combining local and remote infrasound recordings from the 2009 redoubt volcano eruption abstract the explosive phase of the 2009 redoubt volcano eruption produced predominantly short duration high amplitude infrasound signals recorded up to 4500 km away all 19 numbered explosive events were recorded at a local microphone dfr 12 km as well as at an infrasound array in fairbanks alaska i53us 547 km most with high signal to noise ratios the local microphone provides an estimate of the source parameters and comparison between the two datasets allows the unique opportunity to evaluate acoustic source term estimation at a remote array high waveform similarity between dfr and i53us occurs during much of the explosive phase due to strong stratospheric ducting permitting accurate source constraints inferred from i53us data cross correlation analysis after applying a hilbert transform to the i53us data shows how the acoustic energy has passed through a single caustic as predicted by ray theory similar to previous studies significant low frequency infrasound from redoubt recorded at i53us is coincident with high altitude ash emissions the largest events also produced considerable energy at greater than 50 s periods likely related to the initial oscillations of the volcanic plume or jet many of the explosive events have emergent onsets somewhat unusual for explosive short duration eruptions comparison of the satellite derived so2 emissions with the relative amount of acoustic energy at i53us shows a very high statistically significant correlation this study reiterates the utility of using remote infrasound arrays for detection of hazardous emissions and characterization of large volcanic eruptions and demonstrates how under typical meteorological conditions remote infrasound arrays can provide an accurate representation of the acoustic source

geodetic observations during the 2009 eruption of redoubt volcano alaska abstract in march 2009 redoubt volcano about 160 km to the sw of anchorage alaska began its most recent explosive eruption deformation induced by this event was recorded by a gps campaign network consisting of 14 benchmarks which had been established in 1991 after the previous eruption the network was partially reoccupied in 2001 and 2008 and no volcanic deformation was detected during that period in response to precursory unrest starting in january 2009 the alaska volcano observatory temporarily deployed continuously recording gps instruments at four of the campaign benchmarks only days before the onset of explosive activity in march 2009 the only gps instrument recording continuously during the months prior to the eruption was the plate boundary observatory pbo station ac17 about 28 km northeast of the volcano s summit data from this station reveals subtle motion radially outward from the volcano beginning as early as may 2008 which reversed with the onset of explosive activity using simple analytical models we link the precursory activity to a point source intrusion of 0 0194 0 03400 0092 km3 in volume at 13 50 17 3310 17 km below sea level bsl superscripts and subscripts refer to upper and lower ends of confidence intervals at the 95 level during the explosive phase about 0 05 0 10 028 km3 of magma was evacuated from a prolate spheroid with its centroid at 9 17 15 176 92 km bsl a semimajor axis of 4 50 10 001 25 km length and a semi minor axis of 0 475 4 00 3 km the effusive activity is inferred to come from the same source decreasing in volume by 0 0167 0 02280 0106 km3 including observations from seismology and petrology we hypothesize a mid crustal two reservoir system with material sourced from 20 km flowing in at about 13 5 km depth and reheating residual material in the proposed spheroid the mixture migrated to shallower depth 2 4 5 km bsl and reheated material there as this residual magma erupted it was replaced by the material from the spheroidal reservoir at 7 11 5 km depth which renders the shallow source undetectable for geodetic instruments in addition to long term displacements we investigate sub daily kinematic positioning solutions and find that large short term positioning offsets correlate with large explosive events spikes in phase residuals plotted along the sky tracks of individual satellites can be related to individual plumes given favorable satellite station geometry which may be of use in volcano monitoring

localisation of normal faults in multilayer sequences abstract existing conceptual growth models for faults in layered sequences suggest that faults first localise in strong and brittle layers and are later linked in weak and ductile layers we use the discrete element method for modelling the growth of a normal fault in a brittle ductile multilayer sequence the modelling reveals that faults in brittle ductile sequences at low confining pressure and high strength contrast localise first as mode i fractures in the brittle layers low amplitude monoclinal folding prior to failure is accommodated by ductile flow in the weak layers the initially vertically segmented fault arrays are later linked via shallow dipping faults in the weak layers faults localise therefore as geometrically and kinematically coherent arrays of fault segments in which abandoned fault tips or splays are a product of the strain localisation process and do not necessarily indicate linkage of initially isolated faults the modelling suggests that fault tip lines in layered sequences are more advanced in the strong layers compared with weak layers where the difference in propagation distance is most likely related to strength and or ductility contrast layer dependent variations in fault localisation rates generate fringed rather than smooth fault tip lines in multilayers

volcano ice interactions precursory to the 2009 eruption of redoubt volcano alaska abstract in late summer of 2008 after nearly 20 years of quiescence redoubt volcano began to show signs of abnormal heat flow in its summit crater in the months that followed the excess heat triggered melting and ablation of redoubt s glaciers beginning at the summit and propagating to lower elevations as the unrest accelerated a variety of morphological changes were observed including the creation of ice cauldrons areas of wide spread subsidence punctures in the ice carved out by steam and deposition from debris flows in this paper we use visual observations satellite data and a high resolution digital elevation model of the volcanic edifice to calculate ice loss at redoubt as a function of time our aim is to establish from this time series a proxy for heat flow that can be compared to other data sets collected along the same time interval our study area consists of the drift glacier which flows from the summit crater down the volcano s north slope and makes up about one quarter of redoubt s total ice volume of 4 km 3 the upper part of the drift glacier covers the area of recent volcanism making this part of ice mass most susceptible to the effect of volcanic heating moreover melt water and other flows are channeled down the drift glacier drainage by topography leaving the remainder of redoubt s ice mantle relatively unaffected the rate of ice loss averaged around 0 1 m 3 s over the last four months of 2008 accelerated to over twenty times this value by february 2009 and peaked at greater than 22 m 3 s just prior to the first major explosion on march 22 2009 we estimate a cumulative ice loss over this period of about 35 million cubic meters m m 3

experimental modelling of ground deformation associated with shallow magma intrusions abstract active volcanoes experience ground deformation as a response to the dynamics of underground magmatic systems the analysis of ground deformation patterns may provide important constraints on the dynamics and shape of the underlying volcanic plumbing systems nevertheless these analyses usually take into account simplistic shapes sphere dykes sills and the results cannot be verified as the modelled systems are buried in this paper i present new results from experimental models of magma intrusion in which both the evolution of ground deformation during intrusion and the shape of the underlying intrusion are monitored the models consisted of a molten vegetable oil simulating low viscosity magma injected into cohesive fine grained silica flour simulating the brittle upper crust oil injection resulted is sheet intrusions dykes sills and cone sheets the initial topography in the models was flat while the oil was intruding the surface of the models slightly lifted up to form a smooth relief which was mapped through time after an initial symmetrical development the uplifted area developed asymmetrically at the end of the experiments the oil always erupted at the steepest edge of the uplifted area after the experiment the oil solidified the intrusion was excavated and the shape of its top surface mapped the comparison between the uplifted zone and the underlying intrusions showed that 1 the complex shapes of the uplifted areas reflected the complex shapes of the underlying intrusions 2 the time evolution of the uplifted zone was correlated with the evolution of the underlying intrusion and 3 the early asymmetrical evolution of the uplifted areas can be used to predict the location of the eruption of the oil the experimental results also suggest that complex intrusion shapes inclined sheet cone sheet complex sill may have to be considered more systematically in the analyses of ground deformation patterns on volcanoes

effects of tidal stresses on volcanic activity at mount etna italy 1 here we model quantitatively the stress and strain induced by tidal forces as possible triggers of mount etna eruptions during 1989 2000 and 2001 by means of 2d numerical analysis by finite difference method applied to the volcano edifice spectral and vectorial analysis of tidal acceleration indicates that the quasi diurnal semi diurnal and ter diurnal constituents may have induced decompressions up to some kpa in the shallow i e 1 500 m gas saturated magma reservoir which controlled magma vesiculation and the timing of lava fountain activity from the south east crater sec we consider the geological heterogeneities in the volcanic edifice i e rock geometries and properties feeder conduit and vent systems volcanic landforms the magma properties i e bulk modulus volatile content and the ongoing volcano tectonic stresses i e volcano flank deformations which strongly influence the response of eruptive activity to tidal forces indeed the tidal factor may act on flank deformation concomitant to shallow magma inflation the implications of our model may help understand the eruptive behaviour and the disequilibrium state of the volcano and may be useful for hazard assessment at mount etna

quantifying tropospheric volcanic emissions with airs the 2002 eruption of mt etna italy 1 the atmospheric infrared sounder airs is a hyperspectral ir spectrometer orbiting on the eos aqua spacecraft since may 2002 in late october 2002 airs detected lower tropospheric sulfur dioxide and ash emitted by an eruption of mt etna italy in plumes which could be tracked over 1000 km from the volcano into north africa we report retrievals of so2 and ash column amounts and ash particle size in the etna plumes airs total so2 compares favorably with contemporaneous ground based correlation spectrometry cospec measurements retrieval of ash cloud parameters in the eruption plumes permits quantitative studies of distal ash fallout the etna data demonstrate the potential of airs to improve measurements of volcanic so2 and ash loading in the troposphere and to refine our understanding of volcanic cloud composition structure and evolution

normal fault development during two phases of non coaxial extension an experimental study we use scaled experimental analog models to study the effect of a pre existing fault fabric on fault development during extension in our models a homogeneous layer of wet clay undergoes two noncoaxial phases of extension whose directions differ by up to 45 the normal faults that develop during the first phase create a pronounced fault fabric that influences normal fault development during the second phase in all models the pre existing faults are reactivated during the second phase of extension their sense of slip depends on the angle between the first and second phase extension directions specifically the component of dip slip relative to strike slip decreases as the angle between the first and second phase extension directions increases new normal faults also form during the second phase of extension in all models the number of new fault segments increases as the angle between the first and second phase extension directions increases the orientations of the new normal fault segments are both orthogonal and oblique to the second phase extension direction indicating that both the secondphase extension direction and the pre existing fault fabric control the orientation of new fault segments some of the new normal faults cut and offset the pre existing faults whereas others terminate against them producing complex fault patterns and interactions the modeling results explain fault interactions observed in the jeanne d arc rift basin of offshore newfoundland canada and the reactivation of abyssal hill normal faults at outer highs near subduction zones

caledonian plutonism and major lineaments in the sw scottish highlands within the sw grampian highlands several ne sw trending shear zones and faults related to the caledonian transpressional collision are recognized as being distinct from an intersect ing set of nw se trending pre caledonian crustal lineaments which were reactivated during caledonian orogenesis the geochemical and isotopic characteristics of the 425 400 ma granitoids of this region show that they were derived by anatexis of the lower crust associated with a mantle component which provided an influx of mantle heat and or metasomatic fluids their spatial distribution suggests a close genetic relationship with caledonian shear zones having made the fundamental distinction between ascent transport and emplacement arrival configurations possible for granitoid magmas new data are presented for these plutons which show that i a common modal sequence of intrusive phases can be recognized ii these phases are all sited at shear zone or lineament intersections where transtensional zones allowed and facilitated ascent iii emplacement was often by a process of localized in situ ballooning the existence of such lineaments in these orientations in the sw highlands may indicate that the structure of the lower crust can be regarded as a series of blocks bounded by intersecting ductile zones of high strain the establishment of such a pattern of structural interactions within the lower crust could provide a mechanistic framework within which the location of anatectic zones siting and ascent pathways and any subsequent emplacement phenomena can be explained in orogenic belts

determining the three dimensional geometry of a dike swarm and its impact on later rift geometry using seismic reflection data dike swarm emplacement accommodates extension during rifting and large igneous province lip formation with ancient dike swarms serving to localize strain during later tectonic events deciphering three dimensional 3 d dike swarm geometry is critical to accurately calculating magma volumes and magma assisted crustal extension allowing syn emplacement mantle and tectonic processes to be interrogated it is also important for quantifying the influence of ancient dike swarms on post emplacement faulting however the essentially 2 d nature of earth s surface combined with the difficulties in imaging subvertical dikes in seismic reflection data and the relatively low resolution of geophysical data in areas of active diking means our understanding of dike swarm geometry at depth is limited we examine an 25 km wide 100 km long west southwest trending dike swarm imaged due to post emplacement rotation to shallower dips in high quality 2 d and 3 d seismic reflection data offshore southern norway tuned reflection packages correspond to thin 75 m thick closely spaced dikes these data provide a unique opportunity to image and map an ancient dike swarm at variable structural levels crosscutting relationships indicate emplacement occurred in the late carboniferous early permian and was linked to the formation of the ca 300 ma skagerrak centered lip dike swarm width increases with depth suggesting that magma volume and crustal extension calculations based on surface exposures are dependent on the level of erosion during the mesozoic rift related faults localized above and exploited mechanical anisotropies within the dike swarm we demonstrate that seismic reflection data are a powerful tool in understanding dike swarm geometry and the control of dikes on subsequent faulting

evolution of vertical faults at an extensional plate boundary southwest iceland vertical faults having both opening and vertical displacements are common in southwest iceland and hypotheses vary regarding whether they propagated to the surface from below or from the surface downward we address this issue through a study of vertical faults and associated surface fracture zones in regions of both oblique and normal spreading in southwest iceland individual fracture segments are commonly rotated out of the general trend of the fracture zone suggesting oblique motion along subsurface normal faults these faults commonly breach the upper hinge lines of narrow monoclinal folds that flank many fault traces on the hanging wall side based on these field observations and the results of numerical models we propose that 60 758 dipping normal faults in the subsurface propagated to the surface from below vertical fractures formed at the upper tips of the faults at depths of between 250 and 500 m 25 50 of the fault length in response to stress concentrations along the tip line model results indicate that narrow monoclinal folds develop at the surface above these vertical fractures which subsequently breach the monoclines along the upper hinge line forming vertical fault scarps and open fissures at the surface if vertical fractures utilize pre existing cooling joints in basalt to connect directly to the surface the hanging wall is able to pull apart from the footwall without the development of a surface monocline along the fault trace q 2003 elsevier ltd all rights reserved

gas emissions from failed and actual eruptions from cook inlet volcanoes alaska 1989 2006 cook inlet volcanoes that experienced an eruption between 1989 and 2006 had mean gas emission rates that were roughly an order of magnitude higher than at volcanoes where unrest stalled for the six events studied mean emission rates for eruptions were 13 000 t d co2 and 5200 t d so2 but only 1200 t d co2 and 500 t d so2 for non eruptive events failed eruptions statistical analysis suggests degassing thresholds for eruption on the order of 1500 and 1000 t d for co2 and so2 respectively emission rates greater than 4000 and 2000 t d for co2 and so2 respectively almost exclusively resulted during eruptive events the only exception being two measurements at fourpeaked while this analysis could suggest that unerupted magmas have lower pre eruptive volatile contents we favor the explanations that either the amount of magma feeding actual eruptions is larger than that driving failed eruptions or that magmas from failed eruptions experience less decompression such that the majority of h2o remains dissolved and thus insufficient permeability is produced to release the trapped volatile phase or both in the majority of unrest and eruption sequences increases in co2 emission relative to so2 emission were observed early in the sequence with time all events converged to a common molar value of c s between 0 5 and 2 these geochemical trends argue for roughly similar decompression histories until shallow levels are reached beneath the edifice i e from 20 35 to 4 6 km and perhaps roughly similar initial volatile contents in all cases early elevated co2 levels that we find at these high latitude andesitic arc volcanoes have also been observed at mid latitude relatively snow free basaltic volcanoes such as stromboli and etna typically such patterns are attributed to injection and decompression of deep co2 rich magma into a shallower chamber and open system degassing prior to eruption here we argue that the c s trends probably represent tapping of vapor saturated regions with high c s and then gradual degassing of remaining dissolved volatiles as the magma progresses toward the surface at these volcanoes however c s is often accentuated due to early preferential scrubbing of sulfur gases the range of equilibrium degassing is consistent with the bulk degassing of a magma with initial co2 and s of 0 6 and 0 2 wt respectively similar to what has been suggested for primitive redoubt magmas

character mass distribution and origin of tephra fall deposits from the 2009 eruption of redoubt volcano alaska highlighting the significance of particle aggregation abstract the 2009 eruption of redoubt volcano included 20 tephra producing explosions between march 15 2009 and april 4 2009 utc next generation radar nexrad data show that plumes reached heights between 4 6 km and 19 km asl and were distributed downwind along nearly all azimuths of the volcano explosions lasted between 0 8 mm thick including communities along the kenai peninsula 80 100 km and the city of anchorage 170 km trace ash on march 15 a small 4 6 km asl phreatic explosion containing minor non juvenile ash erupted through the summit ice cap the first five magmatic explosions events 1 5 occurred within a 6 hour period on march 23 plumes rose to heights between 5 5 km and 14 9 km asl during 2 to 20 minute duration explosions and were dispersed mainly along a nne trajectory trace ash fall was reported as far as fairbanks owing to a shift in wind direction and heavy snowfall during these events field discrimination among many of these layers was possible all deposits comprise a volumetrically significant amount of particle aggregates yet only event 5 deposits contain coarse clasts including glacier ice the most voluminous tephra fall was deposited on march 24 event 6 from a 15 minute explosion that sent a plume to 18 3 km asl and dispersed tephra to the wnw within 10 km of the vent this deposit contains 1 11 cm pumice clasts in a matrix of 1 2 mm aggregate lapilli a small dome was presumably emplaced between march 23 and march 26 and was subsequently destroyed during 1 14 minute magmatic explosions of events 7 8 march 26 that sent plumes between 8 2 km and 19 km asl ash fell along a broad swath to the ese covering communities along the kenai peninsula with up to 1 mm of ash proximal deposits are largely composed of aggregate lapilli of 1 2 mm with very little coarse juvenile material events 9 18 march 27 sent plumes between 5 2 km and 15 5 km asl during particle size data showing a preponderance of fine ash even in the most proximal locations along with the abundance of aggregate lapilli documented in most samples confirms that particle aggregation played a significant role in the 2009 eruption and induced premature fallout of fine ash

multiparameter quantification of gas release during weak strombolian eruptions at pacaya volcano guatemala 1 activity at pacaya volcano guatemala is characterized by persistent degassing coupled at times with lava effusion and or coincident strombolian style explosions we used 0 25 hz sample rate sulfur dioxide emission data from a uv camera and coincident infrasound recordings to investigate the link between varied emission rates and infrasound events degassing rates varied on two scales during this study smaller more rapid variations on the scale of 1 to 3 minutes are superimposed on larger slower changes over 30 minutes to 1 hour the acoustic record was dominated by repeated n shaped events characteristic of strombolian explosions because of the high resolution of the gas measurements we were able to calculate gas masses for individual explosions from both datasets and find the two estimates agree within an order of magnitude the infrasound explosion records correlate with small pulses in degassing but the longer term degassing trends may represent a deeper process

geometric difference between non feeder and feeder dikes feeder dikes bring magma to the surface non feeder dikes become arrested and never reach the surface the differences if any between these dike types remain largely unexplored because in the field it is normally unknown if a particular dike is a feeder or non feeder here we present measurements of feeder and non feeder dikes exposed from depths of 200 m to the surface in the walls of the a d 2000 caldera collapse of the miyakejima volcano japan a typical feeder thickness reaches a maximum of 2 4 m at the surface decreases rapidly to 1 m at a depth of 20 40 m and then remains constant to the bottom of the exposure by contrast a typical non feeder thickness reaches a maximum of 1 5 2 m at 15 45 m below the tip and then decreases slowly with depth to 0 5 1 m at the bottom of the exposure we propose that free surface effects and magmatic overpressure driving pressure changes during the eruption cause the overall shape of a feeder to differ from that of a non feeder

the granny smith gold deposit the role of heterogeneous stress distribution at an irregular granitoid contact in a greenschist facies terrane the granny smith gold deposits formed late in the structural history of the yilgarn block at a high crustal level in a largely brittle structural regime gold mineralisation is located along a n s striking fault which wraps around the contact of a small granitoid intrusion in different sections of the fault mineralisation may be developed in the granitoid in the adjacent sedimentary sequence and or along the contact between them in the granitoid gold mineralisation is in conjugate networks of thin carbonate quartz veins and their alteration halos small displacements along veins are common in contrast veins and faults in the sedimentary rocks are subparallel to bedding spatial variations in the conjugate vein orientations indicate that the local stress field was heterogeneous and controlled by the shape of the granitoid contact the greatest variations in vein and implied stress orientations occur in zones where the contact is most irregular these are also the areas of richest mineralisation fluid flow was thus focused in a regional scale low mean stress region created by the geometry of the granitoid intrusion its irregular contact caused deposit scale variations in fluid flow and resulted in heterogeneous gold grades along the contact zone

granite magma migration and emplacement along thrusts this paper investigates the influence exerted by brittle tectonic structures in the emplacement of granite plutons in contractional settings we address both cases where contractional tectonics and magma intrusion are 1 coeval to study how active contractional tectonics controls the transport of magma and 2 diachronous to study the role of pre existing structures on the transport of magma in light of new experimental models we show that magma can rise along thrusts ramps and flats this phenomenon occurs for both low viscosity magma basalts to andesite and high viscosity magma dry granite the experimental results also allow the evaluation of the role played by magma viscosity in determining pluton geometries in addition a review of literature demonstrates a spatial and causal relationship between granites and thrusts and highlights the geometric control of magma pathways in the pluton final shape the abundance of subhorizontal and tabular granitic intrusions indicates that the location of inflating granitic sills along thrust flats can be common we argue that active and pre existing flats and ramps thrusts provide a preferential continuous planar anisotropy susceptible to become a granitic magma migration pathway

an overview of the 2009 eruption of redoubt volcano alaska abstract in march 2009 redoubt volcano alaska erupted for the first time since 1990 explosions ejected plumes that disrupted international and domestic airspace sent lahars more than 35 km down the drift river to the coast and resulted in tephra fall on communities over 100 km away geodetic data suggest that magma began to ascend slowly from deep in the crust and reached mid to shallow crustal levels as early as may 2008 heat flux at the volcano during the precursory phase melted 4 of the drift glacier atop redoubt s summit petrologic data indicate the deeply sourced magma low silica andesite temporarily arrested at 9 11 km and or at 4 6 km depth where it encountered and mixed with segregated stored high silica andesite bodies the two magma compositions mixed to form intermediate silica andesite and all three magma types erupted during the earliest 2009 events only intermediate and high silica andesites were produced throughout the explosive and effusive phases of the eruption the explosive phase began with a phreatic explosion followed by a seismic swarm which signaled the start of lava effusion on march 22 shortly prior to the first magmatic explosion early on march 23 2009 utc more than 19 explosions or events were produced over 13 days from a single vent immediately south of the 1989 90 lava domes during that period multiple small pyroclastic density currents flowed primarily to the north and into glacial ravines three major lahars flooded the drift river terminal over 35 km down river on the coast tephra fall deposited on all aspects of the edifice and on several communities north and east of the volcano and at least two and possibly three lava domes were emplaced lightning accompanied almost all the explosions a shift in the eruptive character took place following event 9 on march 27 in terms of infrasound signal onsets the character of repeating earthquakes and the nature of tephra ejecta more than nine additional explosions occurred in the next two days followed by a hiatus in explosive activity between march 29 and april 4 during this hiatus effusion of a lava dome occurred whose growth slowed on or around april 2 the final explosion pulverized the very poorly vesicular dome on april 4 and was immediately followed by the extrusion of the final dome that ceased growing by july 1 2009 and reached 72 m m 3 in bulk volume the dome remains as of this writing effusion of the final dome in the first month produced blocky intermediate to high silica andesite lava which then expanded by means of lava injection beneath a fracturing and annealing cooling surface crust in the first week of may a seismic swarm accompanied extrusion of an intermediate to high silica andesite from the apex of the dome that was highly vesicular and characterized by lower p 2 o 5 content the dome remained stable throughout its growth period likely due to combined factors that include an emptied conduit system steady degassing through coalesced vesicles in the effusing lava and a large crater pit created by the previous explosions we estimate the total volume of erupted material from the 2009 eruption to be between 80 m and 120 m m 3 dense rock equivalent dre the aim of this report is to synthesize the results from various datasets gathered both during the eruption and retrospectively and which are represented by the papers in this publication we therefore provide an overall view of the 2009 eruption and an introduction to this special issue publication

correlations between eruption magnitude so2 yield and surface cooling about the book humans have long marvelled at and feared the odorous and colourful manifestations of volcanic emissions and in some cases have harnessed them for their economic value the degassing process responsible for these phenomena is now understood to be one of the key factors influencing the timing and nature of volcanic eruptions moreover the surface emissions of these volatiles can have profound effects on the atmospheric and terrestrial environment and climate even more fundamental are the relationships between the history of planetary outgassing differentiation of the earth s interior chemistry of the atmosphere and hydrosphere and the origin and evolution of life this book provides a compilation of 23 papers that investigate the behaviour of volatiles in magma the feedbacks between degassing and magma dynamics and the composition flux and environmental atmospheric and climatic impacts of volcanic gas emissions

photogrammetric monitoring of lava dome growth during the 2009 eruption of redoubt volcano abstract the 2009 eruption of redoubt volcano alaska began with a phreatic explosion on 15 march followed by a series of at least 19 explosive events and growth and destruction of at least two and likely three lava domes between 22 march and 4 april on 4 april explosive activity gave way to continuous lava effusion within the summit crater we present an analysis of post 4 april lava dome growth using an oblique photogrammetry approach that provides a safe rapid and accurate means of measuring dome growth photogrammetric analyses of oblique digital images acquired during helicopter observation flights and fixed wing volcanic gas surveys produced a series of digital elevation models dems of the lava dome from 16 april to 23 september the dems were used to calculate estimates of volume and time averaged extrusion rates and to quantify morphological changes during dome growth effusion rates ranged from a maximum of 35 m 3 s 1 during the initial two weeks to a low of 2 2 m 3 s 1 in early summer 2009 the average effusion rate from april to july was 9 5 m 3 s 1 early rapid dome growth was characterized by extrusion of blocky lava that spread laterally within the summit crater in mid to late april the volume of the dome had reached 36 10 6 m 3 roughly half of the total volume and dome growth within the summit crater began to be limited by confining crater walls to the south east and west once the dome reached the steep north sloping gorge that breaches the crater growth decreased to the south but the dome continued to inflate and extend northward down the gorge effusion slowed during 16 april 1 may but in early may the rate increased again this rate increase was accompanied by a transition to exogenous dome growth from mid may to july the effusion rate consistently declined the decrease is consistent with observations of reduced seismicity gas emission and thermal anomalies as well as declining rates of geodetic deflation or inflation these trends suggest dome growth ceased by july 2009 the volume of the dome at the end of the 2009 eruption was about 72 10 6 m 3 more than twice the estimated volume of the largest dome extruded during the 1989 1990 eruption in total the 2009 dome extends over 400 m down the glacial gorge on the north end of the crater with a total length of 1 km width of 500 m and an average thickness of 200 m

lithological controls on igneous intrusion induced ground deformation ground deformation commonly precedes volcanic eruptions although its relationship to underlying intrusion networks is complex we use 3d seismic reflection data to examine the link between a saucer shaped sill and an overlying forced fold formed at the contemporaneous palaeosurface our results highlight a disparity in size between the sill and fold which we attribute to accommodation of magma by overburden uplift and fluid expulsion from the host rock sill transgression occurred in response to plastic deformation of the host rock and did not produce seismically resolvable uplift inversion models of ground deformation should therefore acknowledge host rock behaviour during intrusion supplementary material uninterpreted seismic section and sill thickness fold amplitude data are available at www geolsoc org uk sup18663

geometry and controls on the development of igneous sill related forced folds a 2 d seismic reflection case study from offshore southern australia emplacement of magma in the shallow subsurface can result in the development of dome shaped folds at the earth s sur face these so called forced folds have been described in the fi eld and in subsur face data sets although the exact geometry of the folds and the nature of their relation ship to under lying sills remain unclear and in some cases controversial in this study we use high quality two dimensional 2 d seismic refl ection and borehole data from the ceduna sub basin offshore southern australia to describe the structure and infer the evolution of igneous sill related forced folds in the bight basin igneous complex thirty three igneous sills which were em placed 200 1500 m below the paleo seabed in upper cretaceous rocks are mapped in the ceduna sub basin the intrusions are expressed as packages of high amplitude refl ections which are 32 250 m thick and 7 19 km in diameter we observe fi ve main types of intrusion type 1 strata concordant sills type 2 weakly strata discordant trans gressive sills type 3 saucer shaped sills type 4 laccoliths and type 5 hybrid intru sions which have geometric characteristics of intrusion types 1 3 these intrusions are overlain by dome shaped folds which are up to 17 km wide and display up to 210 m of re lief the edges of these folds coincide with the margins of the underlying sills and the folds display the greatest relief where the underly ing sills are thickest the folds are therefore interpreted as forced folds that formed in response to emplacement of magma in the shallow subsurface the folds are onlapped by lutetian middle eocene strata indicat ing they formed and the intrusions were em placed during the latest ypresian ca 48 ma we demonstrate that fold amplitude is typi cally less than sill thickness even for sills with very large diameter to depth ratios suggest ing that pure elastic bending forced folding of the overburden is not the only process ac commodating magma emplacement and that supra sill compaction may be important even at relatively shallow depths based on the ob servation that the sills intruded a shallowly buried succession the discrepancy between fold amplitude and sill thickness may refl ect loss of host rock volume by fland pore fl uid expulsion from poorly lithifi ed water rich beds this study indicates that host rock composition emplacement depth and deformation mechanisms are important controls on the style of deformation that oc curs during intrusive igneous activity and that forced fold amplitude may not in all cases refl ect the thickness of an underlying igneous intrusion in addition the results of this study suggest that physical and numeri cal models need to model more complex host rock stratigraphies and rheologies if they are to capture the full range of deformation mechanisms that occur during magma em placement in the earth s shallow subsurface

remote observations of eruptive clouds and surface thermal activity during the 2009 eruption of redoubt volcano abstract volcanoes often erupt explosively and generate a variety of hazards including volcanic ash clouds and gaseous plumes these clouds and plumes are a significant hazard to the aviation industry and the ground features can be a major hazard to local communities here we provide a chronology of the 2009 redoubt volcano eruption using frequent low spatial resolution thermal infrared tir mid infrared mir and ultraviolet uv satellite remote sensing data the first explosion of the 2009 eruption of redoubt volcano occurred on march 15 2009 utc and was followed by a series of magmatic explosive events starting on march 23 utc from march 23 april 4 2009 satellites imaged at least 19 separate explosive events that sent ash clouds up to 18 km above sea level asl that dispersed ash across the cook inlet region in this manuscript we provide an overview of the ash clouds and plumes from the 19 explosive events detailing their cloud top heights and discussing the variations in infrared absorption signals we show that the timing of the tir data relative to the event end time was critical for inferring the tir derived height and true cloud top height the ash clouds were high in water content likely in the form of ice which masked the negative tir brightness temperature difference btd signal typically used for volcanic ash detection the analysis shown here illustrates the utility of remote sensing data during volcanic crises to measure critical real time parameters such as cloud top heights changes in ground based thermal activity and plume cloud location

daily monitoring of ecuadorian volcanic degassing from space we present daily measurements of sulfur dioxide so2 emissions from active volcanoes in ecuador and southern colombia between september 2004 and september 2006 derived from the ozone monitoring instrument omi on nasa s eos aura satellite omi is an ultraviolet visible spectrometer with an unprecedented combination of spatial and spectral resolution and global coverage that permits daily measurements of passive volcanic degassing from space we use non interactive processing methods to automatically extract daily so2 burdens and information on so2 sources from the omi datastream maps of monthly average so2 vertical columns retrieved by omi over ecuador and s colombia are also used to illustrate variations in regional so2 loading and to pinpoint sources the dense concentration of active volcanoes in ecuador provides a stringent test of omi s ability to distinguish so2 from multiple emitting sources our analysis reveals that tungurahua reventador and galeras were responsible for the bulk of the so2 emissions in the region in the timeframe of our study with no significant so2 discharge detected from sangay at galeras and reventador we conclude that omi can detect variations in so2 release related to cycles of conduit sealing and degassing which are a critical factor in hazard assessment the omi so2 data for reventador are the most extensive sequence of degassing measurements available for this remote volcano which dominated regional so2 production in june august 2005 at tungurahua the omi measurements span the waning stage of one eruptive cycle and the beginning of another and we observe increasing so2 burdens in the months prior to explosive eruptions of the volcano in july and august 2006 cumulative so2 loadings measured by omi yield a total of 1 16 tg so2 emitted by volcanoes on mainland ecuador s colombia between september 2004 and september 2006 as much as 95 of this so2 may originate from non eruptive degassing approximate apportionment of the total so2 loading indicates that 40 originated from tungurahua with 30 supplied by both reventador and galeras these measurements of volcanic so2 degassing in ecuador confirm omi s potential as an effective economical and risk free tool for daily monitoring of so2 emissions from hazardous volcanoes

a low angle normal fault in the umbria region central italy a mechanical model for the related microseismicity abstract in the northern apennines the upper crust is thinned by a set of east dipping low angle normal faults lanfs the easternmost and more recent of these lanfs is the altotiberina fault atf located in northern umbria the geometry of the atf has been reconstructed matching surface geology with seismic reflection profiles and borehole data the fault whose average dip is 20 borders the upper pliocene quaternary tiber basin and has a displacement of about 8 km the deeper portion of the atf is located below the axial zone of the northern apennines where the strongest instrumental and historical seismicity is recorded the microseismicity of the region m 1 to evaluate the boundary conditions for the brittle activity of the atf the fault can be reactivated for low values of differential stress 1 3 t 10 mpa and tensile fluid overpressure p f 3 e g v 0 93 in the peculiar situation of the northern apennines the deep emissions of large amounts of co 2 documented in the area can be entrapped in their ascent by structural seals e g atf favouring localised fluid overpressures the impossibility of sustaining p f 3 for wide fault portions counteracted by hydraulic fracturing increased permeability under low effective stress and load weakening behaviour for normal faulting would prevent the nucleation of moderate ruptures along the fault the short lived attainment of p f 3 along small fault portions can account for the microseismic activity located along the atf which occurs on rupture surfaces in the range of 10 1 10 3 km 2

modeling the geysers vsp a progress report two years ago workers from the lawrence berkeley laboratories reported a shear wave vsp in the geysers steam field california in which the sv signal from the in line surface shear wave vibrator arrived at the down well geophones about 0 1 s earlier than the sh signal from the cross line vibrator see majer et al geophysics january 1988 the seismograms are shown in figure 1 this delay over a pathlength of about 700 m is remarkable and was attributed to strong crack induced anisotropy large vertical liquid filled fractures striking in the radial direction were suggested as causing sv waves polarized parallel to the plane of the cracks to meet less impedance and travel faster than sh waves which vibrate at right angles to the cracks this is a well established phenomenon

late cretaceous extensional denudation along a marble detachment fault zone in the kirsehir massif near kaman central turkey abstract in the central anatolian crystalline complex cacc 100 km scale metamorphic domains were exhumed in a context of north south plate convergence during late cretaceous to cenozoic times the timing kinematics and mechanisms of exhumation have been the focus of previous studies in the southern nigde massif in this study we investigate the unexplored northern area regarding the tectonic features preserved on the edges of the kirsehir massif based on detailed field mapping in the kaman area where high grade metasediments non metamorphic ophiolites and monzonitic plutons are locally exposed together close to the contact with the ophiolites west dipping foliated marble rich rocks display mylonites and discrete protomylonites with normal shear senses indicating a general top to the w nw direction both of these structures have been brittlely overprinted into cataclastic corridors parallel to the main foliation the mylonite series and superimposed brittle structures together define the kaman fault zone the study of the evolution of calcite deformation fabrics along an ew section supported by electron back scattered diffraction measurements ebsd on representative fabrics indicates that the kaman fault zone represents an extensional detachment in omerhacili in the vicinity of the baranadag quartz monzonite the metamorphic sequence shows static annealing of the calcite mylonitic fabrics this evidence suggests that intrusion took place at shallow depth 10 km into an already exhuming metamorphic sequence as a consequence for the kaman area buried metasediments have been rapidly exhumed between 84 and 74 ma 1 km ma where exhumation along a detachment zone displaying a top to the w nw shear motion took place in the mid to upper crust prior to magmatic intrusion in the late campanian as the intrusion cut through the detachment fault the main shearing deformation ceased brittle tectonics coupled with erosion likely took over during the final unroofing stages at a slower rate

depletion rates of sulfur dioxide in tropospheric volcanic plumes the tropospheric sulfur cycle has been closely studied from the standpoint of anthropogenic emissions but less so with respect to volcanic sources we document here evidence for wide variation in lifetimes of volcanic so2 in the troposphere at one extreme our observations of the plume associated with the lavadome eruption of soufriere hills volcano montserrat suggest loss of gaseous so2 at rates exceeding 10 3 s 1 while this efficent so2 depletion reflects unusual environmental factors published measurements for mount etna s plume approach these rapid rates in such cases source strengths of so2 must significantly exceed apparent fluxes measured several kilometres downwind this implies that meteorological and geographic factors as well as volcanic degassing rates should be considered in the interpretation of fluxes of so2 measured beyond source vents with ramifications for volcano monitoring and eruption prediction furthermore since most calculations of global volcanic fluxes of sulfur and other species to the troposphere are based on extrapolation of so2 flux data they may underestimate true source strengths finally we consider that fast sulfur chemistry may also prevail in convecting eruption columns resulting in partial tropospheric scrubbing of sulfur from stratosphere bound plumes

terrane boundary reactivation barriers to lateral fault propagation and reactivated fabrics rifting across the median batholith zone great south basin new zealand prominent pre existing structural heterogeneities within the lithosphere may localise or partition deformation during tectonic events the ne trending great south basin offshore new zealand formed perpendicular to a series of underlying crustal terranes including the dominantly granitic median batholith zone which along with the boundaries between individual terranes exert a strong control on rift physiography and kinematics we find that the crustal to lithospheric scale southern terrane boundary of the median batholith zone is associated with a crustal scale shear zone that was reactivated during late cretaceous extension between zealandia and australia this reactivated terrane boundary is oriented at a high angle to the faults defining the great south basin we identify a large granitic laccolith along the southern margin of the median batholith expressed as sub horizontal packages of reflectivity and acoustically transparent areas on seismic reflection data the presence of this strong granitic body inhibits the lateral south westward propagation of ne trending faults which segment into a series of splays that rotate to align along the margin as they approach further we also identify two e w and ne sw oriented basement fabrics likely corresponding to prominent foliations which are exploited by small scale faults across the basin we show that different mechanisms of structural inheritance are able to operate simultaneously and somewhat independently within rift systems at different scales of observation the presence of structural heterogeneities across all scales need to be incorporated into our understanding of the structural evolution of complex rift systems

circumpolar transport of a volcanic cloud from hekla iceland 1 hekla volcano iceland erupted on 17 august 1980 and emplaced a sulfur dioxide so2 cloud into the north polar stratosphere at a maximum altitude of 15 km the so2 is tracked using satellite data from the ultraviolet uv nimbus 7 total ozone mapping spectrometer n7 toms and the infrared ir high resolution infrared radiation sounder hirs 2 on the noaa tiros operational vertical sounder tovs platform the eruption emitted 0 5 0 7 tg of so2 which later split into three distinct clouds one of which circled the north pole at the perimeter of an atypically persistent arctic cyclone for six days impacting airspace on three continents separate clouds drifted across eastern russia alaska and canada maximum so2 columns derived from toms and hirs 2 accurately define the volcanic cloud s path and fit trajectories produced by the noaa hybrid single particle lagrangian integrated trajectory hysplit model providing confidence in the model when combined with the so2 measurements trajectory altitudes derived from hysplit provide robust estimates of the altitudes of the so2 clouds 8 15 km which would be elusive using either the satellite data or the trajectory model in isolation near coincident spectrally discrete uv and ir retrievals are compared in the volcanic cloud and indicate good agreement between toms and hirs 2 so2 columns for pixels with similar viewing geometry hekla eruptions which follow a pattern of early explosive venting of volcanic gases with significant stratospheric injection could play a role in promoting arctic ozone loss depending on the phase of the north atlantic oscillation during the eruption

fault zone reactivation kinematics and mechanisms the kinematics and mechanisms of fault zone reactivation are reviewed reactivation is dependent upon fault zone orientation and the existence of weak mylonites along these zones the recognition of reactivation within mylonite zones and the softening processes that first concentrate deformation into these and secondly provide a weak medium for reactivation are discussed attention is given to the darling mobile zone western australia and the redbank zone see obee white this symposium as examples of reactivated zones

localization of volcanic activity 2 effects of pre existing structure abstract the capture of vertically rising dikes by faults is examined with a combination of an analytic solution numerical simulations and field observations one of the numerical solutions and the field observations also provide insight into the intrusion of sills into the hanging wall of faults that are reactivated when lubricated by magma the approximate analytic solution indicates that dike capture by a fault will be limited primarily to steeply dipping faults capture will become easier meaning that it will be possible for faults with shallower dips as the intersection of the dike with the fault occurs at smaller depths capture will also be easier as it is harder for crack to grow in the hanging wall this may be interpreted in terms of a higher tensile strength or in terms of shorter pre existing cracks or higher fracture toughness numerical analysis using a discrete element code confirms this conclusion but also shows that the analytic solutions overestimate the difficulty of intruding a pre existing fault the maximum deviation occurring for faults dipping at 45 this finding that dike capture by faults should be restricted to high angle faults and shallow depths is supported by field observations of exhumed miocene basaltic volcanic terrain in central nevada usa differences in style seen in other regions are attributed to both the rock properties and the regional stress field the numerical solutions also indicate that synintrusive fault slip is likely to lead to formation of sills in the hanging wall at depths of a few hundred meters or less a finding that is also consistent with the field observations in nevada

the influence of normal fault geometry on igneous sill emplacement and morphology magma flow within the subsurface is heavily influenced by the pre existing structure of the upper crust during continental rifting normal faults modify the geometry of igneous networks by providing preferential pathways for the intrusion of magma however the way in which magma intrudes into fault planes is poorly understood here we quantitatively document the relationship between fault architecture and intrusion distribution and geometry using three dimensional seismic reflection data from the exmouth sub basin offshore northwest australia inclined segments of saucer shaped sills intrude several faults along convex into the hangingwall fault plane corrugations we suggest that stress field perturbations associated with the fault plane corrugations provide suitable conditions for fault reactivation as magma conduits pre existing faults also modify sill geometries through the offset of stratigraphic horizons that may be preferentially intruded potentially resulting in the formation of a new sill or the development of minor intrusive steps this work emphasizes the importance of the pre existing structural template in controlling the growth and final geometry of intrusive networks

influence of crystallised igneous intrusions on fault nucleation and reactivation during continental extension abstract continental rifting is commonly accommodated by the nucleation of normal faults slip on pre existing fault surfaces and or magmatic intrusion because crystallised igneous intrusions are pervasive in many rift basins and are commonly more competent i e higher shear strengths and young s moduli than the host rock it is theoretically plausible that they locally intersect and modify the mechanical properties of pre existing normal faults we illustrate the influence that crystallised igneous intrusions may have on fault reactivation using a conceptual model and observations from field and subsurface datasets our results show that igneous rocks may initially resist failure and promote the preferential reactivation of favourably oriented pre existing faults that are not spatially associated with solidified intrusions fault segments situated along strike from laterally restricted fault intrusion intersections may similarly be reactivated this spatial and temporal control on strain distribution may generate 1 supra intrusion folds in the hanging wall 2 new dip slip faults adjacent to the igneous body or 3 sub vertical oblique slip faults oriented parallel to the extension direction importantly stress accumulation within igneous intrusions may eventually initiate failure and further localise strain the results of our study have important implications for the structural of sedimentary basins and the subsurface migration of hydrocarbons and mineral bearing fluids

new technique for dating igneous sills three dimensional seismic interpretation of tertiary sills within the northeast atlantic margin demonstrates that shallow level 20 km long the fill of the minibasin is dated biostratigraphically as 54 6 55 ma which fits well with radiometric dates for the timing of intrusion of sills around this basin ca 53 55 ma the recognition and dating of onlap fill seismic reflector packages that are delimited by forced folds form a new and useful method for dating shallow level igneous intrusions in sedimentary basins a method that provides independent constraints on radiometric dating techniques similar forced folds are recognized from other basins that have shallow level sills suggesting that the technique presented here may be similarly applicable in comparable geologic settings

in situ measurements of tropospheric volcanic plumes in ecuador and colombia during tc4 a nasa dc 8 research aircraft penetrated tropospheric gas and aerosol plumes sourced from active volcanoes in ecuador and colombia during the tropical composition cloud and climate coupling tc 4 mission in july august 2007 the likely source volcanoes were tungurahua ecuador and nevado del huila colombia the tc 4 data provide rare insight into the chemistry of volcanic plumes in the tropical troposphere and permit a comparison of so 2 column amounts measured by the ozone monitoring instrument omi on the aura satellite with in situ so 2 measurements elevated concentrations of so 2 sulfate aerosol and particles were measured by dc 8 instrumentation in volcanic outflow at altitudes of 3 6 km estimated plume ages range from 2 h at huila to 22 48 h downwind of ecuador the plumes contained sulfate rich accumulation mode particles that were variably neutralized and often highly acidic a significant fraction of supermicron volcanic ash was evident in one plume in plume o 3 concentrations were 70 80 of ambient levels downwind of ecuador but data are insufficient to ascribe this to o 3 depletion via reactive halogen chemistry the tc 4 data record rapid cloud processing of the huila volcanic plume involving aqueous phase oxidation of so 2 by h 2o 2 but overall the data suggest average in plume so 2 to sulfate conversion rates of 1 2 h 1 so 2 column amounts measured in the tungurahua plume 0 1 0 2 dobson units are commensurate with average so 2 columns retrieved from omi measurements in the volcanic outflow region in july 2007 the tc 4 data set provides further evidence of the impact of volcanic emissions on tropospheric acidity and oxidizing capacity

numerical modelling of triple junction tectonics at karliova eastern turkey with implications for regional magma transport few places on earth are as tectonically active as the karliova region of eastern turkey in this region complex interactions between the arabian eurasian and anatolian plates occur at the karliova triple junction ktj the relationship between tectonics and magma propagation in triple junction tectonic settings is poorly understood here we present new field and numerical results on the mechanism of magma propagation at the ktj we explore the effects of crustal heterogeneity and anisotropy in particular the geometry and mechanical properties of many faults and layers on magma propagation paths under a variety of tectonic loadings we propose that two major volcanic centres in the area the turnadag volcano and the varto caldera are both fed by comparatively shallow magma chambers at depths of about 8 km which in turn are fed by a single much larger and deeper reservoir at about 15 18 km depth by contrast the nearby ozenc volcanic area is fed directly by the deeper reservoir we present a series of two dimensional and three dimensional numerical models showing that the present tectonic stresses encourage magma chamber rupture and dyke injection the results show that inversion tectonics encourages the formation of magma paths as potential feeder dykes our three dimensional models allow us to explore the local stresses induced by complex loading conditions at the karliova triple junction using an approach that can in future be applied to other similar tectonic regions the numerical results indicate a great complexity in the potential magma dyke paths resulting from local stresses generated by interaction between mechanical layers major faults and magma chambers in particular the results suggest three main controls on magma path formation and eventual eruptions at ktj 1 the geometry and attitude of the associated faults 2 the heterogeneity and anisotropy of the crust and 3 mechanical stress interactions between deep and shallow magma chambers

doppler weather radar observations of the 2009 eruption of redoubt volcano alaska abstract the u s geological survey usgs deployed a transportable doppler c band radar during the precursory stage of the 2009 eruption of redoubt volcano alaska that provided valuable information during subsequent explosive events we describe the capabilities of this new monitoring tool and present data captured during the redoubt eruption the minimax 250 c mm 250c radar detected seventeen of the nineteen largest explosive events between march 23 and april 4 2009 sixteen of these events reached the stratosphere above 10 km within 2 5 min of explosion onset high column and proximal cloud reflectivity values 50 to 60 dbz were observed from many of these events and were likely due to the formation of mm sized accretionary tephra ice pellets reflectivity data suggest that these pellets formed within the first few minutes of explosion onset rapid sedimentation of the mm sized pellets was observed as a decrease in maximum detection cloud height the volcanic cloud from the april 4 explosive event showed lower reflectivity values due to finer particle sizes related to dome collapse and related pyroclastic flows and lack of significant pellet formation eruption durations determined by the radar were within a factor of two compared to seismic and pressure sensor derived estimates and were not well correlated ash dispersion observed by the radar was primarily in the upper troposphere below 10 km but satellite observations indicate the presence of volcanogenic clouds in the stratosphere this study suggests that radar is a valuable complement to traditional seismic and satellite monitoring of explosive eruptions

radiative transfer corrections for accurate spectroscopic measurements of volcanic gas emissions there is widespread use of passive remote sensing techniques to quantify trace gas column densities in volcanic plumes utilizing scattered sunlight as a light source examples include passive doas cospec and the so2 camera in order to calculate trace gas concentrations or volcanic emission fluxes knowledge about the optical path through the plume is necessary in the past a straight photon path through the plume has always been assumed although it was known that this is not always true here we present the results of model studies conducted specifically to quantify the effects of realistic radiative transfer in and around volcanic plumes on ground based remote sensing measurements of so2 the results show that measurements conducted without additional information on average photon paths can be inaccurate under certain conditions with possible errors spanning more than an order of magnitude both over and underestimation of the true column density can occur actual errors depend on parameters such as distance between instrument and plume plume so2 concentration plume aerosol load as well as aerosol conditions in the ambient atmosphere as an example a measurement conducted with an so2 camera is discussed the results of which can only be correctly interpreted if realistic radiative transfer is considered finally a method is presented which for the first time allows the retrieval of actual average photon paths in spectroscopic i e doas measurements of adequate resolution by allowing for a wavelength dependent column density during the evaluation of doas measurements we show how radiative transfer effects can be corrected using information inherently available in the measured spectra thus greatly enhancing the accuracy of doas measurements of volcanic emissions

evaluation of redoubt volcano s sulfur dioxide emissions by the ozone monitoring instrument abstract the 2009 eruption of redoubt volcano alaska provided a rare opportunity to compare satellite measurements of sulfur dioxide so2 by the ozone monitoring instrument omi with airborne so2 measurements by the alaska volcano observatory avo herein we 1 compare omi and airborne so2 column density values for redoubt s tropospheric plume 2 calculate daily so2 masses from mount redoubt for the first three months of the eruption 3 develop simple methods to convert daily measured so2 masses into emission rates to allow satellite data to be directly integrated with the airborne so2 emissions dataset 4 calculate cumulative so2 emissions from the eruption and 5 evaluate omi as a monitoring tool for high latitude degassing volcanoes a linear correlation r2 0 75 is observed between omi and airborne so2 column densities omi daily so2 masses for the sample period ranged from 60 1 kt on 24 march to below detection limit with an average daily so2 mass of 6 7 kt the highest so2 emissions were observed during the initial part of the explosive phase and the emissions exhibited an overall decreasing trend with time omi so2 emission rates were derived using three methods and compared to airborne measurements this comparison yields a linear correlation r2 0 82 with omi derived emission rates consistently lower than airborne measurements the comparison results suggest that omi s detection limit for high latitude springtime conditions varies from 2000 to 4000 t d cumulative so2 masses calculated from daily omi data for the sample period are estimated to range from 542 to 615 kt with approximately half of this so2 produced during the explosive phase of the eruption these cumulative masses are similar in magnitude to those estimated for the 1989 90 redoubt eruption strong correlations between daily omi so2 mass and both tephra mass and acoustic energy during the explosive phase of the eruption suggest that omi data may be used to infer relative eruption size and explosivity further when used in conjunction with complementary datasets omi daily so2 masses may be used to help distinguish explosive from effusive activity and identify changes in lava extrusion rates the results of this study suggest that omi is a useful volcano monitoring tool to complement airborne measurements capture explosive so2 emissions and provide high temporal resolution so2 emissions data that can be used with interdisciplinary datasets to illuminate volcanic processes

strain accommodation by slow slip and dyking in a youthful continental rift east africa continental rifts begin and develop through repeated episodes of faulting and magmatism but strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented in highly evolved rifts tensile stresses from far field plate motions accumulate over decades before being released during relatively short time intervals by faulting and magmatic intrusions1 2 3 these rifting crises are rarely observed in thick lithosphere during the initial stages of rifting here we show that most of the strain during the july august 2007 seismic crisis in the weakly extended natron rift tanzania was released aseismically deformation was achieved by slow slip on a normal fault that promoted subsequent dyke intrusion by stress unclamping this event provides compelling evidence for strain accommodation by magma intrusion in addition to slip along normal faults during the initial stages of continental rifting and before significant crustal thinning

field examples and numerical modelling of oversteps and bends along normal faults in cross section abstract oversteps and bends along cross sections through small scale numerical modelling distinct element analysis has been carried out to simulate the patterns of deformation at oversteps and bends area increase pull apart development and localised stress concentration occur at extensional oversteps and bends stress concentration and a tendency for compaction are typical of contractional oversteps and bends such results are compatible with the structures observed in the field a sensitivity analysis of the modelling has been carried out to investigate the effects of variations in mechanical parameters on deformation although models with weaker properties are more deformable the overall geometry of deformation varies little with variations in mechanical parameters

shear test results for cohesion and friction coefficients for different granular materials scaling implications for their usage in analogue modelling abstract laboratory tests have been carried out on dry granular materials such as quartz sand glass microspheres and sugar with different grain size rounding and sphericity the measurements have been made with a simple shear test machine for different values of normal stress 50 900 pa shear stress has been plotted against normal stress in order to determine the cohesion and coefficient of internal friction for the investigated materials resulting values of cohesion and coefficient of internal friction are mainly dependent on rounding and sphericity while grain size has a less significant influence further the behaviour of the materials for very small normal stresses 0 400 pa is more complex than previously assumed the fracture envelopes for all materials investigated are convex outward for this small range and converge towards a straight failure envelope with increasing normal stress finally in extensional faulting experiments there is no significant change in fault dip with increasing depth therefore the non linear behaviour for small normal stresses is best described as a dependence of the cohesion on the normal stress and not as a dependence of the coefficient of internal friction on the normal stress values for cohesion increase from 0 pa 15 pa at zero normal stress to 137 247 pa 15 pa for normal stresses greater than 250 400 pa the results show that well rounded spherical material is better suited to model brittle behaviour of rocks in crustal and lithospheric scale analogue models than less well rounded material since it has a smaller cohesion and a coefficient of internal friction which is closer to values of natural rocks

so2 loss rates in the plume emitted by soufriere hills volcano montserrat to improve interpretation of volcanic so2 flux data it is necessary to quantify and understand reactions involving so2 in volcanic plumes so2 is lost in volcanic plumes through a number of mechanisms here we report so2 measurements made with miniature ultraviolet spectrometers at soufriere hills volcano montserrat a low altitude volcano 1000 m above sea level whose plume entrains humid marine air in the planetary boundary layer traverses very near 2 km downwind from soufriere hills volcano significantly underestimate at source so2 emission rates on the order of 70 146 when not accounting for the decay rate similar so2 loss is likely to occur in plumes from other tropical low altitude volcanoes under conditions of high relative humidity 20 of active volcanoes worldwide these results suggest that the global volcanic so2 emission rate may be underestimated as the estimates are based on measurements taken downwind of volcanoes by which time significant loss of so2 may have taken place the loss rates calculated here could be used in conjunction with downwind so2 fluxes to estimate at source so2 emission rates from volcanoes with similar environmental conditions to those at soufriere hills volcano

satellite measurement of sulfur dioxide from the redoubt eruptions of 1989 1990 abstract the mass of so 2 emitted by the 16 major explosive eruptions of redoubt volcano between december 1989 and april 1990 have been examined by the total ozone mapping spectrometer toms carried on the nimbus 7 satellite because of low light levels during the winter months toms could not detect so 2 at high northern latitudes thus the major eruptions from december through february could not be monitored unless winds brought the clouds to latitudes lower than about 58 n only two so 2 clouds were observed in the satellite data an approximately 100 kiloton kt cloud on december 16 over nevada and eastern california and a 10 kt cloud on march 9 directly over the volcano we speculate that the major eruption on december 15 at 1015 hour produced the 100 kt cloud seen on december 16 and the mass of so 2 injected into the atmosphere at that time was 175 50 kt

rapid chemical evolution of tropospheric volcanic emissions from redoubt volcano alaska based on observations of ozone and halogen containing gases abstract we report results from an observational and modeling study of reactive chemistry in the tropospheric plume emitted by redoubt volcano alaska our measurements include the first observations of br and i degassing from an alaskan volcano the first study of o 3 evolution in a volcanic plume as well as the first detection of bro in the plume of a passively degassing alaskan volcano this study also represents the first detailed spatially resolved comparison of measured and modeled o 3 depletion in a volcanic plume the composition of the plume was measured on june 20 2010 using base treated filter packs for f cl br i and s at the crater rim and by an instrumented fixed wing aircraft on june 21 and august 19 2010 the aircraft was used to track the chemical evolution of the plume up to 30 km downwind 2 h plume travel time from the volcano and was equipped to make in situ observations of o 3 water vapor co 2 so 2 and h 2 s during both flights plus remote spectroscopic observations of so 2 and bro on the august 19th flight the airborne data from june 21 reveal rapid chemical o 3 destruction in the plume as well as the strong influence chemical heterogeneity in background air had on plume composition spectroscopic retrievals from airborne traverses made under the plume on august 19 show that bro was present 6 km downwind 20 min plume travel time and in situ measurements revealed several ppbv of o 3 loss near the center of the plume at a similar location downwind simulations with the plumechem model reproduce the timing and magnitude of the observed o 3 deficits and suggest that autocatalytic release of reactive bromine and in plume formation of bro were primarily responsible for the observed o 3 destruction in the plume the measurements are therefore in general agreement with recent model studies of reactive halogen formation in volcanic plumes but also show that field studies must pay close attention to variations in the composition of ambient air entrained into volcanic plumes in order to unambiguously attribute observed o 3 anomalies to specific chemical or dynamic processes our results suggest that volcanic eruptions in alaska are sources of reactive halogen species to the subarctic troposphere

successive detachment faults and mantle unroofing at magma poor rifted margins seismic depth images show that magma poor rifted margins between iberia and newfoundland are characterized by two different types of detachment that led to the unroofing of a broad expanse of mantle low angle detachments develop in serpentinites at the base of pre thinned crust and control further crustal thinning these detachments are cut by large offset faults rooting at a steep angle but with an exhumed slip surface and footwall flexurally rotated to a low angle during unroofing successive generations of this second type of detachment lead to the roughly symmetric unroofing of a broad expanse of mantle as new detachments repeatedly cut through the footwall of the preceding detachment leaving the abandoned root zone as landward dipping reflectors within exhumed mantle on both sides of the developing rift

a healing reloading feedback control on the growth rate of seismogenic faults spatial and temporal variations in the growth rates of faults are explained in terms of a stress feedback mechanism operating in the seismogenic upper crust it is based on the idea that seismic rupture of a fault perturbs the surrounding stress field advancing the occurrence of future earthquakes on some faults that are optimally oriented while relaxing stress levels on others if post slip healing is geologically rapid then the earthquakes that are thus induced will contribute to reloading along the earlier rupture zone because of the symmetry of the optimal geometry a positive feedback is set up so that even in areas that are undergoing uniform tectonic straining some faults develop higher displacement rates and grow more rapidly while others experience reduced rates or become inactive using a thin plate elastic model for lithospheric scale faulting it is shown that this healing reloading feedback mechanism drives rapid localisation and the formation of major through going faults moving at plate boundary velocities enhanced displacement rates compared to an isolated fault develop shortly after the onset of deformation along those faults which are optimally positioned in the overall fault population thus the formation of a new plate boundary fault zone is predetermined and is a consequence of rather than the precursor of preferentially high displacement rates also fault segments located at points of rupture symmetry e g the central portion of a fault zone are reloaded more frequently and develop higher displacement rates and consequently have longer segment lengths and or larger displacement to length ratios episodic fault movement through time is a general feature of the model these predictions are consistent with available field observations over a wide range of scales thus elastic brittle failure and healing appear to be important rheological components of the lithosphere on long time scales 104 106 y as well as on the time scale of earthquake recurrence

influence of lithological heterogeneity mechanical anisotropy and magmatism on the rheology of an arc north cascades washington abstract many aspects of crustal dynamics are dependent on changes in rheology and strength with depth in the lithosphere several of the controlling factors for rheology are difficult to study experimentally particularly lithological heterogeneity mechanical anisotropy and magmatism and we focus on these in a study of the deformation patterns in a thick crustal section 5 to 40 km paleodepth through the cretaceous cascades core of the nw cordillera this magmatic arc consists of metamorphosed oceanic and arc terranes intruded by magmatic bodies ranging from heterogeneous brittle deformation marked by serpentinite melange characterizes the shallowest part of the crustal section and the remainder of the section is characterized by heterogeneous fold dominated ductile deformation early tight to isoclinal recumbent folds and associated axial planar fabrics are refolded by one or more cycles of nearly coaxial open to isoclinal upright to overturned folds layering played a mechanically active role during folding at all levels as indicated by cleavage refraction boudinaged layers and kinematic indicators that record fold related shear ductile deformation intensifies in the narrow structural aureoles of plutons and sw directed reverse shear was partitioned into some of the aureoles the poor strain memory of these magmatic bodies makes it difficult to determine if deformation was focused in the pluton magma chambers before they reached the solidus as commonly predicted all of the plutons have magmatic foliations that at least in part reflect regional strains and these foliations are strong in the deeper plutons the thinner sheets acted as competent bodies during folding and boudinage after they reached the solidus but generally did not cause marked strain gradients in their hosts a relative strength profile constructed for the cascades crustal section shows an overall decrease in strength with depth for the ductile part of the arc that fits idealized strength profiles however in more detail relative strengths are markedly variable units were able to accumulate large ductile strains but even small variations in the physical properties of interlayered rock types exerted a strong influence on deformation patterns throughout the mid to deep crustal part of the profile this profile thus emphasizes the complex vertical rheological stratification of arcs at the crustal to thin section scale and should be applicable to many other magmatic arcs

infrasound from tungurahua volcano 2006 2008 strombolian to plinian eruptive activity abstract strombolian to plinian activity from tungurahua volcano ecuador has been recorded by the autonomous infrasound arrays of the acoustic surveillance for hazardous eruptions ashe project since early 2006 our studies suggest that acoustic energy release during large eruptions does appear to broadly scale with eruption intensity this manuscript provides a detailed chronology and characterization of tungurahua s eruptive activity between 2006 and 2008 and demonstrates the ability to constrain source parameters of significant eruptions such as onset duration and escalation at regional distances by combining infrasound and remote sensing techniques the ashe system in ecuador automatically detected over 20 000 volcanic explosions at an array 37 km from tungurahua and was successful at notifying the onset escalation and cessation of a hazardous february 2008 eruption with a latency of 5 min elevated infrasonic energy from sustained and intense tungurahua eruptions correlates well with ash column heights and their lateral extent during the study period the spectra of these sustained explosive eruptions appear to be recurrent readily recognizable and indicative of volcanic jetting and significant atmospheric ash injection the paroxysmal plinian phase of the august 2006 eruption produced an ash cloud that extended well into the stratosphere 24 km coinciding with a shift of the dominant jetting frequency from 0 25 hz to below 0 1 hz and radiation of over 5 107 w of acoustic power transient explosions were often marked by minor or no ash release and are presumed to be more gas rich a change in the acoustic spectrum of volcanic jetting was also detected in the transition from a sustained to collapsed eruption column at the end of the july 14 2006 eruption the jetting spectrum at tungurahua during a period of sustained pyroclastic density current production changes from a typical double peaked to a single peaked spectrum suggesting remote acoustic monitoring can help ascertain the stability and dynamics of an eruptive column

satellite and ground observations of the june 2009 eruption of sarychev peak volcano matua island central kuriles after 33 years of repose one of the most active volcanoes of the kurile island arc sarychev peak on matua island in the central kuriles erupted violently on june 11 2009 the eruption lasted 9 days and stands among the largest of recent historical eruptions in the kurile island chain satellite monitoring of the eruption using moderate resolution imaging spectroradiometer meteorological agency multifunctional transport satellite and advanced very high resolution radiometer data indicated at least 23 separate explosions between 11 and 16 june 2009 eruptive clouds reached altitudes of generally 8 16 km above sea level asl and in some cases up to 21 km asl clouds of volcanic ash and gas stretched to the north and northwest up to 1 500 km and to the southeast for more than 3 000 km for the first time in recorded history ash fall occurred on sakhalin island and in the northeast sector of the khabarovsky region russia based on satellite image analysis and reconnaissance field studies in the summer of 2009 the eruption produced explosive tephra deposits with an estimated bulk volume of 0 4 km3 the eruption is considered to have a volcanic explosivity index of 4 because the volcano is remote there was minimal risk to people or infrastructure on the ground aviation transport however was significantly disrupted because of the proximity of air routes to the volcano

the seismicity of the 2009 redoubt eruption article redoubt volcano erupted in march 2009 following 6 months of precursory seismic activity the 4 5 month long eruptive sequence was accompanied by phreatic and magmatic explosions periods of steady dome growth lahars seismic swarms extended episodes of volcanic tremor and changes in the background seismicity rate this study presents a seismic chronology of the eruption and places it in context with the variety of other geological and geophysical data that were recorded during the eruptive period we highlight 6 notable seismic swarms 3 of which preceded large explosions the swarms varied from an hour to several days in duration and contained tens to over 7000 earthquakes many of the swarms were dominated by low frequency type earthquakes that contained families of repeating events seismic tremor varied considerably in frequency amplitude and duration during the eruption with distinct characteristics accompanying different types of volcanic activity the explosion signals during march 23 24 were the most energetic and the explosions on march 26 29 contained proportionally more low frequency energy 0 033 0 3 hz two seismic stations were particularly well suited to recording lahars that flowed down the drift river valley data from these stations showed that lahars were generated by the majority of the explosion events as well as during the continuous eruptive activity on march 29 when no large explosions occurred we also examine the seismicity which occurred outside of the explosion and swarm episodes and find several families of repeating vt earthquakes which begin shortly before the april 4 explosion and that continue

is there a close spatial relationship between faults and plutons abstract using spatial relationships between individual plutons and faults to support genetic correlations between faulting and magmatism is meaningless since even random magmatic or tectonic processes will result in some plutons adjacent to faults our initial analyses of populations of faults and carboniferous plutons in the armorican massif france and faults and alleghanian plutons in the southern appalachians usa indicate that plutons have broad distributions with respect to faults but with a tendency for plutons to occur away from faults maxima of integrated pluton areas occur at 1 4 appalachians and 1 2 armorican of the distance between the average fault spacing in these orogens although there is a great need for statistical evaluations of relationships between populations of igneous bodies and structures in a wide variety of settings and crustal depths our initial studies suggest that faults do not preferentially channel magma during ascent or emplacement and that these are relatively unfocused processes within orogenic belts

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

emission rates of sulfur dioxide and carbon dioxide from redoubt volcano alaska during the 1989 1990 eruptions airborne measurements of sulfur dioxide emission rates in the gas plume emitted from fumaroles in the summit crater of redoubt volcano were started on march 20 1990 using the cospec method during the latter half of the period of intermittent dome growth and destruction between march 20 and mid june 1990 sulfur dioxide emission rates ranged from approximately 1250 to 5850 t d rates notably higher than for other convergent plate boundary volcanoes during periods of active dome growth emission rates following the end of dome growth from late june 1990 through may 1991 decreased steadily to less than 75 t d the largest mass of sulfur dioxide was released during the period of explosive vent clearing when explosive degassing on december 14 15 injected at least 175 000 50 000 tonnes of so2 into the atmosphere following the explosive eruptions of december 1989 redoubt volcano entered a period of intermittent dome growth from late december 1989 to mid june 1990 during which redoubt emitted a total mass of so2 ranging from 572 000 90 000 tonnes to 680 000 90 000 tonnes from mid june 1990 through may 1991 the volcano was in a state of posteruption degassing into the troposphere producing approximately 183 000 50 000 tonnes of so2 we estimate that redoubt volcano released a minimum mass of sulfur dioxide of approximately 930 000 tonnes while cospec data were not obtained frequently enough to enable their use in eruption prediction so2 emission rates clearly indicated a consistent decline in emission rates between march through october 1990 and a continued low level of emission rates through the first half of 1991 values from consecutive daily measurements of sulfur dioxide emission rates spanning the march 23 1990 eruption decreased in the three days prior to eruption that decrease was coincident with a several fold increase in the frequency of shallow seismic events suggesting partial sealing of the magma conduit to gas loss that resulted in pressurization of the shallow magma system and an increase in earthquake activity unlike the short term so2 decrease in march 1990 the long term decrease of sulfur dioxide emission rates from march 1990 through may 1991 was coincident with low rates of seismic energy release and was interpreted to reflect gradual depressurization of the shallow magma reservoir the long term declines in seismic energy release and in so2 emission rates led avo scientists to conclude on april 19 1991 that the potential for further eruptive activity from redoubt volcano had diminished and on this basis the level of concern color code for the volcano was changed from code yellow volcano is restless earthquake activity is elevated activity may include extrusion of lava to code green volcano is in its normal dormant state

pluton pinning of an active miocene detachment fault system eastern mojave desert california the miocene kingston range halloran hills detachment fault system of the eastern mojave desert california delineates part of the eastern breakaway zone for a profoundly extended area between the sierra nevada and the spring mountains structural blocks the shallow dipping west rooting detachment fault cuts discordantly across paleozoic and precambrian units in the mesozoic foreland fold and thrust belt exhibits west to southwest trending corrugations with structural relief of up to 1 5 km and underlies the terrestrial shadow valley basin middle miocene fault displacement and syntectonic sedimentation in the northern basin were terminated at 12 4 ma by intrusion of the large 130 km 2 shallow level 4 km depth kingston peak pluton across the detachment fault soon after faulting began basin sedimentation and fault displacement southeast of the pluton were not however disrupted by its emplacement and continued to evolve northern pluton pinned and southern pluton free domains were separated by the blacksmith hills fault a northeast striking right slip lateral ramp that accommodated more than 3 km of postpluton differential extension between pinned and nonpinned domains in more western regions late phases of detachment fault related extension beneath formerly pinned areas including western and central parts of the pluton itself are believed to have led to the development of two generations of east striking left slip faults collectively these dextral and sinistral transfer faults illustrate the complex patterns of differential extension and accommodation that can characterize detachment fault systems as adjacent areal domains of extension are generated and die

kinematic evolution of the eastern chalk draw fault during basin and range extension evaluating the role played by preexisting structural fabrics in along strike displacement patterns abstractbasin and range extensional structures in trans pecos texas have been interpreted to be strongly influenced by preexisting structures including igneous centers in the big bend region these igneous centers are interpreted to have deflected propagating faults as they are rheologically strong relative to the surrounding rocks we conducted detailed field mapping and analysis of fracture and fault data along the eastern segment of the chalk draw fault in big bend national park to evaluate its kinematic evolution and interaction with paleogene plutons our primary results document the following key relationships 1 the rosillos laccolith and other paleogene plutons in the study area are pervasively fractured dominantly by northwest striking mode i fractures which generally do not extend into adjacent sedimentary rock sequences 2 throw on the eastern chalk draw fault is strongly asymmetric decreasing rapidly as it enters the rosillos laccolith and 3 analysis of fault slip data in the regio

how do the properties of a pre existing normal fault population influence fault development during a subsequent phase of extension abstract we use scaled experimental analog models to investigate how the properties of a population of pre existing normal faults influence fault development during a subsequent phase of extension in the models a homogeneous layer of wet clay undergoes two phases of extension whose extension directions differ by 45 to vary the properties of the first phase fault population we vary the magnitude of the first phase extension as the magnitude of the first phase extension increases the number average and maximum length and average and maximum displacement of the first phase normal faults increase for a poorly developed first phase fault population new normal faults which strike perpendicular to the second phase extension direction form during the second phase for a well developed first phase fault population many first phase normal faults are reactivated as oblique slip faults during the second phase new normal faults also form these second phase normal faults are shorter and have displacement maxima adjacent to the reactivated first phase faults they are less likely to cut the pre existing first phase faults than second phase normal faults that form in models with a less developed first phase fault population in all models pre existing faults serve as nucleation sites for new faults in models with a well developed first phase fault population the pre existing faults also act as obstacles to the propagation of the second phase normal faults fault geometries in the models vary considerably parallel zig zag or intersecting fault geometries develop depending on whether the first phase fault population is poorly moderately or well developed respectively

a summary of sulfur dioxide emission rate measuremnts from guatemalan volcanoes measurements of the sulfur dioxide so2 emission rate from three guatemalan volcanoes provide data which are consistent with theoretical and laboratory studies of eruptive and shallow magma chamber processes in particular unerupted magma makes a major contribution to the measured so2 emission rates at santiaguito a continuously erupting dacitic volcanic dome varying shallow magma convection rates can explain the variations in so2 emission rates at santiaguito at fuego a basaltic volcano currently in repose so2 emission rate measurements are consistent with a high level magma body that is crystallizing and releasing volatiles at pacaya a continuously erupting basaltic volcano recent so2 emission rate measurements support laboratory simulation studies of strombolian eruptions these studies indicate that the majority of gas escapes during eruptions and little gas escapes between eruptions average so2 emission rates over the last 20 years for santiaguito fuego and pacaya are 80 160 and 260 mg d respectively on a global scale these three volcanoes account for 1 of the annual global volcanic output of so2 santiaguito and pacaya together emit 6 of the total annual so2 emitted by continuously erupting volcanoes even though so2 measurements at these volcanoes have been made infrequently and by different investigators the collective data help to establish a useful baseline by which to judge future changes a more complete record of so2 emission rates from these volcanoes could lead to a better understanding of their eruption mechanisms and reduce the impact of their future eruptions on guatemalan society