atmospheric sulfur dioxide measurements during the 2005 and 2007 eruptions of the piton de la fournaise volcano implications for human health and environmental changes abstract piton de la fournaise is an active volcano located in the south eastern part of reunion island a tiny island found in the south western indian ocean 21 s 55 5 e this volcano erupts regularly at least once a year with notable amount of degassing concerning the volcanic eruptions the regulation of the french ministry of environment on the air quality is mainly focussed on the standards applicable for the sulfur dioxide so 2 in terms of public health and environmental changes air samples have been collected continuously every 10 days on passive diffusion tubes of so 2 an atmospheric tracer of volcanic plumes by ora observatoire reunionnais de l air at 10 sites which have been located around the volcano since september 2005 the mean so 2 concentrations measured over a 10 day period in the absence of any volcanic eruption range between very low values 1 15 g m 3 for all 10 sites however during the december 2005 eruption notable so 2 concentrations factor 5 25 have been measured at the locations situated on the north west flanks of the volcano the so 2 degassing reached concentrations of 65 379 g m 3 which is mainly caused by the volcanic activity when coupled with the local to regional atmospheric circulations land sea breezes easterlies etc a wide range of atmospheric measurements was performed in the vicinity of piton de la fournaise in order to characterize the gaseous and particle emissions during the april may 2007 eruption so 2 concentrations were also measured continuously by sf 2000 analyser at several coastal locations in the vicinity of the volcano during and off eruption activities in the absence of any volcanic eruption the so 2 concentrations showed day to day variations with hourly mean concentrations varying between 1 and 20 g m 3 these values correspond to the background concentrations for this coastal rural location and might as well come in part from non volcanic origin the so 2 concentrations however were increased by a factor 10 30 with a maximum hourly mean concentration of 2486 g m 3 during the april may 2007 eruption hereby several statutory thresholds were exceeded particularly at the tremblet location indeed the information and recommendation threshold 350 g m 3 h as well as the alert threshold 500 g m 3 on 3 h consecutively were exceeded 32 and 5 times respectively at this site these measurements point out that during the times of eruptions with significant amounts of degassing the threshold values for protecting the ecosystems and the air quality for human health were exceeded at several inhabited locations with implications for human health and environmental changes on local to regional scale

oscillatory nature of the okmok volcano s deformation abstract the time dependent deformation of volcanic edifices can help one understand the dynamics of pre eruptive overpressure build up in magma chambers thus geodetic time series recorded at the okmok volcano in alaska show a pattern of fast and short inflations referred to as pulses followed by either slower and longer deflations or time intervals with no deformation this pattern is superimposed onto a longer period inflation a rapid inflation occurred just before the 2008 eruption which suggests that the underlying process may lead to eruptions it is crucial to understand whether such a behavior is driven by external forcing such as melt supply variations or whether it can develop spontaneously within the volcano s plumbing system here we model the observed oscillations 2004 2008 as resulting from the hydraulic interaction between two shallow magma chambers fed by a deeper source region a geometry that is consistent with geochemical petrological and geophysical data the model shows that episodes of periodic fast inflations occur i when a viscosity gradient is present in the vertical pipe for instance as the result of a temperature gradient and ii when the flux supplying the shallower chamber lies between two bounds that we derive analytically the deformation pulses observed at okmok can therewith be fully explained by the internal variability of the magmatic system and do not require time variable external forcing the proposed model can also be seen as an improvement upon the classic hydraulic models regularly used to explain a commonly observed pattern of volcanic deformations i e exponential inflation

physical models of rock avalanche spreading behaviour with dynamic fragmentation the dynamic fragmentation of rock during avalanche motion has been postulated as a mechanism explaining the long runout of large rock avalanches or sturzstrome this paper investigates whether test

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

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

role of olivine cumulates in destabilizing the flanks of hawaiian volcanoes the south flank of kilauea volcano is unstable and has the structure of a huge landslide it is one of at least 17 enormous catastrophic landslides shed from the hawaiian islands mechanisms previously proposed for movement of the south flank invoke slip of the volcanic pile over seafloor sediments slip on a low friction decollement alone cannot explain why the thickest and widest sector of the flank moves more rapidly than the rest or why this section contains a 300 km3 aseismic volume above the seismically defined decollement it is proposed that this aseismic volume adjacent to the caldera in the direction of flank slip consists of olivine cumulates that creep outward pushing the south flank seawards average primary kilauea tholeiitic magma contains about 16 5 wt mgo compared with an average 10 wt mgo for erupted subaerial and submarine basalts this difference requires fractionation of 17 wt 14 vol olivine phenocrysts that accumulate near the base of the magma reservoir where they form cumulates submarine erupted kilauea lavas contain abundant deformed olivine xenocrysts derived from these cumulates deformed dunite formed during the tholeiitic shield stage is also erupted as xenoliths in subsequent alkalic lavas the deformation structures in olivine xenocrysts suggest that the cumulus olivine was densely packed probably with as little as 5 10 vol intercumulus liquid before entrainment of the xenocrysts the olivine cumulates were at magmatic temperatures 1100 c when the xenocrysts were entrained olivine at 1100 c has a rheology similar to ice and the olivine cumulates should flow down and away from the summit of the volcano flow of the olivine cumulates places constant pressure on the unbuttressed seaward flank leading to an extensional region that localizes deep intrusions behind the flank these intrusions add to the seaward push this mechanism ties the source of gravitational instability to the caldera complex and deep rift systems and therefore limits catastrophic sector failure of hawaiian volcanoes to their active growth phase when the core of olivine cumulates is still hot enough to flow

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

evidence for a fossil transform fault in the solund stavfjord ophiolite complex west norwegian caledonides on the island of tviberg west norway a sheeted dike complex is rotated anticlockwise into parallelism with a zone of strong deformation hosting screens of sheared meta ultramafite incompatible element enriched high level plutonic rocks and two swarms of mafic dikes are intruded into sheared and unsheared meta ultramafites intrusion and sinistral shearing of the high level plutonic rocks and an old swarm of mafic dikes took place contemporaneously with sinistral shearing of the meta ultrabasites these field relationships are interpreted to reflect magmatism within a transform fault and the dike rotation is explained as fault drag along a strike slip zone in the transform a younger swarm of mafic dikes striking at a high angle to the shear zones transects all tectonic structures and may reflect a second phase of magmatism within the transform in fault contact with the transform fault related plutonic rocks and dikes lenses of serpentine diatreme breccias and lenses of sediments composed of mafic and ultramafic detritus are hosted in a phyllonitic matrix comprising basic ultrabasic and continent derived detritus this rock unit is interpreted as an ophiolitic melange and it probably started to form when obduction of the ophiolite nucleated on the transform

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

subtle precursors of volcanic eruptions at piton de la fournaise detected by extensometers the highly active piton de la fournaise volcano is an excellent field laboratory to develop and test in a short time span new methods for detecting volcanic precursors since 1995 a network of four extensometers has been installed and has detected extensional shear and vertical movements of fractures in relation to ground deformations of the volcano this study describes new insights in the distribution of stresses in the volcanic edifice between eruptions and during magma intrusions continuous measurements show that all eruptions were preceded several months before by significant fracture movements a constant opening associated with a dextral movement on the south flank and a sinistral movement on the north flank of the volcano these movements can be attributed to a shallow pressure source below the summit craters

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

long term dynamics of piton de la fournaise volcano from 13 years of seismic velocity change measurements and gps observations we study the piton de la fournaise pdf volcano dynamics through the observation of continuous seismic velocity changes from 2000 to 2013 we compute the cross correlations of ambient seismic noise recorded at more than 30 short period and broadband stations of the undervolc temporary seismic experiment and of the pdf volcano observatory network the velocity changes are estimated from the travel time delay measured on the cross correlations computed between pairs of stations we average the relative velocity changes for all pairs of stations and obtain a time series of the velocity change of piton de la fournaise volcano over 13 years from the period 0 5 to 4 s the depth sensitivity of the velocity change is ranging from approximately 100 m to 2500 m a slow decrease of velocity is measured from 2000 and ends with a major eruption that occurred in april 2007 this eruptive episode is followed by an increase of the velocity these long term changes are compared to the deformation of the piton de la fournaise edifice estimated from geodetic measurements an analysis of baseline change between gps stations indicates an inflation of the volcanic edifice prior to april 2007 followed by a deflation since then this deflation predominantly affects the terminal cone seismic velocity changes and deformation have similar long term trends with velocity decrease observed during inflation and velocity increase during deflation however the velocity change magnitude is about 2 orders of magnitude greater than the deformation this suggests nonlinear relation between velocity changes and deformation

body and surface wave reconstruction from seismic noise correlations between arrays at piton de la fournaise volcano body wave reconstruction from ambient seismic noise correlations is an important step toward improving volcano imaging and monitoring here we extract body and surface waves that propagate in piton de la fournaise volcano on la reunion island using ambient noise cross correlation and array processing techniques ambient noise was continuously recorded at three dense arrays each comprising 49 geophones to identify and enhance the green s function from the ambient noise correlation we apply a double beamforming dbf technique between the array pairs the dbf allows us to separate surface and body waves direct and reflected waves and multipathing waves based on their azimuths and slownesses we successfully extract body waves between all the combinations of arrays including the wave that propagates through the active magmatic system of the volcano additionally we identify the effects of uneven noise source distribution and interpret the surface wave reflections

granular flow simulation in a centrifugal acceleration field the use of the geotechnical centrifuge to obtain scaled physical models is a useful tool in geomechanics when dealing with granular flows however the traditional scaling principles are challenge

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

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

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

stress failure and fluid flow deduced from earthquakes accompanying eruptions at piton de la fournaise volcano abstract in the present episode of eruptive activity evidence from seismicity for sustained magma inflow from depth into the edifice of piton de la fournaise is lacking pre eruptive main deformation and shallow seismicity help to identify very small volumes of magma that are in motion beneath the rim of the dolomieu summit crater and oriented along the azimuth of the future vents small magma pockets may reside in the cone above sea level or may be expelled repeatedly due to crystallisation in a small low velocity aseismic region below sea level under the high velocity central plug of the cone in which pre eruptive earthquake swarms are located in cross section the hypocentres define two steep sheets diverging from the aseismic zone at sea level towards 1 5 km above sea level or 1 km beneath the 2632 m high cone however failure induced by increased pressure in the suggested chamber does not account for the observed focal mechanisms the occurrence and timing of magma transport are attested by eruption and seismic activity may be related to magma transport focal mechanisms document strike slip not normal faulting or tensile failure vertical propagation of the edge of a feeder dike may enhance strike slip motion above the edge in a region where effective normal stress is decreased by thermally induced groundwater flow the strike slip mechanisms could also be caused by a tensile shear widening of the horizontal section of vertical conduits fournaise strike slip earthquakes occur in two orientations with p axes orthogonal between them within a single pre eruptive event earthquakes are distributed in the same volume but mechanisms switch from one to another type systematically with time indicating a reversal of stress conditions the orientations of p axes with respect to the epicentral trend suggest that in the later parts of events leading to eruptions a compression of the medium occurs after a dilation in the first part the activated zone might respond successively to the arrival and the departure of the magma on its way from the reservoir at depth to the vent radial to the cone

the november 2002 eruption at piton de la fournaise volcano la reunion island ground deformation seismicity and pit crater collapse an eruption on the eastern flank of piton de la fournaise volcano started on 16 november 2002 after 10 months of quiescence after a relatively constant level of activity during the first 13 days of the eruption lava discharge volcanic tremor and seismicity increased from 29 november to 3 december lava effusion suddenly ceased on 3 december while shallow earthquakes beneath the dolomieu summit crater were still recorded at a rate of about one per minute this unusual activity continued and increased in intensity over the next three weeks ending with the formation of a pit crater within dolomieu based on ground deformation measured by rapid static and continuous gps and an extensometer seismic data and lava effusion patterns the eruptive period is divided into five stages 1 slow summit inflation and sporadic seismicity 2 rapid summit inflation and a short seismic crisis 3 rapid flank inflation onset of summit deflation sporadic seismicity accompanied by stable effusion 4 flank inflation coupled with summit deflation intense seismicity and increased lava effusion and finally 5 little deflation intense shallow seismicity and the end of lava effusion we propose a model in which the pre intrusive inflation of stage 1 in the months preceding the eruption was caused by a magma body located near sea level the magma reservoir was the source of an intrusion rising under the summit during stage 2 in stage 3 the magma ponded at a shallow level in the edifice while the lateral injection of a radial dike reached the surface on the eastern flank of the basaltic volcano causing lava effusion pressure decrease in the magmatic plumbing system followed resulting in upward migration of a collapse front forming a subterranean column of debris by faulting and stoping this caused intense shallow seismicity increase in discharge of lava and volcanic tremor at the lateral vent in stage 4 and eventually the formation of a pit crater in stage 5

a new model for the evolution of the volcanic island of reunion indian ocean the island of reunion has been studied using data from airborne and shipborne magnetic surveys the subaerial history of reunion spans the last 2 1 million years the brunhes matuyama geomagnetic reversal enables differentiation of volcanic rocks older and younger than 0 78 ma the lower submarine flanks are poorly magnetized and are interpreted as landslide deposits the core of the island is composed of highly magnetized rocks piton des neiges volcano is composed mostly of rocks older than 0 78 ma only its western flank and central area include thick piles of younger rocks piton de la fournaise is a highly and normally magnetized edifice but its northern and eastern flanks are underlain at shallow depth by reversely magnetized formations the latter are regarded as remnants of les alizes volcano associated with the grand brule hypovolcanic complex at the matuyama brunhes transition the island was composed of at least two main volcanoes piton des neiges and les alizes and perhaps also of a third old volcano takamaka at the center north of the island piton de la fournaise grows on the flank of les alizes and is a relatively young focus of volcanism these volcanoes have had successive phases of construction and destruction the analysis of magnetic anomalies over reunion was decisive in defining a new coherent model for the evolution of the island

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

shock waves dead zones and particle free regions in rapid granular free surface flows shock waves dead zones and particle free regions form when a thin surface avalanche of granular material flows around an obstacle or over a change in the bed topography understanding and modelling these flows is of considerable practical interest for industrial processes as well as for the design of defences to protect buildings structures and people from snow avalanches debris flows and rockfalls these flow phenomena also yield useful constitutive information that can be used to improve existing avalanche models in this paper a simple hydraulic theory first suggested in the russian literature is generalized to model quasi two dimensional flows around obstacles exact and numerical solutions are then compared with laboratory experiments these indicate that the theory is adequate to quantitatively describe the formation of normal shocks oblique shocks dead zones and granular vacua such features are generated by the flow around a pyramidal obstacle which is typical of some of the defensive structures in use today

petrology of 1977 to 1998 eruptions of piton de la fournaise la reunion island abstract geochemical and petrological variations in 35 historical eruptions from the april 1977 eruption to the march september 1998 eruption at piton de la fournaise have been analyzed for their major elements abundances mineralogical compositions and oxygen isotopes during these 21 years samplings were repeated several times during eruptions as well as temperature measurements since the end of 1977 to 1998 all erupted lavas except 1998 hudson basalt belong to the group of the steady state basalts however evidences for small degrees of differentiation can be observed during a single eruption the earliest lava emitted contains less phenocrysts and has almost always a lower mgo mgo mgo feot than the lavas emitted later suggesting that it is more differentiated from one eruption to the next between 1977 and 1998 bulk compositions are more and more differentiated towards the first lava of 1998 a process of low pressure fractional crystallisation involving small proportions of olivine clinopyroxene and plagioclase allows to explain this evolution a major result of our study is to show that this evolution does not correspond to a unique fractionation trend over the considered period different types of magmas have been distinguished the first magma type erupted from october 1977 to november 1987 was richer in potassium 0 82 wt in average than the second one and apparently derived from the liquid of the 1977 oceanite the second magma type erupted from february 1988 to september 1998 was poorer in k 2 o 0 69 wt in average in march 1998 a third magma type hudson basalt erupted simultaneously with the second one hudson basalt has undergone a wehrlitic fractionation and is supposed to come from a deeper magma reservoir than other erupted magmas for this period from 1977 to 1998 the 18 o of lavas progressively decreases with time together with the increasing chemical differentiation of the magmas by low pressure fractional crystallisation this variation agrees with the hypothesis of magma contamination at shallow level in the altered volcanic edifice vlastelic i deniel c bosq c telouk p boivin p bachelery p famin v staudacher t 2009 this issue pb isotope geochemistry of piton de la fournaise historical lavas journal of volcanology and geothermal research 184 63 78 this issue overall petrological variations are in good agreement with a model of a shallow reservoir discontinuously supplied between 1977 and 1998 the speed of the variations the coexistence of different liquids the chemical evolution of the lavas during the same eruption lead us to favour a model of chemically stratified reservoir constituted by a complex of dykes sills and laccoliths close to the surface and located above larger magma bodies

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

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

investigating the deepest part of a volcano plumbing system evidence for an active magma path below the western flank of piton de la fournaise la reunion island abstract peripheral diffuse degassing of co 2 from the soil occurs across the western flank of piton de la fournaise volcano la reunion island indian ocean along a narrow zone in this area carbon isotopic analysis on soil gas samples highlights significant mixing between magmatic and organic end members the zones with the strongest magmatic signature highest 13 c overlap spatial distribution of hypocenters recorded shortly before and during volcano reactivation and allow discriminating a n135 degassing lineament with a minimum length of 11 km and 140 20 m width such orientation is in accordance with that of an old dyke network along the rift zone and with n120 130 and n140 155 lineaments related to the inheritance of oceanic lithosphere structures our findings show that this n135 lineament represents a preferential magmatic pathway for deep magma transfer below the volcano flank moreover spatial distributions of recent eccentric cones indicate a well founded possibility that future eruptions may by pass the shallow plumbing system of the central area of the volcano taking a lateral pathway along this structure our results also confirm that piton de la fournaise activity is linked to a laterally shifted plumbing system and represent a major improvement in identifying the main high risk area on the densely populated western flank of the volcano

volcanism and the dynamics of open magma chambers the repeated eruption of many volcanoes is now accounted for by events taking place in a subterranean magma chamber which is open in the sense that the inflow of material to the chamber from below leads to a magma pressure p which exceeds the lithostatic pressure pl by an amount greater than the tensile strength of the chamber walls before the contents of the magma chamber have reached thermodynamic and geochemical equilibrium this is the condition which must be satisfied when an eruption occurs we have now derived a relationship giving the critical volume of added material v required to cause an eruption as a function of magma compressibility and the volume by which the chamber expands

scaling and design of landslide and debris flow experiments abstract scaling plays a crucial role in designing experiments aimed at understanding the behavior of landslides debris flows and other geomorphic phenomena involving grain fluid mixtures scaling can be addressed by using dimensional analysis or more rigorously by normalizing differential equations that describe the evolving dynamics of the system both of these approaches show that relative to full scale natural events miniaturized landslides and debris flows exhibit disproportionately large effects of viscous shear resistance and cohesion as well as disproportionately small effects of excess pore fluid pressure that is generated by debris dilation or contraction this behavioral divergence grows in proportion to h3 where h is the thickness of a moving mass therefore to maximize geomorphological relevance experiments with wet landslides and debris flows must be conducted at the largest feasible scales another important consideration is that unlike stream flows landslides and debris flows accelerate from statically balanced initial states thus no characteristic macroscopic velocity exists to guide experiment scaling and design on the other hand macroscopic gravity driven motion of landslides and debris flows evolves over a characteristic time scale l g 1 2 where g is the magnitude of gravitational acceleration and l is the characteristic length of the moving mass grain scale stress generation within the mass occurs on a shorter time scale h gl 1 2 which is inversely proportional to the depth averaged material shear rate a separation of these two time scales exists if the criterion h l

eruptive mechanism on piton de la fournaise volcano associated with the december 4 1983 and january 18 1984 eruptions from ground deformation monitoring and photogrammetric surveys abstract two photogrammetric aerial surveys were carried out over the summit area of the basaltic shield volcano piton de la fournaise indian ocean one survey in 1981 and the second one in 1984 during this time only two eruptions occurred both the december 4 1983 and the january 18 1984 eruptions opened fissures on the southwestern part of the summit because of the slight and erratic ground deformation measured on the dry tilt network by continuous tilt stations and within the geodetic network between 1981 and november 1983 and between february 1984 and june 1984 ground deformations revealed by the two photogrammetric surveys can be essentially associated with the two eruptions large displacement vectors were obtained up to 40 cm horizontal displacement vectors indicate a northeastward ground deformation of the southwestern part of the cone where the effusive vents opened a more diffuse uplift along the main fracture zones that cut the volcanic edifice was observed while east of these fractures only slight less than 10 cm and opposite displacements were observed this displacement field can be associated with the main geological structures of the dome of piton de la fournaise volcano some consequences of the observed displacement field may be outlined for the volcanic observational ground deformation networks to estimate the displacement field revealed by the photogrammetric surveys a simple model of dyke intrusion has been computed this model is based on dislocations and takes into account the main fracture zones good agreement is observed between computed and observed data in the area of the effusive vents some disagreement remains in the northwestern part of the survey area where horizontal deformations are small and erratic and also in the northern part where an uplift was observed that can be associated with the northern active fracture zones

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

physical and numerical modelling of dry granular flows under coriolis conditions in this paper quantitative observations of dry granular flows subject to varying magnitude and direction of coriolis acceleration are presented in order to assess the robustness of the savage hutt

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

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

episodes of pit crater collapse documented by seismology at piton de la fournaise calderas are oval fault bounded depressions in volcanic regions the formation of a small analog a summit pit crater has followed a ten month cycle of eruptive activity at piton de la fournaise volcano reunion island indian ocean in 1985 six short episodes of summit seismic activity with shocks indicating shear failures have been followed by eruptions in five cases the eruptions occurred near the base of the summit cone which is at 2 5 km elevation inside the enclos fouque an ancient caldera 7 km in diameter in another instance the summit seismic crisis did not evolve to an eruption but was followed by a seismic crisis 4 km deeper in march 1986 low level activity both at shallow depth beneath the summit and around 4 km depth to the southeast a simultaneous occurrence not previously observed culminated by a summital swarm on march 18 activity resumed its low level and five hours later a small and short lived eruption occurred at mid distance between the summit and the rim of enclos fouque one day later a flank eruption began at 1000 m elevation outside of the enclos 9 km southeast of the summit four days later effusion began near sea level 14 km southeast of the summit the shift of activity from the vent inside to that outside the enclos occurred whilst both shallow summital and deeper flank seismicity were sustained but without notable shallow activity between one vent and the next then the seismic activity which in all five previous instances stopped when the vents opened persisted for ten days increasing in energy release rate activity only consisted of shallow shocks in the summit area whilst eruption was low on the flank 9 km then 14 km away the focal mechanisms are different from all those previously determined they correspond neither to shear failure nor tensile fracturing by fluid overpressure they suggest cracking due to volume increase in a low fluid flow environment which may be consistent with the simultaneous tapping of magma deeper in the edifice a final paroxysmal seismic crisis lasting one and a half days led to the collapse of a 200 m diameter 80 m deep pit crater inside the dolomieu summital caldera on march 29 this crisis released an order of magnitude more energy than previous activity the long period signature of these seismic events indicates low stress drop with respect to source dimensions sources are shallow however rather than directly marking the progressive development of a depression at the surface they appear to correspond to fractures opening above the retreating magma and progressive stoping of a cavity similarities with seismic observations during the last phase of the fernandina galapagos 8 km2 caldera collapse of june 1968 suggest that the same kind of mechanical behaviour occurred with a scaling of three orders of magnitude in seismic moments and in volumes of collapsed blocks between the two cases

pits rifts and slumps the summit structure of piton de la fournaise a clear model of structures and associated stress fields of a volcano can provide a framework in which to study and monitor activity we propose a volcano tectonic model for the dynamics of the summit of piton de la fournaise la reunion island indian ocean the summit contains two main pit crater structures dolomieu and bory two active rift zones and a slumping eastern sector all of which contribute to the actual fracture system dolomieu has developed over 100 years by sudden large collapse events and subsequent smaller drops that include terrace formation small intra pit collapse scars and eruptive fissures are located along the southern floor of dolomieu the western pit wall of dolomieu has a superficial inward dipping normal fault boundary connected to a deeper ring fault system outside dolomieu an oval extension zone containing sub parallel pit related fractures extends to a maximum distance of 225 m from the pit at the summit the main trend for eruptive fissures is n80 normal to the north south rift zone the terraced structure of dolomieu has been reproduced by analogue models with a roof to width ratio of approximately 1 suggesting an original magma chamber depth of about 1 km such a chamber may continue to act as a storage location today the east flank has a convex concave profile and is bounded by strike slip fractures that define a gravity slump this zone is bound to the north by strike slip fractures that may delineate a shear zone the southern reciprocal shear zone is probably marked by an alignment of large scoria cones and is hidden by recent aa lavas the slump head intersects dolomieu pit and may slide on a hydrothermally altered layer known to be located at a depth of around 300 m our model has the summit activity controlled by the pit crater collapse structure not the rifts the rifts become important on the mid flanks of the cone away from pit related fractures on the east flank the superficial structures are controlled by the slump we suggest that during pit subsidence intra pit eruptions may occur during tumescence however the pit system may become blocked and a flank eruption is more likely intrusions along the rift may cause deformation that subsequently increases the slump s potential to deform conversely slumping may influence the east flank stress distribution and locally control intrusion direction these predictions can be tested with monitoring data to validate the model and eventually improve monitoring

eruption at le piton de la fournaise volcano on 3 february 1981 piton de la fournaise in the island of la reunion indian ocean is a young 0 35 myr old basaltic shield volcano built on the flank of the extinct piton des neiges volcano it is one of the most active volcanoes in the world magma output rate of 0 32 m3 s 1 1 2 and has been under continuous surveillance by the volcanological observatory of the institut de physique du globe de paris since august 1980 the first detailed observations on the volcano reveal a remarkably low level of background seismicity the 3 february 1981 eruption was preceded by a deep event of volcanic origin at depths of 10 15 km on 2 january 20 days of quiescence followed this event until the onset of shallow seismicity close to the eruptive centres on 22 january the eruption began after 13 days of sustained shallow seismicity and occurred in three phases over 92 days and produced about 10 106 m3 of lava

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

cumulate clasts in the bellecombe ash member piton de la fournaise reunion island and their bearing on cumulative processes in the petrogenesis of the reunion lavas abstract among the ejecta from a phreatomagmatic eruption on piton de la fournaise volcano are wehrlitic and gabbroic cumulate clasts these fresh samples comprise olivine fo85 0 to fo69 0 augite en47 1wo44 6wo44 6 to en41 1fs15 4wo43 5 and plagioclase an82 8ab16 8or0 4 to an53 8ab44 8or1 4 with spinel ti rich ferrichromites to ti magnetite and some ilmenite a few percent of highly vesicular interstitial glass is commonly present textures indicate that the cumulates were not wholly crystalline at the time of eruption and that the glass represents a residual intercumulus melt that varies from basaltic to mugearitic sulphide globules typically spherical and up to 40 m diameter represent immiscible melts within the glasses the sulphides contain relatively high contents of cu and ni and appear to be high temperature homogeneous pyrrhotite rich compositions rank order of element abundance in the sulphides is fe s cu ni co and zn wt s although in one sample ni is more abundant than cu lack of correlation between the sulphide globule compositions and their host glasses is probably due to complex partitioning between the silicate melts silicate and oxide crystals sulphide melt and separating volatile phase whereas the cu cu ni at values of the sulphides are similar to those of the sulphide ore bodies from major gabbroic complexes the ni ni fe values are notably high with regard to the low mgo content of their host glasses oxide pairs regarded as reflecting equilibria prior to eruption indicate temperatures of 1017 897 c and log fo2 values of 9 6 12 7 compaction of analogous cumulate mushes with extraction of relatively low density basaltic to mugearitic and ultimately trachytic residual melts is inferred to have yielded the differentiated series lavas and ash flows of the older volcano on reunion piton des neiges the sequence of crystallisation with augite as the second silicate phase rather than plagioclase as is normal in the lava sequences suggests crystallisation at depths 5 km the bellecombe ash cumulate clasts show more evolved assemblages than most other xenolith suites on the volcano in which dunites predominate and are probably products of stagnated magma batches possibly arrested in sill like intrusions in the deeper crust the cumulates are recent components in what is probably a large ca 70 km across layered complex beneath the volcanic edifices accreted during the build up of reunion

resistivity variations related to the large march 9 1998 eruption at la fournaise volcano inferred by continuous mt monitoring abstract the 2645 m high la fournaise volcano located in the southwest of reunion island indian ocean is a shield basaltic volcano where effusive eruptions generally occur along long fissures starting from the summit alongside major fractures that characterize the eruptions dynamism and effusivity between 1992 and 1998 the volcano underwent a quiet period during which few earthquakes were recorded minor seismic activity returned after 1997 and picked up in march 1998 during the 35 h preceding the march 9 eruption from 1996 two autonomous stations csv and bav were installed on the volcano csv was located inside the enclos fouque caldera while bav was positioned 8 2 km nw of the volcano summit horizontal components of the electric and magnetic fields were sampled every 20 s continuous time series were available from 1996 to 1999 at csv and from 1997 to march 1998 at bav data have been processed using both single station and remote reference processing both results show apparent resistivity variations synchronous to the eruption time lapse impedance estimates are computed on overlapping time windows of about two days at both stations the only major decrease of the observed impedance coincides with the march 1998 eruption at csv the resistivity started to drop about five days before the eruption reached several local minima until april and then slowly increased as the volcanic crisis reduced in activity after the end of the crisis in september 1998 the apparent resistivity recovered its pre crisis value the time lapse results also show variability in directionality sharp and elongated phase tensor ellipse residuals appear during the eruption with a n105 orientation suggesting the emergence of an almost ns striking dyke a 1d background model built from mt soundings performed during the quiet period 1996 to february 1998 on which a 3d ns striking dyke was added shows a good agreement with phase tensor residuals and spatial distribution of the resistivity variations observed during the eruption

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

dry granular flow interaction with dual barrier systems multiple barriers are commonly installed along predicted geophysical flow paths to intercept large flow volumes the main criterion for multiple barrier design is volume retained the velocity of t

perturbation to the lithosphere along the hotspot track of la reunion from an offshore onshore seismic transect a 250 km long ne sw lithospheric transect spanning the 40 km wide island of la reunion and its submarine edifice is derived from lines of air gun shots at sea on either side along the assumed hotspot trace seismic records were obtained from an array spanning the whole transect and including sea bottom and land receivers providing a system of reversed and overlapping observations low seismic velocity and hence density is found on average for the whole edifice above the oceanic plate we attribute high velocity anomalies within the edifice to an intrusive core confined under the central northern quarter of the island crossing segment unexpectedly the main seismic interfaces top and bottom of the prevolcanic crust do not show significant flexural downwarping under the island in addition clear multipathing in the recorded wave field requires the presence of a body with a seismic velocity intermediate between the prevolcanic crustal material and the normal mantle this lithospheric structure provides the first example where underplating occur s beneath an active volcanic island suggesting a genetic relationship the underplated body could represent residues of the evolution of primary picritic melts that yield erupted basalts evidence for reflectors deeper in the lithosphere may indicate further related heterogeneity in the plate hotspot model commonly assumed the structural variation along the transect could be interpreted as a variation with time of the amount and physical state of underplated material

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