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

magma degassing buffered by vapor flow through brecciated conduit margins obsidian pyroclasts a common component of rhyolitic tephra preserve a range of volatile contents which has been used to infer syneruptive conditions of magmatic degassing here we show that the textures of obsidian pyroclasts provide information on physical mechanisms of magma flow and degassing along conduit margins obsidian clasts often contain xenoliths sheared bands of lithic powder and textures consistent with magma autobrecciation these features suggest that pyroclastic obsidian primarily forms near conduit walls where magma fragments and reanneals during ascent we use these observations to develop a degassing model for pyroclastic obsidian from the a d 1340 mono craters california eruptions we suggest that degassing was buffered by continual flux of vapor through highly permeable brecciated magma along conduit walls continuous reequilibration of magma with vapor of relatively constant composition not only explains the co 2 h 2 o and d h 2 o data from mono craters pyroclastic obsidian but also requires much lower magmatic co 2 values than the commonly accepted model of closed system degassing taken together the chemical and physical evidence suggests that magma brecciation along conduit walls aids the degassing of ascending rhyolite

petrology and geochemistry of lava and ash erupted from volcan colima mexico during 1998 2005 abstract lava n 8 and bulk ash samples n 6 erupted between july 1999 and june 2005 were investigated to extend time series compositional and textural studies of the products erupted from volcan colima since 1869 in particular we seek to evaluate the possibility that the current activity will culminate in major explosive plinian style event similar to that in 1913 lava samples continue to show relatively heterogeneous whole rock compositions with some significant mafic spikes 1999 2001 as have prevailed since 1976 groundmass sio2 contents continue trends to lower levels that have prevailed since 1961 in the direction of the still lower groundmass sio2 contents found in 1913 scoriae importantly ash samples from investigated vulcanian style explosive eruptions in 2005 are devoid of particles with micro vesiculated groundmass textures such textures characterized the 1913 scoriae signifying expansion of in situ magmatic gas as the propellant of the 1913 eruption all magmas erupted since 1913 appear to have arrived in the upper volcanic conduit system in a degassed state the small to moderate vulcanian style explosive eruptions which have been common since 1999 16 000 events have blasted ash clouds as high as 11 km a s l and sent pyroclastic flows out to distances of 5 km these eruptions do not appear to be powered by expansion of in situ magmatic gas new small lava domes have been observed in the crater prior to many explosive eruptions these plugs of degassed lava may temporarily seal the conduit and allow the build up of magmatic gases streaming upward from below ahead of rising and degassing magma in this interpretation when gas pressure exceeds the strength of the plug seal in the upper conduit an explosive vulcanian style eruption occurs alternatively these explosive eruptions may represent interactions of hot rock and groundwater phreato magmatic

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

exogenous and endogenous growth of the unzen lava dome examined by satellite infrared image analysis abstract phase 1 of the most recent eruption of unzen volcano japan occurred between 1991 and 1993 and involved the endogenous and exogenous addition of magma to a growing summit lava dome the temporal variation between endogenous and exogenous styles of dome growth has an important bearing on the hazard posed by dome collapse and explosive events however such data are difficult to acquire and have previously only been obtained in a fully quantitative manner for the mount st helens dome in that case using detailed photogrammetry here we investigate these competing dome growth processes at unzen via analysis of their thermal emission signals present in shortwave infrared swir satellite imagery we find that both the endogenous and exogenous growth styles exhibit identifiable swir signatures whose magnitude can be related to their respective magma supply rates we find that the swir radiant area corresponding to endogenous growth is around four times larger than that corresponding to exogenous growth at the same magma discharge rate analysis of time series imagery indicates that like mount st helens unzen experienced a temporally decreasing magma discharge rate during phase 1 as time progressed and the discharge rate fell the growth style of the unzen dome changed from exogenous only through exogenous decreasing and endogenous increasing to endogenous only thus relative growth rates at the endogenous and exogenous areas of the unzen dome appear to be at least partly controlled by the overall magma discharge rate as with mount st helens the cause of this relationship was most likely the formation and strengthening of a brittle crust at the surface vent which impeded exogenous growth more effectively as time elapsed and the discharge rate fell these results suggest the similarity of the processes operating at the unzen and mount st helens domes though important differences remain in that dome growth was basically continuous at unzen whilst at mount st helens growth episodes were interspersed by significant periods of repose

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

fracture and compaction of andesite in a volcanic edifice the failure mode of lava dilatant or compactant depends on the physical attributes of the lava primarily the porosity and pore size and the conditions under which it deforms the failure mode for edifice host rock has attendant implications for the structural stability of the edifice and the efficiency of the sidewall outgassing of the volcanic conduit in this contribution we present a systematic experimental study on the failure mode of edifice forming andesitic rocks porosity from 7 to 25 from volcan de colima mexico the experiments show that at shallow depths 1 km while low porosity 10 lava remains dilatant the failure of high porosity lava is compactant and driven by cataclastic pore collapse although inelastic compaction is typically characterised by the absence of strain localisation we observe compactive localisation features in our porous andesite lavas manifest as subplanar surfaces of collapsed pores in terms of volcano stability faulting in the upper edifice could destabilise the volcano leading to an increased risk of flank or large scale dome collapse while compactant deformation deeper in the edifice may emerge as a viable mechanism driving volcano subsidence spreading and destabilisation the failure mode influences the evolution of rock physical properties permeability measurements demonstrate that a throughgoing tensile fracture increases sample permeability i e equivalent permeability by about a factor of two and that inelastic compaction to an axial strain of 4 5 reduces sample permeability by an order of magnitude the implication of these data is that sidewall outgassing may therefore be efficient in the shallow edifice where rock can fracture but may be impeded deeper in the edifice due to compaction the explosive potential of a volcano may therefore be subject to increase over time if the progressive compaction and permeability reduction in the lower edifice cannot be offset by the formation of permeable fracture pathways in the upper edifice the mode of failure of the edifice host rock is therefore likely to be an important factor controlling lateral outgassing and thus eruption style effusive versus explosive at stratovolcanoes

quaternary deposits and glacial stratigraphy in ireland quaternary stratigraphic studies in ireland have been based largely on lithostratigraphy the division of complex sedimentary sequences into the traditional framework of munsterian and midlandian events has created a series of stratigraphic scenarios which cannot be fully substantiated either by biostratigraphy or by facies basin analysis many of the current problems of glacial stratigraphy in ireland therefore arise directly from the field procedures used and the frameworks used to subdivide sedimentary sequences these problems are centred on the selection of type sites the subdivision of sedimentary sequences into unnatural divisions the concepts of direct and indirect stratigraphy classical models of climatically determined ice advance retreat cycles and the genetic inferences of the term till the conceptual basis of various stratigraphic schemes has changed little since the work of farrington 1934 1966 it is argued that a more realistic approach to description and assessment of glacigenic sediments should be based on basinal facies analysis and must include a documentation of the composition and geometry of three dimensional facies variations palaeoenvironmental interpretations of complex glacigenic sequences especially in coastal locations should take account of the influences of marine ice sheets on the sedimentary record in the past most sequences were interpreted in terms of glacioterrestrial models a large body of sedimentary evidence now indicates that shallow glaciomarine environments occurred along the margins of the last ice sheet during its maximum and subsequent retreat phases the locations and patterns of associated icemarginal systems indicate that the magnitude of and patterns of crustal deformation were greater and more complex than formerly realised thus the primary control on sea level variation at successive ice sheet margins was largely a function of glacioisostatic disequilibrium although complex glacial and glacially related sequences are known it is argued here that most of the multiple glacigenic sequences in ireland can be accommodated within the midlandian cold stage the basal units from certain sequences and erratic fans have been attributed to events earlier than the midlandian however it is difficult to compare these traces of earlier events from different sectors of the island due to poor dating correlation and the fact that direct and indirect stratigraphy is not adequately defined or separated the age of the gortian style interglacial sequences the implications of their floristic composition and their relationships to drift stratigraphy remains a major problem in stratigraphic constructions of the irish quaternary the stratigraphic significance of many till units must remain largely unknown until these matters are resolved at present it is not clear if the gortian sequences represent more than one interglacial a series of exposures in ulster provide evidence for major environmental changes during the midlandian cold stage these include an early stadial an early forest biozone 48 1 ka bp an early herb biozone 41 5 ka bp a middle interstadial phase of cold but non glacial aspect 30 5 ka bp a late stadial max 24 22 ka bp and a late glacial climatic oscillation the late midlandian stadial comprises a major glaciation that almost covered the island and a later more restricted phase when drumlins formed in the northern and western parts of the island max 17 ka bp

fumarole monitoring with a handheld infrared camera volcan de colima mexico 2006 2007 abstract this paper describes a methodology for the monitoring of fumarole temperatures at medium ranges 6 km using a handheld infrared camera wavelength range 8 13 5 m as a relationship between fumarole temperatures gas flux and volcanic activity has been demonstrated by a number of studies fumarole temperature data has a potential use as a monitoring tool volcan de colima is an andesitic stratovolcano with a 300 m diameter summit crater formed by the destruction of the 2004 lava dome by a series of explosions in 2005 between january 2006 and august 2007 sequences of thermal images were recorded from a viewpoint 6 km to the north during regular 24 48 hour monitoring excursions the temperatures of fumaroles on the crater rim and the ground surface on the volcano s flanks were measured a methodology was developed to remove data affected by clouds or volcanic water vapour based on rates of temperature change and scatter within the data for the remaining data it is demonstrated mathematically that at this range typical variations in atmospheric transmissivity will affect the apparent temperatures by 2 c while a 25 change in fumarole heat flux would change it by 5 10 c the mean night time apparent temperature of the fumaroles was calculated for each excursion and showed an irregular decline over the 19 month period subtracting the radiant heat flux of flank rocks from those of the fumaroles removes seasonal variations and gives the clearest view of trends in the fumarole heat flux a sharp drop in fumarole temperature during february 2007 coincided with the emergence of a lava dome in the crater the declining fumarole temperature is interpreted to reflect decreasing gas flux from the crater in line with a change in eruptive regime from frequent small ash rich explosions to slow effusion of lava

chemical and isotopic composition of fumarolic gases and the so2 flux from volcan de colima mexico between the 1994 and 1998 eruptions volcan de colima is the most active volcano in mexico including a significant effusive eruption in 1991 and a weak explosive event in 1994 geochemical monitoring of the volcano started in january 1996 with collection of fumarolic gases approximately every 3 months from two sites in the summit crater z3 800 c and z2 400 c chemical compositions of volcanic gases from the z2 fumarole showed a peak in s cl in the middle of 1997 14 15 months before the start of the 1998 lava eruption high temperature volcanic vapors from z3 changed progressively in water isotopic composition and showed a weak trend of increasing hcl hf and a peak in s cl at the same time starting from the summer of 1997 the volcanic water became gradually enriched in deuterium which probably indicated an increasing contribution from deep less degassed magma a negative correlation between d and cl content for the z3 fumarolic gases is explained by shallow degassing of the colima hot lava plug this hypothesis is consistent with published data on cl contents and solubilities in magmas and supported by the observed positive trends of s cl and hcl hf with d for the z3 fumarole until september 1998 the so2 flux from the volcano was at a low level 100 tons day and often below the detection limit of the instrument 30 tons day a sharp increase in the so2 flux was recorded 1 month before the eruption started it jumped from 400 50 tons day to 1600 tons day 2 days before new lava emerged on 20 november 1998 the so2 flux correlated well with seismicity

microcracking during triaxial deformation of porous rocks monitored by changes in rock physical properties i elastic wave propagation measurements on dry rocks we present results from two series of triaxial deformation experiments performed on dry samples of two sandstones darley dale and gosford carried out at confining pressures from 25 mpa to 200 mpa over this pressure range the mode of failure in both these sandstones passes from localized brittle failure with a clear through going fault to distributed cataclastic flow during these experiments stress strain compressional wave velocity vp and shear wave velocity vs measurements were made simultaneously in the direction of the maximum principal compressive loading axis initial application of the hydrostatic confining pressure causes both vp and vs to increase and upon raising the axial stress above the confining pressure both velocities increase further at first generally by only a few percent but then decrease as dilatant crack growth commences during dilatancy vs decreases proportionately more than vp and this decrease is generally of the order of 10 15 these velocity measurements allow changes in rock physical properties to be calculated along with the axial and transverse crack volume density parameters x and z the results from two selected tests are analysed in detail these tests were chosen because they exhibit a typical brittle shear failure and b typical ductile cataclastic flow respectively the full interrogating elastic waveforms were also recorded during testing and these have been used to calculate the seismic quality factors qp and qs to our knowledge this is the first time this has been reported for rock samples undergoing triaxial deformation the changes in q values generally exhibit similar trends to those observed in the velocity measurements but the percentage changes in q are an order of magnitude greater suggesting that this parameter is a more sensitive measure of dilatant crack damage the measurements on dry rock samples reported here provide the basis for comparison with measurments of changes in complementary physical properties made on water saturated rock samples under the same experimental conditions and reported in a companion paper in this issue read et al 1995

persistent summit subsidence at volcan de colima mexico 1982 1999 strong evidence against mogi deflation this paper re examines recent ground deformation measurements at volcan de colima mexico to test the hypothesis that the observed movements are in response to pressure changes within a sub volcanic magma chamber as suggested for other volcanoes by mogi 1958 earthq res inst 36 99 134 measurements of vertical ground deformation across the summit dome complex of volcan de colima from a precise levelling network between 1982 and 1999 together with vertical and horizontal displacements derived from dual frequency gps measurements in 1994 and 1997 show continuous subsidence the deformation pattern derived from the levelling shows that subsidence increases towards the summit the closest stations to the summit 1 1 km distant show a mean subsidence rate of 5 mm per year compared to the reference station at 2 3 km distance which may be subsiding itself vertical displacements of individual stations since 1982 show that the subsidence has been fairly continuous the gps stations which are distributed more widely and include some close to the edge of the active dome confirm summit subsidence the largest measured value a decrease of 280 mm or 93 mm subsidence per year was obtained at the edge of the dome horizontal displacements measured during 1994 1997 also show the largest values at the summit but these are much smaller than the vertical displacements with the maximum rate of 23 mm per year recorded close to the dome it is conclusively shown that these measured movements cannot be due to deflation of a buried mogi source as vertical and horizontal displacements for some stations are in contrary directions to those predicted by the model and there is no consistent pattern to the horizontal movements we attribute the measured deformation to downslope creep settling and compaction of the edifice gravitational spreading or a combination of these processes

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

multiple timescales of cyclical behaviour observed at two dome forming eruptions article i nfo cyclic behaviour over a range of timescales is a well documented feature of many dome forming volcanoes but has not previously been identified in high resolution seismic data from volcan de colima mexico using daily seismic count datasets from volcan de colima and soufriere hills volcano montserrat this study explores par allels in the long term behaviour of seismicity at two long lived systems datasets are examined using multiple techniques including fast fourier transform detrended fluctuation analysis and probabilistic distribution analysis and the comparison of results from two systems reveals interesting parallels in sub surface processes operating at both systems patterns of seismicity at both systems reveal complex but broadly similar long term temporal patterns with cycles on the order of 50 to 200 days these patterns are consistent with previously published spectral analyses of so2 flux time series at soufriere hills volcano and are attributed to variations in the movement of magma in each system detrended fluctuation analysis determined that both volcanic systems showeda systematic relationship betweenthe numberofseismic eventsand the relative roughness ofthetime series and explosionsatvolcande colimashoweda1 5 2 yearcycle neither observation hasaclear explanatory mechanism atvolcandecolima analysisofreposeintervalsbetweenseismiceventsshowslong termbehaviour that responds to changes in activity at the system similar patterns for both volcanic systems suggest a common process or processes driving the observed signal but it is not clear from these results alone what those processes may be furtherattempts to modelconduitprocessesateach volcanomustaccountfor thesimilarities anddiffer ences in activity within each system the identification of some commonalities in the patterns of behaviour dur ing long lived dome forming eruptions atandesiticvolcanoes provides a motivation for investigating further use of time series analysis as a monitoring tool

seismotectonic deformation of the volcanic edifice prior to the 1998 lava eruption of volcan de colima mexico the andesitic stratovolcano volcan de colima is one of the most active volcanoes in mexico the recent eruption of volcan de colima began in november 1998 and was preceded by a 12 month period of seismic activity that included five earthquake swarms about 600 events with magnitudes from 0 5 to 2 7 were located within a 50 km2 area extending northward from the crater of volcan de colima to the pleistocene volcano nevado de colima the majority of hypocenters within this area did not exceed 5 km depth below sea level we investigated earthquake focal mechanisms and seismotectonic deformations of the volcanic edifice focal mechanisms during four earthquake swarms indicated normal faulting associated with extensional processes which is in agreement with the general stress regime near the volcano revealed by field measurements of fault slips earthquakes in the fifth swarm had focal mechanisms associated with inverse faulting showing a significant change in the stress situation just before the beginning of the eruption the calculated deformations varied from 1 3 10 11 to 2 7 10 9 the first swarm of november december 1997 resulted in a n s horizontal elongation that was two times greater than the e w horizontal shortening the volume was also subject to vertical shortening the second and third swarms observed in march and may 1998 showed uniform horizontal n s and e w elongations accompanied by a vertical elongation of the volume in june july 1998 the situation of november december 1997 was repeated with n s horizontal elongation greater than the e w horizontal shortening of the volume accompanied by intensive vertical shortening during the last swarm of october november 1998 slight e w elongation of the seismic volume was accompanied by strong n s shortening and very slight vertical shortening we assume that the seismic activity prior to the 1998 eruption of volcan de colima developed along two intersecting tectonic structures the n s trending colima rift and the e w trending system of faults associated with tamazula fault during the first stage november 1997 july 1998 the passageway for magma was developed along the tamazula fault system under horizontal extension without any surface manifestation in october november 1998 the seismic events began to cluster along the colima rift structures under predominantly compressional stresses this condition culminated with the extrusion of andesitic block lava from the summit crater

thermal imaging and analysis of short lived vulcanian explosions at volcan de colima mexico abstract vulcanian explosions present a major hazard at many active volcanoes but they also provide useful insights into the underlying behaviour of the volcanic system and therefore require close monitoring thermal infrared cameras are an effective tool for imaging vulcanian explosion plumes since they capture detailed temperature information and can reveal the internal dynamics of the plume forming explosions high spatial resolution thermal images of 200 small to moderate sized vulcanian explosions from the summit crater of volcan de colima mexico recorded between 2006 and 2011 were analysed to distinguish different event types and develop an explosion classification scheme explosions display a broad spectrum of sizes and characteristics ranging between two typical end members large impulsive events producing rapidly ascending explosion plumes up to heights of 600 1600 m above the crater rim and small diffusive events with plumes restricted to heights 1 to 29 m s 1 a time series of thermal imagery throughout the period 2006 2011 reveals a weak relationship between apparent plume temperatures and lava dome extrusion with the highest explosion temperatures coinciding with the onset of dome growth in early 2007 temporal variations in the source locations of explosions across the summit crater are also identified and appear to show a close relationship to the patterns of lava dome growth and thermal evolution with explosion source locations associated with the highest temperature thermal features

the porosity of pyroclasts as an indicator of volcanic explosivity abstract the porosity of pyroclasts is a valuable indicator of the character of a volcanic eruption here we analyse the porosity distribution of deposits of 17 different volcanic eruptions covering a broad range of inferred magma properties and observed eruption styles histograms of porosity versus pyroclast frequency show distinctive features in terms of the mean variance modality and skewness we present characteristic porosity distributions for five different eruption style categories dome forming explosive basaltic cryptodome forming subplinian plinian ultraplinian and phreatomagmatic we find that the mean porosity values of the deposits correlate positively with the volcanic explosivity index vei of newhall and self 1982 regardless of the degree of complexity of the individual distributions we then propose causes of the deviations from a general trend in terms of magma viscosity degassing efficiency and cap rock confinement finally a generalised correlation between clast porosity and explosivity of an eruption is developed that should help together with conventional field techniques facilitate the interpretation of pyroclastic sequences even in cases where no direct observation of the eruption exists

evolution of the mechanics of the 2004 2008 mt st helens lava dome with time and temperature the 2004 2008 eruption of mount st helens washington usa formed a typical example of a pelean spiny lava dome with solid spines of crystalline silicic lava extruded along shear zones bounded by fault gouge cashman et al 2008 iverson et al 2006 creation of and movement along shear zones in this erupting lava recorded as shallow micro earthquakes were thus key controls on eruption style and rate in addition to dome stability as eruption style and lava dome stability often change within individual eruptions it is important to identify how the strength of dome rocks changes with temperature time texture and extrusion rate however critical values of the shear strength of dome lava at eruptive temperatures have never been measured we have found in controlled laboratory experiments simulating eruption conditions that dome lava strength increased during the course of the 2004 2008 eruption of mount st helens as the textures became more crystalline and less porous increasing lava strength during the eruption would lead to deformation becoming increasingly localised to shear zones explaining why the extrusion style and centre were so consistent acoustic emissions and microstructure analysis indicate that fracturing was more localised at higher temperatures resulting in higher strengths at eruptive temperature compared to ambient temperatures for later erupted samples the strength of these later erupted samples at eruptive temperatures increased markedly with strain rate this would damp any increases in effusion rate that may result from changes in magma pressure explaining the steady effusion rate at mount st helens from 2004 to 2008

gas storage transport and pressure changes in an evolving permeable volcanic edifice abstract the total volume of gas in a magma dissolved and subsequently exsolved greatly influences the degree of explosiveness of a volcanic system there is a marked contrast between the behaviour of a volcano in an open system compared to one which is closed it is therefore essential to understand the entire degassing process gas transport storage and loss a particular focus of this study is the effect different permeabilities and pressure gradients within a volcanic edifice have on the degree and pattern of the gas velocity gas loss is modelled numerically in two dimensions using a finite element approach which allows the specification of boundary conditions with respect to pressure and different permeability domains within the volcanic edifice by combining the time dependent continuity equation and darcy s law a partial differential equation is derived and solved for the pressure the associated pressure gradient is then used within darcy s law to determine the corresponding gas velocity distribution this method is used not only for stationary systems in equilibrium but also as a time dependent progression it permits the modelling of different situations to study how various volcanic characteristics affect the gas loss the model is used to investigate the change in pressure and gas in response to time dependent scenarios these are a dome collapse or sudden increase in permeability by magma rupture at the conduit margin the formation of cracks within the lava dome and sealing by crystallisation our results show that a combination of high and low permeability regions is required for effective gas storage high permeability allows the gas to enter the system but impermeable areas act to confine the gas thereby increasing its pressure and consequently increasing the amount of gas which may be dissolved in the melt furthermore our results show that permeability is an essential factor influencing the response time to system changes which could be linked in future to deformation and other geophysical observations our model is highly versatile and sheds new light on the understanding of gas storage and transport in a permeable volcanic edifice

pleistocene suvero slide paola basin southern italy abstract the suvero slide covers an area of about 225 km 2 in the paola slope basin on the eastern tyrrhenian margin the shape and lateral extent of the deposit reflect topographic confinement of the slide between the continental slope and a morphologic barrier formed by a margin parallel slope ridge no headwall or slide plane comparable in scale with the slide deposit were found suggesting that quasi in situ deformation of semi consolidated sediments took place when the failed materials reached the floor of the slope basin the failure occurred downslope from a basement high originating from local uplift continued uplift after the suvero slide occurred is documented by the presence of steep upper slope gradients within the study area and by the presence of small scale creep and failure events that postdate the suvero slide

stratovolcano growth by co eruptive intrusion the 2008 eruption of tungurahua ecuador 1 volcanic edifices are constructed by a combination of erupted material and internal growth we use the l band satellite alos to produce insar measurements at tungurahua volcano ecuador we find a maximum of 17 5 cm of uplift on the upper western flank between december 2007 and march 2008 coincident with an eruption in february 2008 the deformation can be modeled using an ellipsoidal or sill like source within the edifice the models require an elongated aspect ratio with a length of 4 6 km the intruded volume of 1 2 106 m3 is roughly equivalent to the bulk erupted volume of 1 5 106 m3 and together the values are roughly equal to the long term magma flux the question remains whether this uplift is permanent thus contributing to the internal growth of the edifice or temporary in which case the magma will be released in a future eruption