long term ground displacement observations using insar and gnss at piton de la fournaise volcano between 2009 and 2014 abstract monitoring ground surface displacement of volcanoes over a long period of time helps improve understanding of the volcano structure dynamics and mechanisms in this paper we investigate the spatio temporal behavior of the long term displacement field at piton de la fournaise volcano la reunion island by means of x band insar and gnss time series analysis from 2009 to 2014 we propose a new correction approach based on principal component analysis to mitigate the long wavelength artifact in the interferograms over the study area our results show that most of the volcanic edifice including the central cone the eastern flank and recent lava flow fields was affected by varying degrees of ground motion more importantly a widespread sector 20 km2 affected by time dependent downward and eastward motion was observed on the eastern flank of piton de la fournaise the combined analysis of insar and gnss time series and previous studies allows us to confirm that this large mobile sector on the eastern flank underwent deformation for at least 7 years following the end of the large march april 2007 eruption including a stage of transient strain from the end of eruption to february 2011 followed by a stage of steady state strain until late 2014 several possible origins including a pre existing structural discontinuity summit stress associated with magmatism and activated fault movement are explored to explain the observed widespread long term seaward motion that is considered to be direct evidence of potential flank instability

on the shape and velocity of fluid filled fractures in the earth summary in this paper i present a model to estimate the shape and velocity of slowly ascending buoyancy driven fluid filled fractures the model considers elastic deformation linear fracture mechanics and fluid flow an attempt is made to incorporate the effect ofthe 2 d fluid pattern on the viscous pressure drop most other models assume that the viscous pressure drop can be approximated by flow through a channel with constant width although the form of the fracture is known to deviate from such a simple shape the 2 d flow in my model has an important consequence for the mechanism of buoyancy driven fracture propagation it predicts a large pressure gradient at the tail of the propagating fracture indicating that the tail of the fracture is most important in hindering the fracture propagation a singularity at the tail of the fracture can be avoided when a small amount of fluid trails in the channel left behind the propagating fracture the trailing and decoupling of fluids at the tail seems to be accompanied by small flow and shape instabilities which is indicated by the jerky movement of the tail observed in propagating air filled fractures in solidified gelatine and by numerical boundary element solutions of the coupled flow deformation fracturing problem by comparing the predictions for propagation velocities with laboratory observations of buoyancy driven fracture propagation in gelatine i derive a non dimensional effective thickness at the tail of the fracture for which trailing of fluids may occur the model is applied to earth relevant problems such as oil and water filled fractures in pressurized sediments or magma filled dykes in the lithosphere which are discussed in the paper

a two step model for dynamical dike propagation in two dimensions application to the july 2001 etna eruption we developed an hybrid numerical model of dike propagation in two dimensions solving both for the magma trajectory and velocity as a function of the source overpressure the magma physical properties density and viscosity as well as the crustal density and stress field this model is used to characterize the influence of surface load changes on magma migration towards the surface we confirm that surface loading induced by volcanic edifice construction tends both to attract the magma and to reduce its velocity in contrast surface unloading for instance due to caldera formation tends to divert the magma to the periphery retarding eruption in both cases the deflected magma may remain trapped at depth amplitudes of dike deflection and magma velocity variation depend on the ratio between the magma driving pressure source overpressure as well as buoyancy and the stress field perturbation our model is then applied to the july 2001 eruption of etna where the final dike deflection had been previously interpreted as due to the topographic load we show that the velocity decrease observed during the last stage of the propagation can also be attributed to the local stress field we use the dike propagation duration to estimate the magma overpressure at the dike bottom to be less than 4 mpa this approach can be potentially used to forecast if where and when propagating magma might reach the surface when having knowledge on the local stress field magma physical properties and reservoir overpressure

insights on the march 1998 eruption at piton de la fournaise volcano la reunion from microgravity monitoring we investigate the temporal gravity changes associated with one of the major recent eruptions at piton de la fournaise volcano march 1998 that occurred after an unusual five year quiet period and initiated a new eruptive cycle repeated microgravity surveys allowed us to measure residual gravity changes up to 100 gal within the enclos fouque caldera for four months before the start of the eruption we first analyzed the temporal gravity changes and the height changes also measured at the gravity benchmarks on the basis of an intrusive dyke model previously proposed for this eruption from insar and tilt data this analysis reveals that such simple model finite rectangular shaped tensile dislocation cannot fit both gravity and geodetic data and leads us to propose a dual source gravity model for this eruption the gravity data inversion using a genetic algorithm search method allows us to quantify the mass change produced by the intrusive dyke 3 9 to 8 7 109kg and to suggest an additional mass increase at sea level depth 4 6 to 7 2 1010kg we interpret the latter as the effect of magma ascent into a reservoir that occurred within the four months before the eruption we suggest that high concentrations of gas content in the magma reservoir account for a higher compressibility of the intruded magma and produce significant mass change with moderate surface deformation the 1996 seismic crisis interpreted as an upward migration of magmatic fluids into a reservoir located at sea level might support such a hypothesis

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

magma propagation at piton de la fournaise from joint inversion of insar and gnss magma propagation is an unsteady process controlled by magma crust interaction to provide information on its dynamics we invert complementary ground deformation data spanning the 8 hr preceding the 26 may 2016 eruption at piton de la fournaise pdf volcano la reunion france data are inverted using 3 d boundary element models combined with a monte carlo inversion method the final geometry of the displacement source is determined based on four interferograms spanning the whole propagation phase while the dynamics of the propagation is inferred from temporal inversion of continuous global navigation satellite system gnss data using the final geometry as an a priori to constrain the source the best modeled magma path consists in a 2 700 m long sill located 800 m above sea level and connected to the eruptive fissure by a subvertical dike the quick opening of the horizontal part of the intrusion could have been favored by limited flank sliding during the early stage of propagation the intrusion then stalled for 5 hr while pressure increased slightly until final upward propagation and eruption volume budget suggests that the eruption was fed by a single batch of magma quickly disconnected from its source the delay prior to the eruption may reflect a limited magma supply finally two mechanisms potentially acting together might have favored the eruption a driving role of magmatic gas and or as often observed at piton de la fournaise an eastward flank slip

in situ stress natural fracture distribution and borehole elongation in the auburn geothermal well auburn new york hydraulic fracturing stress measurements and a borehole televiewer survey were conducted in a 1 6 km deep well at auburn new york this well which was drilled at the outer margin of the appalachian fold and thrust belt in the appalachian plateau penetrates approximately 1540 m of lower paleozoic sedimentary rocks and terminates 60 m into the precambrian marble basement analysis of the hydraulic fracturing tests indicates that the minimum horizontal principal stress increases in a nearly linear fashion from 9 9 0 2 mpa at 593 m to 30 6 0 4 mpa at 1482 m the magnitude of the maximum horizontal principal stress increases in a less regular fashion from 13 8 1 2 mpa to 49 0 2 0 mpa over the same depth range the magnitudes of the horizontal principal stresses relative to the calculated overburden stress are somewhat lower than is the norm for this region and are indicative of a strike slip faulting regime that at some depths is transitional to normal faulting as expected from the relative aseismicity of central new york state however analysis of the magnitudes of the horizontal principal stresses indicates at least to a depth of 1 5 km that frictional failure on favorably oriented preexisting fault planes is unlikely orientations of the hydraulic fractures at 593 and 919 m indicate that the azimuth of the maximum horizontal principal stress at auburn is n83 e 15 in agreement with other stress field indicators for this region the borehole televiewer log revealed a considerable number of planar features in the auburn well the great majority of which are subhorizontal dips 5 and are thought to be bedding plane washouts or drill bit scour marks in addition a smaller number of distinct natural fractures were observed on the borehole televiewer log of these the distinct steeply dipping natural fractures in the lower half of the sedimentary section at auburn tend to strike approximately east west while those in the upper part of the well and in the precambrian basement exhibit no strong preferred orientation the origin of this east west striking fracture set is uncertain as it is parallel both to the contemporary direction of maximum horizontal compression and to a late paleozoic fracture set that has been mapped to the south of auburn in addition to these planar features the borehole televiewer log indicates paired dark bands on diametrically opposite sides of the borehole throughout the auburn well processing of the borehole televiewer data in the time domain revealed these features to be irregular depressions in the borehole wall as these depressions were consistently oriented in a direction at right angles to the direction of maximum horizontal compression we interpret them to be the result of stress induced spalling of the borehole wall breakouts

surface deformation induced by magmatic processes at pacaya volcano guatemala revealed by insar abstract pacaya volcano guatemala is a continuously active basaltic volcano with an unstable western flank despite continuous activity since 1961 a lack of high temporal resolution geodetic surveying has prevented detailed modeling of pacaya s underlying magmatic plumbing system a new temporally dense dataset of interferometric synthetic aperture radar insar radarsat 2 images spanning december 2012 to march 2014 show magmatic deformation before and during major eruptions in january and march 2014 inversion of insar surface displacements using simple analytical forward models suggest that three magma bodies are responsible for the observed deformation 1 a 4 km deep spherical reservoir located northwest of the summit 2 a 0 4 km deep spherical source located directly west of the summit and 3 a shallow dike below the summit periods of heightened volcanic activity are instigated by magma pulses at depth resulting in rapid inflation of the edifice we observe an intrusion cycle at pacaya that consists of deflation of one or both magma reservoirs followed by dike intrusion intrusion volumes are proportional to reservoir volume loss and do not always result in an eruption periods of increased activity culminate with larger dike fed eruptions large eruptions are followed by inter eruptive periods marked by a decrease in crater explosions and a lack of detected deformation co eruptive flank motion appears to have initiated a new stage of volcanic rifting at pacaya defined by repeated nw se oriented dike intrusions this creates a positive feedback relationship whereby magmatic forcing from eruptive dike intrusions induce flank motion

buoyancy driven fracture ascent experiments in layered gelatine laboratory experiments on air filled fracture propagation in solidified homogeneous and layered gelatine have been carried out providing an analogue model for magma filled dikes ascending in the crust the effects of layering on fracture velocity and shape have been analyzed in detail the free surface is found to accelerate approaching fractures layering accelerates or decelerates fractures approaching discontinuities of the elastic parameters depending on the value of the rigidity contrast the shape of fractures are strongly influenced as they pass from one layer to another the observed cross sectional shape when crossing a layer interface and the acceleration with decreasing rigidity can be explained with theoretical models our experiments also reproduce the arrest of fractures in proximity of joints and the formation of sills in the layer below the interface these findings could help in the interpretation of accelerated seismicity and deformation rates observed in volcanic areas

aseismic strike slip associated with the 2007 dike intrusion episode in tanzania abstract in july 2007 an earthquake swarm initiated in northern tanzania near lake natron and lasted for about two months mt oldoinyo lengai located to the southwest of the swarm began to erupt effusively about a month prior to the swarm and increased its eruption intensity on september when the swarm almost ceased several previous studies have already reported the crustal deformation signals associated with the swarm using interferometric synthetic aperture radar insar however nearly all the published data are based on the c band envisat asar images acquired only from the descending path we use the l band alos palsar images acquired from both ascending and descending paths which allow us to examine the deformation signals in more detail in addition to the insar data we employ the offset tracking technique to detect the signals along the azimuth direction using insar and offset tracking data we obtain the full 3d displacement fields associated with the episode besides the horizontal extension and subsidence signals due to the dike intrusion as already reported the inferred full 3d displacements further indicate that the subsiding zone was horizontally moving by 48 cm toward ssw to explain the displacements we performed fault source modeling assuming an elastic half space the fault slip distribution indicates that the contribution of the strike slip component is about 20 of total moment release because almost all the focal mechanisms of earthquakes during the 2007 event indicate nearly pure normal faulting aseismic strike slip must have been responsible for the horizontal movement of the subsiding zone the strike slip at the shallowest depths suggests the presence of transtensive stress which seems to be reasonable to generate the relay zones that are widely observed in the east african rift we also confirmed that the stress changes due to the dike intrusion were consistent with the inferred fault slip distributions

multidimensional small baseline subset msbas for volcano monitoring in two dimensions opportunities and challenges case study piton de la fournaise volcano abstract space borne synthetic aperture radar sar provides an opportunity for monitoring ground deformation at active volcanoes with high temporal and spatial resolutions modern sar satellites acquire very large volumes of data that no longer can be effectively and efficiently processed and interpreted manually the development of novel automatic processing methodologies is warranted in order to fully utilize big data the multidimensional small baseline subset msbas methodology is an example of the semi automatic processing system for computing temporally dense two dimensional horizontal east west and vertical time series of ground deformation from ascending and descending sar imagery acquired by various satellites here msbas is used for mapping ground deformation at the piton de la fournaise volcano la reunion island france during the february 2012 april 2016 period from radarsat 2 data five volcanic eruptions occurred during the june 2014 october 2015 period producing over 60cm of horizontal and over 30cm of vertical ground deformation well resolved in the msbas derived time series validation of dinsar results by comparison with gnss observations and modeling of the two last and largest eruptions was performed validation showed good overall agreement between dinsar and gnss observations while revealing the benefits and limitations of both techniques modeling of fault and dike geometries attempted to explain the dis proportionally large eastward motion of the eastern flank of the piton de la fournaise volcano that occurred during these eruptions we demonstrated that the simple elastic model consisting of two dikes and a sliding surface can account for the observed ground deformation

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

evolution of magma conduits during the 1998 2000 eruptions of piton de la fournaise volcano reunion island 1 at basaltic volcanoes magma is transported to the surface through dikes magma filled fractures but the evolution of these dikes as eruptions proceed is rarely documented in march 1998 after five and a half years of quiescence piton de la fournaise volcano reunion island entered into a new eruptive phase characterized by intense eruptive activity coeruptive displacements recorded by interferometric synthetic aperture radar insar for the first five eruptions of the cycle are analyzed using 3 d boundary element models combined with a monte carlo inversion method we show that the eruptions are associated with the emplacement of lateral dikes rooted at depths of less than about 1000 m except for the first march 1998 event where an additional deeper source is required the dikes are located above preeruptive seismic swarms this is consistent with nearly isotropic stress caused by repeated dike intrusions and low confining pressure enhanced by the presence of pores in the shallowest 1000 m of the edifice the volumes of the modeled dikes represent 17 of the volume of emitted lava showing that exogenous growth plays a major role in building the volcano by taking into account the preeruptive seismicity and tilt data together with the results of insar data modeling we find that dikes first propagate vertically from a source region below sea level before being injected laterally at shallow depth this behavior is consistent with the presence of levels of neutral buoyancy at shallow depth in the edifice

application of open source photogrammetric software micmac for monitoring surface deformation in laboratory models quantifying deformation is essential in modern laboratory models of geological systems this paper presents a new laboratory monitoring method through the implementation of the open source software micmac which efficiently implements photogrammetry in structure from motion algorithms critical evaluation is provided using results from two example laboratory geodesy scenarios magma emplacement and strike slip faulting micmac automatically processes images from synchronized cameras to compute time series of digital elevation models dems and orthorectified images of model surfaces micmac also implements digital image correlation to produce high resolution displacements maps the resolution of dems and displacement maps corresponds to the pixel size of the processed images using 24 mp cameras the precision of dems and displacements is 0 05 mm on a 40 40 cm surface processing displacement maps with matlab scripts allows automatic fracture mapping on the monitored surfaces micmac also offers the possibility to integrate 3 d models of excavated structures with the corresponding surface deformation data the high resolution and high precision of micmac results and the ability to generate virtual 3 d models of complex structures make it a very promising tool for quantitative monitoring in laboratory models of geological systems

imaging magma transport during the 1997 seismic swarm off the izu peninsula japan the spatio temporal evolution of a propagating magma filled crack was estimated from inversion of global positioning system gps data tiltmeters and leveling the dike opened at a maximum rate of 50 millimeters per day and had a peak magma flux of 2 x 10 6 cubic meters per day although the spatial resolution was limited slow upward propagation was resolved during the 9 day long intrusion in contrast the earthquakes migrated rapidly upward during the first 12 hours of the swarm and nearly all of the seismic energy was released in the first 2 days comparison of inversion results with accurate hypocenter locations will lead to improved understanding of magma transport through the brittle crust and of the causes of volcanic seismicity

the off shore continuation of an active basaltic volcano piton de la fournaise reunion island indian ocean structural and geomorphological interpretation from sea beam mapping abstract in 1984 a sea beam survey of the submarine east flank of piton de la fournaise was performed with r v jean charcot three main types of volcanic or volcano tectonic features have been identified 1 1 the subaerial ne and se volcanic rift zones of piton de la fournaise do not extend more than about five kilometers offshore unlike typical hawaiian rift zones which form narrow 2 4 km ridges extending tens of kilometers from the summit the active rift zones of piton de la fournaise widen downslope attaining more than 10 km at their front 2 2 the submarine extension of the grand brule slide is larger than the subaerial portion the entire slide forms a 7 24 km scar bounded by two ramparts to the north and south the slumped material may have moved as a debris flow forming a large talus downslope of the slide however the submarine counterpart of the south area of the grand brule seems to be composed by a slumped block whose structure is apparently not disturbed 3 3 another prominent feature is a conspicuous topographic high that occupies nearly all the center of the surveyed zone this cast flank submarine plateau cannot be associated with any active structure of piton de la fournaise its surface generally dips gently 2 3 and its northern and southern flanks are extensively cut by landslides cones of variable dimensions are observed on the plateau and farther to the east three hypotheses are examined to account for the origin of this morphology a remnant flank of an ancestral fournaise volcano associated with a large buried intrusion found by drilling beneath the grand brule b distinct volcanic massif or c material of a huge and ancient landslide the geophysical data show that the western part of this submarine plateau is reversely magnetized and associated with a moderate positive gravity anomaly this confirms that as suggested by the bathymetric analysis this part of the plateau is relatively coherent conversely the eastern portion of the plateau appears to be poorly magnetized and composed of low density material probably chaotic materials derived from landslides the reversed magnetization of the western part shows that the whole structure is older than 0 7 ma these results show that the volcanic history of piton de la fournaise is more complex than previously thought

assessing the reliability and consistency of insar and gnss data for retrieving 3d displacement rapid changes the example of the 2015 piton de la fournaise eruptions abstract insar and gnss are now the best and most developed techniques in the earth sciences to track deformation especially in volcanology in this study we assess the reliability and consistency of these two techniques for measuring 3 d ground displacements and not only the displacement in the direction of the insar line of sight on volcanoes during rapid changes the use of a large amount of satellite data x c l band as well as right and left looking acquisitions made it possible to retrieve the 3 d displacement components with an unprecedented accuracy we carry out this evaluation on the piton de la fournaise volcano where four eruptions occurred in 2015 the comparison between gnss and insar allows us i to describe the deformation pattern associated with these eruptions ii to quantify the discrepancies between insar and gnss and iii to discuss the limits and the complementarities of insar and gnss the ground deformation patterns associated with the four eruptions of piton de la fournaise in 2015 are typical of this volcano with decimeter ground displacements asymmetrically distributed along the dike path evidencing a preferential eastward motion particularly visible thanks to the broad spatial coverage of insar except for the ns component insar and gnss data are in overall agreement with most of the gnss insar residuals

coherent pan asian climatic and isotopic response to orbital forcing of tropical insolation the oxygen 18 isotope composition of calcite in stalagmites across southern and eastern asia are highly correlated to one another on orbital time scales large negative excursions are coincident with maxima in summer insolation in the subtropics of the northern hemisphere nh these isotopic excursions reflect changes in the precipitation weighted isotopic composition of precipitation 18op we present results from two core experiments using an isotope enabled climate model the high insolation and low insolation experiments in which the model is forced by extrema in nh summer insolation compared to the low insolation experiment the high insolation climate features profound large scale changes in the pattern of monsoon precipitation spanning from africa to southeast asia that are due to changes in the relative contributions of temperature and moisture to the near surface equivalent potential temperature e under high insolation a more rapid increase in land surface temperature in early summer causes the greatest e and hence precipitation to shift from the oceans in low insolation such as today to be over land in high insolation such as the early holocene the model captures the general pattern of isotopic excursions seen in caves spanning from israel to western china including large drops in 18op over eastern tibet 7 the arabian peninsula and northeast africa 4 although there are large changes in precipitation over tibet the change in 18op is due to changes in the 18o of water vapor that is delivered and subsequently precipitated it does not inform on local precipitation amount or intensity

dynamic dyke propagation deduced from tilt variations preceding the march 9 1998 eruption of the piton de la fournaise volcano during the hour preceding the march 9 1998 eruption of the piton de la fournaise volcano the deformation network of the observatory recorded some large deformations in the summit area a broadband seismic station of the geoscope global network rer is located about 8 km away from the summit of the volcano signals from that station may be interpreted as tilt changes the combination of the above two kinds of signals allows by using a tensile fault model to constrain the geometry as well as some characteristics volume propagation velocity of the dyke that intruded the summit area during the hour preceding the beginning of eruptive activity

nyamulagira s magma plumbing system inferred from 15 years of insar nyamulagira located in the east of the democratic republic of congo on the western branch of the east african rift is africa s most active volcano with an average of one eruption every 3 years since 1938 owing to the socio economical context of that region the volcano lacks ground based geodetic measurements but has been monitored by interferometric synthetic aperture radar insar since 1996 a combination of 3d mixed boundary element method and inverse modelling taking into account topography and source interactions is used to interpret insar ground displacements associated with eruptive activity in 1996 2002 2004 2006 and 2010 these eruptions can be fitted by models incorporating dyke intrusions and some namely the 2006 and 2010 eruptions require a magma reservoir beneath the summit caldera we investigate inter eruptive deformation with a multi temporal insar approach we propose the following magma plumbing system at nyamulagira by integrating numerical deformation models with other available data a deep reservoir c 25 km depth feeds a shallower reservoir c 4 km depth proximal eruptions are fed from the shallow reservoir through dykes while distal eruptions can be fed directly from the deep reservoir a dyke like conduit is also present beneath the upper southeastern flank of nyamulagira

models of ground deformation from vertical volcanic conduits with application to eruptions of mount st helens and mount etna we present simple analytical models of ground deformation from inflation of vertical volcanic conduits or pipes we compare three cases corresponding to 1 a pressurized pipe with closed end at the top that resists the internal pressure 2 a pressurized pipe with top open for which the internal deformation is mainly dislocation of the cylindrical walls and 3 a pipe shaped region that dilates for the closed pipe we use eshelby s inclusion theory to model deformation from a thin pressurized elongated prolate ellipsoid in a full space which we express in terms of double forces to satisfy surface boundary conditions we superimpose image solutions by using double forces derived from mindlin s half space solution for the point force for the open pipe we apply the volterra integral to dislocation across a cylindrical surface and generalize it to the half space using mindlin s point force solution these two solutions show marked differences from the line of dilatation solution ratios of maximum horizontal deformation to maximum vertical deformation for the pipe models are significantly greater than values for the center or line of dilatation models this and the more gradual fall off of the deformation with distance may be used as diagnostics for discriminating between pipe like sources and dilatational sources on volcanoes where both components of the deformation field are available as examples we compare the closed pipe model with deformation associated with dome building on mount st helens volcano and tilt predicted by the open pipe model with tilt measured during a period of explosive eruptive activity on mount etna sicily in 1995 comparison between model values and the measurements suggests that the effective elastic moduli of the volcanic cones are very low

the deformation field of the august 2003 eruption at piton de la fournaise reunion island mapped by asar interferometry 1 three independent asar interferograms spanning the august 2003 piton de la fournaise eruption reveal a 3 by 3 km asymmetric pattern of range changes centred on the dolomieu crater northern flank it corresponds to 30 cm of displacement towards the satellite east of the eruptive fissures and 7 cm away from the satellite west of the fissures displacements are caused by dyke emplacement below fissures we model the deformation using a 3d mixed boundary element method for elastic media this consists of a dyke defined by six geometric parameters and an overpressure gradient a neighbourhood algorithm was applied to explore this 7 dimensional parameter space the best fit model is a 57 eastward dipping dyke with a base lying around 1520 m a s l the model provides new evidence of the dyke intrusion related seaward displacements of the volcano eastern flank

analytical model of surface uplift above axisymmetric flat lying magma intrusions implications for sill emplacement and geodesy abstract in this paper we develop a new axisymmetric analytic model of surface uplift upon sills and laccoliths based on the formulation of a thin bending plate lying on an elastic foundation in contrast to most former models also based on thin bending plate formulation our model accounts for i axi symmetrical uplift ii both upon and outside the intrusion the model accounts for shallow intrusions i e the ratio a h 5 where a and h are the radius and depth of the intrusion respectively the main parameter of the model is the elastic length l which is a function of the elastic properties of the bending plate and of the elastic foundation the model exhibits two regimes depending on the ratio a l when a l a l 5 the uplift is mostly restricted upon the intrusion when the elastic foundation is very stiff our model converges towards that of a clamped plate we provide as supplementary material a matlab function that calculates the surface uplift from the set of system and control parameters we discuss three possible applications of our model i the model can be used to describe sill propagation by introducing a propagation criterion for realistic values our model reproduces well the behavior of horizontal intrusions simulated in experiments ii the model can also be used to compute the critical size of saucer shaped sills it shows for instance that a soft elastic foundation favors the horizontal spreading of sills before they form inclined sheets iii we show that the classical mogi point source model cannot be used to constrain sill properties from the surface uplift we thus propose that our model can be used as a valuable alternative to both simple analytical models like mogi s and more complex numerical models used to analyze ground deformation resulting from sill intrusions in active volcanoes

gravity structure of piton de la fournaise volcano and inferred mass transfer during the 2007 crisis abstract the structure and mass transfers at piton de la fournaise volcano are investigated using new on land and offshore measurements the structures are defined using 2 and 3d modelling short wavelength positive anomalies to the w and nw of the central area are interpreted as shallow piles of thick dense lava flows which have filled volcano tectonic depressions several hundreds of meters deep this finding provides a new insight into the evolution of the volcano conversely the currently active central zone is associated with a negative short wavelength anomaly explained by the presence of thin highly vesiculated and fractured lava flows building the central cone low density formations underlying the rivieres des remparts and langevin areas are tentatively interpreted as breccias related to erosion and or to southward directed mass wasting topographic offshore highs in the continuation of the se and ne rift zones of piton de la fournaise are characterized by negative gravity anomalies and reversed magnetic anomalies their interpretation as hyaloclastites and pillow lavas provides a coherent explanation for both types of signals if we admit that they were primarily constructed during the alizes stage two main deeper dense structures are also found the grand brule complex and a complex beneath the plaine des sables and the enclos fouque both are identified as hypovolcanic intrusive complexes the grand brule complex 10 18 km in plan view shows a marked ns elongated geometry unlike the other comparable complexes on the island the plaine des sables enclos fouque complex a more or less circular structure 5 km in diameter is attributed to the ancient shield stage it is centered on the enclos fault suggesting that the paleo center of the ancient shield was located about 1 5 km eastward of the previously proposed location an apparent contradiction was noted between the seismic and gravity images of the internal structure in particular a high velocity cylinder beneath the summit was not detected in the gravity models this contradiction was resolved by considering the relative sensitivity of each method finally the gravity dataset has allowed us to explore the gravity changes that accompanied the major eruptive and volcano tectonic crisis of april 2007 350 m collapse of the summit and emission of 120 106 m3 of lava the change in the mass distribution of the edifice was large enough to be detected in the survey data collected in the central area before and after the crisis however the accuracy was too low for the precise assessment of the mass transfers

neutral buoyancy and the structure of mid ocean ridge magma reservoirs the mechanical structure of the regions for shallow storage and lateral intrusion of mid ocean ridge basalt morb is explored in part by examining the density range appropriate for picritic to tholeiitic liquids and liquid crystal mixtures and its relationship to the nonlinear density depth structure of the ridge magma density spans the range 2 6 to at least 2 82 mg m 3 and incorporates the effects of fractional crystallization on the density evolution the incorporation of olivine phenocrysts and the contributions of water in melt phase density reductions the melt and melt crystal density band crosses the in situ rock density curve over the 1 to 3 km depth interval beneath the volcanic surface within that averaged interval picritic to tholeiitic melt and melt crystal mixtures are in approximate mechanical equilibrium with their surroundings and the interval is referred to as the morb horizon of neutral buoyancy hnb the detailed locations of the transition regions between the negative and neutral buoyancy and between the neutral and positive buoyancy regimes are dependent on melt phase composition as well as the presence of suspended mineral phases and their identity in the east pacific rise the hnb has a 1 1 correspondence with the inferred location of the sheeted dike complex and the seismically detected minimum compressional wave velocity region in ophiolite complexes the region corresponds to the sheeted dike complex and the uppermost isotropic gabbros above the hnb is the region of negative buoyancy seafloor to an averaged 1 km depth within which negative buoyancy forces may induce the descent of nonvesiculated melt this region corresponds to the pillow basalt sediment sequence the region of positive buoyancy extends from 3 km to the depth of melt generation and picritic melt ascends in dikes and veins of finite height 500 m to 11 km and relatively narrow width 20 mm to 100 cm the finite strengths of high temperature fluid weakened rocks mandate finite height melt parcels along the ascent pathway the magmatic source region is therefore never hydraulically connected with the surface nor with the near surface reservoir thus relatively locally integrated buoyancy has a natural role in the ascent of melt from the source region to the region of neutral buoyancy during the final stages of magma ascent hydrothermal fluid circulation enshrouds the hnb in a three dimensional envelope as suggested by the depth extent of alteration mineralogy in ophiolite complexes while hydrothermal cooling may play an important role in arresting the ascent of magma in very low spreading rate environments gravitational equilibrium represents the effectively dominant theme in intermediate and high spreading rate regions such as the east pacific rise elastic crack penetration of rheological transition zones near the hnb identify modes of crack tip morphologic changes as a function of young s modulus ratios e2 e1 above and beneath the transition and affect the style of intrusion while melt buoyancy determines the ultimate equilibrium resting place elastic crack stability considerations relate the vertical magma pressure gradients for tholeiitic pt and picritic pp magmas to the vertically varying gradient in the horizontal stress component h and suggest further subdivision into two horizons of neutral buoyancy one for tholeiitic magma hnbt and one for the picritic liquid olivine mixtures hnbp these intervals are very approximate but are estimated as 600 m to 1400 m and 1400 to 3000 m depth respectively beneath the east pacific rise axis as oceanic lithosphere is created at the rise axis and spreads laterally the horizons of negative buoyancy and neutral buoyancy ride with it and may continue to modulate the subsurface magma dynamics that influence off axis volcanism

deformation of basaltic shield volcanoes under cointrusive stress permutations we performed a microstructural study of piton des neiges la reunion island to understand how intrusions and stresses control each other in basaltic volcanoes our study reveals that three perpendicular intrusions trends coexisted during the 2 myr history of the volcano a n120 140 e rift zone a perpendicular dike trend and swarms of subhorizontal intrusions hereafter called sill zones independently the inversion of fault slip data shows that incompatible paleostress fields recurrently occurred along with the intrusions a dominant nne ssw extension a perpendicular extension and strike slip or compressional regimes the orientations of paleostresses are consistent with the orientations of the three perpendicular intrusion populations we propose that stress accumulation in the edifice under the effect of repeated magma injections resulted in permutations of the principal axes of the stress tensor causing a reorientation of subsequent intrusions stress permutations were cyclical each cycle started with dike injections in an extensional stress field reducing the deviatoric stress and switching the axes of principal stresses and finished with sill intrusions in a compressional stress field sill zones acted as detachment planes restoring the extensional stress field and initiating a new cycle of permutations our model of stress permutations is in agreement with the pattern of eruptions and deformation observed at piton de la fournaise in contrast with the hawaiian model of spreading on a decollement stress permutations in la reunion s volcanoes imply that the basal deformation of the edifices if any is not sufficient to compensate the reduction of deviatoric stress caused by intrusions

cointrusive shear displacement by sill intrusion in a detachment a numerical approach sheared sills are observed at piton des neiges the eroded basaltic volcano of la reunion and are a suspected cause of the coeruptive flank displacement of piton de la fournaise in 2007 we performed a 2 d numerical study to quantify the perturbation induced by sill injection within a volcanic edifice magma is considered as an inviscid and pressurized fluid injected in an initially stable edifice under gravity controlled extension two cases of injection are tested in an elastic homogeneous edifice or along a detachment controlled by a friction law we show that sill injection induces tangential displacements this effect is strongly increased when sills are emplaced along a detachment producing extension behind the injection and potentially ending in a large scale flank collapse sill injections can thus explain the cointrusive shear deformation observed at piton des neiges and the tangential displacements measured at piton de la fournaise in 2007

cyclic magma storages and transfers at piton de la fournaise volcano la reunion hotspot inferred from deformation and geochemical data abstract piton de la fournaise is in a period of intense volcanic activity since 1998 to constrain the magma dynamics responsible for this activity we combined gps ground deformation monitoring interpreted through numerical modelling and geochemistry two cycles of continuous volcano inflation are evidenced for the may 2004 december 2005 period with a rest from march to october 2005 these inflations are consistent with two cycles of compatible major element enrichment in the emitted lavas numerical models indicate that the pressurization of a single magma reservoir may be responsible for the observed pre eruptive inflations of the volcano the reservoir located at 2300 m depth has a radius of 500 m at the beginning of each cycle dykes propagate from the roof of the reservoir and yield eruptions of differentiated basalt near the summit at the end of the cycle dykes propagate from the eastern sidewall of the reservoir and yield distal eruptions of primitive magmas away from the summit the volumes of magma emitted during the primitive eruptions seem too large to explain the surface deformations and therefore suggest some refill of the reservoir by deeper magmas our results may be used to predict the location and lava volume of future eruptions at piton de la fournaise volcano depending on the timing of these eruptions within a cycle of volcanic activity

millennial scale precipitation changes in southern brazil over the past 90 000 years 1 a u th dated 90 000 year long speleothem oxygen isotope record from southern brazil anti correlates remarkably with the cave calcite records from eastern china but positively correlates with the speleothem record from northeastern brazil suggesting an interhemispheric anti phasing of rainfall on both millennial and orbital timescales likely related to displacement in the mean position of the intertropical convergence zone and associated asymmetry in hadley circulation the phase relationships among these records are consistent with the hypothesis that abrupt climate events during the last glacial period are triggered by oceanic circulation changes in the high latitudes and enhanced by tropical feedbacks

a phenomenological model for precursor volcanic eruptions intense explosions of relatively short duration frequently precede large explosive and effusive volcanic eruptions by as much as weeks to months in the case of very viscous magmas1 2 3 4 5 6 in some cases such pre eruption activity has served as a sufficient warning to those living in the vicinity to evacuate and avoid calamity1 precursor events seem to be related to the formation of a magma pathway to the surface but their precise interpretation is a long standing puzzle it has been inferred from theoretical studies that exsolution of volatiles might create an almost separate gas pocket at the tip of a propagating dyke7 8 9 here we explain the role that such a process may have using a laboratory study of the transient propagation of a liquid filled crack with a gas pocket at its tip that grows with time we show that once the gas pocket acquires sufficient buoyancy to overcome the fracture resistance of the host solid the dynamics of the gas pocket rather than those of the liquid determine the velocity of the crack tip furthermore we find that the gas can ultimately separate from the liquid we propose that fast moving gas rich pockets reaching the surface ahead of the main liquid filled fissure could be the origin of many precursor eruptions

monsoons as eddy mediated regime transitions of the tropical overturning circulation monsoons are generally viewed as planetary scale sea breeze circulations caused by contrasts in the thermal properties between oceans and land surfaces that lead to thermal contrasts upon radiative heating1 2 but the radiative heating evolves gradually with the seasons whereas the onset of monsoon precipitation and the associated circulation changes such as reversal of surface winds occur rapidly3 4 here we use reanalysis data to show that the onset of the asian monsoon marks a transition between two circulation regimes that are distinct in the degree to which eddy momentum fluxes control the strength of the tropical overturning circulation rapid transitions of the circulation between the two regimes can occur as a result of feedbacks between large scale extratropical eddies and the tropical circulation5 using simulations with an aquaplanet general circulation model we demonstrate that rapid eddy mediated monsoon transitions occur even in the absence of surface inhomogeneities provided the planet surface has sufficiently low thermal inertia on the basis of these results we propose a view of monsoons in which feedbacks between large scale extratropical eddies and the tropical circulation are essential for the development of monsoons whereas surface inhomogeneities such as land sea contrasts are not

radar interferometry and its application to changes in the earth s surface geophysical applications of radar interferometry to measure changes in the earth s surface have exploded in the early 1990s this new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times the resulting interferogram is a contour map of the change in distance between the ground and the radar instrument these maps provide an unsurpassed spatial sampling density 100 pixels km 2 a competitive precision 1 cm and a useful observation cadence 1 pass month 1 they record movements in the crust perturbations in the atmosphere dielectric modifications in the soil and relief in the topography they are also sensitive to technical effects such as relative variations in the radar s trajectory or variations in its frequency standard we describe how all these phenomena contribute to an interferogram then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments including the four satellites currently in orbit ers 1 ers 2 jers 1 and radarsat the next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement respecting the limits of the technique assessing its uncertainty recognizing artifacts and discriminating different types of signal we then review the geophysical applications published to date most of which study deformation related to earthquakes volcanoes and glaciers using ers 1 data we also show examples of monitoring natural hazards and environmental alterations related to landslides subsidence and agriculture in addition we consider subtler geophysical signals such as postseismic relaxation tidal loading of coastal areas and interseismic strain accumulation we conclude with our perspectives on the future of radar interferometry the objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it

the grand brule exploration drilling new data on the deep framework of the piton de la fournaise volcano part 1 lithostratigraphic units and volcanostructural implications abstract the sinking of a deep drill hole 3003 5 m for geothermal exploration in the eastern part of the piton de la fournaise volcano on reunion island has revealed the underlying lithostratigraphy six principal sequences have been distinguished a 0 440 m subaerial basaltic flows b 440 556 m a transitional series characterized by an alternation of subaerial basalts and submarine deposits vitric basalt and hyaloclastic breccia c 556 616 m submarine basalts lavas and hyaloclastites d 616 890 m subaerial basalts e 890 1010 m submarine basaltic deposits with abundant argillized hyaloclastites f 1010 3003 5 m a layered intrusive complex comprising 1010 1129 m sheets of gabbro injected into the lavas and hyaloclastites 1129 1920 m a zoned intrusion of olivine gabbro and dolerite 1920 3003 5 m stratified cumulate gabbro wehrlite dunite the occurrence of the first submarine deposits at 440 m 268 m below present sea level and the intercalation with them of subaerial basalts down to 890 m 728 m below present sea level tend to support a hypothesis of sliding into the sea during subsidence of the eastern flank of the fournaise massif the intrusive complex intersected from 1010 m down is regarded as a former shallow magma chamber a large positive gravimetric anomaly 40 50 mgal centered over grand brule and attributed to the intrusive complex indicates that its roof forms an ellipse 3 20 km elongated n s stratigraphic and morphological structural evidence on land and on the sea floor and the results of the mineralogical study of this very large magma chamber suggest that it belongs to an ancient edifice proto fournaise whose activity preceded the construction of the present fournaise and ended at about 0 6 ma on land the evidence for this earlier edifice is to be found in the zeolitised basalts and differentiated lavas hawaiites forming the basement to the phase 1 lava flows certain subsidence structures on the present fournaise are interpreted as resulting from settling of the proto fournaise volcano the destabilization of the east flank grand brule area of the currently active volcano and the location of the ne and se rift zones could be attributed to the same phenomenon

monsoons itczs and the concept of the global monsoon earth s tropical and subtropical rainbands such as intertropical convergence zones itczs and monsoons are complex systems governed by both large scale constraints on the atmospheric general circulation and regional interactions with continents and orography and coupled to the ocean monsoons have historically been considered as regional large scale sea breeze circulations driven by land sea contrast more recently a perspective has emerged of a global monsoon a global scale solstitial mode that dominates the annual variation of tropical and subtropical precipitation this results from the seasonal variation of the global tropical atmospheric overturning and migration of the associated convergence zone regional subsystems are embedded in this global monsoon localized by surface boundary conditions parallel with this much theoretical progress has been made on the fundamental dynamics of the seasonal hadley cells and convergence zones via the use of hierarchical modeling approaches including aquaplanets here we review the theoretical progress made and explore the extent to which these advances can help synthesize theory with observations to better understand differing characteristics of regional monsoons and their responses to certain forcings after summarizing the dynamical and energetic balances that distinguish an itcz from a monsoon we show that this theoretical framework provides strong support for the migrating convergence zone picture and allows constraints on the circulation to be identified via the momentum and energy budgets limitations of current theories are discussed including the need for a better understanding of the influence of zonal asymmetries and transients on the large scale tropical circulation

dominant control of the south asian monsoon by orographic insulation versus plateau heating heat emitted from the tibetan plateau as dry heat and water vapour has long been assumed to be the main driver of the south asian summer monsoon but new work suggests that in fact it is the neighbouring mountains that are the major influence william boos and zhiming kuang use an atmospheric model to show that flattening the tibetan plateau has little effect on the monsoon so long as the himalayas and surrounding mountain ranges remain the plateau does boost rainfall locally along its southern edge but it is the build up of hot moist air over india insulated from colder drier air by the himalayas that drives large scale monsoon circulation the elevation of the tibetan plateau is thought to cause its surface to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales here however an atmospheric model is used to show that flattening of the tibetan plateau has little effect on the monsoon provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved the tibetan plateau like any landmass emits energy into the atmosphere in the form of dry heat and water vapour but its mean surface elevation is more than 5 km above sea level this elevation is widely held to cause the plateau to serve as a heat source that drives the south asian summer monsoon potentially coupling uplift of the plateau to climate changes on geologic timescales1 2 3 4 5 observations of the present climate however do not clearly establish the tibetan plateau as the dominant thermal forcing in the region peak upper tropospheric temperatures during boreal summer are located over continental india south of the plateau here we show that although tibetan plateau heating locally enhances rainfall along its southern edge in an atmospheric model the large scale south asian summer monsoon circulation is otherwise unaffected by removal of the plateau provided that the narrow orography of the himalayas and adjacent mountain ranges is preserved additional observational and model results suggest that these mountains produce a strong monsoon by insulating warm moist air over continental india from the cold and dry extratropics these results call for both a reinterpretation of how south asian climate may have responded to orographic uplift and a re evaluation of how this climate may respond to modified land surface and radiative forcings in coming decades

internal structure of piton de la fournaise volcano from seismic wave propagation and earthquake distribution abstract arrival times of seismic waves from local earthquakes are inverted for both locating the source and defining the 3 d velocity heterogeneity of piton de la fournaise the lateral heterogeneity of the 2632 m high edifice is resolved as a high velocity plug 1 5 km in diameter surrounded by a low velocity ring which may be interpreted as due to the construction of fournaise on the flank of the older volcano piton des neiges wave mode conversion detected on three component seismograms provides evidence for boundaries of contrasted velocities pre eruptive swarm earthquakes cluster in the high velocity zone under the dolomieu summit crater low strength and cohesion of the surrounding material account for the lack of seismicity for the final 1 3 km radial flow of magma to the vents in enclos fouque beneath the high velocity plug the existence of a body with low velocity for p and even for s waves is well constrained however the walls and base are poorly defined because of the lack of deep earthquakes for sampling the few earthquakes that are located in this depth region usually occur at a depth of around 1 5 km below sea level in the region of the cone this can be considered providing the upper constraint on the lower limit of the aseismic part of the low velocity body the coincidence in time of their occurrence with the swarms above sea level and the eruptions suggests magmatic activation of the low velocity aseismic volume 1 5 km below sea level under the high velocity plug of the cone further down the concentration of seismicity in two swarms between 2 and 4 km under the eastern flank does not allow the structure to be sampled effectively

magma transport and storage at piton de la fournaise la reunion between 1972 and 2007 a review of geophysical and geochemical data abstract since the middle of the 20th century improvement in volcano monitoring techniques has provided large data sets that can be used to evaluate the evolution of magma plumbing systems at piton de la fournaise volcano abundant eruptive activity and a dense monitoring network are especially conducive to such research analysis of the extensive set of geophysical and geochemical data associated with the last 35 years of activity provides new insights into magma transport and storage at piton de la fournaise two periods of frequent eruptions separated by 6 years of inactivity can be distinguished 1972 1992 and 1998 2007 considering these two periods we show evidence of major changes in the shallow plumbing system in 2000 during 1972 1992 and 1998 2000 lava compositions and weak long term eruptive precursors lasting few days to three weeks characterized by no significant summit inflation and about ten volcano tectonic earthquakes per day suggest that eruptions were fed by the progressive drainage of an occasionally recharged shallow magma reservoir geophysical evidence of shallow magma reservoir recharge was only recorded in 1986 and 1998 in contrast from 2000 to 2007 geophysical data highlight the appearance of long term precursors 1 to 5 months of summit inflation and strong seismicity up to one hundred events per day preceding cycles of successive eruptions each cycle of eruptions was characterized by a sequence 3 to 10 months in duration of summit and near summit proximal eruptions and ended with a distal low altitude oceanite olivine abundances 20 vol eruption on the eastern flank of the volcano within each of these eruptive cycles lavas became progressively more magnesian over time the preferential motion of the eastern flank caused by continuous recharging of the shallow reservoir since 2000 would favour the occurrence of distal eruptions towards this flank at the end of a cycle

dynamics of degassing at kilauea volcano hawaii at kilauea volcano hawaii the recent long lived eruptions of mauna ulu and pu u o o have occurred in two major stages defining a characteristic eruptive pattern the first stage consists of cyclic changes of activity between episodes of fire fountaining and periods of quiescence or effusion of vesicular lava the second stage consists only of continuous effusion of lava we suggest that these features reflect the dynamics of magma degassing in a chamber which empties into a narrow conduit in the volcano chamber gas bubbles rise through magma and accumulate at the roof in a foam layer the foam flows toward the conduit and its shape is determined by a dynamic balance between the input of bubbles from below and the output into the conduit the foam thickness is proportional to lq e2 l g 1 4 where l and l are the viscosity and density of magma e is the gas volume fraction in the foam g is the acceleration of gravity and q is the gas flux the bubbles in the foam deform under the action of buoyancy and the maximum permissible foam thickness is hc 2 e lgr where is the coefficient of surface tension and r is the original bubble radius if this critical thickness is reached the foam collapses into a large gas pocket which erupts into the conduit foam accumulation then resumes and a new cycle begins the attainment of the foam collapse threshold requires a gas flux in excess of a critical value which depends on viscosity surface tension and bubble size hence two different eruption regimes are predicted 1 alternating regimes of foam buildup and collapse leading to the periodic eruption of large gas volumes and 2 steady foam flow at the roof leading to continuous bubbly flow in the conduit the essential result is that the continuous process of degassing can lead to discontinuous eruptive behavior data on eruption rates and repose times between fountaining phases from the 1969 mauna uiu and the 1983 1986 pu u o o eruptions yield constraints on three key variables the area of the chamber roof must be a few tens of square kilometers with a minimum value of about 8 km2 magma reservoirs of similar dimensions are imaged by seismic attenuation tomography below the east rift zone close to the roof the gas volume fraction is a few percent and the gas bubbles have diameters lying between 0 1 and 0 6 mm these estimates are close to the predictions of models for bubble nucleation and growth in basaltic melts as well as to the observations on deep submarine basalts the transition between cyclic and continuous activity occurs when the mass flux of gas becomes lower than a critical value of the order of 103 kg s in this model changes of eruptive regime reflect changes in the amount and size of bubbles which reach the chamber roof

joint analysis of geodetic and earthquake fault plane solution data to constrain magmatic sources a case study from kīlauea volcano abstract a joint analysis of geodetic and seismic datasets from k lauea volcano during a period of magmatic unrest in 2006 demonstrates the effectiveness of this combination for testing and constraining models of magma dynamics for a complex multi source system at the end of 2003 k lauea s summit began a four year long period of inflation due to a surge in magma supply to the volcano in 2006 for the first time since 1982 k lauea s southwest rift zone swrz also experienced inflation to investigate the characteristics of active magma sources and the nature of their interactions with faults in the swrz during 2006 we integrate through coulomb stress modeling contemporary geodetic data from insar and gps with a new catalogue of double couple fault plane solutions for volcano tectonic earthquakes we define two periods of inflation during 2006 based on the rate of deformation measured in daily gps data spanning february to 15 march 2006 period 1 and 16 march to 30 september 2006 period 2 insar data for these two periods are inverted to determine the position change in size and shape of inflation sources in each period our new models are consistent with microseismic activity from each period they suggest that during period 1 deformation in the swrz can be explained by pressurization of magma in a spherical reservoir beneath the south caldera and that during period 2 magma was also aseismically intruded farther to the southwest into the swrz along a sub horizontal plane our coulomb stress analysis shows that the microseismicity recorded in the swrz is induced by overpressurization of the south caldera reservoir and not by magma intrusion into the swrz this study highlights the importance of a joint analysis of independent geophysical datasets to fully constrain the nature of magma accumulation

anatomy of piton de la fournaise volcano la reunion indian ocean the aim of this work is to propose a general model of piton de la fournaise volcano using information from geological and geophysical studies firstly we make a graphical compilation of all available geophysical information along a w e profile secondly we construct a geological section that integrates both the geophysical information and the geological information the lithosphere beneath piton de la fournaise is not significantly flexed and the crust is underlain by an underplating body which might represent the deep magma reservoir for la reunion volcanism piton de la fournaise is a relatively thin volcano lying on a huge volcanic construction attributed mostly to les alizes volcano indeed if the differentiated rocks observed at the bottom of the riviere des remparts are the top of les alizes volcano the interface with piton de la fournaise may be located at about sea level beneath the summit area the endogenous constructions intrusive complexes related to les alizes and piton de la fournaise volcanoes represent a large volume the huge intrusive complex of les alizes volcano probably rests on the top of the oceanic crust and appears to have a buttressing effect for the present eastern volcano tectonic activity of piton de la fournaise the early piton de la fournaise edifice was built around a focus located beneath the plaine des sables area the center subsequently moved 5 6 km eastward to its current location the dense high velocity body beneath the plaines des sables and the western part of the enclos probably corresponds to the hypovolcanic intrusive complex that developed before the volcanic center shifted to its present day position magma reservoirs may have existed and may still exist as illustrated by the march 1998 crisis at the mechanical and density interface between the oceanic crust and the les alizes edifice strong evidence also exists for the presence of a shallower magma reservoir located near sea level beneath the summit the march 1998 pre eruptive seismic pattern location and upward migration seems to be evidence for a transfer of magma between the two reservoirs the dominant structural feature of the central zone is a collapse structure beneath the summit craters above the inferred magma reservoir near sea level the collapsed column constitutes a major mechanical heterogeneity and concentrates most of the seismic intrusive and hydrothermal activity because of its higher permeability and weaker mechanical strength

dansgaard oeschger cycles interactions between ocean and sea ice intrinsic to the nordic seas dansgaard oeschger d o cycles are the most dramatic frequent and wide reaching abrupt climate changes in the geologic record on greenland d o cycles are characterized by an abrupt warming of 10 5 c from a cold stadial to a warm interstadial phase followed by gradual cooling before a rapid return to stadial conditions the mechanisms responsible for these millennial cycles are not fully understood but are widely thought to involve abrupt changes in atlantic meridional overturning circulation due to freshwater perturbations here we present a new high resolution multiproxy marine sediment core monitoring changes in the warm atlantic inflow to the nordic seas as well as in local sea ice cover and influx of ice rafted debris in contrast to previous studies the freshwater input is found to be coincident with warm interstadials on greenland and has a fennoscandian rather than laurentide source furthermore the data suggest a different thermohaline structure for the nordic seas during cold stadials in which relatively warm atlantic water circulates beneath a fresh surface layer and the presence of sea ice is inferred from benthic oxygen isotopes this implies a delicate balance between the warm subsurface atlantic water and fresh surface layer with the possibility of abrupt changes in sea ice cover and suggests a novel mechanism for the abrupt d o events observed in greenland ice cores

dike propagation through layered rocks 1 dike penetration through a succession of upper crustal layers with different densities is studied with a new numerical code for an individual layer to significantly affect dike ascent its thickness must be of order 1 when scaled to the characteristic length scale for the inflated nose region that develops below the dike tip this characteristic length is l q 1 6 g 1 1 2 g 2 3 where and are the viscosity and buoyancy of magma g and are elastic moduli for the encasing rocks q is the magma flow rate and g gravity for basaltic dikes l is 1 km which is of the same order of magnitude as the typical thickness of sedimentary strata and volcanic deposits in such conditions dike ascent proceeds irregularly with large changes of velocity and width at an interface scaling laws for the ascent rate and dike width are derived penetration through low density layers is determined by a local buoyancy balance in the inflated nose region of the dike independently of the total buoyancy of the magma column between source and tip in such conditions a dike develops an internal overpressure that may be large enough to generate a horizontally propagating sill for this to occur the thickness of the low density layers must exceed a threshold value which depends only on the rock strength and on the average negative buoyancy of magma for basaltic melt we estimate that this threshold thickness cannot be less than about 700 m and is 2 km on average

critical fluid injection volumes for uncontrolled fracture ascent hydro fracturing is a routine industrial technique whose safety depends on fractures remaining confined within the target rock volume both observations and theoretical models show that if the fluid volume is larger than a critical value pockets of fluid can propagate large distances in the earths crust in a self sustained uncontrolled manner existing models for such critical volumes are unsatisfactory most are two dimensional and depend on poorly constrained parameters typically the fracture length here we derive both analytically and numerically in three dimensions scale independent critical volumes as a function of only rock and fluid properties we apply our model to gas water and magma injections in laboratory industrial and natural settings showing that our critical volumes are consistent with observations and can be used as conservative estimates we discuss competing mechanisms promoting fracture arrest whose quantitative study could help to assess more comprehensively the safety of hydro fracturing operations

imaging the dynamics of dyke propagation prior to the 2000 2003 flank eruptions at piton de la fournaise reunion island 1 the relationship between shallow magma storage and flank injections in volcanic edifices is rarely documented we analyse the time series of geodetic and seismic data collected at piton de la fournaise volcano la reunion during 9 flank eruptions from 2000 to 2003 the data depicts how magma injections supplied flank eruptions at piton de la fournaise volcano and allows to precisely determine the direction and duration of dike intrusions indicating a two phases pattern consistent over all the eruptions 1 fast vertical migration of the dyke 2 m s from the magma chamber to the surface in 10 to 50 minutes and 2 slower lateral migration 0 2 0 8 m s in tens of minutes to hours controlled by the rift zone geometry

edifice growth deformation and rift zone development in basaltic setting insights from piton de la fournaise shield volcano reunion island abstract the overall morphology of basaltic volcanoes mainly depends on their eruptive activity effusive vs explosive the geometry of the rift zones and the characteristics of both endogenous and exogenous growth processes the origin of the steep geometry of the central cone of piton de la fournaise volcano which is unusual for a basaltic effusive volcano and its deformation are examined with a combination of a detailed morphological analysis field observations gps data from the piton de la fournaise volcano observatory and numerical models the new caldera walls formed during the april 2007 summit collapse reveal that the steep cone is composed of a pyroclastic core inherited from an earlier explosive phase overlapped by a pile of thin lava flows this suggests that exogenous processes played a major role in the building of the steep central cone magma injections into the cone which mainly occur along the n25 30 and n120 rift zones lead to an asymmetric outward inflation concentrated in the cone s eastern half this endogenous growth progressively tilts the southeast and east flanks of the cone and induces the development of a dense network of flank fractures finally it is proposed that intrusions along the n120 rift zone are encouraged by stresses induced by magma injections along the n25 30 rift zone

fracture mode analysis and related surface deformation during dyke intrusion results from 2d experimental modelling surface deformation analysis in volcanic edifices in response to shallow magma intrusion is crucial for assessing volcanic hazards in this paper we discuss the effect of dyke propagation mode on surface deformation through 2d laboratory models our experimental setup consists of a hele shaw cell in which a model magma is injected into a cohesive model crust using an optical image correlation technique particle imaging velocimetry we measured the surface deformation the displacements and the strain field induced by magma emplacement within the country rock we identify two types of intrusion morphologies types a and b which exhibit two evolutional stages during the first stage both types resulted in a vertical dyke at depth its propagation was controlled by both shear deformation and tensile opening the model surface lifted up to form a smooth symmetrical dome resulting in tensile cracks during the second stage types a and b experiments differ when the dyke reaches a critical depth in type a the intrusion gradually rotates forming an inclined sheet dipping between 451 and 651 this rotation results in asymmetrical surface uplift and shear failure upon the tip of the dyke in type b the dyke tip interacts with tensile cracks formed during the first stage this fracture controls the subsequent propagation of the dyke toward the surface in both types of experiments intrusions result in surface uplift which can be accommodated by reverse faults our study suggests that dykes propagate as viscous indenters rather than linear elastic fracturing

sahel megadroughts triggered by glacial slowdowns of atlantic meridional overturning 1 the influence of the large scale ocean circulation on sahel rainfall is elusive because of the shortness of the observational record we reconstructed the history of eolian and fluvial sedimentation on the continental slope off senegal during the past 57 000 years our data show that abrupt onsets of arid conditions in the west african sahel were linked to cold north atlantic sea surface temperatures during times of reduced meridional overturning circulation associated with heinrich stadials climate modeling suggests that this drying is induced by a southward shift of the west african monsoon trough in conjunction with an intensification and southward expansion of the midtropospheric african easterly jet

width change of a planar magma path implication for the evolution and style of volcanic eruptions abstract the width change of a planar path filled with magma is analyzed assuming that the process is controlled by laminar flow of an incompressible viscous magma between movable parallel walls of country rock the analysis shows that the width of a planar path changes at a rate is proportional to the effective opening pressure which is defined as the pressure of the penetrating magma plus the tensile stress component stretching the fluid interface when the opening pressure is a positive constant the fissure widens at an accelerating rate and finally diverges at a critical time constant which depends on the initial size of the fissure and the viscosity of magma as well as on the opening pressure in contrast the fissure gradually narrows under a negative opening pressure this result is applicable to a variety of magmatic processes first the orientation of a volcanic fissure or a dike is such that the tensile stress component is maximized because a fissure with this orientation becomes wider than those at other orientations as it has the minimum value of critical time constant second local irregularities in the geometrical and mechanical conditions of the magma sheet lead to significant variations in fissure width in the widening process this nonuniform increase in width is further exaggerated by mechanical and thermal erosion of the wall rock which makes the irregular surfaces irrecoverable in this manner a planar magma path tends to be split into isolated cylindrical conduits when the magma pressure is reduced and the fissure closes as a whole some actual fissure eruptions such as those at kilauea and izu oshima show evolutionary processes consistent with this prediction another application of the analysis is to explain how the style of a volcanic eruption is determined by the tectonics specifically extensional tectonics which gives a positive opening pressure for any magma pressure allows magma to ascend dispersively along various paths and produces a group of small monogenetic volcanoes in contrast contractional tectonics in which new fissures can be made only for a very high magma pressure concentrates magma into a restricted number of vents and leads to the growth of large polygenetic volcanoes

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

a model for radial dike emplacement in composite cones based on observations from summer coon volcano colorado usa we mapped the geometry of 13 silicic dikes at summer coon an eroded oligocene stratovolcano in southern colorado to investigate various characteristics of radial dike emplacement in composite volcanoes exposed dikes are up to about 7 km in length and have numerous offset segments along their upper peripheries surprisingly most dikes at summer coon increase in thickness with distance from the center of the volcano magma pressure in a dike is expected to lessen away from the pressurized source region which would encourage a blade like dike to decrease in thickness with distance from the center of the volcano we attribute the observed thickness pattern as evidence of a driving pressure gradient which is caused by decreasing host rock shear modulus and horizontal stress both due to decreasing emplacement depths beneath the sloping flanks of the volcano based on data from summer coon we propose that radial dikes originate at depth below the summit of a host volcano and follow steeply inclined paths towards the surface near the interface between volcanic cone and basement which may represent a neutral buoyancy surface or stress barrier magma is transported subhorizontally and radially away from the center of the volcano in blade like dikes the dikes thicken with increasing radial distance and offset segments and fingers form along the upper peripheries of the intrusions eruptions may occur anywhere along the length of the dikes but the erupted volume will generally be greater for dike fed eruptions far from the center of the host volcano owing to the increase in driving pressure with distance from the source observed eruptive volumes vent locations and vent area intrusions from inferred post glacial dike fed eruptions at mount adams washington usa support the proposed model hazards associated with radial dike emplacement are therefore greater for longer dikes that propagate to the outer flanks of a volcano

deep fluid transfer evidenced by surface deformation during the 2014 2015 unrest at piton de la fournaise volcano abstract identifying the onset of volcano unrest and providing an unequivocal identification of volcano reawakening remain challenging problems in volcanology at piton de la fournaise renewal of eruptive activity in 2014 2015 after 41 months of quiescence and deflation was associated with long term continuous edifice inflation measured by gnss inflation started on june 9 2014 and its rate progressively increased through 2015 inflation onset was rapidly followed by an eruption on june 20 21 2014 showing that volcano reactivation can be extremely fast even after long non eruptive phases this short lived eruption involved a shallow source 1 3 1 9 km depth below the summit the inflation that followed and eruptions in 2015 involved a larger depth range of fluid accumulation constrained by inverse modeling at ca 3 9 to 1 2 1 7 km depth this time evolution reveals that volcano reawakening was associated with continuous pressurization of the shallowest parts of its plumbing system triggered by progressive upwards transfer of magma from greater depth a deep magma pulse occurred in mid april 2015 and was associated with deep seismicity 3 to 9 5 km depth and co 2 enrichment in fluids emitted by summit fumaroles from this date ground deformation accelerated and the output rates of eruptions increased culminating in the long lasting large volume august october eruption 36 mm 3 this evolution suggests that deep magma fluid transfer through an open conduit system first provoked the expulsion of the top of the plumbing system in june 2014 and then induced the progressive vertical transfer of the entire plumbing system down to 9 km four eruptions in 2015 the new sustained feeding of the volcano was also at the origin of the hydrothermal system perturbation and the acceleration of the eastern flank motion which favor lateral dike propagation and the occurrence of frequent and increasingly large eruptions our results highlight the fast and progressive way in which basaltic magmatic systems can wake up

mechanical modeling of circumferential and radial dike intrusion on galapagos volcanoes a distinctive and unusual pattern of eruptive fissures is observed on the active volcanoes of the galapagos islands reflecting circumferential dike intrusion near the calderas and radial dike intrusion on the volcano flanks elastic finite element models were used to investigate how a stress field could be produced and maintained to promote both circumferential and radial dike emplacement modeling results show that magma reservoirs of galapagos volcanoes are probably diapiric because this shape promotes both circumferential and radial intrusions but magma pressure alone cannot create the observed pattern of dikes loading by volcano growth and magma reservoir pressure could produce a stress field of suitable orientation but insufficient magnitude the intrusion of circumferential dikes could alter the stress field in a way that promotes future radial diking and vice versa faulting or slumping within the calderas or on the volcano flanks in response to repeated intrusions could also create a stress field conducive to continued intrusion

a shallow dipping dike fed the 1995 flank eruption at fernandina volcano galapagos observed by satellite radar interferometry satellite radar interferometry data reveal strong localized uplift in a semi circular pattern on the southwest flank of fernandina volcano galapagos where an eruption took place in january to april 1995 the observations show a maximum decrease in radar range of 0 75 m and they are consistent with a model of a shallow dipping dike intrusion feeding this fissure eruption we solve for the best fit single rectangular dislocation dike source using non linear inver sion techniques where simulated annealing searching algo rithm is used to avoid local minima the best fit dike is 3 8 km long 2 3 km high 0 86 m thick and with a 34 dip the total dike volume 7 5 x 10 3 km 3 is 40 of the vol ume of extrusive materials estimated to have been produced during the eruption the data do not permit a sub vertical dike implying that the least principal stress direction is not horizontal as is usually assumed

insar monitoring using radarsat 2 data at piton de la fournaise la reunion and karthala grande comore volcanoes piton de la fournaise la reunion and karthala grande comore are the two active volcanoes of the southwestern indian ocean a 14 month april 2013 to june 2014 monitoring period was carried out at both volcanoes using synthetic aperture radar interferometry insar techniques on radarsat 2 data thanks to the seas oi survey of environment assisted by satellite in the indian ocean station 21 sar scenes were acquired over this period and insar results revealed the slow subsidence of the dolomieu caldera floor at piton de la fournaise following the 2009 and 2010 eruptions and the subsidence of the whole cone between april and july 2013 at karthala no evidence of any volcanic activity was found for the period april 2013 to june 2014 the use of systematic insar for volcano monitoring is an efficient tool to study effusive eruptions we showed that during periods of unrest insar is able to pick up early signs of a future eruption and monitor secondary phenomena that require no real time data during an effusive crisis it is still difficult to carry out fully operational insar monitoring but using the example of the june 2014 eruption at piton de la fournaise we show that sar data can help with the detection and tracking of lava flows and active flow paths during effusive eruptions based on sar coherence and sar amplitude these preliminary results are very promising for the future of insar monitoring of active volcanoes and highlight the need for near real time access to sar data in the mapping of active lava flows during effusive eruptions this study also revealed the major role of ground stations like seas oi in the efficiency of this monitoring supplying free near real time remote sensing data to the scientific and institutional communities

magma crystallization and viscosity a study of molten basalts from the piton de la fournaise volcano la reunion island abstract the viscosity of three molten basalts produced by fusion of lavas issued from different eruptions of the piton de la fournaise la reunion island has been investigated above the liquidus and at high degrees of supercooling for all basalts crystallization took place rapidly above the glass transition range which made static measurements problematic because of time dependent non newtonian rheology by contrast reproducible results were obtained in dynamic measurements made at a constant heating rate of 5 k mn partial crystallization resulted in strong viscosity increases which were primarily due to the presence of solid inclusions comparisons with phase equilibria experiments performed for the same samples at higher temperatures show that crystallization takes place differently below the liquidus and at strong degrees of supercooling as recently described for simpler systems these differences in nucleation and growth are controlled by the relative mobilities of the cations diffusing within the melt to attach themselves to crystal melt interfaces a consequence is that the composition evolution of the residual melt differs in equilibrium and irreversible crystallization in turn this contrast induces opposite viscosity variations for the residual melt

a constant influx model for dike propagation implications for magma reservoir dynamics 1 most observations of seismicity rate during dike propagation on basaltic volcanoes show 1 rate stationarity despite possible variations of the dike tip velocity 2 frequent lack of clear and monotonic hypocenter migration following dike propagation and 3 event occurrences located backward with respect to the dike tip position on these bases the origin of the seismicity contemporary to dike intrusion within basaltic volcanoes cannot be solely related to the crack tip propagation seismicity rather appears to be the response of the edifice itself to the volumetric deformation induced by the magma intruding the solid matrix the volume change induced into the volcano edifice over time by the intruding magma is equal to the magma flux injected into the dike from the reservoir the consequence of this is that the stationary seismicity rate observed during the intrusion is a proxy for the magma flux withdrawn from the reservoir we consider a two phase dike propagation model including a first vertical propagation followed by a lateral migration along a lithological discontinuity we explore 1 under which geophysical conditions the vertical dike is fed at constant flow rate of magma and 2 dike propagation patterns implications entailed by constant volumetric flux on the piton de la fournaise volcano case study suggest a minimum size for the magma reservoir of about 1 km3 and a maximum value for the initial magma reservoir overpressure of about 2 2 mpa considering similar magma inflow rates during vertical and lateral dike propagation phases we reproduce independent estimates of propagation velocities rise times and injected volumes when applying the model to the august 2003 piton de la fournaise eruption

boundary conditions for rock fracture analysis using the boundary element method successful numerical models of faults joints and other fractures in a rock mass require specification of appropriate boundary conditions but the choice may not be obvious to illustrate potential pitfalls a single two dimensional fracture is modeled by the displacement discontinuity method of boundary elements using both displacement boundary conditions and traction boundary conditions the results are compared with the analytical solution for a mode i opening crack it is shown that the traction boundary conditions can provide a satisfactory solution while displacement boundary conditions applied to a problem with both continuous and discontinuous displacement components can introduce significant errors

april 2007 collapse of piton de la fournaise a new example of caldera formation collapse calderas are frequent in the evolution of volcanic systems but very few have formed during historical times piton de la fournaise is one of the world s most active basaltic shield volcanoes the caldera collapse which occurred during the april 2007 lateral eruption is one of the few large documented collapse events on this volcano it helps to understand the mode and origin of caldera collapses in basaltic volcanoes field observations gps and seismic data show that the collapse occurred at an early stage of the eruption the cyclic seismic signal suggests a step by step collapse that directly influenced the lateral eruption rate likely the caldera results from the combined effect of i the progressive collapse of the plumbing system above the magma chamber since 2000 and ii the large amount of magma withdrawal during the early stage of the eruption by both a significant intrusion within the edifice and an important emission rate

finding realistic dike models from interferometric synthetic aperture radar data the february 2000 eruption at piton de la fournaise dike intrusions often cause complex ground displacements that are not sufciently explained by simple analytical models we develop a method to nd complex and realistic dike geometries and overpressures from interferometric synthetic aperture radar insar data this method is based on a combination of a boundary element method with realistic topography and a neighbourhood algorithm inversion dike model geometry is roughly a quadrangle with its top reaching the ground the inversion has two stages search and appraisal the appraisal stage involves calculations of model marginal probability density functions using mist val ues calculated during the search stage the mist function takes into account the variance and correlation of data noise synthetic tests show that a model is successfully retrieved within predicted narrow condence intervals we apply the method on insar data of the february 2000 ank eruption at piton de la fournaise and get a trapezoid dike dipping seaward 61 0 n 67 3 with its bottom passing 800n1000 m beneath the summit a model with a basal slip plane does not better explain observed asymmetric displacements and thus this asymmetry is solely attributed to the dipping dike the dike lies above a narrow band of pre eruption seis micity suggesting that lateral magma propagation occurred neglecting topography results in poor modeling at depth and in overestimations of overpressure or opening height both about 30 and volume about 20

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

koolau dike complex oahu intensity and origin of a sheeted dike complex high in a hawaiian volcanic edifice the dike complex in the eroded koolau tholeiitic shield volcano is unique among described dike swarms for its coherence high dike injection intensity relatively uniform and non gaussian 50 to 65 intensity level and lack of dike divergence parts are like a sheeted dike complex though high in an intraplate volcanic edifice a model is proposed in which highly mobile tholeiitic magma having considerable freedom to move through the strongly disjointed volcano seeks zones in which it is gravitationally most stable these zones are marginal parts of the dike complex separating lavas having a lower than magmatic bulk density from a 50 dike complex having a higher than magmatic bulk density this model also explains the strong propensity for the magma of kilauea volcano to remain underground in a gravitationally stable zone magma erupts only when it vesiculates sufficiently often when it has degassed some of it promptly plunges back toward the stable zone again

dynamic and static moduli static and dynamic bulk moduli ks and kd are measured as continuous functions of pressure from zero to 2 3 kilobars for two sandstones a tuff limestone granite and oil shale results for the sandstones and granite are in good agreement with previously reported data with ks kd varying from about 0 5 at atmospheric pressure to close to unity at pressures 2 kilobars and above for rocks behaving elastically under static loading the ks kd ratio is inversely related to the microcrack density for the limestone time dependent deformation associated with pore collapse results in ks kd ratios approaching 0 1 at high pressure upon unloading while initially high 1 0 at high pressures ks kd becomes lower than values obtained during loading at low pressures 1 kilobar due to opening of microcracks generated during pore collapse for the oil shale in which few microcracks exist ks kd remains relatively constant with pressure at a value of about 0 7

constraints on magma transfers and structures involved in the 2003 activity at piton de la fournaise from displacement data piton de la fournaise reunion island had shown 8 months of high activity during 2003 including four eruptions and one intrusion the monitoring networks provided by the volcanological observatory of piton de la fournaise show two different kinds of behavior strong and rapid deformations linked with the magma injections and a slight continuous intereruptive inflation of the summit area inversed modeling based on the deformation data using a three dimensional elastostatic boundary element code combined with seismicity provides new insights into the volcanic feeding system involved in the 2003 activity 1 the 2003 eruptions are fed from a pressurized magma chamber located beneath the summit at 300 m above sea level 2 a vertical path was activated between the magma chamber and the surface during the december 2002 collapse allowing the magma to rise into it and leading to the initial summit eruption in may 2003 3 the august and september 2003 lateral eruptions had been fed by dikes intruding along the same vertical pathway at an estimated velocity of 1 1 to 1 3 m s before intruding the flank into the rift zones at a velocity of 0 2 to 0 8 m s this last point suggests a strong structural control on the dike pathway

a retrospective look at the february 1993 east rift zone intrusion at kīlauea volcano hawaii abstract the february 1993 dike intrusion in the east rift zone erz of k lauea volcano hawai i was recognized from tilt and seismic data but ground based geodetic data were too sparse to constrain the characteristics of the intrusion analysis of interferometric synthetic aperture radar insar from the japan aerospace exploration agency jaxa jers 1 satellite reveals a maximum of 30 cm of line of sight los displacement occurring near makaopuhi crater in the middle erz of k lauea we model this deformation signal as a subvertical dike using a 3d mixed boundary element method 3d mbem paired with a nonlinear inversion algorithm to find the best fit model the best fit dike is located just to the west of makaopuhi crater striking n50 w extends to within 100 m of the surface is 1 3 km in length by 4 2 km in width along strike and has a total volume of 7 4 106 m3 in addition a post intrusion interferogram from jers 1 spanning 1993 1997 was analyzed guided by previous results our model for the 4 year period consists of opening of the deep rift zones by about 0 5 m at 3 8 5 km depth beneath the southwest rift zone swrz erz and the summit a sub horizontal detachment fault is connected to the seaward side of the vertical dike like source to mimic the decollement known to exist beneath the volcano we classify the 1993 dike intrusion as a passive intrusion similar to those that occurred in 1997 and 1999 passive intrusions lack precursory inflation at k lauea s summit and the likely triggering mechanism is persistent deep rift opening combined with seaward motion of the south flank along the basal decollement passive intrusions make forecasting and hazard assessment difficult since they are not preceded by inflation nor by large increases in seismicity

widespread uplift and trapdoor faulting on galapagos volcanoes observed with radar interferometry volcanic uplift caused by the accumulation of magma in subsurface reservoirs is a common precursor to eruptions1 2 but for some volcanoes uplift of metres or more has not yet led to an eruption3 here we present displacement maps of volcanoes in the galapagos islands constructed using satellite radar interferometry that might help explain this dichotomy we show that all but one of the seven volcanoes on the islands of isabela and fernandina deformed during 1992 99 cerro azul and fernandina erupted4 5 6 during the observation period and show evidence of inflation co eruptive deflation and shallow dyke intrusion in contrast the largest volcano sierra negra has not erupted yet exhibits spatially and temporally variable deformation with a maximum uplift of 2 7 m between 1992 and 1999 which can be modelled by a shallow inflating sill inflation during 1997 98 however was accompanied by trapdoor faulting on a steeply dipping fracture system within the caldera repeated trapdoor faulting over geological time has formed an arcuate intra caldera ridge within sierra negra and may have acted to relax stresses above the magma chamber inhibiting summit eruptions similar processes may help explain large uplift unaccompanied by eruptive activity at other volcanoes

role of the structural inheritance of the oceanic lithosphere in the magmato tectonic evolution of piton de la fournaise volcano la reunion island la reunion island is located east of madagascar on the eastern rim of the tectonically inactive mascarene basin this island is composed of three shield volcanoes of which only piton de la fournaise is currently active although the magmatic activity is restricted to piton de la fournaise a scattered seismicity occurs on the whole 200 km wide volcanic edifice and in the underlying oceanic crust we carried out a multiscale analysis to understand 1 the origin of the seismicity in the geodynamic context and 2 the role of the oceanic lithosphere in the deformation of piton de la fournaise and la reunion island analysis of the magmatic system suggests that the magma ascent is controlled by large n25 30 and n125 130 fracture zones located below the enclos depression we also show that the orientation difference between the eruptive fissures and the related dykes result from a rotation of the main principal stress s 1 from vertical to downslope through the surface combining a digital elevation model dem analysis field observations and the geophysical data reveals that the volcano is affected by large fault zones the fault distribution indicates the predominance of a main n70 80 trend magnetic data show the same n80 orientation characterizing the remnant part of the alizes volcano such parallel alignment suggests a control exerted by the underlying alizes volcano on piton de la fournaise furthermore the alignment between the crustal orientations and the structures determined on the island suggests a control of the crustal structures in la reunion s volcano tectonic activity contrary to several volcanic islands such as hawaii and tenerife la reunion volcanoes lie on an upbending crust then we interpret the reactivation of the crustal faults as resulting from a crustal uplift related to the thermal erosion of the base of the lithosphere and or to strong underplating the upward deformation may prevent the spreading of the volcanoes as no evidence of such a mechanism is observed in the bathymetry and the seismic data around the island

inversion of coeval shear and normal stress of piton de la fournaise flank displacement the april 2007 eruption of piton de la fournaise was the biggest volcano eruptive crisis of the 20th and 21st centuries interferometric synthetic aperture radar insar captured a large coeruptive seaward displacement on the volcano s eastern flank which continued for more than a year at a decreasing rate coeruptive uplift and posteruptive subsidence were also observed while it is generally agreed that flank displacement is induced by fault slip we suggest that this flank displacement might have been induced by a sheared sill based on observations of sheared sills at piton des neiges to test this hypothesis we develop a new method to invert a quadrangular curved source submitted to simultaneous pressure and shear stress changes this method based on boundary elements is applied to data acquired along six envisat orbits covering a 14 month period subsequent to the april 2007 eruption posteruptive displacement is well explained by closure and slip of a large 5 km by 8 km and shallow 500 m trapezoidal fracture parallel to the flank and probably coincident with a lithological discontinuity we investigate whether thermal contraction or degassing of a coeruptive sill can explain the displacement such a sill would have to be 10 times thicker than inferred from the coeruptive uplift and solidification time 10 times shorter 20 days than the duration of the posteruptive subsidence 24 to 33 months instead we propose that the posteruptive eastern flank displacement is due to the compaction and ongoing slow slip on a shallow detachment fault

mt etna 2001 eruption new insights into the magmatic feeding system and the mechanical response of the western flank from a detailed geodetic dataset abstract in the last decades the increasing availability of comprehensive geodetic datasets has allowed for more detailed constraints on subsurface magma storage and conduits at several active volcanoes worldwide here by using a large dataset of geodetic measurements collected between early january 2001 and august 2001 we identified at least six different deformation stages that allow us to quantify the surface deformation patterns before during and after the 2001 mt etna volcanic eruption our results are largely in agreement with previous works e g the presence of a deep inflating source and a shallow dike located beneath the north western and upper southern flanks of the volcano respectively however we provide 1 finer resolution of the temporal activity of these magmatic sources leading to 2 new evidence related to the evolution of the magmatic system and the mechanical response of the western flank in particular during the pre eruptive phase results and analysis show a clear change in the ground deformation pattern of the volcano in response to the 20 24 april 2001 seismic swarm that occurred beneath the western flank evolving from a volcano wide inflation to a slight deflation of the summit area we suggest that the source responsible for the volcano wide inflation beginning in the fall of 2000 experienced a drastic reduction in the inflation rate in response to this seismic swarm moreover we provide evidence for the presence of a new inflating source located beneath the upper southern flank at a depth of 7 0 km bsl that triggered both the occurrence of the 20 24 april 2001 seismic swarm and led to the rapid ascent of magma upward to the surface after 12 july the lower vents system was fed by fresh magma rising from this source the presence of this inflating source is inferred by 1 seismological and volcanological observations coming from the 2001 eruption and 2 seismological constraints coming from a previous similar episode that occurred at etna during the 1993 1998 period furthermore both shallow deflations observed after the 20 24 april 2001 seismic swarm and during the first day of the eruption also could be due to the deflation of two adjacent portions of the same shallow 2 km bsl reservoir such reservoirs would feed the activity that occurred at the south east crater after january 2001 and the activity of the upper vents system during the july august eruption in agreement with petrochemical observations through an updated revision of the available data we shed some light on the relevance of pre eruptive activity patterns an important element for an effective volcano monitoring

a quantitative approach to the dike intrusion process inferred from a joint analysis of geodetic and seismological data for the 1998 earthquake swarm off the east coast of izu peninsula central japan 1 a series of earthquake swarms off the east coast of izu peninsula central japan is typically associated with dike intrusion around active volcanoes numerous studies in this region have documented the seismic activity and ground deformations without fully resolving the process of dike intrusion this study involves a joint analysis of geodetic and seismic data from the most recent major activity in this region occurring in 1998 to reveal the process of dike intrusion quantitatively we combine data from a dense gps array including 10 temporary stations with seismic analysis published previously we estimate the location of the dikes from seismic data and the volume of intruded magma from geodetic data combined analysis of both data sets enables us to reveal the kinematic process of dike intrusion associated with the 1998 earthquake swarm the process of dike intrusion is quantitatively modeled using the time evolution of recorded dike volume and the use of seismic hypocenters as an indicator of the site of instantaneous dike intrusion on the basis of these observations we propose the following process of the dike intrusion the magma rose upward through a pathway aligned vertically and created a dike when it lost buoyancy we also evaluate the dike intrusion process quantitatively using a model of a circular dike that grows under a continuous magma supply from a deep magma reservoir from the observational data we infer the time evolution in the dike shape pressure distribution and magma viscosity in the dike the acquired viscosity increases over time and it may be reasonable because magma cools gradually however its value is too large compared to typical basaltic magma expected in this region it may represent magma within the dike that is nearly solidified otherwise the magma is supplied intermittently and the dike growth is mainly controlled by the magma supply rate from a deep reservoir the quantitative description of the dike intrusion process in nature described in this study is very rare and our results provide constraints on several parameters that have not been solved in many previous theoretical studies on the dike intrusion process

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

january 30 1997 eruptive event on kilauea volcano hawaii as monitored by continuous gps a continuous global positioning system gps network on kilauea volcano captured the most recent fissure eruption in kilauea s east rift zone erz in unprecedented spatial and temporal detail the short eruption drained the lava pond at pueu oeo leading to a two month long pause in its on going eruption models of the gps data indicate that the intrusion s bottom edge extended to only 2 4 km continuous gps data reveal rift opening 8 hours prior to the eruption absence of precursory summit inflation rules out magma storage overpressurization as the eruption s cause we infer that stresses in the shallow rift created by the continued deep rift dilation and slip on the south flank decollement caused the rift intrusion

on the propagation path of magma filled dikes and hydrofractures the competition between external stress internal pressure and crack length mixed mode fl uid fi lled cracks represent a common means of fl uid transport within the earth s crust they often show complex propagation paths which may be due to interaction with crustal heterogeneities or heterogeneous crustal stress previous experimental and numerical studies focus on the interplay between fl uid overpressure and external stress but neglect the effect of other crack parameters in this study we address the role of crack length on the propagation paths in the presence of an external heterogeneous stress fi eld we make use of numerical simulations of magmatic dike and hydrofracture propagation carried out using a two dimensional boundary element model and analogue experiments of air fi lled crack propagation into a transparent gelatin block we use a 3 d fi nite element model to compute the stress fi eld acting within the gelatin block and perform a quantitative comparison between 2 d numerical simulations and experiments we show that given the same ratio between external stress and fl uid pressure longer fl uid fi lled cracks are less sensitive to the background stress and we quantify this effect on fl uid fi lled crack paths combining the magnitude of the external stress the fl uid pressure and the crack length we de fi ne a new parameter which characterizes two end member scenarios for the propagation path of a fl uid fi lled fracture our results have important implications for volcanological studies which aim to address the problem of complex trajectories of magmatic dikes i e to forecast scenarios of new vents opening at volcanoes but also have implications for studies that address the growth and propagation of natural and induced hydrofractures

complete gravity study of piton de la fournaise volcano reunion island abstract we present an interpretation of all available gravity data on piton de la fournaise volcano including a new set collected in the summit area using a linear programming inversion method we determine the extension of the grand brule ultramafic body drilled in 1985 and we propose to interpret it as a frozen magma chamber related to a disappeared volcano we also present evidence for superficial mass excess under the enclos fouque and plaine des sables calderas that we link to the present piton de la fournaise volcanism the detailed gravity survey of the summit area allows us to emphasize the great importance of dyke complexes associated with the ne and se rift zones and with the shallow magma chamber a negative anomaly in the summit area is interpreted as a relative minimum between the positive anomaly of grand brule and those of the western part of the enclos fouque and plaine des sables calderas

insar observations of the 1995 fogo cape verde eruption implications for the effects of collapse events upon island volcanoes 1 fogo volcano cape verde islands erupted in april 1995 after 43 years of dormancy about 46 106 m3 of lava erupted during 7 5 weeks from vents on the sw flank of pico do fogo into cha das caldeiras interferograms obtained from 1993 1998 ers sar data show ground deformation due to the feeder dike but lack evidence for any volcano wide deformation related to volume changes of a shallow magma reservoir this suggests that fogo is fed from a relatively deep mantle lithospheric source 16 5 km depth consistent with petrological data this supports the concept that cha das caldeiras is the fill of a collapse scar created by a giant landslide and not a collapse caldera overlying a central shallow magma chamber the disturbance of the magmatic system by giant landslides may explain why some oceanic island volcanoes with high magma supply rates currently lack well developed shallow reservoirs

monitoring an effusive eruption at piton de la fournaise using radar and thermal infrared remote sensing data insights into the october 2010 eruption and its lava flows

ecosystem response to lateglacial and early holocene climate oscillations in the great lakes region of north america abstract fossil pollen plant macrofossils gastropods and elemental and stable isotope geochemistry in a sediment core from twiss marl pond southern ontario canada were used to document climate oscillations during the last glacial interglacial transition 13 000 8500 14 c bp and understand their ecological effects chronology was provided by ams 14 c dating and regional pollen correlation oxygen isotope 18 o results from mollusc shells chara encrustations and bulk carbonates show a classic climate sequence of a warm bolling allerod boa at 12 500 10 920 14 c bp a cold younger dryas yd at 10 920 10 000 14 c bp the holocene warming at 10 000 14 c bp a brief preboreal oscillation pb at 9650 14 c bp and a possible gerzensee killarney g k cooling shortly before 11 000 14 c bp clay sediments at the base of the core contain high herb and shrub pollen and abundant arctic alpine plant macrofossils indicating a treeless tundra with severe soil erosion in watershed during the boa warm period authigenic marl began to be deposited and picea woodland became established the establishment of picea woodland after peaks of 18 o and of carbonate accumulation suggests a lagged response of upland vegetation to boa warming in contrast the occurrence of warmth loving aquatics najas flexilis and typha latifolia at that time indicates sensitive responses of aquatic plants the yd cooling is indicated by a 1 5 negative excursion in 18 o an increase in minerogenic matter and higher concentrations of erosion derived elements al na k ti and v pollen data show no forest transformation in response to yd cooling which is attributed to the insensitive nonecotonal vegetation at that time however more openings in the forests and increased erosion in the watershed are indicated by a slight increase of herb pollen high concentrations of erosion elements and a pediastrum peak the onset of the holocene was marked by an abrupt increase of 2 in 18 o and the replacement of picea woodland by pinus dominated forest the picea recurrence at 9650 14 c bp demonstrates sensitive response of ecotonal vegetation to the pb climate oscillation which is also indicated by 0 4 negative excursion of 18 o these new results suggest the importance of multiproxy records for reliable paleoclimate reconstruction reevaluation and revised chronologies of previously published sites gage street and nichols brook in the eastern great lakes region show their major 18 o shifts correlative to the yd and pb oscillations as documented from twiss marl pond and nearby crawford lake the sequence and magnitude of climatic oscillations from these sites match in detail with records from the atlantic seaboard suggesting that these oscillations are an expression of broad scale probably global climate change rather than local meltwater induced climate cooling