ash was emitted but this agreement improved when a 0 3 m s 1 wind speed correction factor was used flame and modis results were in good agreement on the 6th december and improved when a 0 3 m s 1 offset was applied the corrected data revealed that the only period of time when flame and modis did not track together was coincident with the presence of ash which interferes with the ir imagery and retrieval of so 2 we highlight that combining two independent time series of so 2 flux allows a precise determination of wind speed if there is sufficient time dependent structure in the so 2 signal the observed increase in so 2 flux prior to the ash emission is interpreted as a quiescent release of an accumulated gas phase that drive eruptive activity as previously suggested for the southeast crater system of etna in this case the so 2 flux signal therefore acted as a precursor to the eruptive ash events this work demonstrates that quantitative reconstruction of so 2 flux time series is feasible using modis data opening a new frontier in the use of satellite data to interpret volcanic processes in particular in poorly monitored remote locations

a 220 km2 recently erupted lava field on the east pacific rise near lat 8 s seamarc ii records show a 220 km2 area of unusually high reflectivity on the east pacific rise epr near lat 8 s which we interpret to be a recently erupted lava field this is the only segment of the epr exhibiting high reflectivity over such a large area in our continuous seamarc ii coverage from lat 8 n to 18 n and 3 s to 23 s the lavas appear to issue from the axial neovolcanic zone between lat 8 15 and 8 17 s the lava field extends up to 18km off axis and inundates scarps up to 100 m high on the basis of measurements of scarp heights just outside areas where they are buried we estimate the average thickness of the field to be 70 20 m thus the volume of the lava field is 15 4 km3 in comparison the average annual volcanic budget for the earth is approximately 4 5 km3 and the largest historic basaltic eruption from the icelandic laki fissure in 1783 was approximately 12 3 km3 when did the eruption occur comparative studies of acoustic reflectivity and photographed bottom characteristics elsewhere along the epr suggest that the lava field has little or no sediment cover and is very young this is also one of the only areas on the epr where earthquakes occur that do not appear to be caused by transform faulting if the earthquakes are related to the lava field then major eruptions may have occurred in 1964 1965 and 1969 a large helium plume near lat 13 s may be caused in part by eruptions of the lat 8 s lava field this is consistent with estimates of currents at 2 3 km depth which are such that a plume generated at lat 8 s would eventually appear off axis at lat 13 s our observations suggest that this spreading segment which is bounded by small ridge axis discontinuities at lat 8 05 s and 8 47 s may have been the most volcanically active segment along the epr during the past 25 yr

evolution of the mariana convergent plate margin system the mariana convergent plate margin system of the western pacific provides opportunities for studying the tectonic and geochemical processes of intraoceanic plate subduction without the added complexities of continental geology the system s relative geologic simplicity and the well exposed sections of lithosphere in each of its tectonic provinces permit in situ examination of processes critical to understanding subduction tectonics its general history provides analogs to ancient convergent margin terranes exposed on land and helps to explain the chemical mass balance in convergent plate margins the mariana convergent margin s long history of sequential formation of volcanic arcs and extensional back arc basins has created a series of volcanic arcs at the eastern edge of the philippine sea plate the trenchward edge of the overriding plate has a relatively sparse sediment cover rocks outcropping on the trench s inner slope are typical of the early formed suprasubduction zone s lithosphere and have been subjected to various processes related to its tectonic history pervasive forearc faulting has exposed crust and upper mantle lithosphere many large serpentinized peridotite seamounts are within 100 km of the trench axis from these we can learn the history of regional metamorphism and observe and sample active venting of slab fluids ocean drilling recovered suprasubduction zone lava sequences erupted since the eocene that suggest that the forearc region remains volcanologically dynamic seismic studies and seafloor mapping show evidence of deformation throughout forearc evolution large portions of uplifted southern forearc are exposed at the larger islands active volcanoes at the base of the eastern boundary fault of the mariana trough vary in size and composition along strike and record regional differences in source composition their locations along strike of the arc are controlled in part by cross arc structures that also facilitate formation of submarine volcano chains extending from the base of the fault westward into the back arc basin the western boundary is the west mariana ridge the western portion of the volcanic arc active prior to formation of the mariana trough the trough evolved in a two stage extension process of rifting and subsequent seafloor spreading the back arc basin varies along strike from rifted arc lithosphere with scattered volcanoes but no real spreading center in the north to a complex mid ocean type spreading center south of 20 n the change from initial rifting to true seafloor spreading is also evident across the mariana trough from rifted topography near the west mariana ridge to spreading ridges in the central to eastern basin south of 20 n this morphologic change indicates an early stage of extension with basin and range type topography predominant and volcanism restricted to fissure eruptions along fault block boundaries the spreading ridges and abyssal hill morphology evolved later as new lithosphere was generated at elongate volcanic ridges located in the center of rift valleys the center of extension intersects the active volcanic front differently at either end of the mariana trough in the north extension is by rifting of arc lithosphere where it intersects the arc in the south a major strike slip fault extends from the trench axis across the forearc through the volcanic arc and into the back arc basin arc magmas apparently leak along this fault zone into the forearc and the back arc spreading center the complexity of interrelated tectonism and magmatism in this convergent margin is daunting but studies of arc systems such as this provide the best hope of interpreting many of the exposed terranes accreted to continents comparison of subaerial terranes with recent studies of intraoceanic convergent margins will add to our understanding of plate interactions and of the evolution of the volcanic arcs and extensional back arc basins generated within such environments

a one million year history of the 11 45 n east pacific rise discontinuity bathymetric magnetic and side scan sonar data from a june 1987 seamarc ii cruise aboard the r v moana wave have been combined with additional data in an area 140 km by 154 km centered on the overlapping spreading center pair osc located at 11 45 n on the east pacific rise epr the purpose of this study is to correlate and interpret these data sets in order to determine the recent 1 m y history of this osc the data sets include gridded bathymetry and magnetic field anomalies a side scan sonar mosaic and a fault map the bathymetry and anomaly grids were used as inputs in a three dimensional fourier inversion resulting in a crustal rock magnetization distribution solution the most prominent feature of all five maps is a roughly v shaped anomalous zone centered on the osc the zone is characterized by a positive depth anomaly a negative magnetic field anomaly within the central positive anomaly and a zone of high magnetization in the inversion solution a hummock y texture and sparse curved faults mark the zone in the side scan mosaic and fault map the shape of this zone indicates a short period of northward migration of the discontinuity 0 72 0 6 ma at approximately 75 mm yr followed by slow less than 30 mm yr and then fast 140 200 mm yr southward migration for the past 0 6 m y the anomalous zone is not well defined beyond the edge of the central anomaly which is straight and continuous indicating that if this discontinuity of the epr existed 0 72 ma its offset was negligible the present day axis has an orientation of 349 the edge of the central anomaly has an orientation of 353 and jaramillo age crust to the east of the epr has an orientation of 353 355 this variation in magnetic linealion directions suggests a 4 to 6 counter clockwise change in the direction of spreading in the past 1 m y which seems to have been accommodated by asymmetric spreading variations in mean fault trend with age are consistent with a counter clockwise change in the direction of spreading for the same time period

geochemical transitions in the ancestral iceland plume evidence from the isle of mull tertiary volcano scotland the mull tertiary volcano lies on the eastern edge of the north atlantic igneous province and was active soon after the initiation of the iceland plume detailed sampling of the mull lava pile has allowed temporal changes in the mantle source to be determined a significant change at 700 m above sea level from n morb like to icelandic marks the first arrival beneath the region of mantle from the core of the ancestral plume the earlier basalts represent an outer plume sheath of heated upper mantle from the initiation of magmatism in mull it took 1 9 0 4 ma for this transition to occur

shoshonitic volcanism in the northern mariana arc 1 mineralogic and major and trace element characteristics petrographic and geochemical characteristics of samples dredged from 23 submarine volcanic edifices in the northern mariana and southern volcano arcs define two distinct rock series the central and northern mariana arc to 23 n and the northern volcano arc north of iwo jima are characterized by plagioclase clinopyroxene orthopyroxene titantomagnetite bearing subalkaline rocks including both low k and medium k series the northern mariana arc and southern volcano arc from 23 n to iwo jima are erupting rocks of a shoshonitic series with phenocrysts of plagioclase clinopyroxene olivine and biotite these rocks are less saturated than those of the subalkaline provinces and are substantially enriched in ba 400 900 ppm sr 600 1000 ppm k2o 1 4 5 and k2o na2o 0 4 1 2 relative to the subalkaline lavas ba y and ba zr increase by a factor of 3 to 4 in the shoshonitic rocks but k rb ba sr and k ba are relatively constant throughout the arc there is no relationship between degree of enrichment and volcano volume or degree of fractionation seamounts and islands within each province have the same range of compositions much of the intra edifice variation in lava composition can be modeled by 10 70 crystallization of plagioclase and clinopyroxene with smaller amounts of olivine orthopyroxene and titanomagnetite or by accumulation of 10 40 phenocrysts dominantly plagioclase the differences between parental lavas in the alkalic and subalkalic provinces require melting of two distinct mantle sources the occurrence of this enriched mantle in the northern marianas may be a consequence of the propagation of the mariana trough spreading center into the volcano arc

lava fountains during the episodic eruption of south east crater mt etna 2000 insights into magma gas dynamics within the shallow volcano plumbing system mt etna in sicily italy is well known for frequent effusive and explosive eruptions from both its summit and flanks south east crater se crater one of the four summit craters has been the most active in the last 20 years and often produces episodic lava fountains over periods lasting from a few weeks to months the most striking of such eruptive phases was in 2000 sixty four lava fountains separated by quiescent intervals and sometimes associated with lava overflows occurred that year between january and june a time period during which we consider the volcano to have been in episodic eruption this paper presents mainly results of petrochemical investigations carried out on both tephra and lavas collected during a number of the lava fountain episodes in 2000 the new data have been integrated with volcanological and seismic information in order to correlate the features of the eruptive activity with magma gas dynamics in the plumbing system of se crater the main findings allow us to characterise the 2000 episodic eruption in the framework of the recent se crater activity in particular we infer that the onset of the 2000 eruption was triggered by the ascent of new more primitive and volatile rich magma that progressively intruded into the se crater reservoir where it mixed with the resident more evolved magma furthermore we argue that the 2000 se crater lava fountains largely resulted from the instability of a foam layer accumulated at the top of the underlying reservoir and rebuilt prior to each episode in agreement with the collapsing foam model for lava fountains

shear response to an intrusive episode at mt etna volcano january 1998 inferred through seismic and tilt data abstract the space time evolution of a seismic swarm m d max 3 7 occurring on 9 14 january 1998 at mt etna volcano is analysed the hypocentral pattern and most reliable focal mechanisms indicate that seismic activity during 10 14 january mainly occurred within a fault zone located in the volcano s western flank the fault showed an approximately ne sw overall trend and shallow rupture mode of right lateral strike slip type it is noteworthy that earthquakes occurring during the initial phase 9 january of the swarm showed prevalent dip slip rupture mechanisms which are consistent with tensile opening of an approximately nnw sse trending fault zone this nnw sse structural lineament belongs to a regional lithospheric structure which has also been identified as a main volcano genic structural trend of mt etna the observed continuous tilt data are not explainable by the seismic slip associated with strain released along the ne sw structure however an intrusive source would be compatible with the rupture mechanisms observed during the initial phase of the swarm and could explain the observed tilt therefore we evidence that an intrusive episode occurred along the nnw sse structure starting 9 january and during the following days it forced the ne sw fault system to work in a right lateral mode these mechanisms leading to the february november 1999 summit eruption are analogous to the ones observed before the 1991 93 eruption

rifting history of the northern mariana trough seamarc ii and seismic reflection surveys seamarc ii sidescan sonar data and seismic reflection profiles of the northernmost portion of the mariana trough suggest a rifting rather than a seafloor spreading origin for lithosphere within this active backarc basin of the western pacific variations in morphology along the strike of the backarc basin suggest both a spatial and a temporal variation in the style of extension of the basin the northern mariana trough widens from 70 km near 23 n to 135 km near 21 30 n major active fault zones bound both sides of the backarc basin active rifting and volcanism are predominant in a roughly 20 km wide active rift zone along the eastern arc side of the basin from 24 n to 22 n the locus of active rifting has remained near the volcanic front of the arc during extension and is probably controlled by lithospheric weakness which is greatest at the volcanic front the zone of rifting intersects the active volcanic arc at nikko seamount the distinction between the mechanism for formation of the mariana trough proposed here and that of slow mid ocean ridge spreading is that no true plate boundary has developed in the northernmost mariana trough rather the backarc basin is composed of arc lithosphere intruded by arc and backarc basin magmas volcanism both in the rift zone and throughout the basin is fault controlled south of 22 n the zone of active rifting diverges westward from the arc as the transition to true seafloor spreading is approached the transition to true mid ocean ridge spreading occurs to the south of the survey area described here

shallow plumbing systems for small volume basaltic volcanoes eruptive dynamics in basaltic volcanoes are controlled in part by the conduit geometry however uncertainties in conduit shape and dike to conduit transition geometry have limited our predictive capability for hazards assessments we characterize the subvolcanic geometry of small volume basaltic volcanoes magmatic volatile driven eruptions 0 1 to 0 5 km3 based on a synthesis of field studies of five basaltic volcanoes exposed to varying degrees by erosion and exhibiting feeder dikes conduits and vent areas 250 m depth study areas include east grants ridge new mexico usa basalt ridge east basalt ridge paiute ridge and southeast crater flat nevada usa basaltic feeder dikes 250 to 100 m deep have typical widths of 4 12 m with smooth host rock contacts rhyolite tuff at depths less than 100 m heterogeneities in the host rock form preferential pathways for small dike splays and sills resulting in a 30 m effective width at 50 m depth the development of a complex conduit at depths less than 70 m is reflected in bifurcating dikes and brecciation and incorporation of the country rock the overall zone of effect at depths less than 50 m is 110 m wide 220 m elongated along the feeder dike based on comparisons with theoretical conduit flow models the width of the feeder dike at depths from 250 to 500 m is expected to range from 1 to 10 m and is expected to decrease to about 1 2 m at depths greater than 500 m the flaring shape of the observed feeder systems is similar to results of theoretical modeling using lithostatic pressure balanced flow conditions sizes of observed conduits differ from modeled dimensions by up to a factor of 10 in the shallow subsurface 50 m depth but at depths greater than 100 m the difference is a factor of 2 to 4 this difference is primarily due to the fact that observed eroded conduits record the superimposed effects of multiple eruptive events while theoretical model results define dimensions necessary for a single steady eruption phase the complex details of magma host rock interactions observed at the study areas contact welding brecciation bifurcating dikes and sills and stoping represent the mechanisms by which the lithostatic pressure balanced geometry is attained the similarity in the normalized shapes of theoretical and observed conduits demonstrates the appropriateness of the pressure balanced modeling approach consistent with the conclusions of wilson and head j geophys res 86 2971 3001 1981 for this type of volcano

impulsive tilt variations on mount etna volcano 1990 1993 abstract this study was focussed on the analysis of the fast ground deformations impulsive anomalies recorded at the mt etna tilt array from 1990 to 1993 a period that preceded accompanied and followed the 1991 1993 eruption these fast deformations were recorded as transient anomalies ranging from a few hours to days 1 2 observed contemporaneously at several tilt stations and characterized by variations ranging from one to tens of microradians the signals evidenced volcanic dynamics characterized by tilt anomalies during the non eruptive periods 1990 1993 the pre eruptive period november december 1991 the beginning of the eruption 14 15 december 1991 and the eruption course 1992 in particular pre seismic co eruptive and co seismic anomalies were recorded during the pre eruptive period and the eruption onset in these cases interpretations of the phenomena and comparison to modelling studies are provided furthermore tilt variations affecting the global volcanic edifice were also observed one year before the eruption when they were followed by seismicity and during the eruption course without seismicity we interpreted this last class of tilt variations as due to the push of the magma uprising along the main nnw sse structure crossing mt etna

the 4 5 september 2007 lava fountain at south east crater of mt etna italy abstract continuous monitoring of paroxysmal eruptions at mt etna italy is performed from the istituto nazionale di geofisica e vulcanologia sezione di catania in recent years this activity has allowed us to study fallout deposits and track the evolution of eruptive phases this communication reports on the paroxysm that occurred in the afternoon of 4 september 2007 when a powerful lava fountain started from south east crater at the summit of etna the fountaining formed a plume up to 2 km high for almost 12 h causing abundant tephra fallout in the eastern sector of the volcano and emplacement of a thick about 4 km long clastogenic lava flow extensive area collection of tephra samples from the fallout deposit was performed within a few hours after the end of the paroxysm we calculated a total erupted volume of 3 92 4 9 10 5 m 3 and a total grain size fitted by a gaussian distribution with the mode of 0 and equal to 1 3 the total volume of the clastogenic lava flow deposit that resulted was 2 4 10 6 m 3 the systematic study of paroxysms at etna helps to better investigate etnean type lava fountains and to improve the classification of explosive activity on basaltic volcanoes

a syn eruptive ground deformation episode measured by gps during the 2001 eruption on the upper southern flank of mt etna ground deformation occurring on the southern flank of mt etna volcano during the july august 2001 eruption was monitored by gps measurements along an e w profile crossing the fissure system this profile was measured eight times during the eruption using the stop and go semi kinematic technique horizontal and vertical displacements between gps surveys are reported for each station the most significant event is a deformation episode occurring during the first week of the eruption between 25 27 july displacements were measured on benchmarks close to the eruptive fissure and the tensile 1989 fracture data inversions for measured displacements were performed using the okada model the model shows the narrowing of the 2001 dyke accompanied by a dextral dislocation along an east dipping fault parallel to the 1989 fracture

automated system for magnetic monitoring of active volcanoes in order to provide a basis for short term decision making in the forecasting and monitoring of volcanic activity we developed an entirely automated system of data acquisition and reduction for magnetic data the system mag net is designed to provide monitoring and analysis of magnetic data on etna volcano at large distances from the central observatory the mag net system uses data from an array of continuously recording remote stations spread over the volcanic area and linked by mobile phone to the control center at the local observatory at this location a computer receives the data and performs data sorting and reduction as well as limited evaluation to detect abnormal behavior or breakdown of remote sensors communication software called magtalk is also designed to provide data to distant users with a view to using continuous magnetic observations in advanced analysis techniques for volcano monitoring the mag net system also delivers two graphical user interface based applications to provide an interpretation capability the former called madap speeds up all the data reduction processes in order to evaluate the reliability of magnetic signals the latter called vmm is a procedure for modeling magnetic fields associated with tectonic and volcanic activity to facilitate the identification and interpretation of the sources of a wide spectrum of magnetic signals