atmospheric sulfur dioxide measurements during the 2005 and 2007 eruptions of the piton de la fournaise volcano implications for human health and environmental changes abstract piton de la fournaise is an active volcano located in the south eastern part of reunion island a tiny island found in the south western indian ocean 21 s 55 5 e this volcano erupts regularly at least once a year with notable amount of degassing concerning the volcanic eruptions the regulation of the french ministry of environment on the air quality is mainly focussed on the standards applicable for the sulfur dioxide so 2 in terms of public health and environmental changes air samples have been collected continuously every 10 days on passive diffusion tubes of so 2 an atmospheric tracer of volcanic plumes by ora observatoire reunionnais de l air at 10 sites which have been located around the volcano since september 2005 the mean so 2 concentrations measured over a 10 day period in the absence of any volcanic eruption range between very low values 1 15 g m 3 for all 10 sites however during the december 2005 eruption notable so 2 concentrations factor 5 25 have been measured at the locations situated on the north west flanks of the volcano the so 2 degassing reached concentrations of 65 379 g m 3 which is mainly caused by the volcanic activity when coupled with the local to regional atmospheric circulations land sea breezes easterlies etc a wide range of atmospheric measurements was performed in the vicinity of piton de la fournaise in order to characterize the gaseous and particle emissions during the april may 2007 eruption so 2 concentrations were also measured continuously by sf 2000 analyser at several coastal locations in the vicinity of the volcano during and off eruption activities in the absence of any volcanic eruption the so 2 concentrations showed day to day variations with hourly mean concentrations varying between 1 and 20 g m 3 these values correspond to the background concentrations for this coastal rural location and might as well come in part from non volcanic origin the so 2 concentrations however were increased by a factor 10 30 with a maximum hourly mean concentration of 2486 g m 3 during the april may 2007 eruption hereby several statutory thresholds were exceeded particularly at the tremblet location indeed the information and recommendation threshold 350 g m 3 h as well as the alert threshold 500 g m 3 on 3 h consecutively were exceeded 32 and 5 times respectively at this site these measurements point out that during the times of eruptions with significant amounts of degassing the threshold values for protecting the ecosystems and the air quality for human health were exceeded at several inhabited locations with implications for human health and environmental changes on local to regional scale

volcanic eruption velocities measured with a micro radar a novel technique to quantitatively assess volcanic eruption dynamics is presented we report on measurements of volcanic eruption velocities with a modified micro radar doppler anemometer on stromboli volcano italy the mean vertical eruption velocity recorded during a four day period in late 1996 was around 10 m s which is somewhat on the small side for strombolian eruptions however the activity of stromboli volcano during this period was very weak explaining the relatively small velocities the technique used is much better in resolution than older techniques based on static photos and allows a continuous monitoring of the volcanic activity in addition to the velocity information recorded by the doppler spectrum it also contains information on the density of the ejected material and the size distribution of the particles in the volcanic jet

volcanic tremor at mount etna january 1984 march 1985 its relationship to the eruptive activity and modelling of the summit feeding system spectral analyses of volcanic tremor at etna during january 1984 march 1985 have been performed and the relationship between tremor energy and observed volcanic phenomena have been examined the highest energy levels have been observed during the paroxysmal phases of eruptions whereas a gradual decrease was linked to the lowering of eruptive activity amplitude variations with time of some spectral frequency peaks 0 95 1 20 1 45 1 65 1 80 and 2 40 hz have been compared with volcanic activity at the summit craters and on the basis of these results a new schematic diagram for the feeding system of the summit vents is proposed

broadband measurements of the sources of explosions at stromboli volcano italy during september october 1997 21 three component broadband seismometers were deployed on stromboli volcano at radial distances of 0 3 2 2 km from the active crater to investigate the source mechanisms of strombolian explosions in the 2 50 s band the very long period vlp signals associated with explosions are consistent with two stationary sources repeatedly activated in time vlp particle motions are essentially linear and analyses of semblance and particle motions are consistent with a source centroid offset 300 m beneath and 300 m northwest of the active vents similar vlp waveforms are observed at all 21 stations indicating that the seismograms are source dominated the vlp ground displacement response to each explosion may be qualitatively interpreted as 1 pressurization of the conduit associated with the ascent of a slug of gas 2 depressurization of the conduit in response to mass withdrawal during the eruption and 3 repressurization of the conduit associated with the replenishment of the source with fluid

stratigraphy and remanence acquisition of a palaeomagnetic reversal in alluvial siwalik rocks of pakistan a high resolution record of a palaeomagnetic reversal is documented in miocene alluvial rocks of pakistan we examined lateral variability of lithostratigraphy and palaeomagnetic stratigraphy through the same palaeomagnetic reversal in six correlated sections each section contains one or more palaeomagnetic sites with directions between fully reversed and fully normal the position of the reversal illustrates local relief in the study area and the time transgressive nature of certain stratigraphic units variability in the thickness of the transitional interval indicates contemporaneous variability in sediment accumulation rates different characteristics of palaeomagnetic remanence are associated with the depositional and postdepositional history of these sediments variability in patterns of remanence behaviour is the basis for inferences about post depositional processes we discuss two magnetic parameters that express coherency of palaeomagnetic samples the maximum angle of deviation and the circular standard deviation of particular interest are samples with incoherent palaeomagnetic signals the incoherency of samples is inversely correlated with the thickness of the transitional interval a low rate of sediment accumulation suggested by a thin transitional interval may facilitate a prolonged period of remagnetization through pedogenic or hydrological processes alternatively transition intervals defined by coherent magnetization may be thin as a result of pedogenically induced incoherency

the siwaliks of pakistan time and faunas in a miocene terrestrial setting magnetostratigraphy provides unparalleled chronologic precision for long terrestrial sedimentary records the siwaliks of the potwar plateau northern pakistan present perhaps the best example of a sequence of well dated faunal horizons spanning most of the neogene in a single terrestrial biogeographic province temporal control on fossil localities tied to multiple paleomagnetic sections is ca 0 1 m y less given special conditions of short magnetozone duration or superpositional relationships new correlations are presented for two long sections in the lower siwaliks showing the power and the limitations of mag netostratigraphic correlation within the siwalik depositional setting correlation of potwar fossil localities to those of an east african section also dated paleomagnetically are established with fossil localities from those two biogeographic provinces shown to be coeval on a scale of 10 5 yr the composite biostratigraphy rendered by the thick well exposed well dated potwar siwalik

strombolian explosions 1 a large bubble breaking at the surface of a lava column as a source of sound strombolian activity consists of a series of explosions caused by the breaking of large overpressurized bubbles at the surface of the magma column acoustic pressure has been measured for 36 explosions at stromboli we propose that sound is generated by the vibration of the bubble before it bursts oscillations are driven by an initial overpressure inside the bubble assumed to be initially at rest just below the magma air interface inertia effects cause the bubble to overshoot its equilibrium radius then the bubble becomes underpressurized and contracts because of gas compressibility these oscillations are only slightly damped by viscous effects in the magma layer above the bubble the bubble cannot complete more than one cycle of vibration because of instabilities developing on the magma layer that lead to its breaking near the minimum radius assuming a simple geometry we model this vibration and constrain the radius and length of the bubble and the initial overpressure by fitting a synthetic waveform to the measured acoustic pressure the fit between synthetic and observed waveforms is very good both for frequency 60 rad s 1 and amplitude the initial bubble radius is 1 m and the length varies between several and a few tens of meters from the initial overpressure approximately 105 pa we calculate the maximum radial velocity of ejecta 30 m s 1 the generally good agreement between data and predictions of our model leads us to suggest that acoustic measurements are a powerful tool for the understanding of eruption dynamics

utilization of seismically recorded infrasonic acoustic signals to monitor volcanic explosions the el chichon sequence 1982 a case study infrasonic acoustic signals from five explosive eruptions of el chichon volcano during march 29 through april 4 1982 were recorded by a microbarograph array and seismic research observatory sro seismograph collocated near mckinney texas analyses of these signals for frequencies from 0 0033 to 0 025 h have demonstrated functional relationships of amplitude to frequency consistent with 1 for microbarometric data 2 for vertical mode seismic data and 3 for radial mode seismic data these observed slopes are in agreement with those theoretically predicted by sorrells 1971 estimations of kinetic energy releases by the explosions of el chichon are presented and range from 4 9 1022 ergs to 2 0 1023 for the largest eruption on april 4 1982 to 4 2 1021 to 6 1 1021 ergs for the smallest eruption on april 3 1982 the method of posey and pierce 1971 to estimate the explosivity from long period infrasonic signals is not likely to be applicable strictly speaking to the shorter period data thus it is believed that the energy release for the smallest eruption is overestimated by possibly an order of magnitude comparable estimations of volcanic explosivity from sro radial seismic data and microbarometric array data strongly recommend using sro and international deployment accelerometers network data for far field analyses of volcanic explosions and construction of a rigorous volcanic explosivity scale

the geometry of strombolian explosions insights from doppler radar measurements summary observations of strombolian volcanic explosions were carried out at etna s southeast crater on 2001 july 4 using a ground based pulsed doppler radar voldorad to obtain quantitative constraints on the geometry of the explosions we modelled synthetic doppler spectra by combining the outputs of a ballistic model to compute the theoretical velocities of gas and particles and an electromagnetic scattering model to calculate the synthetic echo power this allowed us to reproduce the shapes of recorded doppler spectra for each volcanic explosion we examined the geometrical distribution of ejected pyroclasts for about 200 explosions and found two main types of explosion each showing a distinctive spectral signature the first type characterized by the triangular shape of their doppler spectra represents 34 per cent of the explosions this spectrum shape is related to a gaussian distribution of the pyroclast ejection angles where most of the volcanic material is ejected vertically within a narrow cone with the particle concentration decreasing radially the second type represents about 12 per cent of the explosions and is characterized by a top hat shaped spectrum it is produced by a uniform distribution of pyroclast ejection angles in this case the bubbles tend to burst above the crater rim and eject the ballistic clasts hemispherically without preferential orientation the majority of the strombolian explosions analysed 54 per cent are intermediate between these end member shapes and show a triangular spectra truncated by a plateau they result from a uniform distribution of ejection angles around the jet axis the continuous radar recordings allowed us to carry out a statistical analysis on the geometrical features of the same 200 strombolian explosions thus we find that 40 is a statistically representative aperture of the dispersion cone characterized by uniform ejecta distribution for explosions having a plateau component i e 2 3 of all explosions studied we also find that 80 per cent of the total particle load remains within this 40 dispersion cone which in our case is oriented nearly vertically such quantification of the geometrical features of strombolian explosions can provide constraints on shallow conduit processes for example the time evolution of the top hat doppler spectra during the paroxysm suggests that the magma level varies over a 15 min timescale

infrasonic waves and volcanic tremor at stromboli the origin of the volcanic tremor is still under debate many theories have been proposed in the last years but none has yet been completely accepted in 1993 highly sensitive pressure sensors 2 175 pa volt used to monitor the explosive activity at stromboli have revealed unexpected correlation between small spike shaped pressure signals 1 2 pa and volcanic tremor these pressure pulses repeat regularly in time with a recurrent period of ca 1 s video camera images allowed us to correlate the pressure pulses with small gas bursts occurring at one of the active vents the striking correlation 0 971 between infrasonic and seismic energy fluctuations is particularly meaningful in the frequency domain infrasonic and seismic signal share the same spectral content 3 hz for every station within a range of 700 m around the craters correlations in time and frequency domain remained unaltered during the 1994 field experiments moreover during 1994 the increased degassing activity has been followed by an increase in pressure release 7 8 pa and by a shift towards higher frequencies 8 hz both in the infrasonic and seismic records infrasonic waves and volcanic tremor show similar energy fluctuations and frequency contents appearing therefore to be produced by the same dynamical process on this basis we claim that volcanic tremor at stromboli originates by continuous outbursting of small gas bubbles in the upper part of the magmatic column

degassing at low magma viscosity volcanoes quantifying the transition between passive bubble burst and strombolian eruption abstract at many volcanoes low magma viscosities allow persistent degassing over a range of styles from explosive strombolian activity to gas puffing and passive degassing it is generally accepted that strombolian eruptions reflect the bursting of large bubbles gas slugs at the magma surface and that relatively quiescent puffing indicates the presence of significantly smaller bubbles or slugs here we address this qualitative range and derive a dimensionless parameter pslim to quantify and distinguish different regimes of burst vigour for pslim 1 passive activity is anticipated and measurable parameters such as infrasonic amplitude will be small for pslim 1 bursting slugs will be energetic and surface effects are anticipated to increase with increasing pslim various physical parameters recorded during laboratory experiments and simulated through numerical models are shown to demonstrate the same trends when parameterised by pslim hence pslim provides a straightforward relationship between changes in measurable surface effects and the system s subsurface physical parameters and for energetic activity of a particular system burst effects are shown to be proportional to the square root of the gas mass involved effect magnitudes are also shown to be a function of atmospheric pressure and application of pslim parameterisation to planetary scenarios produces results in line with our current understanding of planetary volcanism

a parametric and comparative study of different tephra fallout models abstract we perform a parametric and comparative study on three different tephra dispersal models fall3d hazmap and tephra applied to two different scenarios expected for etna volcano these scenarios are similar to the recent 2002 03 and 1990 etna eruptions and correspond respectively to a weak and to a strong plume eruption for each model and scenario we perform a parametric study on several inputs in order to quantify how a variation on a given input parameter i e an uncertainty on the model input affects the results of the model the study considers topographic effects different description for the eruption column column height influence different fits for terminal velocities of particles the effect of particle shape and finally the variation of the modal grain size model differences are quantified by means of a normalized distance that indicates how close in average the results from two different simulations are we also compare predictions from different models to determine under which circumstances the use of a more elaborated model is justified results from our parametric study show that output of the models can be strongly sensitive to the uncertainties and assumptions on input parameters such as mainly mass eruption rate column height distribution of the mass along the column bulk grain size distribution this highlights that for optimal forecasts is urgent to improve the description of these parameters and of some important physical processes like fragmentation and eruption column dynamics further differences between models are often lower than those due to the uncertainties of input parameters although they become more high in simulating weak plumes thus the choice of the model mainly depends on the kind of application such as the need to simulate the evolution of volcanic clouds in the atmosphere finally the use of both a semi analytical hazmap and a fully computational fall3d model for inverting field data of the 2001 etna eruption showed that the best fit parameters are similar for both models and are consistent with values obtained using independent techniques

modelling the rapid near surface expansion of gas slugs in low viscosity magmas the ascent of large gas bubbles slugs in vertical cylindrical conduits and low viscosity magmas is simulated using 1d mathematical and 3d computational fluid dynamic cfd models following laboratory evidence the 1d model defines a constant rise velocity for the slug base and allows gas expansion to accelerate the slug nose through the overlying fluid during ascent the evolution of rapidly expanding gas slugs observed in laboratory experiments is reproduced well and at volcano scales predicts at surface overpressures of several atmospheres without requiring any initial overpressure at depth the near surface dynamics increase slug nose velocities through the overlying magma by a factor of c 2 5 and the gas expansion results in pre burst magma surface velocities of c 35m s21 to examine pressure distributions and the forces exerted on a conduit 3d cfd simulations were carried out at volcano scales the vertical single forces during final slug ascent to the surface are c 106 n two orders of magnitude smaller than those associated with verylong period seismic events at stromboli this supports a previous interpretation of these events in which they are generated by gas slugs flowing through changes in conduit geometry rather than being the direct result of slug eruption processes

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

basaltic thermals and subplinian plumes constraints from acoustic measurements at shishaldin volcano alaska the 1999 basaltic eruption of shishaldin vol cano alaska usa included both strombolian and sub plinian activity as well as a pre subplinian phase inter preted as the local coalescence within a long foam in the conduit although few visual observations were made of the eruption a great deal of information regarding gas ve locity gas flux at the vent and plume height may be inferred by using acoustic recordings of the eruption by relating acoustic power to gas velocity a time series of gas velocity is calculated for the subplinian and pre subplinian phases these time series show trends in gas velocity that are inter preted as plumes or for those signals lasting only a short time thermals the subplinian phase is shown to be com posed of a thermal followed by five plumes with a total expelled gas volume of 1 5 10 7 m 3 the initiation of the subplinian activity is probably related to the arrival of a large overpressurised bubble close to the top of the magma column a gradual increase in low frequency 0 01 0 5 hz signal prior to this trigger bubble may be due to the rise of the bubble in the conduit this delay corresponds to a reservoir located at 3 9 km below the surface in good agreement with studies on other volcanoes the presence of two thermal phases is also identified in the middle of the pre subplinian phase with a total gas release of 4 3 10 6 m 3 and 3 6 10 6 m 3 gas veloc ity at the vent is found to be 82 m s 1 and 90 m s 1 for the subplinian plumes and the pre subplinian thermals respectively the agreement is very good between estimates of the gas flux from modelling the plume height and those obtained from acoustic measurements leading to a new method by which eruption physical parameters may be quantified fur thermore direct measurements of gas velocity can be used for better estimates of the so2 flux released during the eruption

the break back thrust splay of the main dun thrust himalayas of western nepal evidence of an intermediate displacement scale between earthquake slip and finite geometry of thrust systems abstract numerous studies have shown that development of a forward breaking sequence in a thrust belt is accompanied by reactivation of inner faults and development of break back thrusts the partitioning of shortening in the outer and lesser himalayan thrust belt follows these rules tectonic and sedimentary relationships in this thrust belt exemplify out of sequence thrusts in the lesser himalayas and break back imbricate fans close to the mbt main boundary thrust and mdt main dun thrust which are transported during their development above the himalayan basal detachment the displacement along a single splay of the imbricate fan of the mdt was 40 m before abandonment and nucleation of a new inner splay the development of the break back imbricate fan is discontinuous in time furthermore superimposition of ultracataclasite pressure solution cleavage extensional crenulation cleavage and tension gashes in the fault zones suggests that the 40 m displacement occurred by discrete slip events or most probably by a succession of several seismic aseismic deformations these data require several scales of sequential displacement in the outer and lesser himalayas consisting of forward propagation of the thrust system out of sequence reactivation break back nucleation of thrust splays and seismic aseismic fault slip our findings require an intermediate period of tectonism between the 500 ka deformation of the accretionary sediments of the himalayas

evidence for gas influence on volcanic seismic signals recorded at stromboli abstract the meaning of the large variety of seismic waveforms showing different frequencies associated with volcanic activity is still uncertain no definitive model for source dynamics has been proposed yet at present seismic models explaining the origin of the spectral content of the seismic signal are mainly linked to geometrical features of the volcanic conduit and to resonant effects induced by pressure fluctuations in a fluid filled conduit such models assume the physical system to be in a steady state over a long interval of time at stromboli the seismicity produced by each of the three active vents is not stable and can suddenly change in time therefore the application of stable resonator models appears to be unwarranted on the basis of infrared image analyses atmospheric pressure and seismic wavefield signals we show that different frequency contents and different explosive styles occur at stromboli at the same time at different vents moreover we give evidence to support the idea that seismicity and explosivity are both controlled by a variable gas flow regime released during explosions at the top of the magma column we have recognized two main pressure regimes controlling the explositivity at stromboli one is impulsive short and possibly produced by a gas accumulation beneath a cap rock the other has an intermittent regime feature and lasts longer we demonstrate how the first one generates a monochromatic low frequency wavefield while the second shows a high frequency spectrum where the frequency content depends on pressure fluctuations and on pressure gradient we suggest different pressure growth and gas flow in the magma as the common source for both explosive style and seismic wavefield

neogene mammalian faunal change in southern asia correlations with climatic tectonic and eustatic events the fluvial neogene siwalik formations of northern pakistan span long time intervals with only minor hiatuses and being highly fossiliferous are uniquely suited for studies of change in mammalian faunas magnetostratigraphic correlations of a critical stratigraphic section give dates for 45 middle and late miocene biostratigraphic events these mark either first appearances or extinctions in the mammal fauna and show that in the siwaliks there were major fauna turnovers at between 20 and 16 ma and at 9 5 and 7 4 ma two minor faunal events are dated at 13 2 and about 12 ma many species making their first appearance were immigrants from europe or africa and indicate when connections to those regions existed immigration and extinction were the dominant modes of faunal change in situ evolution was much less important the siwalik biostratigraphic record correlates closely to climatic oceanographic and tectonic events which probably controlled immigration into southern asia abiotic events were therefore important factors affecting evolution of the mammal communities

the dynamics of volcanic jets temporal evolution of particles exit velocity from shock tube experiments pyroclast ejection during explosive volcanic eruptions occurs under highly dynamic conditions involving great variations in flux particle sizes and velocities this variability must be a direct consequence of complex interactions between physical and chemical parameters inside the volcanic plumbing system the boundary conditions of such phenomena cannot be fully characterized via field observation and indirect measurements alone in order to understand better eruptive processes we conducted scaled and controlled laboratory experiments by performing shock tube experiments at known conditions we defined the influence of physical boundary conditions on the dynamics of pyroclast ejection if applied to nature we are focusing in the near vent processes where independently of fragmentation mechanism impulsively released gas pyroclast mixtures can be observed these conditions can be met during e g strombolian or vulcanian eruptions parts of plinian eruptions or phreatomagmatic explosions the following parameters were varied 1 tube length 2 vent geometry 3 particle load 4 temperature and 5 particle size distribution gas and particles in the experiments are not coupled st 1 the initial overpressure with respect to atmosphere was always at 15mpa we found a positive correlation of pyroclast ejection velocity with 1 particle load 2 diverging vent walls and 3 temperature as well as a negative correlation with 1 tube length and 2 particle size additionally we found that particle load strongly affects the temporal evolution of particle ejection velocity these findings stress the importance of scaled and repeatable laboratory experiments for a better understanding of volcanic phenomena and therefore volcanic hazard assessment

neogene magnetic polarity stratigraphy of some fluviatile siwalik sections nepal summary the magnetostratigraphy of five new sections through the neogene siwalik group of nepal is presented rock magnetic experiments and detailed thermal demagnetization experiments prove that haematite is the carrier of a primary drm or a pdrm after stepwise thermal demagnetization of specimens from all sections directions of characteristic remanent magnetization were obtained the results show a positive reversal test and exhibit inclination errors of about 20d due to gaps in exposures and extremely variable demagnetization behaviour of the haematite bearing sediments the resulting polarity sequences are poorly defined for some parts of the sections however double sampled parts of some sections yield similar results a correlation with the surai khola section appel rosler corvinus 1991 is proposed based on rock magnetic parameters ams results from three of the sections prove the existence of primary sedimentary magnetic fabrics in these sections with systematic orientations of minimum and maximum susceptibility axes correlation with a standard polarity timescale indicates that the ages of all new sections lie within the age limits of the surai khola section

explosion seismic tomography of a magmatic body beneath etna volatile discharge and tectonic control of volcanism to constrain the upper depth range of lateral heterogeneities beneath mt etna a seismic tomography method with artificial sources is designed to undershoot the target and restrict the depth of seismic propagation by reflection at the top of the basement a strong high velocity anomaly thus imaged southeast of the summit interpreted as a magmatic body is reliably constrained to reach at least as shallow as 2 km depth where exsolution of so2 from magma may occur the high gas output rate of etna allard 1997 hence appears as the normal complement of the huge magma body seismically imaged this magma body is located beneath the volcanic edifice rather than within which attests to the control of volcanism by extension these volatile output and internal structure distinguish mt etna volcanism among current types and may relate to the peculiar context of a recent regional change from subduction related compression to extension

highlights from a seismic broadband array on stromboli volcano an array of nine three component broadband seismometers was deployed in two different configurations on stromboli volcano the analysis of the seismic wavefield related to volcanic explosions revealed some observations which offer a completely new insight into the internal dynamics of a volcano these new observations are restricted to the low frequency range below 1 hz and underline therefore the superiority of broadband recordings over conventional short period observations surprisingly simple wavelets indicate an initially contracting source mechanism gas jets that could not be seen in a short period seismic record at all generate a clear dilatational wavelet in a broadband recording suggesting the same contracting source mechanism the analysis of particle motion and seismic array techniques permits a location of the seismic source we find low frequency signals of 3s and 6s period that are not related to eruptions and do not share a common source with the eruption related events a video recording of visible volcanic activity at the crater region allows one to correlate precisely eruptive features with seismic signals

systematic retrieval of ejecta velocities and gas fluxes at etna volcano using l band doppler radar strombolian type volcanic activity is characterized by a series of gas bubbles bursting at the top of a magma column and leading to the ejection of lava clots and gas emission at the surface the quantitative analysis of physical parameters e g velocity size and mass fluxes controlling the emission dynamics of these volcanic products is very important for the understanding of eruption source mechanisms but remains difficult to obtain in a systematic fashion ground based doppler radar is found to be a very effective tool for measuring ejecta velocities at a high acquisition rate and close to the emission source we present here a series of measurements carried out at mt etna s southeast crater using an l band volcanological doppler radar during the 4 july 2001 strombolian eruptions doppler radar data are supplemented by the analysis of video snapshots recorded simultaneously we provide here a set of physical parameters systematically retrieved from 247 strombolian explosions spanning 15 min and occurring during the paroxysm of the eruption from 21 30 to 21 45 ut the time average values give a maximum particle velocity of v max p 94 7 pm 24 text m s a bulk lava jet velocity of v text pw rad 37 6 pm 1 9 text m s and an initial gas velocity at the source vent of v 0 g 118 4 pm 36 text m s the time averaged particle diameter is found to be about d text pw rad 4 2 pm 2 1 text cm the volume and mass gas fluxes are estimated from time averaged source gas velocities over the sequence duration at q v g 3 11 times 1 0 3 text m 3 text s and q m g 0 5 2 times 1 0 3 text kg s respectively

gas bubble dynamics model for shallow volcanic tremor at stromboli volcanic tremor at stromboli aeolian islands italy is correlated to small infrasonic transients ripepe et al 1996 which repeat almost rhythmically in time in a range between 0 8 and 1 2 s we demonstrate that infrasonic transients are associated to small gas bubble 0 5 m burstings which produces no transients in the seismic signal tremor ground displacement attenuates with the inverse of the distance from the craters indicating that the source is shallow short term energy release shows that infrasonic and seismic signals are linked to the same dynamical process while at the long term scale it is evident that the two signals are controlled by two distinctive mechanisms we suggest that the possible physical model acts in two steps first gas coalescence and then gas bursting in our model the seismic signal is related to the coalescence of a gas bubble from a layer of small bubbles while the infrasonic signal is linked to the bursting of the bubble when it reaches the magma surface gas bubbles could form by free coalescence in magma or could be forced to coalesce by a structural barrier we calculate that forced coalescence induces in magma a pressure change 104 pa 2 orders of magnitude higher than free coalescence and it explains best the tremor ground displacement 10 5 m recorded at stromboli moreover forced coalescence evidences the role of a structural barrier such as a dike in volcanic tremor source dynamics in this gas dynamic process the delay time of 1 2 s between infrasonic pulses could reflect the gas nucleation interval of basaltic magma thomas et al 1993 manga 1996 we propose that the source function for the shallow volcanic tremor at stromboli could be the viscoelastic reaction of the magma to the pressure decrease induced by gas bubble growth rate under constant depressurization the spectrum of our source function is controlled by the time duration of the pressure pulse which represents the viscoelastic relaxation time of the magma and gas bubble growth rate the predicted asymptotic decay of the frequency contents fits the spectral behavior of the volcanic tremor ground displacement recorded at stromboli we show that the same spectral behavior can be found in ground displacement spectra of volcanic tremor recorded on different volcanoes

activity of mount etna preceding the february 1999 fissure eruption inferred mechanism from seismological and geochemical data abstract the february 1999 eruption of mt etna took place through a fissure on the sse flank of the cone of the summit se crater this event was preceded by continuous activity since 1995 sometimes accompanied by violent outbursts from one or more of the three other summit craters ne crater voragine or chasm and bocca nuova and finally by a series of 20 short lived eruptions from the se crater between september 1998 and january 1999 these phenomena could be accounted for by invoking gradual invasion of a shallow small reservoir by more primitive basic and gas rich magma coming from depth the shallow chamber is more likely to be a plexus of dikes which had developed during the previous years 1995 1997 following variations of the local stress field owing to enhanced magma generation and accumulation at the top of the mantle magma injection and mixing is evidenced through geochemistry whereas the state of stress of the volcanic pile and underlying crust is determined using earthquake distributions and focal mechanisms the behaviour of the seismic tremor amplitude appears to be a good indicator of the state of unrest of the volcano although not always directly linked to the relative energy of degassing phenomena

magnetic stratigraphy of cenozoic terrestrial sediments and mammalian dispersal the existing literature on the correlation of the magnetic polarity timescale to vertebrate mammalian chronology for the cenozoic is reviewed for all continents except the soviet union the magnetostratigraphic data from north america is the most complete followed by the indian sub continent ten criteria for rating magnetostratigraphic studies are established and the papers reviewed are rated from 1 10 with 10 being the maximum score the timing of mammalian dispersal is examined against the background of information from magnetostratigraphic studies allied with radiometric dating north american land mammal ages are partly defined on immigrant taxa and the boundaries of the nalma are based on dispersal events it has been suggested that dispersal and evolutionary episodes observed in siwalik sediments were correlative to sea level change deduced from delta 18 o data from benthic foraminifera to test this possibility in the general case dispersal events into north america were determined by us

pulsed vulcanian explosions a characterization of eruption dynamics using doppler radar understanding the dynamics of ongoing volcanic eruptions is essential for predicting the input and transport of volcanic ash in the atmosphere to constrain near vent dynamic processes of explosive vulcanian events we used doppler radar measurements providing tephra velocities and a proxy of the mass flux in two field experiments at volcan de colima mexico and santiaguito guatemala we find that explosive eruptions at both volcanoes consist of individual degassing pulses the analysis of the timing of such pulses shows that both volcanoes have preferred interpulse times of 3 s santiaguito and 2 5 s volcan de colima the interpulse time during one event may change but it often returns to the preferred interpulse time this behavior is similar at both volcanoes and the interpulse time roughly follows a log logistic distribution indicating the interplay of two competing processes these could be short duration degassing of the uppermost conduit versus decreasing permeability due to progressive gas loss and compaction during an eruption

a detailed view into the eruption clouds of santiaguito volcano guatemala using doppler radar 1 using doppler radar technology we are able to show that eruptions at santiaguito volcano guatemala are comprised of multiple explosive degassing pulses occurring at a frequency of 0 2 to 0 3 hz the doppler radar system was installed about 2 7 km away from the active dome on the top of santa maria volcano during four days of continuous measurement 157 eruptive events were recorded the doppler radar data reveals a vertical uplift of the dome surface of about 50 cm immediately prior to a first degassing pulse particle velocities range from 10 to 15 m s in the line of sight of the radar in 80 of the observed eruptions a second degassing pulse emanates from the dome with significantly higher particle velocities 20 25 m s again line of sight and increased echo power which implies an increase in mass flux we carry out numerical experiments of ballistic particle transport and calculate corresponding synthetic radar signals these calculations show that the observations are consistent with a pulsed release of material from the dome of santiaguito volcano

explosion mechanisms at arenal volcano costa rica an interpretation from integration of seismic and doppler radar data 1 we execute an integrated analysis of broadband seismic and doppler radar data to gain insights into the subsurface mechanisms that drive repetitive mildly explosive activity of arenal volcano costa rica we find large variability of both seismic and radar waveforms and nonsystematic relationships between the two seismic recordings display long lasting tremor sequences and numerous explosion quakes radar measurements show that tephra emissions are poorly correlated in both time and energy to the seismic activity tephra emissions were found in association with explosion quakes but also during episodes of tremor and seismic quiescence moreover the exit velocity mass loading and kinetic energy of the emissions show no clear relationship with the coeval seismic amplitude and frequency content we propose a conceptual source model whereby degasing is controlled by opening and closing of fractures that crosscut a rigid cap atop the conduit when the fracture s strength is overcome by the gas pressure building up below it suddenly opens and high velocity gas escapes producing high frequency elastic waves typical of explosion quakes gas release also occurs in relation to periodic opening and closure of the fractures to produce repetitive pressure pulses this being the source of tremor in both cases varying quantities of fragmented material may be carried by the gas which can be detected by the radar if their concentration is high enough moreover the highly variable constantly changing state of lava cap e g thickness fracture network and gas permeability results in nonrepeatable source conditions and explains the complex relationship between tephra emissions and associated seismic signals

echo resonance and hydraulic perturbations in magma cavities application to the volcanic tremor of etna italy in relation to its eruptive activity a study is presented of spectral features of volcanic tremor recorded at mount etna sicily italy following the methods of analysis suggested by the resonant scattering formalism of gaunaurd and uberall 1978 1979a 1979b and the model for hydraulic origin of seidl et al 1981 the periods investigated include summit and flank eruptions that occurred between 1984 and 1993 recordings from a permanent station located near the top of the volcano were used and the temporal patterns associated with a the average spacing bar delta between consecutive spectral peaks in the frequency range 1 6 hz b the spectral shape and c the overall spectral amplitude were analyzed bar delta values are thought to depend on the physical properties of magma such as its density which in turn is controlled by the degree of gas exsolution variations in the spectral shape are tentatively attributed to changes in the geometrical scattering from the boundary of resonant conduits and magma batches finally the overall amplitude at the station should essentially reflect the state of turbulence of magma within the superficial ascending path a limit in the application of the resonant scattering formalism to the study of volcanic tremor is given by the fact that the fundamental modes and integer harmonics are difficult to identify in the frequency spectra as tremor sources are likely within cavities of very complex geometry rather than in spherical or cylindrical chambers as expected by theory this study gives evidence of some correlations between the analyzed temporal patterns and the major events in the volcanic activity related to both lava flow and explosions at the summit vents in particular relatively high values of bar delta have been attained during the se crater eruption of 1984 the complex eruptive phases of september october 1989 and the 1991 1993 flank eruption suggesting the presence of a relatively dense magma for all of these events conversely very low values have been recorded in coincidence with the december 1985 activity and the paroxysmal explosions at the summit craters of early 1990 which are interpreted here as fed by fluid vesiculated magma appreciable modifications in the spectral shape have been observed in relation to changes of the volcanic activity that probably preceded the opening and disactivation of shallow dykes or magma batches finally the overall amplitude seems to be a sensitive indicator of the state of gas turbulence within the shallow conduits as is suggested by the high values attained during phases of intense volcanic activity

first testing of a volcano doppler radar voldorad at mount etna italy a medium power 1 kw doppler radar of limited weight 110 kg and working in the uhf band has been developed for active remote sensing of volcanic eruptions named voldorad this radar is designed to monitor eruptive activities of variable magnitude at medium distance range 0 5 5 km in any weather condition and fills the gap between low and high power radar or sodar systems previously tested on volcanoes voldorad was operated for the first time during an eruption of mt etna on october 11 12 1998 doppler spectra recorded at 1 km distance from the vent reveal powerful echoes during the eruption paroxysm lava fountains which gradually decreased along with declining activity an average vertical velocity of 80 87 m s 1 is inferred for the eruptive jets

ballistics and ash plumes discriminated by doppler radar 1 small scale eruptive ash plumes at arenal volcano costa rica were recorded using a ground based doppler radar voldorad the time velocity distribution of the mass load i e doppler radargrams exhibits two contrasted dynamics recorded simultaneously evidenced by distinctive velocities life spans and transit speeds through the radar beam synthetic doppler radargrams computed with a simple ballistic model indicate that the short lived signal is consistent with the instantaneous projection of ballistics blocks accompanying the ash plume emission the mass of centimeter to decimeter sized ballistics is confidently estimated at 0 5 7 tons whereas the ash plume mass is loosely constrained at 5 8 102 tons assuming a particle diameter of 2 mm close to the vent these quantitative estimates of the mass proportion either falling on the slopes of the volcano or ejected into the atmosphere could help in the modeling and monitoring of tephra dispersal

magnetic polarity stratigraphy of siwalik group sediments of karnali river section in western nepal the remanent magnetization of siltstones and sandstones sampled at 476 levels sites throughout a 3560 m thick molasse sequence belonging to the siwalik group 0 2015 m lower 2015 3560 m middle has been studied by stepwise thermal demagnetization this section is exposed along the karnali river in nepal the natural remanent magnetization nrm usually consists of two components a viscous or thermoviscous component of recent field origin and an ancient characteristic component chrm the former component is of normal polarity and resides either in goethite unblocking temperature 150 c resistant to afd up to 150 mt or in maghemite unblocking temperature 150 400 c goethite contributes up to 90 per cent of the total intensity in the finer variegated muddy samples belonging to the lower half of the section maghemite content is significant in the grey mud free lithologies from the upper half of the section the main component unblocked in the high temperature range commonly 610 680 c and believed to reside in haematite presumably of mostly detrital origin represents a characteristic remanence chrm the tilt corrected chrm directions at individual sites show antipodal clusters ratio of normal to reverse polarity sites 0 62 and yield mean inclinations recording significant inclination shallowing a feature well recorded in the siwaliks this chrm is interpreted to represent a largely primary detrital remanence the chrm data from 430 sites yield the karnali river magnetic polarity sequence whose correlation with the geomagnetic polarity timescale cande kent 1995 suggests a depositional age of 16 ma younger than chron c5cn 1n to 5 2 ma around the top of chron c3r for the 3560 m section sampled hence the karnali river exposes the oldest part of the siwalik group in nepal estimates of the sediment accumulation rate sar average to 32 9 cm kyr 1 for the 10 8 myr time span of deposition

the magnetic polarity stratigraphy of the siwalik group at haritalyangar india and a new last appearance datum for ramapithecus and sivapithecus in asia abstract the haritalyangar india local fauna contains type specimens of several hominoid primates which are assigned a new last appearance datum age based on a magnetic polarity stratigraphy this youngest assigned age for sivapithecus indicus s sivalensis and ramapithecus punjabicus in asia is about 7 0 7 5 m y the age of the holotype specimen of gigantopithecus bilaspurensis is about 6 3 m y the nahan sandstone formation is at least in part contemporary with the nagri formation lithofacies of the potwar plateau pakistan

the himalayan arc large scale continental subduction oroclinal bending and back arc spreading abstract palaeomagnetic results from the himalayan arc and southern tibet compared with simulated apparent polar wander paths for the indian plate show a consistent pattern of rotations of the himalayan arc relative to the indian shield varying gradually from 45 clockwise in the northwestern himalaya to slightly counterclockwise in the lhasa region this pattern is consistent with continental underthrusting of greater india beneath the tibetan plateau since the early miocene over at least 650 km at the longitude of western nepal and oroclinal bending since the latest miocene available palaeomagnetic observations support the steady state model for the formation of the himalayan arc with refinements as follows 1 collision between greater india s northern boundary and southern asia occurred at equatorial latitudes with progressive suturing from palaeocene in the northwestern himalaya until early eocene in the eastern himalaya 2 continuing convergence and indentation of greater india into southern asia over about 2000 km up to the early miocene resulted in southeastward extrusion of indochina and 3 neogene counterclockwise rotational underthrusting of greater india along the main central thrust with pliocene quaternary oroclinal bending of the himalayan arc

the exceptional activity and growth of the southeast crater mount etna italy between 1996 and 2001 between 1971 and 2001 the southeast crater was the most productive of the four summit craters of mount etna with activity that can be compared on a global scale to the opening phases of the pu u k paianaha eruption of k lauea volcano hawai i the period of highest eruptive rate was between 1996 and 2001 when near continuous activity occurred in five phases these were characterized by a wide range of eruptive styles and intensities from quiet non explosive lava emission to brief violent lava fountaining episodes much of the cone growth occurred during these fountaining episodes totaling 105 events many showed complex dynamics such as different eruptive styles at multiple vents and resulted in the growth of minor edifices on the flanks of the southeast crater cone small pyroclastic flows were produced during some of the eruptive episodes when oblique tephra jets showered the steep flanks of the cone with hot bombs and scoriae fluctuations in the eruptive style and eruption rates were controlled by a complex interplay between changes in the conduit geometry including the growth of a shallow magma reservoir under the southeast crater magma supply rates and flank instability during this period volume calculations were made with the aid of gis and image analysis of video footage obtained by a monitoring telecamera between 1996 and 2001 the bulk volume of the cone increased by 36 106 m3 giving a total 1971 2001 volume of 72 106 m3 at the same time the cone gained 105 m in height reaching an elevation of about 3 300 m the total dre volume of the 1996 2001 products was 90 106m3 this mostly comprised lava flows 72 106 m3 erupted at the summit and onto the flanks of the cone these values indicate that the productivity of the southeast crater increased fourfold during 1996 2001 with respect to the previous 25 years coinciding with a general increase in the eruptive output rates and eruption intensity at etna this phase of intense summit activity has been followed since the summer of 2001 by a period of increased structural instability of the volcano marked by a series of important flank eruptions

fidelity and time resolution of the magnetostratigraphic record in siwalik sediments high resolution study of a complete polarity transition and evidence for cryptochrons in a miocene fluviatile section summary the surai khola section in southwest nepal a 5000 m continuously exposed record of fluvial sedimentation since middle miocene was revisited for high resolution magnetostratigraphy in sequences with expected cryptochrons and reversals of the geomagnetic field polarity intervals with durations of a few tens of thousands of years are recorded as zones of stable palaeomagnetic directions polarity transitions are recorded as zones with complex demagnetization behaviour of specimens in the sedimentary column almost antiparallel palaeoremanence directions residing in diverent haematite phases in the same specimens could generally not be separated properly by thermal demagnetization divering demagnetization paths for neighbouring specimens during a reversal suggest that measured transitional directions are not true geomagnetic field directions but rather are generated by the superposition of variable amounts of at least two almost antiparallel components of magnetization accompanying studies of recent river sand deposits demonstrate that these sediments acquire a true depositional remanent magnetization drm with considerable inclination errors and scattered directions for individual specimens

mount etna dense array local earthquake p and s tomography and implications for volcanic plumbing inversion for the three dimensional velocity structure of mount etna is performed with a data set of arrival times of p and s waves of local earthquakes from temporary dense arrays of three component seismographs a high v p body revealed by the original tomography without nearby stations is confirmed and its image is sharpened using new velocity constraints provided by refraction data synthetic tests of v p and v p v s and comparison with an independent artificial source tomography with a fundamentally different geometry consistently calibrate the significance threshold of the resolution indicators the trustworthy part of the image shows a high v p body centered under the southern part of valle del bove above the 6 km below sea level deep basement which extends towards sea level and may be rooted in or through the crust it has a large contrast of over 1 km s with the surrounding sediments and sharp lateral limits and can thus be regarded as made of intrusive material of magmatic origin the massive high v p body is heterogeneous in v p v s the regions inside it where v s is relatively low can then be suspected of containing a proportion of melt or be fractured and act as pressure links or transport zones such features may be structurally linked and appear to be activated in eruptive phenomena by taking into account the heterogeneities in structure and physical state retrieved by seismic tomography a succession of seismic events deformational episodes and geochemical variation in lavas can be discussed with respect to the well observed eruptions

seismic patterns and fluid dynamic features preceding and accompanying the january 15 1990 eruptive paroxysm on mt etna italy abstract on the basis of data collected during a seismological investigation carried out on mt etna italy during a phase of the volcanic activity marked by progressive transition from strombolian bursts to effusive paroxysms at the se crater january 1990 three types of seismic regime have been recognized they are interpreted to be linked to modifications in the regimes of volcanic gases and vapours within the upper levels of the magma column as suggested by recent studies on the dynamics of magmatic fluids our analysis also reveals that the use of usual seismic parameters such as the temporal patterns associated with the occurrence of discrete low frequency events spindles and the coefficient m of the ishimoto iida law can furnish information about variations in the behaviour of the system before the irreversible evolution of the volcanic activity toward eruptive paroxysms

near source doppler radar monitoring of tephra plumes at etna over the last twenty years mount etna has produced more than one hundred explosive events ranging from light ash emissions to violent sub plinian eruptions significant hazards arise from tephra plumes which directly threaten air traffic and generate fallout affecting surrounding towns and infrastructures we describe the first radar system named voldorad 2b fully integrated into a volcano instrumental network dedicated to the continuous near source monitoring of tephra emissions from etna s summit craters this 23 5 cm wavelength pulsed doppler radar is operated in collaboration between the observatoire de physique du globe de clermont ferrand opgc and the istituto nazionale di geofisica e vulcanologia osservatorio etneo ingv oe since 2009 probed volumes inside the fixed northward pointing conical beam total about 1 5 km in length covering the summit craters which produced all recent tephra plumes the backscattered power related to the amount of particles crossing the beam and particle along beam velocities are recorded every 0 23 s providing a proxy for the tephra mass eruption rate radar raw data are transmitted in real time to the volcano monitoring center of ingv oe in catania and are used to automatically release alerts at onset and end of eruptive events processed radar parameters are also made available from the voldorad database online http voldorad opgc fr in addition to eruptive crater discrimination by range gating relative variations of eruption intensity can be tracked including through overcast weather when other optical or infrared methods may fail to provide information short lived dense ash emissions can be detected as illustrated for weak ash plumes from the bocca nuova and new south east craters in 2010 the comparison with thermal images suggests that the front mushroom of individual ash plumes holds the largest particles coarse ash and small lapilli and concentrations at least within the first hundred meters for these short lived ash plumes the highest particle mass flux seems to occur typically within the first 10 s we also analyze data from the first lava fountain generating an ash and lapilli plume on 12 january 2011 that initiated a series of 25 paroxysmal episodes of the new south east crater until april 2012 we illustrate the pulsating behavior of the lava fountain and show that vertical velocities reached 250 m s 1 with brief peaks exceeding 300 m s 1 leading to mean and maximum tephra fluxes dre of 185 and 318 m3 s 1 with peaks exceeding 380 m3 s 1 respectively and a total volume of pyroclasts emitted during the lava fountain phase of 1 3 106 m3 finally we discuss capacities and limits of the instrument along with future work aimed at providing source term inputs to tephra dispersal models in order to improve hazard assessment and risk mitigation at etna

strombolian explosions 2 eruption dynamics determined from acoustic measurements strombolian activity consists of a series of explosions due to the breaking of a large overpressurized bubble at the surface of the magma column acoustic pressure due to sound waves has been measured and analyzed at stromboli for more than 50 explosions three parts can be distinguished in the acoustic pressure waveform which are related to the behavior of the bubble before during and after its bursting before the sharp rise in acoustic pressure the signal is dominated by waves with a frequency of 2 hz which develop on the nose of the bubble they produce sound in air by imposing a rapid motion to the interface and one could detect a bubble travelling in the uppermost 30 m of the magma column when the bubble reaches the air magma interface its strong vibration driven by a large overpressure inside the gas generates the main event with a frequency around 9 hz after the bubble has burst kinematic waves of frequency around 4 5 hz are the main source of sound they develop at the surface of the magma left on the conduit side the three types of motion although determined independently give consistent results furthermore combining the results obtained for the two types of kinematic waves the magma viscosity is estimated to be of 300 65 pa s which is in good agreement with petrological constraints and corroborates the validity of our analysis this suggests that acoustic measurements constitute a powerful tool in the understanding of eruption dynamics

installation of a doppler radar monitoring system at merapi volcano indonesia merapi volcano indonesia is one of the most active dome building volcanoes worldwide instabilities at the growing dome cause rockfalls and hot block and ash flows which can reach run out distances of several kilometers therefore merapi has been monitored extensively for many years however direct visual observation of the dome is often impossible due to cloud coverage of the summit in october 2001 a first prototype doppler radar system was installed to overcome this shortcoming the system is able to penetrate clouds and observe material movements at the dome giving valuable information about dynamic processes in the dome area the system also allows detection of rainfall in several distance intervals for precise positioning of the beam the system was equipped with an electromechanical mounting in 2003 a charge coupled device ccd camera attached to the radar mirror documents the radar beam position and provides visual observation of the dome recorded data camera images and status information are telemetered to the merapi volcano observatory where they can be processed and interpreted status information is also sent via short message service via a global system for mobile communications gsm modem by processing the doppler radar data we are able to discriminate between three different types of instability events sliding dome material dome material gravitationally breaking off the dome and explosive outbursts of dome material due to expansion of volcanic gas in order to independently verify our observations we compared rockfall events detected by the radar system to seismic recordings and found a good correlation

spatio temporal stability analysis applied to monsoon anticyclone flow flow on a beta plane driven by a steady localised anticyclonic forcing of potential vorticity or equivalently a mass source is considered as a simple model of the asian monsoon flow in the upper troposphere previous authors have noted that the response may be steady or unsteady according to the magnitude of the forcing with the unsteadiness manifested as westward eddy shedding a detailed study of the transition between steady and eddy shedding regimes reveals a third regime break up for intermediate forcing magnitude where the flow is steady in the neighbourhood of the forcing but the westward extending plume of low potential vorticity breaks up into isolated anticyclonic vortices some distance away from the forcing region a related spatio temporal instability problem for flow on a beta plane is specified and analysed the flow can be stable convectively unstable or absolutely unstable it is argued that these three stability regimes correspond to the steady break up and eddy shedding regimes for the forced flow and good quantitative correspondence between the regimes is demonstrated by explicit solution of the spatio temporal stability problem

reconstructing eruptive source parameters from tephra deposit a numerical study of medium sized explosive eruptions at etna volcano since the 1970s multiple reconstruction techniques have been proposed and are currently used to extrapolate and quantify eruptive parameters from sampled tephra fall deposit datasets atmospheric transport and deposition processes strongly control the spatial distribution of tephra deposit therefore a large uncertainty affects mass derived estimations especially for fall layer that are not well exposed this paper has two main aims the first is to analyse the sensitivity to the deposit sampling strategy of reconstruction techniques the second is to assess whether there are differences between the modelled values for emitted mass and grainsize versus values estimated from the deposits we find significant differences and propose a new correction strategy a numerical approach is demonstrated by simulating with a dispersal code a mild explosive event occurring at mt etna on 24 november 2006 eruptive parameters are reconstructed by an inversion information collected after the eruption a full synthetic deposit is created by integrating the deposited mass computed by the model over the computational domain i e an area of 7 5 104 km 2 a statistical analysis based on 2000 sampling tests of 50 sampling points shows a large variability up to 50 for all the reconstruction techniques moreover for some test examples power law errors are larger than estimated uncertainty a similar analysis on simulated grain size classes shows how spatial sampling limitations strongly reduce the utility of available information on the total grain size distribution for example information on particles coarser than 4 is completely lost when sampling at 1 5 km from the vent for all columns with heights less than 2000 m above the vent to correct for this effect an optimal sampling strategy and a new reconstruction method are presented a sensitivity study shows that our method can be extended to a wide range of eruptive scenarios including those in which aggregation processes are important the new correction method allows an estimate of the deficiency for each simulated class in calculated mass deposited providing reliable estimation of uncertainties in the reconstructed total whole deposit grainsize distribution

acoustic sounder measurements of the vertical velocity of volcanic jets at stromboli volcano we have used a sodar acoustic doppler sounder to characterize the behavior of volcanoes and in particular to measure the vertical velocities of volcanic jets we have analyzed more than 100 explosions on stromboli volcano eolian islands first results show vertical speeds close to the vent ranging from 20 m s to 80 m s the uncertainty in the measurements is close to 10 due mainly to the inaccurate knowledge of the sound speed in volcanic jets this is small compared to other volcanological methods this method is well suited for monitoring temporal variations during an eruption and should be particularly interesting for the study of the eruptive dynamics of lava fountains the doppler spectrum in explosions appears to be related to different types of echoes and contains information on particle sizes in the jet

explosive volcanic eruptions v observations of plume dynamics during the 1979 soufriere eruption st vincent summary during the 1979 eruption of the soufritre of st vincent west indies a 14min period of explosive activity occurred on april 22 the first three minutes of this activity were filmed five individual explosions formed distinct plumes which fed an eruption column which eventually ascended to a height of over 18 km the ascent velocities of the fronts of these plumes ranged from 8 5 to 61 7m s the half angle of spreading of the plume fronts ranged from 21 5 to 24 one of the plumes was observed to 8 km height and decelerated steadily from 5 1 5 to 23 m s l the main column fed by individual explosions was however observed to accelerate from 8 5 to 58 m s l in the same height interval a theoretical treatment of volcanic plume motion is presented measurements of dimensions velocities and spreading rates from the film are used to estimate plume parameters such as temperature particle content and volume discharge rate of magma from the theoretical relationships these calculations show that the individual plumes became hotter and richer in juvenile ash with time the acceleration of the main eruption column was the result of being fed by increasingly hotter and more ash rich explosions an average volume discharge rate of 12600m3s is estimated from the analysis of the plume motions this value agrees closely with an estimate of discharge rate based on the heat flux required to form an 18 km high column this agreement suggests that theories of convective motions in plumes can be successfully adapted to the volcanic case as long as the effect of hot entrained ash particles is considered

seismic and infrasonic evidences for an impulsive source of the shallow volcanic tremor at mt etna italy during a seismo acoustic experiment we recorded volcanic tremor around the summit craters of mt etna volcano tremor shows amplitude modulation which disappear 900 m from the crater area the infrasonic wavefield is coherent even at distances of 750 m time delay between infrasonic transient is stable around 1 3 s and is consistent with the position of the source in the voragine crater amplitude modulation of tremor is well correlated 0 72 with infrasound amplitude with a time lag of 0 37 s coherent with a shallow position of the source amplitude of volcanic tremor decays over increasing distances according to geometrical spreading of body waves tremor wavefield shows a linear polarization following the same time occourrence as the infrasonic pulses polarization azimuth indicates that wavefield rectilinearity is mostly due to p waves we infer that most of the volcanic tremor we recorded at mt etna is generated by superimposition of small impulsive sources acting at 1 2 s rate caused by pressure instability during magma degassing

in situ observation of dome instabilities at merapi volcano indonesia a new tool for volcanic hazard mitigation understanding the mechanism and repetition frequency of dome instability events at high risk dome building volcanoes located near densely populated areas is one crucial piece of information when dealing with volcanic hazard mitigation although some visual in situ observations of such processes have been made at unzen volcano and on montserrat continuous monitoring of dome activity has been severely hampered by weather conditions such as cloud coverage using a newly designed microwave doppler system we are able to continuously monitor in situ processes at active dome systems with our instrument we can determine the velocity of material breaking off an active dome as well as the approximate amount of material passing through the radar beam allowing us to continuously identify different types of dome instabilities a data set collected during a highly active period at the end of oct early nov 2001 at merapi volcano indicates two different instability types a purely gravitational instabilities and b gravitational instabilities that are followed immediately by an explosion such information continuously collected allows tight constrains on the activity status of dome building volcanoes and is an important information for hazard mitigation the number of instabilities detected by the radar during the observational period is larger than the number of rockfall events detected by the seismic network operated at merapi during that time

three dimensional transport speed of wind drifted ash plumes using ground based radar 1 the main utilization of mobile ground based doppler radars is to quantify the dynamics of eruptive activity by aiming directly at the emission source we show that they can also provide information on the initial lateral transport speed of weak ash plumes bent over by crosswind the method is illustrated by measurements made with a transportable volcano doppler radar voldorad at arenal volcano costa rica the near source displacements of the plume are tracked through echo onsets induced by ash entering successive probed volumes in the radar beam a constant transport velocity is commonly reached within a few seconds of the initial ash emission as wind advection and buoyancy take over momentum the plume azimuth and upraise angles are constrained by comparing the amplitude decrease of the radar echoes as a function of distance from the source with results from a simple geometric plume model the three dimensional vector of the ash cloud transport speed is then reconstructed with an accuracy of a few percent this method may have applications for volcano monitoring for determining pyroclast fluxes for the modeling of tephra dispersal and for remote measurements of volcanic gas fluxes

considerations on ejection velocity estimations from infrared radiometer data a case study at stromboli volcano abstract synchronous recordings of normal strombolian explosions with a thermal camera and infrared radiometers provide a unique opportunity to understand signals from less expensive radiometers using records from stromboli volcano we analyze in particular the limitations of using signals from infrared radiometers alone to quantify the plume ascent kinetics we conclude that infrared radiometers pointing close to the vent either single or coupled are often insufficient for velocity retrieval due to the complex structure and dynamics of the plumes and their evolution with time in addition to practical implementation difficulties in the field this is mainly due to the rapid succession and overlapping of thermal components in the radiometer s field of view optimized geometries of radiometer fields of view and new retrieval methodologies are proposed to improve velocity estimates from one or coupled radiometers

volcanic tremor wave field during quiescent and eruptive activity at mt etna sicily abstract this paper reports the results of an analysis of volcanic tremor at etna in the years 1987 to 1992 the data utilized were obtained from the osservatorio vesuviano s serra la nave permanent station and several seismic surveys carried out by means of portable digital seismic stations equipped with three component geophones the spatial temporal patterns of main parameters such as intensity spectral content polarization and wave composition of volcanic tremor in different phases of etna s activity were studied eruptive activity appears to be significantly correlated with volcanic tremor in particular it is worth pointing out that the magma upwelling in the terminal part of the conduit is characterized by a marked increase in low frequency components 3 4 hz of the spectrum of volcanic tremor hence volcanic tremor at etna can be considered as a short period precursor of eruptions an analysis of polarization and propagation velocity of volcanic tremor shows the presence of love waves overlapping other seismic phases

magnetic polarity stratigraphy and ages of siwalik group rocks of the potwar plateau pakistan abstract six magnetic polarity sections have been established over the potwar plateau region of pakistan including the major stratotypes of the siwalik group in all six sections the dominant feature of the magnetic polarity stratigraphy is a long normal polarity zone which is contained within the nagri formation this conspicuous normal polarity zone has been radiometrically dated at 9 5 0 6 m y which identifies it as magnetic chron 9 radiometric dates from the upper siwalik formation have also been used to identify the chron 2 3 boundary in two of the sections the magnetic polarity stratigraphy of three of the sections has been correlated securely with the accepted magnetic polarity time scale so that the ages of the local stratigraphy are indexed accordingly based exclusively on data from stratotype sections the chinji nagri and dhok pathan formations have nominal age ranges of 10 1 13 1 7 9 10 1 and 5 1 7 9 m y age fluctuations on the order of 105 years may be anticipated for these formational boundaries within radius of some 20 km of the designated stratotype mean sediment accumulation rates during the chinji nagri and dhok pathan interval range from 13 to 52 cm 103 yr essentially linear sediment accumulations are locally maintained over time intervals of several million years the chinji nagri lithofacies boundary marks a transition from slow to faster sediment accumulation over much of the potwar plateau indicating a fundamental sedimentary tectonic change at this time

transition stratigraphy and the problem of remanence lock in times in the siwalik red beds the record of paleomagnetic polarity transitions can provide relative time information in the stratigraphic record on scales of hundreds to thousands of years transition stratigraphy is here used to determine the relative lock in times of several components of magnetization in the siwalik red beds

acoustic measurements of the 1999 basaltic eruption of shishaldin volcano alaska 1 origin of strombolian activity the 1999 basaltic eruption of shishaldin volcano alaska usa displayed both classical strombolian activity and an explosive subplinian plume strombolian activity at shishaldin occurred in two major phases following the subplinian activity in this paper we use acoustic measurements to interpret the strombolian activity acoustic measurements of the two strombolian phases show a series of explosions that are modeled by the vibration of a large overpressurised cylindrical bubble at the top of the magma column results show that the bubble does not burst at its maximum radius as expected if the liquid film is stretched beyond its elasticity but bursting occurs after one cycle of vibration as a consequence of an instability of the air magma interface close to the bubble minimum radius during each strombolian period estimates of bubble length and overpressure are calculated using an alternate method based on acoustic power we estimate gas velocity to be 30 60 m s in very good agreement with synthetic waveforms although there is some variation within these parameters bubble length and overpressure for the first strombolian phase are found to be c82f11 m and 0 083 mpa for the second strombolian phase bubble length and overpressure are estimated at 24f12 m and 0 15 mpa for the first 17 h after which bubble overpressure shows a constant increase reaching a peak of 1 4 mpa just prior to the end of the second strombolian phase this peak suggests that at the time the magma in the conduit may contain a relatively large concentration of small bubbles maximum total gas volume and gas fluxes at the surface are estimated to be 3 3 10 7 and 2 9 10 3 m 3 s for the first phase and 1 0 10 8 and 2 2 10 3 m 3 s for the second phase this gives a mass flux of 1 2 10 3 and 8 7 10 2 kg s respectively for the first and the second strombolian phases

a time framework based on magnetostratigraphy for the siwalik sediments of the khaur area northern pakistan the magnetostratigraphy of eleven new sections in the khaur area of northern pakistan is presented all specimens have been subjected to thermal demagnetization the sections taken in adjacent ravines incising the siwalik formations nearly penpendicular to strike form a temporal framework in which to interpret the biological and lithological information a composite section is constructed from several long sections and is correlated to the magnetic polarity time scale chron 6 to chron 15 providing absolute age information for the biostratigraphic zonations of barry et al 1982 detailed sections along the strike of major stratigraphic marker beds document an isochronous horizon and form the basis for paleoenvironmental reconstructions the preservation of a polarity transition in fluvial sediments suggests continuity of sedimentation on a time scale of 103 104 years

doppler radar sounding of volcanic eruption dynamics at mount etna besides their common use in atmospheric studies doppler radars are promising tools for the active remote sensing of volcanic eruptions but were little applied to this field we present the observations made with a mid power uhf doppler radar voldorad during a 7 h strombolian eruption at the se crater of mount etna on 11 12 october 1998 main characteristics of radar echoes are retrieved from analysis of doppler spectra recorded in the two range gates on either side of the jet axis from the geometry of the sounding the contribution of uprising and falling ejecta to each doppler spectrum can be discriminated the temporal evolution of total power backscattered by uprising targets is quite similar to the temporal evolution of the volcanic tremor and closely reproduces the overall evolution of the eruption before during and after its paroxysm moreover during the sharp decrease of eruptive activity following the paroxysm detailed analysis of video from camera recording radar and seismic measurements reveals that radar and video signals start to decrease simultaneously approximately 2 5 min after the tremor decline this delay is interpreted as the ascent time through a magma conduit of large gas slugs from a shallow source roughly estimated at about 500 m beneath the se crater detailed analysis of eruptive processes has been also made with voldorad operating in a high sampling rate mode signature of individual outburst is clearly identified on the half part of doppler spectra corresponding to rising ejecta temporal variations of the backscattered power exhibit quasi periodic undulations whereas the maximum velocity measured on each spectrum displays a sharp peak at the onset of each outburst followed by a slow decay with time periodicity of power variations between 3 8 and 5 5 s is in agreement with the occurrence of explosions visually observed at the se vent maximum vertical velocities of over 160 m s 1 were measured during the paraoxysmal stage and the renewed activity finally by using a simplified model simulating the radar echoes characteristics we show that when voldorad is operating in high sampling rate mode the power and maximum velocity variations are directly related to the difference in size and velocity of particles crossing the antenna beam

a model for internal dynamical processes on mt etna summary results of studies concerning seismic activity earthquakes and tremor and its relation with eruptive events on mt etna are briefly discussed seismic records collected from 1977 up to 1986 have been analysed and special care was given to observation of changes in some seismic parameters such as the rate of microseismic activity the amplitude and dominant spectral peaks of the volcanic tremor which vary significantly in relation to the occurrence of eruptive events the systematic nature of variations in the seismic parameters considered allows us to propose a preliminary model which puts all the observations made so far into a wide context giving an interpretative hypothesis of the magma uprise mechanisms preceding either summit or flank eruptions summit eruptions are modelled in two stages and occur without changes in the seismic parameters considered except for a sharp increase in tremor amplitude almost coincident in time with the eruption onset flank eruptions are modelled in three stages and follow a simultaneous change of all the mentioned parameters with time the onset of these eruptions is in fact preceded by an increase in both the daily number of shocks and the amplitude of the volcanic tremor as well as a shifting from relatively high values in the dominant peaks of the tremor spectra which appear in the pre eruptive stage towards usual lower frequency values 1 0 2 3 hz

terminal settling velocity measurements of volcanic ash during the 2002 2003 etna eruption by an x band microwave rain gauge disdrometer 1 this is the first report in the scientific literature of direct measurement of the terminal settling velocity of volcanic particles during an eruption field measurements using a continuous wave x band disdrometer were carried out at mt etna on 18 and 19 december 2002 when the explosive activity produced a 4 km high volcanic plume these data allow the estimation of the intensity of the fallout and the measurement of the terminal settling velocities of the volcanic particles in real time the main results are 1 the tested instrument detected coherent falling volcanic particles from 0 2 to 1 mm diameter 2 measured terminal settling velocities were in agreement with both experimental and theoretical methods 3 however the measured velocities were clustered around few discrete values rather than a range of velocities as would be expected if the particles were falling simultaneously and discretely this new methodology has many new applications for local hazard mitigation and improved understanding of fallout processes

image processing of explosive activity at stromboli abstract a new way to study the dynamics of explosive behaviour at different vents of stromboli volcano is proposed the method is based on computer processing of images taken by an infrared film camera at a rate of 4 pictures per second each picture has been digitized by use of an image scanner with a 75 d p i dots per inch resolution and 256 levels of gray then processed and the total mass of the ejected material has been calculated for each photograph with this procedure the flux of ejected matter throughout every single explosive event has been reconstructed the analysis of trajectories made on adequate samples of ejecta has allowed us to evaluate the ejection velocity the mode of the mass flux distribution and the mean value of the velocities calculated for individual particles quantify the kinetic energy of an explosion vents nos 1 and 3 which remained active after the last effusive eruption of 1985 1986 show several explosive patterns the energy of which is measured the observed flux distributions have been checked both numerically and experimentally by modelling impulsive events the computer simulations of the mass distributions have allowed us to speculate on the possible explosive dynamisms two different models have been used a single impulse model confirms the behaviour actually shown by one of the two vents while the behaviour of the other is better depicted by a cumulative trend of successive impulses in rhythmic sequence moreover through the experimental approach we have had the opportunity to test the overall resolution of the method the observed matter flux distribution has then been associated to the seismic signals in order to correlate the dynamics involved in the explosions with the seismic source mechanisms

the magnetostratigraphy of the chitarwata and lower vihowa formations of the dera ghazi khan area pakistan abstract three sections of the chitarwata and lower vihowa formations were sampled along the dalana river on the southeastern flank of the zinda pir dome in the southern sulaiman range near dera ghazi khan pakistan together they provide nearly 800 m of a continuous sedimentary record of the miocene derived from the uplifted himalayan highlands previous studies have examined the middle and upper miocene sediments the siwalik group of the potwar plateau to the north however detailed investigations of earlier periods are impossible in that area due to the absence of oligocene and lower miocene sediments caused by continued overthrusting associated with the himalayan orogeny fortunately the sulaiman basin to the south which was further removed from the tectonic activity provides a record of the early miocene in the form of the chitarwata formation the dalana a b and c sections dga dgb and dgc were examined and sampled for this study a magnetostratigraphic analysis was carried out to correlate and date the chitarwata and vihowa formations exposed in this area the samples were subjected to step wise demagnetization to resolve the primary and secondary remanent magnetization components thermal demagnetization trajectories indicate that the majority of samples have sufficient internal consistency that their calculated polarities are reliable likewise the majority of the 126 measured sites showed statistically significant agreement between the three measured samples per site however the bimodal data set does not pass the reversal test and so is deemed unsuitable for tectonic interpretations the individual sections were initially correlated using lithologic and stratigraphic methods and the relationship was reinforced by the magnetostratigraphy the composite dg section was tentatively correlated with the standard magnetic polarity time scale placing the disconformable base of the chitarwata in the dga section at just older than 22 ma the chitarwata vihowa contact at 18 6 ma and the top of the vihowa in the dgc section at about 16 ma the assignment of these dates to the chitarwata will aid in future biostratigraphic and lithostratigraphic correlation of early miocene sediments effectively extending the well established siwalik faunal sequence back by four million years

continuous monitoring of volcanic eruption dynamics a review of various techniques and new results from a frequency modulated radar doppler system in situ measurement of volcanic eruption velocities is one of the great challenges left in geophysical volcanology in this paper we report on a new radar doppler technique for monitoring volcanic eruption velocities in comparison with techniques employed previously e g photographic methods or acoustic doppler measurements this method allows continuous recordings of volcanic eruptions even during poor visibility also radar doppler instruments are usually light weight and energy efficient which makes them superior to other doppler techniques based on laser light or sound the proposed new technique was successfully tested at stromboli volcano in late 1996 during a period of low activity the recorded data allow a clear distinction between particles rising from the vent and particles falling back towards the vent the mean eruption velocity was approximately 10 m s most of the eruptions recorded by radar were correlated to seismic recordings the correlation between the magnitude of the volcanic shocks and the eruption force index defined in the paper may provide new insights into magma transport in the conduit