comparison and cross checking of historical archaeological and geological evidence for the location and type of historical and sub historical eruptions of multiple vent oceanic island volcanoes

field evidence for flank instability basal spreading and volcano tectonic interactions at mt cameroon west africa the mt cameroon volcano is the highest and most active volcano of the cameroon volcanic line little geological information is available for improving the understanding of the structure of this large volcanic system and its relationship to regional tectonics after reviewing the tectonic evolution of the region the analysis of a digital elevation model and results from a field campaign dedicated to mapping geological structures in the summit area and at the se base of mt cameroon are presented mt cameroon is a lava dominated volcano with long steep over 30 flanks it is elongate parallel to its well defined rift zone the summit plateau is bordered by 10 m high cliffs formed by summit subsidence along normal faults geological profiles were measured along rivers cutting through a topographic step at the se base of mt cameroon this step is associated with deformed miocene sediments from the douala basin that are overlain by volcanic products weak sediments of this area are deformed by 050 060 and 020 030 trending asymmetrical folds verging toward the se and thrusts faults related to the spreading of the volcano over its mechanically weak substratum combined remote sensing and field observations suggest that spreading is accommodated by summit subsidence and flanks sliding both slow spreading movements and catastrophic collapses of the steep flanks are interpreted to result from complex interactions between the growing edifice repeated dyke intrusions the weak sedimentary substratum and tectonic structures

ground deformation and gravity changes accompanying the march 1981 eruption of mount etna abstract we present reults from simultaneous precise levelling and gravity surveys on mount etna covering the period august 1980 august 1981 the flank eruption of march 1981 erupted 18 35 10 5 m 3 of lava following it upward movements of more than 17 cm were observed close to the new fissure and a broad apparently independent uplift of 5 cm was observed 4 km to the west a zone of about 2 cm depression to the east of the fissure is insufficient to account for the volume of magma erupted gravity results show positive changes of up to 63 microgal and display good positive correlation with elevation changes both sets of measurements appear to be due to new intrusion of magma rather than subsurface magma drainage ground deformation close to the new fissure is well modelled by intrusion of a dyke in the zone 100 500 m below the surface striking along the fissure and of dip between 75 90 the gravity changes are modelled as due to a deeper intrusion of magma along the same line but some 1500 m below the surface the changes were not present immediately after the eruption but occurred during the ensuing 5 months it is proposed that this introduction of matter occurred by crack propagation along the fissure in the aftermath of the eruption towards the west of the fissure and some 4 km west of the summit ground deformation is modelled by intrusion of a dyke in the zone 300 1500 m below the surface and dipping at 80 85 again gravity changes appear to be due to magma intrusion at greater depth close to sea level in this case gravity changes are interpreted as due to magma density changes as a result of pressure increase in a larger scale fissure zone this same pressure increase may be forcing the new intrusion close to the surface and makes this part of the volcano a region of especially high risk

amplification of ground motion in fault and fracture zones observations from the tremestieri fault mt etna italy abstract a series of ambient noise measurements have been performed to evaluate their use in detecting the possible influence of tectonic structures on local amplification of seismic waves the area studied is located on the southeastern flank of mt etna a few kilometres north of the town of catania using a mobile station data were collected along three profiles which cross both a fault and an eruptive fracture in addition ambient noise was sampled at two permanent stations installed in close proximity to the fault and at another station located within the city limits of catania and considered to be a reference site analysis using spectral ratio techniques shows there is a tendency towards amplification at the sites located near the fault in h v spectral ratios such amplification is observed in the frequency range 4 0 8 0 hz and the amplitudes of the dominant spectral peaks decrease rapidly over the first few tens of meters from the discontinuity a similar tendency was observed for the sites located on the eruptive fracture zone dominant spectral peaks at 1 8 hz are also common in the study area the theoretical transfer function obtained through 1 d modelling indicates that such peaks can be related to the local stratigraphy the mean h h standard spectral ratio of microtremor evaluated at the permanent station located on the fault also shows an amplification peak at 4 0 hz azimuthal analysis shows that the resonance at 4 0 hz is directional with the maximum in the azimuth range n30 e n80 e

the caldera of volcan fernandina a remote sensing study of its structure and recent activity air photographs taken in 1946 1960 and 1982 together with spot hvr 1 images obtained in april and october of 1988 are used to characterize recent activity in and around the caldera of fernandina volcano west galapagos islands the eruptive and collapse events during this time span appear to be distributed in a nw se band across the summit and caldera on the flanks of the volcano subtle topographic ridges indicate that this is a long term preferred orientation of extra caldera activity as well although radial and arcuate fissures are found on all sectors the caldera is formed from the coalescence of multiple collapse features that are also distributed along a nw se direction and these give the caldera its elongate and scalloped outline the nw and se benches consist of lavas that ponded in once separated depressions that have been incorporated into the caldera by more recent collapse the volume of individual eruptions within the caldera over the observed 42 years appears to be small 4x106 m3 in comparison to the volumes of individual flows exposed in the caldera walls 120 150x106 m3 field observations in 1989 of lavas exposed in the caldera walls and their cross cutting relationships show that there have been at least three generations of calderas and that at times each was completely filled an interplay between a varying supply rate to the volcano and a regional stress regime is suggested to be the cause of long term spatial and volumetric variations in activity when supply is high the caldera is filled in relative to collapse and dikes tend to propagate in all directions through the edifice at other times such as the present supply is relatively low eruptions are small the caldera is far from being filled in and dike propagation is influenced by an extra volcano stress regime

coseismic displacements and creeping along the pernicana fault etna italy in the last 17 years a detailed study of a tectonic structure on a volcano abstract the pernicana fault is a tectonic fault located on mt etna sicily movements across this structure have been monitored over the last 17 years by a levelling network operated by the osservatorio vesuviano during the monitoring period the network has recorded coseismic displacements associated with earthquakes of magnitude 4 5 as well as aseismic displacements we present a detailed analysis of the displacement data aimed at modelling the geometry and mechanism of this fault as well as the size and mechanisms of individual earthquakes we use for interpreting the displacement data two types of inverse methods the first is able to determine from ground deformation data the geometry mechanism and location of a system rectangular faults with homogeneous dislocation the second finds for a fixed fault system geometry the heterogeneous slip distribution giving the best fit to the data the total recorded displacements during the last 17 years are well described by a single homogeneous rectangular normal fault with dislocation and size corresponding to a magnitude 5 7 earthquake thus revealing intense dynamics along such a fault coseismic displacements for individual earthquakes of considerable magnitude account for about 30 of the total deformation when interpreted in terms of an homogenous slip fault as inferred from total deformation some aspects of the data are not well explained thus calling for heterogeneous slip models it is hence possible with a certain approximation to distinguish the slip distributions associated with individual earthquakes from the almost homogeneous slip resulting from the sum of coseismic and aseismic movements the inferred seismic moments for the two larger earthquakes that occurred along this fault are considerable higher than reported in seismic bulletins about 1 degree of magnitude the results obtained here support the important role of levelling data for the detailed study of a peculiar kind of tectonic structure on a volcano aimed at understanding the complex interaction between volcano dynamics and induced movements along well defined structures

three dimensional model of the feeder conduit of the 1983 eruption of mt etna volcano from ground deformation measurements a levelling network and a horizontal distance measuring network down mt etna s south flank were measured before during and after the 1983 eruption we analyse the large movements recorded using theoretical models of surface displacement to determine the shape and position of the feeder conduit that supplied magma to the eruption the results indicate that a dyke the top surface extending nearly horizontally connects the eruption site to a point near the southeast crater the top of the dyke lies at an altitude of 2400 m to 2500 m and dips between 75 and 90 to the west more tentative evidence indicates that the top of the active dyke dropped by about 150 m between the 25th and the 95th day of the eruption and that a small branching dyke 1 km long was emplaced to the east of the main dyke but did not attain the surface the implications of these observation are discussed

prehistoric dyke trends on mount etna implications for magma transport and storage the distributions and alignments of over 200 prehistoric dykes exposed in the walls of the valle del bove caldera on mount etna have been plotted and samples collected from some 10 of those occurring in the southern wall important tectonic trends are reflected by the dykes along which magma movement was facilitated prior to the formation of the caldera close directional relations between the dyke trends and the orientations of historic fissures on the volcano point to the existence of a plexus of interconnecting subsurface fissures immediately to the south east of the summit a model is envisaged within which magma enters this clearing house from depth and is distributed via fissures to other parts of the volcano including the summit region here the interaction of fissures with the conduits of the summit craters is put forward as a mechanism to explain the behaviour of recent activity

the valle del bove mount etna its origin and relation to the stratigraphy and structure of the volcano abstract the valle del bove is a major horseshoe shaped depression some 5 km in diameter and over 1000 m deep carved into the eastern flank of mount etna volcano the origin of the valle del bove has been a subject of debate for over a century but recent models relate it to the collapse of the ancient trifoglietto ii centre of etna either by caldera collapse or phreatomagmatic explosive activity careful morphological analysis shows the valle del bove to have formed after the post trifoglietto ii ellittico and leone centres and therefore to be considerably younger than the trifoglietto ii centre it has also been argued that the pyroclastic deposits that occur on the flanks of the volcano in close spatial relationship with the valle del bove were produced by the same event these pyroclastics are divided on the basis of age and composition into two groups the upper and lower tephra deposits the stratigraphy petrology and radiocarbon date of the lower tephra deposits indicate a trifoglietto ii age at least 20 000 years before the formation of the valle del bove the upper tephra deposits have a strong phreatomagmatic character and are closest in age to the valle del bove there is no evidence however to link them with its formation morphological study shows the valle del bove to consist of a series of coalescing scallops indicative of formation by landsliding the material removed by slope failure and subsequent fluvial transport followed a valley to the coast where it forms a fan shaped accumulation the chiancone consisting of volcaniclastics of fluvial and mudflow origin it is argued that the valle del bove did not result from simple caldera collapse but formed from a series of collapses caused by gravitational slope failure the chiancone is considered to be the product of this collapse

rheology of pig skin gelatine defining the elastic domain and its thermal and mechanical properties for geological analogue experiment applications abstract gelatine is a viscoelastic polymer that has been employed widely in geological analogue experiments to study processes related to the elastic behaviour of rocks such as tensile fracturing seismicity and magma intrusion however the elastic domain of this material has not yet been clearly defined by rheological tests here we describe the rheology and define the elastic domain of 250 bloom 20 mesh pigskin gelatine at concentrations 10 wt and temperatures of 5 25 c however these results are strongly comparable with gelatine of 245 260 bloom new equations are given for the shear and elastic moduli in relationship to temperature and gelatine concentration it is found that at concentrations 3 wt the tested gelatine is best described by a rheological model composed of a combination of kelvin voight and maxwell elements and therefore is not suitable to model elastic behaviour in geological analogue experiments at higher concentrations it is best described by a simpler viscoelastic model comprising a single maxwell element in order to ensure that geological analogue experiments remain within the elastic domain where the elastic component is far greater than the viscous component strain rates should range between 0 1 and 10 s 1 and temperature values should be 3 wt analogue experiments using gelatine approximate the elastic behaviour of natural rocks more closely than previously assumed

the volcanic tectonic cycle of the famous and amar valleys mid atlantic ridge 36 47 n evidence from basalt glass and phenocryst compositional variations for a steady state magma chamber beneath the valley midsections amar 3 the 1978 amar expedition extended the investigation of the mid atlantic ridge that was begun by the 1973 1974 famous expedition from the northern end of the famous rift the original famous area to the narrow central and southern end of the famous rift narrowgate region and into the broad amar valley south of fracture zone b available field and geochemical data allow us to characterize in detail the volcanic tectonic cycle for these two segments of the mid ocean ridge system a dynamic model of the crust forming processes within these two rift valley segments is deduced from 1 variations in the chemical composition of the erupted basaltic liquids as preserved in chilled glassy margins 2 composition and petrographie relationships of megacrysts and phenocrysts that represent cumulus crystallization onto the floor of a shallow magma chamber of a primitive magma that has reached pyroxene saturation early in its evolution and 3 detailed stratigraphie and regional observations that characterize the periodicity of volcanic construction and superimposed tectonism related to the ongoing extension of the valley floor each volcanic cycle is composed of several eruptive episodes that are initially typified by rapidly extruded sheet flows of primitive composition the decreasing extrustion rates at the end of an eruptive event are associated with more evolved liquid compositions that reflect fractionation within the shallow conduits intermixing of magmas is indicated by the relatively limited variability in glass composition not explicable in terms of simple fractionation processes the common evidence of crystal resorption and the apparent disequilibrium between megacrysts phenocrysts and their enclosing glass this indicates control by a crustal magma chamber liquid and crystal compositions and textural relations can best be explained by a three stage crystallization history 1 crystallization of olivine plagioclase and clinopyroxene onto the floor of a magma chamber 2 partial resorption of mineral phases by a superheated undersaturated liquid above the floor 3 intratelluric crystallization of olivine and plagioclase clinopyroxene during rise of melt to the surface through the conduit system above the magma chamber a magma chamber model is suggested for the amar famous rift valleys that satisfies both seismic and geological constraints we propose that a small steady state magma chamber is maintained beneath the topographically higher midsections of each valley segment amar and narrowgate regions but that these thin and terminate near the intersecting fracture zones expansion and contracton of the central magma body is controlled by the fluctuating imbalance between magma supply and chamber crystallization the famous narrowgate rift is currently in a contraction period so that in the northern famous region primitive liquid has erupted at mount venus and mount pluto without intercepting and mixing into the steady state chamber that supplies the mixed magmas to the narrowgate region

insights of dyke emplacement mechanics from detailed 3d dyke thickness datasets abstract dyke thickness datasets offer new insights into the detailed 3d geometry of dyke swarms and an exceptional opportunity to evaluate theoretical emplacement models the swartruggens kimberlite dyke swarm extends over 7 km along strike and intrudes a dolerite quartzite shale and andesitic lava succession the star kimberlite dykes cut shales and sandstones intersect a large dolerite sill and extend 15 km along strike both dyke swarms comprise anastomosing en echelon segments each several hundred metres long in total 1532 swartruggens dyke thickness measurements were taken to 750 m below the surface over a 250 m depth range and 3354 star dyke thickness measurements were taken over a 520 m depth range the swartruggens dyke thicknesses are 0 05 1 95 m mean 0 64 m whereas the star kimberlites range from

climate forcing of volcano lateral collapse evidence from mount etna sicily in this study we present evidence for early holocene climatic conditions providing circumstances favourable to major lateral collapse at mount etna sicily the volcano s most notable topographic feature is the valle del bove a 5 x 8 km cliff bounded amphitheatre excavated from the eastern flank of the volcano its origin due to prehistoric lateral collapse is corroborated by sturtzstrom deposits adjacent to the amphitheatre s downslope outlet but the age nature and cause of amphitheatre excavation remain matters for debate cosmogenic 3 he exposure ages determined for eroded surfaces within an abandoned watershed flanking the valle del bove support channel abandonment ca 7 5 ka bp as a consequence of its excavation in a catastrophic collapse event watershed development was largely dictated by pluvial conditions during the early holocene which are also implicated in slope failure a viable trigger is magma emplacement into rift zones in the eastern flank of a water saturated edifice leading to the development of excess pore pressures consequent reduction in sliding resistance detachment and collapse such a mechanism is presented as one potential driver of future lateral collapse in volcanic landscapes forecast to experience increased precipitation or melting of ice cover as a consequence of anthropogenic warming

how to cope with volcano flank dynamics a conceptual model behind possible scenarios for mt etna abstract volcano flank dynamics poses a serious hazard also involving the inhabited lower slopes mt etna is a well studied unstable volcano and a significant amount of data has been collected on the dynamics of its eastern and southern flanks we first propose a conceptual model to describe and explain flank dynamics at etna we identify the preconditions as due to the differential unbuttressing conditions at the volcano base and the triggering factors as shallow magmatic sources dikes reservoirs evidence and parameters and or observations for flank dynamics are listed summarizing the 1994 2010 period of activity based on this we then propose a set of scenarios possibly occurring in case of unrest of the unstable flanks of mt etna flank unrest is a variation in the steady state condition of the volcano flanks possibly accompanied by significant ground deformation seismicity and eruptions the scenarios may provide a general reference and recommendation in case of five types of multi hazard processes related either as a cause or effect to flank dynamics 1 edifice inflation 2 emplacement of dikes along the ne and or s rifts 3 seismicity along pernicana fault system 4 seismicity on the s sector 5 seismicity along timpe fault system each scenario is analyzed and recommendations are given the scenarios may or may not be related to each other in the sense that the probability of occurrence of one scenario may or may not be contingent or dependent upon the prior occurrence of another these scenarios provide a qualitative analysis of the multi hazard processes related to flank dynamics a more quantitative i e probabilistic characterization is under consideration

intrusive mechanism of the 2008 2009 mt etna eruption constraints by tomographic images and stress tensor analysis abstract since january 2008 several geophysical parameters have evidenced a recharging phase at mt etna volcano culminating with an effusive eruption that began on may 13 2008 seismic activity recorded at mt etna from january 2007 to may 2008 was analyzed in order to provide seismological constraints to the volcano dynamics leading to the eruption a total of 336 selected earthquakes with m l 1 5 were used as data source for this study specifically we calculated 3d velocity and attenuation tomography including a 3d relocation of the events and we computed 53 selected fault plane solutions fpss that were used for stress tensor inversion the most important result obtained from the joint analysis of v p v p v s and p wave attenuation is an anomalous zone with normal to high v p values between 3 5 and 4 5 km s and low v p v s values 1 64 which partially overlaps with a low q p values 50 volume located along a ns trending channel beneath the central crater this can be interpreted as a shallow volume characterized by high temperature where the magma is located with the presence of supercritical fluids the analysis of seismic stress tensor evidenced an extensional regime in the depth range 3 13 km with a vertically oriented 1 this finding may suggest an extensional stress regime probably related to the kinematic response of the volcanic edifice to both a deep magmatic intrusion and a condition of decreased regional compressive stress facilitated by sliding processes of the eastern flank of the volcano

the quaternary stratigraphy of mount etna sicily the effects of differing palaeoenvironments on styles of volcanism using recently published radiometric dates of important horizons within the etna succession correlations are proposed with the late quaternary biostratigraphies of the italian mainland and the mediterranean sea floor this enables palaeoclimatic palaeohydrological and palaeogeographical conditions on etna to be established at stages in the volcano s evolution it is argued that several major volcaniclastic suites were formed through the operation of processes that were under complex environmental rather than simple volcanological control alone in particular it is suggested that certain episodes of phreatomagmatic and laharic activity cannot be related to episodes of more evolved magma production but rather to times during which the environment height and configuration of etna favoured the eruption and emplacement of these deposits the authors reiterate their explanation of the formation of the valle del bove through processes of massive slope failure and indicate that conditions favouring this occurred at an appropriate stage in the history of the volcano it is concluded that on active basaltic volcanoes especially those like etna which are also high mountains the explanation of more violent phases requires the consideration of both internal volcanological and external environmental and morphological variables and that this is particularly important when its development has been set within the context of late quaternary environmental change finally the implications of these findings for the assessment of hazard are considered

from source to surface dynamics of etna s lava fountains investigated by continuous strain magnetic ground and satellite thermal data we investigated the eruptive episodes that occurred at etna volcano on 15 november 2011 and 18 march 2012 using different types of data we present novel data from two recently installed strainmeters that recorded unique signals during the lava fountain phases of these events the strainmeter data integrated with those recorded by the magnetic network and with satellite and ground thermal data allowed us to follow the path of a gas rich magma batch from the source inside the volcano to the surface and atmosphere the amplitude ratio of the volumetric strain changes constrained the storage depth of the magma feeding the lava fountains above 1 5 km below sea level magnetic data revealed an attempted shallow lateral intrusion whereas ground and satellite thermal data furnished a quantification of the total erupted volumes of 2 2 106 m3 for the 15 november event and 3 0 106 m3 for the 18 march event despite different durations of the explosive and effusive phases of the two lava fountain events the total erupted volume was quite similar suggesting the emptying of a shallow storage system displaying a steady behaviour

an archean megacaldera complex the blake river group abitibi greenstone belt abstract the archean blake river group of the southern abitibi greenstone belt is defined as a subaqueous megacaldera compelling evidence include 1 a radial and concentric organization of synvolcanic mafic to intermediate dykes 2 an overall dome geometry defined by the volcanic strata 3 a peripheral distribution of subaqueous volcaniclastic units 4 a zonal distribution of carbonate alteration and 5 a distinct annular synvolcanic inner and outer ring fault pattern three caldera forming events have been identified 1 the early misema caldera 2 the new senator caldera and 3 the well known noranda caldera the multi vent brg mafic volcanic complex developed on a monotonous sequence of tholeiitic basalts forming a submarine plain and experienced a first major collapse that created the giant misema caldera 80 km in diameter an endogenic dyke swarm intruded the synvolcanic fractures and an underlying magma chamber developed major volcaniclastic units were generated by local volcanic centers and summit calderas formed along the outer and inner ring faults this fault system was used as a conduit for co2 rich hydrothermal activity renewed volcanic activity was associated with a resurgent central dome inside the misema caldera this second collapse event created the 35 km by 14 km nw trending new senator caldera this caldera was produced by multi step sagging after the underlying magmatic chamber migrated to the se and formed the flavrian powel plutons the final collapse resulted in the formation of the noranda caldera that generated a well developed 070 trending fracture pattern associated with several vms deposits the multiple caldera setting provides an effective model to explain the presence of vms mineralization along the synvolcanic fractures associated with the three collapse episodes however the importance of the new senator caldera fracture pattern is emphasized because of its role in the positioning of the giant horne mine deposit

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

ground deformation patterns at mt etna from 1993 to 2000 from joint use of insar and gps techniques abstract combined gps measurements and radar interferometry insar have been applied at mt etna to study the ground deformation affecting the volcano both over the long 1993 2000 and short term 1997 1998 and 1998 2000 the aim was to better understand the dynamics of the volcano during the magma recharging phase following the 1991 93 eruption since 1993 insar and gps data indicate that mt etna has undergone an inflation a deep intrusion was detected by insar on the western flank of the volcano between march and may 1997 in the following months this intrusion rose up leading to a seismic swarm occurring in january 1998 in the western sector this now shallow intrusion is confirmed by gps data from 1998 to 2000 a general deflation affecting the upper part of the volcano was detected over the whole study period a continuous eastward to south eastward motion of the eastern sector of the volcano was also evidenced the analytical inversions of gps data inferred a plane dipping about 12 ese located beneath the eastern flank of the volcano at a depth of 1 4 km b s l the movement along this plane is able to reproduce the observed south eastward motion of a sector bounded northward by the pernicana fault westward by the north east rift and the south rift and southward by the mascalucia tremestieri trecastagni fault system insar data have validated this model

mechanisms of magma eruption and emplacement at mt etna between 1989 and 1992 the present eruption sequence of mt etna began during september 1989 with extensive fracturing and culminated in 1991 93 with the largest lava eruption this century1 here we present measurements of gravity and ground deformation which in conjunction with seismic data provide a detailed record of the processes occurring before and during eruption these reflect a complex interplay between magma injection into the paths of lowest compressive stress through the volcano flanks forcing elastic deformation and fracture growth in response to gravitational stresses we find that after the end of the eruptive activity in 1989 fractures in the south southeast flank of the volcano remained unfilled until some months before the 1991 93 eruption these results indicate the utility of microgravity monitoring as the precursory processes that we identify were largely undetected by seismic and ground deformation monitoring

tectonics of nisyros island greece by field and offshore data and analogue modelling abstract we use new on land and offshore structural data and scaled analogue models to analyse the fault tectonic pattern at nisyros island greece which has an active caldera that shows a complicated network of faults fractures and volcano tectonic structures we measured 157 faults that show dominant dip slip normal motions along planes mainly striking ne sw nne ssw and nnw sse inside the caldera dykes necks and morphometric parameters of volcanic domes explosion craters and fumarole pits indicate the control by ne striking discontinuities on magma and gas paths the nnw and ne striking faults bound a major block that underwent repeated downthrow and uplift movements during the late pleistocene holocene experiments with scaled models of caldera resurgence and two magma chambers indicate the formation of an hourglass shaped fault pattern as seen in plan view with an asymmetric increase in the fault offset and a widening of the fault divergence towards the volcano flank all these data suggest that regional fault tectonics and stress state strongly guided magma upwelling and the emplacement of volcanic centres whereas periodical bulging due to the overpressure of a second magma chamber located northwest of the caldera combined with faulting due to tectonic stresses can account for the overall deformation field

dykes and structures of the ne rift of tenerife canary islands a record of stabilisation and destabilisation of ocean island rift zones many oceanic island rift zones are associated with lateral sector collapses and several models have been proposed to explain this link the north east rift zone nerz of tenerife island spain offers an opportunity to explore this relationship as three successive collapses are located on both sides of the rift we have carried out a systematic and detailed mapping campaign on the rift zone including analysis of about 400 dykes we recorded dyke morphology thickness composition internal textural features and orientation to provide a catalogue of the characteristics of rift zone dykes dykes were intruded along the rift but also radiate from several nodes along the rift and form en echelon sets along the walls of collapse scars a striking characteristic of the dykes along the collapse scars is that they dip away from rift or embayment axes and are oblique to the collapse walls this dyke pattern is consistent with the lateral spreading of the sectors long before the collapse events the slump sides would create the necessary strike slip movement to promote en echelon dyke patterns the spreading flank would probably involve a basal decollement lateral flank spreading could have been generated by the intense intrusive activity along the rift but sectorial spreading in turn focused intrusive activity and allowed the development of deep intra volcanic intrusive complexes with continued magma supply spreading caused temporary stabilisation of the rift by reducing slopes and relaxing stress however as magmatic intrusion persisted a critical point was reached beyond which further intrusion led to large scale flank failure and sector collapse during the early stages of growth the rift could have been influenced by regional stress strain fields and by pre existing oceanic structures but its later and mature development probably depended largely on the local volcanic and magmatic stress strain fields that are effectively controlled by the rift zone growth the intrusive complex development the flank creep the speed of flank deformation and the associated changes in topography using different approaches a similar rift evolution has been proposed in volcanic oceanic islands elsewhere showing that this model likely reflects a general and widespread process this study however shows that the idea that dykes orient simply parallel to the rift or to the collapse scar walls is too simple instead a dynamic interplay between external factors e g collapse erosion and internal forces e g intrusions is envisaged this model thus provides a geological framework to understand the evolution of the nerz and may help to predict developments in similar oceanic volcanoes elsewhere

oxygen isotopes in subducted oceanic crust a new perspective from siberian diamondiferous eclogites 1 there are three methods of investigating the oxygen isotope composition of oceanic crust 1 data from drilling obtained samples 2 study of obducted ophiolites and 3 from crustal derived xenoliths however each approach has limitations drilling capabilities are limited to the upper 1 3 km of the oceanic crust ophiolites are segments of oceanic crust and underlying mantle exposed at the earth s surface but their origin and emplacement are still debated nonetheless the study of ophiolite sequences has enabled many of the fundamental observations regarding ancient oceanic crust and the oxygen isotope signature of the upper mantle analyses of ophiolite sequences e g samail reveal 18o variations ranging from isotopically enriched in relation to morb 18o morb to isotopically depleted low 18o morb interpreted to show the effects of seawater interaction at different temperatures mantle derived xenoliths also display compelling geochemical evidence suggesting they are remnants of subducted ocean crust and may in fact be more representative samples some kimberlite hosted diamondiferous eclogite xenoliths with crustal protoliths reveal a marked oxygen isotope disparity between oceanic crust and the upper mantle i e a bimodal distribution of both mantle like 18o 5 6 and isotopically enriched oxygen 18o 6 8 the isotopically high 18o values are often observed in eclogite xenoliths with ultramafic protoliths which form beyond the low temperature alteration zone this finding is in contrast to traditional oxygen isotope versus depth curves of ophiolite sequences here we present a compiled data set from siberian eclogites and pyroxenites that illustrates this bimodality using magnesium number mg as a depth proxy and investigate the conditions that could potentially result in the observed abnormal oxygen isotope variations

temporal variations in gravity at mt etna italy associated with the 1989 and 1991 eruptions results are presented from 11 microgravity surveys on mt etna between 1987 and 1993 a period including the major 1989 and 1991 1993 flank eruptions and subordinate 1990 activity measurements were made with lacoste and romberg d 62 and d 157 gravity meters along a network around the volcano between 1000 and 1900 m a s l and since 1992 a n s summit profile gravity changes of as much as 200 gal were observed at scales from the size of the summit region to that of the volcano none was associated with significant changes in ground elevation the data show an increase in gravity for 2 years before the 1989 eruption the increase is attributed to the accumulation of magma 0 25 1 7 109 m3 in an elongate zone oriented nnw sse between 2 5 and 6 km below sea level part of this magma was injected into the volcanic pile to supply the 1989 and 1990 eruptions it also probably fed the start of the 1991 1993 eruption since this event was not preceded by significant gravity changes a large gravity increase up to 140 gal detected across the volcano between june and september 1992 is consistent with the arrival in the accumulation zone of 0 32 2 2 109 m3 of new magma thus favoring continued flank effusion until 1993 a large gravity decrease 200 gal in the summit region marked the closing stages of the 1991 1993 event and is associated with magma drainage from the upper levels of etna s central feeding system

location and orientation of eruptive fissures and feederdykes at mount etna influence of gravitational and regional tectonic stress regimes abstract lava extrusion from fissures on the flanks of the etna volcano is a common feature of recent activity as evidenced by the eruptions of 1971 1981 1983 and 1985 and was of similar importance during prehistoric times we propose here a model within which the location and orientations of the large majority of historic eruptive fissures on etna s flanks together with their feeder dykes are explained within the framework of a gravitational stress regime stress orientations within this regime are controlled largely by the gross morphology of the volcano but are significantly modified by local topographic anomalies we propose that the gravitational stress regime largely supercedes an earlier developed regional tectonic stress regime which still operates in the sub volcanic basement and may remain the dominant control of eruptive fissure and feeder dyke disposition at lower altitudes on the flanks the proposed model is supported by 1 detailed examination of fissure locations and orientations and the relationship between fissure azimuths and topography 2 precise horizontal distance measurement and vertical ground deformation studies of a recent eruption and 3 qualitative physical modelling experiments in which coloured water is injected into solidified gelatine solutions representing variously shaped volcanic constructs a cautious approach is advocated when extrapolating trends of spatially limited fissure segments for the purpose of locating potential sites of magma ascent and implications of the model for hazard analysis are outlined

the role of deformation in the formation of metamorphic gradients ridge subduction beneath the oman ophiolite two tectonic scenarios have been proposed for genesis and emplacement of the oman ophiolite one suggests that the ophiolite was generated at a spreading center the other suggests generation within an intraoceanic arc an integrated thermal and kinematic model of the temperature stress rock type and displacement fields during early stages of the emplacement of the oman ophiolite was developed to test these two possibilities the thermal evolution was calculated by a finite difference algorithm for heat conduction considering heats of metamorphic reactions deformational heating heat advection by flowing rock mantle heat flow and radioactive heating the stress and displacement fields were calculated by an analytical model using a velocity boundary condition power law constitutive relations and a brittle frictional sliding relationship field observations in oman can be satisfied with the spreading center model but not with the arc model moreover simulations indicate that the ophiolite was probably 2 m y old at the time of intraoceanic thrusting and that shear stresses of 100 mpa were attained during thrusting in addition to satisfying currently available field constraints these simulations also indicate specific further work that will help resolve the controversy over thevolution of this unique orogen future work should be directed toward 1 using thermobarometry and thermochronology to constrain the spatial variation in ptt paths of the metamorphic sole 2 dating the igneous genesis of the ophiolite and 3 using quartzite and dunite recrystallized grain size paleopiezometers to infer stresses during thrusting these simulations point out the important effect synmetamorphic deformation can have on the formation of metamorphic field gradients in contractional fault zones metamorphic field gradients may be normal or inverted and contracted or extended relative to the initial thermobarometric gradient and adjacent fault zone rocks may display crossing pt paths unusually contracted or extended metamorphic field gradients may also develop in the footwalls of normal fault zones where portions of the heating hangingwall accrete to the uplifting cooling footwall

detecting short term evolution of etnean scoria cones a lidar based approach the 2001 and 2002 2003 flank eruptions on mount etna italy were characterized by intense explosive activity which led to the formation of two large monogenetic scoria cones one from each eruption on the upper southern flank of the volcano continuous monitoring of etna especially during flank eruptions has provided detailed information on the growth of these cones they differ in genesis shape and size a set of high resolution 1 m digital elevation models dems derived from light detection and ranging lidar data collected during four different surveys 2004 2005 2006 and 2007 has been used to map morphology and to extract the morphometric parameters of the scoria cones by comparing lidar derived dems with a pre eruption 1998 10 m dem the volume of the two scoria cones was calculated for the first time comparison of the lidar derived dems revealed in unprecedented detail morphological changes during scoria cone degradation in particular the morphologically more exposed and structurally weaker 2002 2003 cone was eroded rapidly during the first few years after its emplacement mainly due to gravitational instability of slopes and wind erosion

structural features of the july august 2001 mount etna eruption evidence for a complex magma supply system we describe the evolution of the volcanic activity and deformation patterns observed at mount etna during the july august 2001 eruption seismicity started at 3000 m below sea level on 13 july accompanied by moderate ground swelling ground deformation culminated on 16 july with the development of a ne sw graben c 500 m wide and c 1 m deep in the cisternazza area at 2600 2500 m above sea level on the southern slope of the volcano on 17 july the eruption started at the summit of mount etna from the se crater central lateral eruptive system from which two radial c 30 m wide c 3000 m long fracture zones associated with eruptive fissures propagated both southward 17 july and northeastward 20 july on 18 july a new vent formed at 2100 m elevation at the southern base of the montagnola followed on the next day by the opening of a vent further upslope at 2550 m eccentric eruptive system the eruption lasted for 3 weeks approximately 80 of the total lava volume was erupted from the 2100 m and the 2550 m vents the collected structural data suggest that the cisternazza graben developed as a passive local response of the volcanic edifice to the ascent of a north south eccentric dyke which eventually reached the ground surface in the montagnola area 18 19 july in contrast the two narrow fracture zones radiating from the summit are interpreted as the lateral propagation from the conduit of the se crater of north south and ne sw oriented shallow dykes 2 3 m wide the evolution of the fracture pattern together with other volcanological data magma ascent and effusion rate eruptive style petrochemical characteristics of the erupted products and petrology of xenoliths within magma suggest that the eccentric and central lateral eruptions were fed by two distinct magmatic systems examples of eccentric activity accompanied by central lateral events have never been described before at etna

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

time seismicity patterns affecting local and regional fault systems in the etna region preliminary results for the period 1874 1913 an analysis of time correlation function and fractal dimension has been performed on the seismic activity that affected mt etna volcano italy during 1874 1913 in order to investigate the behaviour of some suspected magma controlling regional fault systems the time span considered has been characterized by intense seismic and volcanic activity with eight flank eruptions mainly occurring along the same north south fissure system the analysis of historical sources has been used to revise and improve the seismic catalogue all macroseismic information has been reinterpreted using the new european macroseismic scale 1998 ems the results contribute to the definition of the seismic behaviour of some regional fault systems relevant to the geodynamics of the area and provide some insights into the dynamic processes of mt etna volcano

the role of the pernicana fault system in the spreading of mt etna italy during the 2002 2003 eruption flank instability and collapse are observed at many volcanoes among these mt etna is characterized by the spreading of its eastern and southern flanks the eastern spreading area is bordered to the north by the e w trending pernicana fault system pfs during the 2002 2003 etna eruption ground fracturing along the pfs migrated eastward from the ne rift to as far as the 18 km distant coastline the deformation consisted of dextral en echelon segments with sinistral and normal kinematics both of these components of displacement were one order of magnitude larger 1 m in the western previously known portion of the pfs with respect to the newly surveyed 9 km long eastern section 0 1 m this eastern section is located along a pre existing but previously unknown fault where displaced man made structures give overall slip rates 1 1 9 cm year only slightly lower than those calculated for the western portion 1 4 2 3 cm year after an initial rapid motion during the first days of the 2002 2003 eruption movement of the western portion of the pfs decreased dramatically while parts of the eastern portion continued to move these data suggest a model of spreading of the eastern flank of etna along the pfs characterized by eruptions along the ne rift instantaneous short lived meter scale displacements along the western pfs and more long lived centimeter scale displacements along the eastern pfs the surface deformation then migrated southwards reactivating one after the other the nnw sse trending timpe and trecastagni faults with displacements of 0 1 and 0 04 m respectively these structures along with the pfs mark the boundaries of two adjacent blocks moving at different times and rates the new extent of the pfs and previous activity over its full length indicate that the sliding eastern flank extends well below the ionian sea the clustering of seismic activity above 4 km b s l during the eruption suggests a deep decollement for the moving mass the collected data thus suggests a significant movement volume 1 100 km3 of the eastern flank of etna both on shore and off shore

ground deformations and volcanic processes as imaged by cgps data at mt etna italy between 2003 and 2008 1 we analyze the kinematic and crustal deformations of mt etna from 2003 to 2008 as imaged by the mt etna continuous gps cgps network etn net through a careful analysis of gps time series six coherent phases of crustal deformations have been identified three inflation phases and three deflation phases superimposed on a major inflation of the volcanic edifice since 2001 the inversions of gps velocities have enabled 1 a better understanding of the evolution of the volcanic sources acting beneath the volcano 2 analysis of the strain rate patterns and 3 a delineation of potential coupling between volcanic sources and the observed ground deformations the modeling of the pressure sources has shown a separation between inflation and deflation sources the deflation sources show an upward migration from 5 5 toward 2 0 km b s l while the inflation sources are located within 5 5 and 4 0 km b s l our results indicate that the kinematic and ground deformations of the mid upper eastern flank are driven by the interplay between the effect of the magmatic sources and a southeastward motion furthermore clockwise rotations have been detected that prevailed over the eastern motion of the flank during the inflation phases preceding the 2004 2005 and 2006 eruptions finally the accordance between the higher geodetic shear strain rates and the area with the highest seismic energy release shows that measured geodetic shear strain rates can provide useful information on the potential occurrence of seismic activity

gelatins as rock analogs a systematic study of their rheological and physical properties abstract in a laboratory model the behavior of the selected analog material must be properly scaled to nature here we systematically investigate both rheological and physical properties of a wide range of gelatins as functions of temperature composition concentration ageing and applied strain rate results show that gelatins behavior changes gradually from purely elastic to visco elasto brittle to purely viscous nonlinear rheology going from the gel to the sol state the rheological variability of gelatins appears promising for the potential use of these analog materials to simulate crustal and lithospheric rheological behavior in particular we found that pig skin 2 5 wt at 10 c has the required rheological properties for a suitable experimental set up to model crustal deformation

a three dimensional gravity analysis of the east pacific rise from 18 to 21 30 s multibeam bathymetry and gravity coverage of the east pacific rise epr between 18 o and 21 o 30 s is used to investigate the relation between melt supply and tectonic segmentation at ultrafast spreading rates the long wavelength features in the residual anomaly show a good correlation with those in the bathymetry the highest residual anomaly values occur over the broad discordant zone of the 20 o 40 s overlapping spreading center osc for seafloor ages of 0 ma to at least 1 5 ma we interpret the deepening of the bathymetry and the increase of the residual anomaly toward that discordant zone as due to a decrease of 500 200 m of the crustal thickness hence the 20 o 40 s osc has been associated with a reduced magmatic budget for at least the past 1 5 m y and represents a persistent segmentation of the epr this is consistent with models in which mantle upwelling even at the fastest spreading centers is enhanced between large discontinuities rather than evenly distributed along axis however this decrease of the crustal thickness toward an axial discontinuity is several times smaller than that typically documented for slow spreading ridges which suggests that mantle upwelling is less focused at fast spreading ridges or that along axis transport of crustal material is more efficient or both across the study area the residual anomaly decreases toward the nw by 15 20 mgal this regional gradient can be modeled with lateral temperature variations in the upper mantle of up to 60 o c increasing toward the nw this interpretation is consistent with the numerous seamounts present to the nw and the robust magmatic budget of the ridge between 17 o and 18 o s and it could also explain why the ridge segments defined by the smaller oscs between 18 o and 19 o s propagate very rapidly away from the robust area similar patterns of ridge propagation away from the shallowest section of a ridge have been documented near the galapagos and easter island hot spots hence these shorter ridge segments may not be associated with significant individual melt sources rather they may represent a superficial segmentation due to the interaction between the epr and a mantle heterogeneity located between 17 o and 18 o s

scale dependent location of hydrothermal vents stress field models and infrared field observations on the fossa cone vulcano island italy article i nfo hydrothermal venting occurs on numerous volcanoes of various age setting topographic and structural expression vent locations are commonly found not within volcanic craters only but predominantly at the crater margins and topographic highs a case example is vulcano island italy where the control on such vent locations along crater margins remained poorly understood however this paper describes numerical models combined with field observations and infrared imaging to explore the mechanisms that control the ascent paths of fluids in the fossa cone on vulcano using finite element modelling we calculate the gravitational stress in the volcanic edifice imposed by the topography results predict hydrofractures to be arranged in radial patterns at depth and in concentric patterns close to the surface furthermore low compressive stress values are found at the rims of the nested craters we compare the stress models to fumarole field data using a forward looking infrared camera we recorded images of the entire cone images were assembled to a mosaic and geocoded providing the first map of a remotely sensed temperature field in high resolution at la fossa the degassing and high temperature anomalies are found to be located mainly at the crests of the craters predominately in the northern and southern sector of the main crater therefore the stress distribution favours and indeed corresponds to the occurrence of fumaroles at la fossa the stress models also yield compression at the bottom of the crater where temperatures are cool thus we consider that the overall distribution of the fumaroles at the fossa cone is controlled by topography additional mechanisms contribute to the exact position of the degassing sites the influence of the lithological control seems to be strong in the southwestern part of the crater where the fumaroles are located 10 20 m below the inner crater rim in bedded strata in the northern part of the crater the exhalation sites can mainly be found at surface fractures and cracks emphasizing the structural control on the location of the fumaroles at this sector of the fossa cone using combined theoretical modelling and field observations this study helps to shed light into the processes directing fluids in volcanic edifices elsewhere and might contribute to the evaluation of upcoming hazard scenarios

vertical ground deformation on mount etna 1975 1980 we present the results of repeated precise leveling between the years 1975 and 1980 of an 11 km traverse over the summit of mount etna together with data from a network of dry tilt stations measured between 1976 and 1980 both methods demonstrate that little vertical movement occurs except on fresh lava flows which show a consistent pattern of downward movement interpreted as compaction and downhill sliding of lava after it has solidified other small vertical movements of a few centimetres recorded on the leveling traverse appear to be related to activity particularly the eruptions from a new vent area on the southeast side of the summit in 1978 and 1979 models of the recorded movement indicate that a small amount of magma was already stored in a dike below this eruption site as much as two years before it was erupted although the bulk of the magma for these eruptions was not stored in the upper few kilometres of the volcano the latter conclusion is supported by the dry tilt data which are dominated by local movements of 10 to 20 microradians with no consistent pattern of movement over the whole volcano

structural features of the 2007 stromboli eruption abstract on 27 february 2007 two ne sw and nnw sse dike fed effusive vents opened to the north at 650 and 400 m above sea level asl of the summit craters at stromboli forming a fissure parallel to the inner walls of the sciara del fuoco sdf sector collapse depression the formation of these vents was soon followed by rapid subsidence of the summit crater area this partly obstructed the central conduit temporarily choking the fissure and increasing the deformation of the upper part of sdf the reactivation of the nnw sse vent and the opening of a new vent located at 500 m asl fed by a second dike released the internal pressure and surface deformation ceased the eruption then continued again from the 400 m vent after a summit explosion on 15 march until ending in early april after a progressive decrease of magma output repeated ne sw dike intrusions have occurred in recent years close to the upper se limit of the sdf in that zone named bastimento the eruptive fractures traced the discontinuities that borders the sdf increasing the risk of triggering new sector collapse whereas the ne sw trending structures lie along the regional volcano structural trend of the aeolian arc through stromboli the nnw sse vents are oblique to this trend and may be controlled by the anomalous stress field within the unstable flank of the sdf another fundamental aspect of the 2007 eruption is the collapse of the central conduit due to the rapid and deep magma drainage linked to the opening of the 400 m vent the intrusion of dikes and development of flank vents during the 2007 eruption could possibly have triggered catastrophic landslides and related tsunami or eruptive paroxysms but the opening of new effusive vents released the internal pressures diminishing the hazard

comment on the distribution of basaltic volcanism on tenerife canary islands implications on the origin and dynamics of the rift systems by a geyer and j marti tectonophysics 483 2010 310 326 in their article geyer and marti 2010 propose that the evolution and origin of the volcanic islands which constitute the canarian archipelago are strongly controlled by regional tectonic atlantic and african structures in their fig 1a they sketch the geometry of the iberian and moroccan microplates and the respective boundary zones with respect to africa nubia and eurasia mantovani et al 2007 dashed lines indicating presumed plate boundaries cross the canarian archipelago which will therefore be located along a lithospheric fracture the boundary between the moroccan and african nubia microplates this regional fracture extends from the atlas to the atlantis fracture zone coinciding in parts with the propagating fracture postulated by anguita and hernan 1975 in fig 1b of geyer and marti 2010 dashed lines indicate the orientation of the most evident tectonic structures visible on the ocean floor as we show in this comment all of these mapped faults are artifacts

fast deformation processes and eruptive activity at mount etna italy the seismic and deformation patterns observed on mount etna before and during the 1991 1993 eruption the third largest since the seventeenth century in terms of lava volume are consistent with the regional tectonic framework of eastern sicily the pattern of the stress field acting on the intermediate and lower crust was defined at the local scale by focal mechanisms of microearthquakes occurring at depths between 10 and 25 km beneath the volcano they provide evidence for a strike slip compressional stress regime with the maximum compressive component acting approximately n s the fault plane solutions and the spatial and temporal distribution of seismicity indicate that usually sinistral shear ruptures occur along approximately ne sw trending fault zones while dip slip ruptures affect approximately nnw sse trending fault zones the latter include the avenues along which magma ascended during the 1991 1993 eruption seismic observations indicate a local inversion of the stress field acting on the upper crust depth 10 km underlying mount etna which was initiated less than 2 months before the eruptive event and disappeared with its end this is consistent with a local tensile regime that favored the magma ascent through the shallow crust the events preceding the eruption and accompanying its onset tilt anomalies and seismic swarms and those occurring shortly after its beginning a mainshock aftershock seismic sequence and associated coseismic tilts provide important evidence for understanding the dynamics of the two main volcano tectonic structures ne sw and nnw sse trending fault zones and associated intrusive mechanisms on etna the shape and location of the eruption feeding dike have been modeled from ground deformation data this approximately nnw sse modeled dike the seismicity and the position of the fractures are consistent with the regional stress field characterized by 1 oriented approximately n s the geophysical data presented and analyzed in the present paper strongly suggest an overall regional tectonic control as well as an active role for the intruding magma in the dynamics of the volcano

control of rock rheology on deformation style and slip rate along the active pernicana fault mt etna italy abstract the already known part of the active left lateral strike slip pernicana fault on the eastern flank of mt etna volcano has a holocene high slip rate of 1 5 2 7 cm yr but its surface trace abruptly disappears eastward approaching the lower slope of the volcano using geological geomorphological and structural surveys we found that the pernicana deformation zone extends 8 km further to the east beyond this point through a different mechanism as the thickness of the volcanic pile decreases the single e w to ese striking main fault plane gives way to a set of faults arranged in a splay structure which partitions the fault motion here slip rates are 0 4 to 1 4 cm yr on each fault further east where the lava succession is very thin and unfaulted we suggest that lavas are decoupled from plastic deforming sub etnean clay deposits which absorb the strain or that lavas have a too low mass to slide on the very lowest slope of the volcano i e further east lavas are once again thicker and the pernicana deformation zone behaves at the surface once again in a brittle manner locally known as the fiumefreddo fault with a low slip rate of

composition of the samail ocean crust the plutonic rocks of the samail ophiolite in the southeastern oman mountains formed in a spreading ridge magma chamber that was repeatedly replenished by primitive magma an average composition of the parent magma for the samail ocean crust is calculated by mass balance of the igneous stratigraphy the average parent magma was in equilibrium with most early formed cumulus minerals from the ophiolite and is very similar to primitive mid ocean ridge basalt the magma is basaltic in contrast to the picritic melts proposed as parents for some ophiolites although the average parent magma composition is basaltic field evidence suggests that individual batches of magma that fed the magma chamber varied in composition because of mantle processes the primary mantle melts were probably picritic but owing to reaction during ascent through the upper mantle and mixing or density entrapment within an open system crustal level magma chamber these picritic melts were probably not erupted on the seafloor

stress field interactions between overlapping shield volcanoes borehole breakout evidence from the island of hawai i usa acknowledgments this pta2 borehole investigation was funded by the international continental scientific drilling program icdp and by vmapp volcanic margin petroleum prospectivity project vbpr dougalearth tgs in collaboration with the humu ula groundwater research project d a j and s p are partly funded through a norwegian research council centres of excellence project project number 223272 ceed we thank marco groh for the logging operations we thank two anonymous reviewers for the comments and suggestions we are particularly grateful to the associate editor mike poland for his valuable comments and his critical review that greatly improved the manuscript

geophysical study of the east pacific rise 15 n 17 n an unusually robust segment bathymetric side scan sonar magnetic and gravity data from the east pacific rise epr between 15 and 17 n are used to establish the spreading history and examine melt delivery to an unusually robust spreading segment the axial ridge between the orozco transform fault 15 30 n and the 16 20 n overlapping spreading center osc has an average elevation of 2300 m which is 300 m shallower than typical epr depths and its cross sectional area is double the average value for the northern epr the total opening rate is 86 km myr but the inflated segment appears to have spread faster to the east by more than 20 since 0 78 ma the orientation of magnetic isochrons and lineaments in the side scan sonar indicates a 3 counterclockwise rotation of the spreading direction since 1 8 ma c2 and reflects a change in the pacific cocos plate motion the side scan lineaments also show that the percentage of inward facing faults 83 and the spacing between faults 1 5 km are consistent with the spreading rate dependence shown by carbotte and macdonald 1994 however the mean fault length 4 8 km is 1 5 km shorter than expected for the spreading rate and suggests that extensive off axis volcanism has draped the faults gravity analysis shows that the inflated segment has a 12 mgal bull s eye shaped low in residual mantle bouguer anomaly we offer several possible end member models for the anomaly including a prism of 10 partial melt in the mantle and lower crust or a crustal thickness anomaly of 2 25 km kinematic modeling that is based on structure and magnetic data suggests that two large magmatic pulses occurred at approximately 0 8 ma and 0 3 ma and have reshaped the plate boundary geometry and inflated the segment

reconstructing hydraulic conductivity field for hydrogeological modeling in an urban environment abstract hydrogeological analysis of flow is largely based on the concept of hydraulic conductivity in numerical hydrogeological modeling a value of hydraulic conductivity must be assigned at each element of mesh in heterogeneous geological formations this value governs the average behavior of groundwater flow within an aquifer the goals of this study are twofold 1 development of a methodology to transform the description of lithological units into local hydraulic conductivity values and 2 development of a methodology for reconstruction of hydraulic conductivity fields on a 83 km2 of the bordeaux urban area two approaches a 2d approach and a 3d approach based on geostatistical analysis are explained in details and compared for both approaches variographical analysis and ordinary kriging are carried out on the logarithmic of hydraulic conductivity and composite hydraulic conductivity is calculated using thickness weighting to get horizontal and vertical hydraulic conductivities the comparison of both approaches and the assessment of their potential and limitations suggest that the 2d approach is more appropriate than the 3d approach

anatomy of an unstable volcano from insar multiple processes affecting flank instability at mt etna 1994 2008 1 volcano deformation may occur under different conditions to understand how a volcano deforms as well as relations with magmatic activity we studied mt etna in detail using interferometric synthetic aperture radar insar data from 1994 to 2008 from 1994 to 2000 the volcano inflated with a linear behavior the inflation was accompanied by eastward and westward slip on the eastern and western flanks respectively the portions proximal to the summit showed higher inflation rates whereas the distal portions showed several sectors bounded by faults in some cases behaving as rigid blocks from 2000 to 2003 the deformation became nonlinear especially on the proximal eastern and western flanks showing marked eastward and westward displacements respectively this behavior resulted from the deformation induced by the emplacement of feeder dikes during the 2001 and 2002 2003 eruptions from 2003 to 2008 the deformation approached linearity again even though the overall pattern continued to be influenced by the emplacement of the dikes from 2001 to 2002 the eastward velocity on the eastern flank showed a marked asymmetry between the faster sectors to the north and those largely inactive to the south in addition from 1994 to 2008 part of the volcano base south west and north lower slopes experienced a consistent trend of uplift on the order of 0 5 cm yr this study reveals that the flanks of etna have undergone a complex instability resulting from three main processes in the long term 103 104 years the load of the volcano is responsible for the development of a peripheral bulge in the intermediate term 101 years observed from 1994 to 2000 inflation due to the accumulation of magma induces a moderate and linear uplift and outward slip of the flanks in the short term 1 year observed from 2001 to 2002 the emplacement of feeder dikes along the ne and south rifts results in a nonlinear focused and asymmetric deformation on the eastern and western flanks deformation due to flank instability is widespread at mt etna regardless of volcanic activity and remains by far the predominant type of deformation on the volcano

surface deformation in volcanic rift zones abstract the principal conduits for magma transport within rift zones of basaltic volcanoes are steeply dipping dikes some of which feed fissure eruptions elastic displacements accompanying a single dike emplacement elevate the flanks of the rift relative to a central depression concomitant normal faulting may transform the depression into a graben thus accentuating the topographic features of the rift if eruption occurs the characteristic ridge trough ridge displacement profile changes to a single ridge centered at the fissure and the erupted lava alters the local topography a well developed rift zone owes its structure and topography to the integrated effects of many magmatic rifting events to investigate this process we compute the elastic displacements and stresses in a homogeneous two dimensional half space driven by a pressurized crack that may breach the surface a derivative graphical method permits one to estimate the three geometric parameters of the dike height inclination and depth to center and the mechanical parameter driving pressure rock stiffness from a smoothly varying displacement profile direct comparison of measured and theoretical profiles may be used to estimate these parameters even if inelastic deformation notably normal faulting creates discontinuities in the profile geological structures open cracks normal faults buckles and thrust faults form because of stresses induced by dike emplacement and fissure eruption theoretical stress states associated with dilation of a pressurized crack are used to interpret the distribution and orientation of these structures and their role in rift formation

the interaction of volcanic activity in quaternary times upon the evolution of the alcantara and simeto rivers mount etna sicily summary the interaction between volcanic and alluvial sequences is described for the alcantara and simeto valleys mount etna sicily this study provides valuable information on the stratigraphy for prehistoric lavas exposed on the lower western flanks of the volcano eight orders of terrace are recognised in the simeto valley the basal tholeiitic volcanics the oldest exposed lavas of etna are associated with terrace 7 of the simeto which is correlated with either the pre rianian nomentanan erosive phase or the early rianian stage of the pleistocene the earliest evidence of trachybasaltic volcanism in the simeto catchment occurs in terrace 4 which is considered to be of late maspinian age the oldest known volcanics in the north western part of the volcano are related to terrace 3 which is dated at around 20000 bp the alluvial deposits of these terraces provide a valuable sequence of italian quaternary sediments dating back over the last 300000 years the nature of these deposits is described and the probable conditions of their deposition considered the terraces in the upper part of the alcantara are quite different in their mode of formation from the lava capped cut and fill terraces of the simeto valley the current upper course of the alcantara river is considered to be quite youthful versilian in age and the terraces are bench features formed as the river cut down through the lava sequence

three armed rifts or masked radial pattern of eruptive fissures the intriguing case of el hierro volcano canary islands abstract using new surface structural data as well as subsurface structural data obtained from seventeen water galleries we provide a comprehensive model of the volcano tectonic evolution of el hierro canary islands we have identified measured and analysed more than 1700 volcano structural elements including vents eruptive fissures dykes and faults the new data provide important information on the main structural patterns of the island and on its stress and strain fields all of which are crucial for reliable hazard assessments we conducted temporal and spatial analyses of the main structural elements focusing on their relative age and association with the three main cycles in the construction of the island the tinor edifice the el golfo las playas edifice and the rift volcanism a radial strike distribution which can be related to constructive episodes is observed in the on land structures a similar strike distribution is seen in the submarine eruptive fissures which are radial with respect to the centre of the island however the volcano structural elements identified onshore and reflecting the entire volcano tectonic evolution of the island also show a predominant ne sw strike which coincides with the main regional trend of the canary archipelago as a whole two other dominant directions of structural elements n s and wnw ese are evident from the establishment of the el golfo las playas edifice during the second constructive cycle we suggest that the radial striking structures reflect comparatively uniform stress fields during the constructive episodes mainly conditioned by the combination of overburden pressure gravitational spreading and magma induced stresses in each of the volcanic edifices by contrast in the shallower parts of the edifice the ne sw n s and wnw ese striking structures reflect local stress fields related to the formation of mega landslides and masking the general and regional radial patterns

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

evolution of the etna volcano information from the southern wall of the valle del bove caldera abstract the greater part of etna can be regarded as a complex strato shield volcano constructed from the overlapping products of several centres of trachy basaltic activity the valle del bove is a horse shoe shaped caldera 8 km long and 5 km wide cut into the eastern flanks of etna the caldera is one of the few areas on the volcano where historic eruptions have not obscured the products of pre historic centres of activity and these are well exposed in the cliff walls surrounding the caldera examination of these older volcanics provides important information on the eruptive style and internal plumbing of the etna volcano during pre historic times and suggests that both were significantly different from the present day much of the southern wall of the valle del bove represents a surviving portion of the trifoglietto ii volcano the largest pre historic centre of activity a stratigraphy is constructed for the southern wall the trifoglietto ii lavas and pyroclastics rest unconformably upon the eroded remnants of an older centre and are themselves overlain by the products of younger centres all the lavas exposed in the southern wall are of alkalic affinity and comprise a trachybasaltic suite ranging from hawaiite to benmoreite variation in the chemistry of the lavas can be explained by their differentiation at high levels in the crust from a more basic magma of alkali olivine basalt hawaiite composition an anomalous trend in the tio 2 content of the trifoglietto ii lavas may be explained by the fractionation of kaersutite ti rich amphibole a study has been made of the numerous dykes exposed in the walls of the valle del bove the alignments of which parallel trends which are important on etna at the present time it is proposed that the initial opening of the valle del bove occurred sometime between 20 000 and 10 000 y b p as a result of a phreatic or phreato magmatic explosion near the base of the eastern flank of trifoglietto ii this is visualised as triggering a slope failure and resulting in the destruction of much of the centre by a catastrophic landslide this mechanism has much in common with the explosive eruptions which produced both the bandai san japan caldera in 1888 and the mount st helens caldera in may 1980