timing of geothermal activity in an active island arc volcanic setting first 40ar 39ar dating from bouillante geothermal field guadeloupe french west indies mineral separates of adularia have been extracted from three samples of highly silicified hydrothermal breccias newly discovered in the active bouillante geothermal field guadeloupe archipelago and investigated by 40ar 39ar geochronology in order to constrain the timing of geothermal activity in this part of the active lesser antilles island arc the inverse isochron diagram indicates an age of 248 50 ka 2 for all adularia from one breccia sample n 8 with an initial 40ar 36ar ratio of atmospheric composition 309 12 2 attesting that this age is valid this age is concordant with the weighted mean age of 290 40 ka for the same sample adularia from other samples yields concordant ages the obtained 40ar 39ar ages can be related either to the magmatic activity of the bouillante volcanic chain c 850 250 ka ago or to the initiation of the volcanic activity of the active grande decouverte soufriere system 200 ka ago present day our results demonstrate that the bouillante hydrothermal event is coeval with change in the volcanic pulses previously recognized in the magmatic history of the studied area the possible duration calculated for this hydrothermal activity requires at least two superposed volcanic pulses to be developed

possible electrokinetic origin of large magnetic variations at la fournaise volcano abnormal time variations of the geomagnetic field related to volcanic activity have been reported for several decades1 10 two main candidates have been considered for the source mechanism of these volcanomagnetic variations piezomagnetism and electro kinetic effects we considered both of these mechanisms in our attempts to interpret the most spectacular volcanomagnetic variations observed on piton de la fournaise volcano reunion island 11 but now new analysis of the latest data which covers a time span of more than three years leads us to think that water circulation is the main agent of the strong magnetic signals observed on the volcano in addition to the signals that we correlated with the volcano activity11 12 longer period components also exist as shown here with amplitudes and characteristics that have not been reported before we propose that these magnetic variations are generated by electrokinetic effects in which case the water circulation system into this massif would be a sensor for detecting stress changes linked to the volcano activity

combined electromagnetic geochemical and thermal surveys of taal volcano philippines during the period 2005 2006 since 1572 33 phreatic to phreatomagmatic eruptions have occurred on taal volcano philippines some of them causing several hundred casualties considering the time delay between two consecutive eruptions there is an 88 probability that taal volcano should have already erupted since 1992 several phases of seismic activity have been recorded accompanied by ground deformation opening of fissures and surface activity the volcanic activity of taal appears to be controlled by dike injections and magma supply buffered by a hydrothermal system that releases fluids and heat through boiling and subsequent steaming in early 2005 a multidisciplinary project was launched for studying the hydrothermal activity to map the hydrothermal system combined surveys were carried out to investigate self potential total magnetic field ground temperature and carbon dioxide soil degassing along with satellite thermal imaging of the main crater lake the elevated temperatures and high concentrations of carbon dioxide as well as electromagnetic anomalies indicate large scale hydrothermal degassing this process is enhanced along the tectonic features e g crater rim and faults of the volcano while active fissures opened along the e w northern flank during the 1992 1994 seismic activity heat and fluids from the hydrothermal system are essentially released in the northern part of the crater which is bounded to the south by a suspected nw se fault along which seismicity seems to take place and dikes are thought to be intruded during the january 2005 surveys a new seismic crisis started and the felt earthquakes prompted spontaneous evacuation of hundreds of inhabitants living on the volcano repeated surveys show changes of self potential total magnetic field and ground temperature with time without any noticeable spatial enlargement these observations suggest that the northern flank located between the crater rim and the 1992 1994 fissures is connected with a deep thermal source in main crater and is reactivated during seismic crises this sector could be subjected to flank failure

the development mechanism of gravel bars in rivers the development stability and growth direction of gravel mid channel bars in rivers were studied by analyzing sediment distribution and vegetation development along the bars field studies and sediment sampling were conducted in the source region of the yellow and lancang rivers on the qinghai plateau the results showed that the gravel bars in rivers always grow in the upstream direction because gravel and sand are deposited at the upstream end of the bars gravel bedload stopped at the bar head sand and silt moved as suspended load during the flood season and were deposited at the bar tail due to vegetation resistance consequently sediment size varied from gravel to sand and silt along the bars from the head to the tail on the bar surface dense vegetation coverage normally grew at the bar tail while only pioneer species occurred at the bar head the prevalent phenomena demonstrated the upstreamward growth of mid channel bars

volcanomagnetic effects observed on piton de la fournaise volcano reunion island 1985 1987 a permanent network of four to six telemetered magnetic stations has been installed on piton de la fournaise volcano in october 1985 and 1986 eight eruptive sequences have occurred since then some of which affected only the summit whereas others affected the whole massif volcanomagnetic variations are observed with each of these volcanic events the geomagnetic field intensity is measured simultaneously every minute at each station with a precision of 0 25 nt nanotesla the main results are the following volcanomagnetic variations observed with eruptions have amplitudes of several nanoteslas to more than 10 nt with characteristic time durations ranging from l min or less to several months a good correlation between the magnetic variations recorded at the different stations is observed spatial and temporal properties of the volcanomagnetic field appear to be controlled by the features of the eruptions several days before the beginning of the december 1985 march july november december 1986 and january 1987 eruptions changes in the intensity differences are observed with amplitudes of a few nanoteslas up to 5 nt at stations located close to the active part of the rift zone variations are also observed in the most remote stations for larger eruptions in march 1986 november december 1986 and january 1987 correlations between magnetic variations ground deformations and seismic activity have been observed for the december 1985 march 1986 november december 1986 and january 1987 events three main mechanisms could account for the observed volcanomagnetic variations piezomagnetic effects electrokinetic effects and electrical resistivity changes since variations in the stress field in the surroundings can modify the induced and natural magnetizations of magnetized rocks the circulation of water through the interconnected pore network microcracks faults aquifers and also the electrical resistivity of geological structures through the modification of the properties of the pore network

the 1975 1977 crisis of la soufriere de guadeloupe f w i a still born magmatic eruption on july 8 1976 eruptive activity broke out at la soufriere de guadeloupe f w i after about one year of increasing seismic activity seismic activity continued to increase until august 1976 reaching more than 1500 events a 200 fold increase over the preceding quiet period of a few years and an energy output of about 1017 ergs in a day a total of 26 major phreatic eruptions similar to the july 8 outburst took place during an eight months period the steam blasts that characterized the eruptions gave rise to particle and sometimes block charged plumes that deposited an estimated 106 m3 of solids the h2o rich gases emitted during the blasts presumably contained other gases h2s so2 co2 that were partly adsorbed on solid particles all material was erupted at temperatures of the order of 100 to 200 c the observation of vertical migration of earthquake foci in less than a few hours and over about 6 km depth and of abnormal variations of the geomagnetic field indicate a deep energy source for the phreatic eruptions a small proportion of the gases adsorbed on solid particles had a magmatic origin however most of the steam and the tephra seemed to originate from superficial levels of a hydrothermal system similar phreatic eruptions have occurred several times in recorded history in the case of la soufriere the origin of the phreatic eruptions is best described by an abnormal energy input versus steady state from a crustal magma chamber the occurrence of truly magmatic eruptions is presumably inhibited by an extensive hydrothermal system the abrupt release of more power from the magma chamber could have resulted in an explosive pyroclastic eruption substantial improvement of the guadeloupe volcano observatory has followed the 1975 1977 crisis permanent telemetered geophysical networks and regular geochemical observations have provided a five year data base of the volcano behavior in its noneruptive state which can be compared to crisis situations

evidence for a new shallow magma intrusion at la soufriere of guadeloupe lesser antilles insights from long term geochemical monitoring of halogen rich hydrothermal fluids more than three decades of geochemical monitoring of hot springs and fumaroles of la soufriere of guadeloupe allows the construction of a working model of the shallow hydrothermal system this system is delimited by the nested caldera structures inherited from the repeated flank collapse events and the present dome built during the last magmatic eruption 1530 ad and which has been highly fractured by the subsequent phreatic or phreatomagmatic eruptions because it is confined into the low volume highly compartmented and partially sealed upper edifice structure the hydrothermal system is highly reactive to perturbations in the volcanic activity input of deep magmatic fluids the edifice structure sealing and fracturing and meteorology wet tropical regime the current unrest which began with a mild reactivation of fumarolic activity in 1990 increased markedly in 1992 with seismic swarms and an increase of degassing from the summit of the dome in 1997 seismic activity increased further and was accompanied by a sudden high flux hcl rich gas from summit fumaroles we focus on the interpretation of the time series of the chemistry and temperature of fumarolic gases and hot springs as well as the relative behaviours of halogens f cl br and i this extensive geochemical time series shows that the deep magmatic fluids have undergone large changes in composition due to condensation and chemical interaction with shallow groundwater scrubbing it is possible to trace back these processes and the potential contribution of a deep magmatic source using a limited set of geochemical time series t co2 and total s content in fumaroles t and cl in hot springs and the relative fractionations between f cl br and i in both fluids coupling 35 years of geochemical data with meteorological rainfall data and models of ion transport in the hydrothermal aquifers has allowed us to identify a series of magmatic gas pulses into the hydrothermal system since the 1976 1977 crisis the contrasting behaviours of s and cl bearing species in fumarolic gas and in thermal springs suggests that the current activity is the result of a new magma intrusion which was progressively emplaced at shallow depth since 1992 although it might still be evolving the characteristics of this new intrusion indicate that it hasalready reached a magnitude similar to the intrusion that was emplaced during the 1976 1977 eruptive crisis the assessment of potential hazards associated with evolution of the current unrest must consider the implications of recurrent intrusion and further pressurization of the hydrothermal system on the likelihood of renewed phreatic explosive activity moreover the role of hydrothermal pressurization on the basal friction along low strength layers within the upper part of the edifice must be evaluated with regards to partial flank collapse at this stage enhanced monitoring research and data analysis is required to quantify the uncertainties related to future scenarios of renewed eruptive activity and magmatic evolution

variation of the electrical resistivity of large rock samples with stress many experimental and theoretical efforts have been devoted to the study of the electrical properties of rocks e g brace et al 1965 madden 1982 parkhomenko 1982 yamazaki 1966 special attention has been paid to possible relationships between variations of mechanical stresses inside the rock and variations of its electrical properties in reference to a possible technique of predicting earthquakes raleigh et al 1977 these studies were generally performed on small decimeter sized samples but the complexity of the physical processes involved and the heterogeneity of rocks in the field make it necessary to try to get results from larger blocks with dimensions of several decimeters sobolev et al 1983 or of meters this study it also appears quite desirable to look for information on the electrical properties of rocks at different scales from a centimeter to a kilometer say to see if some scaling laws could be experimentally established these scaling laws would allow inference of electrical properties at a given scale from the knowledge of the electrical properties at a smaller scale madden 1976 scaling law methods seem to be promising in seismogenesis studies e g allegre et al 1984 turcotte 1986

zn isotope compositions of the thermal spring waters of la soufriere volcano guadeloupe island abstract to trace the sources and pathways of zn in hydrothermal systems the zn isotope compositions of seventeen water samples from eight thermal springs and six gas samples from two fumaroles from la soufriere an active volcano on guadeloupe island french west indies fwi were analyzed using a method adapted for purifying zn from fe and so4 enriched thermal solutions the fumaroles are enriched in zn 100 to 8000 times compared to the local bedrock and have isotopic compositions 66zn values from 0 21 to 0 35 similar to or slightly higher than fresh andesite 0 21 the enrichment of zn in the thermal springs compared with the surface waters shows that zn behaves as a soluble element during hydrothermal alteration but is significantly less mobile than na the 66zn values of most of the spring waters are relatively constant approximately 0 70 indicating that the thermal springs from la soufriere are enriched in heavy isotopes i e 66zn compared to the host rocks from 0 14 to 0 42 only three thermal springs have lower 66zn values as low as 0 43 while the zn in the fumaroles is essentially derived from magma degassing which is consistent with a previous study on merapi volcano toutain et al 2008 we show that the zn in the thermal springs is mainly derived from water rock interactions the 66zn enriched isotopic signature in most of the spring waters can be explained qualitatively by the precipitation at depth of sulfide minerals that preferentially incorporate the light isotopes this agrees with the isotopic fractionation that was recently calculated for aqueous complexes of zn the few thermal springs with lower 66zn values also have low zn concentrations indicating the preferential scavenging of heavy zn isotopes in the hydrothermal conduits this study shows that unlike chemical weathering under surface conditions hydrothermal alteration at high temperatures significantly fractionates zn isotopes and enriches thermal waters in heavy zn isotopes e g 66zn continental hydrothermal systems therefore constitute a source of heavy zn isotopes to the oceans this should be taken into account in the global oceanic budget of zn

electrical tomography of la soufriere of guadeloupe volcano field experiments 1d inversion and qualitative interpretation the soufriere of guadeloupe lava dome consists of several 3d domains of relatively unaltered massive andesite separated by major radial fractures that reach at least up to about half of the dome s height more than 20 000 geo electrical measurements made on the top and the flanks of the lava dome are used to construct the first geophysical image of the internal structure of this active volcano the main features of the apparent conductivity structure of the lava dome are high conductivity regions associated with the strongly altered material of present and fossil hydrothermal zones local 1d inversions of data subsets belonging to regions where the geological structure is supposed laterally invariant confirm the structures observed in the pseudo sections the relatively stable units lie above a basal inclined layer of highly conductive geological materials interpreted to be more altered and thus characterised by reduced internal friction and probably increased pore pressure past and current hydrothermal fluid circulation through these fractures has promoted rock alteration and particularly along the base of the dome that likely contributes to the instability of parts of the edifice

noble gas isotopes in hydrothermal volcanic fluids of la soufriere volcano guadeloupe lesser antilles arc article the ascending magmatic component in la soufriere volcano guadeloupe lesser antilles was investigated by measuring noble gas concentrations and isotopic ratios in thermal springs and fumaroles a clear magmat ic helium signal 4 he 3 he 89 000 r ra 8 equivalent to the morb value is recorded in most fluids 3 he fluxes in both fumarole and springs have been estimated and related to 3 he content in the magma chamber in order to explain the 3 he flux measured at the surface we conclude that the magma chamber must be reg ularly fed by fresh magma batches using our new results and data from literature we propose that the his torical activity of la soufriere volcano can be explained by both abnormal energy inputs from new batches of magma in the chamber and cycles of clogging opening of the hydrothermal system we propose a new sce nario for the origin of the 1976 1977 crisis whereby a fresh batch of magma could have been emplaced prior to 1968 possibly between 1959 and 1962 in the magma chamber the resulting heat flux is not stored in the different aquifers but preferentially evacuated through fractures reactivated or created during the 1956 phre atic eruption only when the self sealing of the hydrothermal system is sufficiently developed can pressure and temperature within the aquifers rapidly increase to trigger a crisis

joint inversion of p wave velocity and density application to la soufriere of guadeloupe hydrothermal system we present the result of a 3 d gravity and p wave traveltime joint inversion applied to the hydrothermal system of la soufri ere of guadeloupe the joint inversion process is used here to overcome the different resolution limitations attached to the two data sets p wave traveltimes were obtained from three active seismic surveys that were conducted from 2001 to 2007 gravity data collected during a microgravity campaign is described in a companion paper we use a joint inversion process based on a bayesian formulation and a deterministic iterative approach the coupling between slowness and density is introduced through a supplementary constraint in the misfit function that tries to minimize the distance between parameter values and a theoretical relationship this relationship is derived from measurements on samples representative of mt pel ee of martinique and la soufri ere volcanoes we chose a grid discretization that leads to an under determined problem that we regularize using spatial exponential covariance between the nodes parameters our results are compared to geophysical electromagnetic results obtained using resistivity and vlf surveys they confirm the presence of highly contrasted dense fast and light slow zones in la soufri ere dome and crater basement our images suggest however that some non conductive zones may be massive andesite bodies rather than argilized zones and that these bodies may have deeper roots than hypothesized

flank failure directed blast eruption at soufriere guadeloupe french west indies a 3 000 yr old mt st helens an extensive apparently monogenic debris flow deposit in the basse terre st claude area of southern guadeloupe is contemporaneous with pyroclastic surge deposits that cover an area of at least 60 km2 these 3 000 yr old deposits were emplaced by the avalanching of a sector of soufriere volcano and an associated directed blast similar to the 1956 bezymianni and the may 18 1980 mt st helens eruptions

influence of rainfalls on heat and steam fluxes of fumarolic zones six months records along the ty fault soufriere of guadeloupe lesser antilles fumarolic zones are permeable areas where both steam and heat are expelled to the atmosphere surface fluxes and flows which are representative of the intensity of the hydrothermal circulation in depth can be monitored by thermometers thermal infrared cameras spectrometers or condensers however the superficial activity of fumarolic zones can be modified by the meteorological conditions in particular the rainfalls which might result in erroneous estimations from this perspective we developed a set of physical equations to quantify the effects of rainfalls on the thermal behavior of fumarolic zones results were faced to continuous measurements achieved at the ty fault fumarolic zone la soufriere volcano guadeloupe lesser antilles during six months in 2010 using six vertical series of thermometers measuring the heat transfer in the ground and one condenser measuring the rising steam flux results demonstrate that in the absence of rainfalls heat and steam flux reach an equilibrium that is representa tive of the geothermal flux in depth conversely after the rainfalls the cooling of the ground provokes a deepening of the condensation level the related soil temperature drop can be estimated by computing the heat required to warm the infiltrated water up to boiling temperature while the recovery rate is directly linked to the geothermal flux our observations allow defining in which conditions flux are at steady state but also to build a first order numer ical model allowing estimating both the physical parameters of the ground thermal conductivity precipitation efficiency coefficient and surface flux constant and the long term thermal behavior of the hydrothermal system in particular our results predict that the hydrothermal activity must vanish on the zones where the geothermal flux drops under a certain threshold 60 w m 2 at la soufriere the existence of this limit may have strong implications for the precipitation rate of minerals and the possible reactivation of the fumarolic zones during volcanic crises

knowledge transmission and apprentice flint knappers in the acheulo yabrudian a case study from qesem cave israel abstract we present the techno typological characteristics of a lithic assemblage earlier that 300 ka originating from the southern area of qesem cave a middle pleistocene site in central israel aspects of knapping trajectories were examined in detail including core analyses demonstrating that the southern area assemblage has some distinguishable features in comparison with lithic assemblages from other areas of the cave these features permit in our opinion to suggest that various levels of knapping skills are reflected in this particular assemblage most probably characterizing both skilled knappers and unexperienced knappers or knappers in the process of learning thus these data may permit a preliminary assessment of knowledge transmission relating to flint knapping that has taken place in the southern area of qesem cave during the late lower paleolithic in the levant

structure and hydrogeological functioning of an insular tropical humid andesitic volcanic watershed a multi disciplinary experimental approach summary the aim of the study is to establish an hydrogeological scheme of the structure and the functioning of andesitic volcanic systems in the insular and humid tropical context a watershed has been instrumented at fefe in guadeloupe french west indies in the lesser antilles to measure rainfall runoff and piezometric fluctuations between 2003 and 2006 given the heterogeneity of the volcanic deposits a multi disciplinary approach has been used a geological and an hydrogeological survey an hydrodynamic approach hydraulic tests and signal processing of hydrological time series and finally an hydrogeochemical approach major elements and some trace elements two main superposed aquifer respectively in aerial deposits and in recent nuees ardentes glowing ash and lava flows as well as the underlying aquiclude the highly weathered older substratum were identified at a local scale some hydrogeological heterogeneities internal to the aquifers were highlighted and related to a polyphased building up of the geological formations hydraulic relationships between the multi layered aquifers such as the confinement of the deep aquifer upstream of the basin were identified groundwater stream exchanges were characterised detailing various contributions of the shallow and the deep aquifers to stream and spring waters significant river losses were also observed at a global scale within such relatively permeable volcanic formations the aquifer recharge is about 85 of the annual effective rainfall for an average rainfall year the hydrogeological scheme appears to be coherent with a geological structure of cut and fill paleovalleys frequently observed in andesitic areas consequently groundwater drainage axis are mainly localised in recent nuees ardentes deposits whereas the inversion of relief characteristic of volcanic areas explains the non superposition of surface water and groundwater divides and both surface water losses and springs finally this work shows the highly heterogeneous hydrogeological processes occurring in volcanic formations of andesitic type it also shows the relationships between the geological structure and the hydrogeological functioning of such basins and proposes an affordable methodological approach to investigate such a hydrogeological context in depth

a model for episodic degassing of an andesitic magma intrusion 1 episodic magmatic degassing has been observed at numerous volcanoes especially those of intermediate composition it can span timescales from years to decades here we propose a physical model for the degassing of a shallow magma intrusion to explain this phenomenon the magma cools by convection which leads to melt crystallization volatile exsolution and magma overpressure when the pressure reaches a critical value wall rocks fracture and the exsolved gas escapes the intrusion then returns to the initial lithostatic pressure and a new cooling crystallization degassing cycle occurs a series of such cycles leads to episodic degassing the trend and timescale of the degassing process are mainly governed by magma cooling two degassing regimes are exhibited an early phase with a high frequency of gas pulses and a later phase with a lower gas pulse frequency the transition between these two regimes is caused by the viscosity increase when the magma crystallinity exceeds the crystal percolation threshold we find that the time to this transition is dependent on magma volume to a first approximation where observations are available from sustained geochemical surveillance the model provides constraints on key aspects of the subsurface magmatic system with estimation of the volume of an intrusion and tensile strength of the surrounding rocks it therefore represents a relevant tool for volcanic surveillance and hazard assessment

magnetic measurements on la soufriere volcano guadeloupe lesser antilles 1976 1984 a re examination of the volcanomagnetic effects observed during the volcanic crisis of 1976 1977 abstract during the seismovolcanic crisis of 1976 1977 at la soufriere on guadeloupe a magnetic network of 12 reference markers was set up measurements of the intensity of the earth s magnetic field carried out up to once a day at each marker showed volcano magnetic variations of several nanoteslas nt the variations at certain markers were more or less concealed by transient magnetic variations due to anomalies in conductivity as early as 1978 measurements were resumed and a telemetering network was coupled with the network of reference markers to which 4 new markers were added a detailed study of conductivity anomalies was carried out on the entire volcano contrasts in conductivity linked to the existence of a superficial conducting surface on a ssw nne axis located south of the volcano caused a great lack of homogeneity in the field variations measured at the surface variations greater than about 10 nt appeared in the difference in intensity of the earth s magnetic field between two stations no long term magnetic variation was observed between 1978 and 1984 on the network of markers the accuracy of measurements of volcanic effects was at best 2 nt measurements carried out on the telemetering network during the night refined these results since their accuracy was 1 nt the only significant volcanic crisis between 1978 and 1984 5 7 january 1981 seems to be observed by telemetering stations all the measurements carried out in periods of volcanic inactivity make it possible to re examine the crisis of 1976 1977 though volcanomagnetic effects over short periods cannot be accurately determined variations with a time constant of several weeks were present over the entire volcano these variations were as high as 7 8 nt in remote stations and they can be linked to the three major phases of eruptive activity at la soufriere during the crisis of 1976 1977

degassing at la soufriere de guadeloupe volcano lesser antilles since the last eruptive crisis in 1975 77 result of a shallow magma intrusion in the 15 years following the last crisis of phreatic type in 1975 77 the hydrothermal and seismic activity of la soufriere de guadeloupe has displayed an episodic behavior superimposed on a long term decay as inferred from seismicity and degassing monitored through fumarolic emissions and cl content in thermal springs in particular the evolution of the cl content can be explained by a succession of magmatic gas injections into the hydrothermal system this episodic supply of gas may be associated to the thermodynamic evolution of a batch of magma intruded at shallow depth around 1976 progressive magma cooling crystallization gas exsolution and pressure buildup lead to cyclic failure of host rock around the intrusion and episodic release of gas with a decreasing frequency as cooling proceeds this physical model allows to reproduce the pattern of degassing activity of la soufriere including the decreasing frequency of cl pulses with time our preferred forward model of cl pulses involves a magma intrusion volume in the range 0 01 0 52 km 3 and a tensile strength of the surrounding rock in the range 0 1 0 6 mpa these results reinforce the hypothesis of a shallow magma intrusion triggering the 1975 77 crisis and provide an explanation for the degassing and seismic activities observed until 1992

the volcanic activity of la soufriere of guadeloupe lesser antilles structural and tectonic implications abstract among observations made on la soufriere volcano guadeloupe to monitor its its activity are temperature measurements temperature of fumaroles hot springs ground surface and water inside two boreholes 80 and 90 m deep those measurements proved to be of prime importance in understanding mechanisms working in the volcano and governing its activity they lead with other observations such as self potential measurements and geochemical analysis of fumaroles and hot springs to a possible interpretation of phreatic activity rather different from the one retained earlier which was essentially based on seismic data in this model the magma reservoir is only in a stable state and in particular supplies heat at a constant rate to the overlying geological structures the cycle of volcanic activity and period of quiescence is interpreted as due to a cycle of clogging and reopening of the system of fractures transferring heat from a lower aquifer to an upper one and eventually to the atmosphere the model is discussed in regard of other geophysical observations in particular seismicity some inferences are made concerning a new phase of activity and suitable observations to predicit it

space and ground based measurements of sulphur dioxide emissions from turrialba volcano costa rica remotely sensed measurements of sulphur dioxide so2 emitted by turrialba volcano costa rica are reported for the period september 2009 january 2011 these measurements were obtained using images from advanced spaceborne thermal emission and reflexion radiometer ozone monitoring instrument and a ground based uv camera these three very different instruments provide flux measurements in good agreement with each other which demonstrate that they can be integrated for monitoring so2 fluxes fluxes from turrialba increased fourfold in january 2010 following a phreatic explosion that formed a degassing vent in the w crater of turrialba since then the so2 flux has remained high 30 50 kg s but seems to be showing a slowly decreasing trend we interpret this evolution as the start of open vent degassing from a recently intruded magma body the opening of the degassing vent decreased the confining pressure of the magma body and allowed the gases to bypass the hydrothermal system

mercury gas emissions from la soufriere volcano guadeloupe island lesser antilles abstract quantifying mercury hg emissions from active volcanoes is of particular interest for better constraining the global cycle and environmental impact of this highly toxic element here we report on the abundance of total gaseous tgm hg 0 g hg ii g and particulate hg p mercury in the summit gas emissions of la soufriere andesitic volcano guadeloupe island lesser antilles where enhanced degassing of mixed hydrothermal magmatic volatiles has been occurring since 1992 from the southern summit crater we demonstrate that hg in volcanic plume occurs predominantly as gaseous mercury with a mean tgm hg p mass ratio of 63 combining the mean tgm h 2 s mass ratio of the volcanic plume 3 2 10 6 measured close to the source vent with the h 2 s plume flux 0 7 t d 1 determined simultaneously allows us to estimate a gaseous mercury emission rate of 0 8 kg yr 1 from la soufriere summit dome somewhat lower tgm s tot mass ratio in fumarolic gases from the source vent 4 4 10 7 suggests that plume chemical composition is not well represented by the emission source fumaroles due to chemical processes prior to or upon discharge current mercury emission from la soufriere volcano represents a very small contribution to the estimated global volcanic budget for this element

carbon and helium isotopes in thermal springs of la soufriere volcano guadeloupe lesser antilles implications for volcanological monitoring abstract la soufriere guadeloupe lesser antilles is one of the most active and dangerous volcanoes of the lesser antilles arc the renewal of the volcanic activity at la soufriere requires replenishment of the volatile poor andesitic stored magma with more primitive volatile rich basaltic magma this event will trigger early release of large quantities of highly volatile species like co 2 and helium in the hydrothermal system to use these precursors first their baseline abundances and their behaviour in the hydrothermal system must be known during the current phase of dormancy in this study we have combined a previous systematic investigation of noble gases with carbon data of hydrothermal fluids flowing out of la soufriere the results for dissolved gases reveal that an intense interaction between rising magmatic volatiles and groundwaters currently takes place at la soufriere we show that the pristine magmatic composition with a 13 c co2 value of 3 19 0 03 a 3 he 4 he ratio of 8 1 0 2 r a and a co 2 3 he ratio of 1 03 0 18 10 10 may vary during the ascent of magmatic fluids due to either fractionation or mixing processes with meteoric water and or an organic component here we provide a baseline for co 2 and helium isotopes at each monitored spring and describe the superficial processes affecting both elemental and isotopic ratios

a new scenario for the last magmatic eruption of la soufriere of guadeloupe lesser antilles in 1530 a d evidence from stratigraphy radiocarbon dating and magmatic evolution of erupted products la soufriere of guadeloupe is a dangerous volcano characterized over the last decade by moderate seismic and fumarolic unrest in the last 15 000 years it has experienced phreatic and magmatic eruptions and unusually numerous flank collapse events sometimes associated with a magmatic eruption we propose a new age of 1530 a d and a new eruptive scenario for the last magmatic eruption on the basis of a novel statistical analysis of radiocarbon age dates and new field and geochemical data this eruption is the only magmatic eruption likely to have occurred in guadeloupe during the last 1400 years the eruption mainly involved an andesitic magma which in the first phase of the eruption partially mixed with a slightly more differentiated magma stored in a small and shallow magma chamber ascent of magma to the surface generated a partial collapse of the hydrothermally altered edifice that increased the magma discharge and led to a sub plinian phase with scoria fallout and column collapse pyroclastic flows followed by near vent pyroclastic scoria fountains the eruption ended with growth of a lava dome our revised interpretation of the last magmatic eruption of la soufriere constitutes the most likely key to a future magmatic eruption scenario for this volcano which displays strong evidence of unrest since 1992

thermodynamics of gas and steam blast eruptions eruptions of gas or steam and non juvenile debris are common in volcanic and hydrothermal areas from reports of non juvenile eruptions or eruptive sequences world wide at least three types or end members can be identified 1 those involving rock and liquid water initially at boiling point temperatures boiling point eruptions 2 those powered by gas primarily water vapor at initial temperatures approaching magmatic gas eruptions and 3 those caused by rapid mixing of hot rock and ground or surface water mixing eruptions for these eruption types the mechanical energy released final temperatures liquid water contents and maximum theoretical velocities are compared by assuming that the erupting mixtures of rock and fluid thermally equilibrate then decompress isentropically from initial near surface pressure 10 mpa to atmospheric pressure maximum mechanical energy release is by far greatest for gas eruptions 1 3 mj kg of fluid rock mixture about one half that of an equivalent mass of gunpowder and one fourth that of tnt it is somewhat less for mixing eruptions 0 4 mj kg and least for boiling point eruptions 0 25 mj kg the final water contents of crupted boiling point mixtures are usually high producing wet sloppy deposits final erupted mixtures from gas eruptions are nearly always dry whereas those from mixing eruptions vary from wet to dry if all the enthalpy released in the eruptions were converted to kinetic energy the final velocity v max of these mixtures could range up to 670 m s for boiling point eruptions and 1820 m s for gas eruptions highest for high initial pressure and mass fractions of rock m r near zero for mixing eruptions v max ranges up to 1150 m s all observed eruption velocities are less than 400 m s largely because 1 most solid material is expelled when m r is high hence v max is low 2 observations are made of large blocks the velocities of which may be less than the average for the mixture 3 heat from solid particles is not efficiently transferred to the fluid during the eruptions and 4 maximum velocities are reduced by choked flow or friction in the conduit