broadband recording of strombolian explosions and associated very long period seismic signals on mount erebus volcano ross island antarctica in december 1996 and january 1997 broadband seismometers were deployed on the summit plateau of mount erebus at radial distances of 0 7 1 4 and 1 9 km from the central crater and lava lake strombolian explosions at erebus previously have been observed to produce seismic and acoustic energy between 1 and 6 hz new observations document significant energy with spectral peaks as grave as 20 s nearly identical very long period vlp signals begin 1 5 s prior to explosions have dilatational onsets and persist for up to 150 s similar vlp waveforms were recorded at all three stations indicating that the seismograms are essentially source dominated particle motions suggest an initial depth for the vlp source of up to several hundred meters migrating deeper in the course of 15 s such explosion associated vlp signals may indicate a nondestructive lossy resonance or nonlinear fluid flow excitation within the shallow magmatic system

fault location by radon and mercury detection at an active volcano in nicaragua the masaya caldera complex nicaragua with the active crater santiago fig 1 is the site of present day basaltic volcanism1 2 some of the faults that bound the caldera and lie within it can be located geologically others are postulated a possible older caldera rim lies to the south of the present margin to investigate whether one can identify faults in this environment of active volcanism concentrations of radon and mercury in the regolith were determined at 232 selected points in and adjacent to the caldera higher concentrations of hg0 or rn or both occurred over 75 of the known structures studied some hitherto suspected structures were confirmed while others were not lack of a chemical signature may be ascribed to the absence of a structure inappropriate sampling sites post fault lava cover or other sealing of the structure we show here how the use of rn and hg0 determinations has helped in structural analysis at this active volcano

the crystallization of lava lakes thermal convection driven by the kinetic undercooling of solidification can produce compositional and textural variations in an initially uniform lava flow that is cooled predominantly from above we show that such kinetic undercooling is sufficient to drive convection at high rayleigh numbers even in shallow lava lakes we then employ a theoretical model that includes the effects of convection at high rayleigh number to make predictions of the complete evolution of the lava we show that predictions of the rate of growth of solid crust at the surface of the lake do not differ much from predictions made by ignoring effects due to convection however convective motions do shorten the time for complete solidification because when they are driven by kinetic undercooling there is internal crystallization in addition to that occurring near the cooled upper boundary of the lava this important effect which is absent from purely conductive models predicts stratification and zonation of the lava in agreement with field observations we also examine the effect of taking into account the heat transfer to the country rock below the lava lake and determine how the evolution of the lava lake varies with the viscosity of the lava

unique strainmeter observations of vulcanian explosions soufriere hills volcano montserrat july 2003 gravity waves propagated at 30 m s 1 eruption volumes estimated from plume height and strain data are 0 32 0 42 10 6 0 26 0 49 10 6 and 0 81 0 84 10 6 m 3 f or explosions 3 5 respectively consistent with quasi cylindrical conduit drawdown 2 km the duration of vigorous explosion is given by the strain signature indicating mass fluxes of order 10 7 kg s 1 conduit pressures released reflect static weight of porous gas charged magma and exsolution generated overpressures of order 10 mpa citation voight b et al 2010 unique strainmeter observations of vulcanian explosions soufriere hills volcano montserrat july 2003 geophys res lett 37 l00e18 doi 10 1029 2010gl042551

the challenging retrieval of the displacement field from insar data for andesitic stratovolcanoes case study of popocatepetl and colima volcano mexico abstract despite the ability of synthetic aperture radar sar interferometry to measure ground motion with high resolution application of this remote sensing technique to monitor andesitic stratovolcanoes remains limited specific acquisition conditions characterizing andesitic stratovolcanoes mainly vegetated areas with large elevation ranges induce low signal coherence as well as strong tropospheric artefacts that result in small signal to noise ratio we propose here a way to mitigate these difficulties and improve the sar measurements we derive ground motions for two of the most active mexican stratovolcanoes popocatepetl and colima volcano from the time series of sar data acquired from december 2002 to august 2006 the sar data are processed using a method that combines both persistent scatterers and small baseline approaches stratified tropospheric delays are estimated for each interferogram using inputs from the global atmospheric model narr up to a maximum of 10 rad km these delays are validated using spectrometer data as well as the correlation between the wrapped phase and the elevation the tropospheric effect is removed from the wrapped phase in order to improve the unwrapping process on popocatepetl we observe no significant deformation the colima summit area exhibits a constant subsidence rate of more than 1 cm year centered on the summit but enhanced reaching more than 2 cm year around the 1998 lava flow we model this subsidence considering both a deflating magma source at depth and the effect of the eruptive deposits load

applicability of insar to tropical volcanoes insights from central america measuring volcano deformation is key to understanding the behaviour of erupting vol canoes and detecting those in periods of unrest satellite techniques provide the opportunity to do so on a global scale but with some notable exceptions the deformation of volcanoes in the tropics has been understudied relative to those at higher latitudes largely due to technical difficulties in applying interferometric synthetic aperture radar insar we perform a systematic survey of the central american volcanic arc to investigate the appli cability of interferometric synthetic aperture radar insar to volcanoes in the tropics volcano characteristics that may prevent insar measurement include 1 dense vegetation cover 2 per sistent activity and 3 steep slopes measurements of deformation are further inhibited by atmos pheric artefacts associated with 4 large changes in topographical relief we present a systematic method for distinguishing between water vapour artefacts and true deformation our data show a linear relationship c 2 cm km between the magnitudes of water vapour artefacts and volcano edifice height for high relief volcanoes e g fuego guatemala 3763 m a s l above sea level errors are of the order of 4 5 cm across the volcano s edifice but are less than 2 cm for lower relief e g masaya nicaragua 635 m a s l examples such as arenal atitlan and fuego illustrate that satellite acquisition strategies incorporating ascending and descending tracks are particularly important for studying steep sided volcanoes poor coherence is primarily associated with temporal decorrelation which is typically more rapid in southern central america where evergreen broadleaf vegetation dominates land use classification is a better predictorof decorrelation rate thanvegetationindex comparisonof coher ence for different radar wavelengths match expectations high resolution x band radar is best suited to local studies where high resolution digital elevation models dems exist while l bandwavelengths are necessary for regional surveys however this is the first time that relation ships between phase coherence and time perpendicular baseline radar wavelength and land use have been quantified on the scale of a whole volcanic arc

benchmarking and developing numerical finite element models of volcanic deformation article i nfo volcanic deformation during an unrest episode can provide valuable insights into potential magmatic plumbing system dynamics paramounttothis isa modellinking therecorded ground movement to thecausative source at depth most models employ analytical techniques due to their simplicity but these are limited in their approach due to a number of necessary assumptions and restricted to crude subsurface representations we address this problem by providing guidelines and example model files to benchmark against a simple analytical model with a numerical finite element approach using comsol multiphysics the boundary conditions should also be applicable to other finite element modeling packages then due to the flexibility of the finite element meth od this allows a progression of adding increasing complexities to reproduce the likely intricacies of the subsur face we thus provide further guidelines and accompanying model files to incorporate subsurface heterogeneity

deflection of dykes into sills at discontinuities and magma chamber formation abstract many rift zones contain composite volcanoes central volcanoes most of which are supplied with magma from shallow crustal magma chambers volcanotectonic studies of eroded rift zones such as in iceland as well as geophysical studies indicate that many shallow magma chambers evolve from sills here i provide field description of sills and extinct magma chambers in the quaternary and tertiary palaeorift zones of iceland focusing on the felsic pluton of slaufrudalur southeast iceland as a fine example of a magma chamber developed through the injection of sills in this paper i review analyse and develop further two related mechanisms for the deflection of dykes into sills and thus the potential initiation of a magma chamber namely a cook gordon debounding delamination and b stress barriers and propose a third mechanism c favourable material toughness ratios due to elastic mismatch difference in young s moduli or stiffnesses of layers in contact in the cook gordon mechanism a weak contact opens up as a result of dyke induced tensile stress this mechanism is likely to operate primarily at shallow depths as is supported by field observations and numerical models a stress barrier is a layer where the local stress is unfavourable to a particular type of rock fracture here a dyke field observations and numerical models show that on meeting a stress barrier a dyke either changes into a sill or becomes arrested the material toughness mechanism indicates that when the upper layer at a contact has the same or less stiffness than the lower layer hosting the dyke there is little tendency for the dyke to become deflected into the contact however when the upper layer is stiffer such as when a stiff basaltic lava flow is on the top of a soft pyroclastic layer the dyke tends to become deflected into the contact to form a sill field results suggest that all these mechanisms may cause dyke deflection into sills and may operate together particularly where the rock consists of alternating soft and stiff layers since the quaternary lava pile in iceland has many more soft hyaloclastite layers than the tertiary lava pile these mechanisms were probably very efficient in generating sills and by implication shallow magma chambers during the quaternary this may be one reason why in comparison with the tertiary lava pile the quaternary lava pile contains so many sills and extinct plutons and active shallow magma chambers

transitions between explosive and effusive eruptions of silicic magmas water rich silicic magmas may erupt explosively giving rise to massive columns of fragmented ash1 5 or effusively as viscous bubbly lavas to form lava domes6 8 complex cycles of explosive and effusive eruptions are often observed8 12 although these two eruption mechanisms have been modelled independently1 8 the conditions under which a volcano exhibits a particular style of eruption are not known and the transitions between eruption styles are poorly understood by modelling the ascent of magma along a permeable conduit we show here that for small magma chamber overpressures the style of eruption explosive or effusive is dependent on the magma flow rate we also identify a critical overpressure above which only explosive eruptions occur complex eruption sequences follow naturally for example if a shallow magmatic system is supplied with magma at an intermediate flow rate the eruption will be slow and effusive until the chamber over pressure becomes too large an explosive eruption then relieves the overpressure and an effusive eruption style resumes we suggest that monitoring of temporal variations in chamber overpressure for example by measuring ground deformation can be used to assess whether a passively effusing volcano has the potential to erupt explosively

incorporating seismic observations into 2d conduit flow modeling conduit flow modeling aims to understand the conditions of magma at depth and to provide insight into the physical processes that occur inside the volcano low frequency events characteristic to many volcanoes are thought to contain information on the state of magma at depth therefore by incorporating information from low frequency seismic analysis into conduit flow modeling a greater understanding of magma ascent and its interdependence on magma conditions and physical processes is possible the 2d conduit flow model developed in this study demonstrates the importance of lateral pressure and parameter variations on overall magma flow dynamics and the substantial effect bubbles have on magma shear viscosity and on magma ascent the 2d nature of the conduit flow model developed here allows in depth investigation into processes which occur at or close to the wall such as magma cooling and brittle failure of melt these processes are shown to have a significant effect on magma properties and therefore on flow dynamics by incorporating low frequency seismic information an advanced conduit flow model is developed including the consequences of brittle failure of melt namely friction controlled slip and gas loss this model focuses on the properties and behaviour of magma at depth within the volcano and their interaction with the formation of seismic events by brittle failure of melt

the pit craters and pit crater filling lavas of masaya volcano lava flowing into a pit crater will become entrapped to form an inactive lava lake at masaya volcano nicaragua pit filling lavas are exposed in the walls of nindiri santiago and san pedro pits mapping of these lavas shows that fill can involve emplacement of both a a and pahoehoe with single fill units ranging in thickness from 2 to 22 m thick units with columnar joints were emplaced as simple inactive lava lakes during high effusion rate episodes sequences of thinner units which can form pit floor shields or compound lakes were emplaced at lower effusion rates lava withdrawal caused unsupported sections of three 20 m thick units to subside resulting in unit flexure and faulting and viscous peeling features reveal that subsidence occurred while at least one unit was still partially molten where withdrawal has not occurred fill sequences are flat lying and symmetrically distributed around the feeder structures cinder cones and dykes the filled nindiri pit holds 5 107 m3 of lava in a 215 m thick sequence partial fill of santiago pit with 1 107 m3 of lava has filled the pit with a 110 m thick lava sequence of which 50 has been consumed by formation of a secondary pit altogether 6 4 107 m3 of lava was erupted into nindiri and santiago during 1525 1965 with 94 of this volume remaining pit contained the remainder forms a north flank lava flow field pit development and filling is a dynamic and ephemeral process having short lived effects on volcano morphology where pits develop and fill over hours to centuries however pits play an important role in shaping an edifice representing lava sinks and controlling whether lavas are trapped or able to spread onto the flanks

stability and instability of quiescently active volcanoes the case of masaya nicaragua quiescently active volcanoes are enigmatic due to their restlessness but lack of eruptive activity i present a model of coupled conduit convection and foam accumulation to explain degassing behavior of masaya an active volcano in nicaragua that is currently emitting large amounts of gas but not erupting gas rich magma is transported through a conduit 2 6 m in radius and then released into a shallow reservoir the magma is degassed in the reservoir and forms a foam 1 3 m thick at the top with bubbles 20 60 m in diameter the foam layer is stable because the input of gas into the foam is balanced by gas release through a vent to the surface if the foam layer is destabilized the volcano can erupt explosively the most likely cause of foam destabilization is a large injection of volatile rich magma from deeper levels into the shallow conduit reservoir system thereby increasing magma fluxes and gas fluxes exsolving large gas bubbles and reducing surface tension of the magma

models of ground deformation from vertical volcanic conduits with application to eruptions of mount st helens and mount etna we present simple analytical models of ground deformation from inflation of vertical volcanic conduits or pipes we compare three cases corresponding to 1 a pressurized pipe with closed end at the top that resists the internal pressure 2 a pressurized pipe with top open for which the internal deformation is mainly dislocation of the cylindrical walls and 3 a pipe shaped region that dilates for the closed pipe we use eshelby s inclusion theory to model deformation from a thin pressurized elongated prolate ellipsoid in a full space which we express in terms of double forces to satisfy surface boundary conditions we superimpose image solutions by using double forces derived from mindlin s half space solution for the point force for the open pipe we apply the volterra integral to dislocation across a cylindrical surface and generalize it to the half space using mindlin s point force solution these two solutions show marked differences from the line of dilatation solution ratios of maximum horizontal deformation to maximum vertical deformation for the pipe models are significantly greater than values for the center or line of dilatation models this and the more gradual fall off of the deformation with distance may be used as diagnostics for discriminating between pipe like sources and dilatational sources on volcanoes where both components of the deformation field are available as examples we compare the closed pipe model with deformation associated with dome building on mount st helens volcano and tilt predicted by the open pipe model with tilt measured during a period of explosive eruptive activity on mount etna sicily in 1995 comparison between model values and the measurements suggests that the effective elastic moduli of the volcanic cones are very low

stability of lava lakes a physical model of a generic lava lake system is developed we derive the requisite conditions for the existence of an equilibrium lava lake in which magmastatic pressure at the base of the conduit balances the pressure in the underlying magmatic reservoir the stability of this lava lake system is tested by investigating the response of the system to perturbation we develop a graphical method based on the system s pressure depth profile to predict the subsequent behaviour of the system despite the simplicity of the modelled system we find a broad behavioural spectrum initially the rise of bubbles through the magma is ignored in this case both stable long lived lava lakes and unstable lakes that are prone to sudden draining are predicted the stability of the system is shown to be controlled by lake conduit geometry the solubility and gas expansion laws and the magma s volatile content we show that an unstable lake must collapse to a new stable equilibrium subsequent recharge of the system by for example conduit overturn would promote a return to the original equilibrium giving rise to cyclic behaviour such a mechanism is consistent with lava lake behaviour during the 1983 1984 pu u o o eruption of kilauea when the rise of bubbles through the magma is considered our model predicts that stable lakes must drain over time we therefore deduce that persistently degassing stable lava lakes such as those observed at mt erebus antarctica and mauna ulu kilauea hawaii must have an effective conduit convection mechanism or an exogenous supply of bubbles from depth

time dependent land uplift and subsidence in the santa clara valley california from a large interferometric synthetic aperture radar data set 1 we invert 115 differential interferograms derived from 47 synthetic aperture radar sar scenes for a time dependent deformation signal in the santa clara valley california the time dependent deformation is calculated by performing a linear inversion that solves for the incremental range change between sar scene acquisitions a nonlinear range change signal is extracted from the ers insar data without imposing a model of the expected deformation in the santa clara valley cumulative land uplift is observed during the period from 1992 to 2000 with a maximum uplift of 41 18 mm centered north of sunnyvale uplift is also observed east of san jose seasonal uplift and subsidence dominate west of the silver creek fault near san jose with a maximum peak to trough amplitude of 35 mm the pattern of seasonal versus long term uplift provides constraints on the spatial and temporal characteristics of water bearing units within the aquifer the silver creek fault partitions the uplift behavior of the basin suggesting that it acts as a hydrologic barrier to groundwater flow while no tectonic creep is observed along the fault the development of a low permeability barrier that bisects the alluvium suggests that the fault has been active since the deposition of quaternary units

conditions for detection of ground deformation induced by conduit flow and evolution 1 at mature andesitic volcanoes magma can reach the surface through the same path for several eruptions thus forming a volcanic conduit because of degassing cooling and crystallization magma viscosity increase in the upper part of the conduit may induce the formation of a viscous plug we conducted numerical simulations to quantify the deformation field caused by this plug emplacement and evolution stress continuity between newtonian magma flow and elastic crust is considered plug emplacement causes a ground inflation correlated to a decrease of the magma discharge rate a parametric study shows that surface displacements depend on three dimensionless numbers the conduit aspect ratio radius length the length ratio between the plug and the conduit and the viscosity contrast between the plug and the magma column larger displacements are obtained for high viscosity plugs emplaced in large aspect ratio conduits we find that only tiltmeters or gps located close to the vent a few hundred meters might record the plug emplacement at immediate proximity of the vent plug emplacement might even dominate the deformation signal over dome growth or magma reservoir pressurization effects for given plug thicknesses and viscosity profiles our model explains well the amplitude of tilt variations from 1 to 25 rad measured at montserrat and mt st helens we also demonstrate that at montserrat even if most of the tilt signal is due to shear stress induced by magma flow pressurization beneath the plug accounts for 20 of the signal

tilt prior to explosions and the effect of topography on ultra long period seismic records at fuego volcano guatemala 1 ground tilt is measured from broadband seismic records prior to frequent explosions at fuego volcano guatemala we are able to resolve tilt beginning 20 30 minutes prior to explosions followed by a rapid reversal in deformation coincident with explosion onsets the tilt amplitude and polarity recorded on the horizontal channels vary from station to station such that the steep and unusual topography of the upper cone of fuego appears to affect the ultra long period signals we account for the effect of topography and attempt to constrain the tilt source depth and geometry through finite difference modeling the results indicate a shallow spherical pressure source and that topography must be considered when attempting to model tilt sources at volcanoes with steep topography the tilt signals are interpreted as pressurization of the shallow conduit beneath a crystallized plug followed by elastic deflation concurrent with explosive pressure release

eruption prediction aided by electronic tiltmeter data at mount st helens telemetry from electronic tiltmeters in the crater at mount st helens contributed to accurate predictions of all six effusive eruptions from june 1981 to august 1982 tilting of the crater floor began several weeks before each eruption accelerated sharply for several days and then abruptly changed direction a few minutes to days before extrusion began each episode of uplift was caused by the intrusion of magma into the lava dome from a shallow source causing the dome to inflate and eventually rupture release of magma pressure and increased surface loading by magma added to the dome combined to cause subsidence just prior to extrusion

an active ring fault detected at tendurek volcano by using insar 1 although ring faults are present at many ancient deeply eroded volcanoes they have been detected at only very few modern volcanic centers at the so far little studied tendurek volcano in eastern turkey we generated an ascending and a descending insar time series of its surface displacement field for the period from 2003 to 2010 we detected a large 105 km2 region that underwent subsidence at the rate of 1 cm yr during this period source modeling results show that the observed signal fits best to simulations of a near horizontal contracting sill located at around 4 5 km below the volcano summit intriguingly the residual displacement velocity field contains a steep gradient that systematically follows a system of arcuate fractures visible on the volcano s midflanks rapideye satellite optical images show that this fracture system has deflected holocene lava flows thus indicating its presence for at least several millennia we interpret the arcuate fracture system as the surface expression of an inherited ring fault that has been slowly reactivated during the detected recent subsidence these results show that volcano ring faults may not only slip rapidly during eruptive or intrusive phases but also slowly during dormant phases

shallow crustal mechanics from volumetric strain data insights from soufriere hills volcano montserrat volumetric strain data from the 29 july 2008 vulcanian explosion of the soufriere hills volcano provide an excellent opportunity to probe the mechanical properties of the volcanic edifice and the shallow crust beneath montserrat we use finite element analysis to constrain the geometry of the shallow plumbing system as well as edifice and crustal mechanical properties for mechanically plausible pressure drops associated with dilatational volumetric strains recorded during the explosive activity our results from both forward and inverse models indicate a conduit radius of 40 m and a length of 1500 m and hence much larger conduit dimensions than previously suggested in order to fit the syneruptive volumetric strain data for a conduit pressure drop of 10 mpa the conduit needs to be surrounded by a halo of mechanically compliant rocks for which the best fit models indicate a width of 600 m and a young s modulus of 1 gpa young s moduli for the main edifice and the shallow crust up to 1000 m below sea level are found to be 10 gpa our best fit inverse model predicts a syneruptive radial conduit contraction by 0 24 m with a corresponding volume loss of 0 1 mm3 implying only partial emptying of the conduit upon the explosion this study demonstrates the critical role of edifice and shallow crustal mechanics for strain partitioning on montserrat our findings may have implications for the assessment of conduit processes at other dome building volcanoes

two billion year old evaporites capture earth s great oxidation major changes in atmospheric and ocean chemistry occurred in the paleoproterozoic era 2 5 1 6 billion years ago increasing oxidation dramatically changed earth s surface but few quantitative constraints exist on this important transition this study describes the sedimentology mineralogy and geochemistry of a two billion year old and 800 m thick evaporite succession from the onega basin in russian karelia the deposit consists of a basal unit dominated by halite 100 m followed by anhydrite magnesite 500 m and dolomite magnesite 200 m dominated units the evaporite minerals provide a robust constraint that marine sulfate concentrations were at least 10 mmol kg representing an oxidant reservoir equivalent to over 20 of the modern ocean atmosphere oxidizing capacity these results show that substantial amounts of surface oxidant accumulated during this critical transition in earth s oxygenation

the evolution of elastic moduli with increasing crack damage during cyclic stressing of a basalt from mt etna volcano article i nfo volcanic edifices such as mt etna italy are commonly subject to repeated cycles of stress over time due to the combination of magma emplacement from deep reservoirs to shallow depths and superimposed tectonic stresses such repeated stress cycles lead to anisotropic deformation and an increase in the level of crack damage within the rocks of the edifice and hence changes to their elastic moduli which are a key parameter for reliable modelling of deformation sources we therefore report results of changes in elastic moduli measured during increasing amplitude cyclic stressing experiments on dry and water saturated samples of etna basalt in all experiments the young s modulus decreased by approximately 30 over the total sequence of loading cycles and the poisson s ratio increased by a factor of approximately 3 0 5 microseismicity in terms of acoustic emission ae output was also recorded throughout each experiment our results demonstrate that ae output only re commences during any loading cycle when the level of stress where ae ceased during the unloading portion of the previous cycle is exceeded a manifestation of the kaiser stress memory effect in cycles where no ae output was generated we also observed no change in elastic moduli this result holds for both mechanical and thermal stressing our results are interpreted in relation to measurements of volcano tectonic seismicity and deformation at mt etna volcano

discrimination of geophysical phenomena in satellite radar interferograms various geophysical phenomena are recorded in the interference patterns formed by differencing two synthetic aperture radar sar images the fringes generated by the topographic relief can be removed using a digital elevation model dem the remaining fringes map the change in satellite to ground range which occurred between the acquisition times of the two images by comparing different pairs of images spanning different intervals of time it is possible to discriminate between geophysical signal and interferometric artifact here we apply this pair wise logic to the area around the 1992 landers california earthquake using sar images acquired by the ers 1 satellite the range varies with time as a constant step impulsive or sloping function examples of each type include a dem error an aftershock two atmospheric perturbations and postseismic afterslip respectively their signatures are identified and separated using the pair wise logic

insights into the 3d architecture of an active caldera ring fault at tendurek volcano through modeling of geodetic data abstract the three dimensional assessment of ring fault geometries and kinematics at active caldera volcanoes is typically limited by sparse field geodetic or seismological data or by only partial ring fault rupture or slip here we use a novel combination of spatially dense insar time series data numerical models and sand box experiments to determine the three dimensional geometry and kinematics of a sub surface ring fault at tendurek volcano in turkey the insar data reveal that the area within the ring fault not only subsides but also shows substantial westward directed lateral movement the models and experiments explain this as a consequence of a sliding trapdoor ring fault architecture that is mostly composed of outward inclined reverse segments most markedly so on the volcano s western flanks but includes inward inclined normal segments on its eastern flanks furthermore the model ring fault exhibits dextral and sinistral strike slip components that are roughly bilaterally distributed onto its northern and southern segments respectively our more complex numerical model describes the deformation at tendurek better than an analytical solution for a single rectangular dislocation in a half space comparison to ring faults defined at glen coe fernandina and bar arbunga calderas suggests that sliding trapdoor ring fault geometries may be common in nature and should therefore be considered in geological and geophysical interpretations of ring faults at different scales worldwide

steady downslope movement on the western flank of arenal volcano costa rica the edifice of a volcano is a unique deformational environment dependent not just on active volcanic processes but also on its composition structure and morphology we measured the deformation of volcan arenal costa rica using interferograms constructed from both alos and radarsat data between 2005 and 2009 the volcano s western flanks are moving downslope at an angle of 55 below the horizontal plane and a consistent rate of at least 7 cm yr we use the pattern rate and direction of motion to test several hypotheses for its origin our favored explanation is creep along a shallow sliding plane most likely the interface between deposits postdating the 1968 lateral blast eruption and the older lavas and paleosoils beneath our measurement of slope movement adds to a small set of rate measurements for gravity driven deformation at volcanoes and is distinctive in both its relatively high rate and shallow origin observation of deformation at arenal contributes both to the assessment of particular hazards around arenal itself and more generally to the study of the stability of young stratovolcanoes

a geochemical and geophysical investigation of the hydrothermal complex of masaya volcano nicaragua abstract masaya volcano nicaragua is a persistently active volcano characterized by continuous passive degassing for more than 150 years through the open vent of santiago crater this study applies self potential soil co 2 and ground temperature measurements to highlight the existence of uprising fluids associated to diffuse degassing structures throughout the volcano the diffuse degassing areas are organized in a semi circular pattern and coincide with several visible and inferred surface volcanic structures cones fissure vents and likely consist of a network of buried faults and dykes that respectively channel uprising flow and act as barrier to gravitational groundwater flow water depths have been estimated by multi scale wavelet tomography of the self potential data using wavelets from the poisson kernel family compared to previous water flow models our water depth estimates are shallower and mimic the topography typically less than 150 m below the surface between 2006 and 2010 the depths of rising fluids along the survey profiles remained stable suggesting that hydrothermal activity is in a steady state this stable activity correlates well with the consistency of the volcanic activity expressed at the surface by the continuously passive degassing when compared to previous structural models of the caldera floor it appears that the diffuse degassing structures have an important effect on the path that shallow groundwater follows to reach the laguna de masaya in the eastern part of the caldera the hydrogeological system is therefore more complex than previously published models and our new structural model implies that the flow of shallow groundwater must bypass the intrusions to reach the laguna de masaya furthermore these diffuse degassing structures show clear evidence of activity and must be connected to a shallow magmatic or hydrothermal reservoir beneath the caldera as such the heat budget for masaya must be significantly larger than previously estimated

h2och4naclco2 inclusions from the footwall contact of the tanco granitic pegmatite estimates of internal pressure and composition from microthermometry laser raman spectroscopy and gas chromatography abstract fluid inclusions in tourmaline and quartz from the footwall contact of the tanco granitic pegmatite s e manitoba were studied using microthermometry mt laser raman spectroscopy lrs and gas chromatography gc ch 4 bearing aqueous inclusions occur in metasomatic tourmaline of the footwall amphibolite contact the internal pressures estimated from mt are lower than those obtained from lrs mean difference 54 19 bars the difference is probably due to errors in the measurement of th ch 4 v and to the presence of clathrate at th ch 4 v into which co 2 had been preferentially partitioned lrs estimates of pressure 125 184 bars are believed to be more accurate aqueous phase salinities based on lrs estimates of pressure are higher than those derived using the data from mt 10 20 eq wt nacl the composition of the inclusions determined by gc bulk analysis is 97 3 mol h 2 o 2 2 mol ch 4 0 4 mol co 2 250 ppm c 2 h 6 130 ppm n 2 33 ppm c 3 h 8 11 ppm c 2 h 4 and 3 ppm c 3 h 6 plus trace amounts of c 4 hydrocarbons the composition is broadly similar to that calculated from mt 92 h 2 o and 8 ch 4 with 7 eq wt nacl dissolved in the aqueous phase and 2 mol co 2 dissolved in the ch 4 phase as expected due to the dominance of a single generation of inclusions in the tourmaline however two important differences in composition are 1 i the ch 4 to co 2 ratio of this fluid determined by gc is 5 33 which is significantly lower than that indicated by mt 49 0 and 2 ii the h 2 o content estimated from mt is 92 mol compared to 98 mol from gc gc analyses may have been contaminated by the presence of secondary inclusions in the tourmaline however the rarity of the latter suggests that they cannot be completely responsible for the discrepancy the differences may be accounted for by the presence of clathrate during measurement of th ch 4 critical which would reduce co 2 relative to ch 4 in the residual fluid and by errors in visually estimating vol h 2 o the compositions of the primary inclusions in tourmaline are unlike any of those found within the pegmatite and indicate that the fluid was externally derived probably of metamorphic origin inclusions in quartz of the border unit of the pegmatite are secondary and are either aqueous 18 to 30 eq wt cacl 2 th total 184 14 c or carbonic tm co 2 for the carbonic inclusions ranges from 57 5 to 65 4 c and is positively correlated with th co 2 analyses of x ch 4 based on lrs agree within 5 mol of those derived from mt and together indicate a range of compositions from 5 to 50 mol ch 4 in the co 2 phase bulk analysis by gc gives 99 0 mol h 2 o 0 6 mol co 2 0 4 mol ch 4 160 ppm n 2 7 ppm c 2 h 6 4 ppm c 3 h 8 and 2 ppm c 2 h 4 with trace amounts of cos carbonyl sulphide and c 3 h 6 the level of h 2 o in the analysis is consistent with the dominance of the aqueous inclusions in these samples and the ch 4 co 2 ratios are consistent with estimates from mt and lrs the preservation of variable ratios of ch 4 co 2 in inclusions 2 diffusion out of the inclusions nor reduction of fluids leaving the pegmatite were responsible for the more oxidized chemistries of the border unit inclusions relative to those in the tourmaline of the metasomatised amphibolite the compositions of the inclusions in the quartz lie between those of the fluid trapped by the tourmaline externally derived and the measured composition of a co 2 bearing pegmatitic fluid which indicates that the secondary fluids trapped in the border unit quartz were produced by late mixing

cyclic ground tilt associated with the 2004 2008 eruption of mount st helens 1 the long term behavior of the 2004 2008 effusive eruption of mount st helens was characterized by a gradual decline in the rates of seismicity dome growth and broad scale ground deformation but shallow near periodic drumbeat earthquakes over timescales of minutes indicated episodic short term behavior in part to better characterize this behavior and any associated ground deformation a network of tiltmeters was installed and recorded thousands of cyclic tilt events within the crater the duration of these events from minutes to hours was too long for them to be directly caused by the drumbeat seismicity tilt events were characterized by a recoverable asymmetric pattern of rapid tilt away from the vent followed by a more gradual reversal were highly correlated between different tiltmeters in the crater sometimes occurred in association with volcanic seismicity and ceased at the end of the eruption tilt vectors converged on a point just south of the center of the preexisting 1980s lava dome and the absence of detectable tilt outside the crater suggests a shallow source 1 km we examine several models including cycles of conduit pressurization and plug slip or gas loss and stick slip behavior on the interface between the ascending plug and the 1980s lava dome the small number of stations within the crater prevents a unique determination of source type or geometry but results are consistent with a mechanism involving extrusion of the semisolid dacite plug and or cycles of conduit pressurization

constraints on magma flux from displacements data at merapi volcano java indonesia the displacement field has been monitored in the vicinity of the crater rim at mount merapi indonesia from 1993 to 1997 during this period the volcanic activity has been quasicontinuous with dome growth explosions and pyroclastic flows we measured a nine point network every year with the global positioning system static method interpretation of results is conducted with a three dimensional elastostatic boundary elements code that takes into account topography fractures and complex magma source geometry the inversion technique yields an estimate of the variation with time of the boundary conditions at the magma duct interface together with the probability associated with the best model the young s modulus of the equivalent continuum is found to be very low of the order of 1 gpa a feature which suggests that a viscoelastic behavior may be more appropriate for this rock mass given the observed seismic velocities for the domain of interest a striking compatibility is outlined between observed deformations and the rate of occurrence of multiphase seismic events once the main fractures of the structure have been taken into consideration this suggests that the summit elastic or viscoelastic deformation field is controlled by the magma flux within the duct rather than by magma pressure variations in addition a nonelastic displacement has been identified at the westernmost point of the network this was considered critical for the stability of the summit structure a concern whose validity has been verified a posteriori by the july 1998 explosion

satellite based measurements of surface deformation reveal fluid flow associated with the geological storage of carbon dioxide interferometric synthetic aperture radar insar gathered over the in salah co sub 2 storage project in algeria provides an early indication that satellite based geodetic methods can be effective in monitoring the geological storage of carbon dioxide an injected volume of 3 million tons of carbon dioxide from one of the first large scale carbon sequestration efforts produces a measurable surface displacement of approximately 5 mm year using geophysical inverse techniques we are able to infer flow within the reservoir layer and within a seismically detected fracture fault zone intersecting the reservoir we find that if we use the best available elastic earth model the fluid flow need only occur in the vicinity of the reservoir layer however flow associated with the injection of the carbon dioxide does appear to extend several kilometers laterally within the reservoir following the fracture fault zone

transient deformation associated with explosive eruption measured at masaya volcano nicaragua using interferometric synthetic aperture radar abstract deformation caused by processes within a volcanic conduit are localised transient and therefore challenging to measure however observations of such deformation are important because they provide insight into conditions preceding explosive activity and are important for hazard assessment here we present measurements of low magnitude transient deformation covering an area of 4 km 2 at masaya volcano spanning a period of explosive eruptions 30th april 17th may 2012 radial uplift of duration 24 days and peak displacements of a few millimeters occurred in the month before the eruption but switched to subsidence 27 days before the onset of the explosive eruption on 30th of april uplift resumed during and continued for 16 days after the end of the explosive eruption period we use a finite element modelling approach to investigate a range of possible source geometries for this deformation and find that the changes in pressurisation of a conduit 450 m below the surface vent radius 160 m and length 700 m surrounded by a halo of brecciated material with a young s modulus of 15 gpa gave a good fit to the insar displacements we propose that the pre eruptive deformation sequence at masaya is likely to have been caused by the movement of magma through a constriction within the shallow conduit system although measuring displacements associated with conduit processes remains challenging new high resolution insar datasets will increasingly allow the measurement of transient and lower magnitude deformation signals improving the method s applicability for observing transitions between volcanic activity characterised by an open and a closed conduit system

gravity changes and passive so2 degassing at the masaya caldera complex nicaragua an understanding of the mechanisms responsible for persistent volcanism can be acquired through the integration of geophysical and geochemical data sets by interpreting data on micro gravity ground deformation and so2 flux collected at masaya volcano since 1993 it is now clear that the characteristically cyclical nature of the activity is not driven by intrusion of additional magma into the system rather it may be due in large part to the blocking and accumulation of gas by restrictions in the volcano substructure the history of crater collapse and formation of caverns beneath the crater floor would greatly facilitate the trapping and storage of gas in a zone immediately beneath san pedro and the other craters another mechanism that may explain the observed gravity and gas flux variations is the convective overturn of shallow pre existing degassed cooled dense magma that is replaced periodically by lower density hot gas rich magma from depth buoyant gas rich magma rises from depth and is emplaced near the surface resulting in the formation and fluctuation of a low density gas rich layer centred beneath nindiri and santiago craters as this magma vigorously degasses it must cool increase in density and eventually sink five stages of activity have been identified at masaya since 1853 and the most recent data suggest that the system may have been entering another period of reduced degassing in 2000 this type of analysis has important implications for hazard mitigation because periods of intense degassing are associated with poor agricultural yields and reduced quality of life a better understanding of persistent cyclically active volcanoes will allow for more effective planning of urban development and agricultural land use

shallow open system evolution of basaltic magma beneath a subduction zone volcano the masaya caldera complex nicaragua abstract lavas and pyroclastic material from the masaya caldera complex have a number of distinctive geochemical features relative compositional homogeneity low al2o3 and high feo contents a tholeitic differentiation trend and elevated large ion lithophile lil element concentrations e g ba 800 ppm on cmas projections their compositions always fall on or near low pressure cotectics in addition the basalts of masaya have unusually high 87sr 86sr and 10be masaya has exhibited medium term compositional cycles best exhibited by the sawtoothed changes in tio2 and feo mgo there are also a number of longer term compositional changes which are abrupt and generally coincide with caldera formation many of the geochemical characteristics of masaya coupled with a number of volcanological observations indicate masaya is underlain by a large shallow open system magma chamber perhaps on the order of 10 km3 in size although fractional crystallization is a significant magmatic process in masaya s open system chamber magma mixing contamination is equally important magma mixing is necessary to explain the discontinuous stratigraphic changes in magma composition observed at masaya and crustal contamination is necessary to explain their generally elevated 87sr 86sr and lil element concentrations two components therefore have been admixed into the magma chamber of masaya a lil poor basaltic component such has been erupted from the nearby nejapa and granada cinder cones and a lil rich acidic component such has been erupted from the nearby calderas of apoyo and apoyeque admixtures of the former have dominated admixtures of the latter ended with caldera formation ironically open system behavior has exerted fundamental control on the maintenance of relative compositional homogeneity

shear stress along the conduit wall as a plausible source of tilt at soufriere hills volcano montserrat 1 surface deformations recorded in close proximity to the active lava dome at soufriere hills volcano montserrat can be used to infer stresses within the uppermost 1000 m of the conduit system most deformation source models consider only isotropic pressurisation of the conduit we show that tilt recorded during rapid magma extrusion in 1997 could have also been generated by shear stresses sustained along the conduit wall these stresses are a consequence of pressure gradients that develop along the conduit numerical modelling incorporating realistic topography can reproduce both the morphology and half the amplitude of the measured deformation field using a realistic shear stress amplitude equivalent to a pressure gradient of 3 5 104 pa m 1 along a 1000 m long conduit with a 15 m radius this shear stress model has advantages over the isotropic pressure models because it does not require either physically unattainable overpressures or source radii larger than 200 m to explain the same deformation

interpretation of ground surface changes prior to the 2010 large eruption of merapi volcano using alos palsar aster tir and gas emission data abstract understanding precursory signals is essential to forecast eruptions hazards and mitigate risks satellite observations have been shown to increasingly contribute to this goal we use differential inteferometric synthetic aperture radar d insar and sar backscattering intensity data from alos palsar to define a time series of ground surface displacements for the 2006 2010 inter eruptive period at merapi volcano we correlate trends in the displacement data to trends for summit temperature determined using data from the aster sensor and to gas emission data we show that processing of the satellite data must be performed carefully before meaningful interpretations can be drawn for example after careful removal of the topographic effect on phase delays we detect only subtle inter eruptive episodes of cyclic deformation in the d insar and sar backscattering data these small mostly sub centimeter displacements contrast with meter scale pre eruptive displacements along an electronic distance measurement edm line on the south flank of the volcano we suggest that this difference is a consequence of localized movement within the summit area a result that has important implications for understanding merapi s structure for monitoring network design and for eruption forecasting although small merapi s inter eruptive deformation cycles are also seen in thermal data from aster and gas emissions accordingly we interpret these cycles as the result of successive movement of individual magma batches migrating upward from deeper to shallower storage systems located along a ne dipping conduit in view of magma migration prior to eruptions these cycles may also serve as a precursory signal for large eruptions at merapi such as the one that took place in early november 2010

permanent tremor of masaya volcano nicaragua wave field analysis and source location the masaya volcano nicaragua is a basaltic caldera in a subduction zone the permanent source of the volcanic tremor was located inside santiago crater at the lava lake s position and 400 m below the ne rim and therefore corresponds to superficial magma activity we used two tripartite arrays 90 m side one semicircular array r 120 m in 1992 and two semicircular arrays r 60 m and a 2500 m long linear array radiating out from the source and on the flank of the crater in 1993 we used both a cross spectrum method and a correlation method to determine the wave delay time between the reference station and the other stations of an array and to quantify the wave field using the delays therefore by intersecting the back azimuth wave directions from the arrays we could pinpoint the source additionally the correlation coefficients obtained as functions of frequency for the three components of motion confirm the inferred position of the source of tremor the tremor s wave field is composed of comparable quantities of dispersed rayleigh and love surface waves whose phase velocities lie in the ranges 730 1240 m s at 2 hz and 330 550 m s at 6 hz the dispersive phase velocities were inverted to obtain crustal structures with a minimal number of layers the resulting velocity models are similar for the northern and southern parts of the volcano after geometrical spreading corrections q2hz 14 and q3hz 31 were determined along the northern linear array the typical low velocities and low q corresponding to the cone structure and are similar to those of other basaltic volcanoes like puu oo hawaii and klyuchevskoy kamchatka

abrupt onset of the little ice age triggered by volcanism and sustained by sea ice ocean feedbacks 1 northern hemisphere summer temperatures over the past 8000 years have been paced by the slow decrease in summer insolation resulting from the precession of the equinoxes however the causes of superposed century scale cold summer anomalies of which the little ice age lia is the most extreme remain debated largely because the natural forcings are either weak or in the case of volcanism short lived here we present precisely dated records of ice cap growth from arctic canada and iceland showing that lia summer cold and ice growth began abruptly between 1275 and 1300 ad followed by a substantial intensification 1430 1455 ad intervals of sudden ice growth coincide with two of the most volcanically perturbed half centuries of the past millennium a transient climate model simulation shows that explosive volcanism produces abrupt summer cooling at these times and that cold summers can be maintained by sea ice ocean feedbacks long after volcanic aerosols are removed our results suggest that the onset of the lia can be linked to an unusual 50 year long episode with four large sulfur rich explosive eruptions each with global sulfate loading 60 tg the persistence of cold summers is best explained by consequent sea ice ocean feedbacks during a hemispheric summer insolation minimum large changes in solar irradiance are not required

volcanic dilemma flow or blow volcanic eruptions can be either slow outpourings of lava or explosive ejections of fragmented rock in his perspective dingwell discusses the physical and chemical properties of magma that lead to these two styles of eruption new experiments and computer simulations are pointing to the involvement of solidlike behavior of liquid magma when it makes a transition to a glass

lava lake level as a gauge of magma reservoir pressure and eruptive hazard forecasting volcanic activity relies fundamentally on tracking magma pressure through the use of proxies such as ground surface deformation and earthquake rates lava lakes at open vent basaltic volcanoes provide a window into the uppermost magma system for gauging reservoir pressure changes more directly at k lauea volcano hawai i usa the surface height of the summit lava lake in halema uma u crater fluctuates with surface deformation over short hours to days and long weeks to months time scales this correlation implies that the lake behaves as a simple piezometer of the subsurface magma reservoir changes in lava level and summit deformation scale with and shortly precede changes in eruption rate from k lauea s east rift zone indicating that summit lava level can be used for short term forecasting of rift zone activity and associated hazards at k lauea