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

shallow system rejuvenation and magma discharge trends at piton de la fournaise volcano la reunion island basaltic magma chambers are often characterized by emptying and refilling cycles that influence their evolution in space and time and the associated eruptive activity during april 2007 the largest historical eruption of piton de la fournaise ile de la reunion france drained the shallow plumbing system 240 106 m3 and resulted in collapse of the 1 km wide summit crater following these major events piton de la fournaise entered a seven year long period of near continuous deflation interrupted in june 2014 by a new phase of significant inflation by integrating multiple datasets lava discharge rates deformation seismicity gas flux gas composition and lava chemistry we here show that the progressive migration of magma from a deeper below sea level storage zone gradually rejuvenated and pressurized the above sea level portion of the magmatic system consisting of a vertically zoned network of relatively small volume magma pockets continuous inflation provoked four small 5 106 m3 eruptions from vents located close to the summit cone and culminated during august october 2015 with a chemically zoned eruption that erupted 45 15 106 m3 of lava this two month long eruption evolved through i an initial phase of waning discharge associated to the withdrawal of differentiated magma from the shallow system into ii a month long phase of increasing lava and so2 fluxes at the effusive vent coupled with co2 enrichment of summit fumaroles and involving emission of less differentiated lavas to end with iii three short lived 2 day long pulses in lava and gas flux coupled with arrival of cumulative olivine at the surface and deflation the activity observed at piton de la fournaise in 2014 and 2015 points to a new model of shallow system rejuvenation and discharge whereby continuous magma supply causes eruptions from increasingly deeper and larger magma storage zones downward depressurization continues until unloading of the deepest least differentiated magma triggers pulses in lava and gas flux accompanied by rapid contraction of the volcano edifice that empties the main shallow reservoir and terminates the cycle such an unloading process may characterize the evolution of shallow magmatic systems at other persistently active effusive centers

driving mechanism of tectonic activity in the northern apennines quantitative insights from numerical modeling 1 it is shown by numerical modeling that the recent deformation pattern observed in the northern apennines mainly characterized by progressive eastward migration and bowing of the belt thrusting activity along its external front and tensional tectonics in the internal area can be reproduced at a first approximation by applying a belt parallel se nw compression to the chain which is simulated as a structural system characterized by a high mechanical strength and decoupled from the surrounding zones the above compressional regime obtained by imposing kinematic boundary conditions to the model causes the outward escape of crustal wedges from the chain in particular the northeastward displacement of the romagna marche umbria units and the counterclockwise rotation and northwestward displacement of the ligurian units this kinematics produces compressional to transcompressional strain along the external front of the chain and tensional to transtensional strain in the internal area in line with the observed features that concern both strain style and orientation of principal strains evidence and arguments supporting the kinematic boundary conditions and the model parameterization adopted in modeling are discussed numerical experiments have also been carried out to evaluate the influence of major features of the model parameterization and boundary conditions we have adopted in modeling and to provide insights into the possible influence of strong decoupling earthquakes in the central apennines on tectonic and seismic activity in the northern apennines

volcano destabilization by magma injections in a detachment we report the discovery of a detachment fault within reach of structural investigation in a shield volcano piton des neiges la reunion hotspot the detachment exposed by erosion is located between the top of an extinct gabbroic magma chamber and a cover of debris avalanche deposits the fault simultaneously concentrated ductile and brittle deformation toward the sea hydrothermal alteration in the greenschist facies and repeated sill injections of basic magmas our study of this exceptional detachment exposure suggests that two mechanisms participate in volcano flank failure hydrothermal alteration likely sustained by the heat of cooling sills induces slow inter intrusion deformation whereas sill injections in the fault may trigger rapid cointrusive slip this twofold process of destabilization might currently occur on some active volcanoes such as piton de la fournaise

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

uncovering the hidden signature of a magmatic recharge at piton de la fournaise volcano using small earthquakes we apply a template matching method to detect and locate preeruptive earthquakes at piton de la fournaise volcano in 2014 and 2015 this approach enabled the detection of many events and unveiled persistent seismicity features through multiple eruptions shallow earthquakes define a ring shaped structure beneath the main crater the repetitive occurrence of events along this structure suggests that it corresponds to a preexisting zone of weakness within the edifice we also show evidence of deep magma transfer in 2015 more than 5000 deep earthquakes define an upward migration immediately followed by the occurrence of shallow events leading to an eruption 20 days later this suggests the creation of a hydraulic connection between the lower part of the volcanic system and a magma reservoir located near sea level we can envisage than such replenishments of the shallow reservoir occurred in the past but were undetected because of limited deep earthquake detections

gravitational sliding of the mt etna massif along a sloping basement geological field evidence and laboratory modelling indicate that volcanoes constructed on slopes slide downhill if this happens on an active volcano then the movement will distort deformation data and thus potentially compromise interpretation our recent gps measurements demonstrate that the entire edifice of mt etna is sliding to the ese the overall direction of slope of its complex rough sedimentary basement we report methods of discriminating the sliding vector from other deformation processes and of measuring its velocity which averaged 14 mm year 1 during four intervals between 2001 and 2012 though sliding of one sector of a volcano due to flank instability is widespread and well known this is the first time basement sliding of an entire active volcano has been directly observed this is important because the geological record shows that such sliding volcanoes are prone to devastating sector collapse on the downslope side and whole volcano migration should be taken into account when assessing future collapse hazard it is also important in eruption forecasting as the sliding vector needs to be allowed for when interpreting deformation events that take place above the sliding basement within the superstructure of the active volcano as might occur with dyke intrusion or inflation deflation episodes

crustal structures and the eastern extent of lower paleozoic shelf strata within the central appalachians a seismic reflection interpretation reprocessing of line pr3 proprietary seismic reflection data has delineated grenvillian paleozoic and mesozoic structures within the appalachian foreland blue ridge and piedmont of the central appalachians in virginia and west virginia the eastern portion of pr3 can be correlated along strike with the western portion of line i 64 reprocessed earlier at virginia tech the combined seismic reflection data image the crust from the eastern valley and ridge blue ridge piedmont and atlantic coastal plain provinces within the piedmont large as much as 10 km wide reflective structures imaged on both lines pr3 and i 64 are interpreted to be thrust sheets that might be composed of deformed catoctin evington group and possibly younger metamorphosed rocks a concealed extension of the green springs mafic mass intrudes a thrust sheet imaged along the pr3 profile the blue ridge piedmont allochthon was transported north west along the blue ridge thrust which ramps upward 12 km east of the surface exposure of the mountain run fault westward along line pr3 the blue ridge thrust maintains an undulating geometry the maximum thickness of the blue ridge allochthon is interpreted to be 4 5 km the blue ridge allochthon is generally acoustically transparent and overlies lower paleozoic shelf strata the maximum thickness of these strata is 8 km shelf strata are interpreted to extend in the subsurface 5 km east of the surface exposure of the mountain run fault the northeastward extension of the brevard fault zone where they are truncated by the blue ridge thrust at a depth of 10 5 km 3 5 s various folds and blind thrusts are imaged beneath the appalachian foreland however the foreland has not experienced the same degree of deformation as observed in the eastern provinces a basement uplift 45 km wide is imaged beneath the valley and ridge province and is interpreted as having formed prior to late cambrian time farther west reflections imaged beneath the glady fork anticline in the appalachian plateau are interpreted as a positive flower structure associated with wrench fault tectonics relatively few deep 9 km crustal reflections are imaged along line pr3 the majority of reflections that do exist at these depths are observed beneath the piedmont and eastern blue ridge the high reflectivity associated with the grenvillian basement in these areas might be the result of the paleozoic orogenies and extension related to late proterozoic and mesozoic rifting

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

new behaviour of the piton de la fournaise volcano feeding system la reunion island deduced from gps data influence of the 2007 dolomieu caldera collapse after 15 months of summit deflation the unrest of piton de la fournaise renewed in august 2008 with several seismic crises and the re pressurization of the plumbing system the successive seismic crises sometime accompanied by ground displacements detected by gps were associated with inter eruptive dyke intrusions it was the first time since the implementation of the observatory that such successive inter eruptive magma migrations not reaching the surface were observed at piton de la fournaise the change in the volcano activity with an increase in the frequency of pure dyke intrusions have followed the dolomieu caldera collapse of april 2007 and reveals its strong influence on the new eruptive regime stress changes in the volcanic edifice have temporarily at least favoured the arrest of dykes in depth during these successive dyke intrusions magma stopped at shallow depth to form transitory magma storages before to erupt during three successive small summit eruptions september 21st october 2nd 2008 november 27th and december 14th 2008 february 4th 2009 the same kind of change in the pre eruptive and eruptive behaviour can be expected on other volcanoes having experienced a summit caldera collapse

time averaged discharge rate of subaerial lava at kīlauea volcano hawai i measured from tandem x interferometry implications for magma supply and storage during 2011 2013 differencing digital elevation models dems derived from terrasar add on for digital elevation measurements tandem x synthetic aperture radar imagery provides a measurement of elevation change over time on the east rift zone ezr of k lauea volcano hawai i the effusion of lava causes changes in topography when these elevation changes are summed over the area of an active lava flow it is possible to quantify the volume of lava emplaced at the surface during the time spanned by the tandem x data a parameter that can be difficult to measure across the entirety of an 100 km2 lava flow field using ground based techniques or optical remote sensing data based on the differences between multiple tandem x derived dems collected days to weeks apart the mean dense rock equivalent time averaged discharge rate of lava at k lauea between mid 2011 and mid 2013 was approximately 2 m3 s which is about half the long term average rate over the course of k lauea s 1983 present erz eruption this result implies that there was an increase in the proportion of lava stored versus erupted a decrease in the rate of magma supply to the volcano or some combination of both during this time period in addition to constraining the time averaged discharge rate of lava and the rates of magma supply and storage topographic change maps derived from space based tandem x data provide insights into the four dimensional evolution of k lauea s erz lava flow field tandem x data are a valuable complement to other space air and ground based observations of eruptive activity at k lauea and offer great promise at locations around the world for aiding with monitoring not just volcanic eruptions but any hazardous activity that results in surface change including landslides floods earthquakes and other natural and anthropogenic processes

dynamics of piton de la fournaise volcano observed by passive image interferometry with multiple references abstract activity of piton de la fournaise pdf volcano in la reunion island modifies the seismic velocities within the edifice using the 2010 and 2011 data from a network of 21 seismic stations in the vicinity of pdf changes of seismic velocities are investigated using passive image interferometry i e interferometry of seismic noise correlations as noise correlations change significantly over time in response to volcanic activity a method is presented that allows us to measure continuous long term velocity changes with high and constant accuracy by using multiple periods as reference a long term velocity increase is found that averages about 0 25 per year this trend is superimposed by short term changes that exhibit a clear connection with summit seismo tectonic earthquakes indicating the effect of volcanic activity characteristic signatures of velocity changes are identified for post eruptive periods of deflation that show an increase of velocity associated with subsidence observed by gps periods of pre eruptive inflation are characterized by decreasing velocity seismic crises can be associated with either increasing or decreasing velocity depending on whether the magma movement leads to deflation due to an eruption emptying the shallow plumbing system or to inflation caused by a non eruptive intrusion with a simple assumption about the spatial sensitivity of the measurements both processes are found to have the strongest effect in the central summit area of the volcano which also shows the strongest surface displacements during the time investigated here we do not observe a dependence of the velocity change on the location of the erupting fissures instead the distribution of changes for the three inflation periods and the two eruptions are similar indicating that the velocity changes observed here reflect the dynamics of a shallow magma reservoir rather than the effect of the eruption at the surface

edifice strength and magma transfer modulation at piton de la fournaise volcano 1 from 2003 to 2007 eruptive activity at piton de la fournaise was shown to follow cycles comprising many summit proximal eruptions and finishing by a distal eruption gps measurements evidenced striking asymmetric deformation between its western and eastern flanks horizontal displacements recorded during interdistal periods showed a characteristic amplitude at the top of the eastern flank displacements recorded at the base of the summit cone showed a bimodal distribution with low amplitudes during interdistal periods and large ones during distal eruptions to account for displacement asymmetry characteristic amplitude and large flank displacement we modeled the volcanic edifice using a drucker prager elastoplastic rheology friction angles of 15 and 30 were needed to model the displacements respectively during distal eruptions and interdistal periods this change shows that strain weakening occurred during distal events large plastic displacement that occurred in the eastern flank during distal eruptions relaxed the horizontal elastic stress accumulated during interdistal periods it triggered summit deflation horizontal magma transfer and distal flank eruption and reset the eruptive cycle our elastoplastic models also show that simple source geometries may induce large eastern flank displacements that would be explained by a complex geometry in a linear elastic edifice magma supply is often thought to control volcano s eruptive activity with surface deformation reflecting changes in magma supply rate the volcano s response being linear our results bring some evidences that on piton de la fournaise time space discretization of magma transfer may be the result of the edifice s nonlinear response rather than changes in magma supply

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

analogue modeling of flank instability at mount etna understanding the driving factors 1 mount etna is characterized by significant flank instability whose triggering factors are still a matter of debate we use analog models to investigate the role of different factors in the models a cone and base of granular material simulate the volcanic edifice and its basement the asymmetric geometry of the basement simulates the topographic gradient around the volcano injections of silicone sets a and b and low viscosity vegetable oil set c simulate the pressurization of plutonic complex deep reservoirs and the emplacement of dikes respectively other experiments set d reproduce regional extensional tectonics in the last 105 years within layers with different cohesion simulating strength differences in the basement laser scanner and control points allow the tracking of surface deformation with submillimeter precision the asymmetric topography enhances flank instability on the side with the weakest confinement i e seaside providing the preparing factor for instability in sets a and b any type of pressurized reservoir enhances up to 10 times the amount of flank instability toward the seaside with respect to the other flanks of the volcano in set c dike emplacement enhances seaside flank instability up to 8 times regional tectonics and crustal layering in set d enhance flank instability up to 2 and 1 3 times respectively considering the duration and frequency of the simulated processes in nature we propose a semiquantitative evaluation and hierarchy of the factors controlling flank instability at etna magmatic activity point like source inflation and dike emplacement provides the most important triggering factor extensional tectonics in the last 105 years and crustal layering are more than 10 times less effective this study shows the importance of differential buttressing at the volcano base for flank instability this condition is an important indication to expect asymmetric activity in any volcano flank eruptions and deformation

crystallographic preferred orientations of plagioclase via grain boundary sliding in a lower crustal anorthositic ultramylonite to clarify the rheological properties and deformational mechanisms that operate within lower crustal shear zones we analyzed deformation microstructures and fabrics in plagioclase grains from high strain regions of intrafolial drag folds of an anorthositic ultramylonite from langoya vesteralen northern norway these grains have developed weak crystallographic preferred orientations cpos other than deformation twinning they do not show any indications of intracrystalline plasticity or dynamic recrystallization in some domains of the drag fold plagioclase cpos are more distinct but the majority of inferred slip systems are not consistent with the main slip systems in plagioclase these suggest that neither dislocation creep nor dislocation accommodated grain boundary sliding gbs produced the plagioclase cpos but rather grain rotation via gbs along specific grain boundaries parallel or subparallel to crystallographic planes of 010 100 or 110 which led to an alignment of the easy slip grain boundaries in the flow direction that produced the observed cpo patterns the anisotropy of dissolution and growth rates may have been responsible for the development of the specific grain boundaries

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

rapid deformation of the south flank of kilauea volcano hawaii the south flank of kilauea volcano has experienced two large magnitude m 7 2 and m 6 1 earthquakes in the past two decades global positioning system measurements conducted between 1990 and 1993 reveal seaward displacements of kilauea9s central south flank at rates of up to about 10 centimeters per year in contrast the northern side of the volcano and the distal ends of the south flank did not displace significantly the observations can be explained by slip on a low angle fault beneath the south flank combined with dilation deep within kilauea9s rift system both at rates of at least 15 centimeters per year

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

the mechum river formation virginia blue ridge a record of neoproterozoic and paleozoic tectonics in southeastern laurentia neoproterozoic metasedimentary rocks of the mechum river formation crop out in an elongate northeast southwest trending belt in the central virginia blue ridge province the northwestern contact of the mechum river formation is nonconformable above mesoproterozoic basement whereas the southeastern contact is a set of steeply dipping brittle reverse faults that juxtapose basement against mechum river rocks the internal structure of the belt consists of northwest verging open to tight moderately to steeply plunging asymmetric folds although previous workers have interpreted the outcrop belt of the mechum river formation as a graben formed during laurentian rifting structural relations require that its present geometry is a structural inlier related to paleozoic contractional deformation strain analysis reveals that grain scale deformation processes produced up to 35 percent shortening during foliation development whereas map scale folds account for an additional 30 to 50 percent shortening restoration of the mechum river formation to its pre contractional geometry reveals little about the geometry of the original depositional basin the bounding reverse faults on the east side of the mechum river formation are interpreted as out of sequence structures that developed after regional folding metamorphism and foliation development that may be related to the emplacement of the blue ridge thrust sheet over a tectonic ramp sediment transport indicators are consistent with a source area to the east suggesting that the mechum river formation was separated from similar units in the eastern blue ridge by an asymmetric basement high that may have been produced by block rotation above listric normal faults

4 d noise based seismology at volcanoes ongoing efforts and perspectives monitoring magma pressure buildup at depth and transport to surface is a key point for improving volcanic eruption prediction seismic waves through their velocity dependence to stress perturbations can provide crucial information on the temporal evolution of the mechanical properties of volcanic edifices in this article we review past and ongoing efforts for extracting accurate information of temporal changes of seismic velocities at volcanoes continuously in time using records of ambient seismic noise we will first introduce the general methodology for retrieving accurate seismic velocity changes from seismic noise records and discuss the origin of seismic velocity temporal changes in rocks we will then discuss in a second part how noise based monitoring can improve our knowledge about magmatic activity at a long years to a short days time scale taking example from piton de la fournaise volcano la reunion we will also mention ongoing efforts for operational noise based seismic monitoring on volcanoes further we will discuss perspectives for improving the spatial localization of detected velocity changes at depth with a special focus on the use of dense seismic arrays in the last part we will finally explore the complex response of volcanic regions to seismic shaking with an example from japan and show how imaging seismic velocity susceptibility allows characterizing the state of pressurized fluids in volcanic regions

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

relationship between the ellisville pluton and chopawamsic fault establishment of significant late ordovician faulting in the appalachian piedmont of virginia

the april 2007 eruption and the dolomieu crater collapse two major events at piton de la fournaise la reunion island indian ocean abstract after 10 years of high activity and 24 eruptions piton de la fournaise pdf produced on april 2 to may 1 2007 one of its most voluminous and intense eruption since at least one century the eruption focused at 590 m elevation in the grand brule on the south east flank of piton de la fournaise 7 km away from summit it was located close to the southern cliff of the grand brule volcano tectonic collapse the rempart du tremblet and to the nearby village called le tremblet and it highly rattled and incommoded the inhabitants there eleven hours after the beginning of the eruption the lava flows reached the sea and created 0 45 km 2 of new land until the end of eruption in the night of april 5 the rock column beneath dolomieu crater started to collapse with a piston like mechanism into the magma chamber forming within less than 24 h the most recent and well documented caldera we report in this paper the chronology of these two related major events in the recent activity of pdf seen by the scientific networks of the volcanological observatory ovpf ipgp and field observations which allowed to back up the scenario of the caldera formation and to quantify these two exceptional episodes

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

identifying rift zones on volcanoes an example from la reunion island indian ocean we describe a methodology for identifying complex rift zones on recent or active volcanoes where structures hidden by recent deposits and logistical conditions might prevent carrying out detailed fieldwork la reunion island was chosen as a test site we used georeferenced topographic maps aerial photos and digital terrain models to perform a statistical analysis of several morphometric parameters of pyroclastic cones this provides a great deal of geometric information that can help in distinguishing the localisation and orientation of buried magma feeding fractures which constitute the surface expression of rift zones it also allowed the construction of a complete gis database of the pyroclastic cones la reunion is a perfect example where past and active volcanic rift zones are mostly expressed by clusters of monogenic centres the data has been validated in the field and compared and integrated with the distribution and geometry of dyke swarms results show the presence of several main and secondary rift segments of different ages locations and orientations whose origin is discussed considering regional tectonics local geomorphology and volcano deformation

hyaloclastites and the slope stability of hawaiian volcanoes insights from the hawaiian scientific drilling project s 3 km drill core abstract core samples recovered during the hawaiian scientific drilling project hsdp drilling project reveal that the upper 1 km of the submarine flank of mauna kea is comprised mainly of hyaloclastites progressive very low temperature alteration of these hyaloclastites has been accompanied by systematic transformations in physical properties of these deposits hyaloclastite deposits which directly underlie ca 1 km of subaerially emplaced lavas are very poorly consolidated but over a depth interval of ca 500 m compaction and especially precipitation of zeolitic pore filling cements associated with palagonitization of sideromelane have eliminated porosity as well as promoted the consolidation of these hyaloclastites the latter is reflected in unconfined compressive strengths which increase from mean values respectively of 2 5 and 4 6 mpa in weakly consolidated smectite rich hyaloclastites from the incipient 1080 to 1335 mbsl and smectitic 1405 1573 mbsl alteration zones to a mean value of 10 0 mpa in the more highly consolidated hyaloclastites of the palagonitic zone of alteration from 1573 mbsl to the bottom of the drill hole conversely overlying intercalated and underlying lava flows are generally much less altered and have mean compressive strengths which are 1 to 2 orders of magnitude greater then hyaloclastites at equivalent depths the shear strengths of the hyaloclastites also increase with depth and grade of alteration but are uniformly and substantially lower in the lavas those hyaloclastites exhibiting the highest grade of alteration i e palagonitic also exhibit the highest measured strengths and thus the alteration of hyaloclastites appears to strengthen as opposed to weaken the flanks of the edifice however the contrast in strength between hyaloclastites and lavas may be a primary factor in localizing destabilization and the zones of weak and poorly consolidated hyaloclastites may facilitate slumping by servings as hosts for shallow detachment surfaces on the unsupported flanks of these volcanoes

deformation mechanism maps for feldspar rocks abstract deformation mechanism maps for feldspar rocks were constructed based on recently published constitutive laws for dislocation and grain boundary diffusion creep of wet and dry plagioclase aggregates the maps display constant temperature contours in stress grain size space for strain rates ranging from 10 16 to 10 12 s 1 two fields of dominance of grain boundary diffusion controlled creep and dislocation creep are separated by a strongly grain size sensitive transition zone for wet rocks diffusion controlled creep dominates below a grain size of about 0 1 1 mm depending on temperature stress strain rate and feldspar composition plagioclase aggregates containing up to 0 3 wt water as often found in natural feldspars are more than 2 orders of magnitude weaker than dry rocks the strength of water bearing feldspar rocks is moderately dependent on composition and water fugacity for a grain size range of about 10 50 m commonly observed in natural ultramylonites the deformation maps predict that diffusion controlled creep is dominant at greenschist to granulite facies conditions low viscosity estimates of 10 18 10 19 pa s from modeling postseismic stress relaxation and channel flow of the continental lower crust can only be reconciled with laboratory experiments assuming dislocation creep at high temperatures 900 c or at lower temperatures diffusion creep of fine grained rocks possibly localized in abundant high strain shear zones for similar thermodynamic conditions and grain size lower crustal rocks are predicted to be less than order of magnitude weaker than upper mantle rocks

long term mass transfer at piton de la fournaise volcano evidenced by strain distribution derived from gnss network basaltic volcanoes are among the largest volcanic edifices on the earth these huge volcanoes exhibit rift zones and mobile flanks revealing specific stress field conditions in this paper we present new deformation data issued from the global navigation satellite systems gnss network installed on piton de la fournaise density of the gnss stations allowed us to reach a sufficient resolution to perform a spatially significant analysis of strain at the scale of the active part of the volcano since 2007 summit inflation during preeruptive eruptive sequences summit extension cone flanks contraction alternates with summit deflation during posteruptive rest periods summit contraction cone flanks extension and generates a pulsation of the volcano this volcano pulsation increases rock fracturing and damage decreases the rock stiffness and increases the medium permeability the deformation regime of the mobile eastern flank evidences mass transfer in depth from the summit to the east during the long term summit deflation recorded between 2011 and 2014 the upper eastern flank extended steadily eastward whereas the lower eastern flank contracted simultaneous extension and eastward displacement of the upper eastern flank and eastward contraction of the middle and lower eastern flank contributes to build the grandes pentes relief steeping the topographic slope we relate the eastern flank topographic slope spatial variations to rock or basal friction angle changes the lower flank contraction process is an evidence of its progressive loading by the upper eastern flank which brings this flank closer to an eventual instability

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

crystallographic preferred orientation development by dissolution precipitation creep abstract crystallographic preferred orientations cpos in deformed rocks are commonly interpreted as resulting from crystal plastic deformation mechanisms where deformation is achieved by the movement of dislocations in this paper we investigate the possibility of cpo development by dissolution precipitation creep or pressure solution a numerical model is presented which simulates the development of a grain aggregate that deforms by reaction controlled dissolution precipitation creep grains are simulated as rectangular boxes that change their shape by growth or dissolution of their surfaces depending on the normal stresses acting on the individual surfaces grains can also rotate due to an applied vorticity for non coaxial deformation and if they have a non equidimensional shape for each strain increment stress that is applied to the grains is the same for all grains while individual grains deform and rotate by different amounts a variety of cpos develop at moderate strains depending on the reaction rates of the different crystal surfaces and type of deformation uni axial shortening plane strain pure shear and simple shear the modelling results confirm that dissolution precipitation creep may play a role in cpo development in rocks

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

seismic anisotropy and its precursory change before eruptions at piton de la fournaise volcano la reunion the piton de la fournaise volcano exhibits frequent eruptions preceded by seismic swarms and is a good target to test hypotheses about magmatically induced variations in seismic wave properties we use a permanent station network and a portable broadband network to compare seismic anisotropy measured via shear wave splitting with geodetic displacements ratios of compressional to shear velocity vp vs earthquake focal mechanisms and ambient noise correlation analysis of surface wave velocities and to examine velocity and stress changes from 2000 through 2012 fast directions align radially to the central cone and parallel to surface cracks and fissures suggesting stress controlled cracks high vp vs ratios under the summit compared with low ratios under the flank suggest spatial variations in the proportion of fluid filled versus gas filled cracks secular variations of fast directions and delay times dt between split shear waves are interpreted to sense changing crack densities and pressure delay times tend to increase while surface wave velocity decreases before eruptions rotations of may be caused by changes in either stress direction or fluid pressure these changes usually correlate with gps baseline changes changes in shear wave splitting measurements made on multiplets yield several populations with characteristic delay times measured incoming polarizations and fast directions which change their proportion as a function of time an eruption sequence on 14 october 2010 yielded over 2000 shear wave splitting measurements in a 14 h period allowing high time resolution measurements to characterize the sequence stress directions from a propagating dike model qualitatively fit the temporal change in splitting

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

rift zones and magma plumbing system of piton de la fournaise volcano how do they differ from hawaii and etna on ocean basaltic volcanoes magma transfer to the surface proceeds by subvertical ascent from the mantle lithosphere through the oceanic crust and the volcanic edifice possibly followed by lateral propagation along rift zones we use a 19 year long database of volcano tectonic seismic events together with detailed mapping of the cinder cones and eruptive fissures to determine the geometry and the dynamics of the magma paths intersecting the edifice of piton de la fournaise volcano we show that the overall plumbing system from about 30 km depth to the surface is composed of two structural levels that feed distinct types of rift zones the deep plumbing system is rooted between piton des neiges and piton de la fournaise volcanoes and has a n30 40 orientation above 20 km below sea level bsl the main axis switches to a n120 orientation which permits magma transfer from the lithospheric mantle to the base of the oceanic crust below the summit of piton de la fournaise the related nw se rift zone is 15 km wide linear spotted by small to large pyroclastic cones and related lava flows and emits slightly alkaline magmas resulting from high pressure fractionation of clinopyroxene olivine this rift zone has low magma production rate of 0 5 3 6 10 3 m 3 s 1 and an eruption periodicity of around 200 years over the last 30 ka seismic data suggest that the long lasting activity of this rift zone result from regional nne ssw extension which reactivates inherited lithospheric faults by the effect of underplating and or thermal erosion of the mantle lithosphere the shallow plumbing system b11 km bsl connects the base of the crust with the central cone it is separated from the deep plumbing system by a relatively large aseismic zone between 8 and 11 km bsl which may represent a deep storage level of magma the shallow plumbing system feeds frequent short lived summit and flank ne and se flanks eruptions along summit and outer rift zones respectively summit rift zones are very active 0 1 0 25 m 3 s 1 short 2 3 km and present an orthogonal pattern confined to the central active cone of piton de la fournaise outer ne and se rift zones are much less active 4 7 3 10 3 m 3 s 1 and extend from inside the enclos fouque caldera to bound the mobile eastern volcano flank we show that the outer rift zones are almost aseismic and are genetically linked to the seaward flank displacements whose most recent events where detected in 2004 and 2007 east flank sliding is itself triggered by shallow b 2 km depth sill intrusions we propose that the subvertical magma intrusions along the perpendicular summit rift zones sill intrusions and subsequent magma injections along the outer rift zones are controlled by cycles of stress permutations we thus tentatively propose that as for piton de la fournaise the regional stress field acting on etna and hawaiian volcanoes is an important parameter in the control of the magma transfer along their deep plumbing system whereas the dynamics of their summit system is governed by shallow stress variations above 5 10 km bsl due to edifice deformation and magma transfers

the spectrum of persistent volcanic flank instability a review and proposed framework based on kīlauea piton de la fournaise and etna abstract persistent motion of the south flank of k lauea volcano hawai i has been known for several decades but has only recently been identified at other large basaltic volcanoes namely piton de la fournaise la reunion and etna sicily thanks to the advent of space geodetic techniques nevertheless understanding of long term flank instability is based largely on the example of k lauea despite the large differences in the manifestations and mechanisms of the process when viewed through a comparative lens for example the rate of flank motion at k lauea is several times that of etna and piton de la fournaise and is accommodated on a slip plane several km deeper than is probably present at the other two volcanoes gravitational spreading also appears to be the dominant driving force at k lauea given the long term steady motion of the volcano s south flank regardless of eruptive intrusive activity whereas magmatic activity plays a larger role in flank deformation at etna and piton de la fournaise k lauea and etna however are both characterized by heavily faulted flanks while piton de la fournaise shows little evidence for flank faulting a helpful means of understanding the spectrum of persistent flank motion at large basaltic edifices may be through a framework defined on one hand by magmatic activity which encompasses both magma supply and edifice size and on the other hand by the structural setting of the volcano especially the characteristics of the subvolcanic basement or subhorizontal intravolcanic weak zones a volcano s size and magmatic activity will dictate the extent to which gravitational and magmatic forces can drive motion of an unstable flank and possibly the level of faulting of that flank while the volcano s structural setting governs whether or not a plane of weakness exists beneath or within the edifice and can facilitate flank slip considering persistent flank instability using this conceptual model is an alternative to using a single volcano as a type example especially given that the example is usually k lauea which defines an extreme end of the spectrum and can provide a basis for understanding why flank motion may or may not exist on other large basaltic volcanoes worldwide

deformation partitioning during folding and transposition of quartz layers abstract banded iron formation bif from the quadrilatero ferrifero southeastern brazil shows a compositional layering with alternating iron rich and quartz rich layers this layering was intensively folded and transposed at a centimeter millimeter scale through a component of bedding parallel shear related to flexural slip at middle to high greenschist facies conditions 400 450 c the microstructure and c axis fabrics of normal limbs inverted limb and hinge zones of a selected isoclinal fold were analyzed combining optical and scanning electron microscopy sem and digital image analysis in the normal limbs recrystallized quartz grains show undulose extinction relatively dry grain boundaries c axes at high angle to foliation and a pervasive grain shape fabric gsf indicating operation of crystal plastic processes in the inverted limb quartz grains show more serrated and porous wet grain boundaries the gsf is similar to that of the normal limb but c axes are oriented at 90 to those of the normal limb we interpreted these characteristics as reflecting operation of solution precipitation deformation in inverted limbs as a consequence of grains having been rotated to an orientation that was hard to basal a glide but easy to dissolution precipitation creep this deformation partitioning between crystal plasticity and solution transfer during folding transposition of quartz may explain the common occurrence of layered quartz rocks where individual layers show alternating c axis fabrics with opposite asymmetries but a consistent gsf orientation such characteristics may reflect an earlier event of pervasive folding transposition of a preexisting layering

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

retrieving 65 years of volcano summit deformation from multitemporal structure from motion the case of piton de la fournaise la reunion island the structure from motion photogrammetry technique enables use of historical airborne photography to achieve high resolution 3d terrain models we apply this method on piton de la fournaise volcano la reunion which allows a unique opportunity to retrieve high resolution 1 5 0 11 m digital elevation models and precise deformation maps of the volcano since 1950 our results provide evidence that the summit volume increased throughout the study period at a stable rate of 2 2 mm3 yr between 1950 and 2000 increasing by a factor of four to 8 0mm3 yr prior to the major 2007 eruption which was accompanied by summit caldera collapse at the same time summit deformation was asymmetric with 9 2 2 5 m of eastward seaward displacement and 1 3 2 5 m to the west during 1950 2015 our results reveal a temporal evolution in the volcano magma influx rate and deformation tracking these fluxes and the long lived preferential eastern motion is crucial to mitigate risks associated to flank destabilization

the 2007 eruptions and caldera collapse of the piton de la fournaise volcano la reunion island from tilt analysis at a single very broadband seismic station seismic records from la reunion island very broadband geoscope station are investigated to constrain the link between the 2007 eruptive sequence and the related caldera collapse of the piton de la fournaise volcano tilt estimated from seismic records reveals that the three 2007 eruptions belong to a single inflation deflation cycle tilt trend indicates that the small volume summit eruption of 18 february occurred during a phase of continuous inflation that started in january 2007 inflation decelerated 24 days before a second short lived small volume eruption on 30 march almost simultaneous with a sudden large scale deflation of the volcano deflation rate which had stabilized at relatively low level increased anew on 1 april while no magma was erupted followed on 2 april by a major distal eruption and on 5 april by a summit caldera collapse long term tilt variation suggests that the 2007 eruptive succession was triggered by a deep magma input

the role of the pernicana fault system in the spreading of mt etna italy during the 2002 2003 eruption flank instability and collapse are observed at many volcanoes among these mt etna is characterized by the spreading of its eastern and southern flanks the eastern spreading area is bordered to the north by the e w trending pernicana fault system pfs during the 2002 2003 etna eruption ground fracturing along the pfs migrated eastward from the ne rift to as far as the 18 km distant coastline the deformation consisted of dextral en echelon segments with sinistral and normal kinematics both of these components of displacement were one order of magnitude larger 1 m in the western previously known portion of the pfs with respect to the newly surveyed 9 km long eastern section 0 1 m this eastern section is located along a pre existing but previously unknown fault where displaced man made structures give overall slip rates 1 1 9 cm year only slightly lower than those calculated for the western portion 1 4 2 3 cm year after an initial rapid motion during the first days of the 2002 2003 eruption movement of the western portion of the pfs decreased dramatically while parts of the eastern portion continued to move these data suggest a model of spreading of the eastern flank of etna along the pfs characterized by eruptions along the ne rift instantaneous short lived meter scale displacements along the western pfs and more long lived centimeter scale displacements along the eastern pfs the surface deformation then migrated southwards reactivating one after the other the nnw sse trending timpe and trecastagni faults with displacements of 0 1 and 0 04 m respectively these structures along with the pfs mark the boundaries of two adjacent blocks moving at different times and rates the new extent of the pfs and previous activity over its full length indicate that the sliding eastern flank extends well below the ionian sea the clustering of seismic activity above 4 km b s l during the eruption suggests a deep decollement for the moving mass the collected data thus suggests a significant movement volume 1 100 km3 of the eastern flank of etna both on shore and off shore

velocity variations associated with the large 2010 eruption of merapi volcano java retrieved from seismic multiplets and ambient noise cross correlation we present a study of the seismic velocity variations that occurred in the structure before the large 2010 eruption of merapi volcano for the first time to our knowledge the technique of coda wave interferometry is applied to both families of similar events multiplets and to correlation functions of seismic noise about half of the seismic events recorded at the summit stations belong to one of the ten multiplets identified including 120 similar events that occurred in the last 20 hr preceding the eruption onset daily noise cross correlation functions ncf were calculated for the six pairs of short period stations available using the stretching method we estimate time series of apparent velocity variation avv for each multiplet and each pair of stations no significant velocity change is detected until september 2010 from 10 october to the beginning of the eruption on 26 october a complex pattern of avv is observed with amplitude of up to 1 5 per cent velocity decrease is first observed from families of deep events and then from shallow earthquakes in the same period avv with different signs and chronologies are estimated from ncf calculated for various station pairs the location in the horizontal plane of the velocity perturbations related with the avv obtained from ncf is estimated by using an approach based on the radiative transfer approximation although their spatial resolution is limited the resulting maps display velocity decrease in the upper part of the edifice in the period 12 25 october after the eruption onset the pattern of velocity perturbations is significantly modified with respect to the previous one we interpret these velocity variations in the framework of a scenario of magmatic intrusion that integrates most observations the perturbation of the stress field associated with the magma migration can induce both decrease and increase of the seismic velocity of rocks thus the detected avvs can be considered as precursors of volcanic eruptions in andesitic volcanoes without taking their sign into account

seismicity rate before eruptions on piton de la fournaise volcano implications for eruption dynamics 1 individual eruptions are difficult to foresee using daily seismicity at piton de la fournaise pdlf volcano except within a few hours from the eruption time however when using a superposed epoch analysis for all of the 15 eruptions in the 1988 2001 period we find that the seismicity rate increases 2 weeks before the eruption time as t te t a te being the eruption time such an increase mimics the pattern of stacked foreshock sequences i e a power law increase in seismicity rate before earthquakes that is proposed to emerge from aftershocks properties helmstetter et al 2003 it argues for the bursts of seismicity rate before eruptions to both result from the volcano dynamics volume or pressure increase induced by magma and from the cascades of earthquake interactions this latter process produces stochastic fluctuations in the seismicity rate that perturb any single pre eruption time series the pdlf seismicity highlights a brittle pre eruption damage process which starts at least 2 weeks prior to eruption time because this increase is only measured upon averaging it suggests that during the brittle damage phase the direct effect of volcano dynamics on the seismicity rate remains on the same order of magnitude as the seismicity rate triggered by volcano earthquake interactions

preferred orientation of anorthite deformed experimentally in newtonian creep abstract synthetic anorthite aggregates were deformed in a paterson gas deformation apparatus at confining pressures up to 400 mpa in torsion and axial compression at temperatures between 950 c and 1200 c samples deformed in torsion under newtonian creep display development of texture or crystallographic preferred orientation as documented with synchrotron x ray diffraction measurements complex diffraction patterns were deconvoluted with the rietveld method to obtain quantitative texture information torsion samples deformed up to shear strains of 4 and samples deformed in compression at higher stresses to total strains of 0 3 develop clear textures texture and shape preferred orientation spo of torsion samples display a monoclinic pattern with an asymmetry inclined against the sense of shear consistent with polycrystal plasticity simulations that assume the deformation is accomplished by dislocation glide these results show that a material deforming in linear viscous creep can develop a strong texture in striking contrast to the paradigm that the presence of a texture precludes low stress newtonian behavior our observations show that the presence or absence of crystallographic preferred orientation is not sufficient to uniquely infer the dominant rheological mechanical regime as sometimes applied for interpretation of seismic anisotropy in the earth

the silurian to permian history of a metamorphic core complex in lofoten northern scandinavian caledonides 1 the lofoten archipelago exposes precambrian baltic basement and caledonian allochthonous sequences within a 1000 km long chain of gravity and magnetic highs and structural culminations along the extended british and norwegian continental shelf previous regional geophysical studies indicate that post caledonian extension and development of the northern norwegian shelf occurred during broadly defined carboniferous permian cretaceous jurassic and early tertiary events structures related to these events are known to young westward we report field structural and 40ar 39ar thermochronologic data from rocks exposed in lofoten that further define the history and style of post caledonian extension the islands of southwest lofoten also represent the most outboard exposures of caledonian basement in northern norway that presumably formed the middle to deep crustal core of the orogen metasedimentary rocks and penetratively deformed basement in lofoten record high grade silurian devonian metamorphism and top to the east hereinafter tops east thrusting followed by episodes of late devonian to early carboniferous tops west ductile extension which progressed into oblique left slip movements the structural style and timing of silurian contraction in this area are remarkably similar to that determined for the more forelandward areas on the mainland 120 km to the east supporting the inference that distal parts of the baltic continental margin that were once deeply subducted are presently exposed in lofoten the timings of post devonian structural events that affected rocks in lofoten are partially constrained by the ages of unconformities and strata known to be preserved in graben flanking the lofoten culmination the radiometric age and structural data presented in this study in combination with stratigraphic constraints suggest a westward progression through time of extensional deformation over a protracted interval of silurian to permian time the latest permian extension in lofoten is largely characterized by brittle structures that formed at conditions substantially less than 300 c compared to the exhumation history of the southern western gneiss region the depth of caledonian continental a type subduction and subsequent unroofing of lofoten are of lesser magnitude and the present erosional level remained in the middle crust for a much longer interval of time the permian 40ar 39ar mineral ages documented in this study are the youngest such ages yet identified in scandinavia these ages relate to episodes of deformation and cooling in response to extensional tectonic events that occurred roughly 100 m y after comparable effects identified on the caledonian mainland our preferred explanation for the carboniferous permian radiometric ages structural evolution and stratigraphic data for lofoten is that they all developed in the context of a long lived cordilleran style metamorphic core complex

magmatically triggered slow slip at kilauea volcano hawaii we demonstrate that a recent dike intrusion probably triggered a slow fault slip event sse on kilauea volcano9s mobile south flank our analysis combined models of advanced land observing satellite interferometric dike intrusion displacement maps with continuous global positioning system gps displacement vectors to show that deformation nearly identical to four previous sses at kilauea occurred at far field sites shortly after the intrusion we model stress changes because of both secular deformation and the intrusion and find that both would increase the coulomb failure stress on possible sse slip surfaces by roughly the same amount these results in concert with the observation that none of the previous sses at kilauea was directly preceded by intrusions but rather occurred during times of normal background deformation suggest that both extrinsic intrusion triggering and intrinsic secular fault creep fault processes can lead to sses

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

timing of a large volcanic flank movement at piton de la fournaise volcano using noise based seismic monitoring and ground deformation measurements in volcanic domains magma transport and pressure build up induce high stress strain perturbations in the surrounding volcanic edifice that may lead to volcanic flank movements and possible instability in this study we focus on the 2007 march april episode of volcanic activity at piton de la fournaise pdf volcano la r eunion island this episode was associated with a large volume of emitted lava 240 106 m3 and a 340 m caldera collapse we present observations of continuous seismic velocity changes measured using cross correlations of ambient seismic noise over 10 yr at pdf overall we observe a large velocity reduction starting a few days prior to the major 2007 april 2 eruption comparison of seismic velocity change measurements with observations of deformation from insar and gps shows that the seismic velocity reduction coincided with a widespread flank movement starting at the time of injection of magma to feed an initial eruption a few days before the 2007 april 2 eruption we emphasize the potential of noise based seismic velocity change measurements together with geodetic observations to detect and monitor possibly hazardous slope instabilities

integrating seismic reflection and geological data and interpretations across an internal basement massif the southern appalachian pine mountain window usa the southern appalachian pine mountain window exposes 1 1 ga grenvillian basement and its metasedimentary paleozoic cover through the allochthonous inner piedmont the issue of whether the crustal block inside the window was either transported above the master appalachian late alleghanian decollement or is an autochthonous block that was overridden by the decollement has been debated for some time new detrital zircon geochronologic data from the cover rocks inside the window suggest this crustal block was derived from gondwana but docked with laurentia before the alleghanian event reprocessed deep seismic reflection data from west central georgia pr and poststack noise reduction amplitude variation analysis and prestack depth migration indicate that a significant band of subhorizontal reflections occurs almost continuously beneath the window collinear with the originally recognized decollement reflections north of the window a marked variation in the decollement image from strong and coherent north of the window to more diffuse directly beneath the window is likely a partial consequence of the different geology between the inner piedmont and the window the more diffuse image beneath the window may also result from imaging problems related to changes in topography and fold of cover i e signal to noise ratio two alternative tectonic models for the pine mountain window can partially account for the observed variation in the decollement reflectivity 1 the pine mountain block could be truncated below by a relatively smooth continuation of the decollement the window would thus expose an allochthonous basement duplex or hors block thrust upward from the south along the late proterozoic rifted continental margin 2 the window represents localized exhumation of autochthonous basement and cover along a zone of distributed intrabasement shearing directly beneath the window either model is viable if only reflector geometry is considered model 1 is favored if both geometry and kinematics of blue ridge piedmont thrust sheet emplacement are incorporated in either model the southern margin of the window merges to the west with the iapetan early alleghanian central piedmont suture which juxtaposes north american affinity piedmont rocks to the north and exotic panafrican rocks of the carolina avalon terrane to the south immediately south of the window this suture dips southward and merges in the lower crust with the late alleghanian suture joining the appalachians with gondwana

the effects of rock heterogeneities on dyke paths and asymmetric ground deformation the example of piton de la fournaise reunion island during pre eruptive periods and eruptions piton de la fournaise volcano shows an asymmetric magma induced pattern of deformation the origin of this asymmetry is not well constrained and the pre eruptive deformation does not have a satisfactory explanation here we present data on the past history and complex structure of the volcano we also provide new field data on exposed dykes in the volcano the field data confirm that the eruptive centre has migrated through time our field data indicate average dyke dips of about 80 by contrast inferred dips of recent feeder dykes using geodetic data are 53 75 we explain this difference as being partly due to the models used to infer the dyke dips from geodetic data which assume the host rock to be homogeneous and isotropic when fractures and the other heterogeneities are taken into account in the models the inferred dyke dips become similar to those of the exposed dykes new numerical models indicate that when the complex internal structure of the volcano is taken into account part of the asymmetry of the ground deformation can be explained part of the deformation asymmetry however is due to the curved structure of the rift system resulting in the injection of curved dykes and the dyke dips 2008 elsevier b v all rights reserved

correlating hydrothermal system dynamics and eruptive activity a case study of piton de la fournaise volcano la reunion abstract piton de la fournaise volcano la reunion island is a basaltic shield volcano which underwent an intense cycle of eruptive activity between 1998 and 2008 self potential and other geophysical investigations of the volcano have shown the existence of a well established hydrothermal system within the summit cone the present study investigates the relationship between changes in the hydrothermal system and eruptive activity at the summit cone of piton de la fournaise here we consider the depth of the hydrothermal activity section to be the area where the hydrothermal flow is the most intense along its path ten complete loop self potential surveys have been analyzed through multi scale wavelet tomography mwt to characterize depth variations of the hydrothermal system between 1993 and 2008 our mwt models strongly support the existence of six main hydrothermal flow pathways associated with the main edifice structure each of these pathways is part of the main hydrothermal system and is connected to the main hydrothermal reservoir at depth in both 2006 and 2008 around dolomieu crater based on our results the hydrothermal activity sections are located between 2300 and 2500 m a s l which correlate well with the elevation of the observed fumarole belt within the post 2007 collapse crater wall our results show that the depths of the local hydrothermal activity sections change substantially over the investigated period vertical displacement of the main potential generation area associated with these hydrothermal activity sections is observed on the order of several hundred meters at the transition between the period of quiescence 1993 1997 and the resumption of eruptive activity in 1998 and 2007 respectively from 1999 to march 2008 the hydrothermal system was consistently located at relatively shallow depths by quantitatively determining the vertical displacement of hydrothermal fluids over 16 years we identify a significant link between hydrothermal system and magmatic activity hydrothermal system depth below the surface is an indicator of the activity level pressurization depressurization of the volcano within the shallow magmatic systems thus when used in conjunction with long term volcano monitoring this approach can contribute substantially to detection of the precursory signals of changes in volcanic activity

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

sheet intrusions and deformation of piton des neiges and their implication for the volcano tectonics of la reunion abstract to understand the volcano tectonic history of piton des neiges the dormant volcano of la reunion we measured in the field the orientation of sheeted intrusions and deformation structures and interpreted the two datasets separately with a paleostress inversion results show that the multiple proposed rift zones may be simplified into three trends 1 a n30 e 5 km wide linear rift zone running to the south of the edifice active in the shield building 2 48 0 43 ma and terminal stages 190 22 ka 2 a curved n110 to n160 e rift zone widening from 5 km to 10 km toward the nw flank essentially active during the early emerged shield building 1 3 ma and 3 two sill zones 1 km thick in total in the most internal parts of the volcano active in the shield building and terminal stages in parallel deformation structures reveal that the tectonics of the edifice consisted in three end member stress regimes sharing common stress axes 1 nw se extension affecting in priority the south of the edifice near the n30 e rift zone 2 nne ssw extension on the northern half of the volcano near the n110 160 e rift zone 3 compression occurring near the sill zones with a ne sw or nw se maximum principal stress these three stress regimes are spatially correlated and mechanically compatible with the injection trends combined together our data show that the emerged piton des neiges underwent sector spreading delimited by perpendicular rift zones as observed on piton de la fournaise the active volcano of la reunion analogue experiments attribute such sector spreading to brittle edifices built on a weaker substratum we therefore conclude that la reunion volcanoes are both brittle as opposed to hawaiian volcanoes or mount etna whose radial spreading is usually attributed to a ductile body within the edifices

the 2007 caldera collapse of piton de la fournaise volcano source process from very long period seismic signals abstract in april 2007 piton de la fournaise volcano experienced its largest caldera collapse in at least 300 yr this event consisted of a series of 48 subsidence increments characterized by very long period vlp seismic signals equivalent to m w 4 4 to 5 4 source analysis of vlp events suggests a piston like mechanism with a collapsing crack source corresponding to the contraction of the magma reservoir and a single force representing the collapse of the above rock column we show that the collapse dynamics is primarily controlled by magma withdrawal from the reservoir which was likely in a bubbly state at the time of the event similar to the 2018 kilauea collapse we observe a reduction of the time interval between successive subsidence increments which results from the acceleration of magma withdrawal and a progressive weakening of the edifice at the beginning of the sequence

the misorientation index development of a new method for calculating the strength of lattice preferred orientation abstract using orientation data from experimentally deformed olivine we explore some practical problems with the j index a commonly applied measure of fabric strength we show that the j index is highly dependent on several factors including the number of discrete data in the orientation distribution function odf and arbitrary numerical parameters specified for its calculation because of this non uniqueness we conclude that the j index is difficult to interpret and should only be applied with caution as an alternative to the j index we propose a new measure of fabric strength that is based on the distribution of uncorrelated misorientation angles this m index is shown to be insensitive to the parameters specified for its calculation for typical deformed olivine samples we show that 150 discrete data are adequate to quantify fabric strength using the m index technique the m index correlates well with seismic anisotropy particularly for materials of the same fabric type therefore we conclude that the m index technique is well suited for the quantification of fabric strength and the comparison of like materials

spatiotemporal evolution of dike opening and decollement slip at kīlauea volcano hawai i 1 rapid changes in ground tilt and gps positions on k lauea volcano hawai i are interpreted as resulting from a shallow two segment dike intrusion into the east rift zone that began at 1217 utc 0217 hst on 17 june 2007 and lasted almost 3 days as a result of the intrusion a very small volume of basalt about 1500 m3 erupted on 19 june northward tilt at a coastal tiltmeter subsidence of south flank gps sites southeastward displacements at southwestern flank gps sites and a swarm of flank earthquakes suggest that a slow slip event occurred on the decollement beneath k lauea s south flank concurrent with the rift intrusion we use 4 min gps positions that include estimates of time dependent tropospheric gradients and ground tilt data to study the spatial and temporal relationships between the two inferred shallow steeply dipping dike segments extending from the surface to about 2 km depth and decollement slip at 8 km depth we invert for the temporal evolution of distributed dike opening and decollement slip in independent inversions at each time step using a nonnegative least squares algorithm on the basis of these inversions the intrusion occurred in two stages that correspond spatially and temporally with concentrated rift zone seismicity the dike opening began on the western of the two segments before jumping to the eastern segment where the majority of opening accumulated dike opening preceded the start of decollement slip at an 84 confidence level the latter is indicated by the onset of northward tilt of a coastal tiltmeter displacements at southwest flank gps sites began about 18 h later and are interpreted as resulting from slow slip on the southwestern flank additional constraints on the evolution of the intrusion and decollement slip come from inversion of an envisat interferogram that spans the intrusion until 0822 utc on 18 june 2007 combined with gps and tilt data this inversion shows that up to 0822 utc on 18 june decollement slip is only required in a limited region offshore of ka ena point a similar inversion of the complete event which includes gps and tilt data up to 21 june and a second envisat interferogram spanning the complete intrusion until 21 june shows decollement slip spread westward across the south flank this may suggest westward migration of the decollement slip as the event progressed

formation of the april 2007 caldera collapse at piton de la fournaise volcano insights from gps data abstract on april 5th 2007 a major collapse of the dolomieu summit crater occurred at piton de la fournaise volcano la reunion island to constrain the origin and the dynamics of the collapse we modelled continuous gps displacements preceding and accompanying this event our results reveal that the dolomieu collapse formed by a piston like mechanism in which the fast draining of the shallow magma reservoir at the beginning of the march 30th may 1st 2007 eruption caused a gravity driven downward displacement of its roof during the five days preceding the collapse summit deflation was caused by volume change through the fractured rock column above the shallow magma chamber due to the closure of voids or small scale cavities or the upward stoping and migration of an underground cavity since 2000 weakening of the rock column by repeated refilling and draining of the shallow magma chamber favoured its destabilization on april 5th 7 h before the onset of the collapse the deflation source was located at 300 m depth revealing the initiation of the collapse at very shallow depth the sudden collapse on april 5th was followed by continuous cyclic subsidence until april 6th each cycle was characterized by a progressive inward deflation of the summit zone and ended by sudden summit outward displacements caused by stress relaxation following a collapse event subsidence of the stoped column in the magma reservoir during the collapse of the crater on april 5th and 6th acted as a piston thus increasing the eruption rate the collapse occurred in only 24 h by successive events and increased the depth of the dolomieu crater by 340 m after april 6th only minor readjustments of the summit cone occurred with slight summit deflation and small landslides of the caldera walls

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 damage model for volcanic edifices implications for edifice strength magma pressure and eruptive processes monitoring of large basaltic volcanoes such as piton de la fournaise la reunion island france has revealed preeruptive accelerations in surface displacements and seismicity rate over a period of between 1 h and several weeks before magma reaches the surface such eruptions are attributed to ruptures of pressurized magma reservoirs elastic models used to describe surface deformation would assume that accelerations in surface deformation are due to increases in reservoir pressure this assumption requires changes in magma or pressure conditions at the base of the magma feeding system that are unrealistic over the observed timescale another possible cause for these accelerations is magma pressure in the reservoir weakening the volcanic edifice in the present study we modeled such weakening by progressive damage to an initially elastic edifice we used an incremental damage model with seismicity as a damage variable with daily increments elastic moduli decrease linearly with each damage increment applied to an initially elastic edifice with constant pressure at the base of the system this damage model reproduces surface displacement accelerations quite well when damage is sufficient process dynamics is controlled by the damage parameter taken as the ratio between the incremental rupture surface and the surface to be ruptured in this case edifice strength and magma reservoir pressure decrease with decreasing elastic moduli whereas surface displacement accelerates we discuss the consequences of pressure decreases in magma reservoirs