recent emerged reef terraces of the yenkahe resurgent block tanna vanuatu implications for volcanic landslide and tsunami hazards emerged reef terraces record the extraordinarily rapid holocene uplift rate of the fault bounded yenkahe resurgent block yrb located within a partially submerged quaternary caldera on tanna island vanuatu southwest pacific the presently active volcano yasur is located at the western end of the yrb episodic uplift of the yrb is probably associated with the movement of magma below the yenkahe area a historically recorded uplift at port resolution bay in a d 1878 raised the shoreline 15 m this a d 1878 event was accompanied by a local earthquake and a tsunami that reached 12 m elevation coral samples from terraces at mean altitudes of 155 m and 15 m above present sea level yield 230 th 234 u dates of a d 1002 pm 10 and a d 1868 pm 4 respectively these ages imply a mean uplift of 156 mm yr for the yrb since a d 1002 until a d 1992 this volcanically related uplift occurs within the context of regional uplift of the southern new hebrides arc the late holocene uplift r

seasat altimetry and the south atlantic geoid 1 spectral analysis this paper presents a discussion of the spectral characteristics of geoid profiles derived from seasat alitmetry in the south atlantic individual profile spectra are computed and averaged in seven separate geodynamic provinces mid atlantic ridge flanks walvis and rio grande aseismic ridges and argentine and cape basins three distinct wavebands can be identified in most spectra for wavelengths shorter than 35 km the spectra are typical of white noise with a 7 cm rms amplitude typical of seasat altimeter measurement noise for wavelengths between 300 and 800 km our uppermost limit since original profiles are 1700 km long the spectra are in reasonable agreement with kaula s empirical rule and are compatible with a pratt thermal boundary layer compensation mechanism with an ill defined compensation depth of 30 60 km the paper centers on the description of the 35 300 km part of the spectra computation of an impedance for each province requires good knowledge of its bathymetry which is far from satisfactory as yet in the south atlantic we show that for wavelengths longer than 80 km the squared amplitude spectrum of bathymetry varies as the inverse of wave number we propose that this relationship might also hold at shorter wavelengths although it is not observed due to presently insufficient data using these spectral estimates and correcting for the mean depth of the topography we derive impedance actually response function estimates separately for each province the data are well accounted for by a regional compensation scheme based on elastic flexure models elastic thickness the best resolved parameter ranges from 2 to 5 km for the ridge and flanks and the crustal thickness from 4 to 13 km crustal thickness appears to be larger on the east flank demonstrating a general lack of symmetry between east and west in the south atlantic which appears to hold at all wavelengths and is also expressed in the bathymetry the rio grande rise involves low but nonzero elastic thickness and large crustal thickness 25 35 km in agreement with previously proposed models of local airy compensation the walvis ridge appears to imply a larger elastic thickness in excess of 8 km if the crustal thickness is less than 20 km which may be due to emplacement on older lithosphere therefore despite a lack of sufficient bathymetric control geoid data can be used at the scale of the entire south atlantic to provide reasonable information on thermomechanical compensation in the various provinces the spectral structure emphasizes the 35 300 km spectral window and should be used in constructing band pass filters that can separately enhance features related to plate kinematics or sublithospheric convection

seasat altimetry the north atlantic geoid and evaluation by shipborne subsatellite profiles a geological evaluation of geoid anomalies over the north atlantic is presented with emphasis on short 40 300 km wavelength undulations mapped by seasat radar altimetry long 3000 km and intermediate 300 3000 km wavelength undulations constrain subcrustal processes and are briefly reviewed portions of three seasat revolutions revs totaling 9300 km were followed by research ship which measured gravity magnetics topography and for a 800 km segment also seismic reflection data to form a ground truth data set for comparison to the altimetry the intermediate wavelength geoid the residual upon removal of a 14 14 long wavelength surface correlates with plate age slope 10 cm m y over cenozoic crust and major fracture zones appear as geoid steps a 3 5 to 5 m high over the bermuda rise may reflect thermal rejuvenation created within the plate 40 50 ma short wavelength geoid anomalies typically 10 50 cm in the open ocean were analyzed by high pass 200 or 400 km cutoff along track filtering and smoothing the vertical deflection computed from the seasat geoid compares well with one based on seismic reflection shipborne free air gravity except for a higher frequency cutoff correlates closely with geoid anomalies except near seamounts the principal contribution to geoid anomalies is fracture zone topography all major and many minor fracture zones fz s appear as geoid lineations particularly between the 15 20 and kane fz from the ridge axis to anomaly 34 the wsw trend of fz s between anomaly 21 and 34 is clearly expressed in the altimetry as is the smooth geoid over mid cretaceous smooth basement formed by fast spreading crustal ribbons 50 150 km wide of higher or lower geoid parallel fz trends some geoid lineations are oblique to both isochron and fz trends east of the puerto rico trench such anomalies may reflect compressional deformation within atlantic lithosphere

magma dynamics feeding yasur s explosive activity observed using thermal infrared remote sensing 1 a thermal infrared thermometer was used to record the passage of hot gases and fragments across a measurement area located at the exit of one of yasur s active vents recording was completed over 2 h during september 2011 a total of 200 explosive events were recorded we define two types of event low energy events with typical thermal energies of 14 kj and high energy events with typical thermal energies of 97 kj around 180 low energy events were recorded which together released 457 kj of radiant energy in contrast only 20 high energy events were recorded but they released 2042 kj we suggest that low energy events originate from a relatively shallow degassed magma reservoir and are associated with bursting of bubbles formed by bubble coalescence during ascent instead high energy events originate from a relatively deep fresh magma reservoir and are associated with slugs formed by foam collapse

the roar of yasur handheld audio recorder monitoring of vanuatu volcanic vent activity abstract we describe how near field audio recording using a pocket digital sound recorder can usefully document volcanic activity demonstrating the approach at yasur vanuatu in may 2014 prominent emissions peak at 263 hz interpreted as an organ pipe mode high pass filtering was found to usefully discriminate volcano vent noise from wind noise and autocorrelation of the high pass acoustic power reveals a prominent peak in exhalation intervals of 2 5 4 and 8 s with a number of larger explosive events at 200 s intervals we suggest that this compact and inexpensive audio instrumentation can usefully supplement other field monitoring such as seismic or infrasound a simple estimate of acoustic power interpreted with a dipole jet noise model yielded vent velocities too low to be compatible with pyroclast emission suggesting difficulties with this approach at audio frequencies perhaps due to acoustic absorption by volcanic gases

itrf2000 a new release of the international terrestrial reference frame for earth science applications 1 for the first time in the history of the international terrestrial reference frame the itrf2000 combines unconstrained space geodesy solutions that are free from any tectonic plate motion model minimum constraints are applied to these solutions solely in order to define the underlying terrestrial reference frame trf the itrf2000 origin is defined by the earth center of mass sensed by satellite laser ranging slr and its scale by slr and very long baseline interferometry its orientation is aligned to the itrf97 at epoch 1997 0 and its orientation time evolution follows conventionally that of the no net rotation nnr nuvel 1a model the itrf2000 orientation and its rate are implemented using a consistent geodetic method anchored over a selection of itrf sites of high geodetic quality ensuring a datum definition at the 1 mm level this new frame is the most extensive and accurate one ever developed containing about 800 stations located at about 500 sites with better distribution over the globe compared to past itrf versions but still with more site concentration in western europe and north america about 50 of station positions are determined to better than 1 cm and about 100 sites have their velocity estimated to at or better than 1 mm yr level the itrf2000 velocity field was used to estimate relative rotation poles for six major tectonic plates that are independent of the trf orientation rate a comparison to relative rotation poles of the nuvel 1a plate motion model shows vector differences ranging between 0 03 and 0 08 m y equivalent to approximately 1 7 mm yr over the earth s surface itrf2000 angular velocities for four plates relative to the pacific plate appear to be faster than those predicted by the nuvel 1a model the two most populated plates in terms of space geodetic sites north america and eurasia exhibit a relative euler rotation pole of about 0 056 0 005 m y faster than the pole predicted by nuvel 1a and located about 10 n 7 e more to the northwest compared to that model

seismoacoustic measurements during the july august 2001 eruption of mt etna volcano italy abstract on july 18 2001 two main eruptive vents opened on the southern flank of mount etna volcano italy at 2100 m and 2550 m a s l respectively the former vent fed mild strombolian activity and lava flows while the latter represented the main explosive vent producing strong phreato magmatic explosions explosions at this latter vent however shifted to a strombolian style in the following days before switching back to phreato magmatic activity towards the end of the eruption which ended on august 9 2001 on august 3 a small seismoacoustic array was deployed close to the eruptive vents the array was composed of three stations which recorded seismic and infrasonic waves coming from both of the eruptive vents a further seismoacoustic station equipped with a thermal infrared sensor was also installed several kilometers north of the first array seismic signals relating to the strombolian activity at the 2100 m vent were characterized by a strong decompression at the source analysis of the time delays between seismic infrasonic and infrared event onsets also revealed that ejection velocities during explosions from both vents were subsonic time delays between the onset of explosive events apparent in the infrared and infrasound data indicated that the explosion source at the 2550 m vent was located 220 250 m below the crater rim in comparison the depth of the seismic source was estimated to be between 230 and 335 m below the rim this converts to 120 150 and 130 235 m below the preexisting ground surface in addition time delays between seismic and infrasonic signals recorded for the lower 2100 m vent also revealed a seismic source that was no more than a few tens of meters deeper than the fragmentation surface

temporal behavior and temperatures of yasur volcano vanuatu from field remote sensing observations may 2014 abstract we documented eruption activity at three primary vents at yasur volcano tanna island vanuatu using portable instrumentation in the field over a period of 5 h on 21 may 2014 and acquired aerial images of the craters and vents on 22 may 2014 although limited in duration our observations of eruption intervals durations temperatures and speeds of ejected material illustrate the characteristics of the activity at the time at each of the primary vents providing a useful snapshot of eruption behavior and revealing continued variability at yasur in comparison to other observation campaigns hand held high resolution near infrared observations of one of the vents gave peak temperatures of 850 c to 930 c for ejected clasts with a maximum temperature of 1033 c these temperatures are significantly higher than previous measurements because exposed lavas could be resolved at timescales less than a second our aerial near infrared images allowed us to estimate the combined area of the active vents within the crater to be 150 m 2 and comparison to modis radiance measurements in the same time frame yields temperatures averaged over the combined vent area of 530 730 c in the context of previous observations at yasur the activity in may 2014 exhibited lower overall intensity as well as differences in the nature of the eruptions at the various vents providing insight regarding the temporal variability of yasur s activity

seafloor tectonic fabric from satellite altimetry abstract ocean floor structures with horizontal scales of 10 to a few hundred kilometers and vertical scales of 100 m or more generate sea surface gravity anomalies observable with satellite altimetry prior to 1990 altimeter data resolved only tectonic lineaments some seamounts and some aspects of mid ocean ridge structure new altimeter data available since mid 1995 resolve 10 km scale structures over nearly all the world s oceans these data are the basis of new global bathymetric maps and have been interpreted as exhibiting complexities in the sea floor spreading process including ridge jumps propagating rifts and variations in magma supply this chapter reviews the satellite altimetry technique and its resolution of tectonic structures gives examples of intriguing tectonic phenomena and shows that structures as small as abyssal hills are partially resolved a new result obtained here is that the amplitude of the fine scale 10 80 km roughness of old ocean floor is spreading rate dependent i

thermal seismic and infrasound observations of persistent explosive activity and conduit dynamics at santiaguito lava dome guatemala abstract in january 2003 we deployed a seismo acoustic array along with thermal sensors to define the dynamics and source characteristics of persistent intermittent explosive activity at the santiaguito lava dome guatemala seismic and acoustic waveforms accompanying thermal transients i e the thermal signature produced by the vertical ash plumes allowed discrimination of 35 explosions from minor degassing events during the 15 5 h observation period characteristics of thermal transients along with elastic and thermal energy flux from the explosive ash emissions allowed for a standardized measurement of eruption intensity duration frequency and repose interval using the thermal data we calculated a range of minimum exit velocities of 16 76 m s and convective rise rates of 9 26 m s to heights of 100 and 600 m above the vent source depths for the explosions were calculated using the thermo acoustic delay indicating a source 100 620 m below the vent the intensity of the explosions based on thermal amplitude and proxies for elastic energy released is not dependent on repose interval or depth the data support the notion for shear induced fragmentation at the conduit walls due to stick slip movement of the upper degassed part of the magma column as a source mechanism loci of explosion depths suggest that this operates within a 500 m thick dacite plug in the uppermost portion of the conduit

global glacial isostatic adjustment palaeogeodetic and space geodetic tests of the ice 4g vm2 model analyses of the global process of glacial isostatic adjustment and post glacial relative sea level change continue to deliver important insights into earth system form and process one successful model of the related phenomenology is based upon a spherically symmetric internal viscoelastic structure for the solid earth which has been denoted vm2 and a model of the most recent deglaciation event of the current ice age denoted ice 4g the primary purpose of this paper is to describe several new a posteriori tests that have recently been performed to further investigate the quality of this global solution to the inverse problem for both mantle viscosity and deglaciation history that is posed by the observables associated with this large scale geodynamic phenomenon i focus especially upon the misfits of observations to the theoretical predictions of this model which i am currently using to further refine its properties and upon predictions made using it of geophysical signals that should soon become visible in the context of the gravity recovery and climate experiment grace satellite mission among the required refinements to ice 4g one that is necessary to eliminate a recently revealed misfit to space geodetic constraints on the present day rate of radial motion at the yellowknife location well to the west of hudson bay and a similar misfit to absolute gravity measurements to the southwest of the bay is the insertion of a keewatin dome of thick ice centred over yellowknife with a ridge of ice extending to the south east in the geomorphological literature the existence of such a keewatin dome previously has been hypothesised but chronological control was lacking on the surface features that suggested its former existence an important additional constraint that requires the late glacial existence of this important feature consists of new inferences of the last glacial maximum lowstand of the sea from sites in the far field of the main concentrations of land ice copyright 2002 john wiley sons ltd

space geodetic constraints on glacial isostatic adjustment in fennoscandia analysis of global positioning system gps data demonstrates that ongoing three dimensional crustal deformation in fennoscandia is dominated by glacial isostatic adjustment our comparison of these gps observations with numerical predictions yields an earth model that satis es independent geologic constraints and bounds both the average viscosity in the upper mantle 5 x 10 20 to 1 x 10 21 pascal seconds and the elastic thickness of the lithosphere 90 to 170 kilometers we combined gps derived radial motions with fennoscandian tide gauge records to estimate a regional sea surface rise of 2 1 0 3 mm year furthermore ongoing horizontal tectonic motions greater than 1 mm year are ruled out on the basis of the gps derived three dimensional crustal velocity field

classification landing distribution and associated flight parameters for a bomb field emplaced during a single major explosion at stromboli italy we propose a novel approach to studying a ballistic bomb deposit favorable circumstances a unique dispersal axis an operational thermal video camera and application of an innovative methodology allowed estimates of volume and mass erupted and definition of mass partitioning between bombs of various sizes this allowed the creation of a multidisciplinary database for a single major explosion at stromboli volcano italy the type locality of strombolian eruptions the dispersion and direction of the deposit were consistent with a major explosion on 21 january 2010 field data comprised 780 mapped bomb locations and sizes and were organized into a gis with a lidar derived digital elevation model as its base this allowed us to define the landing distribution and flight parameters for erupted bombs the data defined discontinuous deposition to build a cluster dominated bomb field with a total deposit volume of 10 m3 a mass of 2 104 kg and a grain size dominated by large bombs 1 m in diameter the parameters defined here for a major eruption at stromboli show that the strombolian style of volcanism and its deposits need to be treated carefully and a different approach is needed in the future to truly characterize and classify such small but globally common explosive eruptions the recognition that sedimentation from such eruptions will be uneven leads to the important conclusion that isopachs and isopleths cannot be used to estimate eruption volumes for such explosions

inference of mantle viscosity from grace and relative sea level data summary gravity recovery and climate experiment grace satellite observations of secular changes in gravity near hudson bay and geological measurements of relative sea level rsl changes over the last 10 000 yr in the same region are used in a monte carlo inversion to infer mantle viscosity structure the grace secular change in gravity shows a significant positive anomaly over a broad region 3000 km near hudson bay with a maximum of 2 5 gal yr 1 slightly west of hudson bay the pattern of this anomaly is remarkably consistent with that predicted for postglacial rebound using the ice 5g deglaciation history strongly suggesting a postglacial rebound origin for the gravity change we find that the grace and rsl data are insensitive to mantle viscosity below 1800 km depth a conclusion similar to that from previous studies that used only rsl data for a mantle with homogeneous viscosity the grace and rsl data require a viscosity between 1 4 1021 and 2 3 1021 pa s an inversion for two mantle viscosity layers separated at a depth of 670 km shows an ensemble of viscosity structures compatible with the data while the lowest misfit occurs for upper and lower mantle viscosities of 5 3 1020 and 2 3 1021 pa s respectively a weaker upper mantle may be compensated by a stronger lower mantle such that there exist other models that also provide a reasonable fit to the data we find that the grace and rsl data used in this study cannot resolve more than two layers in the upper 1800 km of the mantle

glacial isostatic adjustment i the forward problem summary the isostatic adjustment of a radially stratified visco elastic spheroid is treated using space time green functions for the associated surface mass load boundary value problem these impulse response functions are convolved with a heaviside function to give the time dependent deformation of the planet which would be produced by a unit point mass brought up from infinity at t 0 and allowed to remain on the surface the resulting heaviside green functions can be employed to simulate all of the important signatures of glacial isostatic adjustment given a space time dependent surface mass load consisting of ice sheet ablation histories and a model of the simultaneous filling of the ocean basins these source terms are simply convolved with the heaviside green function appropriate to a specific response signature a realistic model of the spatial distribution of the main late pleistocene ice loads and of their temporal disintegration is constructed the response of two visco elastic earth models is computed and compared to a global set of relaxation data relative sea level curves on the basis of this initial comparison of theory and observation the possibility that the lower mantle has a viscosity which is significantly in excess of the viscosity of the upper mantle is excluded in addition clear evidence of the presence of the lithosphere has been found in relaxation data from sites which were near the edge of the laurentide ice sheet such data should therefore prove useful as a basis for analysis of lateral variations in lithosphere thickness further extensions of the calculation are suggested

the gravsat signal over tectonic features the range rate between two close gravitational satellites gravsat in low earth orbit has been evaluated over model tectonic features such as mountains and ranges fracture zones and trenches models are locally compensated and consist of both point mass dipoles and sheet mass dipoles masses and depths of compensation are chosen to approximate known gravity signatures the results show that for two satellites at 160 km altitude with 3 separation significant signal power 1 m s remains for most extended features at wavelengths less than 200 km furthermore there is strong sensitivity in the signal from these features to lateral and vertical changes of the order of 1 km and less in addition the signal of hidden geologic structures such as dikes salt domes and ore bodies may also stand above 1 m s for this low orbiting pair thus it may prove to be efficient to model the high frequency gravsat signal directly in terms of the parameters of tectonic topographic features and their compensation

glaciation induced perturbations in the earth s rotation a new appraisal we revisit the theory and predictions of glaciation induced perturbations in both the rotation rate of the earth or j 2 and the wander of the rotation pole with respect to the surface geography the two most common theoretical formulations associated with polar wander driven by the surface loading of a viscoelastic earth e g sabadini et al 1982 wu and peltier 1984 appear to disagree by one on the number of rotational normal modes associated with a surface gravitational response having n normal modes we show using a generalized theory that the two formalisms yield essentially equivalent predictions we next consider a benchmark comparison of recent predictions of present day polar wander speed due to glacial isostatic adjustment henceforth gia these comparisons confirm the validity of certain previous analyses e g spada et al 1992a they also reveal that predictions of polar wander speed can be sensitive to an assumption of incompressibility previous studies have noted that predictions of j 2 rotation rate as a function of lower mantle viscosity differ significantly in form from analogous predictions of polar wander speed we investigate these differences by considering the contribution to the predicted anomalies from the individual normal modes of relaxation we find that the normal mode structure of the j 2 rotation rate predictions is fundamentally different from that which characterizes the polar wander response and this difference reflects the distinct physical mechanisms which govern these anomalies finally using a large suite of forward computations as well as the calculation of a set of frechet kernels we investigate the sensitivity of our predictions to variations in the viscoelastic earth model we find for example that a previously noted sensitivity of polar wander speed predictions to variations in lithospheric thickness is only valid for earth models with relatively weak lower mantle viscosities 5 x 10 21 pa s

magma budgets and steady state activity of vulcano and stromboli we present three models for magma budget during steady state volcanic activity by which non erupted magma is emplaced as dykes or cumulates or crystallises in place using gas and thermal data we apply our models at vulcano to calculate degassing cooling and crystallisation of magma at a rate of 40 375 kg s 1 within a magma body with an upper surface at a 2 km depth at stromboli we calculate a steady magma supply of 300 1300 kg s 1 to shallow 1 km depths

sea level change glacial rebound and mantle viscosity fornorthern europe northwestern europe remains a key region for testing models of glacial isostasy because of the good geological record of crustal response to the glacial unloading since the time of the last glacial maximum models for this rebound and associated sea level change require a detailed knowledge of the ice sheet geometry including the ice thickness through time existing ice sheet reconstructions are strongly model dependent and inversions of sea level data for the mantle response may be a function of the model assumptions thus inverse solutions for the sea level data are sought that include both ice and earth model parameters as unknowns sea level data from fennoscandia the north sea the british isles and the atlantic and english channel coasts have been evaluated and incorporated into the solutions the starting ice sheet for fennoscandia is based on a reconstruction of a model by denton hughes 1981 that is characterized by quasi parabolic cross sections and symmetry about the load centre both global northwestern europe as a whole and regional subsets of the data solutions have been made for earth model parameters and ice height scaling parameters the key results are as follows 1 the response of the upper mantle to the changing ice and water loads is spatially relatively homogenous across scandinavia the north sea and the british isles 2 this response can be adequately modelled by an effective elastic lithosphere of thickness 65 85 km and by an effective upper mantle viscosity from the base of the lithosphere to the 670 km depth seismic discontinuity of about 3 4 1020 pa s the effective lower mantle viscosity is at least an order of magnitude greater 3 the ice thickness over scandinavia at the time of maximum glaciation was only about 2000 m much less than the 3400 m assumed in the denton hughes model 4 the ice profiles are asymmetric about the centre of the ice sheet with those over the western part being consistent with quasi parabolic functions whereas the ice heights over the eastern and southern regions increase much more slowly with distance inwards from the ice margin

thermal seismic and infrasonic evidences of variable degassing rates at stromboli volcano abstract during june 1999 we measured the amplitude and rate number of events per second at which gas exited the vent at stromboli volcano as discrete gas bursts or puffs this allowed us to identify two styles of gas burst puffing activity the first is characterized by frequent rapidly rising puffs the second by less frequent slowly rising puffs each style persisted over 5 40 min long durations and was associated with a high and low number of strombolian explosions per hour respectively each period was also associated with characteristic delay times between the arrival of the infrasonic and thermal signals during strombolian explosions the delays were longer during vigorous puffing periods to explain our observations we propose a model in which the degassing process cycles between vigorous and weak degassing phases during vigorous degassing phases bubble layers ascend the conduit at a frequency of 0 5 1 0 s 1 this high degassing level reflects a gas rich magma column and leads to an increased rate in the formation of shallow foams and hence an increase in puffing and explosive activity as well as a higher free surface level and or gas jet velocity during weak phases bubble layers ascend the conduit at a reduced frequency of 0 2 0 3 s 1 during such times the magma column is poor in gas this leads to a decreased rate of foam layer formation and hence a reduction in puffing and explosive activity as well as a lower free surface level and or gas jet velocity variations in puffing activity can thus be used to track changes in the rate at which the shallow system is supplied by fresh gas rich magma our observations indicate that the two degassing styles last from 5 to 40 min and that the switch from one to the other occurs over a matter of minutes

dynamics of the 5 april 2003 explosive paroxysm observed at stromboli by a near vent thermal seismic and infrasonic array 1 on 5 april 2003 an array of thermal infrasonic and seismic sensors tracked the dynamics of a major explosive paroxysmal event at stromboli the thermal signal recorded a decline 1 hour before the paroxysm which itself lasted 6 5 minutes and opened with a 14 s low thermal amplitude phase this was followed by three main explosive phases with gas and ejecta velocities of 324 and 185 m s being calculated for the first phase the delay time between thermal and infrasonic signals indicates a very shallow 150 m source for fragmentation a strong tilt component in the seismic signals shows that the conduit began to expand at least 90 s before the explosion large seismic amplitudes were recorded during the emission onset the seismic signal can thus be related to stress build up followed by release during the ejection of the gas particles mixture we calculate that the cloud of hot gas and ash emitted during the explosion had an overpressure of 3 8 mpa and involved 5 7 105 m3 2 9 106 kg of gas

shallow magma mingling driven strombolian eruptions at mt yasur volcano vanuatu 1 mt yasur volcano vanuatu has been increasingly recognized for its high frequency strombolian eruptions strombolian activity is often regarded as a product of the rapid ascent of gas slugs originating from a deep magma which mingle with a batch of shallow magma upon eruption heterogeneous crystal distribution as well as bimodal bubble size distributions in the eruptive products generally supports this view here the strombolian activity at mt yasur is analyzed a rheological investigation indicates that the basaltic andesitic eruptive products contain an apparently homogeneous glass phase and yet exhibit evidence of a distinct range of glass transition temperatures with multiple peaks occurring in individual samples such anomalous behavior is proposed to result from the mingling of magmas with contrasting oxidation states the unstable nature of the measured glass transition behavior leads us to the inference that mingling is located in the shallow parts of the eruptive conduits partly driven by rejuvenation of material slumped from the crater walls into an open conduit system the dynamics of this process may expose the periodicity of the eruptions themselves

roughness of the marine geoid from seasat altimetry the geographical variability of short wavelength geoid power spectra geoid roughness has been mapped for the world s oceans between latitudes 72 deg n and 72 deg s a spectral analysis of seasat altimeter data reduced to sea surface heights has been performed at 2 min intervals for 15 consecutive days of the 3 day repeat orbit the geoid roughness represented by these spectra for wavelengths shorter than about 220 km is separated from the total sea height variance and is displayed in the form of a global contour map the global average geoid roughness is 32 cm rms varying from a high in excess of 2 m rms near deep ocean trenches to a low of 2 cm rms in the southeast pacific near the east pacific rise this average value agrees well with previous estimates based on gravimetry and geos 3 altimetry in general the smoothest areas in the marine geoid overlie relatively young sea floor adjacent mid ocean spreading centers where even short wavelength topographic variations tend to be isostatically compensated

strombolian eruptions and dynamics of magma degassing at yasur volcano vanuatu abstract open vent basaltic volcanoes account for a substantial portion of the global atmospheric outgassing flux largely through passive degassing and mild explosive activity we present volcanic gas flux and composition data from yasur volcano vanuatu collected in july 2018 the average volcanic plume chemistry is characterised by a mean molar co2 so2 ratio of 2 14 h2o so2 of 148 and so2 hcl of 1 02 the measured mean so2 flux in the period of 6th to 9th july is 4 9 kg s 1 therefore the mean fluxes of the other species are 7 5 kg s 1 co2 208 kg s 1 h2o and 4 8 kg s 1 hcl the degassing regime at yasur volcano ranges from passive to active styles with the latter including strombolian activity and spattering gases emitted during active degassing are enriched in so2 over hcl and co2 over so2 relative to passive degassing with co2 so2 ratios of 2 85 0 17 so2 hcl of 1 6 0 22 and h2o so2 of 315 78 8 gases emitted during passive degassing have co2 so2 ratios of 1 96 0 12 so2 hcl of 0 50 0 07 and h2o so2 of 174 43 5 we use a model of volatile degassing derived from melt inclusion studies metrich et al 2011 combined with our observations of chemical variations in the outgassing bubbles to propose a mechanism for magma degassing in the conduit at yasur we envisage a shallow conduit filled with crystal rich magma forming a viscous and mobile plug that develops an effective yield strength from the surface to a depth of at least 2000 m in which bubbles are trapped grow ascend towards the surface and burst in a typical strombolian eruption deeper bubbles released during active degassing are enriched in co2 and so2 compared to bubbles released during passive degassing which are sourced from close to the surface and are consequently hcl rich

dynamics of degassing at kilauea volcano hawaii at kilauea volcano hawaii the recent long lived eruptions of mauna ulu and pu u o o have occurred in two major stages defining a characteristic eruptive pattern the first stage consists of cyclic changes of activity between episodes of fire fountaining and periods of quiescence or effusion of vesicular lava the second stage consists only of continuous effusion of lava we suggest that these features reflect the dynamics of magma degassing in a chamber which empties into a narrow conduit in the volcano chamber gas bubbles rise through magma and accumulate at the roof in a foam layer the foam flows toward the conduit and its shape is determined by a dynamic balance between the input of bubbles from below and the output into the conduit the foam thickness is proportional to lq e2 l g 1 4 where l and l are the viscosity and density of magma e is the gas volume fraction in the foam g is the acceleration of gravity and q is the gas flux the bubbles in the foam deform under the action of buoyancy and the maximum permissible foam thickness is hc 2 e lgr where is the coefficient of surface tension and r is the original bubble radius if this critical thickness is reached the foam collapses into a large gas pocket which erupts into the conduit foam accumulation then resumes and a new cycle begins the attainment of the foam collapse threshold requires a gas flux in excess of a critical value which depends on viscosity surface tension and bubble size hence two different eruption regimes are predicted 1 alternating regimes of foam buildup and collapse leading to the periodic eruption of large gas volumes and 2 steady foam flow at the roof leading to continuous bubbly flow in the conduit the essential result is that the continuous process of degassing can lead to discontinuous eruptive behavior data on eruption rates and repose times between fountaining phases from the 1969 mauna uiu and the 1983 1986 pu u o o eruptions yield constraints on three key variables the area of the chamber roof must be a few tens of square kilometers with a minimum value of about 8 km2 magma reservoirs of similar dimensions are imaged by seismic attenuation tomography below the east rift zone close to the roof the gas volume fraction is a few percent and the gas bubbles have diameters lying between 0 1 and 0 6 mm these estimates are close to the predictions of models for bubble nucleation and growth in basaltic melts as well as to the observations on deep submarine basalts the transition between cyclic and continuous activity occurs when the mass flux of gas becomes lower than a critical value of the order of 103 kg s in this model changes of eruptive regime reflect changes in the amount and size of bubbles which reach the chamber roof

time scales of foam stability in shallow conduits insights from analogue experiments volcanic systems can exhibit periodical trends in degassing activity characterized by a wide range of time scales understanding the dynamics that control such periodic behavior can provide a picture of the processes occurring in the feeding system towards this end we analyzed the periodicity of outgassing in a series of decompression experiments performed on analogue material argon saturated silicone oil plus glass beads fibers scaled to serve as models of basaltic magma to define the effects of liquid viscosity and crystal content on the time scale of outgassing we investigated both 1 pure liquid systems at differing viscosities 100 and 1000 pa s 2 particle bearing suspensions diluted and semi diluted the results indicate that under dynamic conditions e g decompressive bubble growth fluid ascent within the conduit the periodicity of foam disruption may be up to several orders of magnitude less than estimates based on the analysis of static conditions this difference in foam disruption time scale is inferred to result from the contribution of bubble shear and bubble growth to inter bubble film thinning the presence of particles in the semi diluted regime is further linked to shorter bubble bursting times likely resulting from contributions of the presence of a solid network and coalescence processes to the relative increase in bubble break up rates finally it is argued that these experiments represent a good analogue of gas piston activity i e the periodical rise and fall of a basaltic lava lake surface implying a dominant role for shallow foam accumulation as a source process for these phenomena this article is protected by copyright all rights reserved

spatiotemporal variations in eruption style and magnitude at yasur volcano vanuatu part 2 extending strombolian eruption classifications in this companion study to simons et al bull volcanol 82 2020a we examine strombolian style explosive activity at yasur vanuatu over 11 weeks via seismic thermal infrared and visual observations in part 1 of this study simons et al bull volcanol 82 2020a we investigated the link between variations in the surface expression and style of volcanism at yasur in relation to vent shallow conduit and shallow magma reservoir processes now in part 2 based on the database of 4998 explosions we describe define and classify yasur s strombolian eruption styles and magnitudes and compare and contrast to stromboli and other similar centres the styles of most of yasur s explosions fit with other known strombolian eruptions but they are 2 3 times more frequent and with higher average eruption heights than at stromboli observed activity at yasur also produced more ash than at stromboli the most powerful eruptive periods are dominated by type 2a explosions ballistics and ash and type 2b ash dominated explosions a new type of strombolian style explosion was observed at yasur and is here termed a type 3 explosion they occur when vents are buried by a thick cap of loose poorly sorted pyroclastic breccia type 3 explosions begin as a series of emergent ash rich jets that rupture and fountain from the breccia cover generating prolonged jetting of ash to form vigorous low plumes the loose breccia cover apparently dissipates the violent early phase of the explosion the greatest hazard of type comes from their occurrence with little warning from a smooth crater floor without an apparent vent and after longer than typical intervals between eruptions the findings extend the observed range of strombolian explosion styles and imply that surficial vent cover and burial may influence gas slug stability and contribute to variations in ash and ballistic output

oceanographic and geophysical applications of satellite altimetry since the last quadrennial report new satellite altimeter data have not been generally available nevertheless important progress has been made from analyses of geos 3 and seasat data the marine gravity field has been determined to an extraordinary resolution and accuracy and important solid earth geophysical interpretations made in the area of oceanography statistical estimates of the variability of dynamic topography have been published methods for incorporating altimeter data into numerical models have been developed and applied and tentative but interesting determinations of the mean circulation have been made in addition altimeter waveform analysis has made it possible to use altimeter data to determine elevations of major ice fields finally important new insights into the nature of satellite ephemeris error and its influence on altimetrically derived sea surface topography have been achieved

characteristics of puffing activity revealed by ground based thermal infrared imaging the example of stromboli volcano italy puffing i e the frequent 1 s ca release of small 0 1 10 m3 over pressurized pockets of magmatic gases is a typical feature of open conduit basaltic volcanoes worldwide despite its non trivial contribution to the degassing budget of these volcanoes and its recognized role in volcano monitoring detection and metering tools for puffing are still limited taking advantage of the recent developments in high speed thermal infrared imaging we developed a specific processing algorithm to detect the emission of individual puffs and measure their duration size volume and apparent temperature at the vent as a test case we applied our method at stromboli volcano italy studying snapshots of 1 min collected in the years 2012 2013 and 2014 at several vents in all 3 years puffing occurred simultaneously at three or more vents with variable features at the scale of the single vent a direct relationship links puff temperature and radius suggesting that the apparent temperature is mostly a function of puff thickness while the real gas temperature is constant for all puffs once released in the atmosphere puffs dissipate in less than 20 m on a broader scale puffing activity is highly variable from vent to vent and year to year with a link between average frequency temperature and volume from 136 puffs per minute 600 k above ambient temperature 0 1 m3 and the occasional ejection of pyroclasts to 20 puffs per minute 3 k above ambient 20 m3 and no pyroclasts frequent small hot puffs occur at random intervals while as the frequency decreases and size increases an increasingly longer minimum interval between puffs up to 0 5 s appears these less frequent and smaller puffs also display a positive correlation between puff volume and the delay from the previous puff our results suggest an important role of shallow bubble coalescence in controlling puffing activity the smaller and more frequent puffing at hotter vents is in agreement with the rapid rise of small gas pockets with only limited coalescence while slower rise allowing more time for coalescence leads to larger but less frequent puffing at colder vents this link between puffing style and vent thermal state points to a feedback between gas flux and magma temperature and viscosity where higher gas flux stirs and heats the magma which by getting less viscous becomes a preferential way for bubble rise such a link has implications for the monitoring of the state of the shallow conduit at open vent volcanoes as well as for determination of their total gas budget relevant for hazard forecast and environmental studies

continuous gps measurements of postglacial adjustment in fennoscandia 1 geodetic results 1 data collected under the auspices of the bifrost gps project yield a geographically dense suite of estimates of present day three dimensional 3 d crustal deformation rates in fennoscandia johansson et al 2002 a preliminary forward analysis of these estimates milne et al 2001 has indicated that models of ongoing glacial isostatic adjustment gia in response to the final deglaciation event of the current ice age are able to provide an excellent fit to the observed 3 d velocity field in this study we revisit our previous gia analysis by considering a more extensive suite of forward calculations and by performing the first formal joint inversion of the bifrost rate estimates to establish insight into the physics of the gia response in the region we begin by decomposing a forward prediction into the three contributions associated with the ice ocean and rotational forcings from this analysis we demonstrate that recent advances in postglacial sea level theory in particular the inclusion of rotational effects and improvements in the treatment of the ocean load in the vicinity of an evolving continental margin involve peak signals that are larger than the observational uncertainties in the bifrost network the forward analysis is completed by presenting predictions for a pair of fennoscandian ice histories and an extensive suite of viscoelastic earth models the former indicates that the bifrost data set provides a powerful discriminant of such histories the latter yields bounds on the assumed constant upper and lower mantle viscosity nu um nu lm specifically we derive a 95 confidence interval of 5 x 10 20 less than or equal to nu um less than or equal to 10 21 pa s and 5 x 10 21 less than or equal to nu lm less than or equal to 5 x 10 22 pa s with some preference for elastic lithospheric thickness in excess of 100 km the main goal of the bayesian inverse analysis is to estimate the radial resolving power of the bifrost gps data as a function of depth in the mantle assuming a reasonably accurate ice history we demonstrate that this resolving power varies from similar to 200 km near the base of the upper mantle to similar to 700 km in the top portion of the lower mantle we conclude that the bifrost data are able to resolve structure on radial length scale significantly smaller than a single upper mantle layer however these data provide little constraint on viscosity in the bottom half of the mantle finally elements of both the forward and inverse analyses indicate that radial and horizontal velocity estimates provide distinct constraints on mantle viscosity

pyroclast tracking velocimetry illuminates bomb ejection and explosion dynamics at stromboli italy and yasur vanuatu volcanoes a new image processing technique pyroclast tracking velocimetry was used to analyze a set of 30 high speed videos of strombolian explosions from different vents at stromboli italy and yasur vanuatu volcanoes the studied explosions invariably appear to result from the concatenation of up to a hundred individual pyroclast ejection pulses all these pulses share a common evolution over time including 1 a non linear decrease of the pyroclast ejection velocity 2 an increasing spread of ejection angle and 3 an increasing size of the ejected pyroclasts these features reflect the dynamic burst of short lived gas pockets in which the rupture area enlarges while pressure differential decreases we estimated depth of pyroclast release to be approximately 1 and 8 m below the surface at stromboli and yasur respectively in addition explosions featuring more frequent pulses also have higher average ejection velocities and larger total masses of pyroclasts these explosions release a larger overall amount of energy stored in the pressurized gas by a combination of more frequent and stronger ejection pulses in this context the associated kinetic energy per explosion ranging 103 109 j appears to be a good proxy for the explosion magnitude differences in the pulse defining parameters among the different vents suggest that this general process is modulated by geometrical factors in the shallow conduit as well as magma specific rheology indeed the more viscous melt of yasur compared to stromboli is associated with larger vents producing fewer pulses but larger pyroclasts

integrating puffing and explosions in a general scheme for strombolian style activity strombolian eruptions are among the most common subaerial styles of explosive volcanism worldwide distinctive features of each volcano lead to a correspondingly wide range of variations of magnitude and erupted products but most papers focus on a single type of event at a single volcano here in order to emphasize the common features underlying this diversity of styles we scrutinize a database from 35 different erupting vents including 21 thermal infrared videos from stromboli italy etna italy yasur vanuatu and batu tara indonesia from puffing through rapid explosions to normal explosions with variable ejection parameters and relative abundance of gas ash and bombs using field observations and high speed thermal infrared videos processed by a new algorithm we identify the distinguishing characteristics of each type of activity and how they may relate and interact in particular we record that ash poor normal explosions may be preceded and followed by the onset or the increase of the puffing activity while ash rich explosions are emergent i e with inflation of the free surface followed directly by emission of increasingly large gas pockets overall we see that all strombolian activities form a continuum arising from a common mechanism and are modulated by the combination of two well established controls 1 the length of the bursting gas pocket with respect to the vent diameter and 2 the presence and thickness of a high viscosity layer in the uppermost part of the volcanic conduit

itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters 1 unlike the past international terrestrial reference frame itrf versions where global long term solutions were combined the itrf2005 uses as input data time series weekly from satellite techniques and 24 h session wise from very long baseline interferometry of station positions and daily earth orientation parameters eops the advantage of using time series of station positions is that it allows to monitor station non linear motion and discontinuities and to examine the temporal behavior of the frame physical parameters namely the origin and the scale the itrf2005 origin is defined in such a way that it has zero translations and translation rates with respect to the earth center of mass averaged by the satellite laser ranging slr time series spanning 13 years of observations its scale is defined by nullifying the scale and its rate with respect to the very long baseline interferometry vlbi time series spanning 26 years of observations the itrf2005 orientation at epoch 2000 0 and its rate are aligned to the itrf2000 using 70 stations of high geodetic quality the estimated level of consistency of the itrf2005 origin at epoch 2000 0 and its rate with respect to the itrf2000 is respectively 0 1 0 8 5 8 mm and 0 2 0 1 1 8 mm yr along the x yand z axis we estimate the formal errors on these components to be 0 3 mm and 0 3 mm yr we believe that this low level of agreement between the two frame origins is most probably due to the poor slr network geometry and its degradation over time the itrf2005 combination involving 84 co location sites revealed a scale inconsistency of 1 ppb 6 3 mm at the equator at epoch 2000 0 and 0 08 ppb yr between the slr and vlbi long term solutions as obtained by the stacking of their respective time series possible causes of this inconsistency may include the poor slr and vlbi networks and their co locations local tie uncertainties systematic effects and possible inconsistent model corrections used in the data analysis of both techniques for the first time of the itrf history the itrf2005 rigorous combination provides self consistent series of eops including polar motion from vlbi and satellite techniques and universal time and length of day from vlbi only a velocity field of 152 sites with an error less than 1 5 mm yr is used to estimate absolute rotation poles of 15 tectonic plates that are consistent with the itrf2005 frame this new absolute plate motion model supersedes and significantly improves that of the itrf2000 which involved six major tectonic plates citation altamimi z x collilieux j legrand b garayt and c boucher 2007 itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters j geophys res 112 b09401

machine learning as a detection method of strombolian eruptions in infrared images from mount erebus antarctica abstract mount erebus antarctica has a persistent lava lake with strombolian eruptions volcanic eruptions can be automatically detected with multiple methods such as cross correlation of seismic recordings and identifying anomalies in gas emissions we demonstrate a new method of detecting strombolian eruptions by training a convolutional neural network to automatically categorize eruptions in infrared images obtained from the rim of the crater above the ray lava lake atop mount erebus over 9 million images were obtained from previous research peters et al 2014a the infrared images were shot during a span of over 2 years one image every 2 s when weather conditions did not hinder the electrical supply training was performed with infrared images of the eruptions detected through seismic cross correlation with a stacked waveform eruptions detected using machine learning on infrared images from december 2013 through december 2014 correctly categorized 84 of the detections as eruptions the remaining 16 were caused by effects from the plume confounding the neural network nearly all of the eruptions detected utilizing seismic cross correlation were also categorized correctly by the neural network during periods for which image data was available we concluded machine learning is an effective method for classifying the characteristics of strombolian eruptions which further improves the ability to study their origins while assessing the hazards posed by volcanic eruptions

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

extraction of the m2 ocean tide from seasat altimeter data summary three complementary methods for the extraction of the m2 ocean tide using seasat altimetry are presented and compared the first method that developed by cartwright alcock which provides point measurements of the tide at the crossovers of the seasa t repeat orbit ground track has been applied to a study of the tide in tropical ocean areas the other two methods involve spatial expansions of m2 in terms of either surface spherical harmonics in the case of the method developed by mazzega or platzman normal modes of the world ocean the results obtained by each method from only one month of seasat data reproduce many features of the tide represented in recent tidal models and promise well for satellite altimetry as a future source of tidal knowledge

ice age cycles earth s rotation instabilities and sea level changes a new class of multilayered viscoelastic earth models based on prem is applied to the modeling of earth s rotation instabilities and associated sea level changes induced by the occurrence of pleistocene ice age cycles that match the oxygen isotope records over the last 0 8 myr the novelty of our approach stands on the usage for the first time in post glacial rebound induced sea level studies of a fully analytical scheme based on normal mode theory that allows to deal with complexities of the real earth such as lithospheric and mantle layering sphericity and self gravitation the ice models are based on ice 3g our results show that differences in true polar wander tpw and tpw induced sea level changes between earth models with a few layers and models having enough layers so that saturated continuum limits are reached can amount factors 2 to 3 this may change conclusions derived from some earlier studies on polar wander induced changes in climate that were based on earth models with a limited amount of layers the results indicate that models containing about 15 layers with a stratified lower mantle and transition zone have reached saturated continuum responses for both tpw and tpw induced sea level changes stratification of the lithosphere is not important this is in contrast with the sensitivity of post seismic deformation models this difference in sensitivity on the radial profile of the earth model can be explained with simple arguments on the dependence on zonal degree

m2 ocean tide at cobb seamount from seasat altimeter data seasat altimetry reduced to sea surface heights and harmonically analyzed at the frequencies of the dominant tidal components provides a direct measurement of m2 ocean tide parameters near cobb seamount in the northeast pacific comparison of these altimetric tide parameters with those determined from a bottom pressure gauge located on the summit of cobb seamount shows fair agreement in amplitude 43 cm versus 81 cm and good agreement in greenwich phase angle 243 versus 242 degrees the precision of the altimeter solution is estimated at 8 cm in amplitude and 10 degrees in phase angle

ice 3g a new global model of late pleistocene deglaciation based upon geophysical predictions of post glacial relative sea level change a new high resolution global model of late pleistocene deglaciation is inferred on the basis of geophysical predictions of postglacial relative sea level variations in which the ice ocean solid earth interaction is treated in a gravitationally self consistent fashion for the purpose of these analyses the radial viscoelastic structure of the planet is assumed known on the basis of previously published sensitivity tests on solutions of the forward problem only radiocarbon controlled relative sea level histories from sites that were actually ice covered with one or two additions are employed to constrain the model leaving relative sea level rsl data from sites that were not ice covered to be employed to confirm its consistency results for these confirmatory analyses are reported elsewhere here the new deglaciation model referred to as ice 3g is compared to previous models derived by several independent means and tested against a number of additional observations other than sea level histories including geologically controlled retreat isochrones oxygen isotope data from deep sea sedimentary cores and coral terrace elevations the latter two observations strongly constrain the net sea level rise that has occurred since the onset of deglaciation and therefore the mass of ice that melted during the last glacial interglacial transition

holocene relative sea level change isostatic subsidence and the radial viscosity structure of the mantle of northwest europe belgium the netherlands germany southern north sea abstract a comprehensive observational database of holocene relative sea level rsl index points from northwest europe belgium the netherlands northwest germany southern north sea has been compiled in order to compare and reassess the data collected from the different countries regions and by different workers on a common time depth scale rsl rise varies in magnitude and form between these regions revealing a complex pattern of differential crustal movement which cannot be solely attributed to tectonic activity it clearly contains a non linear glacio and or hydro isostatic subsidence component which is only small on the belgian coastal plain but increases significantly to a value of ca 7 5 m relative to belgium since 8 cal ka bp along the northwest german coast the subsidence is at least in part related to the post glacial collapse of the so called peripheral forebulge which developed around the fennoscandian centre of ice loading during the last glacial maximum the rsl data have been compared to geodynamic earth models in order to infer the radial viscosity structure of the earth s mantle underneath nw europe lithosphere thickness upper and lower mantle viscosity and conversely to predict rsl in regions where we have only few observational data e g in the southern north sea a very broad range of earth parameters fit the belgian rsl data suggesting that glacial isostatic adjustment gia only had a minor effect on belgian crustal dynamics during and after the last ice age in contrast a narrow range of earth parameters define the southern north sea region reflecting the greater influence of gia on these deeper older samples modelled rsl data suggest that the zone of maximum forebulge subsidence runs in a relatively narrow wnw ese trending band connecting the german federal state of lower saxony with the dogger bank area in the southern north sea identification of the effects of local scale factors such as past changes in tidal range or tectonic activity on the spatial and temporal variations of sea level index points based on model data comparisons is possible but is still complicated by the relatively large range of earth model parameters fitting each rsl curve emphasising the need for more high quality observational data

magma and volatile supply to post collapse volcanism and block resurgence in siwi caldera tanna island vanuatu arc v24c 04 allen s r 2005 complex spatterand pumice rich pyroclastic deposits from an andesitic caldera forming eruption the siwi pyroclastic sequence tanna vanuatu bulletin of volcanology 67

viscous gravitational relaxation summary this paper is concerned with a detailed examination of the response of maxwell models of the planet to surface mass loads particular attention is devoted to an examination of the factors which determine the isostatic response since the understanding of this response is crucial in a number of different geodynamic problems one particular example which we discuss in detail is concerned with the prediction of free air gravity anomalies produced by large scale deglaciation events using the methods developed here we are able to provide the first direct assessment of the importance of initial isostatic disequilibrium on the observed relative sea level variations and free air gravity anomalies forced by the melting of the laurentide ice sheet we are therefore able to estimate the extent to which such initial disequilibrium might influence the inference of mantle viscosity from isostatic adjustment data our calculations establish that free air gravity data although they are sensitive to the degree of initial disequilibrium provide an extremely high quality constraint upon the viscosity of the lower mantle

first estimate of volcanic so2 budget for vanuatu island arc abstract the spatial and temporal coverage of measurements of volcanic gas emissions remains patchy however over the last decade emissions inventories have improved thanks to new measurements of some of the lesser known volcanic areas we report on one such region the vanuatu island arc in the southwest pacific for which we now have sufficient systematic observations to offer a systematic emissions inventory our new estimate is based on so 2 flux measurements made in the period 2004 2009 with ultraviolet spectroscopy techniques for the following volcanoes yasur lopevi ambrym ambae gaua and vanua lava from south to north these are the first ever measurements for lopevi gaua and vanua lava the results reveal the vanuatu arc as one of earth s prominent sources of volcanic degassing with a characteristic annual emission to the atmosphere of 3 tg of so 2 representing about 20 of hitherto published global estimates our new dataset highlights the sustained prodigious degassing of ambrym volcano whose 5 gg day 1 mean flux of so 2 represents nearly two thirds of the total budget for the vanuatu arc this confirms ambrym as one of the largest volcanic sources worldwide comparable to etna often considered as the most vigorous source of volcanic emission on earth we also report a high degassing for ambae of 2 gg day 1 so 2 representing more than 28 of the vanuatu arc budget thus 90 of the so 2 output from vanuatu is focused in the central part of the arc from ambrym and ambae where magmas originate from enriched indian type mantle and where peculiar tectonic conditions could favor high magma production rates

lithosphere thickness and mantle viscosity inverted from gps derived deformation rates in fennoscandia summary crustal deformation in fennoscandia is associated with the glacial isostatic adjustment gia process that is caused by ongoing stress release of the mantle after removal of the late pleistocene ice sheet by 10 cal ka bp with an earth model of defined structure and rheology and an ice sheet model of known melting history the gia process can be simulated by geophysical models and the surface deformation rates can be calculated and used to compare with global positioning system gps observations therefore the crustal deformation rates observed by gps in fennoscandia provide constraints on the geophysical models on the basis of two ice sheet models anu ice and ice 5g reconstructed independently by the australian national university anu and university of toronto we use the gps derived deformation rates to invert for lithosphere thickness and mantle viscosity in fennoscandia the results show that only a three layer earth model can be resolved from current gps data providing robust estimates of effective lithosphere thickness upper and lower mantle viscosity the earth models estimated from inversion of gps data with two different ice sheet models define a narrow range of parameter space the lithosphere thickness between 93 and 110 km upper mantle viscosity between 3 4 and 5 0 1020 pa s and lower mantle viscosity between 7 1021 and 13 1021 pa s the estimates are consistent with those inverted from relative sea level indicators

textural and geophysical characterization of explosive basaltic activity at villarrica volcano 1 villarrica volcano chile is one of the most active volcanoes in south america its activity is currently characterized by continuous degassing from a summit lava lake vent punctuated by explosive events during november 2004 a multidisciplinary experiment was deployed for a 10 d period to define the style of emission and infer shallow conduit dynamics at this basaltic center this involved collection of thermal seismic and infrasonic data to describe the background activity confined inside the crater and use of samples to texturally and chemically characterize the ejecta from more energetic explosions able to attain the crater rim the background activity was characterized by gas bursting with a frequency of 9 events per minute this involved emission of gas puffs fed by bubble bursting with larger bursts emplacing sheets of magma onto the lower crater walls the ejecta population from the more energetic events was characterized by the coexistence of both scoriae and golden pumice these two types of clasts have different textures but identical glass compositions suggesting that they underwent different conduit histories the golden pumice is interpreted as the expanding inner part of a short lived jet fed by a rapidly ascending magma batch the scoria forms the outer portion of the jet and comprises degassed material entrained during passage of the fresh batch through material residing in the upper most portion of the conduit we thus have a largely degassed upper column that feeds persistent bubble bursting through which fresh batches occasionally rise to feed events of relatively higher energy

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

postglacial rebound and sea level contributions to changes in the geoid and the earth s rotation axis summary the rate of change of the spherical harmonic degree 2 component of the earth s gravitational potential coa 20 and polar wander velocity are two signals which are sensitive to late pleistocene deglaciation current changes in sea level and deep mantle viscosity diierent load and earth models have been used in earlier papers to predict the component of these geophysical signals caused by the collapse of the last great ice sheets and recent melting of polar ice caps in this paper we present a systematic analysis of the dependence of the predictions on parameters of the ice and earth model we show that the key parameters of the ice model which govern the predictions are the mass the location of the centre of mass and the midpoint of the deglaciation phase of secondary importance is the length of the deglaciation phase and the mean ice load prior to the last glacial maximum these conclusions enable us to make a more robust inference of mantle viscosity than has been made before allowing for the uncertainties in the model of late pleistocene and present deglaciation as previous authors have shown the lower mantle viscosity is the most important rheological parameter and therefore thecoa 20 observation complements sea level observations which are primarily sensitive to lithospheric thickness and the viscosity of the upper part of the mantle using realistic constraints on the sizes locations and timing of deglaciation of the late pleistocene ice sheets and current changes in polar ice caps the observation of coa 20 is used to infer lower mantle viscosity as a function of the present rate of sea level change if the present rate of non steric sea level change is 1 mm yr 1 and that change has been occurring for less than 1000 years then the lower mantle viscosity satis es log10 glm 21 82 0 15 which is consistent with inferences drawn from recent sea level analyses and con rms other analyses of thecoa 20 observation if the polar wander signal is produced entirely by postglacial rebound and current sea level change no more than 20 per cent of the present contribution to global sea level change comes from greenland the above conclusions also hold if the density discontinuities at 420 and 670 km are modelled as phase boundaries rather than material chemical boundaries

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos

explosive volcanic activity at mt yasur a characterization of the acoustic events 9 12th july 2011 abstract volcanic processes occur in a wide range of temporal and spatial scales however a key step of magma ascent is recognizable in the dynamics of gas and magma in the shallow plumbing system where volatiles play a fundamental role in controlling the eruptive style with the aim of investigating shallow degassing processes an experimental setup was deployed at mt yasur an active volcano located in tanna island vanuatu arc from 9th to 12th july 2011 the setup comprised high speed and thermal cameras as well as a microphone capable of recording both in the infrasonic and audible range the analysis of acoustic signals validated by observing images from the high speed and thermal cameras has enabled characterizing the explosive activity during the investigated period two types of explosions distinct for spectral features and waveforms were observed i minor events corresponding to small overpressurized bursts occurring almost continuously ii major events characterizing the strombolian activity at mt yasur by investigating variation in the occurrence rate of the minor events we found that on a short timescale the dynamics responsible for the two types of explosions are decoupled these results together with previous literature data bring additional evidence of the existence of distinct sources of degassing finally major events can be distinguished as emergent events i e long lasting signals corresponding to ash rich explosions and impulsive events featuring shorter duration and larger amplitude

simultaneous estimation of global present day water transport and glacial isostatic adjustment global water transport between oceans and continents during the transition from glacial to interglacial times has been enormous the viscoelastic solid earth has been responding to this unloading of large ice masses with a rise of the land masses in a process termed glacial isostatic adjustment in addition significant changes in the land ocean water distribution occur at present as both present day changes in the ice water thickness and glacial isostatic adjustment affect space geodetic measurements it is difficult to untangle the relative contributions of these two processes here we combine gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure to simultaneously estimate present day water transport and glacial isostatic adjustment we determine their separate contributions to movements in the geocentre which occur in response to changes in the earth s mass distribution with uncertainties below 0 1 mm yr 1 according to our estimates mass losses between 2002 and 2008 in greenland alaska yukon and west antarctica are 104 23 101 23 and 64 32 gt yr 1 respectively our estimates of glacial isostatic adjustment indicate a large geocentre velocity of 0 72 0 06 mm yr 1 in the polar direction we conclude that a significant revision of the present estimates of glacial isostatic adjustments and land ocean water exchange is required present day changes in the thickness of ice sheets and glacial isostatic adjustment both affect space geodetic measurements a combination of gravity measurements and geodetic data of surface movement with a data assimilating model of ocean bottom pressure allows the simultaneous estimation of present day water transport and glacial isostatic adjustment