role of permeability and storage in the initiation and propagation of natural hydraulic fractures 1 joint sets within sedimentary basins are commonly interpreted to have formed by tensile failure in conditions where pore fluid pressure was elevated such tensile fractures are inferred to be a part of the process that relieves high fluid pressure by locally increasing rock permeability in spite of the importance of this feedback mechanism the detailed mechanics of hydraulic fracture genesis remain poorly understood we describe the results of both experimental and numerical studies of hydraulic fracture genesis on the basis of an experimental protocol that combines rock extension with elevated pore fluid pressure such that the hydraulic fracture criterion is met in the sample interior this is achieved by simultaneously dropping both minimum stress and external pore fluid pressure inducing a large fluid pressure drop between the sample interior and its ends poroelastic modeling suggests that the pore fluid pressure is highest close to but not at the sample ends and is locally maintained at levels that meet the hydraulic fracture criterion for up to 50 s application of this experimental protocol to an impure sample of sandstone resulted in the generation of several hydraulic fractures subparallel to the maximum principal stress fracturing did not occur in a drained test on the same sample demonstrating that the elevated pore fluid pressure was critical to fracture formation to better understand the experimental results we explore the role of rock permeability and storage on fracture processes using a numerical model that directly couples a lattice boltzmann model for fluid mechanics with a discrete element model for solid mechanics like the experiment the numerical simulations produced opening mode fractures when operated to replicate the conditions of the experiment fractures preferentially occur in portions of the model inferred to be mechanically weak local fluid pressure gradients strongly influence the state of stress in the solids and thereby fracture growth increasing the model permeability increases fracture propagation rate decreases sample deformation and increases fracture spacing sample deformation increases and fracture spacing decreases with increasing overpressure it appears that bulk forcing of the solid via fluid seepage forces is important in fracture genesis explaining the key roles of permeability and diffusivity in the hydrofracture process

evidence for li rich brines and early magmatic fluid rock interactionin the larderello geothermal system abstract the geochemical features of fluids accompanying the first stages of geothermal activity linked to magmatic intrusions have been documented for the larderello geothermal system italy deep drilling has provided samples which preserve evidence of this early geothermal activity four wells san pompeo 2 monteverdi 7 sasso 22 and serrazzano vc 11 penetrated the deeper parts of the larderello system located in a metamorphic basement underlying the tertiary nappe complex which constitutes the main aquifer at larderello the drill holes terminated close to the inferred roof of a granitic complex thought to be responsible for geothermal activity fluid inclusion data were obtained from recrystallized quartz lenses and quartz veins in samples displaying high temperature assemblages plagioclase actinolite biotite tourmaline clinopyroxene andradite wollastonite and also from magmatic quartz in a leucogranite dike the inclusions are mainly secondary in origin oriented in fluid inclusion planes fip related to hydrothermal circulation in the larderello system several generations of high temperature fluids were trapped and include 1 1 h2o co2 dominated vapors displaying variable but significant contents of ch4 and n2 2 2 aqueous vapors containing licl with variable salinity 3 3 aqueous licl brine often oversaturated with respect to halite at room temperature 4 4 complex brine always oversaturated at room temperature with respect to two halite and sylvite or more n 4 salts the presence of licl was confirmed by identification of the salt hydrate licl 5h2o at very low temperature using raman spectroscopy bulk salinities could be roughly estimated at around 30 wt eq licl for the licl brine geometric and chronologic relationships between fip reveal close relationships and mutual contamination between the h2o co2 vapors and licl brine indicating synchronism in their trapping these fluids were generated and trapped at pressures of 100 130 mpa nearly 23 mpa above the estimated present day lithostatic pressure this implies a denudation rate between 0 2 and 0 5 mrn a 1 since the onset of hydrothermal activity compatible with the setting of larderello in a young tortonian collision belt fluid inclusion trapping temperatures 425 650 c show a monotonous increase towards the inferred granite and are around 100 200 c higher than the highest present day temperatures the results are interpreted as recording the interaction between magmatic and contact metamorphic fluids in the early larderello system the h2o co2 vapors resulted from the reheating of the basement metamorphic series often c rich under relatively high temperatures during contact metamorphism lirich fluids expelled from an underlying li rich leucogranite migrated through the metamorphic series and the already cooled granite dikes and experienced local boiling the fluid inclusion data demonstrate the involvement of magmatic fluids during the initial development of this high energy geothermal field

moment tensor inversions of m 3 earthquakes in the geysers geothermal fields california microearthquakes have come into high public awareness due to being induced by the development and exploitation of enhanced and natural geothermal fields hydrofracturing and co2 sequestration sites characterizing and understanding the faulting process of induced earthquakes which is generally achieved through moment tensor inversion could both help in risk prediction and in reservoir development monitoring however this is a challenging task because of their lower signal to noise ratio at frequencies typically used in earthquake source analyses therefore higher resolution velocity models and modeling of seismic waves at higher frequencies are required in this study we examine both the potentials to obtain moment tensor solutions for small earthquakes and the uncertainty of those solutions we utilize a short period seismic network located in the geysers geothermal field in northern california and limit our study to that which would be achieved by industry in a typical reservoir environment we obtain full moment tensor solutions of m 3 earthquakes using waveform modeling and first motion inversions we find that these two data sets give complimentary but yet different solutions some earthquakes correspond possibly to complex processes in which both shear and tensile failures occur simultaneously or sequentially this illuminates the presence of fluids at depth and their role for the generation of these small magnitude earthquakes finally since first motions are routinely obtained for all magnitude earthquakes our approach could be extended to small earthquakes where noise level and complex green s functions prohibit using waveforms in moment tensor inversions

multiple steady states in exchange flows across faults and the dissolution of co2 this is the author accepted manuscript the final version is available from cup via http journals cambridge org download php file 2fflm 2fflm769 2fs0022112015001007a pdf code 58f6f56d3a1302266ca4bcf617ba24df

el nino as a mediator of the solar influence on climate 1 using a climate model of intermediate complexity we simulate the response of the el nino southern oscillation enso system to solar and orbital forcing over the holocene solar forcing is reconstructed from radiocarbon production rate data using various scaling factors to account for the conflicting estimates of solar irradiance variability as estimates of the difference since the maunder minimum range from 0 05 to 0 5 of the solar constant we consider these two extreme scenarios along with the intermediate case of 0 2 we show that for large or moderate forcings the low pass filtered east west sea surface temperature gradient along the equator responds almost linearly to irradiance forcing with a short phase lag about a decade wavelet analysis shows a statistically significant enhancement of the century to millennial scale enso variability for even a moderate irradiance forcing in contrast the 0 05 case displays no such enhancement orbitally driven insolation forcing is found to produce a long term increase of enso variability from the early holocene onward in accordance with previous findings when both forcings are combined the superposition is approximately linear in the strong scaling case overall the sea surface temperature response is of the magnitude required and is persistent enough to induce important climatic perturbations worldwide the results suggest that enso may plausibly have acted as a mediator between the sun and the earth s climate a comparison to key holocene climate records from the northern hemisphere subtropics and midlatitudes shows support for this hypothesis

annual cycle of subsurface thermal structure in the tropical atlantic ocean abstract the subsurface thermal structure in the tropical atlantic ocean 30 n 20 s east of 80 w is studied on the basis of an extensive data bank of subsurface soundings calendar monthly maps are presented showing mixed layer depth base of thermocline thermocline thickness and vertical temperature gradient across the thermocline these maps are complemented by vertical cross sections depicting mixed layer depth base of thermocline and selected isotherms a zonal profile along the equator 50 w 10 e a meridional transect across the eastern atlantic 4 n 18 s and a meridional section across the central atlantic 30 n 18 s the basinwide subsurface thermal structure is dominated by the annual cycle of the surface wind field with extrema around april and august the mixed layer is relatively shallow between 20 n and 10 s with overall grater depth in the western as compared to the eastern portion of the basin two systems of annual cycle variation of mixed layer depth stand out i along the eq

variations on the concentration of 222rn in the subsurface of the volcanic island of tenerife canary islands 1 a simple theoretical model based on the assumption that radon is transported by molecular diffusion combined with advective flow induced by barometric pressure is used to investigate radon exhalation at three subsurface monitoring sites in the volcanic island of tenerife canary islands the model is intended to filter out all known contributions to radon flux in an attempt to find potential precursory signals of seismic and or volcanic activity for the period of observations 1 december 2000 to 1 april 2001 variations on radon concentration predicted by the model were in good agreement with those measured confirming they were induced by atmospheric pressure changes

thermal inertia and reversing buoyancy in flow in porous media 1 the displacement of fluids through porous rocks is fundamental for the recharge of geothermal and hydrocarbon reservoirs grant et al 1982 lake 1989 for contaminant dispersal through the groundwater bear 1972 and in controlling mineral reactions in permeable rocks phillips 1991 in many cases the buoyancy force associated with density differences between the formation fluid and the displacing fluid controls the rate and pattern of flow through the permeable rock phillips 1991 barenblatt 1996 turcotte and schubert 2002 here using new laboratory experiments we establish that a striking range of different flow patterns may develop depending on whether this density contrast is associated with differences in temperature and or composition between the two fluids owing to the effects of thermal inertia in a porous rock thermal fronts lag behind compositional fronts woods and fitzgerald 1993 turcotte and schubert 2002 so that two zones of different density develop in the region flooded with injected fluid this can lead to increasing decreasing or even reversing buoyancy in the injected liquid in the latter case it may then form a double flood front spreading along both the upper and lower boundary of the rock recognition of these different flow regimes is key for predicting sweep efficiency and dispersal patterns in natural and engineered flows and offers new opportunities for the enhanced recovery of natural resources in porous rocks

gravity currents with residual trapping motivated by geological carbon dioxide co 2 storage we present a vertical equilibrium sharp interface model for the migration of immiscible gravity currents with constant residual trapping in a two dimensional confined aquifer the residual acts as a loss term that reduces the current volume continuously in the limit of a horizontal aquifer the interface shape is self similar at early and at late times the spreading of the current and the decay of its volume are governed by power laws at early times the exponent of the scaling law is independent of the residual but at late times it decreases with increasing loss owing to the self similar nature of the current the volume does not become zero and the current continues to spread in the hyperbolic limit the leading edge of the current is given by a rarefaction and the trailing edge by a shock in the presence of residual trapping the current volume is reduced to zero in finite time expressions for the up dip migration distance and the final migration time are obtained comparison with numerical results shows that the hyperbolic limit is a good approximation for currents with large mobility ratios even far from the hyperbolic limit in gently sloping aquifers the current evolution is divided into an initial near parabolic stage with power law decrease of volume and a later near hyperbolic stage characterized by a rapid decay of the plume volume our results suggest that the efficient residual trapping in dipping aquifers may allow co 2 storage in aquifers lacking structural closure if co 2 is injected far enough from the outcrop of the aquifer

fluid inclusion gas compositions from an active magmatic hydrothermal system a case study of the geysers geothermal field usa abstract hydrothermal alteration and the active vapor dominated geothermal system at the geysers ca are related to a composite hypabyssal granitic pluton emplaced beneath the field 1 1 to 1 2 million years ago deep drill holes provide a complete transect across the thermal system and samples of the modern day steam the hydrothermal system was liquid dominated prior to formation of the modern vapor dominated regime at 0 25 to 0 28 ma maximum temperatures and salinities ranged from 440 c and 44 wt nacl equivalent in the biotite hornfels adjacent to the pluton to 305 c and 5 wt nacl equivalent at distances of 1730 m from the intrusive contact the major minor and noble gas compositions of fluid inclusions in the hydrothermally altered rocks were integrated with microthermometric and mineralogic data to determine their sources and the effects of mixing and boiling major and minor gaseous species were released from the inclusions by crushing or thermal decrepitation noble gases were released by crushing the samples were analyzed by mass spectrometry the analyses document the presence of magmatic crustal and meteoric components in the trapped fluids hydrothermal fluids present during the liquid dominated phase of the system contained gaseous species derived mainly from crustal and magmatic sources at the geysers n 2 ar ratios greater than 525 and 3 he 4 he ratios of 6 10 7 ra are diagnostic of a magmatic component crustal gas has co 2 ch 4 ratios less than 4 n 2 ar ratios between 45 and 525 and low 3 he 4 he ratios 0 5 ra meteoric fluids have co 2 ch 4 ratios greater than 4 and n 2 ar ratios between 38 air saturated water and 84 air however n 2 ar ratios between 15 and 110 can result from boiling ratios less than 15 reflect the incorporation of n 2 into nh 3 bearing clay minerals in the central geysers the incursion of meteoric fluids occurred during the transition from the liquid to vapor dominated regime variations in the relative ch 4 co 2 and h 2 contents of the gas analyses demonstrate that boiling took place under open system conditions the gas data indicate that the inclusions have remained closed to the diffusion of he and h 2 since their formation

near lithostatic pore pressure at seismogenic depths a thermoporoelastic model summary a model is presented for pore pressure migration through a transition layer separating a meteoric aquifer at hydrostatic pressure from a deeper reservoir at lithostatic pressure this configuration is thought to be pertinent to the south iceland seismic zone sisz and to other tectonically active regions of recent volcanism where volatiles are continuously released by ascending magma below the brittle ductile transition poroelastic parameters are computed for basaltic rock the model is 1 d the fluid viscosity is temperature dependent and rock permeability is assumed to be pressure dependent according to a dislocation model of a fractured medium environment conditions are considered pertinent to basalt saturated with water at shallow depth case i and at mid crustal depth case ii if the intrinsic permeability of the rock is high no significant effects are observed in the pressure field but advective heat transfer shifts the brittle ductile transition to shallower depths if the intrinsic permeability is low the pressure dependent permeability can propagate near lithostatic pore pressures throughout most of the transition layer while the temperature is practically unaffected by advective contributions so that the rock in the transition layer remains in brittle condition geometrical parameters characterizing the fracture distribution are important in determining the effective permeability in particular if an interconnected system of fractures develops within the transition layer the effective permeability may increase by several orders of magnitude and near lithostatic pore pressure propagates upwards these modelling results have important bearings on our understanding of seismogenic processes in geothermal areas and are consistent with several geophysical observations in the sisz in connection with the two 2000 june m 6 5 earthquakes including i fluid pressure pulses in deep wells ii low resistivity at the base of the seismogenic layer iii low vp vs ratio and time dependent seismic tomography iv heterogeneity of focal mechanisms v shear wave splitting vi high b value of deep foreshocks vii triggered seismicity and viii radon anomalies

stable isotope studies of rocks and secondary minerals in a vapor dominated hydrothermal system at the geysers sonoma county california the geysers a vapor dominated hydrothermal system is developed in host rock of the franciscan formation which contains veins of quartz and calcite whose 18 o values record the temperatures and isotopic compositions of fluids prevailing during at least two different episodes of rock fluid interaction the first episode took place at about 200 c during which marine silica and carbonate apparently interacted with ocean water entrapped in the sediments to form veins of quartz and calcite whose 18 o values were around 19 and 16 respectively the calculated water mineral ratios were less than unity the water may have profoundly influenced the 18 o values of spilitic basalts during their metamorphism to greenstones serpentinization and structural emplacement of ophiolite slabs were isotopically unrelated to this episode which was essentially a low grade post cretaceous burial metamorphism d h ratios of actinolite chlorite and micas in host rocks were more profoundly altered during this episode than were 18 o 16 o ratios a paleogeothermal gradient of about 53 c km has been inferred for this episode from 18 o depth distributions of vein minerals the second episode in part recorded by cogenetic vein quartz and calcite 18 o values of 4 to 6 and 1 to 3 respectively began with large quantities of meteoric water circulating in fractures in the rock at temperatures of 160 180 c in response to the initiation of the pliocene pleistocene clear lake magmatism the temperature rose and with the restricted circulation of fluids the ancestral hot water system evolved into the presently active vapor dominated system which according to the cogenetic vein quartz and calcite 18 o values involved temperatures as high as 320 c and fluid mineral ratios near unity the change in the oxygen isotopic composition of the serpentinite within the host rock during this later activity was negligible the 13 c values of vein calcite at the geysers reflect both a marine carbonate and organic component of carbon but carbon isotope exchange has been facilitated by the vapor dominated hydrothermal fluid to a greater degree than in any other episode or in other hot water systems

geothermal energy release at the solfatara of pozzuoli phlegraean fields phreatic and phreatomagmatic explosion risk implications the h2o co2 and h2s outputs at the solfatara of pozzuoli have been measured and a map of the exhaling areas has also been made the energy released at the surface by the fluids has been estimated to be 1019 ergs day

an advective reflective conceptual model for the oscillatory nature of the enso recent findings about zonal displacements of the pacific warm pool required a notable modification of the delayed action oscillator theory the current leading theory for the el nino southern oscillation enso simulations with a linearized coupled ocean atmosphere model resulted in 3 to 6 year enso like oscillations with many of the variable model parameters found to be very close to their observed values this simple model suggests that ocean processes that are ignored or underestimated in the delayed action oscillator theory such as zonal current convergence zonal advection of sea surface temperature and equatorial wave reflection from the eastern ocean boundary are fundamental to the development of the enso in particular to its manifestations in the central equatorial pacific

oxygen isotope systematics in an evolving geothermal system coso hot springs california abstract oxygen isotope and clay mineralogy studies have been made on whole rock samples and feldspar separates from three wells along the high temperature west flank of the coso geothermal system california the reservoir rocks have experienced variable 18o 16o depletion with 18o values ranging from primary values of 7 5 down to 4 6 spatial patterns of clay mineral distributions in the three wells are not closely correlated with the distributions expected from measured pre production temperature profiles but do correlate with spatial patterns of 18o 16o depletion indicating that the stability of clay minerals in the three wells is a function of fluid rock interaction in addition to temperature detailed 18o measurements in the three wells identify a limited number of localized intervals of extensive 18o 16o depletion these intervals document localized zones of higher permeability in the geothermal system that have experienced significant fluid infiltration water rock interaction and oxygen isotopic exchange with the geothermal fluids the local zones of maximum 18o 16o depletion in each well correspond closely with current hot water production zones most feldspar separates have measured 18o values too high to have completely attained oxygen isotope exchange equilibrium with the reservoir fluid at pre production temperatures in general the lower the 18o value of the feldspar the closer the feldspar approaches exchange equilibrium with the geothermal fluid this correlation suggests that fracture induced increases in permeability increase both fluid infiltration and the surface area of the host rock exposed to geothermal fluid promoting fluid rock interaction and oxygen isotope exchange the two most 18o 16o depleted feldspar samples have 18o values too low to be in exchange equilibrium with the pre production reservoir fluid at pre production temperatures these discrepancies suggest that the reservoir fluid in the west flank of the coso geothermal system was hotter and or had a lower 18o value due to fluid rock interaction at higher permeability in the past

hot fluid migration in compressible saturated porous media summary solutions for heat and pressure transfer in compressible thermoporoelastic fluid saturated media are presented a hot and pressurized fluid reservoir is envisaged which comes into contact with a cold saturated half space the boundary between them is either pervious or impervious in the 1 d problem two coupled non linear equations are obtained for the temperature and pressure fields which are solved employing the self similarity method the thermally induced pressure in the half space is found to be generally relevant for low intermediate permeability media in the pervious boundary problem the thermal interaction gives rise to a striking effect in low permeability materials the induced pressure increases away from the boundary up to a maximum before declining to vanishingly small values further away a backflow is driven by the reverse pressure gradient from the point of maximum towards the reservoir the same effect is present although to a lesser extent in intermediate permeability materials saturated with liquid water under low boundary pressures in the impervious boundary problem the thermally induced pressure is relevant even for high permeability media the temperature field is affected by fluid flow only in the pervious boundary problem for high permeability media saturated with low viscosity fluids subjected to high overpressure over the boundary the conductive approximation which is obtained after neglecting the advection and the dissipation terms in the heat transfer equation is found to be applicable even to high permeability rocks under the impervious boundary conditions even if the previous conclusions are not strictly applicable to problems with different geometries the present solutions seem to bear important consequences on fluid migration mechanisms in volcanic areas where the backflow identified in low permeability media seems to be a viable mechanism for water enrichment by magma ascending through a dyke or emplaced in a magma chamber surrounded by colder water saturated low permeability rocks pore pressure and temperature can be also very effective in providing rock deformation depending on the rock type and boundary conditions either the pore pressure contribution or the thermal contribution may be dominant inflation episodes which are often observed in volcanic areas can be interpreted in a similar way thermoporoelastic effects might also be relevant in fault regions after the sudden frictional heating of water embedded between fault surfaces the theory may be also applied e g mc tigue 1986 to the modelling of areas of nuclear waste disposal

controls on the dissolution of co2 plumes in structural traps in deep saline aquifers 1 sequestration of carbon dioxide in deep saline aquifers has been proposed and investigated as a viable solution to help mitigate carbon emissions from fossil fuels much research has been directed at understanding the transitions of supercritical co2 from being a mobile fluid phase to being trapped by capillarity or dissolved in groundwater such transitions lead to a reduction in mobility of co2 and hence in the risk of leakage to the surface following injection buoyant plumes of co2 migrate updip towards structural traps in the geological strata however some of this co2 may be capillary trapped in pore spaces or dissolved in groundwater en route since co2 saturated groundwater only has a small co2 concentration the dissolution of any large structurally trapped plumes of co2 may be controlled by the availability of unsaturated groundwater in an aquifer of finite vertical extent this may be rate limited by a combination of i the background hydrological flow coupled with ii the slow lateral exchange of relatively dense co2saturated groundwater with unsaturated groundwater in an inclined aquifer this may be controlled by the slow along aquifer component of gravity structurally trapped plumes of co2 may therefore persist for many thousands of years and since they are potentially highly mobile may represent an important contribution to the long term risks associated with co2 sequestration at particular sites

fracturing processes due to temperature and pressure nonlinear waves propagating in fluid saturated porous rocks a model is proposed of rock deformation fracturing in the subsurface of hydrothermal systems in response to deep fluid rock temperature and pore fluid pressure perturbations carried upward by hot and pressurized fluid fronts since during these episodes of unrest one also has to take into account that rock parameters can evolve a model of fluid diffusivity change as a function of pore fluid pressure is described through reformulating the linear thermoporoelastic equations rock deformation fracturing is thus thought of as being associated with migration of thermomechanical nonlinear waves which travel upward associated with an increase in concurrent fluid diffusivity on dynamical grounds it is assumed that on the boundary of the two superimposed horizons the overlying rock suddenly starts rupturing caused by the arrival of supercritical water from below which drives up a pore fluid pressure excess in this connection the purpose of this analysis is to investigate the general evolution of the subsurface pressure and temperature fields assuming that the original signal is itself strong enough to generate fracturing processes of the overburden rock on its arrival a general formulation provides evidence of nonlinear thermal waves compensated waves and residual pressure burgers waves that can be found for every value of the system parameters a mechanical analogy is also presented which is treated analytically and numerically allowing one to gain intuitive insight into such complex phenomena a characteristic of these nonlinear processes is that the resulting timescales of the order of years for the case of the campi flegrei and the izu peninsula can be particularly small corresponding to quick hyperthermal phenomena during the filtrating movement of fluid toward the earth s surface

subsurface propagation of thermomechanical kinks through hydrothermal fluid saturated porous horizons in this paper a one dimensional nonlinear analytical model for the mechanism of subsurface fluid rock coupling dynamics in hydrothermal systems is proposed the model is based upon the modern thermoporoelasticity theory and its two nonlinear heat like equations namely the stress diffusion equation and the fluid rock energy equation on the lower boundary of a subsurface fluid saturated porous horizon a buried thermomechanical source is supposed to build up so that coupled fluid rock temperature and pore fluid pressure changes are generated these changes are thought of as being related to the heaviside step function which is here adopted as the initial condition to be combined with burgers equation obtained in the case of small fluid diffusivity in the stress diffusion equation by using the hopf cole transformation an analytical solution corresponding to a solitary wave such as a thermomechanical kink is found that propagates upward through the fluid saturated thermoelastically reactive porous horizon thus supplying changes in the thermomechanical properties of the fluid emissions as the wave approaches the ground surface some cases of episodes of unrest are considered for some hydrothermal systems showing the agreement between our theoretical curves of fluid surface signals and the enhanced activity in the fluid emissions in this connection the upsurge of thermomechanical solitary shock waves such as kinks can be used as an indicator of thermal energy buildup and approaching mechanical destabilization at depth in both volcanic and geothermal systems

genesis of mud volcanoes in sedimentary basins a solitary wave based mechanism 1 mud volcanoes represent the ground surface morphological expression of highly focused fluid flow inside sedimentary basins sedimentary basins show usually the presence of overpressured compartments encapsulated by low permeability bounds seals which can have different origins capillary barriers with high entry capillary pressure diagenetically sealed formations a mud volcano can be formed in response to the hydrofracturation of such a permeability barrier when introducing the pressure dependence of permeability in poroelasticity the theory predicts the upsurge of fluid pressure fronts after the hydrofracturation of the seal initial shock these fronts take the form of hydro mechanical non linear shock waves which are solutions of a burgers type equation these solitary waves are associated with an upsurge of pore water which depends on the pore fluid pressure gradient carried up with the waves the arrival of these waves at the ground surface can generate mud volcanoes type features with spots of highly focused flow

the volcano electric effect 1 the formation of a magmatic intrusion at depth is responsible for the formation of various thermohydromechanical thm disturbances including the upsurge of shock waves and diffusion of pressure fronts in the volcanic system we couple electromagnetic theory maxwell equations and thermoporoelasticity biot equations to look at the ground surface electrical signature of these thm disturbances the nature of this coupling is electrokinetic i e associated with water flow relative to the mineral framework and the drag of the excess of charge located in the vicinity of the pore water mineral interface the groundwater flow disturbance being related here to the thm disturbances in drained conditions a new set of laboratory data shows that the electrokinetic coupling is very substantial in fractured basaltic and volcaniclastic materials and in scoria with several hundreds of millivolts of electrical potential gradient produced per megapascal of pore fluid pressure variations our theoretical analysis predicts the diffusion of electromagnetic disturbances and quasi static electrical signals these signals can be used as precursors of a volcanic eruption indeed electromagnetic phenomena recorded at the ground surface of a volcanic system once properly filtered to remove external contributions provide a direct and quasi instantaneous insight into the thm disturbances occurring in the heart of the volcanic structure prior and during a volcanic event tomography of the quasi static electrical field is discussed and applied to self potential profiles performed at the piton de la fournaise volcano during the preparation phase of the march 1998 eruption

pore scale simulation of density driven convection in fractured porous media during geological co2 sequestration 1 global warming is attributed to the excessive emission of greenhouse gases one of whose main components is carbon dioxide co2 a promising long term solution for mitigating global warming is geological co2 sequestration which is the capture and storage of enormous amounts of co2 in underground reservoirs in order to reduce co2 build up in the atmosphere in this study a pore scale lattice boltzmann method was used to simulate density driven convection in a porous medium with a fracture to study geological co2 sequestration in deep saline aquifers the co2 brine interface was located at the top of the domain both fracture width and body force were varied to generate different ra numbers in order to investigate the effect of ra on the convection all simulated data can be fitted by the same trend implying that the characteristic length of the system was dominated by the fracture width when ra was high enough increasing ra did not reduce the critical time for the onset of instability apparently also it did not increase the maximum peak vertical velocity noticeably therefore there existed asymptotic values for the critical time and maximum peak vertical velocity with high ra numbers the high frequency oscillation of turbulence greatly enhanced the dissolution of co2 into brine after the onset of convective instability the brine with a high co2 concentration intruded into the underlying unaffected brine which increased the interfacial area between the co2 rich brine and unaffected brine and consequently favored the migration of co2 into the fracture and porous medium this study is the first pore scale one investigating density driven convection during geological co2 sequestration in deep saline aquifers whereas most existing research is focused on the field scale and the dissolved co2 concentration at the top boundary is usually assumed to be saturated

the 2002 2003 eruption of stromboli italy evaluation of the volcanic activity by means of continuous monitoring of soil temperature co2 flux and meteorological parameters 1 from december 2002 to july 2003 stromboli volcano was characterized by a new effusive stage of eruption after a period of extraordinary strombolian activity signals recorded in two continuous monitoring stations during the eruption which have already been presented in very recent papers evidenced anomalies in the co2 flux just before the onset of the eruption a more detailed analysis carried out on the data subset acquired during the eruption integrated by daily field observations of the scientific personnel working at the volcanological observatory in stromboli showed that co2 flux and soil temperature are strictly related to volcanic events furthermore the relative minima and maxima of the two parameters showed a strong correlation with wind speed and direction this fact was especially true at the summit station whereas at the coastal sites seasonal and meteorological effects masked the volcanic signal the analysis of the wind data particularly the relationships between wind speed and direction air and soil temperature and local circulation of atmospheric air masses revealed that during the eruption in the summit area of stromboli air movements were not only related to atmospheric circulation but were also significantly affected and in certain cases caused by volcanic activity this conclusion was reached by observing several anomalies such as the discrepancies in the wind direction between the two stations higher air temperatures at the summit site and inversion of direction for wind before and after the reopening of the conduit in a major explosion on 5 april 2003 the relationships found between volcanic activity soil temperatures co2 fluxes and wind speed and direction indicate that soil temperature measurements in an open conduit volcano such as in this case could be used to monitor the level of volcanic activity along with co2 flux furthermore the possible volcanic origin of a peculiar type of air circulation identified in the summit area of stromboli suggests that the separation between volcanic and atmospheric signals might not be obvious requiring monitoring over a wide area rather than a single location

effects of permeability and porosity evolution on simulated earthquakes numerical simulations are a fundamental tool to access the typical conditions attained during earthquake instabilities and to simulate the large number of dissipative processes taking places during faulting in this study we consider a single degree of freedom spring slider system a simplified fault model which can describe the whole seismic cycle and the dynamics of a fault with spatially homogeneous properties we assume a rate and state dependent friction in which we incorporate the effects of pore fluid pressure thermally pressurized as a consequence of the frictional heat produced during sliding we explore in a single framework the role of the time variations of the porosity permeability or both ultimately leading to changes in hydraulic diffusivity which has been recognized as one of the key parameters in thermally pressurized faults our synthetic ruptures show that the changes in the hydraulic diffusivity only due to porosity variations do not markedly affect the earthquake recurrence cycle time the traction evolution and the thermal history of the fault on the contrary when the evolutions of both the porosity and the permeability are accounted for the cycle time is significantly reduced this result has a clear implication in the context of the hazard assessment

mechanism for joint saturation in mechanically layered rocks an example from southern israel abstract over 700 joint spacings were measured along a 190 m scanline within a single limestone bed of the turonian gerofit formation southern israel by investigating joints belonging to a single systematic set confined to a bed of uniform thickness one can factor out the major influences of bed thickness lithology and mechanical properties on joint set development joint spacing distributions and fracture spacing ratios fsr vary dramatically along the length of the scanline and correlate directly with throughgoing fracture zones belonging to the same tectonic stress regime regions cross cut by fracture zones display narrower median joint spacings fsr of 1 3 and unimodal joint spacing distributions where fracture zones are absent joint spacings have wider medians fsr of 0 8 and multimodal distributions because fracture zones most likely represent areas of high strain and laboratory experiments demonstrate a systematic decrease in fracture spacing with increasing strain regions of the bed cross cut by fracture zones are likely at a more advanced stage of joint set development and hence closer to saturation than other regions joint saturation in the gerofit formation may be achieved by a shift in scale from single layer to multi layer jointing as the development of throughgoing joints prevents the formation of additional bedding confined joints

particles in fluid inclusions from yellowstone national park bacteria micrometre sized particles resembling microorganisms have been found in liquid rich fluid inclusions in hydrothermal quartz crystals from a research drill hole in yellowstone national park wyoming the particles are moving apparently in brownian motion the 1 2 mm long quartz crystals were obtained from fractures in late pleistocene rhyolite at depths of 59 5 102 1 and 102 5 m the measured temperature and pressure at 102 1 m where about 99 of the moving particles were found were about 190 c and 1 24 mpa respectively homogenization temperatures 190 280 c of fluid inclusions at this depth mostly exceed measured temperatures which suggests that the fluid inclusions probably did not form under present day conditions instead the fluid inclusions probably formed 45 000 14 000 b p at a much higher pressure owing to the weight of at least 490 m of glacial ice only 3 of the more than 200 quartz crystals examined contain up to several hundred rodlike threadlike or irregular shaped moving particles fluid inclusions in 17 other quartz crystals each contain one or two moving particles that were observed only because of their continuous brownian motion

episodic fluid expulsion from geopressured sediments numerical simulation of fluid explusion from geopressured sediments using a one dimensional finite difference model shows that large volumes of fluid can be transported through a fractured seal during short lived 100 year expulsion events in this model abnormal fluid pressures are maintained by an impermeable seal when the fluid pressure exceeds 85 of the lithostatic pressure a vertical fracture opens in the seal providing a permeable pathway from the geopressured sediments into the overlying section fluid pressure in the seal decreases as fluid flows through the fracture closing the fracture as sediments in the seal compact once the fracture closes the seal remains impermeable until fluid flowing from deeper in the section increases fluid pressure to the fracture criteria a process that takes 10 000 500 000 years fractures emplaced in relatively incompressible seals such as compacted and or cemented sediments remain open for 20 50 years fluid fluxes through the seal integrated over the life of these events are 1 5 107 kg m2 and temperatures in the overlying sediments are increased by 5 20 c these temperature anomalies decay to less than half their original value in 300 years suggesting that the thermal anomalies observed in wells that are attributed to fluid expulsion formed in response to a very recent or currently active event

fluid mineral equilibria in a hydrothermal system roosevelt hot springs utah the availability of fluids and drill cuttings from the active hydrothermal system at roosevelt hot springs allows a quantitative comparison between the observed and predicted alteration mineralogy calculated from fluid mineral equilibria relationships comparison of all wells and springs in the thermal area indicates a common reservoir source and geothermometer calculations predict its temperature to be higher 288 c 10 than the maximum measured temperature of 268 c the composition of the deep reservoir fluid was estimated from surface well samples allowing for steam loss gas release mineral precipitation and ground water mixing in the well bore this deep fluid is sodium chloride in character with approximately 9700 ppm dissolved solids a ph of 6 0 and gas partial pressures of o2 ranging from 10 32 to 10 35 atm co2 of 11 atm h2s of 0 020 atm and ch4 of 0 001 atm comparison of the alteration mineralogy from producing and nonproducing wells allowed delineation of an alteration pattern characteristic of the reservoir rock theoretical alteration mineral assemblages in equilibrium with the deep reservoir fluid between 150 and 300 c in the system na2o k2o cao mgo feo fe2o3 al2o3 h4sio4 h2o h2s co2 hcl were calculated minerals theoretically in equilibrium with the calculated reservoir fluid at 240 c include sericite k feldspar quartz chalcedony hematite magnetite and pyrite this assemblage corresponds with observed higher temperature 210 c alteration assemblage in the deeper parts of the producing wells the presence of montmorillonite and mixed layer clays with the above assemblage observed at temperatures 210 c corresponds with minerals predicted to be in equilibrium with the fluid below 240 c alteration minerals present in the reservoir rock that do not exhibit equilibrium with respect to the reservoir fluid include epidote anhydrite calcite and chlorite these may be products of an earlier hydrothermal event or processes such as boiling and mixing or a result of errors in the equilibrium calculations as a result of inadequate thermochemical data

local coupled equatorial variability versus remote enso forcing in an intermediate coupled model of the tropical atlantic the relative roles played by the remote el nino southern oscillation enso forcing and the local air sea interactions in the tropical atlantic are investigated using an intermediate coupled model icm of the tropical atlantic the oceanic component of the icm consists of a six baroclinic mode ocean model and a simple mixed layer model that has been validated from observations the atmospheric component is a global atmospheric general circulation model developed at the university of california los angeles ucla in a forced context the icm realistically simulates both the sea surface temperature anomaly ssta variability in the equatorial band and the relaxation of the atlantic northeast trade winds and the intensification of the equatorial westerlies in boreal spring that usually follows an el nino event the results of coupled experiments with or without pacific enso forcing and with or without explicit air sea interactions in the equatorial atlantic indicate that the background energy in the equatorial atlantic is provided by enso however the time scale of the variability and the magnitude of some peculiar events cannot be explained solely by enso remote forcing it is demonstrated that the peak of ssta variability in the 1 3 yr band as observed in the equatorial atlantic is due to the local air sea interactions and is not a linear response to enso seasonal phase locking in boreal summer is also the result of the local coupling the analysis of the intrinsic sustainable modes indicates that the atlantic el nino is qualitatively a noisedriven stable system such a system can produce coherent interdecadal variability that is not forced by the pacific or extraequatorial variability it is shown that when a simple slab mixed layer model is embedded into the system to simulate the northern tropical atlantic nta sst variability the warming over nta following el nino events have characteristics location and peak phase that depend on air sea interaction in the equatorial atlantic in the model the interaction between the equatorial mode and nta can produce a dipolelike structure of the ssta variability that evolves at a decadal time scale the results herein illustrate the complexity of the tropical atlantic ocean atmosphere system whose predictability jointly depends on enso and the connections between the atlantic modes of variability

micromechanical modeling of cracking and failure in brittle rocks dynamic micromechanical models are used to analyze crack nucleation and propagation in brittle rock models of rock are created by bonding together thousands of individual particles at points of contact the feasibility of using these bonded particle models to reproduce rock mechanical behavior is explored by comparing model behavior to results from actual laboratory tests on different rock types the behavior of two granite models are examined in detail to study cracking and failure patterns that occur during compressional loading because discontinuum models are being used the rock models are free to crack and break apart under stress such that the micromechanics of cracking can be examined stress waves are allowed to propagate outward from each crack and it is shown that these dynamic waves significantly affect the rock behavior as the peak stress in the modeled rock is approached and many of the bonds are close to breaking a passing wave from a nearby crack is sufficient to break more bonds this causes clusters of cracks to be created and then eventual macroscopic shear failure occurs as these clusters connect to bisect the sample the failure patterns observed in the granite models are similar to those observed in actual laboratory tests

the near surface equatorial indian ocean in 1979 part i linear dynamics different wind field analyses are used to force a one layer adiabatic model of the near equ torial surface circulation in the indian ocean in 1979 the model simulates the major features of the obse atlons ea tward jets were present in april may and in october november in the central indian ocea n in phase with the local winds the seasonal changes of thermocline depth in the western part of the basin are related to the near equatorial currents significant discrepancies are also found some are due to the uncertainty in the wind fiel ds correlation between different wind fields are only of the order of 0 75 for the low frequencies and mag ltud s can vary by a factor of 1 5 others are attributed fo model inadequacies especially the ne ect of nonhnean y and the oversimplification of the vertical structure ther is an unrealistic energy focus in the central indian ocean though in general seasonal changes are underestimated by at least 30 simpler dynamics failed to produce a reasonable agreement over the whole basin a yoshida jet did well for the currents in the central part of the basin but did not reproduce the mass changes in the west sverdrup equilibrium reproduces the model zonal slope of the thermocline but not the currents

age and thermal history of the geysers plutonic complex felsite unit geysers geothermal field california a 40ar 39ar and u pb study abstract sixty nine ion microprobe spot analyses of zircons from four granite samples from the plutonic complex that underlies the geysers geothermal field yield 207pb 206pb vs 238u 206pb concordia ages ranging from 1 13 0 04 ma to 1 25 0 04 1 ma the weighted mean of the u pb model ages is 1 18 0 03 ma the u pb ages coincide closely with 40ar 39ar age spectrum plateau and terminal ages from coexisting k feldspars and with the eruption ages of overlying volcanic rocks the data indicate that the granite crystallized at 1 18 ma and had cooled below 350 c by 0 9 1 0 ma interpretation of the feldspar 40ar 39ar age data using multi diffusion domain theory indicates that post emplacement rapid cooling was succeeded either by slower cooling from 350 to 300 c between 1 0 and 0 4 ma or transitory reheating to 300 350 c at about 0 4 0 6 ma subsequent rapid cooling to below 260 c between 0 4 and 0 2 ma is in agreement with previous proposals that vapor dominated conditions were initiated within the hydrothermal system at this time heat flow calculations constrained with k feldspar thermal histories and the present elevated regional heat flow anomaly demonstrate that appreciable heat input from sources external to the known geysers plutonic complex is required to maintain the geothermal system this requirement is satisfied by either a large underlying convecting magma chamber now solidified emplaced at 1 2 ma or episodic intrusion of smaller bodies from 1 2 to 0 6 ma

interannual long equatorial waves in the tropical atlantic from a high resolution ocean general circulation model experiment in 1981 2000 we investigate the tropical atlantic vertical structure variability 1981 2000 based on the clipper ocean general circulation model ogcm we aim at determining to what extent the observed interannual variability can be explained by the low frequency wave dynamics the linear vertical modes of the ogcm climatological stratification are estimated along the equator the baroclinic mode contributions to surface zonal current and sea level anomalies are calculated and analyzed at interannual timescales the second baroclinic mode is the most energetic the first third mode exhibits a variability peak in the west east the summed up contribution of the high order baroclinic modes 4 6 is as energetic as the gravest modes and is largest in the east wave components are then derived by projection onto the associated meridional structures the effect of longitudinal boundaries near the equator is taken into consideration equatorial kelvin and rossby waves propagations with phases speed close to the theory are identified for the first three baroclinic modes the comparison with a multimode linear simulation corroborates the propagating properties of the ogcm waves coefficients an estimation of the meridional boundary reflection efficiency indicates that wave reflections take place at both boundaries a 65 reflection efficiency is found at the eastern boundary our study suggests that low frequency wave dynamics is to a large extent at work in the tropical atlantic on the basis of what is known on the pacific el nino southern oscillation mode this may provide a guidance for investigating ocean atmosphere mechanisms that can lead to the atlantic zonal equatorial mode

assimilation of topex sea level measurements with a reduced gravity shallow water model of the tropical pacific ocean sea surface height variability measured by topex is analyzed in the tropical pacific ocean by way of assimilation into a wind driven reduced gravity shallow water model using an approximate kalman filter and smoother the analysis results in an optimal fit of the dynamic model to the observations providing a dynamically consistent interpolation of sea level and estimation of the circulation nearly 80 of the expected signal variance is accounted for by the model within 20 of the equator and estimation uncertainty is substantially reduced by the voluminous observation notable features resolved by the analysis include seasonal changes associated with the north equatorial countercurrent and equatorial kelvin and rossby waves significant discrepancies are also found between the estimate and topex measurements especially near the eastern boundary improvements in the estimate made by the assimilation are validated by comparisons with independent tide gauge and current meter observations the employed filter and smoother are based on approximately computed estimation error covariance matrices utilizing a spatial transformation and an asymptotic approximation the analysis demonstrates the practical utility of a quasi optimal filter and smoother

sensitivity of an intermediate ocean atmosphere coupled model of the tropical pacific to its oceanic vertical structure an intermediate ocean atmosphere coupled model icm of the tropical pacific is used to investigate the sensitivity of the coupled system to the oceanic vertical structure the model consists of a three baroclinicmode tropical pacific ocean and a gill tropical atmosphere the mixed layer is similar to the zebiak and cane zc coupled atmosphere ocean model but uses a different parameterization for subsurface temperature derived from xbt data a 100 yr simulation is made and the long term variability of the icm is briefly discussed and compared with the the observations and the zc model the icm reproduces regular enso events with a spectrum peak centered at the period 3 5 yr the presence of higher order vertical modes in the oceanic component of the model allows for reduced off equatorial variability of zonal current and thermocline anomalies and for finer meridional scale for sst anomaly variability in comparison with a simulation with one baroclinic mode only the nature of the processes sustaining the oscillations in the icm is then investigated based on the coupled instabilities and delayed oscillator theories it

on the propagation of nonlinear transients of temperature and pore pressure in a thin porous boundary layer between two rocks abstract the dynamics of transients of fluid rock temperature pore pressure pollutants in porous rocks are of vivid interest for fundamental problems in hydrological volcanic hydrocarbon systems deep oil drilling this can concern rapid landslides or the fault weakening during coseismic slips and also a new field of research about stability of classical buildings here we analyze the transient evolution of temperature and pressure in a thin boundary layer between two adjacent homogeneous media for various types of rocks in previous models this boundary was often assumed to be a sharp mathematical plane here we consider a non sharp physical boundary between two adjacent rocks where also local steady pore pressure and or temperature fields are present to obtain a more reliable model we also investigate the role of nonlinear effects as convection and fluid rock frictions often disregarded in early models these nonlinear effects in some cases can give remarkable quick and sharp transients all of this implies a novel model whose solutions describe large sharp and quick fronts we also rapidly describe transients moving through a particularly irregular boundary layer

the geysers clear lake area california thermal waters mineralization volcanism and geothermal potential manifestations of a major thermal anomaly in the geysers clear lake area of northern california include the late pliocene to holocene clear lake volcanics the geysers geothermal field abundant thermal springs and epithermal mercury and gold mineralization the epithermal mineralization and thermal springs typically occur along high angle faults within the broad san andreas transform fault system that forms the western boundary of the north american plate in this area the young volcanic rocks overlie mesozoic marine rocks of the great valley sequence which have been thrust above the coeval franciscan complex and penecontemporaneously dropped back down along low angle detachment faults many of the waters of the region are nonmeteoric as defined by their isotopic signature one type of isotopically shifted water emerges from or near great valley sequence rocks and is the most chloride rich it is interpreted to be evolved connate in origin a second type evolved meteoric water has moderate chloride contents high boron contents and high b cl ratios and is found locally in franciscan rocks notably at the sulphur bank mercury mine where it probably results from near closed system repeated boiling of meteoric water in host rocks that also contribute organic components to the water at the sulphur bank mine fracturing of otherwise impermeable franciscan rocks by faulting has created a localized zone of permeability in which thermal water boils repeatedly with limited venting to the surface boron rich fluids were apparently present at depth in the geysers geothermal field when intrusion of silicic magma occurred because the concealed intrusion of felsite is surrounded by a halo of tourmaline bearing hornfels the volume of this poorly dated early to middle quaternary intrusive body probably exceeds the 100 km 3 of erupted clear lake volcanics similar intrusions may have occurred in the eastern part of the area at wilbur springs and the mclaughlin mine where gold deposition and evidence of hydrothermal phenomena suggest more magmatic activity than is indicated by the small exposed bodies of early quaternary basaltic lava the clear lake volcanics are the present locus of volcanism in the northern coast ranges and progressively older volcanic centers occur to the south geophysical data suggest that a large silicic magma body may be centered north of the geysers steam field providing the heat for the geothermal field geothermal power production has peaked at the geysers and pressure declines indicate significant depletion of the fluid resource the vapor dominated field evolved from a preexisting hydrothermal system within fractured otherwise impermeable franciscan metamorphic rocks a deep water table of saline fluid has been postulated to be present under the steam field but no chloride rich water has been found at drillable depth we propose that recently discovered isotopically shifted steam in the northwest geysers area indicates the presence not of deep connate water but xather of boiled down boron rich franciscan evolved meteoric water this water is likely to be present in limited quantities and will not provide a significant hot water resource for geothermal power production at the geysers field or from the main clear lake volcanic field

wind stress variations and interannual sea surface temperature anomalies in the eastern equatorial pacific abstract vertical advection of temperature is the primary mechanism by which el nino southern oscillation enso time scale sea surface temperature sst anomalies are generated in the eastern equatorial pacific variations in vertical advection are mediated primarily by remote wind forced thermocline displacements which control the temperature of water upwelled to the surface however during some enso events large wind stress variations occur in the eastern pacific that in principle should affect local upwelling rates the depth of the thermocline and sst in this study the impact of these wind stress variations on the eastern equatorial pacific is addressed using multiple linear regression analysis and a linear equatorial wave model the regression analysis indicates that a zonal wind stress anomaly of 0 01 n m 2 leads to approximately a 1 c sst anomaly over the nino 3 region 5 n 5 s 90 150 w due to changes in local upwelling rates wind stress variations of this magnitude occurred in the easte

the effect of drainage on the capillary retention of co2 in a layered permeable rock buoyant plumes of co 2 spreading through water saturated permeable rock bounded by layers of lower permeability tend to spread laterally as they advance they may gradually leak through fractures or discontinuities in the lower permeability boundary leading to a gradual waning of the original plume and dispersal of co 2 higher in the formation with a finite release of co 2 the trailing edge of the plume recedes with time and capillary forces tend to trap a fraction of this co 2 within the pore space this also leads to a gradual waning of the plume with time and limits the mass of co 2 which can leak through the boundary and rise higher into the formation we explore the balance between these two effects and calculate some of the controls on the fraction of the co 2 plume which becomes trapped within the original layer of rock

the effect of fluid thermal expansivity on thermo mechanical solitary shock waves in the underground of volcanic domains this work is a further development of the modern thermo poro elasticity theory which has recently been applied to understand how fluid rock coupling dynamics related to unrest episodes in volcanic domains can both determine and occur with ground deformation and rock fracturing processes in particular by reformulating the energy equation one of the two nonlinear heat like equations upon which the thermo poroelasticity theory is based it is shown here how fluid thermal expansivity may influence fluid migration during its movement through subsurface volcanic porous per meable horizons with these new considerations it is found that a recent theory in which fluid rock coupling dynamics is interpreted in terms of thermal and mechanical solitary shock wave propagation remains valid however the natural time scale of the propagating wave is reduced and consequently darcy s velocity is increased as a result of fluid thermal expansivity

the evolution of volcano hosted geothermal systems based on deep wells from karaha telaga bodas indonesia temperature and pressure surveys fluid samples and petrologic analyses of rock samples from deep drill holes at the karaha telaga bodas geothermal field on the volcanic ridge extending northward from galunggung volcano west java have provided a unique opportunity to characterize the evolution of an active volcano hosted geothermal system wells up to 3 km in depth have encountered temperatures as high as 353 c and a weakly altered granodiorite that intruded to within 2 to 3 km of the surface the intrusion is shallowest beneath the southern end of the field where an acid lake overlies a nearly vertical low resistivity structure 10 ohm m defined by magnetotelluric measurements this structure is interpreted to represent a vapor dominated chimney that provides a pathway to the surface for magmatic gases four distinct hydrothermal mineral assemblages document the evolution of the geothermal system and the transition from liquid to vapor dominated conditions the earliest assemblage represents the initial liquid dominated system generated during emplacement of the granodiorite between 5910 76 and 4200 150 y bp tourmaline biotite actinolite epidote and clay minerals were deposited contemporaneously at progressively greater distances from the intrusive contact assemblage 1 at 4200 150 y bp flank collapse and the formation of the volcano s crater kawah galunggung resulted in catastrophic decompression and boiling of the hydrothermal fluids this event initiated development of the modern vapor dominated regime chalcedony and then quartz were deposited as the early low salinity liquids boiled assemblage 2 both vapor and liquid rich fluid inclusions were trapped in the quartz crystals liquid rich fluid inclusions from the southern part of the field record salinities ranging from 0 to 26 weight percent nacl cacl 2 equivalent and locally contain fluorite daughter crystals we suggest based on temperature salinity relationships and evidence of boiling that these fluids were progressively concentrated as steam was lost from the system however mixing with fluids derived from the underlying intrusion or generated during the formation of acid so 4 water on the vapor dominated chimney margins could have contributed to the observed salinities as pressures declined co 2 and so 4 rich steam heated water drained downward depositing anhydrite and calcite assemblage 3 in the fractures limiting further recharge fluid inclusions with salinities up to 31 weight percent nacl equivalent were trapped in these minerals as the descending water vaporized the final assemblage is represented by precipitates of nacl kcl and fecl x deposited on rock surfaces in portions of the vapor dominated zone that boiled dry vapor dominated conditions extend over a distance of at least 10 km and to depths below sea level deep wells drilled into the underlying liquid dominated reservoir in the northern and central part of the volcanic ridge produce low salinity fluids representing recent recharge of meteoric and steam heated water the evolution of volcanic hosted vapor dominated geothermal systems can be described by a five stage model stage 1 involves the formation of an over pressured liquid dominated geothermal system soon after magmatic intrusion in stages 2 and 3 pressures progressively decrease and a curtain of steam heated water surrounding a magmatic vapor dominated chimney at 350 c and 14 2 mpa develops the relatively low pressure near the base of the chimney causes liquid inflow adjacent to the intrusion and the development of a secondary marginal vapor dominated zone in stage 4 the magmatic vapor discharge from the intrusion becomes small vapor pressure declines and the secondary vapor dominated zone expands above the intrusion in stage 5 the vapor dominated zone floods because heat from the intrusion is insufficient to boil all liquid inflow a more common liquid dominated volcanic hosted system then develops

viscous and gravitational contributions to mixing during vertical brine transport in water saturated porous media the transport of fluids miscible with water arises in groundwater contamination and during remediation of the subsurface environment for concentrated salt solutions i e brines the increased density and viscosity determine mixing processes between these fluids and ambient groundwater under downward flow conditions gravitational and viscous forces work against each other to determine the interfacial mixing processes historically mixing has been modeled as a dispersive process as viscous fingering and as a combination of both using approaches that were both analytical and numerical a compilation of previously reported experimental data on vertical miscible displacements by fluids with significant density and viscosity contrasts reveals some agreement with a stability analysis presented by hill 1952 additional experimental data on one dimensional dispersion during downward displacement of concentrated salt solutions by freshwater and freshwater displacement by brines support the stability analysis and provides an empirical representation for dispersion coefficients as functions of a gravity number and a mobility ratio

fluid inclusion and isotopic systematics of an evolving magmatic hydrothermal system the geysers california is the site of a long lived hydrothermal system that initially developed 1 5 2 m y ago in response to the intrusion of a hypabyssal granitic pluton although wells drilled into the geysers produce only dry steam fluid inclusion isotopic and mineralogic data demonstrate that the present vapor dominated regime evolved from an earlier and more extensive liquid dominated hydrothermal system circulation of these early fluids produced veins characterized by tourmaline biotite actinolite clinopyroxene within the pluton and adjacent biotite rich hornfels actinolite ferroaxinite epidote and epidote chlorite within the intermediate parts of the thermal system and calcite in the outer parts potassium feldspar and quartz are present in all assemblages pressure corrected homogenization temperatures and apparent salinities of fluid inclusions trapped in vein minerals range from 440 c and 44 wt nacl equivalent within the hornfels 600 m from the pluton to 325 c and 5 wt nacl equivalent at distances of approximately 1500 m from the intrusion we suggest that the shallow moderate salinity fluids are connate waters modified by water rock interactions while the high salinity fluids are interpreted as magmatic brines halite dissolution temperatures of inclusions in the hornfels and pluton indicate that the magmatic fluids were trapped at lithostatic pressures 300 900 bars in contrast homogenization temperatures of the connate fluids suggest trapping under hydrostatic pressures of less than several hundred bars whole rock 18o values of samples from the geysers display systematic variations with respect to depth location within the field and grade of alteration at depths below 610 m relative to mean sea level the 18o values are strongly zoned around a northwest southeast trending low located near the center of the steam reservoir as the pluton beneath the geysers is approached the 18o values decrease from approximately 14 per mil near the surface to 4 to 7 per mil within the hornfels the 18o values then increase to 8 to 10 per mil at the intrusive contact and thereafter vary little within the pluton calculated rock water fractionation factors suggest that temperature was the dominant control on the vertical decrease in the isotopic values of the reservoir rocks in contrast the increase in the 18o values within the hornfels suggest equilibration with an isotopically heavy fluid and or decreasing water rock ratios the formation of vapor dominated conditions is reflected in the abrupt appearance of low salinity 0 0 0 4 wt nacl equivalent fluid inclusions with homogenization temperatures near 265 c these inclusion fluids are thought to represent steam condensate that formed as the early liquid dominated system boiled off bladed calcite which is corroded in places and late stage clays provide mineralogic evidence of boiling and the formation of an acidic condensate in the upper part of the reservoir and in the overlying caprock at greater depths however clear mineralogic evidence of boiling is lacking the present vapor dominated regime at the geysers consists of two hydraulically connected steam reservoirs within the main steam reservoir pressures are vaporstatic and temperatures are nearly constant at 240 c beneath this reservoir in the northwestern third of the field temperatures as high as 342 c have been encountered wells drilled into this deeper reservoir discharge corrosive cl bearing steam

localization of self potential sources in volcano electric effect with complex continuous wavelet transform and electrical tomography methods for an active volcano 1 this study concerns the fluid flow circulation associated with magmatic intrusion during volcanic eruptions from electrical tomography studies the objective is to localize and characterize the sources responsible for electrical disturbances during a time evolution survey between 1993 and 1999 of an active volcano the piton de la fournaise we have applied a dipolar probability tomography and a multi scale analysis on synthetic and experimental sp data we show the advantage of the complex continuous wavelet transform which allows to obtain directional information from the phase without a priori information on sources in both cases we point out a translation of potential sources through the upper depths during periods preceding a volcanic eruption around specific faults or structural features the set of parameters obtained vertical and horizontal localization multipolar degree and inclination could be taken into account as criteria to define volcanic precursors

a numerical model for low frequency equatorial dynamics a f st efficient numerical procedure for modeling the linear low frequency motions on an equatorial beta plane is develo the model is capable of simulating the seasonal and interannual variability in realistically shaped ocean basins forc d by realistic winds the timestep allowed is the order of days rather than hours as allowed by more conventional schemes the numerical method is designed around the special characteristics f low frequency equato al waves a crucial element is the formulation of proper boundary conditions including those for a partial boundary such as the western end of the gulf of guinea the resp nse of an a i ntic shaped basin to a periodic wind is compared with the analytic results of cane and sarachlk for a mendlonally unbounded ocean the response along the equator is essentially the same narrow boundary layer forms along the guinea coast too narrow to be a single coastally trapped wave it is the sum of many modes the near lack of phase variation along the coast and the smallness of the phase difference be ween the equator and the coast are additional contrasts to the results for an initial value probl m studied by moore and others the implication is that the annually recurring upwelling in the gulf of guinea cannot be adequately modeled as the response to an impulsively applied wind stress

formation of the cold tongue and enso in the equatorial pacific basin abstract this paper proposes a mechanism that explains how coupled dynamics alone can spontaneously give rise to a realistic west east asymmetric mean state and an enso like interannual variability without requiring the existence of an external preexisting west east asymmetry in circulation the essence of the newly proposed mechanism is that the basinwide ocean atmosphere coupling acts to reduce the effective restoring force as a result the coupled oceanic waves travel more and more slowly within the equatorial ocean basin as the coupling strength increases when the coupling strength reaches a critical value the zonally leveled thermocline becomes unstable as a result of the weakening of the effective restoring force at which the theoretical limit of the traveling timescale would be infinite without nonlinearity due to nonlinearity in the coupled system this primary air sea interaction instability leads to a west east asymmetric mean state in which the atmosphere has a prevailing easterly and the

geophysical characterization of the northwest geysers geothermal field california abstract the clear lake volcanic field in northern california is the youngest and northern most part of a long lived volcanic system that has produced recent 10 ka eruptions adjacent to the clear lake volcanic field is the world s largest energy producing geothermal field the geysers the hottest part of the geyser s geothermal field is in the northwest where temperatures reach 400 c at 3 km depth low permeability high thermal gradients and low steam saturation prescribed development of an enhanced geothermal system egs in the northwest geysers to increase energy producing capacity though the northwest geysers is known to be the hottest part of the field geophysical methods have failed to adequately image any inferred heat source this project aims to image the heat source of the northwest geysers using newly collected gravity and magnetotelluric mt measurements gravity data were jointly modeled with existing magnetic data along a two dimensional profile aligned with an existing geologic cross section the key feature of the potential field model is a low density low susceptibility body at 5 km depth bmsl under the egs mt data were modeled in three dimensions to characterize subsurface resistivity structure where the upper 3 km of the resistivity model agrees well with existing data lithologic and steam saturation are estimated from modeled resistivity values using existing geophysical data below 3 km depth bmsl the resistivity model images a possible young intrusion under the egs a possible zone of partial melt

the fluid inclusion and mineralogic record of the transition from liquid to vapor dominated conditions in the geysers geothermal system california the geysers an active vapor dominated geothermal system related to a hypabyssal granitic pluton was liquid dominated from its inception at 1 2 to 0 3 ma when the modern vapor dominated regime formed as the hydrothermal liquids boiled off a vapor dominated heat pipe developed in which the flow of steam was balanced by downward percolation of condensate a record of the transition from liquid to vapor dominated conditions is contained within late stage quartz and calcite crystals that are common in the upper part of the steam reservoir and overlying cap rock samples from three localities were examined in detail quartz from these veins is characterized by corroded crystal faces solid inclusions of contemporaneous calcite that are generally etched coeval high and low salinity fluid inclusions primary low salinity liquid rich inclusions and abundant vapor rich inclusions primary vapor rich inclusions up to 2 mm across were trapped mainly on rhombic and prism faces of skeletal quartz crystals during periods of rapid growth these inclusions nucleate crystals of co2 that disappear by sublimation rather than melting at temperatures ranging from 92 9 to 56 7 c liquid rich fluid inclusions from veins near the top of the modern steam reservoir yield homogenization temperatures ranging from 304 to 188 c these temperatures commonly exceed boiling point to depth relationships based on the paleoground surface suggesting that pressures were initially greater than hydrostatic temperature salinity relationships indicate that the early shallow liquids had salinities of 1 5 to 2 wt percent nacl equiv and that boiling began by 300 c as the fluids boiled off salinities of the residual liquid increased to 3 to 4 wt percent nacl equiv trapping of low salinity fluids 0 0 0 5 wt nacl equiv interpreted as condensate in primary liquid rich inclusions suggest vapor dominated conditions had begun to develop by the time temperatures had dropped to 290 c the primary origin of these inclusion fluids indicates that they were capable of depositing quartz and calcite during the evolution of the vapor dominated system the hydrothermal fluids were at different times but at the same location undersaturated in equilibrium or oversaturated with respect to quartz and calcite the hydrothermal fluids initially deposited quartz and calcite as they boiled off dissolution of these minerals occurred as the condensate which was initially undersaturated with respect to quartz and calcite percolated down subsequent deposition of these minerals occurred as the condensate or mixtures of condensate and boiled liquid that leaked back into the fractures vaporized during periods of intermittent pressure reduction the top of the vapor dominated system migrated downward with time as the overlying fractures were progressively sealed off today pressures within the steam reservoir are vaporstatic and temperatures range from 240 to at least 342 c

rock deformation and fracturing processes due to nonlinear shock waves propagating in hyperthermal fluid pressurized domains an analytical model for rock deformation and fracturing processes due to nonlinear waves of temperature and pressure and evolving with particularly large velocities in a fluid saturated rock over a hyperthermal aquifer is here discussed as in classical studies by rice and cleary 1976 mctigue 1986 and also bonafede 1991 and natale and salusti 1996 the upper fluid saturated matrix is considered homogeneous thermoelastic and isotropic in a one dimensional formulation as regards the nonlinear wave generation mechanism at the boundary between the two horizons the hot fluid from below is forced upward by a pressure gradient thus giving rise to strong pressure and temperature perturbations in such a context in order to schematize wave induced rock deformation and fracturing processes we assume a continuous temperature and pressure dependence of model parameters such as fluid diffusivity and thermal expansivity of the rock and fluid the solution we obtain is a strong shock wave corresponding to nonlinear fluid migration mechanisms in turn enhanced by the flow through the induced fractures in the overlying rock it has to be stressed that once such a process starts off it may be amplified and also may produce rather catastrophic behavior in the natural system this model essentially provides a theoretical tool for interpreting such geophysical effects in particular for volcanic complexes such as the rabaul caldera long valley caldera campi flegrei the island of vulcano or similar kinds of geological system

propagation of the seasonal upwelling in the eastern equatorial atlantic abstract several mechanisms have been proposed to explain the coastal and equatorial upwelling in the eastern atlantic guinea gulf the most controversial is the mechanism of remote wind forcing in the western equatorial atlantic suggested by moore et al 1978 most of the possible explanations for the upwelling and their relative importance are discussed in view of recent observations detailed analysis of daily sea surface temperature sst collected at 16 coastal stations along the northern coast of the guinea gulf reveals that the upwelling event propagates westward along this coast at a mean speed of 0 7 m s 1 similar analysis of historical monthly mean sst data shows that the coastal upwelling event propagates poleward from 1 s to at least 13 s at the same phase speed furthermore the northern hemisphere and southern hemisphere coastal upwelling signals seem to start at the same time from the equator the same kind of analysis applied to hydrographic data from a station situated 41 km off abid

boiling and fluid mixing in the chlorite zone of the larderello geothermal system abstract the geochemical features of the geothermal fluids produced within the boiling zone in the relatively shallow parts of the larderello geothermal system italy have been documented as a result of deep drilling which provided samples from 1480 to 2500 m depth four wells monteverdi 1 monteverdi 2a sasso 22 and capannoli 2b have been sampled in the intermediate parts of the larderello aquifer located in a metamorphic basement underlying the tertiary nappe complex which constitutes the shallow aquifer at larderello fluid inclusions from recrystallized quartz lenses and quartz veins in samples displaying a predominant quartz chlorite epidote adularia paragenesis have been studied by microthermometry and raman spectroscopy the inclusions are primary and pseudo secondary in origin when formed in authigenic quartz or of secondary origin when located in fluid inclusion planes related to microfracturing of metamorphic quartz lenses several generations of fluids are present and include h 2 o co 2 dominated vapours and liquids and a series of aqueous liquids for the most part of relatively low salinity the t m ice of both early and late inclusions are mostly between 0 0 and 4 5 c indicating that the salinities of the hydrothermal fluid were very low to moderate however rare fluid inclusions with lower t m ice from 4 9 to 25 0 c were also observed these inclusions may record the occasional input of saline fluids which may be derived from the interaction of the hydrothermal waters with the evaporites present in the shallow part of the larderello field at capannoli 2b earliest h 2 o co 2 liquids were trapped under minimal pressures of 610 645 bars which bracket the estimated present day lithostatic pressure 640 bars in all other samples the main stage of quartz chlorite crystallization occurs under boiling conditions attested by the presence of liquid and vapour rich inclusions that in some instances can be texturally interpreted to be coeval their trapping conditions 350 375 c 160 215 bars are higher than the present day temperatures at the same depth later fluid inclusions attest to a significant cooling of the fluids down to temperatures similar to the present day temperatures during this time pressures were close to hydrostatic conditions most fluid inclusions were trapped within the liquid field this indicating that a significant pressure drop has since affected the main aquifers or fractured zones which are at present under vaporstatic conditions

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

thermal history of the acoculco geothermal system eastern mexico insights from numerical modeling and radiocarbon dating abstract acoculco is a geothermal prospective area hosted by a volcanic caldera complex in the eastern trans mexican volcanic belt surface manifestations are scarce and consist of gas discharges co2 rich and acid sulfate springs of low temperature whereas hydrothermal explosive activity is profusely manifested by meter scale craters and mounds of hydrothermal debris and breccias silicic alteration extends for several square kilometers around the zone with gas manifestations and explosive features affecting surficial volcanic rocks primarily tuffs and breccias in the subsurface an argillic alteration zone ammonium illite extends down to a depth of 600 m and underneath it a propylitic zone epidote calcite chlorite occurs down to 1000 m thermal logs from an exploratory borehole eac 1 drilled in 1995 down to 1810 m showed a conductive heat transfer regime under high geothermal gradient 140 c 1000 m in contrast the thermal profile established from temperatures of homogenization of fluid inclusions measured on core samples from the same drill hole suggests that convection occurred in the past through the upper 1400 m of the geothermal system a drop in permeability due to the precipitation of alteration minerals would have triggered the cessation of the convective heat transfer regime to give place to a conductive one with the purpose of determining when the transition of heat transfer regime occurred we developed a 1d model that simulates the time depth distribution of temperature according to our numerical simulations this transition happened ca 7000 years ago this date is very recent compared to the lifespan of the geothermal system in addition radiocarbon chronology indicates that the hydrothermal explosive activity postdates the end of the convective heat transfer regime having dated at least three explosive events at 4867 5295 1049 1417 and 543 709 y cal bp therefore hydrothermal explosions arise from the self sealing of the acoculco geothermal system involving a natural hazard that could affect future geothermal power infrastructure

the geysers cobb mountain magma system california part 2 timescales of pluton emplacement and implications for its thermal history abstract over 400 ion microprobe u pb isotopic ages measured for zircons extracted from 24 geothermal wells that penetrate the geysers plutonic complex gpc allow us to conclude that the entire known extent of the gpc crystallized during the early pleistocene nine samples of the microgranite porphyry that forms the shallow cupola 100 1 500 m below sea level mbsl of the gpc yield the oldest model u pb age 1 75 0 01 ma after correction for initial u series disequilibrium errors 1 twelve samples from the main intrusive phase orthopyroxene biotite granite present at depths 1 250 mbsl define a crystallization age of 1 27 0 01 ma this coincides with the age determined for a structurally and compositionally distinct body of granodiorite 1 25 0 01 ma n 5 samples that is intruded over a similar depth range two petrographically distinct varieties of orthopyroxene biotite granite yield ages of 1 46 0 03 gpc21 6000 and 1 16 0 02 ma ca5636 74f 21 three samples u pb zircon ages for dikes intruded in metagraywacke country rocks overlap with those obtained from the main body of the gpc and include the youngest material identified dike sample negu2 st1 7700 1 11 0 03 ma overall the u pb results demonstrate that the main body of the gpc 300 km3 was emplaced and crystallized within the upper crust over a short time interval 0 2 ma that overlaps with zircon crystallization ages of overlying silicic volcanic units

shock wave radon surface signals associated with the upsurge of t p solitons in volcanic systems abstract the present paper introduces a theoretical model in order to describe ground surface anomalies of radon emissions as a volcano is perturbed from its quiescent steady state based upon modern thermo poro elasticity theory which has been found to successfully explain rock deformation fracturing these anomalies are considered as being due to the build up of a buried thermo mechanical source which in turn gives rise to the upsurge of a thermo mechanical or t p soliton this sort of fluid solitary wave travelling upwards through induced deformed fractured horizons locally perturbes a pre existing stationary radon concentration profile as the wave approaches the ground surface in order to model radon anomalies a diffusive convective transport equation of radon is adopted with darcy s velocity change controlled by the upsurge of the t p soliton as a result a new flow mechanism of radon emission is found which we call shock wave radon propagation some cases of volcanic eruptions which have been preceded and accompanied by anomalies in radon emissions are examined in the light of the model a reasonably good agreement in the pattern between the observed radon concentration changes and the theoretical curves is found a theoretical tool for volcanic surveillance is thus proposed corresponding to both an effort to shed more light on the correlations that may exist between geophysics and geochemistry of fluid emissions and the recognition through ground surface radon anomalies of subsurface thermo mechanical instabilities possibly preceding volcanic eruptions