ree th and u behaviour during hydrothermal and supergene processes in a granitic environment the two mica granites which host the two main uranium deposits from the northwestern massif central france margnac fanay and le bernardan deposits were hydrothermally altered both before and during the deposition of the primary u mineralization both altered rocks and mineralizations were then subjected to supergene processes we have analyzed the rare earth elements ree th and u in fresh and altered mineralized and barren whole rocks and in the pitchblendes to study the behaviour of these elements during hydrothermal and supergene processes in a granitic environment when fluids are aqueous with a low salt content mainly chloride then irrespective of temperature 400 450 c for feldspar episyenitization 350 c for mica episyenitization and 100 150 c for the quartz coffinite montmorillonite adularia stage the ree patterns and parameters the hree lree fractionation the th concentration and the th ce ratio are not modified this indicates that monazite which controls these elements in the two mica granites remains stable under such conditions in contrast when ligands are present in the solutions co2 3 or hco 3 with the pitchblende stage at 350 c hpo2 4 or other phosphorous anions during supergene events at low temperatures ree are either leached or concentrated depending on the prevailing redox conditions and there is hree lree fractionation the ree content of the newly formed minerals pitchblende appears to be mainly controlled in such deposits by the fluid composition

magma supply dynamics at westdahl volcano alaska modeled from satellite radar interferometry 1 a group of satellite radar interferograms that span the time period from 1991 to 2000 shows that westdahl volcano alaska deflated during its 1991 1992 eruption and is reinflating at a rate that could produce another eruption within the next several years the rates of inflation and deflation are approximated by exponential decay functions having time constants of about 6 years and a few days respectively this behavior is consistent with a deep constant pressure magma source connected to a shallow reservoir by a magma filled conduit an elastic deformation model indicates that the reservoir is located about 6 km below sea level and beneath westdahl peak we propose that the magma flow rate through the conduit is governed by the pressure gradient between the deep source and the reservoir the pressure gradient and hence the flow rate are greatest immediately after eruptions pressurization of the reservoir decreases both the pressure gradient and the flow rate but eventually the reservoir ruptures and an eruption or intrusion ensues the eruption rate is controlled partly by the pressure gradient between the reservoir and surface and therefore it too decreases with time when the supply of eruptible magma is exhausted the eruption stops the reservoir begins to repressurize at a high rate and the cycle repeats this model might also be appropriate for other frequently active volcanoes with stable magma sources and relatively simple magma storage systems

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

physicochemical models of effusive rhyolitic eruptions constrained with insar and dem data a case study of the 2011 2012 cordon caulle eruption abstract the 9 month long 2011 2012 eruption of cordon caulle southern andes chile is the best instrumentally recorded rhyolitic eruption to date and the first time that the effusion of a rhyolitic flow has been observed in detail we use interferometric synthetic aperture radar insar with time lapse digital elevation models dems and numerical models to study the dynamics of coupled magma reservoir deflation and lava effusion insar recorded 2 2 2 5 m of subsidence after the first three days of the eruption which can be modeled using a spheroidal magma reservoir at a depth of 5 km 20 km long and with a pressure drop of 20 30 mpa the source is elongated in the nw se direction and its large dimensions imply a large plumbing system active throughout the eruption and spanning neighboring volcanoes with a slight change in the geometry halfway through the effusive phase tandem x and pleiades dems record the extrusion of both the rhyolitic lava flow and the intrusion of a shallow laccolith around the eruptive vent after the third day of the eruption with a total volume of 1 45 km3 dre the laccolith was emplaced during the first month of the eruption during both the explosive and effusive stages of the eruption both the reservoir pressure drop and the extruded volume time series follow quasi exponential trends and can be explained by a model that couples the reservoir pressure decrease time and pressure dependent variations in the magma properties inside of the reservoir and conduit flow this model predicts both the temporal evolution and amplitude of both time series during the effusive phase and a magma compressibility of 10 10 pa 1 half the reported compressibility of the magma of the sub plinian explosive phase further we estimate that the reservoir contained 1 3 wt dissolved h2o at the onset of lava effusion with no exsolved co2 and h2o in the reservoir throughout the effusive phase this implies that the magma was significantly degassed after the explosive phase the remaining volatiles in the magma after the explosive stage might have caused magma fragmentation consistent with the hybrid explosive effusive style observed during the waning of the eruption

possible structural control on the 2011 eruption of puyehue cordon caulle volcanic complex southern chile determined by insar gps and seismicity

global variability in subduction thrust zone forearc systems deviations of slip vector azimuths of interplate thrust earthquakes from expected plate convergence directions at oblique subduction zones provide kinematic information about the deformation of forearcs and indirect evidence on the dynamics of the plate boundary a global survey of slip vectors at major trenches of the world reveals a large variability in the kinematic response of forearcs to shear produced by oblique convergence the variability in forearc deformation inferred from slip vector deflections is suggested to be caused by variations in forearc rheology rather than in the stresses acting on subduction zone thrust faults estimated apparent macroscopic rheologies range from elastic to perfectly plastic or viscous forearc rheologies inferred from slip vectors do not correlate with age of the subducting lithosphere but continental forearcs or old arcs appear to deform less than oceanic or young arcs the inferred absence of forearc deformation at continental arcs from this study is counter to inferences drawn from compiled geologic information on forearc faults correlations of the apparent forearc rheology with backarc spreading convergence rate slab dip arc curvature and downdip length of the thrust contact are poor however great subduction zone earthquakes occur where forearcs are apparently more elastic i e less deformed by oblique convergence which suggests that the mechanical properties of forearcs rather than stress magnitude on thrust faults control both the kinematic behavior of forearcs and where great subduction zone earthquakes occur

high rates of inflation during a noneruptive episode of seismic unrest at semisopochnoi volcano alaska in 2014 2015

morpho structural evolution of the cordon caulle geothermal region southern volcanic zone chile insights from gravity and 40ar 39ar dating the cordon caulle geothermal region 40 5 s is a 13 km 6 km nw se elongate volcano tectonic depression hosting numerous monogenetic volcanic centers fumaroles and hot springs most of which occur spatially associated with the edges of the depression volcanism started at approximately 0 3 ma with dominantly mafic effusions and expressed ultimately in post glacial and historic dacite rhyolite eruptions 1921 1922 and 1960 three ne trending gravimetric profiles were carried out across the depression of cordon caulle yielding a residual negative anomaly with the greatest amplitude 20 mgal at the center of the depression a 2d gravity model given by a 490 m thick shallow body with a density contrast 650 kg m3 interpreted as a shallow package of dacite rhyolite lavas and tephra was found to match the residual anomaly a dense rock equivalent volume of felsic material on the order of 28 km3 25 of the total output of cordon caulle is derived from this thickness previous workers explain the origin of felsic rocks at cordon caulle in terms of the orientation of the borders of cordon caulle relative to the maximum stress direction 1 i e ne trending prevailing during the quaternary according to which nw trending domains were compressional favoring stagnation storage and differentiation of magmas the dominantly monogenetic style of volcanism the plateau like morphology and the negative bouguer anomaly on the contrary are interpreted as an indication of extensional tectonics intra arc extension is proposed to be related to coseismic or postseismic stress relaxation accompanying major thrust events such as the great 1960 chilean earthquake which is consistent at cordon caulle with the direction of propagation of dikes of the 1960 eruption i e coseismic extension and present day subsidence inferred from insar data i e postseismic extension prior to the quaternary 8 2 1 6 ma nearly east west compression prevailed at the intra arc zone a 5 44 0 04 ma old granodiorite intrusion bracketed by two sub parallel branches of the regional margin parallel liquine ofqui fault zone lofz in a prominent pop up structure 15 km to the east of cordon caulle accounts for reverse reactivation of the lofz and rapid fault related exhumation of basement rocks 1 mm year we argue that under compression reverse reactivation of the lofz was facilitated by the combined effect of cyclic increase in fluid pressure induced by magmatic hydrothermal input and removal of lithostatic load induced by glacial erosion 1 5 mm year in the vicinity of cordon caulle

continuous mixing of crystal mush and replenished magma in the ongoing unzen eruption zoning profiles of magnetite phenocrysts in the successively effused dacite of the ongoing unzen eruption from 1991 wereanalyzed to estimate the time scale of magma mixing the dacite was formed by mixing of relatively high and low temperature t end member magmas the magnetite phenocrysts derived from the low t magma are reversely zoned by the mixing with high t magma a diffusion calculation for reequilibration of the reverse zonings gives the time interval from magma mixing to quenching for the mixed dacite erupted from may 1991 to may 1993 the typical diffusion time was estimated to be a few months regardless of the effused sequence for 2 yr this indicates that the mixing was continuous during the effusion the invariability of the other mixing signatures such as the thickness of reaction rims around biotite phenocrysts also supports the continuous mixing model low t end member magma is estimated by mass balance calculation to be a crystal rich mush of dacitic composition these observations lead to a model wherein the highly crystallized remnant magma of the preceding activity has been mixed with the newly injected hot magma of similar bulk composition just prior to the effusion the proposed mechanism implies that this type of magma mixing is an inevitable process in periodically erupting polygenetic volcanoes

ridge segmentation and the magnetic structure of the southwest indian ridge at 50 30 e 55 30 e and 66 20 e implications for magmatic processes at ultraslow spreading centers 1 the aim of this paper is to investigate the relationships between the segmentation and the magnetic structure of the ultraslow spreading southwest indian ridge contrary to faster spreading ridges magnetization usually decreases from high values along the neovolcanic axis to low values in the nontransform discontinuities there is a direct correlation between the deepening of the axial valley and the decrease of the magnetization from the neovolcanic axis toward the deepest parts of the axial discontinuities we suggest that less frequent eruptions as the distance from the segment center and the length of these discontinuities increase result in thinner extrusive lavas and thus control the along axis magnetization variations by thinning the magnetic source layer a unique segment centered at 50 28 e shows a marked low magnetization anomaly at its center similarly to the segments of the slow spreading mid atlantic ridge we suggest that in this segment both the mantle temperature and the magmatic activity are high enough for the lavas not to be highly fractionated a higher rate of melt production to the west of gallieni transform fault may have created some form of reservoir where mixing of melts occurs and where crystalline fractionation is low producing low magnetization lavas to the east magma chambers may be smaller with cooler mantle temperatures resulting in restricted mixing and significant fractionation which may lead to relatively high intensity magnetization lavas finally we propose that serpentinization of peridotites has no significant contribution to the variation of the magnetization along the axial valley off axis in thin crust areas upper mantle rocks may become progressively more altered as distance from the axis increases the strong faulting and alteration of a thin basaltic cap and underlying upper mantle rocks can produce the disappearance of the magnetic reversal pattern and the increase of the magnetization which is observed along the traces of the largest amagmatic discontinuities by contrast in thicker crust areas the upper mantle rocks are shielded from the alteration and the serpentinization process may be delayed resulting as on the mid atlantic ridge in slightly more positive magnetization values along the traces of axial discontinuities regardless of polarity

petrological and experimental constraints on the pre eruption conditions of holocene dacite from volcan san pedro 36 s chilean andes and the importance of sulphur in silicic subduction related magmas we present an experimental and petrological study aimed at estimating the pre eruptive conditions of a holocene dacitic lava from volcan san pedro 36 s chilean andes phase equilibrium experiments were performed at temperatures t from 800 to 950 c and mainly at 200 mpa but also at 55 150 and 406 mpa oxygen fugacity fo2 ranged from the ni nio buffer nno to 3 5 log units above nno 3 5 and water contents from 3 to 6 wt we also report several experiments where we added sulphur 0 1 1 wt s to the dacite the main mineral assemblage of the dacite hornblende orthopyroxene plagioclase is stable at 200 50 mpa 850 10 c with 4 5 5 5 wt h2o in the melt and at fo2 of nno 1 2 0 2 in accord with the crystallinity mineral proportions and t fo2 determination from fe ti oxides of the lava however biotite which is also present in the dacite is stable at these same t fo2 conditions only in experiments with 0 1 wt s added this result is in accord with the occurrence of pyrrhotite in the lava and with the presence of s in glass inclusions and biotite 300 ppm and up 170 ppm respectively moreover the zoning patterns and compositions of plagioclase phenocrysts together with the presence of high temperature minerals e g clinopyroxene in the lava suggest that the petrological history of the dacite is more complex than a single near equilibrium crystallization stage and could be explained by short lived 100 years temperature fluctuations 50 c in the magma reservoir

thermal deformation and degassing remote sensing time series ce 2000 2017 at the 47 most active volcanoes in latin america implications for volcanic systems

the lateral growth and coalesence of magma systems thermal and mechanical models of magma reservoir growth need to be reconciled with deformation patterns and structural relationships observed at active magma systems geophysical observations provi

deposition of the 2011 2012 cordon caulle tephra chile 40 s in lake sediments implications for tephrochronology and volcanology tephras preserved in lake sediments are commonly used to synchronize sedimentary archives of climate and environmental change and to correlate them with terrestrial environments they also provide opportunities to reconstruct volcanic explosive activity e g eruption frequency and tephra dispersal although sedimentary processes may affect the record of tephras in lakes lake sediments are generally considered as one of the best archives of tephra stratigraphy the 2011 2012 eruption of cordon caulle volcano chile 40 degrees s offered an ideal opportunity to study the processes affecting tephra deposition in lakes although the prevailing westerlies transported the erupted pyroclastic material away from nearby puyehue lake the tephra was identified within this relatively large lake with a thickness ranging from 1 to 10cm this is in contrast with smaller lakes where tephra thickness was in agreement with ashfall distribution maps geomorphological observations and sedimentological analyses provide evidence that the tephra deposited in puyehue lake entirely consists of material reworked from the upper watershed transported by rivers and distributed by lake currents according to particle size and density our results have important implications for tephrochronology and volcanology they suggest that 1 lakes do not act as passive tephra traps 2 lakes with large watersheds record more eruptions than smaller lakes which only register direct ashfalls affecting conclusions regarding the recurrence of volcanic eruptions and 3 using lakes with large watersheds for isopach mapping systematically leads to an overestimation of erupted tephra volumes smaller lakes with limited drainage basins are generally better suited for volcanological studies

volcanic subsidence triggered by the 2011 tohoku earthquake in japan the 2011 tohoku earthquake caused high levels of crustal deformation in japan analysis of satellite radar and gps data show that the earthquake caused nearby volcanic regions to subside instantaneously creating elliptical depressions that are parallel to the direction of quake induced crustal extension

geochemical constraints on the role of tuffisite veins in degassing at the 2008 09 chaiten and 2011 12 cordon caulle rhyolite eruptions abstract hybrid activity during the rhyolitic eruptions of chaiten 2008 09 and cordon caulle 2011 2012 in chile has offered unprecedented insights into the enigmatic and complex degassing processes occurring during eruptions of silicic magma highly permeable transient fracture networks within the conduit can act as outgassing channels their interaction with deeper volatile rich melt can account for both punctuated explosive activity and large scale degassing of the system leading towards predominantly effusive behaviour in this study we characterise trace element concentrations and 210pb 226ra systematics within pyroclastic material from the recent eruptions at chaiten and cordon caulle volcanoes results reveal how gas fluxing from deep volatile rich reservoirs to the surface within magmatic conduits can be recorded by trace elements and 210pb 226ra disequilibria in tuffisite veins tuffisite veins particle filled fracture networks are present in volcanic bombs from both eruptions trace element heterogeneity associated with tuffisites preserves evidence for degassing at chaiten enrichments e g cu and depletions e g mo li and bi are identified in vein material and clasts transported within veins and record multiple degassing events at cordon caulle enrichments of volatiles in an early vein e g tl and bi and depletions in a later vein e g cd in pb and tl reflect interactions between glassy clasts and the carrier gas phase that transported them in contrast 210pb and 226ra which can be fractionated during degassing are mostly in secular equilibrium modelling suggests that the disparity between the signals preserved in these two types of chemical signatures reflects the brevity of degassing events and the relative volumes of tuffisite veins and the bodies of degassing magma that they source gas from the lack of preserved 210pb enrichments in tuffisite veins at both volcanoes places an upper limit on the mass of deeper bubble rich magma outgassed via tuffisites during their lifetime this study shows that both the presence and absence of sample scale geochemical heterogeneity can be used to place constraints on syn eruptive physical processes and underlines the value of analysing a wide suite of trace element species

complex dynamics of small moderate volcanic events the example of the 2011 rhyolitic cordon caulle eruption chile after decades of repose puyehue cordon caulle volcano chile erupted in june 2011 following a month of continuously increasing seismic activity the eruption dispersed a large volume of rhyolitic tephra over a wide area and was characterized by complex dynamics during the initial climactic phase of the eruption 24 30 h on 4 5 june 11 14 km high plumes dispersed most of the erupted tephra eastward towards argentina reaching as far as the atlantic ocean this first eruptive phase was followed by activity of lower intensity leading to the development of a complex stratigraphic sequence mainly due to rapid shifts in wind direction and eruptive style the resulting tephra deposits consist of 13 main layers grouped into four units each layer was characterized based on its dispersal direction sedimentological features and on the main characteristics of the juvenile fraction texture density petrography chemistry the lowest part of the eruptive sequence unit i corresponding to the tephra emitted between 4 and 5 june is composed of alternating lapilli layers with a total estimated volume of ca 0 75 km3 these layers record the highest intensity phase during which a bent over plume dispersed tephra towards the southeast east with negligible up wind sedimentation products emitted during 5 6 june unit ii signaled an abrupt shift in wind direction towards the north leading to the deposition of a coarse ash deposit in the northern sector ca 0 21 km3 in volume followed by a resumption of easterly directed winds a third phase unit iii began on 7 june and resulted in tephra deposits in the eastern sector and ballistic bombs around the vent area a final phase unit iv started after 15 june and was characterized by the emission of fine grained white tephra from ash charged plumes during low level activity and the extrusion of a viscous lava flow timing and duration of the first eruptive phases were constrained based on comparison of the dispersal of the main tephra layers with satellite images showing that most of the tephra was emitted during the first 72 h of the event the analyzed juvenile material tightly clusters within the rhyolitic field with negligible chemical variations through the eruptive sequence textural observations reveal that changes in eruption intensity and consequently in magma ascent velocity within the conduit and complex interactions between gas rich and gas depleted magma portions during ascent resulted in vesicular clasts with variable degrees of shear localization and possibly in the large heterogeneity of the juvenile material

diffusion coupling between trace and major elements and a model for calculation of magma residence times using plagioclase residence times of plagioclase crystals in magma reservoirs can be determined by modeling the compositional zoning of trace elements in these crystals we present a formulation to model diffusion of trace elements in plagioclase paying special attention to certain thermodynamic and kinetic aspects in particular we account for the compositional dependence on anorthite content of the chemical potential and diffusion coefficients of trace elements e g mg the choice of suitable boundary conditions and potential effects of diffusion in more than one dimension we show that contrary to intuition diffusive fluxes of trace elements may be coupled to major element concentration gradients and ignoring such coupling can lead to incorrect estimates of timescales we illustrate application of the model using plagioclase crystals from a suite of gabbroic xenoliths from a holocene dacitic lava flow of volcan san pedro chilean andes 36 s the inferred timescale for metasomatism of the xenoliths by evolved liquids is on the order of 100 30 to 148 yr and serves to illustrate how trace element zoning in plagioclase provides a window into timescales of magmatic processes inaccessible by isotopic or other methods

triggering of volcanic eruptions although earthquakes and volcanic eruptions are each manifestations of large scale tectonic plate and mantle motions it is usually thought that the occurrences of these events are not directly related there have been some studies however in which triggering of volcanic eruptions by earthquakes remote from the volcano has been proposed1 2 the 1992 landers southern california earthquake caused triggered seismicity at very large distances3 including the magmatically active4 long valley caldera region which also experienced a significant coincident deformation transient5 motivated by this demonstration of the ability of a distant earthquake to disturb a volcanic system and the earlier studies of specific cases of eruption triggering we examine here the historical record of eruptions and earthquakes to see if there are indeed significantly more eruptions immediately following large earthquakes we find that within a day or two of large earthquakes there are many more eruptions within a range of 750 km than would otherwise be expected additionally it is well known6 that volcanoes separated by hundreds of kilometres frequently erupt in unison the characteristics of such eruption pairs are also consistent with the hypothesis that the second eruption is triggered by earthquakes associated with the first

pre eruptive ground deformation of azerbaijan mud volcanoes detected through satellite radar interferometry dinsar abstract mud volcanism is a process that leads to the extrusion of subsurface mud fragments of country rocks saline waters and gases this mechanism is typically linked to hydrocarbon traps and the extrusion of this material builds up a variety of conical edifices with a similar morphology to those of magmatic volcanoes though smaller in size the differential interferometry synthetic aperture radar dinsar technique has been used to investigate the ground deformation related to the activity of the mud volcanoes of azerbaijan the analysis of a set of wrapped and unwrapped interferograms selected according to their coherence allowed the detection of significant superficial deformation related to the activity of four mud volcanoes the ground displacement patterns observed during the period spanning from october 2003 to november 2005 are dominated by uplift which reach a cumulative value of up to 20 and 10 cm at the ayaz akhtarma and khara zira island mud volcanoes respectively however some sectors of the mud volcano edifices are affected by subsidence which might correspond to deflation zones that coexist with the inflation zones characterized by the dominant uplift important deformation events caused by fluid pressure and volume variations have been observed both 1 in connection with main eruptive events in the form of pre eruptive uplift and 2 in the form of short lived deformation pulses that interrupt a period of quiescence both deformation patterns show important similarities to those identified in some magmatic systems the pre eruptive uplift has been observed in many magmatic volcanoes as a consequence of magma intrusion or hydrothermal fluid injection moreover discrete short duration pulses of deformation are also experienced by magmatic volcanoes and are repeated over time as multiple inflation and deflation events

the prevalence and significance of offset magma reservoirs at arc volcanoes determining the spatial relations between volcanic edifices and their underlying magma storage zones is fundamental for characterizing long term evolution and short term unrest we compile centroid

the pb isotopic systematics during crustal contamination of subcrustal magmas the hercynian magmatism in the serie dei laghi southern alps italy abstract the pb isotopic composition and pb u and th concentrations of a series of hercynian granite plutons and mafic intermediate stocks and dykes belonging to the serie dei laghi western southern alps have been analyzed the initial pb isotope ratios of both the granites and the dykes are typical of the lower crust and are spread over a significant range 206 pb 204 pb 280 17 883 18 530 207 pb 204 pb 280 15 597 15 710 and 208 pb 204 pb 280 38 077 38 708 four dykes all at the same locality display evidence of post emplacement fluid circulation with mobilization of u and pb in spite of the pb isotopic crustal signature of the studied rock series the 87 sr 86 sr ratios reach values as low as 0 704 in the dykes and as low as 0 707 in the granites suggesting a mantle contribution in the genesis of both lithologies indeed when compared with the metasediments from the same area the magmatic rocks have somewhat lower initial 207 pb 204 pb ratios which weakly trend towards the less radiogenic pb isotopic composition of the mantle the relationships between the pb isotopic composition and the pb content along with the pb and sr isotopic covariation suggest that the suite under examination was generated from a mantle derived primary magma that underwent extensive crustal contamination a primary magma similar to the neighbouring ivrea mafic complex has been inferred further assimilation of crustal material is particularly evident in the dykes while the granites appear to have been generated mainly by crystal fractionation processes from the intermediate magma already contaminated

eruptive history geochronology and magmatic evolution of the puyehue cordon caulle volcanic complex chile forty three 40 ar 39 ar age determinations of lava flows domes ignimbrites and dikes plus 14 c dates from seven distal tephra layers combined with stratigraphy geochemistry and sr and th isotope data establish an eruptive chronology for the puyehue cordon caulle volcanic complex at 40 5 s in the andean southern volcanic zone svz the complex preserves 131 km 3 of lava and tephra that erupted from numerous vents widely separated in time and space approximately 80 of the total volume consists of basaltic to andesitic lava that formed two broad shield volcanoes between 314 and 70 ka the modern puyehue stratovolcano was built on the southerly shield during the past 69 k y following a hiatus of 25 k y puyehue has erupted 15 km 3 of basaltic to rhyolitic magma that spans the entire compositional range found in the southern svz and evolved via at least six phases including 1 basaltic andesitic to dacitic lavas between 69 and 32 ka 2 a shift to bimodal magma compositions that is first expressed by a rhyodacite mingled with inclusions of mgo rich basaltic andesite at 34 ka 3 dacitic to rhyolitic flows and domes from 19 to 12 ka 4 basaltic to basaltic andesitic flows between 15 and 12 ka 5 subsequent rhyolitic dome growth in several effusive and explosive stages between 7 and 5 ka followed by 6 a powerful series of phreatomagmatic and sub plinian eruptions at ca 1 1 ka that obliterated the preceding rhyolite domes and formed the present 2 5 km diameter 280 m deep summit crater along the cordon caulle fissure zone 5 km 3 of rhyodacitic to rhyolitic lavas domes and cones have formed during the past 16 5 k y including explosive and effusive eruptions in 1921 1922 and 1960 eruptive rates were nonuniform over time with background growth at 0 04 km 3 k y or less punctuated by spurts at up to 0 90 km 3 k y the time averaged rate 0 42 km 3 k y is nearly double that at the tatara san pedro complex 500 km to the north during the past 300 k y these findings indicate that within a single arc the magmatic and eruptive fluxes at individual frontal volcanoes can be highly variable the last three stratocone building events on puyehue began during periods of deglaciation suggesting a relationship between unloading of ice and ease of magma ascent puyehue basalt exhibits subtle changes in 238 u 230 th 87 sr 86 sr and trace element composition over time that signal shifts in the composition and degree of melting of the mantle wedge or the extent to which basalt was modified by assimilation of heterogeneous crustal melts the complex has become exceptionally bimodal and more explosive over time with recent rhyolites evolving by extreme crystal fractionation of mafic magma and lesser volumes of andesite and dacite created via mixing of rhyolite and basalt despite the high flux of basalt during the past 300 k y no large silicic magma reservoir formed in the upper crust instead 238 u 230 th data favor rapid ascent of several small bodies of basaltic and silicic magma from the lower crust promoted perhaps by conduits that reflect strike slip faulting beneath the complex

isotopic evidence from the ivrea zone for a hybrid lower crust formed by magmatic underplating the large mafic complex overlying mantle peridotites in the ivrea zone of northern italy originated by underplating of mantle derived magma onto the base of continental crust and may be a unique outcrop of typical mafic lower crust sampled elsewhere only by mafic xenoliths neodymium and strontium isotope data show that the magmas assimilated large and roughly uniform proportions of crustal material the resulting hybrid magmas have the same isotopic signature as and may represent the lower crustal roots of upper crustal hercynian granitoid intrusions

recent unrest 2002 2015 imaged by space geodesy at the highest risk chilean volcanoes villarrica llaima and calbuco southern andes abstract villarrica llaima and calbuco volcanoes are the most active and dangerous volcanoes in the southern andes and we use interferometric synthetic aperture radar insar observations from multiple satellites ers 2 envisat alos radarsat 2 cosmo skymed terrasar x sentinel 1a and alos 2 to constrain ground deformation that spans episodes of unrest and eruption at all three volcanoes between 2002 and 2015 we find episodes of ground deformation at each volcano which we invert using analytic elastic half space models to make some of the first geophysical inferences about the source depths of potential magma chambers at llaima we interpret that the vei 2 april 3 2009 eruption was preceded by 6 15 cm of precursory ground uplift one month before from a source 5 km below the surface on the western side of the edifice the vei 2 march 3 2015 villarrica eruption was followed by a short lived uplift of 5 cm in the se part of the volcano from a source depth of 6 km the vei 4 april 22 23 2015 calbuco eruption produced 12 cm of coeruptive subsidence from a source depth 8 11 km and offset 2 km s from the summit importantly we do not find clear evidence that the january 1 2008 the march 3 2015 and april 22 2015 eruptions at llaima villarrica and calbuco volcanoes were preceded by either transient or continuous ground uplift there are several possible explanations for the lack of precursory deformation at each volcano it is possible that any precursory deformation occurred only hours before the eruption e g at calbuco pre eruptive inflation was canceled by co eruptive subsidence as we inferred happened during the april 2009 llaima eruption the pre eruptive deformation was too small to be detectable in areas with persistent topography correlated phase delays pressurized source are deep or that open vent volcanoes like villarrica and llaima do not pressurize at all three volcanoes x and c band interferograms decorrelate in a few weeks due to vegetation snow and ice and have persistent atmospheric phase delays that we find cannot be reliably removed with available global weather models the low number of sar acquisitions therefore makes it challenging to reliably measure unaliased deformation we recommend a multi satellite observing strategy with short repeat periods frequently acquired high resolution digital elevation models and with acquisitions during every satellite overflight that may improve the temporal resolution of measurements

subsidence at southern andes volcanoes induced by the 2010 maule chile earthquake large earthquakes in subduction zones can affect nearby volcanoes analysis of ground deformation following the 2010 earthquake in maule chile shows that some volcanoes subsided by up to 15 cm probably because of quake triggered release of hydrothermal fluids

co eruptive subsidence and post eruptive uplift associated with the 2011 2012 eruption of puyehue cordon caulle chile revealed by dinsar abstract the 2011 2012 eruption of the puyehue cordon caulle volcanic complex southern andes chile was associated with complex surface deformation affecting an area of roughly 50 by 50 km we report here differential sar interferometry dinsar results of pre co and post eruptive deformation from envisat asar cosmo skymed and alos 2 palsar scenes acquired between early 2011 and early 2017 no clear pre eruptive deformation is observed during five months before the eruption although some patterns could be interpreted as showing inflation occurring between april and may 2011 co eruptive interferograms show a complex deformation pattern consisting in a major deflation lobe 120 cm los lengthening centered 10 km nw of the eruption vent accompanied by smaller uplift and subsidence regions in the vicinity of the vent re inflation began immediately after the end of the eruption a first pulse lasted 3 years between 2012 and 2015 accumulating 70 cm uplift we detect here a second pulse beginning in june 2016 and still ongoing in february 2017 reaching 12 cm in half a year inverse modeling with spherical cavity and spheroidal sources locates re inflation sources at a depth ranging between 8 and 11 km under the surface it suggests re filling of the reservoir occurring after the draining of a shallow magma chamber during the 2011 2012 eruption

ground surface deformation patterns magma supply and magma storage at okmok volcano alaska from insar analysis 1 intereruption deformation 1997 2008 eruption magma storage had increased by 3 7 5 2 1 0 7 m 3 or 85 100 of the 1997 eruption volume we propose that the supply rate decreased in response to the diminishing pressure gradient between the shallow storage zone and a deeper magma source region eventuallytheeffectsofcontinuingmagmasupplyandvesiculationofstoredmagmacaused acriticalpressurethresholdtobeexceeded triggeringthe2008eruption asimilarpatternof initially rapid inflation followed by oscillatory but generally slowing inflation was observed prior to the 1997 eruption in both cases withdrawal of magma during the eruptions depressurized the shallow storage zone causing significant volcano wide subsidence and initiating a new intereruption deformation cycle

locating magma reservoirs using insar and petrology before and during the 2011 2012 cordon caulle silicic eruption abstract we combine petrological and insar observations to probe the origin of deformation of cordon caulle volcano in southern chile before and during the 2011 2012 eruption the erupted rhyodacite is crystal poor and was stored at about 900 c with ca 4 wt h2o and 220 ppm co2 in the melt corresponding to a storage depth of about 6 7 km in addition to a previously documented 2007 2008 deformation episode we find three pre eruptive deformation episodes the first between 2008 and 2009 that covers 400 km2 with a maximum uplift of 18 5 cm the second between february and march 2010 that covers 20 km2 with a maximum uplift of 10 cm and the third between march and may 2011 that covers 40 km2 with a maximum uplift of 6 cm modeling of the 2008 2009 deformation episode suggests source depths of about 5 9 km consistent with the petrologically determined magma storage depth the sum of modeled source volume changes from 2007 to 2009 is about 12 times smaller than the observed erupted volume our calculation of magma compressibility shows that there must have been a significant volume of pre existing magma in the reservoir to account for this difference co eruptive subsidence shows evidence for three distinct magma sources and pre eruptive inflation is seen at two of the three sources modeled deformation sources are located 2 10 km from the 2011 2012 eruptive vent and coincide with the vents from previous historical eruptions 1921 22 1960 and with the neighboring puyehue volcano this implies the existence of an interconnected magma plumbing system that allows for pressure transfer and which covers an area of at least 20 km2 thus the deformation and geochemical characteristics of cordon caulle resemble those of a large silicic caldera system the presence of a mafic crystal clot demonstrates the existence of basaltic melts in the silicic reservoir but we find that the mafic magmas reached the reservoir at least several hundred years before eruption therefore if the pre eruptive deformation was caused by replenishment to a shallow reservoir the new magma was silicic and similar to the pre existing magma and or there was no interaction between the two we find that pre eruptive deformation can occur in pulses and reach its peak years before eruption and thus lack of deformation does not necessarily imply that eruption is not imminent

rapid reinflation following the 2011 2012 rhyodacite eruption at cordon caulle volcano southern andes imaged by insar evidence for magma reservoir refill cordon caulle is a large fissural volcano that has erupted rhyodacitic magma of the same composition in its past three historical eruptions in 1921 1960 and 2011 2012 there was significant ground deformation observed before and during the 2011 2012 eruption here we use c and x band insar time series results to document post eruptive uplift up to 0 8 m between march 2012 and may 2015 with los rates up to 45 cm yr that have been largely aseismic along with subsidence in the 2011 2012 lava flow the 2012 uplift rate is one of the largest for silicic systems and was likely produced by the intrusion of 0 125 km3 of magma in the same tectonically controlled plumbing system that has been active during the historical eruptions nevertheless the uplift ended before the reservoir refilled with the erupted volume maybe due to a change in the pressure gradient produced by the 2011 2012 eruption

dynamics of wind affected volcanic plumes the example of the 2011 cordon caulle eruption chile the 2011 cordon caulle eruption represents an ideal case study for the characterization of long lasting plumes that are strongly affected by wind the climactic phase lasted for about 1 day and was classified as subplinian with plumes between 9 and 12 km above the vent and mass flow rate mfr on the order of 107 kg s 1 eruption intensity fluctuated during the first 11 days with mfr values between 106 and 107 kg s 1 this activity was followed by several months of low intensity plumes with mfr 106 kg s 1 plume dynamics and rise were strongly affected by wind during the whole eruption with negligible upwind spreading and sedimentation the plumes that developed on 4 6 and 20 22 june can be described as transitional i e plumes showing transitional behavior between strong and weak dynamics while the wind clearly dominated the rise height on all the other days resulting in the formation of weak plumes individual phases of the eruption range between volcanic explosivity indices veis 3 and 4 while the cumulative deposit related to 4 7 june 2011 is associated with veis 4 and 5 crosswind cloud and deposit dispersal of the first few days are best described by a linear combination of gravitational spreading and turbulent diffusion with velocities between 1 and 10 m s 1 downwind cloud velocity for the same days is best described by a linear combination of gravitational spreading and wind advection with velocities between 17 and 45 m s 1 results show how gravitational spreading can be significant even for subplinian and small moderate eruptions strongly advected by wind and with low richardson number and low mfr

facies interpretation of middle carboniferous to lower permian pope succession limestone of cache creek group fort st james central british columbia lithostratigraphy and microfacies of the bashkirian to asselian pope succession limestone of the cache creek group near fort st james central british columbia were lithologically grouped into five facies associations a to e on the basis of fusulines and conodonts facies associations a to d and the lower part of facies association e are time equivalent ranging from the lower bashkirian to lower kasimovian and the upper part of facies association e is dated as upper gzhelian to asselian the pope succession limestone is interpreted to have been built on a basaltic basement of an oceanic plateau or seamount in an open ocean realm the limestone is devoid of terrigenous grains is associated with basaltic rocks and laterally grades into deeper water spicular cherts microfacies analysis of facies associations a to e showed that they exhibit characteristic facies of a deep water basinal setting b marginal basin to lower slope c shallow subtidal bank margin d peritidal algal mound on the bank

3d gravity inversion and thermodynamic modelling reveal properties of shallow silicic magma reservoir beneath laguna del maule chile abstract active large volume silicic magma systems are potentially the most hazardous form of volcanism on earth knowledge of the location size and physical properties of silicic magma reservoirs is therefore important for providing context in which to accurately interpret monitoring data and make informed hazard assessments accordingly we present the first geophysical image of the laguna del maule volcanic field magmatic system using a novel 3d inversion of gravity data constrained by thermodynamic modelling the joint analysis of gravity and thermodynamic data allows for a rich interpretation of the magma system and highlights the importance of considering the full thermodynamic effects on melt density when interpreting gravity models of active magmatic systems we image a 30 km 3 low density volatile rich magma reservoir at around 2 km depth containing at least 85 melt hosted within a broader 115 km 3 body interpreted as wholly or partially crystallised 70 crystal cumulate mush our model suggests a magmatic system with shallow crystal poor magma overlying deeper crystal rich magma even though a large density contrast 600 kg m 3 with the surrounding crust exists the lithostatic load is 50 greater than the magma buoyancy force suggesting buoyancy alone is insufficient to trigger an eruption the reservoir is adjacent to the inferred extension of the troncoso fault and overlies the location of an intruding sill driving present day deformation the reservoir is in close proximity to the 2 0 km 3 nieblas rln eruption at 2 3 ka which we calculate tapped approximately 7 of the magma reservoir however we suggest that the present day magma system is not large enough to have fed all post glacial eruptions and that the location or size of the system may have migrated or varied over time with each eruption tapping only a small aliquot of the available magma the presence of a shallow reservoir of volatile rich near liquidus magma in close proximity to regional scale faulting has important implications for volcano monitoring and hazard mitigation

mineral textures and zoning as evidence for open system processes investigations of mineral textures and zoning as evidence for open system processes during magmatic evolution have always been a centerpiece of petrological studies and have provided some of the best evidence for magma mixing and crustal contamination for many decades e g milch 1905 kuno 1936 eichelberger 1975 sato 1975 anderson 1976 in fact evidence from mineral studies was instrumental in the acceptance of magma mixing as important petrological process ever since it was initially proposed by bunsen 1851 in recent years mineral studies are invigorated by the development of high precision high resolution analytical instruments and techniques through which textural information and compositional data are combined e g jerram and davidson 2007 as minerals respond texturally and compositionally to changing magmatic environments they preserve in their crystal growth stratigraphy a wealth of information regarding their past history of magmatic processes and compositions cf ginibre et al 2007 on the other hand magmatic liquids melts are snapshots of current magmatic states and provide less direct evidence of the processes responsible for their evolution in addition liquids may crystallize thereby destroying the direct evidence they provide with an appropriate set of observations and measurements we can correlate textures with mineral compositions and thus produce a richer composite picture of magmatic evolution than compositional data of minerals alone this contribution reviews the zoning and textures of minerals frequently encountered in volcanic rocks many of which apply equally to plutonic rocks and the interpretations ascribed to these features in terms of open system magmatic processes first i will address the analytical tools that are used to acquire textural and compositional data followed by a brief review of open system processes and a summary of the relevant textures from that point on i will address some mineral specific aspects followed by a discussion

an insar based survey of volcanic deformation in the central andes we extend an earlier interferometric synthetic aperture radar insar survey covering about 900 remote volcanos of the central andes 14 27 s between the years 1992 and 2002 our survey reveals broad 10s of km roughly axisymmetric deformation at 4 volcanic centers two stratovolcanoes are inflating uturuncu bolivia and hualca hualca peru another source of inflation on the border between chile and argentina is not obviously associated with a volcanic edifice here called lazufre and a caldera cerro blanco also called robledo in northwest argentina is subsiding we explore the range of source depths and volumes allowed by our observations using spherical ellipsoidal and crack like source geometries we further examine the effects of local topography upon the deformation field and invert for a spherical point source in both elastic half space and layered space crustal models we use a global search algorithm with gradient search methods used to further constrain best fitting models inferred source depths are model dependent with differences in the assumed source geometry generating a larger range of accepted depths than variations in elastic structure source depths relative to sea level are 8 18 km at hualca hualca 12 25 km for uturuncu 5 13 km for lazufre and 5 10 km at cerro blanco deformation at all four volcanoes seems to be time dependent and only uturuncu and cerro blanco were deforming during the entire time period of observation inflation at hualca hualca stopped in 1997 perhaps related to a large eruption of nearby sabancaya volcano in may 1997 although there is no obvious relation between the rate of deformation and the eruptions of sabancaya we do not observe any deformation associated with eruptions of lascar chile at 16 other volcanoes that had recent small eruptions or fumarolic activity or associated with a short lived thermal anomaly at chiliques volcano we posit a hydrothermal system at cerro blanco to explain the rate of subsidence there for the last decade we calculate the ratio of the volume of magma intruded to extruded is between 1 10 and that the combined rate of intrusion and extrusion is within an order of magnitude of the inferred geologic rate

transient volcano deformation sources imaged with interferometric synthetic aperture radar application to seguam island alaska 1 thirty interferometric synthetic aperture radar insar images spanning various intervals during 1992 2000 document coeruptive and posteruptive deformation of the 1992 1993 eruption on seguam island alaska a procedure that combines standard damped least squares inverse methods and collective surfaces identifies three dominant amorphous clusters of deformation point sources predictions generated from these three point source clusters account for both the spatial and temporal complexity of the deformation patterns of the insar data regularized time series of source strength attribute a distinctive transient behavior to each of the three source clusters a model that combines magma influx thermoelastic relaxation poroelastic effects and petrologic data accounts for the transient interrelated behavior of the source clusters and the observed deformation basaltic magma pulses which flow into a storage chamber residing in the lower crust drive this deformational system a portion of a magma pulse is injected into the upper crust and remains in storage during both coeruption and posteruption intervals this injected magma degasses and the volatile products accumulate in a shallow poroelastic storage chamber during the eruption another portion of the magma pulse is transported directly to the surface via a conduit roughly centered beneath pyre peak on the west side of the island a small amount of this magma remains in storage during the eruption and posteruption thermoelastic contraction ensues this model made possible by the excellent spatial and temporal coverage of the insar data reveals a relatively simple system of interrelated predictable processes driven by magma dynamics

structural controls of volcanism in transversal chains resheared faults and neotectonics in the cordon caulle puyehue area 40 5 s southern andes abstract the nature of the relationship between tectonics and volcanism in a specific area is the result of the interaction between the crustal structures of the basement and ongoing regional stress field in the southern andes different kinematic environments represented by two nearly orthogonal active fissure systems show apparently incompatible arrays of volcanic chains moreover a local quaternary compressive regime is inferred from basement faults however these mutually orthogonal chains which are also oblique to the volcanic front have contrasting magma evolution and eruptive styles that can be related with their tectonic setting whereas northeast trending monogenetic cones carran los venados can be interpreted as resulting from magma upwelling along regional tension cracks in a quaternary dextral transpressive compressive domain northwest striking fissure system cordon caulle volcanic complex can be the result of extensional fault reactivation and long magma residence in the upper crust different kinematic environments cause contrasting magma evolution and eruptive styles a two way coupling mechanism is suggested for to explain local depart of the regional stress field geometric array of extensional features and final magmatic evolution in these volcanic domains of the southern andes

temporal development of the 1999 intrusive episode in the eyjafjallajokull volcano iceland derived from insar images eyjafjallajokull volcano located in southern iceland is characterized by its quiet nature only about a handful of earthquakes associated with the volcanic system had been detected prior to the 1990s earthquake swarms did however occur in 1994 and 1999 here we investigate the spatio temporal evolution of a magmatic intrusion associated with the 1999 earthquake swarm via analysis of produced surface deformation a series of interferometric synthetic aperture radar insar images spanning various periods of the intrusion show that in 1999 surface deformation occurred mainly on the southern flanks of the volcano the deformation amounts to more than 20 cm of range change inverse modeling resolves the deformation source to be a sill intrusion at 6 3 km depth sill opening was up to 1 m and the total intruded volume amounts to 0 03 km3 the insar data display a migration of the center of deformation through time enabling us to create time dependant sill opening models furthermore we investigate the spatio temporal distribution of earthquakes and find that the distribution supports the insar derived model and additionally provides indications for a possible site of a feeder channel magmatic flow rate estimates indicate an initial intrusion rate of 4 6 m3 s declining over a few weeks

deformation patterns magma supply and magma storage at karymsky volcanic center kamchatka russia 2000 2010 revealed by insar abstract under a complex geological region influenced by the subduction of the pacific plate kamchatka peninsula is one of the most active volcanic arcs in the pacific rim due to logistical difficulty in instrumentation shallow magma plumbing systems beneath some of the kamchatkan volcanoes are poorly understood insar offers a safe and quick method for monitoring volcanic deformation with a high spatial resolution in this study a group of satellite radar interferograms that span the time interval from 2000 to 2010 shows eruptive and non eruptive deformation at karymsky volcanic center kvc kamchatka russia all the interferograms provide details of the activity around the kvc during 2000 2010 as follows 1 from 2000 to 2004 the karymsky an akademia nauk area deflated and the ms maly semyachik area inflated 2 from 2004 to 2006 the karymsky an area deflated with ongoing eruption while the ms area subsided without eruption 3 from 2006 to 2008 as with 2000 2004 the karymsky an area deflated and the ms area inflated 4 from 2008 to 2010 the karymsky an area inflated up to 3 cm and the ms area subsided point source models suggest that two magma reservoirs provide a good fit to the observed deformation one source is located beneath the area between karymsky and an at a depth of approximately 7 0 km and the other one is situated beneath ms at a depth of around 5 8 km synchronous deformation patterns suggest that two magma systems are fed from the same deep magma source and connected by a fracture zone the insar results are consistent with gps ground deformation measurements seismic data and petrological constraints

measuring effusion rates of obsidian lava flows by means of satellite thermal data abstract space based thermal data are increasingly used for monitoring effusive eruptions especially for calculating lava discharge rates and forecasting hazards related to basaltic lava flows the application of this methodology to silicic more viscous lava bodies such as obsidian lava flows is much less frequent with only few examples documented in the last decades the 2011 2012 eruption of cordon caulle volcano chile produced a voluminous obsidian lava flow 0 6 km3 and offers an exceptional opportunity to analyze the relationship between heat and volumetric flux for such type of viscous lava bodies based on a retrospective analysis of modis infrared data mirova system we found that the energy radiated by the active lava flow is robustly correlated with the erupted lava volume measured independently we found that after a transient time of about 15 days the coefficient of proportionality between radiant and volumetric flux becomes almost steady and stabilizes around a value of 5 106 j m 3 this coefficient i e radiant density is much lower than those found for basalts 1 108 j m 3 and likely reflects the appropriate spreading and cooling properties of the highly insulated viscous flows the effusion rates trend inferred from modis data correlates well with the tremor amplitude and with the plume elevation recorded throughout the eruption thus suggesting a link between the effusive and the coeval explosive activity modelling of the eruptive trend indicates that the cordon caulle eruption occurred in two stages either incompletely draining a single magma reservoir or more probably tapping multiple interconnected magmatic compartments

limited overlap between the seismic gap and coseismic slip of the great 2010 chile earthquake the mw 8 8 chile earthquake on 27 february 2010 occurred in a broad region where tectonic loading has been accumulating since the great 1835 earthquake a joint inversion of tsunami and geodetic data suggests that the 2010 earthquake rupture only partly overlapped with the zone of preseismic locking

intrusion triggering of the 2010 eyjafjallajokull explosive eruption the ash cloud that brought chaos to european air traffic in april this year was the result of emissions from an icelandic volcano that had been intermittently active for about 18 years a combination of detailed space based geodetic measurements and seismic monitoring of the eyjafjallajkull volcano in the run up to the ash producing explosive summit eruption reveals an unusual deformation pattern that may be attributed to its off rift setting with relatively cool subsurface structure and limited magma at shallow depth as to the predictability of such a dramatic reawakening the immediate precursors to the initial eruption of the volcano in 2010 were subtle and difficult to detect but the clear signs of volcanic unrest during the weeks months and years preceding it may provide better clues to the catastrophic explosion

storage and eruption of near liquidus rhyolite magma at cordon caulle chile the last three eruptions at the cordon caulle volcanic complex chile have been strikingly similar in that they have started with relatively short pre eruptive warning and produced chemically homogeneous rhyolite to rhyodacite magma with glassy to aphyric texture these characteristics collectively call for an understanding of the storage conditions leading to the rise and extraction of crystal poor silicic magma from volcanoes we have analyzed and experimentally reproduced the mineral assemblage and glass chemistry in rhyolite magma produced in the most recent eruption of cordon caulle and we use these to infer magma storage and ascent conditions fe ti oxide mineral geothermometry suggests that the rhyolite was stored at 870 920 c at these temperatures the phenocryst assemblage plag an37 cpx opx mag ilm can be reproduced under h2o saturated conditions of between 100 and 50 mpa corresponding to crustal depths between about 2 5 and 5 0 km the shallow and relatively hot magma storage conditions have implications for the rapid onset degassing efficiency and progression from explosive to mixed pyroclastic effusive eruption style at cordon caulle

magma storage region processes inferred from geochemistry of fe ti oxides in andesitic magma soufriere hills volcano montserrat w i analyses of fe ti oxides help constrain models of magma storage region processes for the soufriere hills volcano montserrat w i and provide clear evidence of the nature of transient heating events in the magma storage region to constrain timescales of magma heating and remobilization the tio2 zoning patterns in a time series of natural titanomagnetites were compared with those produced in controlled phase equilibrium experiments on the andesite most samples of andesite erupted from 1995 to 2002 contain titanomagnetite crystals with uniform core compositions tio278 wt many crystals are characterized by rimward increases in tio2 interpreted to be ti diffusion gradients caused by heating of the andesite by invading basaltic magma some andesites erupted during periods of the highest observed mass eruption rate however contain titanomagnetite with uniformly low tio2 contents from core to rim the observation that no ti diffusion gradients and no elevated core tio2 contents occur in the vast majority of titanomagnetite grains in magma batches that were erupted more than 2 years after the onset of the present eruption strongly suggests first that heating of the batches of andesite occurred just before eruption and second that injection of basaltic magma has continued throughout the eruption heat but little mass may be transferred from the invading basalt to the andesite in the magma storage region by injection of dikes or formation of sills ponding of basaltic magma at the base of a pre existing andesitic magma storage region is the simplest explanation consistent with observations the fe ti oxide data strongly suggest that an internal conduit within the andesitic magma storage region carries magma from the zone of heating to the overlying conduit which carries the magma through the upper arc crust in this model the magma chamber is being emptied from the bottom at the contact between pre existing andesite and newly intruded basalt

the role of volatiles in magma chamber dynamics many andesitic volcanoes exhibit effusive eruption activity1 with magma volumes as large as 107 109 m3 erupted at rates of 1 10 m3 s 1 over periods of years or decades during such eruptions many complex cycles in eruption rates have been observed with periods ranging from hours to years2 3 4 5 6 7 longer term trends have also been observed and are thought to be associated with the continuing recharge of magma from deep in the crust and with waning of overpressure in the magma reservoir here we present a model which incorporates effects due to compressibility of gas in magma we show that the eruption duration and volume of erupted magma may increase by up to two orders of magnitude if the stored internal energy associated with dissolved volatiles can be released into the magma chamber this mechanism would be favoured in shallow chambers or volatile rich magmas and the cooling of magma by country rock may enhance this release of energy leading to substantial increases in eruption rate and duration

time scales of magmatic processes from modeling the zoning patterns of crystals the advent of polarized light microscopy in the middle of the 19th century allowed mineralogists and petrologists interested in igneous rocks to recognize the widespread occurrence of fine scale heterogeneities in the optical properties of minerals e g see young 2003 for details the interpretation of mineral zoning patterns as archives of magmatic processes has been with us for some time e g larsen et al 1938 tomkeieff 1939 the development of the electron microprobe in the 1960 s allowed mineral zoning profiles to be quantitatively analyzed and modeled e g bottinga et al 1966 moore and evans 1967 enhanced textural observations permitted recognition of many kinds of detailed structures during the growth and dissolution of magmatic minerals fig 1 e g anderson 1983 pearce and kolisnik 1990 and these processes were also explored using experimental and numerical models e g albarede and bottinga 1972 lofgren 1972 kirkpatrick et al 1976 loomis 1982 major element zoning patterns are routinely measured and with the arrival of the ion microprobe the identification of heterogeneous distribution of trace elements opened the window for more realistic and sophisticated scenarios and models fig 1 e g kohn et al 1989 blundy and shimizu 1991 singer et al 1995 we now measure abundances of naturally occurring isotopes at the scale of tens of micrometers e g davidson et al 2007a ramos and tepley 2008 and this allows in situ dating of crystals e g cooper and reid 2008 figure 1 a nomarski dic image of a plagioclase crystal from a gabbroic xenolith of volcan san pedro costa et al 2002 the crystal shows a well defined core and a rim separated by an oscillatory zoned interval ion microprobe analysis pits and the trace of the electron microprobe traverse between the pits are evident b major

application of independent component analysis to multi temporal insar data with volcanic case studies a challenge in the analysis of multi temporal interferometric synthetic aperture radar insar data is distinguishing and separating volcanic tectonic and anthropogenic displacements from each other and from atmospheric or orbital noise independent component analysis ica is a method for decomposing a mixed signal based on the assumption that the component sources are non gaussian and statistically independent ica has potential as a tool for exploratory analysis of insar data and in particular for testing whether geophysical signals are related or independent this article presents tests of the applicability of ica to insar using synthetic data and application to sentinel 1a archive images from two contrasting examples of volcano deformation co eruptive subsidence associated with the april 2015 eruption of calbuco chile was identified in spatial patterns found by maximising both spatial and temporal independence spatial patterns and rates of lava subsidence were retrieved using ica analysis of interferograms from paricutin lava fields mexico and found to be consistent with previous observations i demonstrate that ica is an appropriate method for the analysis of volcanic signals in the presence of atmospheric noise and propose a strategy for the automatic identification of geophysical displacements using cluster analysis of the spatial patterns of independent components this approach allows the detection of geophysical processes on a range of scales and provides a test of signal independence where multiple displacement sources are active

cristobalite in the 2011 2012 cordon caulle eruption chile cristobalite is a low pressure high temperature polymorph of sio2 found in many volcanic rocks its volcanogenic formation has received attention because 1 pure particulate cristobalite can be toxic when inhaled and its dispersal in volcanic ash is therefore a potential hazard and 2 its nominal stability field is at temperatures higher than those of magmatic systems making it an interesting example of metastable crystallization we present analyses by xrd sem epma laser raman and synchrotron ct of representative rhyolitic pyroclasts and of samples from different facies of the compound lava flow from the 2011 2012 eruption of cordon caulle chile cristobalite was not detected in pyroclasts negating any concern for respiratory hazards but it makes up 0 23 wt of lava samples occurring as prismatic vapour deposited crystals in vesicles and or as a groundmass phase in microcrystalline samples textures of lava collected near the vent which best represent those generated in the conduit indicate that pore isolation promotes vapour deposition of cristobalite mass balance shows that the sio2 deposited in isolated pore space can have originated from corrosion of the adjacent groundmass textures of lava collected down flow were modified during transport in the insulated interior of the flow where protracted cooling additional vesiculation events and shearing overprint original textures in the most slowly cooled and intensely sheared samples from the core of the flow nearly all original pore space is lost and vapour deposited cristobalite crystals are crushed and incorporated into the groundmass as the vesicles in which they formed collapse by strain and compaction of the surrounding matrix holocrystalline lava from the core of the flow achieves high mass concentrations of cristobalite as slow cooling allows extensive microlite crystallization and devitrification to form groundmass cristobalite vapour deposition and devitrification act concurrently but semi independently both are promoted by slow cooling and it is ultimately devitrification that most strongly contributes to total cristobalite content in a given flow facies our findings provide a new field context in which to address questions that have arisen from the study of cristobalite in dome eruptions with insight afforded by the fundamentally different emplacement geometries of flows and domes

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

reconstruction of total grain size distribution of the climactic phase of a long lasting eruption the example of the 2008 2013 chaiten eruption the 2008 2013 eruption of chaiten volcano chile was a long lasting eruption whose climactic phase may 6 2008 produced a sub plinian plume with height ranging between 14 and 20 km that dispersed to the ne reaching the atlantic coast of argentina the erupted material was mainly of lithic origin 77 wt resulting in a unimodal total grain size distribution tgsd dominated by coarse ash 77 wt with md of 2 7 and of 2 4 lapilli clasts 2 mm dominate the proximal deposit within 20 km of the vent while coarse 63 m 2 mm and fine ash 400 km do not significantly affect the determination of the tgsd in contrast gaps in data sampling in the medial deposit in particular the gap between 50 and 350 km from vent that coincides with shifts in sedimentation regimes have large impacts on estimates of tgsd particle number distribution for this deposit is characterized by a high power law exponent 3 0 following a trend very similar to the vesicle size distribution in the juvenile pyroclasts although this could be taken to indicate a bubble driven fragmentation process we suggest that fragmentation was more likely the result of a shear driven process because of the predominance of non vesicular products lithics and obsidians and the large fraction of coarse ash in the tgsd

magmatic evolution of the puyehue cordon caulle volcanic complex 40 s southern andean volcanic zone from shield to unusual rhyolitic fissure volcanism abstract magmas erupted from quaternary volcanoes of southern andes between 37 and 46 s latitude are mainly basaltic to andesitic however pccvc 40 s shows a singular magmatic evolution due to the abnormal evacuation of rhyolites especially in the last 100 ka in addition pccvc is the result of juxtaposing products from the nw trending alignment of cordillera nevada caldera cordon caulle fissure volcano and the puyehue stratocone using 40 ar 39 ar and 14 c geochronology it can be established that they evolved since ca 500 ka as coeval but separated vents with a first stage of shield volcanism followed by repeated collapses that formed an internal nw elongated graben from ca 100 ka volcanic activity occurred in both a fissure system cordon caulle and a central volcano puyehue holocene explosive eruptions mainly in the puyehue crater accompanied the dome growing along a nw trending fissure system last historical eruptions were in 1921 and 1960 when nw fissures of cordon caulle fed rhyodacitic lava flows in 1960 the fissure eruption was triggered by a remote mw 9 5 thrust earthquake cordillera nevada caldera presents a reduced compositional range 52 63 sio 2 and geochemical features of low pressure magma mixing and assimilation instead cordon caulle and puyehue volcanoes have a wide silica range 48 71 sio 2 and an outstanding affinity which can be modelled with initial high pressure fractional crystallization moderate magma mixing and subsequent low pressure fractional crystallization from a common parental source the exceptional magmatic evolution and eruptive style of pccvc in southern andes could be related with the physics of the plumbing system which in turn can be controlled by external factors as the structure of the continental crust and the ongoing stress regime

pre hercynian mantle lead transfer to basement rocks as indicated by lead isotopes of the schwarzwald crystalline sw germany lead isotopes of k feldspars from five granites of the se schwarzwald and from metamorphites are positively correlated in 207 204 as well as 208 204 vs 206 204 diagrams

volcanic hotspots of the central and southern andes as seen from space by aster and modvolc between the years 2000 and 2010

high effusion rates of the cordon caulle 2011 2012 eruption southern andes and their relation with the quasi harmonic tremor high effusion rates of intermediate to high silica lavas seem to be less uncommon than previously thought in particular during their initial eruptive stages in this study we report satellite based time averaged discharge rates for the 2011 2012 effusive phase at cordon caulle which are well correlated with the evolution of the quasi harmonic tremor the most significant seismic signal after the initial explosive stage such a correspondence could become a key method for detection of the onset of effusive phases especially in remote and or very cloudy areas supplying an additional tool for effective warnings and near real time hazards appraisal

an insar based survey of volcanic deformation in the southern andes we use interferometric synthetic aperture radar insar to search for surface deformation in the southern andes 40 s 46 s and 49 s 53 s associated with magmatic processes although the available data are not optimal we can constrain the amount of volcanic deformation at about 27 holocene volcanoes between the years 1993 1999 we detect inflation of cerro hudson volcano following its 1991 eruption and use spherical and non spherical models to constrain the source of deformation to be between 4 and 8 km below sea level we measure the rate of deformation to be about 5 cm year in the radar line of sight and infer that the maximum deformation could exceed 10 cm year in the center of the caldera within the errors of the measurements the rate of deformation is constant from 1993 1998 10 30 10 6 m 3 year at this rate 100 200 years is required to accumulate the volume of material erupted in 1991