volcano dome dynamics at mount st helens deformation and intermittent subsidence monitored by seismicity and camera imagery pixel offsets the surface deformation field measured at volcanic domes provides insights into the effects of magmatic processes gravity and gas driven processes and the development and distribution of internal dome structures here we study short term dome deformation associated with earthquakes at mount st helens recorded by a permanent optical camera and seismic monitoring network we use digital image correlation dic to compute the displacement field between successive images and compare the results to the occurrence and characteristics of seismic events during a 6 week period of dome growth in 2006 the results reveal that dome growth at mount st helens was repeatedly interrupted by short term meter scale downward displacements at the dome surface which were associated in time with low frequency large magnitude seismic events followed by a tremor like signal the tremor was only recorded by the seismic stations closest to the dome we find a correlation between the magnitudes of the camera derived displacements and the spectral amplitudes of the associated tremor we use the dic results from two cameras and a high resolution topographic model to derive full 3 d displacement maps which reveals internal dome structures and the effect of the seismic activity on daily surface velocities we postulate that the tremor is recording the gravity driven response of the upper dome due to mechanical collapse or depressurization and fault controlled slumping our results highlight the different scales and structural expressions during growth and disintegration of lava domes and the relationships between seismic and deformation signals

sound velocities of majorite garnet and the composition of the mantle transition region the composition of the mantle transition region characterized by anomalous seismic wave velocity and density changes at depths of approximately 400 to 700 km has remained controversial some have proposed that the mantle transition region has an olivine rich pyrolite composition whereas others have inferred that it is characterized by pyroxene and garnet rich compositions piclogite because the sound velocities in pyrolite estimated from laboratory data are substantially higher than those seismologically observed although the velocities of the olivine polymorphs at these pressures wadsleyite and ringwoodite have been well documented those of majorite another significant high pressure phase in the mantle transition region with realistic mantle compositions have never been measured here we use combined in situ x ray and ultrasonic measurements under the pressure and temperature conditions of the mantle transition region to show that majorite in a pyrolite composition has sound velocities substantially lower than those of earlier estimates owing to strong nonlinear decreases at high temperature particularly for shear wave velocity we found that pyrolite yields seismic velocities more consistent with typical seismological models than those of piclogite in the upper to middle parts of the region except for the potentially larger velocity jumps in pyrolite relative to those observed at a depth of 410 km in contrast both of these compositions lead to significantly low shear wave velocities in the lower part of the region suggesting possible subadiabatic temperatures or the existence of a layer of harzburgite rich material supplied by the subducted slabs stagnant at these depths

volcanic drumbeat seismicity caused by stick slip motion and magmatic frictional melting during volcanic eruptions solidifying magma ascends through the volcanic conduit often accompanied by repetitive drum beat seismicity laboratory experiments on magma samples from soufriere hills volcano montserrat and mount st helens volcano usa show that viscous melt formed at the surface between the rising magma and conduit walls can temporarily halt magma ascent accentuating the cyclical seismicity

high pressure behavior of kyanite decomposition of kyanite into stishovite and corundum the pressure stability of kyanite was experimentally reversed with the use of a multi anvil apparatus kyanite was found to decompose into its oxides stishovite and corundum between 14 or 0 5 gpa at 1000 degrees c and 17 5 or 1 0 gpa at 2000 degrees c reliable thermodynamic calculations can be performed to temperatures of approximately 1500 degrees c up to this temperature the location of the equilibrium kyanite corundum stishovite determined in this study constrains the equilibrium coesite stishovite a set of thermodynamic data was calculated by linear programming from the kyanite breakdown reaction and the coesite stishovite equilibrium feasible values for the fitted thermo dynamic properties are 28 5 to 26 3 mpa k for the temperature derivative of the bulk modulus dk dt p of kyanite 815254 to 813635 j mol for g 0 sub 1298 of stishovite and 24 6 to 26 3 j mol k for s 0 sub 1298 of stishovite the experimental results indicate 1 that in peraluminous eclogites of basaltic or sedimentary origin stishovite may coexist stably with corundum at a depth greater than 420 450 km and 2 that in an inhomogeneous al enriched mantle corundum could be a minor constituent in the lower mantle

the 2004 2008 dome building eruption at mount st helens washington epilogue the 2004 2008 dome building eruption at mount st helens ended during winter 2007 2008 at a time when field observations were hampered by persistent bad weather as a result recognizing the end of the eruption was challenging but important for scientists trying to understand how and why long lived eruptions end and for public officials and land managers responsible for hazards mitigation and access restrictions in hindsight the end of the eruption was presaged by a slight increase in seismicity in december 2007 that culminated on january 12 13 2008 with a burst of more than 500 events most of which occurred in association with several tremor like signals and a spasmodic burst of long period earthquakes at about the same time a series of regular localized small amplitude tilt events thousands of which had been recorded during earlier phases of the eruption came to an end thereafter seismicity declined to 10 20 events per day until january 27 28 when a spasmodic burst of about 50 volcano tectonic earthquakes occurred over a span of 3 h this was followed by a brief return of repetitive drumbeat earthquakes that characterized much of the eruption by january 31 however seismicity had declined to 1 2 earthquakes per day a rate similar to pre eruption levels we attribute the tilt and seismic observations to convulsive stagnation of a semisolid magma plug in the upper part of the conduit the upward movement of the plug ceased when the excess driving pressure which had gradually decreased throughout the eruption as a result of reservoir deflation and increasing overburden from the growing dome was overcome by increasing friction as a result of cooling and crystallization of the plug

oblique photogrammetry with visible and thermal images of active lava flows digital images from hand held cameras are increasingly being acquired for scientific purposes particularly where non contact measurement is required however they frequently consist of oblique views with significant camera to object depth variations and occlusions that complicate quantitative analyses here we report the use of oblique photogrammetric techniques to determine ground based thermal camera orientations position and pointing direction and to generate scene information for lava flows at mount etna sicily multiple images from a consumer grade digital slr camera are used to construct a topographic model and reference associated ground based thermal imagery we present data collected during the 2004 2005 eruption and use the derived surface model to apply viewing distance corrections to account for atmospheric attenuation to the thermal images on a pixel by pixel basis for viewing distances of 100 to 400 m the corrections result in systematic changes in emissive power of up to 3 with respect to values calculated assuming a uniform average viewing distance across an image

modelling the lava dome extruded at soufriere hills volcano montserrat august 2005 may 2006 part i dome shape and internal structure lava domes comprise core carapace and clastic talus components they can grow endogenously by inflation of a core and or exogenously with the extrusion of shear bounded lobes and whaleback lobes at the surface internal structure is paramount in determining the extent to which lava dome growth evolves stably or conversely the propensity for collapse the more core lava that exists within a dome in both relative and absolute terms the more explosive energy is available both for large pyroclastic flows following collapse and in particular for lateral blast events following very rapid removal of lateral support to the dome knowledge of the location of the core lava within the dome is also relevant for hazard assessment purposes a spreading toe or lobe of core lava over a talus substrate may be both relatively unstable and likely to accelerate to more violent activity during the early phases of a retrogressive collapse soufriere hills volcano montserrat has been erupting since 1995 and has produced numerous lava domes that have undergone repeated collapse events we consider one continuous dome growth period from august 2005 to may 2006 that resulted in a dome collapse event on 20th may 2006 the collapse event lasted 3 h removing the whole dome plus dome remnants from a previous growth period in an unusually violent and rapid collapse event we use an axisymmetrical computational finite element method model for the growth and evolution of a lava dome our model comprises evolving core carapace and talus components based on axisymmetrical endogenous dome growth which permits us to model the interface between talus and core despite explicitly only modelling axisymmetrical endogenous dome growth our core talus model simulates many of the observed growth characteristics of the 2005 2006 shv lava dome well further it is possible for our simulations to replicate large scale exogenous characteristics when a considerable volume of talus has accumulated around the lower flanks of the dome model results suggest that dome core can override talus within a growing dome potentially generating a region of significant weakness and a potential locus for collapse initiation

identification of structural controls in an active lava dome with high resolution dems volcan de colima mexico monitoring the topography of active lava domes is critical for detecting changes that may trigger or influence collapse or explosive activity internal dome structure and conditions are more difficult to elucidate but also play vital roles here we describe the exposure following an explosion of significant scarps in the active dome at volcan de colima mexico that are interpreted as evidence of brittle failure planes and a complex internal dome morphology in the first use of automated 3d computer vision reconstruction techniques structure from motion and multi view stereo sfm mvs on an active volcanic dome we derive high resolution surface models from oblique and archive photographs taken with a consumer camera the resulting 3d models were geo referenced using features identified in a web sourced orthoimage no ground based measurements were required in december 2010 the dome 2 14 106 m3 had a flat upper surface reflecting an overall ductile emplacement regime between then and may 2011 a period of low explosivity was accompanied by a small volume loss 0 4 105 m3 and arcuate steps appeared in the dome surface suggesting the presence of localized planes of weakness the complex array of summit scarps was exposed following a significant explosion in june 2011 and is interpreted to be the surface expression of fault planes in the dome the 1 m resolution dems indicated that the region of greatest volume loss was not coincident with the assumed location of the conduit and that heterogeneity within the dome may have been important during the june explosion

long period earthquakes and co eruptive dome inflation seen with particle image velocimetry dome growth and explosive degassing are fundamental processes in the cycle of continental arc volcanism johnson et al present novel optical geodetic observations to constrain the sources responsible for long period volcanic earthquakes which are coincident with frequent explosive eruptions at santiaguito volcano guatemala they find that acceleration in deformation of the volcanic dome extracted from high resolution optical image processing is coincident with recorded long period seismic sources based on these observations abrupt mass shift of solidified domes conduit magma or magma pads seem to be part of the mechanism responsible for generating long period earthquakes at silicic volcanic systems this study presents optical geodetic observations to constrain the sources responsible for long period volcanic earthquakes which are coincident with frequent explosive eruptions at santiaguito volcano guatemala it is found that acceleration in deformation of the volcanic dome extracted from the high resolution optical image processing is coincident with recorded long period seismic sources on the basis of these observations abrupt mass shift of solidified domes conduit magma or magma pads seem to be part of the mechanism responsible for generating long period earthquakes at silicic volcanic systems dome growth and explosive degassing are fundamental processes in the cycle of continental arc volcanism1 2 because both processes generate seismic energy geophysical field studies of volcanic processes are often grounded in the interpretation of volcanic earthquakes3 although previous seismic studies have provided important constraints on volcano dynamics4 5 6 such inversion results do not uniquely constrain magma source dimension and material properties here we report combined optical geodetic and seismic observations that robustly constrain the sources of long period volcanic earthquakes coincident with frequent explosive eruptions at the volcano santiaguito in guatemala the acceleration of dome deformation extracted from high resolution optical image processing is shown to be associated with recorded long period seismic sources and the frequency content of seismic signals measured across a broadband network these earthquake sources are observed as abrupt subvertical surface displacements of the dome in which 20 50 cm uplift originates at the central vent and propagates at 50 m s 1 towards the 200 m diameter periphery episodic shifts of the 20 80 m thick dome induce peak forces greater than 109 n and reflect surface manifestations of the volcanic long period earthquakes a broad class of volcano seismic activity that is poorly understood and observed at many volcanic centres worldwide7 on the basis of these observations the abrupt mass shift of solidified domes conduit magma or magma pads may play a part in generating long period earthquakes at silicic volcanic systems

fine scale modeling of the boundary layer wind field over steep topography 1 this paper describes the adaptation of wind fields to steep and complex terrain using fine scale numerical modeling the work is motivated by the need of high resolution flow fields to predict snow transport and snow cover development for avalanche warning purposes applying the nonhydrostatic and compressible atmospheric prediction model advanced regional prediction system arps to steep alpine topography the boundary layer flow was simulated and evaluated against measurements the adaptation of the wind field to steep terrain for specific initial and boundary conditions was simulated the topography used in our study has a length scale of 500 m a typical height of 150 m and maximum slopes of 45 numerical experiments with idealized triangular ridges were conducted to find an adequate model configuration this analysis indicates that a high resolution grid with horizontal spacing of at least 25 m and vertical spacing of 3 m near the surface is necessary to reproduce small scale flow features such as speed up separation and recirculation the onset of flow separation is highly sensitive to initial and boundary conditions slope angle and surface roughness the results of the comparison between the model simulations and measurements on our experimental site show that typical wind field characteristics are well reproduced the simulated wind fields have been used to drive a numerical three dimensional snow drift model which is presented in a companion paper by lehning et al 2008

transmission electron microscope observation of the high pressure form of magnesite retrieved from laser heated diamond anvil cell abstract we applied focused ion beam fib technique to make a thin foil for transmission electron microscope tem observations of mgco3 magnesite and its new high pressure form magnesite ii recovered from laser heated diamond anvil cell lhdac both of which should play fundamental roles in the circulation of carbon in the lower mantle heterogeneous microstructures due to significant temperature gradients were observed along the axial direction of the disk sample 100 m in diameter and 30 m thick in spite of double sided laser heating and the use of thermal insulators between the diamond anvil and the sample the central portion of the mgco3 sample was found amorphous while the peripheral part remained magnesite on the basis of electron diffraction measurements with tem this and our earlier results based on in situ x ray diffraction measurements suggest that magnesite transformed to magnesite ii only at the central part where the temperatures should have been significantly higher than those near the pressure medium magnesite ii was amorphisized on release of pressure in contrast to our interpretation that it was converted back to magnesite based solely on in situ x ray diffraction measurements the new method of combining the fib technique with tem observation thus provides important information on phase transitions under very high pressure using lhdac which may be overlooked by in situ optical and x ray diffraction measurements

first principles investigations on the elasticity and phase stability of grossular garnet 1 in order to understand the fate of subducted continental materials by means of mechanisms such as tectonic erosion and sediment subduction it is important to understand the high pressure stability and elastic properties of grossular garnet we study these questions using the first principles computation method grossular garnet was found to dissociate into an assemblage of casio3 ca perovskite pv and al2o3 corundum cor at about 23 4 gpa accompanied by remarkable jumps of compressional wave 8 0 shear wave 11 6 bulk sound 5 7 velocities and density 12 1 although pv with the grossular garnet composition was suggested experimentally after the decomposition reaction this phase was found to be less stable than an assemblage of capv and cor at pressures higher than 20 gpa this indicates that observed pv with the grossular garnet composition is metastable but can be obtained because of the slow kinetics of the garnet decomposition reaction our results imply that the dissociation of grossular garnet as well as that of jadeite included in continental materials subducted into the deep mantle increases the complexity of the 660 km discontinuity and can explain seismically observed multiple reflections we have also investigated the anisotropy of elastic velocities of grossular garnet capv and cor and found that capv is the most anisotropic mineral this implies that capv could produce seismic anisotropy in the uppermost lower mantle

faulting within the mount st helens conduit and implications for volcanic earthquakes the 2004 2008 eruption of mount st helens produced seven dacite spines mantled by cataclastic fault rocks comprising an outer fault core and an inner damage zone these fault rocks provide remarkable insights into the mechanical processes that accompany extrusion of degassed magma insights that are useful in forecasting dome forming eruptions the outermost part of the fault core consists of finely comminuted fault gouge that is host to 1 to 3 mm thick layers of extremely fine grained slickenside bearing ultracataclasite interior to the fault core there is an 2 m thick damage zone composed of cataclastic breccia and sheared dacite and interior to the damage zone there is massive to flow banded dacite lava of the spine interior structures and microtextures indicate entirely brittle deformation including rock breakage tensional dilation shearing grain flow and microfaulting as well as gas and fluid migration through intergranular pores and fractures in the damage zone slickenside lineations and consistent orientations of riedel shears indicate upward shear of the extruding spines against adjacent conduit wall rocks paleomagnetic directions demagnetization paths oxide mineralogy and petrology indicate that cataclasis took place within dacite in a solidified steeply dipping volcanic conduit at temperatures above 500 c low water content of matrix glass is consistent with brittle behavior at these relatively high temperatures and the presence of tridymite indicates solidification depths of more than a million small and low frequency drumbeat earthquakes with coda magnitudes m d 2 slip patches possibly along observed extensive principal shear zones within the fault core but probably not along the smaller riedel shears although our field and structural data are compatible with stick slip models they do not rule out seismic and infrasound models that call on resonance of steam filled fractures to generate the drumbeat earthquakes we suggest that stick slip and gas release processes may be coupled and that regardless of the source mechanism the distinctive drumbeat earthquakes are proving to be an effective precursor for dome forming eruptions our data document a continuous cycle of deformation along the conduit margins beginning with episodes of fracture in the damage zone and followed by transfer of motion to the fault core we illustrate the cycle of deformation using a hypothetical cross section of the mount st helens conduit extending from the surface to the depth of magmatic solidification

high pressure phase relations and thermodynamic properties of caal4si2o11 cas phase abstract phase relations in caal4si2o11 were examined at 12 23 gpa and 1000 1800 c by multianvil experiments a three phase mixture of grossular kyanite and corundum is stable below about 13 gpa at 1000 1800 c at higher pressure and at temperature below about 1200 c a mixture of grossular stishovite and corundum is stable indicating the decomposition of kyanite above about 1200 c caal4si2o11 cas phase is stable at pressure higher than about 13 gpa the triple point is placed at 14 7 gpa and 1280 c the equilibrium boundary of formation of cas phase from the mixture of grossular kyanite and corundum has a small negative slope and that from the mixture of grossular stishovite and corundum has a strongly negative slope while the decomposition boundary of kyanite has a small positive slope enthalpies of the transitions were measured by high temperature drop solution calorimetry the enthalpy of formation of caal4si2o11 cas phase from the mixture of grossular kyanite and corundum was 139 5 15 6 kj mol and that from the mixture of grossular stishovite and corundum was 94 2 15 4 kj mol the transition boundaries calculated using the measured enthalpy data were consistent with those determined by the high pressure experiments the boundaries in this study are placed about 3 gpa higher in pressure and about 200 c lower in temperature than those by zhai and ito zhai s ito e 2008 phase relations of caal4si2o11 at high pressure and high temperature with implications for subducted continental crust into the deep mantle phys earth planet inter 167 161 167 combining the thermodynamic data measured in this study with those in the literature dissociation boundary of cas phase into a mixture of ca perovskite corundum and stishovite and that of grossular into ca perovskite plus corundum were calculated to further constrain the stability field of cas phase the result suggests that the stability of cas phase would be limited at the bottom of transition zone and top of the lower mantle when sediments are subducted into the deep mantle it is also suggested that cas phase may be stable at the depth of the upper part of the lower mantle when partial melting of basalt occurs at the depth

models of tremor and low frequency earthquake swarms on montserrat recent observations from soufriere hills volcano in montserrat reveal a wide variety of low frequency seismic signals we discuss similarities and differences between hybrid earthquakes and long period events and their role in explosions and rockfall events these events occur usually in swarms and occasionally merge into tremor an observation that can shed further light on the generation and composition of harmonic tremor we use a 2d finite difference method to model major features of low frequency seismic signatures and compare them with the observations a depth dependent velocity model for a fluid filled conduit is introduced which accounts for the varying gas content in the magma and the impact on the seismic signals is discussed we carefully analyse episodes of tremor that show shifting spectral lines and model those in terms of changes in the gas content of the magma as well as in terms of a time dependent triggering mechanism of low frequency resonances in this way we explain the simultaneous occurrence of low frequency events and tremor with a spectral content comprising integer harmonics

insights into lava dome and spine extrusion using analogue sandbox experiments abstract lava dome formation is a common process at stratovolcanoes involving the shallow intrusion or extrusion of viscous lava and may lead to the rise of spines spines are protrusions observed to extrude episodically during lava dome growth yet the structural and mechanical factors controlling their formation are only partially understood here we provide new detailed insight into lava dome growth and the production of spines using a novel set of analogue experiments extruding sand plaster mixtures from a fixed diameter conduit under isothermal conditions we trace displacement and strain with photogrammetric methods for precise and detailed monitoring of the extrusion process results show initial dome growth forming a steep sided and flat topped shape through extrusion of new material leading to slumping of oversteepening slopes forming a talus spines are found to protrude at a later stage through the dome surface along discrete circular faults that originate from the conduit walls starting a cycle of spine growth and collapse as our spines only appear after prolonged extrusion we relate their appearance to the compaction and strengthening of material within the conduit we find that spine diameter height and volume are positively correlated with increasing cohesion and therefore material strength the spine diameter was also observed to be smaller or equal to the diameter of the underlying conduit as shear extrusion occurs along vertical to outward dipping fault planes for natural domes our findings imply that spine growth may be the consequence of compaction and densification via porosity loss shearing and or outgassing of conduit magma during ascent more efficient compaction will yield wider and taller spines as a result of increasing rock strength our study further highlights the relevance of analogue experiments in the study of lava domes and spines which remain one of the most hazardous and unpredictable features at dome forming volcanoes worldwide

phase relations for caal2si2o8 anorthite composition in the system caoal2o3sio2 at 14 gpa abstract multi anvil experiments at 14 gpa and 1500 c reveal that caal 2 si 2 o 8 anorthite composition undergoes subsolidus disproportionation into grossular ca 3 al 2 si 3 o 12 stishovite sio 2 and a calcium aluminosilicate phase of composition caal 4 si 2 o 11 this last phase cas was first synthesised by irifune et al 1994 earth planet sci lett 126 351 368 in a continental crust composition at p t conditions appropriate for the transition zone in the system cao al 2 o 3 sio 2 a new three phase assemblage grossular stishovite cas encountered at 14gpa replaces the grossular stishovite kyanite assemblage known to be stable at around 10gpa because of an univariant reaction between grossular and kyanite that yields stishovite and cas by 1600 c another univariant reaction between grossular and stishovite produces cas plus liquid schreinemakers analysis suggests that given ca al rich lithologies the cas phase should be stable at transition zone pressures

phase transformations in subducted oceanic crust and buoyancy relationships at depths of 600 800 km in the mantle abstract phase transformations in a representative oceanic crust composition morb have been studied at pressures up to 28 gpa at 1200 c and 1500 c using a multi anvil apparatus the assemblage of majorite casio 3 rich perovskite stishovite which is displayed by the morb composition at pressures above 20 gpa was found to transform further into an assemblage containing a new aluminous phase at pressures above 25 gpa this al phase has a complex composition and is also relatively sodium rich its x ray diffraction pattern is similar to that observed for mgal 2 o 4 calcium ferrite type and is tentatively indexed on the basis of an orthorhombic cell yielding a zero pressure density of 3 87 2 g cm 3 majorite garnet was found to remain as the most abundant phase at the highest pressure studied 28 gpa and does not appear likely to transform to perovskite until pressures exceed 29 30 gpa these results imply that the basaltic crust component of subducted oceanic lithosphere would be 0 1 0 2 g cm 3 less dense than surrounding mantle pyrolite between the depths of 660 800 km thereby confirming an earlier hypothesis of anderson moreover the underlying layer of harzburgite would be 0 05 g cm 3 less dense than pyrolite throughout most of this depth interval these buoyancy relationships contribute to a barrier which impedes and may sometimes prevent the entry of slabs into the lower mantle

monitoring lava dome growth during the 2004 2008 mount st helens washington eruption using oblique terrestrial photography abstract we present an analysis of lava dome growth during the 2004 2008 eruption of mount st helens using oblique terrestrial images from a network of remotely placed cameras this underutilized monitoring tool augmented more traditional monitoring techniques and was used to provide a robust assessment of the nature pace and state of the eruption and to quantify the kinematics of dome growth eruption monitoring using terrestrial photography began with a single camera deployed at the mouth of the volcano s crater during the first year of activity analysis of those images indicates that the average lineal extrusion rate decayed approximately logarithmically from about 8 m d to about 2 m d 2 m d from november 2004 through december 2005 and suggests that the extrusion rate fluctuated on time scales of days to weeks from may 2006 through september 2007 imagery from multiple cameras deployed around the volcano allowed determination of 3 dimensional motion across the dome complex analysis of the multi camera imagery shows spatially differential but remarkably steady to gradually slowing motion from about 1 2 m d from may through october 2006 to about 0 2 1 0 m d from may through september 2007 in contrast to the fluctuations in lineal extrusion rate documented during the first year of eruption dome motion from may 2006 through september 2007 was monotonic 0 10 m d to gradually slowing on time scales of weeks to months the ability to measure spatial and temporal rates of motion of the effusing lava dome from oblique terrestrial photographs provided a significant and sometimes the sole means of identifying and quantifying dome growth during the eruption and it demonstrates the utility of using frequent long term terrestrial photography to monitor and study volcanic eruptions

phase transformations of ca3al2si3o12 grossular garnet to the depths of the earth s mantle transition zone abstract high pressure and high temperature phase transformations of ca 3 al 2 si 3 o 12 grossular garnet were examined at 19 26 gpa and 700 2000 k using kawai type multi anvil apparatus coupled with in situ x ray diffraction xrd recovered samples were analyzed by a combination of micro focused x ray diffraction xrd and transmission electron microscopy tem the results show that grossular garnet gradually transforms to an al rich casio 3 perovskite at 22 26 gpa and 1000 1400 k the transition boundary can be expressed as p gpa 0 0082 t k 33 05 when the garnet completely disappears we observed orthorhombic casio 3 perovskite with a grossular composition at 20 24 gpa and temperatures above 1500 k the cas phase with the composition caal 4 si 2 o 11 appears to accommodate excess al from the perovskite along with two distinct populations of al bearing casio 3 perovskites with al content of 3 7 and 10 0 wt al 2 o 3 respectively the pressure and temperature of these transitions correspond to the lowermost part of the transition zone and therefore it suggests that ca rich aluminosilicates could provide alternative candidates to explain multiple seismic reflections near the 660 km depth discontinuity

explosive dome eruptions modulated by periodic gas driven inflation volcan santiaguito guatemala breathes with extraordinary regularity as the edifice s conduit system accumulates free gas which periodically vents to the atmosphere periodic pressurization controls explosion timing which nearly always occurs at peak inflation as detected with tiltmeters tilt cycles in january 2012 reveal regular 26 6 min inflation deflation cycles corresponding to at least 101 kg s of gas fluxing the system very long period vlp earthquakes presage explosions and occur during cycles when inflation rates are most rapid vlps locate 300 m below the vent and indicate mobilization of volatiles which ascend at 50 m s rapid gas ascent feeds pyroclast laden eruptions lasting several minutes and rising to 1 km vlps are not observed during less rapid inflation episodes instead gas vents passively through the conduit producing no infrasound and no explosion these observations intimate that steady gas exsolution and accumulation in shallow reservoirs may drive inflation cycles at open vent silicic volcanoes

dynamics of seismogenic volcanic extrusion at mount st helens in 2004 05 the 2004 05 eruption of mount st helens exhibited sustained near equilibrium behaviour characterized by relatively steady extrusion of a solid dacite plug and nearly periodic shallow earthquakes here we present a diverse data set to support our hypothesis that these earthquakes resulted from stick slip motion along the margins of the plug as it was forced incrementally upwards by ascending solidifying gas poor magma we formalize this hypothesis with a dynamical model that reveals a strong analogy between behaviour of the magma plug system and that of a variably damped oscillator modelled stick slip oscillations have properties that help constrain the balance of forces governing the earthquakes and eruption and they imply that magma pressure never deviated much from the steady equilibrium pressure we infer that the volcano was probably poised in a near eruptive equilibrium state long before the onset of the 2004 05 eruption

a comparison of measurement methods terrestrial laser scanning tachymetry and snow probing for the determination of the spatial snow depth distribution on slopes determination of the spatial snow depth distribution is important in potential avalanche starting zones both for avalanche prediction and for the dimensioning of permanent protection measures knowledge of the spatial distribution of snow is needed in order to validate snow depths computed from snowpack and snowdrift models the inaccessibility of alpine terrain and the acute danger of avalanches complicate snow depth measurements e g when probes are used so the possibility of measuring the snowpack using terrestrial laser scanning tls was tested the results obtained were compared to those of tachymetry and manual snow probing laser measurements were taken using the long range laser profile measuring system riegl lpm i800ha the wavelength used by the laser was 0 9 mm near infrared the accuracy was typically within 30 mm the highest point resolution was 30 mm when measured from a distance of 100 m tachymetry measurements were carried out using leica tcrp1201 systems snowpack depths measured by the tachymeter were also used the datasets captured by tachymetry were used as reference models to compare the three different methods tls tachymetry and snow probing this is the first time that the accuracy of tls systems in snowy and alpine weather conditions has been quantified the relative accuracy between the three measurement methods is bounded by a maximum offset of 8 cm between tls and the tachymeter the standard deviation is 1 2 cm and between manual probing and tls it is up to 1 10 cm for maximum distances for the tls and tachymeter of 300 m

evaluating links between deformation topography and surface temperature at volcanic domes results from a multi sensor study at volcan de colima mexico abstract dome building activity is common at many volcanoes and due to the gravitational instability a dome represents one of the most hazardous volcanic phenomena shallow volcanic processes as well as rheological and structural changes of the dome affecting the fluid transport have been linked to transitions in eruptive activity also hydrothermal alteration may affect the structural integrity of the dome increasing the potential for collapse however mapping the deformation and details of fluid escape at the summit of steep sloped volcanoes and integrating these with other types of data is challenging due to difficult access and poor coverage here we present for the first time the near vertical and near horizontal surface deformation field of a quiescent summit dome and the relationships with degassing and topographic patterns our results are derived from high resolution satellite radar interferometry insar time series based on a year of terrasar x spotlight acquisitions and structure from motion sfm processing of overflight infrared data at volcan de colima mexico the identified deformation is dominated by localized heterogeneous subsidence of the summit dome exceeding rates of 15 cm yr and strongly decreasing over the year 2012 up to the renewal of explosive and extrusive activity in early 2013 we tentatively attribute the deformation to the degassing cooling and contraction of the dome and shallow conduit material we also find that the results strongly differ depending on the chosen insar time series method which potentially overprints the true physical complexities of small scale shallow deformation processes the combined interpretation of the deformation and infrared data reveals a complex spatial relationship between the degassing pathways and the deformation while we observe no deformation across the crater rim fumaroles discontinuities in the deformation field are more commonly observed around the dome rim fumaroles and occasionally on the dome upper surface we propose that the deformation pattern is also linked to processes controlling the fumarole formation and distribution topography permeability and volcanic activity and the lack of direct relationships may be explained by how the influence of these processes varies across the volcanic summit the presented work provides a new approach for safely monitoring the activity and stability of internal dome structures as well as for constraining and validating models of dome degassing pathways and densification processes

influence of extrusion rate and magma rheology on the growth of lava domes insights from particle dynamics modeling abstract lava domes are structures that grow by the extrusion of viscous silicic or intermediate composition magma from a central volcanic conduit repeated cycles of growth are punctuated by collapse as the structure becomes oversized for the strength of the composite magma that rheologically stiffens and strengthens at its surface here we explore lava dome growth and failure mechanics using a two dimensional particle dynamics model the model follows the evolution of fractured lava with solidification driven by degassing induced crystallization of magma the particle dynamics model emulates the natural development of dome growth and rearrangement of the lava dome which is difficult in mesh based analyses due to mesh entanglement effects the deformable talus evolves naturally as a frictional carapace that caps a ductile magma core extrusion rate and magma rheology together with crystallization temperature and volatile content govern the distribution of strength in the composite structure this new model is calibrated against existing observational models of lava dome growth results show that the shape and extent of the ductile core and the overall structure of the lava dome are strongly controlled by the infusion rate the effects of extrusion rate on magma rheology are sensitive to material stiffness which in turn is a function of volatile content and crystallinity material stiffness and material strength are key model parameters which govern magma rheology and subsequently the morphological character of the lava dome and in turn stability degassing induced crystallization causes material stiffening and enhances material strength reflected in non newtonian magma behavior the increase in stiffness and strength of the injected magma causes a transition in the style of dome growth from endogenous expansion of a ductile core to stiffer and stronger intruding material capable of punching through the overlying material and resulting in the development of a spine or possibly inducing dome collapse simulation results mimic development of a megaspine upon the influx of fresh magma which leads to the re direction of magma flow creating a new shear zone and the switching of dome growth from one side to the other our model shows similar dome growth dynamics as observed at soufriere hills volcano montserrat indicating a strong correlation between extrusion rate and its subsequent effect on mechanical properties and variations in magma rheology

automated identification location and volume estimation of rockfalls at piton de la fournaise volcano since the collapse of the dolomieu crater floor at piton de la fournaise volcano la reunion in 2007 hundreds of seismic signals generated by rockfalls have been recorded daily at the observatoire volcanologique du piton de la fournaise ovpf to study rockfall activity over a long period of time automated methods are required to process the available continuous seismic records we present a set of automated methods designed to identify locate and estimate the volume of rockfalls from their seismic signals the method used to automatically discriminate seismic signals generated by rockfalls from other common events recorded at ovpf is based on fuzzy sets and has a success rate of 92 a kurtosis based automated picking method makes it possible to precisely pick the onset time and the final time of the rockfall generated seismic signals we present methods to determine rockfall locations based on these accurate pickings and a surface wave propagation model computed for each station using a fast marching method these methods have successfully located directly observed rockfalls with an accuracy of about 100 m they also make it possible to compute the seismic energy generated by rockfalls which is then used to retrieve their volume the methods developed were applied to a data set of 12 422 rockfalls that occurred over a period extending from the collapse of the dolomieu crater floor in april 2007 to the end of the undervolc project in may 2011 to identify the most hazardous areas of the piton de la fournaise volcano summit

the source of infrasound associated with long period events at mount st helens 1 during the early stages of the 2004 2008 mount st helens eruption the source process that produced a sustained sequence of repetitive long period lp seismic events also produced impulsive broadband infrasonic signals in the atmosphere to assess whether the signals could be generated simply by seismic acoustic coupling from the shallow lp events we perform finite difference simulation of the seismo acoustic wavefield using a single numerical scheme for the elastic ground and atmosphere the effects of topography velocity structure wind and source configuration are considered the simulations show that a shallow source buried in a homogeneous elastic solid produces a complex wave train in the atmosphere consisting of p sv and rayleigh wave energy converted locally along the propagation path and acoustic energy originating from the source epicenter although the horizontal acoustic velocity of the latter is consistent with our data the modeled amplitude ratios of pressure to vertical seismic velocity are too low in comparison with observations and the characteristic differences in seismic and acoustic waveforms and spectra cannot be reproduced from a common point source the observations therefore require a more complex source process in which the infrasonic signals are a record of only the broadband pressure excitation mechanism of the seismic lp events the observations and numerical results can be explained by a model involving the repeated rapid pressure loss from a hydrothermal crack by venting into a shallow layer of loosely consolidated highly permeable material heating by magmatic activity causes pressure to rise periodically reaching the pressure threshold for rupture of the valve sealing the crack sudden opening of the valve generates the broadband infrasonic signal and simultaneously triggers the collapse of the crack initiating resonance of the remaining fluid subtle waveform and amplitude variability of the infrasonic signals as recorded at an array 13 4 km to the nw of the volcano are attributed primarily to atmospheric boundary layer propagation effects superimposed upon amplitude changes at the source

seismic and acoustic recordings of an unusually large rockfall at mount st helens washington 1 on 29 may 2006 a large rockfall off the mount st helens lava dome produced an atmospheric plume that was reported by airplane pilots to have risen to 6 000 m above sea level and interpreted to be a result of an explosive event however subsequent field reconnaissance found no evidence of a ballistic field indicating that there was no explosive component the rockfall produced complex seismic and infrasonic signals with the latter recorded at sites 0 6 and 13 4 km from the source an unusual very long period 50 s infrasonic signal was recorded a signal we model as the result of air displacement two high frequency infrasonic signals are inferred to result from the initial contact of a rock slab with the ground and from interaction of displaced air with a depression at the base of the active lava dome

eruption dynamics at mount st helens imaged from broadband seismic waveforms interaction of the shallow magmatic and hydrothermal systems 1 the current eruption at mount st helens is characterized by dome building and shallow repetitive long period lp earthquakes waveform cross correlation reveals remarkable similarity for a majority of the earthquakes over periods of several weeks stacked spectra of these events display multiple peaks between 0 5 and 2 hz that are common to most stations lower amplitude very long period vlp events commonly accompany the lp events we model the source mechanisms of lp and vlp events in the 0 5 4 s and 8 40 s bands respectively using data recorded in july 2005 with a 19 station temporary broadband network the source mechanism of the lp events includes 1 a volumetric component modeled as resonance of a gently nnw dipping steam filled crack located directly beneath the actively extruding part of the new dome and within 100 m of the crater floor and 2 a vertical single force attributed to movement of the overlying dome the vlp source which also includes volumetric and single force components is 250 m deeper and nnw of the lp source at the sw edge of the 1980s lava dome the volumetric component points to the compression and expansion of a shallow magma filled sill which is subparallel to the hydrothermal crack imaged at the lp source coupled with a smaller component of expansion and compression of a dike the single force components are due to mass advection in the magma conduit the location geometry and timing of the sources suggest the vlp and lp events are caused by perturbations of a common crack system

the nature of the 660 kilometer discontinuity in earth s mantle from global seismic observations of pp precursors the 660 kilometer discontinuity which separates earth s upper and lower mantle has been detected routinely on a global scale in underside reflections of precursors to ss shear waves here we report observations of this discontinuity in many different regions using precursors to compressional pp waves the apparent absence of such precursors in previous studies had posed major problems for models of mantle composition we find a complicated structure showing single and double reflections ranging in depth from 640 to 720 kilometers that requires the existence of multiple phase transitions at the base of the transition zone the results are consistent with a pyrolite mantle composition

extreme frictional processes in the volcanic conduit of mount st helens usa during the 2004 2008 eruption abstract the 2004 2008 eruption of mount st helens saw the extrusion of seven high viscosity spines and formation of discrete shear zones along the conduit margin at spine 7 this shear zone consists of four structurally distinct layers the outer surface gouge l1 crosscuts a dark banded layer l2 which grades into a moderately sheared layer l3 and undeformed rock l4 inside the spine field observations porosity measurements geochemistry mineralogy microstructure crystal size and shape distribution kinetic properties and magnetic analyses chart the evolution of deformation processes and products throughout the eruption gouge formation was concomitant with characteristic microseismic drumbeats at depths 0 5 1 km in addition the seismic record shows two larger earthquakes with similar seismic signatures in august 2006 which we conclude represent larger slip amounts along the conduit margin of spine 7 extensive slip resulted in frictional heating on the order of several hundreds of degrees melting the highly viscous crystalline ascending magma plug and forming a pseudotachylyte high ambient temperatures in the conduit resulted in near equilibrium melting and slow recrystallisation thus impeding the development of signature pseudotachylyte characteristics and hindering identification thus frictional melting and recrystallisation in ascending magma plugs may be a common but unidentified phenomena at composite volcanoes worldwide

high pressure phase relations in the system caal4si2o11 naal3si3o11 with implication for na rich cas phase in shocked martian meteorites abstract high pressure phase relations in the system naal 3 si 3 o 11 caal 4 si 2 o 11 were examined at 13 23 gpa and 1600 1900 c using a multianvil apparatus a ca aluminosilicate with caal 4 si 2 o 11 composition designated cas phase is stable above about 13 gpa at 1600 c in the system naal 3 si 3 o 11 caal 4 si 2 o 11 the cas phase dissolving naal 3 si 3 o 11 component coexists with jadeite corundum and stishovite below 22 gpa above which the cas phase coexists with na rich calcium ferrite corundum and stishovite at 1600 c the solubility of naal 3 si 3 o 11 component in the cas solid solution increases with increasing pressure up to about 50 mol at about 22 gpa above which the solubility decreases with pressure the maximum solubility of naal 3 si 3 o 11 component in the cas phase increases with temperature up to around 70 mol at 1900 c at 22 gpa the dissociation of naalsi 2 o 6 jadeite to naalsio 4 calcium ferrite plus stishovite occurs at about 22 gpa lattice parameters of the cas phase with the hexagonal ba ferrite structure change with increase of the naal 3 si 3 o 11 component a axis decreases and c axis slightly increases resulting in decrease of molar volume enthalpies of the cas solid solutions were measured by high temperature drop solution calorimetry techniques the results show that enthalpy of hypothetical naal 3 si 3 o 11 cas phase is much higher than the mixture of naalsi 2 o 6 jadeite corundum and stishovite and is close to that of the mixture of naalsio 4 calcium ferrite corundum and stishovite when we adopt the na ca ratio of 75 25 of the natural na rich cas phase in a shocked martian meteorite zagami the phase relations determined above suggest that the natural cas phase crystallized from melt at pressure around 22 gpa and temperature close to or higher than 2000 2200 c the inferred p t conditions are consistent with those estimated using other high pressure minerals in the shocked meteorite

inhomogeneous precipitation distribution and snow transport in steep terrain 1 the inhomogeneous snow distribution found in alpine terrain is the result of wind and precipitation interacting with the snow surface over topography we introduce and explain preferential deposition of precipitation as the deposition process without erosion of previously deposited snow and thus in absence of saltation a numerical model is developed describing the relevant processes of saltation suspension and preferential deposition the model uses high resolution wind fields calculated with a meteorological model arps the model is used to simulate a 120 h snow storm period over a steep alpine ridge for which snow distribution measurements are available the comparison to measurements shows that the model captures the larger scale snow distribution patterns and predicts the total additional lee slope loading well however the spatial resolution of 25 m is still insufficient to capture the smaller scale deposition features observed the model suggests that the snow distribution on the ridge scale is primarily caused by preferential deposition and that this result is not sensitive to model parameters such as turbulent diffusivity drift threshold or concentration in the saltation layer

grounding line migration and high resolution calving dynamics of jakobshavn isbrae west greenland 1 we performed three field campaigns in 2004 2007 and 2010 at the southern margin of the jakobshavn isbrae west greenland in order to infer flow velocities and their changes from photogrammetric time lapse imagery with a temporal resolution of 20 min and a spatial spacing of about 30 m on the glacier surface area wide analysis of more than 3000 three dimensional trajectories at individual glacier positions allow for both the mapping of the grounding line and the detailed observation of flow variations during major calving events from 2004 to 2010 the grounding line of jakobshavn isbrae retreated 3 5 0 2 km considering previously published results the grounding line retreat amounts to 6 km since 1985 the glacier has an ephemeral floating tongue that can establish during the readvance of the glacier front and break apart after large calving events observations of a major calving event show that an acceleration of flow velocities coincides with the onset of the break up during which flow velocities of up to 70 m d can be reached moreover large vertical displacements of the glacier front in the order of 15 m and lowering of 8 m at positions 500 m beyond the calving front were observed 2 days before the calving event after the break up the glacier slowly adjusts to the new boundary conditions within the next 4 5 days flow velocity variations caused by calving were detected up to 1 km upstream only which indicates that individual calving events have no immediate effect on the large scale glacier dynamics

high pbehavior of anorthite composition and some phase relations of the cao al2o3 sio2 system to the lower mantle of the earth and their geophysical implications 1 multianvil experiments with long experimental durations have been made with the anorthite composition caal2si2o8at pressure temperature p t conditions of 14 25 gpa and 1400 2400 c at subsolidus conditions these experiments demonstrated three phase assemblages grossular gr kyanite ky stishovite st at 14 gpa gr calcium alumino silicate phase cas st at 18 gpa and cas casio3 perovskite capv st at above 20 gpa which are related by the reactions gr ky cas st and gr st cas capv following the method of schreinemakers we combined our data with the literature data to deduce ap tphase diagram for a portion of the cao al2o3 sio2system at subsolidus conditions which subsequently helped to solve some long lasting discrepancies in the high pbehavior of the compositions of anorthite and grossular the crystal chemistry of the cas and capv solid solutions was examined and new substitution mechanisms were firmly established along the solidus the melting reaction at 14 gpa is peritectic while that at 22 gpa is eutectic for both pressures st is the first phase to melt out and the melt is generally andesitic for the an composition its density starts to be significantly higher than the density of pyrolite at 2 5 gpa a much lower pressure than that for the or ab or qtz composition 7 5 10 gpa so that the an enriched continental crust material should readily plunge into the upper mantle

electron microscopy of high pressure phases synthesized from natural garnets in a diamond anvil cell implications for the mineralogy of the lower mantle abstract in order to identify the crystalline hosts for aluminium and calcium in the deep mantle the high pressure transformations of natural garnets pyrope grossular and fe rich garnet have been prepared at high pressures 40 and 50 gpa and temperatures between 1000 and 2500 k in a laser heated diamond anvil cell dac the recovered high pressure phases have been studied by analytical transmission electron microscopy atem the host minerals for al and ca appear to depend on temperature and iron content 1 at moderate temperature and without significant amounts of iron in the starting material the main host minerals for ca and al aluminium are casio 3 perovskite and a compound with an unknown structure and a ca mg al 2 sio 6 composition 2 at higher temperature the main host minerals for ca and al are respectively casio 3 perovskite and a new high pressure phase of al 2 sio 5 having the v 3 o 5 structure 3 when the iron content is sufficiently large in the starting material fe fe mg 15 the major host mineral for ca and al is a compound with a hollandite type structure and a ca mg fe al 2 si 2 o 8 composition whatever the temperature the solubility of al in mg perovskite was also studied it appears that this solubility strongly decreases with increasing pressure and slightly increases with temperature such behaviour of al in the deep mantle could lead to the occurrence of a progressive phase change in the lower mantle mineralogical models of the deep mantle are then discussed in the light of the above results

plastic deformation of garnets systematics and implications for the rheology of the mantle transition zone abstract plastic properties of materials with garnet structure have been studied under wide temperature conditions ranging from room temperature to 95 of the melting temperatures using uniaxial compression and hot microhardness tests garnets studied include single crystals of oxide garnets y 3 al 5 o 12 gd 3 ga 5 o 12 and y 3 fe 5 o 12 and silicate garnets various solid solutions including grossular almandine andradite pyrope spessartine and uvarovite both uniaxial compression and hot hardness tests indicate that there is a general trend in the plasticity of garnets when the data are compared at normalized conditions t t m and and that the resistance to plastic deformation in garnets is significantly higher than most of the other minerals in the earth s mantle based on both stress dip tests and microstructural observations it is proposed that the creep strength of garnet is largely controlled by the resistance to dislocation glide rather than by recovery processes this conclusion is consistent with the high peierls stress inferred from the hot hardness tests the high peierls stress in garnets is presumably due to the large unit cell i e long burgers vectors and or the bcc packing which are common to all garnets we postulate therefore that the present results can be applied to the strength of high pressure garnet majorite and suggest that garnet rich layers in the earth such as subducted oceanic crust in the transition zone or a possibly garnet rich bottom part of the transition zone will be considerably stronger than surrounding regions

volcano geodesy recent developments and future challenges abstract ascent of magma through earth s crust is normally associated with among other effects ground deformation and gravity changes geodesy is thus a valuable tool for monitoring and hazards assessment during volcanic unrest and it provides valuable data for exploring the geometry and volume of magma plumbing systems recent decades have seen an explosion in the quality and quantity of volcano geodetic data new datasets some made possible by regional and global scientific initiatives as well as new analysis methods and modeling practices have resulted in important changes to our understanding of the geodetic characteristics of active volcanism and magmatic processes from the scale of individual eruptive vents to global compilations of volcano deformation here we describe some of the recent developments in volcano geodesy both in terms of data and interpretive tools and discuss the role of international initiatives in meeting future challenges for the field

low cost volcano deformation monitoring optical strain measurement and application to mount st helens data summary this paper describes an innovative method of volcano deformation measurements applied to camera images taken from the 2004 2008 eruption period at mount st helens dome growth was thought to be characterized by sustained near linear rates of a solid dacite plug through spatial digital image correlation dic analysis of the camera images new evidences arise that the deformation and strain rate of the spine was more complex dic yielded cumulative and incremental displacements strain and shear planes at decimetre resolution it was found that dome extrusion rates are highly non linear decelerating prior to partial collapse followed by a pronounced dome extrusion increase and direction change associated processes have been identified through dic such as shallow landslides and reworking of talus apron material the work highlights the strengths of camera strain monitoring and illustrates that dome growth and collapse is a very dynamic process complexly interplaying with the surrounding

sector collapse forming at casita volcano nicaragua catastrophic sector collapse occurs when a volcano becomes structurally unable to support its own load one process particularly capable of weakening the edifice is hydrothermal activity it can produce high pore pressures and alter strong rock to clays alteration can extend progressively over long periods 100 yr allowing deformation to develop slowly before collapse an important finding is that structures produced by such deformation are recognizable and could permit collapse prediction we present the case of casita nicaragua where hydrothermal activity has been weakening the edifice core causing flank spreading altering original constructional shape and steepening flank slopes one side is slumping outward producing a crescentic scar with a basal bulge we identify this feature as the site of a potential sector collapse with conditions ripe for failure

subevents of long period seismicity implications for hydrothermal dynamics during the 2004 2008 eruption of mount st helens 1 one of the most striking aspects of seismicity during the 2004 2008 eruption of mount st helens msh was the precise regularity in occurrence of repetitive long period lp or drumbeat events over sustained time periods however this precise regularity was not always observed and at times the temporal occurrence of lp events became more random in addition accompanying the dominant lp class of events during the 2004 2008 msh eruption there was a near continuous randomly occurring series of smaller seismic events these subevents are not always simply small amplitude versions of the dominant lp class of events but appear instead to result from a separate random process only loosely coupled to the main lp source mechanism we present an analysis of the interevent time and amplitude distributions of the subevents using waveform cross correlation to separate lp events from the subevents we also discuss seismic tremor that accompanied the 8 march 2005 phreatic explosion event at msh this tremor consists of a rapid succession of lps and subevents triggered during the explosion in addition to broadband noise from the sustained degassing immediately afterward seismicity returned to the pre explosion occurrence pattern this triggering in relation to the rapid ejection of steam from the system and subsequent return to pre explosion seismicity suggests that both seismic event types originated in a region of the subsurface hydrothermal system that was 1 in contact with the reservoir feeding the 8 march 2005 phreatic explosion but 2 not destroyed or drained by the explosion event finally we discuss possible thermodynamic conditions in a pressurized hydrothermal crack that could give rise to seismicity pressure drop estimates for typical lp events are not generally large enough to perturb pure water in a shallow hydrothermal crack into an unstable state however dissolved volatiles such as co2 may lead to a more unstable system increasing the seismogenic potential of a hydrothermal crack subject to rapid heat flux the interaction of hydrothermal and magmatic systems beneath msh in 2004 2008 thus appears able to explain a wide range of observed phenomena including subevents lp events larger md 2 events and phreatic explosions

subduction of continental crust and terrigenous and pelagic sediments an experimental study abstract an important role for the recycling of terrigenous sediments in the mantle was proposed by armstrong 1 2 aspects of this hypothesis have been tested via an experimental study of phase equilibria in a composition similar to that of average upper continental crust over the pressure interval 6 24 gpa this composition is sufficiently close to those of the principal argillaceous and siliceous classes of pelagic sediments to use the results to interpret the behaviour of these latter sediments in addition to terrigenous sediments during subduction the subsolidus phase relationships displayed by lithologies derived from these materials are complex with major roles being played by k hollandite garnet na clinopyroxene and stishovite continentally derived lithologies achieve densities similar to or greater than surrounding mantle at depths greater than 200 km the geodynamical implications of these buoyancy relationships are discussed a reconnaissance study has also been made to assess the melting and element partitioning behaviours in the subducted continental crust lithologies during partial melting at relatively low pressures 5 10 gpa orthoclase wadeite and k hollandite are eliminated near the solidus whereas the stability field of na clinopyroxene extends to temperatures well above the solidus liquids formed by small to moderate degrees of partial melting of subducted continentally derived lithologies in this pressure interval have high k na ratios and high sio2 contents at higher pressures 16 24 gpa the stability fields of k hollandite and stishovite extend towards the liquidus whereas sodium bearing phases are eliminated much closer to the solidus resultant partial melts consequently possess relatively low k na ratios and sio2 contents lead possesses a high crystal liquid partition coefficient in k hollandite whereas uranium is excluded the broad stability field of k hollandite during partial melting of these lithologies at pressures above 15 gpa therefore has the capacity to cause fractionation of lead from uranium the petrological and geochemical implications of these results are discussed in the context of the partial melting of terrigenous materials during subduction and the interactions of the partial melts with the surrounding mantle

improved constraints on the estimated size and volatile content of the mount st helens magma system from the 2004 2008 history of dome growth and deformation 1 the history of dome growth and geodetic deflation during the 2004 2008 mount st helens eruption can be fit to theoretical curves with parameters such as reservoir volume bubble content initial overpressure and magma rheology here assumed to be newtonian viscous with or without a solid plug in the conduit center data from 2004 2008 are consistent with eruption from a 10 25 km3 reservoir containing 0 5 2 bubbles an initial overpressure of 10 20 mpa and no significant sustained recharge during the eruption we used curve fits to project the eruption s final duration and volume early projections predicted a final volume only about half of the actual value but projections increased with each measurement implying a temporal increase in reservoir volume or compressibility a simple interpretation is that early effusion was driven by a 5 10 km3 integrated core of fluid magma this core expanded with time through creep of semi solid magma and host rock

the lusi drone a multidisciplinary tool to access extreme environments abstract extreme and inaccessible environments are a new frontier that unmanned and remotely operated vehicles can today safely access and monitor the lusi mud eruption ne java island indonesia represents one of these harsh environments that are totally unreachable with traditional techniques here boiling mud is constantly spewed tens of meters in height and tall gas clouds surround the 100 m wide active crater the crater is surrounded by a 600 m diameter circular zone of hot mud that prevents any approach to investigate and sample the eruption site in order to access this active crater we designed and assembled a multipurpose drone the lusi drone is equipped with numerous airborne devices suitable for use on board of other multicopters during the missions three cameras can complete 1 video survey 2 high resolution photogrammetry of desired and preselected polygons and 3 thermal photogrammetry surveys with infra red camera to locate hot fluids seepage areas or faulted zones crater sampling and monitoring operations can be pre planned with a flight software and the pilot is required only for take off and landing a winch allows the deployment of gas mud and water samplers and contact thermometers to be operated with no risk for the aircraft during the winch operations that can be performed automatically the aircraft hovers at a safety height until the tasks controlled by the winch embedded processor are completed the drone is also equipped with gps connected co2 and ch4 sensors gridded surveys using these devices allowed obtaining 2d maps of the concentration and distribution of various gasses over the area covered by the flight path the device is solid stable even with significant wind affordable and easy to transport the lusi drone successfully operated during several expeditions at the ongoing active lusi eruption site and proved to be an excellent tool to study other harsh or unreachable sites where operations with more conventional methods are too expensive dangerous or simply impossible

phase transition in casio3 perovskite abstract a phase transition in pure casio3 perovskite was investigated at 27 to 72 gpa and 300 to 819 k by in situ x ray diffraction experiments in an externally heated diamond anvil cell the results show that casio3 perovskite takes a tetragonal form at 300 k and undergoes phase transition to a cubic structure above 490 580 k in a pressure range studied here the transition boundary is strongly temperature dependent with a slightly positive dt dp slope of 1 1 1 3 k gpa it is known that the transition temperature depends on al2o3 content dissolved in casio3 perovskite kurashina et al phys earth planet inter 145 2004 67 74 the phase transition in casio3 3 wt al2o3 perovskite therefore could occur in a cold subducted mid oceanic ridge basalt morb crust at about 1200 k in the upper to mid lower mantle this phase transition is possibly ferroelastic type and may cause large seismic anomalies in a wide depth range

numerical modeling of blowing and drifting snow in alpine terrain in mountainous regions snow transport due to wind significantly influences snow distribution and as a result avalanche danger a physically based numerical two layer model is developed to simulate blowing and drifting snow in alpine terrain one layer describes the driving wind field and the transport in suspension the description is based on the atmospheric boundary layer equations using an e model for the turbulent closure the second layer describes the transport due to saltation including erosion and deposition of snow here conservation equations for mass and momentum are formulated for the mixture of snow and air particle trajectory calculations are used to parameterize quantities characterizing the saltation layer both layers are mutually coupled by boundary conditions a two way coupling between particles and airflow is taken into account comparisons between simulation results and field measurements around an alpine crest show encouraging results

compressibility of the calcium aluminosilicate cas phase to 44 gpa abstract in situ x ray diffraction measurements on a calcium aluminosilicate cas phase have been carried out using a laser heated diamond anvil cell up to a pressure of 44 gpa employing a synchrotron radiation source cas is the major mineral formed from sediments subducted into the earth s mantle the sample was heated using a yag laser after each pressure increment to relax the deviatoric stress in the sample x ray diffraction measurements were carried out at t 300 k using an angle dispersive technique the pressure was calculated using an internal platinum metal pressure calibrant the birch murnaghan equation of state for the cas phase obtained from the experimental unit cell parameters showed a density of 0 3 888 g cm 3 and a bulk modulus of k 0 229 9 gpa for k 0 4 7 0 7 when the first pressure derivative of the bulk modulus was fixed at k 0 4 then the value of k 0 239 2 gpa from the experimental compressibility the density of the cas phase was observed to be lower than the density of co existing al bearing stishovite calcium perovskite calcium ferrite type phases and fe al bearing mg perovskite in subducted sediments in the lower mantle therefore the density of subducted sediments in the lower mantle decreases with increasing mineral proportion of the cas phase

pathways for degassing during the lava dome eruption of mount st helens 2004 2008 the ability of volatiles to escape rising magma regulates the explosivity of a volcanic system during silicic lava dome eruptions strain localization at the conduit margin occurs during magma ascent creating a damage halo with implications for gas escape here we report the first systematic study of permeability network anisotropy across the marginal shear zone of the a d 2004 2008 lava dome at mount st helens washington state usa the results show increasingly large permeability anisotropy of as much as four orders of magnitude over 4 m moving from the interior of the spine through the damage halo we find the permeability to be essentially isotropic in the spine interior but highly anisotropic in the damage zone and fault core our examination of the dome rocks reveals that the permeability anisotropy depends strongly on the presence of vertically oriented shear layers here we show that the rate of escape of volatiles will be several orders of magnitude higher vertically through a conduit margin shear zone than horizontally into the conduit wall

dome growth and coulee spreading controlled by surface morphology as determined by pixel offsets in photographs of the 2006 merapi eruption abstract at many explosive volcanoes viscous domes extrude which are destroyed by complete or partial collapses although the growth and development of silicic domes and the associated flow and collapse mechanisms are of vital importance for understanding the occurrence and scale of pyroclastic flows quantitative measurements of dome deformations are limited we report on a sequence of photographs taken of a growing and deforming dome a sequence in 2006 featuring the merapi dome taken from similar camera positions allow the application of a digital image correlation algorithm the aim being to detect and explore the temporal evolution of pixel offsets the results suggest that the dome underwent deformation in two regions between september and october 2006 i dome growth and spreading at the volcano summit and ii coulee flow through a narrow canyon the latter is associated with strain localization and flow acceleration which indicates that the displacements and flow velocities at silicic domes are governed by the topographic structure into which the flows develop the downslope motion of the distal parts of the flow and apron slumps continued during episodes of dome extrusion by gravitational spreading an analysis of the 2006 merapi dome and coulee displacement also provides insights into processes that may occur along the newly established southerly eruption direction which also may have influenced pyroclastic flows associated with the 2010 eruption

morphological and structural changes at the merapi lava dome monitored in 2012 15 using unmanned aerial vehicles uavs abstract dome building volcanoes undergo rapid and profound topographic changes that are important to quantify for the purposes of hazard assessment however as hazardous lava domes often develop on high altitude volcanoes that exhibit steep sided topography it is challenging to obtain direct field access and thus to analyze these morphological and structural changes merapi volcano in indonesia is a type example of such a volcano as soon after its 2010 eruption a new lava dome developed this dome was partially destroyed during six distinct steam driven explosions that occurred between 2012 and 2014 here we investigate the topographic and structural changes associated with these six steam driven explosions by comparing close range photogrammetric data obtained before and after these explosions to accomplish this we performed two uav campaigns in 2012 and 2015 by applying the structure from motion sfm technique we are able to construct three dimensional point clouds assess their quality by comparing them to a terrestrial laser scanning tls dataset and generate high resolution digital elevation models dems and photomosaics the comparison of these two dems and photomosaics reveals changes in topography and the appearance of fractures in the 2012 dataset we find a dense fracture network striking to the nnw sse in the post eruptive 2015 dataset we see that this nnw sse fracture trend is much more strongly expressed we also detect the formation of aligned and elongated explosion craters which are associated with the removal of over 200 000 m3 of dome material most of which 70 was deposited outside the crater region therefore this study suggests that the locations of the steam driven explosions at merapi volcano were controlled by the reactivation of preexisting structures moreover some of the newly developed and reactivated fractures delineate a block on the southern slope of the dome which could become structurally unstable and potentially lead to rock avalanche hazards this study therefore demonstrates the significance of characterizing structural fingerprints during the development of lava domes and exemplifies the value of topographic and fracture mapping which is becoming increasingly feasible when using uavs even on high and steep stratovolcanoes

rapid low cost photogrammetry to monitor volcanic eruptions an example from mount st helens washington usa we describe a low cost application of digital photogrammetry using commercially available photogrammetric software and oblique photographs taken with an off the shelf digital camera to create sequential digital elevation models dems of a lava dome that grew during the 2004 2008 eruption of mount st helens msh volcano renewed activity at msh provided an opportunity to devise and test this method because it could be validated against other observations of this well monitored volcano the datasets consist of oblique aerial photographs snapshots taken from a helicopter using a digital single lens reflex camera twelve sets of overlapping digital images of the dome taken during 2004 2007 were used to produce dems and to calculate lava dome volumes and extrusion rates analyses of the digital images were carried out using photogrammetric software to produce three dimensional coordinates of points identified in multiple photos the evolving morphology of the dome was modeled by comparing successive dems results were validated by comparison to volume measurements derived from traditional vertical photogrammetric surveys by the us geological survey cascades volcano observatory our technique was significantly less expensive and required less time than traditional vertical photogrammetric techniques yet it consistently yielded volume estimates within 5 of the traditional method this technique provides an inexpensive rapid assessment tool for tracking lava dome growth or other topographic changes at restless volcanoes

a new natural high pressure na ca hexaluminosilicate caxna1 x al3 xsi3 xo11 in shocked martian meteorites a ca na hexaluminosilicate whose ca end member was previously synthesized in numerous high pressure experiments has been identified by raman spectroscopy in heavily shocked martian meteorites this mineral has a structural formula close to caxna1 x al3 xsi3 xo11 and is similar to the calcium aluminum silicate phase previously synthesized in high pressure experiments performed on anorthite and rocks of basaltic composition this new mineral occurs in shock melt pockets in two distinct settings and is intimately intergrown with sio2 stishovite the first setting encountered in zagami consists of idiomorphic equant crystals overgrown by acicular stishovite that crystallized from a melt of labradorite composition the second setting contains the na ca hexaluminosilicate phase intergrown with stishovite and hollandite and was formed during partial melting at high pressures the mineralogical association na ca hexaluminosilicate stishovite was observed in shock melt pockets which have distinct bulk compositions in seven martian shergottites this new mineral represents after majorite the second natural occurrence of a silicate mineral with silicon in both four and six coordination the assemblage stishovite na ca hexalummosilicate sets constraints on the pressure and temperature conditions that prevailed during shock in some of the studied meteorites the na ca hexaluminosilicate mineral is a potential carrier of al and na during subduction of oceanic crust in the lower mantle of the earth c 2003 elsevier b v all rights reserved

phase relations of harzburgite and morb up to the uppermost lower mantle conditions precise comparison with pyrolite by multisample cell high pressure experiments with implication to dynamics of subducted slabs

experiments on the indentation process during cryptodome intrusions new insights into mount st helens deformation scaled experiments were carried out to study the deformation of a volcanic edifice by forcible intrusion of a cryptodome as the magma analogue is injected vertically into a sand cone asymmetric deformation is caused by the formation of a curved major shear fault which dips inward from one side of the cone to the opposite edge of the intrusion the path of the ascending silicone deviates to follow the trajectory of the fault and a lateral bulge grows slowly from the footwall of the fault the oblique push makes the bulge migrate outward causing extension upslope to form an asymmetric graben in the hanging wall of the major shear fault we suggest that the pattern of internal deformation within mount st helens prior to the may 18 1980 eruption was similar to that observed in our scaled models

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

instruments and methods simulating complex snow distributions in windy environments using snowtran 3d we present a generalized version of snowtran 3d version 2 0 that simulates wind related snow distributions over the range of topographic and climatic environments found globally this version includes three primary enhancements to the original liston and sturm 1998 model 1 an improved wind sub model 2 a two layer sub model describing the spatial and temporal evolution of friction velocity that must be exceeded to transport snow the threshold friction velocity and 3 implementation of a three dimensional equilibrium drift profile sub model that forces snowtran 3d snow accumulations to duplicate observed drift profiles these three sub models allow snowtran 3d to simulate snow transport processes in variable topography and different snow climates in addition snowtran 3d has been coupled to a high resolution spatially distributed meteorological model micromet to provide more realistic atmospheric forcing data micromet distributes data precipi tation wind speed and direction air temperature and relative humidity obtained from meteorological stations and or atmospheric models located within or near the simulation domain snowtran 3d has also been coupled to a spatially distributed energy and mass balance snow evolution modeling system snowmodel designed for application in any landscape and climate where snow is found snowtran 3d is typically run using temporal increments ranging from 1 hour to 1 day horizontal grid increments ranging from 1 to 100 m and time spans ranging from individual storms to entire snow seasons

high pressure transitions of diopside and wollastonite phase equilibria and thermochemistry of camgsi2o6 casio3 and casi2o5 catisio5 system abstract phase transitions of camgsi2o6 diopside and casio3 wollastonite were examined at pressures to 23 gpa and temperatures to 2000 c using a kawai type multiavil apparatus enthalpies of high pressure phases in casio3 and in the casi2o5 catisio5 system were also measured by high temperature calorimetry at 17 18 gpa diopside dissociates to casio3 rich perovskite mg rich mg ca sio3 tetragonal garnet gt above about 1400 c the solubilities of casio3 in garnet and mgsio3 in perovskite increase with temperature at 17 18 gpa below about 1400 c diopside dissociates to ca perovskite mg2sio4 stishovite the mg si phases coexisting with ca perovskite change to mg2sio4 stishovite to ilmenite and finally to mg perovskite with increasing pressure casio3 wollastonite transforms to the walstromite structure and further dissociates to ca2sio4 larnite casi2o5 titanite the latter transition occurs at 9 11 gpa with a positive clapeyron slope at 1600 c larnite titanite transform to casio3 perovskite at 14 6 0 6 gpa calibrated against the transition pressure of mg2sio4 the enthalpies of formation of casio3 walstromite and casi2o5 titanite from the mixture of cao and sio2 quartz at 298 k have been determined as 76 1 2 8 and 27 8 2 1 kj mol respectively the latter was estimated from enthalpy measurements of titanite solid solutions in the system casi2o5 catisio5 because casi2o5 titanite transforms to a triclinic phase upon decompression the enthalpy difference between titanite and the triclinic phase is only 1 5 4 8 kj mol using these enthalpies of formation and those of larnite and casio3 perovskite the transition boundaries in casio3 have been calculated the calculated boundaries for the wollastonite walstromite larnite titanite transitions are consistent with the experimental determinations within the errors the calculated boundary between larnite titanite and ca perovskite has a slope of 1 3 1 8 0 4 mpa k and is located at a pressure about 2 gpa higher than that determined by am mineral 79 1994 1219

degassing processes during lava dome growth insights from santiaguito lava dome guatemala abstract eruptions of intermediate magma may be explosive or effusive the development of open system degassing has been proposed as a pre requisite for effusion of intermediate magma however processes leading to open system degassing are poorly understood to better understand degassing processes during lava dome extrusion we report high temporal resolution so2 emission rate measurements collected with an ultra violet imaging camera at santiaguito guatemala santiaguito is an ideal case study as the dome lava is compositionally very similar to products of the 1902 plinian eruption of the parental santa maria volcano we find that degassing is weak 0 4 1 kg s 1 but continuous and explosions are associated with small increases in emission rates up to 2 3 kg s 1 continuous repose degassing occurs through a shallow cap rock which likely represents a proto crust on the block lava flow which is extruded from the same vent the continual permeability of the upper conduit argues against a mechanism of explosion triggering in which gas pressure builds beneath a viscous cap rock or plug rather we consider degassing data better consistent with a model of shear fracturing at the conduit margins using field constraints we model the viscosity of santiaguito magma as a function of depth and show that conditions for shear fracturing are met from 150 600 m to the surface this is in line with independent estimates of explosion initiation depth we show that repose timescales are orders of magnitude longer than the timescale for shear fracture and suggest that explosions are triggered when a continuous network of smaller scale fractures develops at which point decompression occurs and an explosion is triggered fracture healing occurs by viscous relaxation however near to the surface where viscosity is highest an unconsolidated gouge layer may develop our model implies that the observed explosions are a by product of extrusion shear fracturing can drive open system degassing of crystal rich intermediate magma at shallow levels in the conduit as high magma viscosity is able to overcome the low strain rates associated with slow ascent of magma

an experimental study of the garnet perovskite transformation in the system mgsio3mg3al2si3o12 phase transformations in the system mgsio3 mg3al2si3o12 have been studied at pressures between 22 and 28 gpa at 1500 c using a multi anvil apparatus majorite garnet with less than about 10 wt al2o3 was found to completely transform into an orthorhombic perovskite structure over a pressure interval between 24 and 27 gpa whereas pyrope garnet disproportionated into sub aluminous perovskite plus corundum solid solutions at pressures greater than 26 5 gpa alumina contents in the perovskite structure are dependent on temperature and increase from 11 wt at 1500 c to 17 wt at 1800 c at a pressure of 27 gpa the alumina content of perovskite also in creases with increasing pressure such that aluminous perovskite with the pyrope composition 25 mol al2o3 should be formed by about 30 40 gpa these observations are consistent with our recent experimental results on a pyrolite composition which demonstrated that no separate aluminous phase exists in the upper part of the lower mantle the entire inventory of al2o3 in pyrolite can be accommodated in solid solution in magnesium silicate perovskite

the transition from endogenous to exogenous growth of lava domes with the development of shear bands the transition from an endogenous to an exogenous regime of lava dome growth must be achieved by the formation of discontinuities within the dome such transitions and vice versa are an important characteristic of most long lived lava domes and often coincide with significant changes in the dynamics of magma supply and lava dome collapse events for the purpose of this paper following recent experimental and observational evidence we assume that such a transition occurs when shear bands are generated a model for the formation of shear bands and therefore the growth transition within a dome and coupled conduit domain is presented shear bands are most likely to initiate at the junction of the conduit and base of the dome where the shear stress experienced between new lava entering the dome and existing lava is greatest stress accumulation within the shear bands is likely to lead to brittle shear resulting in the formation of fractures finite element modelling of lava flow shows that such shear bands only develop for certain extrusion rates and lava viscosities similarly the growth regime of the lava dome will depend upon the extrusion rate and viscosity within the conduit which is largely controlled by volatile loss and the growth of crystals in the upper part of the conduit we consider a simplified rheology during lava dome growth considering isothermal conditions with crystal growth the development of shear bands in the conduit is explored with a numerical model parameterized with values appropriate for soufriere hills volcano montserrat during october to december 1996 this lava dome forming eruption experienced a transition from endogenous to exogenous growth as it grew in height by about 90 m modelling indicates that the observed fall in magma extrusion rate from about 2 0 m3s 1 to 0 5 m3s 1 as a result of the increased pressure head from the dome and the evolution in viscosity could have subsequently changed the dome growth regime due to the development of shear bands our models provide insight into the shear stress fields possible within the conduit and the shear stresses required for shear band development

in situ observation of the decomposition of kyanite at high pressures and high temperatures in situ observations of the decomposition of kyanite al 2 sio 5 were carried out in a multi anvil high pressure apparatus using synchrotron radiation where the phase change from kyanite to stishovite corundum was observed at high pressures and high temperatures the phase boundary of this decomposition at t 1200 1900 k and p 5 15 gpa was determined to be p gpa 10 2 0 0016 t k previous studies using the quench method showed a discrepancy in the transition pressure of the decomposition our results using in situ observations resolve this dispute

pointcatcher software analysis of glacial time lapse photography and integration with multitemporal digital elevation models terrestrial time lapse photography offers insight into glacial processes through high spatial and temporal resolution imagery however oblique camera views complicate measurement in geographic coordinates and lead to reliance on specific imaging geometries or simplifying assumptions for calculating parameters such as ice velocity we develop a novel approach that integrates time lapse imagery with multi temporal digital elevation models to derive full 3d coordinates for natural features tracked throughout a monoscopic image sequence this enables daily independent measurement of horizontal ice flow and vertical ice melt velocities by combining two terrestrial laser scanner surveys with a 73 day sequence from solheimajokull iceland variations in horizontal ice velocity of 10 were identified over timescales of 25 days an overall surface elevation decrease of 3 0 m showed rate changes asynchronous with the horizontal velocity variations demonstrating a temporal disconnect between the processes of ice surface lowering and mechanisms of glacier movement our software pointcatcher is freely available for user friendly interactive processing of general time lapse sequences and includes monte carlo error analysis and uncertainty projection onto dem surfaces it is particularly suited for analysis of challenging oblique glacial imagery and we discuss good features to track both for correction of camera motion and for deriving ice velocities

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

phase relations of caal4si2o11 at high pressure and high temperature with implications for subducted continental crust into the deep mantle abstract phase relations of the cas phase caal4si2o11 have been investigated at pressures of 10 23 gpa and at temperatures of 1000 1600 c by means of the quench method using the kawai type high pressure apparatus an assemblage of grossular gr corundum cor kyanite ky is stable up to about 10 gpa and at the temperatures examined the assemblage converts into the cas phase at 1600 c and higher pressures below 1450 c however the assemblage first changes to that of gr cor stishovite st corresponding to the dissociation of ky into cor st and then converts to the cas phase with increasing pressure the gr cor st cas boundary has a negative dp dt slope and the gr ky cor cas boundary has a near horizontal slope the triple point at which gr cor ky st and the cas phase coexist is located at around 11 5 gpa and 1450 c stability of the cas phase up to 23 gpa and 1600 c indicates that the cas phase is an important host of al and ca in the continental crust subducted into deep mantle comparison of the densities between the pyrolitic mantle and the subducted continental crust indicates that the continental crust provides a plunging force to the slab subducted into the upper mantle and transition zone whereas the continental crust in turn gives a buoyancy in the lower mantle as the consequence of the substantial changes in mineral assemblage in both the continental crust and pyrolitic mantle through the 660 km discontinuity the formation of the cas phase plays an important role in changing the density of the subducting continental crust

causes and consequences of pressurisation in lava dome eruptions abstract high total and fluid pressures develop in the interior of high viscosity lava domes and in the uppermost parts of the feeding conduit system as a consequence of degassing two effects are recognised and are modelled quantitatively first large increases in magma viscosity result from degassing during magma ascent strong vertical gradients in viscosity result and large excess pressures and pressure gradients develop at the top of the conduit and in the dome calculations of conduit flow show that almost all the excess pressure drop from the chamber in an andesitic dome eruption occurs during the last several hundred metres of ascent second microlites grow in the melt phase as a consequence of undercooling caused by gas loss rapid microlite growth can cause large excess fluid pressures to develop at shallow levels theoretically closed system microlite crystallization can increase local pressure by a few tens of mpa although build up of pressure will be countered by gas loss through permeable flow and expansion by viscous flow microlite crystallization is most effective in causing excess gas pressures at depths of a few hundred metres in the uppermost parts of the conduit and dome interior some of the major phenomena of lava dome eruptions can be attributed to these pressurisation effects including spurts of growth cycles of dome growth and subsidence sudden onset of violent explosive activity and disintegration of lava during formation of pyroclastic flows the characteristic shallow level long period and hybrid seismicity characteristic of dome eruptions is attributed to the excess fluid pressures which are maintained close to the fracture strength of the dome and wallrock resulting in fluid movement during formation of tensile and shear fractures within the dome and upper conduit

back analysis of drifting snow measurements over an instrumented mountainous site the nemo numerical model of drifting snow whose general outlines are presented in this paper is based on a physical model for saltation and turbulent diffusion the model needs a set of input parameters including fall velocity threshold shear velocity shear velocity mass concentration and roughness which are obtained from empirical formulae and wind speed measured at a given height to better determine the required field data in an alpine context our experimental site col du lac blanc 2700 m a s l french alps was first equipped with one anemometer and blowing snow acoustic sensors which proved not to be accurate enough for research purposes in the current state of development even though a new calibration curve was used we therefore set up a snow particle counter and we returned to the traditional robust mechanical traps and a 10 m mast with six anemometers two temperature sensors and a depth sensor to better determine friction velocity and aerodynamic roughness based on the studied drifting snow events we conclude 1 the proportionality of the aerodynamic roughness to the square of the friction velocity was confirmed but with a varying proportionality ratio depending on the snowdrift event 2 values of s u f were relatively well approximated by empirical formulae from data originating from antarctica and 3 snowdrift concentration profiles obtained by pomeroy s semi empirical formulae for the saltation layer coupled with a theoretical approach for the diffusion layer overestimated the concentration profiles for the studied blowing snow event

a two species model of aeolian sand transport the transport of sand by wind results from the equilibrium between the erosion of grains dragged by the flow and the resulting slow down of the wind velocity the dynamical mechanisms governing the saturation of the sand flux are investigated theoretically we first demonstrate that previous models based on the assumption that all the grains have the same trajectory are either not self consistent or lead to unstable solutions a model based on a discrete number of states is derived which solves these problems two well defined species of grain appear which correspond to saltons high energy grains and reptons grains ejected from the sand bed by the impact of saltons they play specific roles the negative feedback of the transport on the wind is limited to the reptation layer while most of the transport is due to saltation the model is further simplified benefiting from the existence of these two species and the dependencies of the threshold velocity the saturated flux the aerodynamic roughness and the saturation length are derived and compared to experimental measurements

computational fluid dynamic cfd simulation of snowdrift in alpine environments including a local weather model for operational avalanche warning a new continuum approach to snowdrift modelling is introduced in addition numerical studies are carried out to identify the influence of time varying wind conditions on snowdrift simulations we compare the snowdrift patterns at grimming mountain austria derived using a time averaged wind field and a time varying wind field obtained from the numerical weather prediction model inca the results show significant differences in the deposition patterns and snow depth even after a 6 hour drift period using time averaged boundary conditions leads to an underprediction of the resulting snow depth caused by averaging the wind speed which lets gusts of wind disappear while snow transport is a non linear function of the wind speed using numerical weather prediction models for snowdrift simu lation therefore provides enhanced knowledge of the snow depth for local avalanche warning services

wind influence on snow depth distribution and accumulation over glaciers 1 in mountain regions wind is known to cause snow redistribution while physically based models of snow redistribution have been developed for flat to gently rolling terrain extension of these findings to steep terrain has been limited by the complexity of wind fields in such areas in this study we applied a nonhydrostatic and compressible atmospheric prediction model to steep alpine topography and compared the results to a fully distributed data set of snow depth estimations the results show reduced horizontal wind velocity as well as an increasing downward vertical wind velocity over areas with the largest winter accumulation which are mostly glacierized we show that the wind velocity normal to the local surface which should be zero in a nondivergent flow field and is a direct measure of increased or decreased local deposition is a function of small scale features of local topography the correlation between wind fields snow accumulation and glacierization suggests that accurate modeling of wind fields over glacierized areas in complex terrain is a key factor for understanding the mass balance distribution of glaciers

metastable mantle phase transformations and deep earthquakes in subducting oceanic lithosphere earth s deepest earthquakes occur as a population in subducting or previously subducted lithosphere at depths ranging from about 325 to 690 km this depth interval closely brackets the mantle transition zone characterized by rapid seismic velocity increases resulting from the transformation of upper mantle minerals to higher pressure phases deep earthquakes thus provide the primary direct evidence for subduction of the lithosphere to these depths and allow us to investigate the deep thermal thermodynamic and mechanical ferment inside slabs numerical simulations of reaction rates show that the olivine spinel transformation should be kinetically hindered in old cold slabs descending into the transition zone thus wedge shaped zones of metastable peridotite probably persist to depths of more than 600 km laboratory deformation experiments on some metastable minerals display a shear instability called transformational faulting this instability involves sudden failure by localized superplasticity in thin shear zones where the metastable host mineral transforms to a denser finer grained phase hence in cold slabs such faulting is expected for the polymorphic reactions in which olivine transforms to the spinel structure and clinoenstatite transforms to ilmenite it is thus natural to hypothesize that deep earthquakes result from transformational faulting in metastable peridotite wedges within cold slabs this consideration of the mineralogical states of slabs augments the traditional largely thermal view of slab processes and explains some previously enigmatic slab features it explains why deep seismicity occurs only in the approximate depth range of the mantle transition zone where minerals in downgoing slabs should transform to spinel and ilmenite structures the onset of deep shocks at about 325 km is consistent with the onset of metastability near the equilibrium phase boundary in the slab even if a slab penetrates into the lower mantle earthquakes should cease at depths near 700 km because the seismogenic phase transformations in the slab are completed or can no longer occur substantial metastability is expected only in old cold slabs consistent with the observed restriction of deep earthquakes to those settings earthquakes should be restricted to the cold cores of slabs as in any model in which the seismicity is temperature controlled via the distribution of metastability however the geometries of recent large deep earthquakes pose a challenge for any such models transformational faulting may give insight into why deep shocks lack appreciable aftershocks and why their source characteristics including focal mechanisms indicating localized shear failure rather than implosive deformation are so similar to those of shallow earthquakes finally metastable phase changes in slabs would produce an internal source of stress in addition to those due to the weight of the sinking slab such internal stresses may explain the occurrence of earthquakes in portions of lithosphere which have foundered to the bottom of the transition zone and or are detached from subducting slabs metastability in downgoing slabs could have considerable geodynamic significance metastable wedges would reduce the negative buoyancy of slabs decrease the driving force for subduction and influence the state of stress in slabs heat released by metastable phase changes would raise temperatures within slabs and facilitate the transformation of spinel to the lower mantle mineral assemblage causing slabs to equilibrate more rapidly with the ambient mantle and thus contribute to the cessation of deep seismicity because wedge formation should occur only for fast subducting slabs it may act as a parachute and contribute to regulating plate speeds wedge formation would also have consequences for mantle evolution because the density of a slab stagnated near the bottom of the transition zone would increase as it heats up and the wedge transforms to denser spinel favoring the subsequent sinking of the slab into the lower mantle

constraints on the geomorphological evolution of the nested summit craters of lascar volcano from high spatio temporal resolution terrasar x interferometry small scale geomorphological changes that are associated with the formation development and activity of volcanic craters and eruptive vents are often challenging to characterize as they may occur slowly over time can be spatially localized and difficult or dangerous to access using high spatial and high temporal resolution synthetic aperture radar sar imagery collected by the german terrasar x tsx satellite in spotlight mode in combination with precise topographic data as derived from pleiades 1a satellite data we investigate the surface deformation within the nested summit crater system of lascar volcano chile the most active volcano of the central andes our aim is to better understand the structural evolution of the three craters that comprise this system to assess their physical state and dynamic behavior and to link this to eruptive activity and associated hazards using multi temporal sar interferometry mt insar from ascending and descending orbital geometries we retrieve the vertical and east west components of the displacement field this time series indicates constant rates of subsidence and asymmetric horizontal displacements of all summit craters between june 2012 and july 2014 as well as between january 2015 and march 2017 the vertical and horizontal movements that we observe in the central crater are particularly complex and cannot be explained by any single crater formation mechanism rather we suggest that short term activities superimposed on a combination of ongoing crater evolution processes including gravitational slumping cooling and compaction of eruption products as well as possible piston like subsidence are responsible for the small scale geomorphological changes apparent in our data our results demonstrate how high temporal resolution synthetic aperture radar interferometry insar time series can add constraints on the geomorphological evolution and structural dynamics of active crater and vent systems at volcanoes worldwide

image based measurement of flux variation in distal regions of active lava flows 1 understanding the processes involved with the advance of lava flows is critical for improving hazard assessments at many volcanoes here we describe the application of computer vision and oblique photogrammetric techniques to visible and thermal images of active a flows in order to investigate distal flow processes at mount etna sicily photogrammetric surveys were carried out to produce repeated topographic data sets for calculation of volumetric lava flux at the flow fronts velocity profiles from a distal channel were obtained by rectification of a thermal image sequence and are used to investigate the rheological properties of the lava significant variations of the magma flux were observed and pulses of increased flux arrived within the flow front region on timescales of several hours the pulses are believed to be the distal result of more frequent flux changes observed in the vent region hence they reflect the importance of flow processes which are believed to cause the coalescence of flux pulses along the channel system as well as short period variations in effusion rate in considering advance processes for the individual flow fronts it must be assumed that they were fed by a highly unsteady flux which was volumetrically at least an order of magnitude lower than that observed near the vent