ground deformation caused by magma ascent in an open conduit this study examines magma ascent processes of three basic types prior to intermittent explosions such as vulcanian or strombolian types specifically their relations to volcano ground deformation such repetitive explosions eject magma from an open conduit at short time intervals consequently magma pressure is expected to decrease at the conduit and or reservoir and thereby deflate the volcano then magma within the conduit rises exerting normal and shear stresses on the conduit wall thereby inflating the volcano diffusive mass transfer of water molecules from the melt to bubbles might occur subject to a sudden depressurization by eruption when magma includes numerous small gas bubbles such gas bubble expansion lifts the magma in the conduit calculations of ground deformation on a semi infinite medium for such rising magma show that vertical and radial displacements and tilt motions recorded in the far fields are proportional to the 1 5 power of time for low viscosity magma gas bubbles might rise in the melt because of buoyancy force the gas bubbles expand rapidly with time because of decreased ambient pressure pushing the magma upward in the conduit consequently the volcano slowly inflates initially then the rate of deformation increases over time eventually engendering a rapid inflation immediately before eruption these temporal changes in ground deformations contrast against cases in which magma does not include gas bubbles in such cases amplitudes of ground deformation increase almost linearly or even decrease with time at far fields these differences which are recognized as basic characteristics of temporal changes of ground deformation enable us to know the driving forces of magma in an open conduit and to evaluate the gas bubble behavior quantitatively in magma before eruption

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

remarkable cyclic ground deformation monitored in real time on montserrat and its use in eruption forecasting telemetered high resolution tiltmeters were installed in montserrat in summer of 1995 in december 1996 and in may 1997 the 1995 installations several km from the soufriere hills vent were too distant to yield useful data however the 1996 and 1997 installations on the crater rim revealed 6 14 h inflation cycles caused by magma pressurization at shallow depths 0 6 km below the base of dome the tilt data correlated with seismicity explosions and pyroclastic flow activity and were used to forecast times of increased volcanic hazard to protect scientific field workers and the general public

insar observations and models of crustal deformation due to a glacial surge in iceland surges are common at all the major ice caps in iceland ice masses of gigatons may shift from the upper part of the outlet glacier towards the terminus in a few months advancing the glacier front by up to several kilometres the advancing ice front may be up to 100 m thick increasing the load on crustal rocks correspondingly we use the observed change in crustal loading during a surge of the western part of the vatnajokull ice cap iceland during 1993 1995 and the corresponding elastic crustal deformation surveyed with interferometric synthetic aperture radar to investigate the material properties of the solid earth in this region crustal subsidence due to the surge reaches 75mm at the edge of the si ujokull outlet glacier this signal is mixed with a broad uplift signal of 12 mm yr relative to our reference area caused by the ongoing retreat of vatnajokull in response to climate change we disentangle the two signals by linear inversion finite element modelling is used to investigate the elastic earth response of the surge as well as to confirm that no significant viscoelastic deformation occurred as a consequence of the surge the modelling leads to estimates of the young s modulus and poisson s ratio of the underlying earth comparison between the observed and modelled deformation fields is made using a bayesian approach that yields the estimate of a probability distribution for each of the free parameters residuals indicate a good agreement between models and observations one layer elastic models result in a young s modulus of 43 2 49 7 gpa 95 per cent confidence and poisson s ratio of 0 0 27 after removal of outliers our preferred model with two elastic layers provides a better fit to the whole surge signal this model consists of a 1 km thick upper layer with an average young s modulus of 12 9 15 3 gpa and poisson s ratio of 0 17 overlying a layer with an average young s modulus of 67 3 81 9 gpa and poisson s ratio of 0 25

silicic lava effusion controlled by the transition from viscous magma flow to friction controlled flow silicic magma forms a vertical fault in volcanic conduits via the brittle ductile transition the formation of the fault changes flow type from viscous flow to friction controlled flow here we investigate flow dynamics of magma by coupling a one dimensional conduit flow model with an experimentally calibrated brittle ductile transition the numerical simulation demonstrates that the length of magma plug at which friction controlled flow becomes the main flow type depends on magma flux because of crystallization kinetics and the ductile brittle transition at high flux a short plug forms because nonequilibrium crystallization inhibits an increase of magma viscosity this results in the effusion of less viscous lava and large shear stress at the shallow part of the conduit in contrast the long plug that forms under low flux cannot maintain large shear stress due to weakness of the magmatic fault which causes the extrusion of a solidified lava spine

collection and three dimensional modeling of gps and tilt data at merapi volcano java we study here the deformations associated with the november 1996 to march 1997 eruption period at mount merapi central java one of the most active volcanoes in indonesia this activity period includes a vertical explosion on january 17 and an increase of the lava dome volume by about 3 106 m3 two global positioning system gps campaigns have been carried out on a six benchmark network at the beginning and at the end of the period relative displacements with respect to the reference point show an average subsidence of 6 5 cm a multicomponent tilt station installed on the southeast flank 3 km from the summit recorded a tilt of 11 1 0 7 rad in the tangential direction and 0 9 0 4 rad in the radial direction these data are interpreted using a three dimensional 3 d elastic model based on the mixed boundary element method and a near neighbor monte carlo inversion interpretation of tilt data requires an accurate mesh for discretizing the 3 d topography the final result supports a horizontal elliptic magma source located 8 5 0 4 km below the summit and 2 0 4 km to the east of it in particular the data cannot be consistent with the location of a magma chamber determined from seismic activity analysis i e 2 km below the summit the computed depth depends strongly on the source shape and cannot be constrained properly because of the small amount of data the computed deflation of 11 2 106 m3 is about 3 times larger than the observed increase in the lava dome volume this difference is attributed to rock avalanches and pyroclastic flows on the flanks of the volcano

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

overview of the 2006 eruption of mt merapi abstract in the last part of the 20th century and the beginning of the 21st century mt merapi in central java indonesia erupted about every 2 5 years most of the eruptions were low in explosivity with vei 3 or less eruptions usually involve the formation of a lava dome either in the beginning or in the end of the eruptive episode for the 2006 eruption the precursory signal was first observed in the middle of the year 2005 with a decrease in edm slope distances to points on the rim an increase of seismicity and a possible increase of so 2 emissions those early events marked the beginning of a more continuous period of inflation which led to the eruption in total the pre eruption displacement of the southern rim reached at least 2 4 m toward the measuring station in kaliurang kal from late april until june 2006 a lava dome grew on the summit with a volume that gradually increased until it reached about 4 1 million m 3 in 38 days the total of erupted magma was about 5 3 million m 3 dense rock equivalent dre the dome subsequently collapsed in three steps from june 4 to june 14 leaving an open scar on its southeast side in this paper we detail the changes of dome morphology that were monitored by taking successive photographs from similar positions the eruption in 2006 marked a significant change in summit morphology from west southwestward opening during the 20th century to the currently southeast orientation also an mw 6 4 earthquake occurred on 26 may midway through the eruption which adds interesting questions about the relationship of the eruption and the earthquake edm data from 2006 and previous eruptions show that the summit remains inflated after each eruption i e no significant deflation occurs following eruptions the lack of post eruption deflation suggests that magma remains in the shallow parts of the edifice after the eruption as a result the complex of summit lava domes and their intrusive roots grow with time and merapi s rim and summit become progressively more unstable and prone to collapse

understanding cyclic seismicity and ground deformation patterns at volcanoes intriguing lessons from tungurahua volcano ecuador abstract cyclic seismicity and ground deformation patterns are observed on many volcanoes worldwide where seismic swarms and the tilt of the volcanic flanks provide sensitive tools to assess the state of volcanic activity ground deformation at active volcanoes is often interpreted as pressure changes in a magmatic reservoir and tilt is simply translated accordingly into inflation and deflation of such a reservoir tilt data recorded by an instrument in the summit area of tungurahua volcano in ecuador however show an intriguing and unexpected behaviour on several occasions prior to a vulcanian explosion when a pressurisation of the system would be expected the tilt signal declines significantly hence indicating depressurisation at the same time seismicity increases drastically envisaging that such a pattern could carry the potential to forecast vulcanian explosions on tungurahua we use numerical modelling and reproduce the observed tilt patterns in both space and time we demonstrate that the tilt signal can be more easily explained as caused by shear stress due to viscous flow resistance rather than by pressurisation of the magmatic plumbing system in general our numerical models prove that if magma shear viscosity and ascent rate are high enough the resulting shear stress is sufficient to generate a tilt signal as observed on tungurahua furthermore we address the interdependence of tilt and seismicity through shear stress partitioning and suggest that a joint interpretation of tilt and seismicity can shed new light on the eruption potential of silicic volcanoes

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

the effects of thermomechanical heterogeneities in island arc crust on time dependent preeruptive stresses and the failure of an andesitic reservoir using ground deformation data from soufriere hills volcano shv we present results from numerical modeling of the temperature and time dependent stress evolution in a mechanically heterogeneous crust prior to reservoir failure and renewed eruptive activity the best fit models do not allow us to discriminate between a magmatic plumbing system consisting of either a single vertically elongated reservoir or a series of stacked reservoirs a prolate reservoir geometry with volumes between 50 and 100 km3 reservoir pressure changes between 4 and 7 mpa and reservoir volume changes between 0 03 and 0 04 km3 with magma compressibility between 4 10 11 and 1 10 9 pa 1 provide plausible thermomechanical model parameters to explain the deformation time series around an order of magnitude less overpressure than is generally inferred from homogeneous elastic crustal models reservoir failure is predicted to occur at the crest of the reservoir except for reservoirs with highly compressible magma 4 10 9 pa for which subhorizontal sill formation is predicted upon reservoir failure introducing a deep crustal hot zone modulates the partitioning of strains into the hotter underlying crust and results in a further reduction in overpressure estimates to values of around 1 2 mpa upon reservoir failure deduced volume fluxes are consistent with constraints from thermal modeling of active subvolcanic systems and imply dynamic failure of a compressible magma mush column feeding eruptions at shv our interpretation of the results is that the combined thermomechanical effects of a deep crustal hot zone and hot encasing rocks around a midcrustal andesitic reservoir fundamentally alter the time dependent subsurface stress and strain partitioning upon reservoir priming these effects substantially influence surface strains recorded by volcano geodetic monitoring

relationships between volcano gravitational spreading and magma intrusion volcano spreading with its characteristic sector grabens is caused by outward flow of weak substrata due to gravitational loading this process is now known to affect many present day edifices a volcano intrusive complex can form an important component of an edifice and may induce deformation while it develops such intrusions are clearly observed in ancient eroded volcanoes like the scottish palaeocene centres or in geophysical studies such as in la reunion or inferred from large calderas such as in hawaii the canaries or galapagos volcanoes volcano gravitational spreading and intrusive complex emplacement may act simultaneously within an edifice we explore the coupling and interactions between these two processes we use scaled analogue models where an intrusive complex made of golden syrup is emplaced within a granular model volcano based on a substratum of a ductile silicone layer overlain by a brittle granular layer we model specifically the large intrusive complex growth and do not model small scale and short lived events such as dyke intrusion that develop above the intrusive complex the models show that the intrusive complex develops in continual competition between upward bulging and lateral gravity spreading the brittle substratum strongly controls the deformation style the intrusion shape and also controls the balance between intrusive complex spreading and ductile layer related gravitational spreading in the models intrusive complex emplacement and spreading produce similar structures to those formed during volcano gravitational spreading alone i e grabens folds en echelon fractures therefore simple analysis of fault geometry and fault kinetic indicators is not sufficient to distinguish gravitational from intrusive complex spreading except when the intrusive complex is eccentric from the volcano centre however the displacement fields obtained for 1 a solely gravitational spreading volcano and for 2 a gravitational spreading volcano with a growing and spreading intrusive complex are very different consequently deformation fields like those obtained from geodetic monitoring can give a strong indication of the presence of a spreading intrusive complex we compare the models with field observations and geophysical evidence on active volcanoes such as la reunion island indian ocean ometepe island nicaragua and eroded volcanic remnants such as ardnamurchan scotland and suggest that a combination between gravitational and intrusive complex spreading has been active

analysis of the seismic activity associated with the 2010 eruption of merapi volcano java abstract the 2010 eruption of merapi is the first large explosive eruption of the volcano that has been instrumentally observed the main characteristics of the seismic activity during the pre eruptive period and the crisis are presented and interpreted in this paper the first seismic precursors were a series of four shallow swarms during the period between 12 and 4 months before the eruption these swarms are interpreted as the result of perturbations of the hydrothermal system by increasing heat flow shorter term and more continuous precursory seismic activity started about 6 weeks before the initial explosion on 26 october 2010 during this period the rate of seismicity increased almost constantly yielding a cumulative seismic energy release for volcano tectonic vt and multiphase events mp of 7 5 10 10 j this value is 3 times the maximum energy release preceding previous effusive eruptions of merapi the high level reached and the accelerated behavior of both the deformation of the summit and the seismic activity are distinct features of the 2010 eruption the hypocenters of vt events in 2010 occur in two clusters at of 2 5 to 5 km and less than 1 5 km depths below the summit an aseismic zone was detected at 1 5 2 5 km depth consistent with studies of previous eruptions and indicating that this is a robust feature of merapi s subsurface structure our analysis suggests that the aseismic zone is a poorly consolidated layer of altered material within the volcano deep vt events occurred mainly before 17 october 2010 subsequent to that time shallow activity strongly increased the deep seismic activity is interpreted as associated with the enlargement of a narrow conduit by an unusually large volume of rapidly ascending magma the shallow seismicity is interpreted as recording the final magma ascent and the rupture of a summit dome plug which triggered the eruption on 26 october 2010 hindsight forecasting of the occurrence time of the eruption is performed by applying the material failure forecast method ffm using cumulative real time seismic amplitude rsam calculated both from raw records and on signals classified according to their dominant frequency stable estimates of eruption time with errors as small as 4 h are obtained within a 6 day lapse time before the eruption this approach could therefore be useful to support decision making in the case of future large explosive episodes at merapi

deposit loading and its effect on co eruptive volcano deformation abstract erupting volcanoes commonly exhibit characteristic ground deformation that is typically interpreted in terms of pressure changes of magma reservoirs within the crust however other processes may also be significant since 1995 the soufriere hills volcano montserrat has erupted about 1 km3 of magma over five discrete extrusive phases with clear cycles of associated ground deformation recorded by gps here we consider the contribution to deformation by loading of the ground surface with erupted deposits we estimate topographic change and net deformation for the whole eruption to date between november 1995 and february 2010 we derive the surface load distribution using differenced digital elevation data which additionally enables us to constrain the budget of erupted lava about a third of the lava erupted from soufriere hills since 1995 remains in subaerial onshore deposits more than previously thought another third is emplaced immediately offshore and the remaining third has been transported further afield we combine the deposit thickness map with representative deposit densities to calculate surface load and model the deformation response using finite elements our results show that net displacements accumulated over 14 years on montserrat tens of centimetres could be explained by loading of erupted deposits on the flanks the proportion of the observed deformation that can be explained by loading alone depends on crustal rheology using rheology structures favoured in the literature our forward modelled displacements are remarkably similar to long term observations down to detail that we ascribe to localised load topography interaction results suggest that the shallow crust beneath montserrat is more compliant than usually assumed in geodetic models with more rigid rheology at depth loading is largely accommodated by elastic strain in the shallow crust top few kilometres with negligible contribution from intra crustal viscous flow over the time period investigated we thus infer that the role of stress transfer from the surface load in metering magma reservoir behaviour must be negligible but may influence degassing in the shallow conduit for example our findings suggest that when volcanic ground deformation accompanies a voluminous eruption geodetic model inversions will be misled if data are not appropriately corrected for the surface loading effect

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

volcano tectonic control of merapi s lava dome splitting the november 2013 fracture observed from high resolution terrasar x data abstract volcanism at active andesite dacite volcanoes is often associated with the formation and collapse of circular shaped protrusions of extruded highly viscous lava the so called domes which are emplaced in the near summit region growing domes may experience stable and instable structural phases with a gradual transition in between dome collapse and the break off of instable blocks of viscous lava may lead to pyroclastic flows one of the most lethal hazards at stratovolcanoes at merapi volcano indonesia a new dome started growing in the summit region in the amphitheater formed in the course of the climactic 2010 eruption three years later the dome reached a height of approximately 100 m and diameters of 220 and 190 m with a plateau like surface area of 40 000 m2 approximately on 18 11 2013 an explosion occurred without identified precursors leaving a major fracture cutting the complete dome structure based on high resolution terrasar x satellite radar imagery we could identify the linear fracture traceable over 200 m in the long axis up to 40 m wide after geocoding of the radar amplitude imagery the fractures azimuthal trend could be compared to other structural lineaments indicative of a significant nnw sse structural direction that has formed on merapi volcano in the past the merapi dome fractured in a nw se direction and is consistent with the alignment of regional tectonic structures and of anticipated directions of pyroclastic flows the fracture may be part of a larger volcano tectonic system and may affect the dynamics and the stability of the merapi dome

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

the weathering of granitic rocks in a hyper arid and hypothermal environment a case study from the sor rondane mountains east antarctica abstract weathering processes in hyper arid and hypothermal environments are key to our understanding of geomorphological processes and landscape evolution in antarctica and likely on mars a number of studies have focused on the weathering of basaltic rocks in antarctica however the nature of the weathering of quartzofeldspathic rocks a common rock type on earth has received less attention and remains unclear here we explore the weathering of granitic rocks which are a type of quartzofeldspathic rock and the associated weathering products in the sor rondane mountains of east antarctica to obtain quantitative information regarding the physical and chemical weathering of granitic rocks in hyper arid and hypothermal environments various petrological techniques were used to analyze the physical and chemical weathering of the rocks loss on ignition loi values and the major element composition obtained from the crust and core of the rock samples indicate that the production of hydrous clay minerals in this area is very limited examination under a microscope together with laser raman microspectroscopy of thin sections from the crust and core of the samples indicate that goethite grains form mainly in veins within the crust which is consistent with the contrasts seen in the fe 3 fe 2 and color strength index csi values obtained from the core and crust a negative correlation between rock hardness and degree of weathering as measured from the crust of the samples indicates that the weathered samples are softer than the core this indicates that cracking and subsequent vein formation cause a reduction in the hardness of the crust and an increase in staining via the formation of goethite grains that develop in the veins furthermore electron probe microanalyzer epma analysis indicates that the original fe ti oxide grains are altered by weathering and change to hematite or a non stoichiometric fe ti compound associated with ilmenite grains in the case of a greater degree of weathering these findings reveal that the weathering of granitic rocks in a hyper arid and hypothermal environment is controlled mainly by oxidation including iron hydroxide formation in veins formed by the thermal expansion and contraction of rock forming minerals frost shattering and or salt fretting and fe ti oxide alteration in the rock interior importantly these physical and chemical weathering processes are unlikely to require a liquid water supply from the environment snow or vapor hence the restricted supply of liquid water and salt is the most probable explanation for the extremely slow weathering rates in the sor rondane mountains we therefore conclude that the weathering process observed in this area is a typical feature of quartzofeldspathic rocks under hyper arid and hypothermal conditions and potentially also on mars in situ color measurements essentially express the amount of iron hydroxide on the rock surface thus in situ and satellite measurements of the color of exposed rocks in antarctica can potentially provide quantitative information regarding the degree of weathering

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

a hybrid model for the summit region of merapi volcano java indonesia derived from gravity changes and deformation measured between 2000 and 2002 three dimensional displacements and gravity changes were measured at 20 points between 2000 and 2002 at merapi volcano java indonesia former models focused on the modeling of a single magmatic source located in the summit region of the volcano such models do not fit to our measurements between 2000 and 2002 a new hybrid model approach is developed consisting of an elastic gravitational source described by a mass and energy term as well as a combined dip slip strike slip fault zone in the summit region both nonlinear optimization problems given by the common inversion of three dimensional displacements and gravity changes are solved by applying a genetic algorithm the hybrid model fits the measurements accurately tested by fisher test statistics furthermore our model for merapi volcano confirms previous structural models for this region so that the new model is statistically proven as well as physically reliable

temporal and spatial variation of the surface albedo of the morteratschgletscher switzerland as derived from 12 landsat images this investigation uses landsat images from 12 days in 1999 and 2000 to study the spatial and temporal variation in surface albedo of a glacier with a rugged topography morteratschgletscher switzerland our retrieval method considers all processes that substantially influence the relationship between the satellite signal and the surface albedo the correction for the anisotropy of the reflected radiation field of ice and snow ranges up to 0 10 depending on wavelength band solar zenith angle and surface type we analyzed the uncertainties in the retrieval method and mainly expect errors in satellite derived albedos for areas with large variation in topography and high albedos the latter is due to application of bidirectional reflectance distribution function brdf parameterizations for the anisotropic correction to albedos outside the parameterizations validity on average satellite derived albedos exceed the measured surface albedo by 0 03 the glacier tongue is characterized by bands of low and high albedo relating to ice with higher and lower concentrations of debris the ice albedo shows no dependence on altitude except at 2000 2200 m a s l it increases during summer which is likely associated with rainfall as concluded from a comparison between summer rainfall and measured albedos

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

combination of a pressure source and block movement for ground deformation analysis at merapi volcano prior to the eruptions in 2006 and 2010 abstract we analyzed ground deformation prior to the eruptions in 2006 and 2010 at merapi volcano central java indonesia ground deformation was monitored by electronic distance measurement edm by measuring the slope distance toward 12 reflectors installed near the summit from five benchmarks on flanks every day a large change of slope distance csd was detected on the southeast and south baselines and a minor csd was detected on the north and northwest baselines during the pre eruptive stages of both the 2006 and 2010 eruptions we applied a block movement model to the south and southeast baselines and a spherical pressure source model to the csds on the north and northwest baselines using the finite element method fem the rates of block movement southward and the volume change of the pressure source increased on april 7 2006 and continued at constant rates until the appearance of a new lava dome on april 26 prior to the eruption in 2010 the block movement southeastward and the volume increase of the pressure source accelerated in the middle of october and acceleration continued until the first outburst on october 26 2010 temporal patterns of the block movement and the increase in the volume of the pressure source correlate well with the increase in seismicity of vt and mp earthquakes the pressure sources were obtained at a depth of 2 0 5 km below the summit and this position corresponds to the aseismic zone of vt earthquakes magma injection at the shallow part of this region causes an increase in the volume of the pressure source and inflation of the ground of the summit triggered gravitational slip southeastward or southward of the ground surface the volumes increases of the pressure sources were 9 7 1 m m 3 and 17 6 0 8 m m 3 in 2006 and 2010 respectively the volume increase is related to the scale and type of the eruption the effusive eruption in 2006 had a volcanic explosivity index vei of 2 and the explosive eruption in 2010 had a vei of 4 the directions and amounts of the block movement are strongly related to topography hydrothermally weak zone and underground gap near the summit between west and east domes

mechanical discontinuities monitoring at merapi volcano using kinematic gps merapi volcano java indonesia is in almost continuous activity with growth of an andesitic lava dome this dome frequently collapses to form potentially deadly glowing avalanches explosions and nuees ardentes to monitor the evolution of surface displacements and to model the associated magmatic sources we established a global positioning system gps network in 1993 and have measured it each year using the static gps method however the limited number of benchmarks and the geometry of the network did not allow us to precisely locate major mechanical discontinuities within the edifice precisely locating these discontinuities is of central importance because they delimit areas of potential instability and provide means to evaluate potential volumes of falling material the kinematic gps method offers a way to partially solve the problem of temporal and spatial sampling of the displacement field but its accuracy is usually insufficient to monitor small displacements we propose here a strategy of field measurements and adjustments which combines kinematic positioning 1 min and rapid static baselines 15 min to get a 1 5 cm error 95 confidence at merapi summit we have installed about 50 benchmarks covering the area around the main crater field measurements of this new network with our method take a few hours and the data processing has been automated we present the results of 8 surveys from 1999 to 2002 a period that includes a dome collapse in january 2001 our results show large horizontal displacements towards the northwest starting in july 2000 and reaching about 50 cm in amplitude in november 2000 that we interpret as precursors to the dome collapse we also locate two presently active discontinuities at the summit of the volcano this approach can be implemented easily on other active volcanoes

modeling the density at merapi volcano area indonesia via the inverse gravimetric problem 1 merapi is a high risk andesitic volcano in central java indonesia very little information is known about the detailed regional density structure around merapi and its neighbor volcano merbabu we compute a subsurface three dimensional 3 d model of anomalous density for the volcanoes merapi and merbabu in central java indonesia by inversion of the gravity field as input for the inversion methodology gravity observations from 443 points whose 3 d coordinates are determined by gps are used the inversion algorithm is based on an explorative approach to fit a least squares condition including a balancing factor between the minimization of the residuals and the anomalous mass a mean density about 2242 kg m3 for the region of merapi and merbabu has been computed by least squares adjustment results of the inversion show major low density contrasts up to 242 kg m3 and positive structures about 264 kg m3 referred to the determined mean density a density anomaly relative high with densities up to 264 kg m3 is connecting the volcanoes in a 152 course from nw to se and might be built of older basaltic lava low density contrasts about 242 kg m could be found in agreement with magnetotelluric and electromagnetic results generally the identified high and low density bodies are in agreement with the results of other geophysical methods such as electromagnetic and magnetotelluric prospecting or geological formations and structures a porosity about 21 is derived for the largest negative density bodies about 242 kg m3 furthermore the density model gives some new information about the controversial origin of a hill formation near merapi and is also used to discuss the possible existence of a shallow magma chamber which is also a controversial subject generally the density model serves as basic information for the interpretation of geodetic and geophysical observations and confirms existing results from magnetotellurics electromagnetics and seismic data interpretation

control of magma flow in dykes on cyclic lava dome extrusion 1 lava dome eruptions are commonly characterized by large fluctuations in discharge rate with cyclic behaviour on time scalesranging from hours to decades examples include bezymianny volcano russia merapi java santiaguito guatemala mt st helens usa mt unzen japan and soufriere hills volcano montserrat previous models have assumed simple cylindrical conduits for magma transport but extrusions are mainly fed by dykes with cylindrical geometries developing only at shallow levels the widths of dykes embedded in an elastic medium are influenced by local magma pressure affecting flow rates and system dynamics strongly we develop a model for magma flow in dykes which predicts intense pulsations of magma extrusion for the case of a constant source pressure the period time scale is determined by the elastic deformation of the dyke walls and the length to width ratio of the dyke the dyke acts like a volumetric capacitor storing magma as pressure increases and then releasing magma in a pulse of extrusion for the soufriere hills volcano cyclic extrusions with time scales of a few weeks are predicted for dykes 300 500 m long and 3 6 m wide matching observations the model explains the sharp onset of tilt pulsations and seismic swarms citation costa a o melnik r s j sparks and b voight 2007 control of magma flow in dykes on cyclic lava dome extrusion geophys res lett 34 l02303 doi 10 1029 2006gl027466

three dimensional modeling of the 1983 1984 eruption at piton de la fournaise volcano reunion island displacement vectors on 125 points over a 6 km 2 area were calculated zlotnicki et al 1990 for piton de la fournaise volcano reunion island from photogrammetric surveys conducted in september 1981 and again in september 1984 an eruptive crisis with two episodes occurred during the 3 years between the surveys we modeled the displacements from the photogrammetric surveys using a three dimensional mixed boundary element method the model shows that both eruptive episodes were fed by a single dike oriented 165 from north as the dike approached the ground surface it divided into segments that rotated into an en echelon pattern the model that best fits all observations suggests that the stress state within the volcano is quasi isotropic such that horizontal stresses equal the overburden these high horizontal stresses are incompatible with an elastic edifice loaded merely by gravitational forces however they may be attributed to the cumulative effect of repeated dike intrusions

effect of mechanical heterogeneity in arc crust on volcano deformation with application to soufriere hills volcano montserrat west indies 1 analyses of volcano surface deformation are commonly based on models that assume mechanical homogeneity of rocks surrounding the causative pressure source here we present a detailed study that shows the differences in deduced surface deformation caused by source pressurization accounting for either mechanical homogeneity or mechanical heterogeneity of encasing rocks in a volcanic arc setting using finite element models accounting for crustal heterogeneity from seismic data we test for a range of source geometries and intermediate crustal depths and explore the misfits of deduced source parameters from the two families of models in the second part of this study we test the results from the generic study against cgps data from two deformation periods the 2003 2005 ground inflation and the 2005 2007 ground deflation at soufriere hills volcano montserrat west indies to inform on source parameters accounting for a variable crustal rigidity with depth as deduced by seismic analysis beneath montserrat we find the data to be best explained by pressurization and depressurization of a slightly prolate midcrustal magma chamber that is centered between 11 5 and 13 km below sea level about 640 m ne of the active vent considering source dimension and source pressure changes we demonstrate that magma compressibility and viscoelasticity of host rocks considerably affect dynamics in the midcrustal magmatic system of soufriere hills volcano and need to be accounted for as first order effects in geodetic data analyses and modeling

controls of conduit geometry and wallrock elasticity on lava dome eruptions abstract many lava dome building eruptions show periodic to complex non periodic pulsatory activity typical time scales associated with this activity range from hours to decades previous studies modelled the ascent of magma using a set of transient 1 d transport equations accounting for degassing induced crystallization kinetics gas exsolution and viscosity increase due to crystal growth these models assumed flow in a cylindrical conduit with a fixed cross section area since several observations suggest that extrusions are mainly fed by dykes with cylindrical geometries developing only at shallow levels here we generalised the model to the flow geometry represented by an elliptical dyke with major and minor semi axes changing with depth quasi static elastic deformation of the dyke is accounted by an analytical solution that couples cross section area with the magmatic overpressure the effects of the main dyke geometrical parameters and boundary conditions on the eruption dynamics were investigated the presence of a deformable dyke can lead to a more complex periodic behaviour with a wider range of time scales and cyclicity patterns with respect to a uniform cylindrical conduit there is a regime where the period of pulsations is controlled by the elasticity of the dyke and a regime where the period is controlled by the volume of the magma chamber intermediate regimes are possible periodic variations in discharge rate are also possible for both fixed pressure in dyke source region and fixed influx rate into the dyke our study emphasizes the strong non linearities and complex behaviours of lava dome eruptions from a forecasting and hazard perspective intrinsic uncertainties in governing parameters may make volcanic systems in some circumstances unpredictable on the other hand lava dome systems may also develop episodic and systematic behaviours so that behaviour becomes predictable for a while