geological geophysical and thermal characteristics of the salton sea geothermal field california abstract the salton sea geothermal field is the largest water dominated geothermal field in the salton trough in southern california within the trough local zones of extension among active right stepping right lateral strike slip faults allow mantle derived magmas to intrude the sedimentary sequence the intrusions serve as heat sources to drive hydrothermal systems we can characterize the field in detail because we have an extensive geological and geophysical data base the sediments are relatively undeformed and can be divided into three categories as a function of depth 1 low permeability cap rock 2 upper reservoir rocks consisting of sandstones siltstones and shales that were subject to minor alterations and 3 lower reservoir rocks that were extensively altered because of the alteration inter granular porosity and permeability are reduced with depth field permeability is enhanced by renewable fractures i e fractures that can be reactivated by faulting or natural hydraulic fracturing subsequent to being sealed by mineral deposition in the central portion of the field temperature gradients are high near the surface and lower below 700 m surface gradients in this elliptically shaped region are fairly constant and define a thermal cap which does not necessarily correspond to the lithologic cap at the margin of the field a narrow transition region with a low near surface gradient and an increasing gradient at greater depths separates the high temperature resource from areas of normal regional gradient geophysical and geochemical evidence suggest that vertical convective motion in the reservoir beneath the thermal cap is confined to small units and small scale convection is superimposed on large scale lateral flow of pore fluid interpretation of magnetic resistivity and gravity anomalies help to establish the relationship between the inferred heat source the hydrothermal system and the observed alteration patterns a simple hydrothermal model is supported by interpreting the combined geological geophysical and thermal data in the model heat is transferred from an area of intrusion by lateral spreading of hot water in a reservoir beneath an impermeable cap rock

strombolian explosions 1 a large bubble breaking at the surface of a lava column as a source of sound strombolian activity consists of a series of explosions caused by the breaking of large overpressurized bubbles at the surface of the magma column acoustic pressure has been measured for 36 explosions at stromboli we propose that sound is generated by the vibration of the bubble before it bursts oscillations are driven by an initial overpressure inside the bubble assumed to be initially at rest just below the magma air interface inertia effects cause the bubble to overshoot its equilibrium radius then the bubble becomes underpressurized and contracts because of gas compressibility these oscillations are only slightly damped by viscous effects in the magma layer above the bubble the bubble cannot complete more than one cycle of vibration because of instabilities developing on the magma layer that lead to its breaking near the minimum radius assuming a simple geometry we model this vibration and constrain the radius and length of the bubble and the initial overpressure by fitting a synthetic waveform to the measured acoustic pressure the fit between synthetic and observed waveforms is very good both for frequency 60 rad s 1 and amplitude the initial bubble radius is 1 m and the length varies between several and a few tens of meters from the initial overpressure approximately 105 pa we calculate the maximum radial velocity of ejecta 30 m s 1 the generally good agreement between data and predictions of our model leads us to suggest that acoustic measurements are a powerful tool for the understanding of eruption dynamics

modelling the rapid near surface expansion of gas slugs in low viscosity magmas the ascent of large gas bubbles slugs in vertical cylindrical conduits and low viscosity magmas is simulated using 1d mathematical and 3d computational fluid dynamic cfd models following laboratory evidence the 1d model defines a constant rise velocity for the slug base and allows gas expansion to accelerate the slug nose through the overlying fluid during ascent the evolution of rapidly expanding gas slugs observed in laboratory experiments is reproduced well and at volcano scales predicts at surface overpressures of several atmospheres without requiring any initial overpressure at depth the near surface dynamics increase slug nose velocities through the overlying magma by a factor of c 2 5 and the gas expansion results in pre burst magma surface velocities of c 35m s21 to examine pressure distributions and the forces exerted on a conduit 3d cfd simulations were carried out at volcano scales the vertical single forces during final slug ascent to the surface are c 106 n two orders of magnitude smaller than those associated with verylong period seismic events at stromboli this supports a previous interpretation of these events in which they are generated by gas slugs flowing through changes in conduit geometry rather than being the direct result of slug eruption processes

238u 226ra and 210pb in some vent waters of the galapagos spreading center the concentrations of sup 226 ra sup 238 u and sup 210 pb have been measured in waters from the mussel bed and the rose garden thermal fields at the galapagos spreading center over a temperature range of approx 2 5 16 sup 0 c the sup 226 ra t plots yield slopes of 0 112 and 0 036 dpm kg sup 0 c for the mussel bed and the rose garden respectively yielding a global hydrothermal sup 226 ra flux less than 5 of that required to sustain the oceanic inventory sup 238 u concentration in waters 9 sup 0 c is the same as that in ambient sea water whereas water hotter than approx 9 sup 0 c shows a decreasing trend with temperature to zero sup 238 u at approx 29 sup 0 c sup 210 pb concentration in mussel bed increases with temperature and extrapolated to approx 350 sup 0 c yields a sup 210 pb concentration considerably less than that expected from sup 222 rn decay and basalt alteration

uranium geochemistry in geopressured geothermal aquifers of the u s gulf coast formation water from u s gulf coast geopressured geothermal sandstone aquifers has been analyzed to determine the geochemistry of uranium in these systems results of chemical analyses and chemical equilibrium modeling indicate the formation waters are in equilibrium with uraninite uo2 and coffinite usio4 the 234u238u activity ratios in the formation waters range from 1 06 to 1 69 these isotopic data suggest that at formation temperatures uranium is continually reequilibrating chemically and isotopically between water a solid phase of either uo2 or usio4 and a component of 234u supplied to solution from the aquifer matrix material by alpha recoil processes

winter regime of temperature and precipitation as a factor of snow cover distribution and its stratigraphy the investigation of spatial and temporal variability of the snow cover in northern eurasia snow depth density thermal characteristics water equivalent includes large scale fieldwork modelling and analysis of meteorological data of two winters 2004 05 and 2005 06 from 38 weather stations situated in different climatic conditions and physico geographical zones common regularities and features of snow cover variability are revealed for these winters despite their contrasting temperature and precipitation regimes and differences from an average winter as the time of appearance duration and depth of snow cover the number of snowfalls and date of melting the modelling of snow cover stratigraphy is based on viscous compression and recrystallization laws meteorological information temperature wind velocity and precipitation is used as input for the model the output is the specific snow cover stratigraphy according to positioning in different physical geographical regions and due to the possible variation as determined by winter temperature and precipitation regimes the peculiarity of snow cover stratigraphy at the regional scale depends on the meteorological conditions of its formation as well as on the character of landscapes a satisfactory correlation of the modelled typical columns of the snow cover formed in 2004 05 and 2005 06 in different regions of russia and of real columns is revealed

226ra and222rn contents of galapagos rift hydrothermal waters the importance of low temperature interactions with crustal rocks abstract hydrothermal waters collected by alvin from the galapagos spreading center are enriched in 222 rn by factors of 50 200 over bottom waters the 226 ra in the same samples however is enriched by less than a factor of four over bottom waters enrichments of 222 rn result primarily from recoil from rock surfaces while 226 ra enrichments are dominantly produced by high temperature alteration of cooling ridge volcanics the abundances of both nuclides exhibit positive correlations with temperature the data extrapolate to bottom water temperatures and compositions demonstrating the importance of seawater mixing different vents however have different mixing lines and vents with high 222 rn have low 226 ra we propose these patterns result from variations in the extent of low temperature crustal interaction with the hydrothermal fluids low temperature crustal waters can maintain high steady state 222 rn contents due to the recoil additions to the fluids the 226 ra however is strongly adsorbed at low temperatures resulting in low concentrations of this nuclide in low temperature crustal waters thus physical mixing of a crustal water component with hydrothermal waters or variable crustal path lengths of the hydrothermal fluids can account for the variable mixing lines and 222 rn 226 ra values of the hot springs the 222 rn 226 ra value appears to be a sensitive indicator of low temperature crustal interaction values 100 have experienced extensive crustal interaction and are indicative of diffuse hydrothermal flow values between 1 and 10 are indicative of primary hydrothermal fluids which have not experienced significant interaction with the crust values of 222 rn 226 ra between 10 3 and 10 4 are indicative of interaction of the hydrothermal fluids with sediments such values are observed in water samples from the galapagos hydrothermal mounds

formation and strengthening of layers of dry faceted crystals above artificial melt freeze crusts from overburden stress in a controlled environment layers of faceted crystals were grown from naturally fallen snow above wet snow layers in a temperature controlled laboratory static loads were then applied to the weak layers to represent overburden snow eleven experiments with constant loads were analyzed equivalent to 260 to 1500 pa of overburden stress the density of the slab above the weak layer increased with time following a power law relationship with an average exponent of 0 10 shear strength of the weak layer increased with time for all experiments also following a power law relationship early time rates of strength gain averaged 250 pa day 1 for the constant load experiments over the first 3 5 days decreasing to an average of 1 pa day 1 after approximately 30 days exponents for the power law relationships ranged between 0 09 and 0 35 with an average of 0 26 0 08 sintering was likely the dominant process for strength gain although densification probably contributed as well three experiments were conducted in which the overburden

an improved method for ra isotope 226ra 228ra 224ra measurements by gamma spectrometry in natural waters application to co2 rich thermal waters from the french massif central abstract an improved method was developed to measure 226 ra 228 ra and 224 ra in freshwaters by gamma spectrometry radium was selectively extracted from acidified samples using specific filters 3m empore radium rad disks the latter was subsequently analysed by gamma spectrometry simultaneous and direct determination of the activities of the three isotopes was performed by comparison of gamma rays of the radium rad disks with those of a calibrated standard disk this efficient and reliable method allowed a reduction of sample processing to a few hours this technique was applied to analyse the ra isotope compositions of several co 2 rich hydrothermal springs of the western border of the limagne graben french massif central the studied springs emerge from a succession of granitic outcrops lined up along a major fault their chemical compositions evolve from calcic and magnesian chloro bicarbonated to sodic bicarbonated all the springs display high ra activities probably linked to high co 2 content and or high cation content of these waters with various ra isotope ratios 226 ra activity ranges from 588 to 2287 mbq l and 228 ra activity from 260 to 1590 mbq l whereas 224 ra displays an activity between 245 and 1808 mbq l four of the six analysed springs have 228 ra 226 ra activity ratios lower than 0 7 thus significantly lower than the ratio expected from an interaction with a calc alkaline granitoid typically having 232 th 238 u activity ratio between 1 and 2 low 228 ra 226 ra ratio 0 27 of the northern water montpensier suggests the existence in this area of a zone of u concentration possibly resulting from u mobilization and accumulation induced by previous hydrothermal events the 224 ra 228 ra ratios display smaller variations they suggest short transit times from the zone of ra leaching to the surface a few days or a very shallow addition of 224 ra e g from a localised zone where 228 th could be preferentially adsorbed on the mineral surfaces in some cases these ratios might be used to infer differences in transit times of waters between neighboring springs

the geochemistry of ca sr ba and ra sulfates in some deep brines from the palo duro basin texas the geochemistry of ca sr ba and ra sulfates in some deep brines from the palo duro basin of north texas was studied to define geochemical controls on radionuclides such as 90sr and 226ra published solubility data for gypsum anhydrite celestite barite and raso4 were first reevaluated in most cases using the ion interaction approach of pitzer to determine solubility products of the sulfates as a function of temperature and pressure ionic strengths of the brines were from 2 9 to 4 8 m their temperatures and pressures up to 40 c and 130 bars saturation indices of the sulfates were computed with the ion interaction approach in one brine from the arkosic granite wash fades and four from the carbonate wolfcamp formation all five brines are saturated with respect to gypsum anhydrite and celestite and three of the five with respect to barite all are undersaturated by from 5 to 6 orders of magnitude with respect to pure raso4 226ra concentrations in the brines which ranged from 10 11 3 to 10 12 7 m are not controlled by raso4 solubility or adsorption but possibly by the solubility of trace ra solid solutions in sulfates including celestite and barite

slug stability in flaring geometries and ramifications for lava lake degassing long lived persistently active lava lakes are rare but have been studied extensively because they may provide a natural laboratory for studying magmatic convection in basaltic and other low viscosity volcanoes however lava lakes differ from other volcanic systems in various ways particularly geometry the presence of the lava lake requires a sudden and significant flaring of the conduit the goal of this paper is to advance our understanding of the effect that a sudden increase in the conduit width has on the stability of large gas slugs and bubbles ascending from the plumbing system we investigate this question by linking analog laboratory experiments to direct numerical simulations in two dimensions we find that the rapid change in the geometry associated with the transition from the conduit to the lava lake causes large gas slugs to break up the nondimensional regime over which we observe the breakup depends sensitively on the flare angle of the lava lake and the importance of inertial effects in the flow implying that degassing related eruptive activity at open system volcanoes is sensitive to the upper conduit and lake geometries applying this idea to the likely geometries and viscosities of actual lava lakes our study suggests that all lava lakes except erebus fall well within the regime where large gas slugs are prone to breakup

reply to the comment by mike r james et al on it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity 1 the current paradigm for normal eruptions at stromboli volcano and strombolian type activity more generally posits that each eruption represents the burst of a large pocket of gas commonly referred to as slug at the free surface of themagma column this slug model has been investigated and refined primarily through analog fluid dynamical experiments at the laboratory scale there is no doubt that these studies have advanced our understanding of strombolian eruptions considerably however given the very fundamental status of the slug model for our current thinking about strombolian type eruptions it is paramount to carefully assess all underlying assumptions of the model one important uncertainty lies in the scaling behavior of the observed slug dynamics in the laboratory scale invariance requires all nondimensional numbers to be identical but it is generally not feasible to match all of the nondimensional numbers characterizing the volcanic conduit exactly in a laboratory experiment numerical computations offer a means of directly comparing slug dynamics at drastically different scales suckale et al 2010b we find that the very large slugs in volcanic conduits are more prone to dynamic instabilities and breakup than the comparatively small slugs in laboratory settings this finding in itself does of course not disprove the slug model it merely points to potentially important differences in slug stability at volcanic scales as opposed to laboratory scales 2 being careful and critical of the errors and interpretations of numerical simulations is important similarly the appropriateness of laboratory analogs must also be examined james et al 2011 raise a valid point asking whether our simulations are capable of reproducing stable slug rise in water figure 1 shows a computation performed for the experimental parameters provided by james et al 2011 in agreement with the analog experiments we do indeed find that this slug rises stably in water i e the slug ascends buoyantly within the conduit without experiencing catastrophic breakup as defined by suckale et al 2010b thus the experiments by james et al 2011 do not appear to contradict our computations we also reproduce computationally stable slug flow at finite reynolds number re shown in the experiment specified by jaupart and vergniolle 1989 suckale et al 2010b it is worth noting that in both cases the set of nondimensional numbers characterizing the experiment are not identical to those thought to be representative of the volcanic conduit and thus potential differences in the fluid dynamical behavior are not unexpected 3 that we observe stable slugs in water but not in magma supports an argument raised by james et al 2011 namely that re is an insufficient parameter for comparing slug dynamics at different spatial scales we welcome their discussion of the drawbacks of using a single re to describe slugs focusing on re to characterize our computations was a purely pragmatic decision first re is commonly used for the purpose of comparing fluid dynamical computations at different scales second we were able to use estimates for re characterizing strombolian slugs based on observational data measured at stromboli vergniolle and brandeis 1996 third we observed a correlation between re and breakup within the regime we investigated which is not unexpected since re is an indirect measure of the size of a gas bubble or slug that being said a more comprehensive set of nondimensional numbers is undoubtedly needed to evaluate scaling behavior of slugs for different fluid dynamical regimes including nondimensional criteria that capture the wavelength of potential interface instabilities in relation to the curvature of the interface and the time scale associated with instability growth to the time scale associated with advection of the instability along the interface our study is a first step toward gaining a better understanding of slug stability 4 from a theoretical point of view very large and dynamic gas volumes are not expected to be indefinitely stable the light gas slug moves underneath a column of very heavy magma and this unstable density stratification is prone to the formation of rayleigh taylor instabilities at the essentially flat upper surface of the slug grace et al 1978 developed a semiempirical rationalization of this process that affords rough estimates of maximum stable sizes as listed in table 1 of suckale et al 2010b the appeal of this model lies primarily in its simplicity but this very simplicity also department of earth atmospheric and planetary sciences massachusetts institute of technology cambridge massachusetts usa department of mathematics and statistics mcgill university montreal quebec canada

hydrogeochemistry and weathering on the yilgarn block western australia ferrolysis and heavy metals in continental brines abstract groundwater samples collected from salt lakes over the archean yilgarn block of western australia show the influence of climate on geochemical weathering patterns major element compositions in salt lake groundwaters show little systematic trend but there are marked differences in ph and fe cu and pb concentrations in the alkaline carbonated systems of the arid northeastern part compared to concentrations of the same elements in groundwater systems of the mediterranean type climatic region of the wheatbelt in the southwestern part of the block in this latter region in addition to higher rainfall input the groundwater systems have steeper hydraulic gradients weathering bedrock is closer to the surface and oxidation and hydrolysis of iron ferrolysis is evident in weathering profiles a combination of vertical diffusion and horizontal groundwater flow is thought to be responsible for the development of ferrolysis and acidity in groundwaters in this region anomalously high concentrations of heavy metals particularly lead are observed in some of the acid saline groundwaters the formation of laterite which is a ubiquitous feature of the yilgam block landscape is a process probably closely linked to ferrolysis

comment on it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity by j suckale b h hager l t elkins tanton and j c nave

snow crystal growth with varying surface temperatures and radiation penetration the temperature field is derived for a sinusoidally varying surface temperature with varying solar radiation penetration the growth rates of snow crystals are calculated to explain the rapidly growing layers of faceted crystals i e depth hoar that form just below the surface at high altitudes and in polar snow the solutions also show that a layer of wet snow can exist just below the surface even on days when the surface temperature remains sub freezing

radium isotopes in saline seepages south western yilgarn western australia abstract water samples from saline seepages in the south western yilgarn block of western australia contain high activities of the four naturally occurring radium isotopes activities of up to 310 pci l for 226ra and 1720 pci l for 228ra were measured and the 228 ra 226 ra ratio averaged 6 1 activities of the two short lived radium isotopes were also high 223ra activities of up to 94 pci l were found with an average 226 ra 223 ra ratio of 3 3 considerably lower than the natural abundance ratio of 21 4 activities of up to 23 pci l 227ac the long lived t 1 2 22 years grandparent of 223ra were also measured the analysis of surface granite samples the probable source rocks of the radium gave th u activity ratios of around 1 5 the higher 228 ra 226 ra ratios of the waters were attributed to readily leached 228ra in the weathered granites as a result of thorium remaining after weathering leach experiments on u th ore by nacl solutions showed that all four radium isotopes were equally leached sulphate anions reduced the 226ra and 228ra leaching to a greater extent than for 223ra and 224ra suggesting that the latter isotopes were being supported in solution by parent isotopes in particular this suggested 227ac was leached into the sulphate solution but this does not fully account for the amount of 227ac seen in the seepage waters

field investigation of near surface metamorphism of snow buried surface hoar and near surface faceted crystals are known to lead to deadly avalanches over the course of three winter seasons a field investigation detailing the environmental conditions leading to the formation of these crystals was performed weather stations on north and south facing aspects were established the weather data were accompanied by detailed daily observations and grain scale photographs of the snow surface during the three seasons 35 surface hoar and 47 near surface facets events were recorded the mean weather conditions for the entire dataset all three seasons and both stations were compared to the nights when surface hoar formed the comparison yielded five parameters that were statistically linked to the formation of surface hoar incoming longwave radiation snow surface temperature wind velocity relative humidity and the air snow temperature difference a similar comparison between the daytime mean values for all days with near surface facet events revealed three parameters with statistically significant differences thus these parameters short and longwave radiation and relative humidity could be statistically linked to facet formation this research also suggests that environmental conditions in the daytime hours before and after surface hoar formation are statistically similar to the conditions causing near surface facet formation

mechanical and structural properties of weak snow layers measured in situ weak layers such as buried surface hoar or depth hoar frequently form the failure plane of slab avalanches therefore the mechanical properties of such layers in relation to their snow structure have been investigated since it is difficult to transport samples containing a weak layer into cold rooms the mechanical measurements have to be made in situ we investigate strain rate dependency of shear strength by measuring concurrently strength deformation and acceleration using a digital force gauge attached to a 0 05 m 2 shear frame to which an accelerometer and a displacement sensor are fixed in doing so a dynamic force comparable to a driving skier is applied the measurements cover a strain rate range 10 2 to 1 s 1 the samples fail in a brittle manner the shear strength values cover the range 0 2 2 8 kpa the dataset is also used to approximate the coefficient g the shear modulus for different weak layers the snow structure has been analysed macroscopically in the field and for some layers representative snow samples have been extracted in order to prepare in the cold laboratory single sided serial planes with cuts every 0 1 mm recorded by video the analysis of these snow samples should have given the relation between some mechanical properties strength strain and the structural properties due to basic problems in defining the connection between complex snow grains e g surface hoar we were unable to complete this part in due time only preliminary results on this aspect are presented here based on our long term database containing macroscopic structural and strength data of weak layers a relationship between snow type and shear strength has been established

theory of metamorphism of dry snow the growth of ice particles in dry seasonal snow is caused by vapor diffusion among particles due to temperature gradients imposed on the snow cover the diffusion is calculated by using the potential field solutions for electrostatically charged particles the stereography of snow is represented by using a log normal distribution function for a geometrical enhancement factor defined here reasonable crystal growth rates and supersaturations are found the transition between the growth of highly faceted crystals and the growth of highly rounded crystals is determined by the critical supersaturation for the onset of dislocation aided growth thermal convection and the continuous movement of vapor around the particles due to the imposed temperature gradient are accommodated in the theory although both have little effect relative to the interparticle diffusion the growth of a layer of faceted crystals just below semi permeable crusts is explained by showing that crusts can cause the local supersaturation to exceed the critical value faceted crystals are shown to grow most rapidly in the lower warmer portions of the snow cover because of temperature effects on growth rate

snow avalanche formation 1 snow avalanches are a major natural hazard endangering human life and infrastructure in mountainous areas throughout the world in many countries with seasonally snow covered mountains avalanche forecasting services reliably warn the public by issuing occurrence probabilities for a certain region however at present a single avalanche event cannot be predicted in time and space much about the release process remains unknown mainly because of the highly variable layered character of the snowpack a highly porous material that exists close to its melting point the complex interaction between terrain snowpack and meteorological conditions leading to avalanche release is commonly described as avalanche formation it is relevant to hazard mapping and essential to short term forecasting which involves weighting many contributory factors alternatively the release process can be studied and modeled this approach relies heavily on snow mechanics and snow properties including texture while the effect of meteorological conditions or changes on the deformational behavior of snow is known in qualitative or semiquantitative manner the knowledge of the quantitative relation between snow texture and mechanical properties is limited but promising developments are under way fracture mechanical models have been applied to explain the fracture propagation and micromechanical models including the two competing processes damage and sintering have been applied to explain snow failure there are knowledge gaps between the sequence of processes that lead to the release of the snow slab snow deformation and failure damage accumulation fracture initiation and fracture propagation simultaneously the spatial variability that affects damage fracture initiation and fracture propagation has to be considered this review focuses on dry snow slab avalanches and shows that dealing with a highly porous media close to its melting point and processes covering several orders of scale from the size of a bond between snow grains to the size of a mountain slope will continue to be very challenging

geochim cosmochim acta m a a schoonen and h l barnes erratum to schoonen and barnes 1991 mechanisms of pyrite and marcasite formation from solution iii hydrothermal processes 55 3491 3504

a numerical model to simulate snow cover stratigraphy for operational avalanche forecasting laws of snow metamorphism have been introduced in a numerical model which simulates the evolution of temperature density and liquid water profiles of snow cover as a function of weather conditions to establish these laws the authors have summarized previous studies on temperature gradient and on wet snow metamorphism and they have also conducted metamorphism experiments on dry or wet fresh snow samples an original formalism was developed to allow a description of snow with parameters evolving continuously throughout time the introduction of laws of metamorphism has improved significantly the derivation of the settlement of internal layers and of snow covered albedo which depend on the simulated stratigraphy i e the type and size of snow grains of different layers of the snow cover the model was tested during a whole winter season without any re initialization comparison between the simulated characteristics of the snow cover and the observations made in the field are described in detail the model proved itself to be very efficient in simulating accurately the evolution of the snow cover stratigraphy throughout the whole winter season

naturally occurring radionuclides and their geochemical interactions at a geothermal site in the north german basin the activities of the most common naturally occurring radionuclides 238u 226ra 210pb 228ra 228th and 40k were measured by gamma ray spectrometry in samples from reservoir rocks geothermal fluids and mineral precipitates at the geothermal research site gros schonebeck north german basin results demonstrated that the specific activity of the reservoir rock is within the range of the mean concentration in the upper earth crust of 800 bq kg for 40k and 60 bq kg for radionuclides of the 238u and 232th series respectively the geothermal fluid showed elevated activity concentrations up to 100 bq l for 226ra 210pb and 228ra as compared to concentrations found in natural groundwater their concentration in filter residues even increased up to 100 bq g these residues contain predominantly two different mineral phases a sr rich barite sr baso4 and laurionite pbohcl which both precipitate upon cooling from the geothermal fluid thereby they presumably enrich the radionuclides of ra by substitution of ba and pb analysis of these precipitates further showed an increased 226ra 228ra ratio from around 1 1 7 during the initial months of fluid production indicating a change in fluid composition over time which can be explained by different contributions of stimulated reservoir rock areas to the overall produced fluid

it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity this is the second paper in a two part series examining numerical simula tions of buoyancy driven ow in the presence of large viscosity contrasts in the rst pa per we demonstrated that a combination of three numerical tools an extended ghost uid type method the level set approach and the extension velocity technique accurately simulate complex interface dynamics in the presence of large viscosity contrasts in this paper we use this three fold numerical method to investigate bubble dynamics in the conduits of basaltic volcanos with a focus on normal strombolian eruptions strombolian type activity named after the famously episodic eruptions at stromboli volcano is char acterized by temporally discrete fountains of incandescent clasts the mildly explosive nature of normal strombolian activity as compared to more eusive variants of basaltic volcanism is related to the presence of dissolved gas in the magma yielding a complex two phase ow problem we present a detailed scaling analysis allowing identication of the pertinent regime for a given ow problem the dynamic interactions between gas and magma can be clas sied into three non dimensional regimes based on bubble sizes and magma viscosity re solving the uid dynamics at the scale of individual bubbles is not equally important in all three regimes as long as bubbles remain small enough to be spherical their dy namic interactions are limited compared to the rich spectrum of coalescence and breakup processes observed for deformable bubbles in particular once inertia ceases to be neg ligible one key nding in our simulations is that both large gas bubbles and large conduit lling gas pockets slugs are prone to dynamic instabilities that lead to their rapid breakup during buoyancy driven ascent we provide upper bound estimates for the maximum sta ble bubble size in a given magmatic system and discuss the ramications of our results for two commonly used models of normal strombolian type activity the rise speed dependent rsd model and the collapsing foam cf model

array tracking of infrasonic sources at stromboli volcano 1 infrasonic arrays are a powerful tool for volcanic monitoring and hazard assessment explosions were recorded at stromboli using a small aperture array of 4 infrasonic stations allowing precise vent location the acoustic signals were delayed and summed revealing the existence of two main groups of infrasonic waves the ne crater produces short 3 s high amplitude 20 80 pa pressure waves while the sw crater produces small acoustic pressure 10 30 pa with long 5 15 s coda the two groups reflect different in explosive styles and similar spectral content centered on 5 6 hz when stacked together acoustic waveforms for each crater reveal the same pressure pulse which indicates a common source process we infer that the acoustic onset at both craters is generated by the burst of a large gas bubble while the acoustic coda is controlled by a sustained pressure release

234u and238u concentration in brine from geopressured aquifers of the northern gulf of mexico basin abstract the 234 u and 238 u concentration in brine from six gulf coast geopressured aquifers has been determined the results reveal very low uranium concentrations from 0 003 to 0 03 g l and uranium activity ratios slightly greater than unity from 1 06 to 1 62 reducing conditions within the aquifers are responsible for the low uranium concentrations the uranium activity ratios observed are well below those calculated using theoretical considerations of alpha particle recoil effects this can be explained by interference with alpha recoil nuclides entering the liquid phase as a result of quartz overgrowths on sand grains and high temperature re equilibration that tends to minimize the effects of the alpha recoil process the fact that the uranium activity ratios of the brines are slightly greater than unity instead of the equilibrium value of 1 000 indicates that either the alpha particle recoil blocking and re equlibration effects are not complete or that another process is operative that enriches the fluid in excess 234 u by selectively removing uranium from radiation induced damage sites in the mineral sand grain matrix

an energy and mass model of snow cover suitable for operational avalanche forecasting a numerical model has been developed to simulate energy and mass evolution of snow cover at a given location as a function of meteorological conditions precipitation air temperature humidity wind velocity and incoming short wave and long wave radiation this model named crocus was first tested on a well instrumented field during a whole winter showing its ability to simulate the important phenomena affecting the evolution of the snow layers high temperature gradients wetting compaction and melting freezing cycles a second test was conducted at two locations in the french network used for operational avalanche forecasting though the weather observations are made there only twice daily the snow profiles calculated by the model were very close to those obtained once a week by a pit observation crocus proved itself sufficient to be considered now as a useful objective tool for operational avalanche forecasting

formation of refrozen snowpack layers and their role in slab avalanche release 1 in a variety of snow climates numerous slab avalanches release over crusts consisting of refrozen snow slab avalanches sometimes release in weak layers of faceted crystals that developed while underlying wet layers froze into crusts often within a day weak layers of faceted crystals can also develop when less permeable and more conductive crusts alter the temperature and vapor pressure gradients these processes create interfaces where differences in grain radii can contribute to weak bonding in western canada layers of faceted crystals facet layers on crusts are most common in early and late winter when thaws and rain are more frequent also thin facet layers occur in spring when surface melting by solar radiation is common shear strength tests on facet layers show an initial strength loss during faceting followed by a slow strength increase the spatial distribution of poorly bonded crusts can be interpreted from the interaction of terrain and meteorology that caused the antecedent wet layer

uranium series disequilibrium studies of granitic rocks abstract igneous plutons of the canadian shield which are to be considered as possible storage sites for radioactive waste should be free from any evidence of past mobility of chemical species through the rock however cores taken from some plutons to depths of up to 1 km reveal the presence of hydrous low temperature alteration along joints and fractures and within the body of the rock to test whether such rocks or any others have been subjected to chemical transport in geologically recent times we may study the state of radioactive equilibrium between 238 u 235 u and 232 th and their short lived daughterisotopes members of the decay series of these parent isotopes have half lives ranging from a few hours to 0 25 ma also the chemical characteristics of the various daughters vary significantly allowing us to test the mobility of isotopes of similar half life but differing chemistry if the rock has been chemically undisturbed for 10 ma or more then the activity in d p m g of each daughter in these decay schemes will be equal to that of its parent isotope conversely if the rock was chemically disturbed 10 n a ago then some daughter isotopes with half lives t 10 n a will be out of equilibrium with their parents preliminary results are presented showing disequilibrium effects in samples from atikokan ontario

the behaviour of short lived radiogenic lead isotopes 214pb and212pb in groundwaters and laboratory leaching experiments abstract the concentrations of 214 pb half life 26 4minutes and 22 rn half life 3 84days have been measured in deep groundwaters of gujarat india the results show that the abundance of 214 pb in the water is only 25 of that expected from its production through the radioactive decay of dissolved 222 rn this deficiency if modelled in terms of a first order removal yields a residence time of 10 minutes for 214 pb in these waters the estimated residence time for 214 pb is the shortest observed for any nuclide in natural water systems and suggests that reactive nuclides lead like could be removed from aqueous phases to adjoining solid surfaces on extremely short time scales results of laboratory experiments using the 212 pb 224 ra pair are compatible with the observed fast removal of 214 pb from groundwaters re evaluation of 234 th residence times in these waters using a model with a recoil flux of 234 th into aqueous phase the same as that of 222 rn yields values in the range of 23 to minutes very similar to that of 214 pb this concordancy in the residence times seems to suggest that the geochemical behaviour of 234 th and 214 pb in these waters is quite similar

state of disequilibrium between 238u 234u 226ra and 222rn in groundwater from bedrock abstract approximately one thousand drilled wells were investigated for their natural radioactivity the determinations of 238u 234u 226ra and 222rn from 310 samples showed a high state of radioactive disequilibrium between the members of the uranium series present in water the 238 u 226 ra activity ratio usually fell in the range 1 20 and the 238 u 222 rn activity ratio in the range 1 20 10 4 the highest activity ratios being from samples with an elevated uranium content the 234 u 238 u activity ratio varied between 0 76 and 4 67 the most frequent values showing a 60 excess of 234u in the samples most of the 234 u 238 u activity ratios near unity were found in samples with a high uranium content several drilled wells with anomalously high uranium contents were found in southern finland the average 226ra and 222rn contents of these wells were not exceptionally high which suggests high mobility of uranium in groundwater from the areas involved

the dynamics of slug trains in volcanic conduits evidence for expansion driven slug coalescence strombolian volcanism is a ubiquitous form of activity driven by the ascent and bursting of bubbles of slug morphology whilst considerable attention has been devoted to understanding the behaviour of individual slugs in this regime relatively little is known about how inter slug interactions modify flow conditions recently we reported on high temporal frequency strombolian activity on etna in which the larger erupted slug masses were followed by longer intervals before the following explosion than the smaller bursts pering et al 2015 we hypothesised that this behaviour arose from the coalescence of ascending slugs causing a prolonged lag before arrival of the next distinct bubble here we consider the potential importance of inter slug interactions for the dynamics of strombolian volcanism by reporting on the first study into the behaviour of trains of ascending gas slugs scaled to the expansion rates in volcanic conduits this laboratory analogue study illustrates that slugs in trains rise faster than individual slugs and can be associated with aspects of co current flow the work also highlights that coalescence and inter slug interactions play an important role in modulating slug train behaviour we also report for the first time on slug coalescence driven by vertical expansion of the trailing slug a process which can occur even where the leading slug base ascent velocity is greater than that of the trailing slug

seismicity on volcanoes generated by gas slug ascent 1 very long period vlp signals provide a unique insight into the source process of seismic signals recorded on active or restless volcanoes this is due to the large wavelengths that may allow the structural heterogeneity to be ignored hence source inversions can be calculated the source process involved in such events is thought to be related to magma transport gas slug ascent or dike resonance initiated by a fluid driven process numerical modelling of gas slug ascent constrained by results from published laboratory experiments shows that this process is capable of generating long period and vlp like signals inputting the fluid dynamic derived forces into an elastic medium with volcano like topography vlp signals are reproduced a moment tensor inversion is performed on these synthetic vlp signals retrieving the correct input source mechanism a pipe structure

bubble mobility in mud and magmatic volcanoes the rheology of particle laden fluids with a yield stress such as mud or crystal rich magmas controls the mobility of bubbles both the size needed to overcome the yield stress and their rise speed we experimentally measured the velocities of bubbles and rigid spheres in mud sampled from the davis schrimpf mud volcanoes adjacent to the salton sea southern california combined with previous measurements in the polymer gel carbopol we obtained an empirical model for the drag coefficient and bounded the conditions under which bubbles overcome the yield stress yield stresses typical of mud and basaltic magmas with sub mm particles can immobilize millimeter to centimeter sized bubbles at stromboli volcano italy a vertical yield stress gradient in the shallow conduit may immobilize bubbles with diameter

234u 238u activity ratios of dissolved uranium in groundwaters from a jurassic limestone aquifer in england abstract uranium contents and234u 238u activity ratios have been determined for groundwaters from the lincolnshire limestone artesian aquifer in eastern england changes in the quantitative and isotopic chemistry of the dissolved uranium are explained in terms of a mixing model involving the rapidly moving fissure water and much older water stored in the pore system of this oolitic limestone the western part of the aquifer closest to recharge is dominated by oxidising groundwaters which then enter a reducing zone towards the east where there is an abrupt decrease in eh and the chlorinity of the groundwaters begins to increase uranium contents in the oxidising zone range from 0 7 to 3 4 g kg 1 and234u 238u activity ratio of this dissolved uranium is close to unity the equilibrium value the uranium content decreases abruptly when the grounwaaters enter the reducing zone averaging 0 04 g kg 1 east of the oxidation reduction barrier simultaneously with the decrease in uranium content there is an increase in234u 238u activity ratio and this ratio increases to a maximum within 7 km of the oxidation reduction barrier this increase in activity ratio is attributed to enhanced234u solution due to234th recoil from uraniferous fissure surfaces east of the oxidising zone the activity ratio of dissolved uranium in the ancient pore waters could in principle reach high values due to234th recoil from the oolith surfaces however the activity ratio actually declines further east and this can only be explained as a consequence of mixing with pore waters in which the uranium activity ratio is closer to equilibrium 234th recoil from the oolith surfaces has probably been inhibited by sealing of the uranium bearing surfaces in the process of oolith cementation

uranium thorium series radionuclides in brines and reservoir rocks from two deep geothermal boreholes in the salton sea geothermal field southeastern california naturally occurring u and th series radionuclides have been analyzed in high temperature brines 300 c 25 wt dissolved solids and associated rocks from two deep geothermal wells located on the northeastern margin of the salton sea geothermal field ssgf these data are part of a study of the ssgf as a natural analog of possible radionuclide behavior near a nuclear waste repository constructed in salt beds and permit evaluation of some characteristics of water rock interaction in the ssgf rock brine concentration ratios rc dpm g rock dpm g brine were found to vary from near unity for isotopes of ra pb and rn to about 5 105 for 232th the high sorptivity of 232th is closely followed by that of 238u and 234u rc 5 104 suggesting that u is retained in the 4 oxidation state by the reducing conditions in the brines the relatively high solubility of 210pb and 212pb is attributed to formation of chloride complexes while the high ra solubility is attributed to chloride complexing a lack of suitable adsorption sites due to the high brine salinity and temperature and the reducing conditions that prevent mno2 and raso4 from forming the 228ra226ra ratios in the brines are approximately equal to those of their parents 232th230th in associated rocks indicating that ra equilibration in the brine rock system is achieved within the mean life of 228ra 8 3 years the 224ra228ra ratios in these brines are about 0 7 indicating that either 1 brine composition is not homogeneous and 224ra decays in fracture zones deficient in ra and th as the brine travels to the wellhead or 2 ra equilibration in the brine host rock system is not complete within the mean life of 224ra 5 2 days because the desorption of 224ra from the solid phase is impeded the 228ac228ra activity ratio in the ssgf brines studied is 0 1 and from this ratio the residence time of 228ac in the brine before sorption onto solid surfaces is estimated to be 70 minutes indicating the potential for rapid removal of reactive isotopes fom brines the brine is greatly enriched in 226ra 2 3 dpm g about 104 105 times that of its parent 230th while reservoir rocks are about 10 deficient in 226ra relative to 230th material balance calculations for 2226ra and 18o suggest that brines reside in the reservoir for 102 103 years that the ssgf formed 10 000 40 000 years b p and that porosity cannot be more than 20