earthquakes good tidings tidal stresses in the earth s crust don t seem to influence earthquakes water wells on the other hand seem strangely sensitive to seismic activity explanations are now proposed

active and passive microwave signatures of antarctic firn by means of field measurements and satellite data the angular dependence and polarization behaviour of back scattering and emission of polar firn at 5 2 ghz and 10 3 ghz were measured during an oversnow traverse in dronning maud land antarctica the signatures emphasize the importance of snow stratification in the interpretation of microwave remote sensing measurements highest backscattering coefficients and little angular variations were observed for refrozen firn near the coast in permanently dry snow areas with high accumulation rates and homogeneous snow morphology showed low backscattering coefficients and high emissivities pronounced layering and related density variations in low accumulation zones resulted in increased polarization differences of brightness temperatures and increased like polarized backscattering coefficients this behaviour is confirmed by the analysis of c band scatterometer measurements of the active microwave instrument aboard the european space agency s ers 1

external modulation of volcanic activity summary time and again records of seismovolcanic activity that show a diurnal and semi diurnal modulation have been related to the earth s tidal stress field as an external triggering mechanism several seismic data sets from different volcanoes are examined including stromboli volcano italy mt ruapehu new zealand and merapi and batur indonesia where in some cases weather data are also incorporated a comparison with theoretical body tides in the spectral domain reveals strong evidence against a correlation between seismovolcanic activity and tidal stress however other parameters such as temperature and barometric pressure show the same diurnal and semi diurnal modulation and are therefore candidates for a possible external modulation of volcanic activity several mechanisms are discussed for stromboli a clear correlation between volcanic activity and barometric pressure is shown

effects of tidal stresses on volcanic activity at mount etna italy 1 here we model quantitatively the stress and strain induced by tidal forces as possible triggers of mount etna eruptions during 1989 2000 and 2001 by means of 2d numerical analysis by finite difference method applied to the volcano edifice spectral and vectorial analysis of tidal acceleration indicates that the quasi diurnal semi diurnal and ter diurnal constituents may have induced decompressions up to some kpa in the shallow i e 1 500 m gas saturated magma reservoir which controlled magma vesiculation and the timing of lava fountain activity from the south east crater sec we consider the geological heterogeneities in the volcanic edifice i e rock geometries and properties feeder conduit and vent systems volcanic landforms the magma properties i e bulk modulus volatile content and the ongoing volcano tectonic stresses i e volcano flank deformations which strongly influence the response of eruptive activity to tidal forces indeed the tidal factor may act on flank deformation concomitant to shallow magma inflation the implications of our model may help understand the eruptive behaviour and the disequilibrium state of the volcano and may be useful for hazard assessment at mount etna

reflectivity modeling of a ground penetrating radar profile of a saturated fluvial formation major horizons in radar reflection profiles may correlate with contacts between stratigraphic units or with structural breaks such as fault surfaces minor reflections may be caused by clutter or in some cases may indicate material properties or structure within stratigraphic units in this study we examine the physical basis for major and minor reflections observed in a shallow unconfined fluvial aquifer near boise idaho u s a we compare a 2d profile from a surface ground penetrating radar reflection transect with the 1d modeled reflection profiles at three wells adjacent to the surface reflection profile the 1d models are based on dielectric constant and electrical conductivity values from borehole logs and vertical radar profile data reflections at the water table capillary fringe at the base of a sand filled channel and at the base of two sand rich lenses in a cobble dominated unit are recognizable in the surfacereflection profile and in all 1d reflectivity models less prominent reflections in stratigraphic units occur in both the surface profile model and the reflectivity model although such minor reflections are not correlated easily general similarities in their presence and location indicate that sometimes the reflections may be useful for recognizing internal facies structure or character

patterns of earthquakes and the effect of solid earth and ocean load tides at mount st helens prior to the may 18 1980 eruption seismographs near mount st helens volcano recorded an earthquake swarm lasting nearly 2 months prior to the catastrophic may 18 1980 eruption the earthquakes are divided into four classes based on station cpw 116 km seismogram characteristics 1 events with sv p amplitude ratio 3 and dominant frequency 3 hz 2 events with sv p ratio between 1 and 3 and dominant frequency 2 hz 3 events similar to characteristic 2 but with a strong probably surface wave phase just after the s phase and 4 events with frequencies between 1 and 2 hz lacking a clear s phase the seismicity pattern for each of the four classes is unique and we assume each group of events with similar wave forms represents a common physical process depth source area or fault orientation maximum likelihood b values range between 0 97 0 05 and 1 81 0 09 for the four groups we calculate solid earth stress and strain tides at the average hypocentral depth of 4 km we also calculate stress and strain tides induced by ocean loading their amplitudes are typically 20 40 those of the solid earth tides at the location of mount st helens a weak but significant correlation exists between the latter two classes of events and the tides for a time interval of about 5 days preceding the first onset of volcanic tremor and about 5 days thereafter the polarity of the correlation is opposite for the two classes of events in each case the phase of the correlation changes systematically with time the changes coinciding with the onset of tremor on march 31 and with a pronounced decrease in earthquake energy release rate on april 3 there are no significant correlations between the tides and the number of events or energy release of these two classes of earthquakes during any other interval between march 20 and may 18 1980 the first two classes of events show no evidence of significant tidal correlation at any time during the study period

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

viscosity of hydrous etna basalt implications for plinian style basaltic eruptions water dissolved in a silicate melt can strongly influence its physical properties and thus magma behavior during crystallization degassing foaming and fragmentation etna is a basaltic volcano whose activity is dominated by effusive eruptions which have long represented a threat to the densely populated surrounding area recently recognition of the products of a plinian eruption 122 b c has raised further issues for hazard assessment at etna and other basaltic volcanoes constraining the behavior of etna magma under conditions relevant to both effusive and explosive hazards requires viscosity data under conditions near the glass transition here we have investigated the viscosity of hydrous etna lava in order to better understand eruptive processes which characterize this volcano the experimental methods which have been used include piston cylinder synthesis of the hydrated melts micropenetration viscometry for low temperature viscosity measurements and near infrared spectroscopy for the evaluation of sample homogeneity and measurements of water content additionally scanning calorimetric determinations were performed to check whether incipient crystallization had occurred sample compositions were determined using electron microprobe analysis and 57fe mossbauer spectroscopy results from this study are compared with previous reports of trachytic phonolitic and model calc alkaline rhyolite hpg8 compositions the viscosity of the basaltic melt dry and wet has been parameterized in terms of temperature and water content via the non arrhenian equation log10 4 643 5 812 44 427 04 h2o t k 499 31 28 74 ln h2o where is the viscosity in pa s h2o is the water content in wt and t is the temperature in kelvin we observe that the viscosity of alkali basalt at more than 0 5 wt h2o is similar to that of an alkaline trachyte agnano monte spina eruption phlegrean fields and much higher than that of a peralkaline phonolite teide tenerife at similar silica contents and nbo t for water contents above 1 5 wt the viscosity of the basalt is similar to that of rhyolitic melts with similar water contents at temperatures ranging from 1 050 to 1 150 c and with water contents between 0 5 and 2 3 wt eruptive conditions the viscosities calculated using the equation defined in this study are 1 in reasonable agreement with those calculated using shaw s model and 2 much lower than those experimentally determined in a previous study however outside these temperature and water content ranges the agreement with shaw s model 1972 breaks down

earth tides and etnean volcanic eruptions an attempt at correlation of the two phenomena during the 1983 1985 and 1986 eruptions abstract an attempt has been made to correlate volcanic events on mt etna and moon sun attraction during the eruptions of 28 march 6 august 1983 12 march 13 july 1985 and 30 october 1986 the possibility of a trigger effect has been supposed for eruptive phenomena that originate by small and continuous external forces under particular stress conditions on the volcanic structure the parameters compared for the two phenomena are the hourly mean tremor amplitude recorded at serra la nave station and the hourly value of the vertical and of the two partial horizontal north south and east west components of the tidal acceleration induced by the moon sun system the relationship between two series of values the former for the tremor amplitude and the latter for one of the tidal acceleration components were then tested by statistical methods based on the information theoretic measure of interdependence between any pair of signal sequences the results show an effect of the horizontal tidal components on well known tectonic structures which may be widened or closed in contrast there is little evidence that the uprise of magma masses might depend on the vertical tidal attraction

spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas the eruption of mount etna in 2000 was notable for an exceptional series of 64 periodic lava fountains propelling lava fragments to heights of up to 900 metres it has been difficult to determine which of two suggested sources of power gas release from the magma itself during its rapid ascent or a build up of pressure from gas accumulated at depth is the driving force for these dramatic jets but one of the etna fountains provided volcanologists with the opportunity to use remote sensing not that remote see picture on the following page to determine the infrared spectra of the gas phase this revealed the chemical composition of the gas that powered this fountain as consistent with an origin in an accumulated gas layer lava fountains are spectacular continuous gas jets propelling lava fragments to heights of several hundred metres which occasionally occur during eruptions of low viscosity magmas1 2 3 4 5 whether they are generated by the effervescent disruption of fast rising bubbly melt2 3 4 5 or by the separate ascent of a bubble foam layer accumulated at depth6 7 still remains a matter of debate8 no field measurement has yet allowed firm discrimination between these two models a key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase this composition should differ markedly depending on whether the magma degassing occurs before or during eruption9 10 here we report the analysis of magmatic gas during a powerful 250 600 m high lava fountain measured with fourier transform infrared spectroscopy11 12 13 14 on mount etna sicily the abundances of volcanic gas species determined from absorption spectra of lava radiation reveal a fountain gas having higher co2 s and s cl ratios than other etnean emissions14 15 16 17 18 and which cannot derive from syn eruptive bulk degassing of etna basalt19 20 instead its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1 5 km depth below the erupting crater

mayon volcano philippines some insights into stress balance abstract mayon volcano is part of the bicol volcanic chain a peninsula in the south east of luzon island mayon s eruptive history during this century is fairly periodic with eruptions nearly every 10 years during the last two eruptions indications for tidal triggering of activities were found from statistical analyses hints for such a correlation exist for a number of volcanoes the statistical analysis of the seismicity points to a tidal triggering at mayon volcano in order to verify these indications the pressure balance between internal and external forces was computed the computations show that an interrelation between volcanic activities and tides especially ocean loading is probable for this purpose a global ocean model is improved by a regional model and a model of the local areas in order to consider the tidal distribution and the complicated geometry of the coasts the method of farrell w e 1972 deformation of the earth by surface loads rev geophys space physics 10 761 797 is used to calculate the ocean tidal loading the pressure increase in the vent due to vesiculation was tentatively modelled assumed a temperature decrease of 2 c per year the resulting stress is compared to the stress produced by the tidal forces body tides and ocean tidal loading it turns out that during a period of several days the small tidal forces may affect the stress balance considerably if the volcano is already in a critical state using fe modelling we estimate by neglecting all external forces how fast pressure can build up in the vent and to which extent the different physical parameters influence the pressure increase the maximum pressure resulting from the crystallization of the melt is compared with the maximum pressure yielding when in addition tidal forces are acting

high resolution of glacial ice stratigraphy a ground penetrating radar study of pegasus runway mcmurdo station antarctica ground penetrating radar gpr has been used to detect areas of present or potential structural weakness beneath a 3 2 km snow covered ice runway on the ross ice shelf antarctica the bandwidths of the transmitted wavelets were centred near 500 mhz the data show many horizons up to tens of metres long and occurring to about a 9 m depth below which a brine intrusion limits penetration the horizons are interpreted as discrete scatterers because of their diffraction nature and loss of higher frequencies with depth the presence of porous ice or dispersed water is interpreted from wavelet phase the water may be associated with apparent deepening and fading of the brine horizon if the above interpretation is correct water occurs at depths to 3 5m and extends as much as 40 m horizontally which is greater and deeper than known previously at 3 5 m depth the water may be adsorbed on mineral particles rather than remain free migration of the diffractions with a single layer migration scheme shows all horizons above the brine layer to be small dielectric perturbations within the ice stacking and hilbert transformation of the data reveal slight folding along the length of the runway loss of high frequency amplitude in the wavelets suggests that higher frequency radar might improve resolution only in the top few metres

high resolution dielectric profiling of ice cores a new method for high resolution 3 mm dielectric profiling of ice cores is described the method measures the capacitance and conductance of the ice at a single frequency chosen to be 50 khz in this case the technique requires only a few minutes per metre of core and no sophisticated data analysis the system is designed to operate on ice cores that have been cut longitudinally providing one flat and one curved surface the 50 khz conductance is dependent on the acid and neutral salt concentrations in the ice the new method was tested successfully on the grip core from summit greenland in 1991 it is useful for detecting seasonal variations in impurities in both acidic holocene ice and in normally alkaline wisconsin ice

spatial and temporal variability of snow accumulation using ground penetrating radar and ice cores on a svalbard glacier a 50 mhz ground penetrating radar was used to detect horizontal layers in the snowpack along a longitudinal profile on nordenskjoldbreen a svalbard glacier the profile passed two shallow and one deep ice core sites two internal radar reflection layers were dated using parameters measured in the deep core radar travel times were converted to water equivalent yielding snow accumulation rates along the profile for three time periods 1986 99 1963 99 and 1963 86 the results show 40 60 spatial variability in snow accumulation over short distances along the profile the average annual accumulation rate for 1986 99 was found to be about 12 higher than for the period 1963 86 which indicates increased accumulation in the late 1980s and 1990s

a comparison of seismic and radar methods to establish the thickness and density of glacier snow cover we show that geophysical methods offer an effective means of quantifying snow thickness and density opportunistic efficient but non optimized seismic refraction and ground penetrating radar gpr

etna 2002 eruption imaged from continuous tilt and gps data 1 on the night of october 26 2002 intense explosive activity and lava effusion began suddenly on the southern flank of mt etna at an altitude of 2750 m during the 27 and 28 october a long field of eruptive fractures propagated radially along the north eastern flank of the volcano ground deformation changes recorded between 26 and 27 october from gps and tilt data collected at the permanent geodetic network of mt etna were modeled to infer the positions and dimensions of the two dikes the observed deformation pattern was consistent with a response of the edifice to a composite mechanism consisting of a vertical uprising dike in the upper southern flank and a lateral intrusion propagating along the north eastern sector the first dike which triggered the eruption crossed the volcano edifice in a few hours and was located in the same area as the 2001 eruption while the second lateral dike which crossed the ne flank was the primary cause of the recorded deformation pattern

a comparison of radio echo sounding data and electrical conductivity of the grip ice core the depth of reflecting layers in arctic ice sheets has been determined by electromagnetic echo sounding using a varying distance between transmitter and receiver to determine the radar wave velocity the depth of the radar reflecting layers is compared with a profile of electrical conductivity measurements ecms from the greenland ice core project grip ice core in order to determine the velocity of the radar waves in the ice cap by using several reflecting layers it is possible to isolate the firn correction of the wave velocity and to estimate the accuracy of the calculated electromagnetic wave velocity the measured firn correction is compared with the correction calculated from the density profile and a comparison between the depth profiles of ecm and radar based on the corrected electromagnetic wave velocity is presented this profile shows that acid layers which originate from major volcanic eruptions show up as reflecting radar horizons

spatial mapping of multi year superimposed ice on the glacier kongsvegen svalbard ground penetrating radar gpr and satellite ers 2 synthetic aperture radar sar are used to map the thickness and extent of the superimposed ice si zone on the surge type glacier kongsvegen svalbard gpr imagery shows sub horizontal si layers lying unconformably above a discrete boundary below this boundary the ice has a gpr signature similar to that of ice further down glacier in the ablation zone this boundary is posited to represent the closing of crevasses that were created during the last surge of kongsvegen in 1948 open crevasses would have interrupted the formation of sheet layers of si due to efficient vertical drainage of the snowpack aerial photographs suggest that the crevasses closed sometime in the period 1956 66 a classified sar image from 2003 is used to delineate the extent of the si zone the si extent in the sar image agrees well with the si zone mapped by gpr using the si spatial depth distribution we estimate the mean annual accumulation of superimposed ice to be 0 16 0 06 m w e a 1 locally up to 0 43 m a 1 w e this corresponds to 15 33 of the local winter balance and 5 10 of the total winter balance measured since 1987

periodic gravity changes at poas volcano costa rica the measurement of gravity over active volcanoes is usually aimed either at the development of sub surface structural models1 4 or the investigation of temporal changes in gravity associated with magma movements5 13 the positive gravity anomaly over poas volcano costa rica4 indicates the presence of a cylindrical pipe of denser material extending to several kilometres depth although the volcano is active this feature has remained apparently stable for at least the past four years however our programme of high precision microgravity studies indicates changes with amplitudes of 120 gal at the crater rim and 50 gal on the flanks with a periodicty of 30 days these data are interpreted in terms of either relative movements of several metres between the magma body and the stable volcanic edifice or of cyclic density change related to the degree of vesiculation or crystallization of the magma there is a possibility that these variations are tidally induced such studies may have wider relevance in analysing previously unrecognized components of microgravity change and in the monitoring of active volcanoes

volcano tectonic activity along structures of the unstable ne flank of mt etna italy and their possible origin abstract we describe the prehistoric historic activity of the main and minor volcano tectonic structures of the northeastern flank of mt etna giving new data which provide a clearer view of how destabilized volcanoes react to magma pressure and gravity forces data are mostly based on new lithostratigraphic surveys and on offset measurements of late pleistocene holocene deposits and historic man made features the north east rift ne rift is a volcanic rift that has guided mostly explosive but also secondary effusive activity since the end of the pleistocene monogenetic cones and explosive craters are strongly elongated and aligned along 66 main surface fractures and several others hidden but inferred from sinkhole alignments the opening direction is locally oblique with a left lateral component in the north eastern segment of the rift at the ne tip of the rift the movements are relieved by the normal left lateral pernicana fault pf an 11 km long structure comprising e w fault segments connected by right stepping en echelon faults our study demonstrates that the very high slip rates at a centennial scale of these structures are well constrained and similar ne rift 0 6 1 8 cm a pf 0 5 2 2 cm a and have been also recognized in the latest pleistocene holocene 2 7 cm a the e w fiumefreddo fault ff has normal left lateral kinematics and a historic slip rate of 0 1 cm a ripa della naca faults strike ne and are covered by unfaulted

dynamic perennial firn aquifer on an arctic glacier ice penetrating radar and gps observations reveal a perennial firn aquifer pfa on a svalbard ice field similar to those recently discovered in southeastern greenland a bright widespread radar reflector separates relatively dry and water saturated firn this surface the phreatic firn water table is deeper beneath local surface elevation maxima shallower in surface lows and steeper where the surface is steep the reflector crosscuts snow stratigraphy we use the apparent deflection of accumulation layers due to the higher dielectric permittivity below the water table to infer that the firn pore space becomes progressively more saturated as depth increases our observations indicate that pfas respond rapidly subannually to surface forcing and are capable of providing significant input to the englacial hydrology system

importance of gravitational spreading in the tectonic and volcanic evolution of mount etna the interaction between gravity and thermal effects largely determines the structural and magmatic evolution of volcanic constructs at scales spanning several orders of magnitude from small cones to the oceanic crust1 3 although gravitational spreading is a direct consequence of this interaction and a fundamental process in volcano growth it is rarely recognized as such here we describe a striking example of this process at etna volcano in italy the volcano and its clay rich substratum are slowly spreading towards the east and south driven by gravity spreading produces extensional structures in the summit region and contpressional structures at the base of the volcano eastward movement of the volcanic edifice over a stationary magma supply may be the cause of an apparent westward migration of volcanic activity as gravitational spreading seems to control the location and magnitude of shallow seismicity and flank eruptions an appreciation of its effects could become an essential element of future volcanic hazard evaluation our model proposed here for etna may also be relevant to a reinterpretation of the geological history of a number of other volcanoes

sources of backscatter at 5 3 ghz from a superimposed ice and firn area revealed by multi frequency gpr and cores we investigate the major sources of backscatter at 5 3 ghz within the superimposed ice and firn areas of a polythermal glacier two ground penetrating radar systems an 800 mhz impulse system and a polarimetric 5 3 ghz frequency modulated continuous wave system are used to acquire along glacier profiles in the accumulation area of kongsvegen svalbard the 800 mhz response is used to map reflection horizons in the glacier using cores from the superimposed ice and firn areas the causes of these reflection horizons in terms of snow firn and ice layers are investigated superimposing the reflection horizons on the co polarized and cross polarized 5 3 ghz profile we are able to determine how the 5 3 ghz frequency responds to the different media scattering at rough interfaces and volume scattering occur in the superimposed ice area and are apparently caused by air bubble number size and distribution in the firn the strongest return originates from below the previous summer surface consistent with previous findings at approximately the same depth strong incoherent scattering begins the rapid decrease in coherent reflections indicates the significance of scattering in the firn

the relationship between late quaternary deformation and volcanism of mt etna eastern sicily new evidence from the sedimentary substratum in the catania region abstract stratigraphical and structural analyses have been carried out on the late quaternary foredeep succession forming the etnean substratum in the catania region eastern sicily in order to investigate in detail the chronology of deformation events that have accompanied a significant period of the eruptive activity of mt etna i e from 240 ka to the present this episode was characterised at about 200 ka by a main change of the petrochemical features of the emitted products from sub alkaline to alkaline this can be related to an evolving mantle diapir located beneath the volcano the new stratigraphical and structural field data presented in this paper constrain the development from 240 to 125 ka of nw se trending dextral faults associated with minor e w to ne sw oriented accommodation thrusts and nnw sse trending normal faults that originated in a dominant transpressive regime strike slip tectonics were active during the earlier emissions of sub alkaline lavas 320 200 ka old and part of the ancient alkaline products 180 100 ka old from scattered eruptive systems which developed in local transtensive zones distributed throughout the whole etnean region a major change in the mode of deformation since 125 ka bp was related to the propagation of a normal fault belt along the ionian coast of the catania region and the eastern sectors of the etnean edifice this process was associated with the growth of open folds that deformed the entire foredeep sequence exposed along the southern boundary of the etnean edifice during this period eruptive activity concentrated along the main extensional features where steady and very efficient feeding systems originated this resulted in a rapid increase in the volume of emitted alkaline products that gave rise to the construction of the modern stratovolcano during the last 80 ka the collected data emphasise some main aspects of the relationship between tectonic deformation at a regional scale and volcanism in the etna area firstly the mode of deformation at the onset of etnean volcanism seems to be inadequate to explain the emplacement at depth of a mantle diapir related to the occurrence of a hotspot almost independent from the local crustal dynamics on the other hand the late quaternary structural assemblages recognised on the surface can be interpreted as direct effects of the europe africa convergence rather than as the products of deformation induced by the emplacement of the mantle diapir in the different stages of etnean evolution a direct relationship exists between the mode of deformation and the distribution as well as the capacity of the feeding systems in particular the amounts of emitted products in the different stages depend on the intensity of crustal stretching associated with deformation rather than the volume of available molten material at depth these conclusions represent a new perspective for the interpretion of the early stages and subsequent evolution of the volcanic activity of mt etna the proposed model also represents an useful tool in deciphering the relationship between the deformation path seismicity and volcanic activity of mt etna

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

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

improved method to determine radio echo sounding reflector depths from ice core profiles of permittivity and conductivity we present a technique that modifies and extends down hole target methods to provide absolute measures of uncertainty in radar reflector depth of origin we use ice core profiles to model wave propagation and reflection and then cross correlate the model results with radio echo sounding res data to identify the depth of reflector events stacked traces recorded with res near the epica drill site in dronning maud land antarctica provide reference radargrams and dielectric properties along the deep ice core form the input data to a forward model of wave propagation that produces synthetic radargrams cross correlations between synthetic and res radargrams identify differences in propagation wave speed they are attributed to uncertainties in pure ice permittivity and are used for calibration removing conductivity peaks results in the disappearance of related synthetic reflections and enables the unambiguous relation of electric signatures to res features we find that i density measurements with attenuation or dielectric profiling are too noisy below the firn ice transition to allow clear identification of reflections ii single conductivity peaks less than 0 5 m wide cause the majority of prominent reflections beyond a travel time of about 10 s 900 m depth and iii some closely spaced conductivity peaks within a range of 1 2m cannot be resolved within the res or synthetic data our results provide a depth accuracy to allow synchronization of age depth profiles of ice cores by res modeling of isochronous internal structures and determination of wave speed and of pure ice properties the technique successfully operates with dielectric profiling and electrical conductivity measurements suggesting that it can be applied at other ice cores and drill sites

age estimates of isochronous reflection horizons by combining ice core survey and synthetic radar data 1 ice core records and ice penetrating radar data contain complementary information on glacial subsurface structure and composition providing various opportunities for interpreting past and present environmental conditions to exploit the full range of possible applications accurate dating of internal radar reflection horizons and knowledge about their constituting features is required on the basis of three ice core records from dronning maud land antarctica and surface based radar profiles connecting the drilling locations we investigate the accuracies involved in transferring age depth relationships obtained from the ice cores to continuous radar reflections two methods are used to date five internal reflection horizons 1 conventional dating is carried out by converting the travel time of the tracked reflection to a single depth which is then associated with an age at each core location and 2 forward modeling of electromagnetic wave propagation is based on dielectric profiling of ice cores and performed to identify the depth ranges from which tracked reflections originate yielding an age range at each drill site statistical analysis of all age estimates results in age uncertainties of 5 10 years for conventional dating and an error range of 1 16 years for forward modeling for our radar operations at 200 and 250 mhz in the upper 100 m of the ice sheet comprising some 1000 1500 years of deposition history final age uncertainties are 8 years in favorable cases and 21 years at the limit of feasibility about one third of the uncertainty is associated with the initial ice core dating the remaining part is associated with radar data quality and analysis

decompression experiments identify kinetic controls on explosive silicic eruptions 1 eruption intensity is largely controlled by decompression induced release of water rich gas dissolved in magma it is not simply the amount of gas that dictates how forcefully magma is propelled upwards during an eruption but also the rate of degassing which is partly a function of the supersaturation pressure pcritical triggering gas bubble nucleation high temperature and pressure decompression experiments using rhyolite and dacite melt reveal compositionally dependent differences in the pcritical of degassing that may explain why rhyolites have fueled some of the most explosive eruptions on record

spatial variability at shallow snow layer depths in central dronning maud land east antarctica spatial variability at swallow snow layer depths in central dronning maud land east antarctic

mechanisms for ground surface fracturing and incipient slope failure associated with the 2001 eruption of mt etna italy analysis of ephemeral field data abstract during the july august 2001 eruption of mt etna development of extensional fractures faults and grabens accompanied magma intrusion and subsequent volcanic activity during the first days of the eruption we performed an analysis of attitude displacement and propagation of fractures and faults exposed on the ground surface in two sites torre del filosofo and valle del leone located along the same fracture system in the region surrounding the valle del bove depression on the eastern flank of mt etna fractures and faults formed as the consequence of a shallow intruding dyke system that fed the several volcanic centres developed along the fracture system the investigated sites differ in slope attitude and in geometrical relationships between fractures and slopes in particular the fracture system propagated parallel to the gentle slope

radar response of firn exposed to seasonal percolation validation using cores and fdtd modeling we use ground penetrating radars gprs firn cores and electromagnetic finite difference time domain fdtd numerical modeling to characterize the gpr response to a frozen high arctic firn pack as a result of extensive summertime percolation the firn pack comprises a high fraction of ice layers lenses and vertical glands we show that the gpr response on the firn pack mainly depends on the following 1 the thickness of the ice layers 2 the distance between layers 3 the layer roughness and 4 the presence or absence of elliptical ice lenses using 3 d fdtd modeling we show that the gpr is not sensitive to typical ice glands which implies that the gpr underestimates firn heterogeneity such that firn stratigraphy in percolation and wet snow zones could be incorrectly interpreted as being better preserved than it actually is we find that thin ice layers 0 05 m or multiple thin ice layers give a strong response thicker ice layers typically give a weaker backscatter per unit area mainly due to the lack of interference of the reflections from the upper and lower interfaces but are due to their continuity easily trackable ice layers with a thickness comparable to the gpr wavelength give 180deg phase shifted upper and lower reflections and are in general separated by a band of low gpr response due to the lack of permittivity contrast within the ice layers despite the ice lenses relatively short horizontal correlation length as inferred from cores bands of high amplitude clutter caused by these features can be traced over several kilometers in gpr profiles

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

statistical analysis of intermittent volcanic tremor associated with the september 1989 summit explosive eruptions at mount etna sicily the pattern of volcanic tremor accompanyingthe 1989 september eruption at the south east summit crater of mount etna is studied in specific sixteen episodes of lava fountaining which occurred in the first phase of the eruption are analysed their periodic behaviour also evidenced by autocorrelation allows us to define the related tremor amplitude increases as intermittent volcanic tremor episodes focusingon the reg ular intermittent behaviour found for both lava fountains and intermittent volcanic tremors we tried an a posteriori forecast usingsimple statistical methods based on linear regression and the student t test we performed the retrospective statistical forecast and found that several eruptions would have been successfully forecast in order to focus on the source mechanism of tremor linked to lava fountains we investigated the relationship between volcanic and seismic parameters a mechanism based on a shallow magma batch regularly refilled from depth is suggested 1 2002 elsevier science b v all rights reserved

ground based measurements of spatial and temporal variability of snow accumulation in east antarctica the east antarctic ice sheet is the largest highest coldest driest and windiest ice sheet on earth understanding of the surface mass balance smb of antarctica is necessary to determine the present state of the ice sheet to make predictions of its potential contribution to sea level rise and to determine its past history for paleoclimatic reconstructions however smb values are poorly known because of logistic constraints in extreme polar environments and they represent one of the biggest challenges of antarctic science snow accumulation is the most important parameter for the smb of ice sheets smb varies on a number of scales from small scale features sastrugi to ice sheet scale smb patterns determined mainly by temperature elevation distance from the coast and wind driven processes in situ measurements of smb are performed at single points by stakes ultrasonic sounders snow pits and firn and ice cores and laterally by continuous measurements using ground penetrating radar smb for large regions can only be achieved practically by using remote sensing and or numerical climate modeling however these techniques rely on ground truthing to improve the resolution and accuracy the separation of spatial and temporal variations of smb in transient regimes is necessary for accurate interpretation of ice core records in this review we provide an overview of the various measurement techniques related difficulties and limitations of data interpretation describe spatial characteristics of east antarctic smb and issues related to the spatial and temporal representativity of measurements and provide recommendations on how to perform in situ measurements

radio wave depolarization and scattering within ice sheets a matrix based model to link radar and ice core measurements and its application crystal orientation fabric cof has a large influence on ice sheet flow earlier radar studies have shown that cof based birefringence occurs within ice sheets radio wave scattering in polar ice results from changing physical properties of permittivity and conductivity that arise from differing values of density acidity and cof we present an improved mathematical model that can handle all these phenomena together we use this matrix based model to study the two way propagation of depolarized radio waves that scatter at both isotropic and anisotropic boundaries based on numerical simulations we demonstrate how cof affects the radar signals in terms of radar polarization and frequency we then compare the simulated features with vhf radar data obtained at two contrasting inland sites in east antarctica where cof is known from ice core studies these two sites are dome fuji located near a dome summit and mizuho located in a converging ice flow region data at dome fuji are dominated by typical features resulting from birefringence in contrast both birefringence and anisotropic scattering affect the radar data at mizuho we argue that radar methods can be used to determine principal axes and strength of birefringence in the ice sheets

techniques for measuring high resolution firn density profiles case study from kongsvegen svalbard on an 11 m firn ice core from kongsvegen svalbard we have used dielectric profiling dep to measure electrical properties and digital photography to measure a core optical stratigraphy cos profile we also used a neutron scattering probe np to measure a density profile in the borehole from which the core was extracted the np and dep derived density profiles were similar showing large scale 30 cm variation in the gravimetric densities of each core section fine scale features 10 cm are well characterized by the cos record and are seen at a slightly lower resolution in both the dep and np records which show increasing smoothing a combination of the density accuracy of np and the spatial resolution of cos provides a useful method of evaluating the shallow density profile of a glacier improving paleoclimate interpretation mass balance measurement and interpretation of radar returns

revealing the nature of radar reflections in ice dep based fdtd forward modeling 1 successful simulation of ground penetrating radar gpr traces in polar ice is achieved by numerical finite difference time domain fdtd forward modeling properties of the modeled medium are taken from high resolution dielectric profiling dep of the upper 100 m of an ice core from dronning maud land antarctica the gpr reference trace is calculated from stacking of a normal moveout corrected common midpoint survey carried out near the borehole location the excellent agreement of synthetic and gpr based results demonstrates the capability of fdtd models to reproduce radargrams from ice core properties for interpretation of radio echo sounding data and emphasizes the exploitation of radar data for improved interpretations of glaciological climate proxys in addition to presenting modeling results we perform sensitivity experiments to investigate the nature and origin of radar reflection in ice discuss reasons for the failure of modeling studies in the past and indicate new approaches

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