the january 1998 earthquake swarm at axial volcano juan de fuca ridge hydroacoustic evidence of seafloor volcanic activity on january 25 1998 at 11 33z an intense swarm of earthquakes began within the summit caldera of axial volcano central juan de fuca ridge jdfr the earthquake swarm was detected using the u s navy hydrophones in the northeast pacific ocean the earthquake swarm lasted 11 days and produced 8247 detected 1037 located earthquakes during the first two days of the swarm earthquake activity migrated from the summit caldera 50 km along the south rift zone of axial volcano at rates of 0 92 0 13 and 0 23 0 09 m s 1 earthquake epicenter migration is characteristic of a lateral magma dike injection the largest three swarm earthquakes occurred within the caldera their timing and mechanisms are consistent with adjustment of the caldera floor as magma is removed from beneath the summit earthquakes with short t wave rise times shallow focal depths cluster at two spots along the summit and south rift zone and are considered possible seafloor eruption sites in situ ground deformation and hydrothermal plume monitors and later shipboard observations confirmed the occurrence of a seafloor volcanic eruption at the volcano s summit

geology of a vigorous hydrothermal system on the endeavour segment juan de fuca ridge a high precision high resolution geologic map explicitly documents relationships between tectonic features and large steep sided sulfide sulfate silica deposits in the vigorously venting endeavour hydrothermal field near the northern end of the juan de fuca ridge water depth in the vent field varies from 2220 to 2200 m location of the most massive sulfide structures appears to be controlled by intersections of ridge parallel normal faults and other fracture fissure sets that trend oblique to and perpendicular to the overall structural fabric of the axial valley the fractured basaltic substrate is primarily composed of well weathered pillow and lobate flows as presently mapped the field is about 200 by 400 m on a side and contains at least 15 large 1000 m3 sulfide edifices and many tens of smaller commonly inactive sulfide structures the larger sulfide structures are also the most vigorously venting features in the field they are commonly more than 30 m in diameter and up to 20 m in height actively venting sulfide structures in the northern portion of the field stand higher and are more massive than active structures in the southern portion of the field which tend to be slightly to distinctly smaller maximum venting temperatures of 375 c are associated with the smaller structures in the southeastern portion of the field highest temperature venting fluids from the more massive structures in the northern portion of the field are consistently 20 30 c lower hydrothermal output from individual active sulfide features varies from no flow in the lower third of the edifice to vigorous output from fracture controlled black smoker activity near the top of the structures a different type of high temperature venting takes place from the upper sides of the structures in the form of overflow from fully exposed quiescent pools of buoyant 350 c vent water trapped beneath overhanging sulfide sulfate silica ledges or flanges these flanges are attached to the upper outer walls of the large sulfide edifices two types of diffuse venting in the endeavour field include a lower temperature 8 15 c output through colonies of large tubeworms and 25 50 c vent fluid that seems to percolate through the tops of overhanging flanges the large size and steep walled nature of the these structures evidently results from sustained venting in a mature hydrothermal system coupled with dual mineral depositional mechanisms involving vertical growth by accumulation of chimney sulfide debris and lateral growth by means of flange development

scintillation structure of a turbulent tidal flow we describe observations of fine structure in a turbulent tidal channel on the british columbia coast obtained with towed and vertical conductivity temperature and depth profiles and a novel acoustic technique the acoustic scheme involves the detection of the scattering of sound waves by fine structure moving through a pair of acoustic paths that traverse the channel the larger scale flow and also the fine structure can be observed in this way providing a time series measurement of the flow properties as the tidal current changes the channel is characterized by periods of intense mixing through most of the tidal cycle near slack water it becomes stratified and although it remains active the outer scale of the turbulence decreases to 2 3 m the fine scale variability is a sensitive function of flow speed and stratification

the relative effect of particles and turbulence on acoustic scattering from deep sea hydrothermal vent plumes revisited the relative importance of suspended particles and turbulence as backscattering mechanisms within a hydrothermal plume located on the endeavour segment of the juan de fuca ridge is determined by comparing acoustic backscatter measured by the cabled observatory vent imaging sonar covis with model calculations based on in situ samples of particles suspended within the plume analysis of plume samples yields estimates of the mass concentration and size distribution of particles which are used to quantify their contribution to acoustic backscatter the result shows negligible effects of plume particles on acoustic backscatter within the initial 10 m rise of the plume this suggests turbulence induced temperature fluctuations are the dominant backscattering mechanism within lower levels of the plume furthermore inversion of the observed acoustic backscatter for the standard deviation of temperature within the plume yields a reasonable match with the in situ temperature measurements made by a conductivity

jarosite occurrence in the deccan volcanic province of kachchh western india spectroscopic studies on a martian analog locality the sulfate mineral jarosite is considered a key indicator of hydrous acidic and oxidizing conditions on the surface of early mars here we report an analog terrestrial locality hosting jarosite from matanumadh kachchh western india using detailed spectroscopic studies on weathered basalts of the deccan volcanic province and overlying tuffaceous shales and sandstones of the matanumadh formation hyperspectral data in the visible near infrared 350 2500 nm to midinfrared 4000 400 cm 1 region of the electromagnetic spectrum and x ray diffraction patterns have been acquired on samples collected from the field to detect and characterize the hydrous sulfate and phyllosilicate phases present at the studied site hydrous sulfates occur in association with al rich phyllosilicates kaolinite that overlie a zone of fe mg smectites in altered basalts jarosite is found within both saprolitic clay horizons altered from the basalt and within variegated sandstone and shale clay units overlying the saprolite it mostly occurs as secondary veins with or without gypsum jarosite is also seen as coatings on kaolinite clasts of varying shapes and sizes within the tuffaceous variegated sandstone unit we argue that the overall geological setting of the matanumadh area with this unusual mineral assemblage developing within altered basalts and in the overlying sedimentary sequence mimics the geological environment of many of the identified jarosite localities on mars and can be considered as a martian analog from this perspective

observations of dual slantwise circulations above a cool undercurrent in a mesoscale convective system a series of mesoscale convective systems mcss was observed in the uk during one of the intensive observation periods iop 3 in the convective storm initiation project csip a detailed case study of one of the mcss involving some novel interpretation of single doppler radar data reveals the evolution of stacked slantwise circulations associated with elevated upright convection a feature of this occasion was the existence near the surface of a strong undercurrent of cool air flowing against the direction of travel of the storm the air feeding both the upright and slantwise ascent originated not from near the surface but rather from layers between 1 and 3 km the upright convection was intense at first and was accompanied by a region of dry subsidence surrounding it together with the alternating layers of slantwise ascent and descent within the storm s precipitation area when the elevated upright convection weakened vigorous slantwise motions continued for some time but their slope decreased from the initial 1 in 4 to 1 in 9 the lowermost layer of slantwise descent corresponded to a moderately intense rear inflow jet the rear inflow jet did not penetrate the cool undercurrent and reach the surface instead beneath where it impacted the warm air capping the undercurrent the undercurrent took on the structure of a gravity wave without stagnation the raised head of the undercurrent lifted overlying air of high wet bulb potential temperature sufficiently to overcome the convective inhibition copyright c 2010 royal meteorological society

mineral abundances at the final four curiosity study sites and implications for their formation abstract a component of the landing site selection process for the mars science laboratory msl involved the presence of phyllosilicates as the main astrobiological targets gale crater was selected as the msl landing site from among 4 down selected study sites gale eberswalde and holden craters mawrth vallis that addressed the primary scientific goal of assessing the past habitability of mars a key constraint on the formation process of these phyllosilicate bearing deposits is in the precise mineralogical composition we present a reassessment of the mineralogy of the sites combined with a determination of the modal mineralogy of the major phyllosilicate bearing deposits of the four final study sites from the modeling of near infrared spectra using a radiative transfer model the largest abundance of phyllosilicates 30 70 is found in mawrth vallis the lowest one in eberswalde http www nasa gov mission pages msl news msl20130312 html is consistent with the compositions modeled for the eberswalde and holden deltaic rocks at gale the paucity the small diversity and the low abundance of nontronite do not favor a complex and long drainage system localized aqueous processes in space and time environments could have produced both nontronites and sulfates however most materials in gale are unfortunately dust covered so that orbital data are limited by spatial resolution and surficial fines that could dilute and obscure the spectral influence of phyllosilicates in the rocks potential formation processes of diverse and abundant mawrth vallis deposits include low temperature hydrothermal alteration in marine environments and or pedogenesis

corrosion morphology and cave wall alteration in an alpine sulfuric acid cave kraushohle austria abstract whereas most karstic caves worldwide are formed by carbonic acid a small but significant number of sub surface cavities are the product of sulfuric acid speleogenesis sas in the eastern alps no cave has so far been attributed to this type in this multidisciplinary study we demonstrate that kraushohle in northern styria was indeed formed by sas the cave pattern shows individual chambers 3d mazes and blind galleries as well as typical sas morphologies such as cupolas gypsum replacement pockets corrosion notches and convection niches ceiling pendant drip holes are described here for the first time and these corrosion features are fully consistent with the sas model other features of kraushohle include thick gypsum deposits with strongly depleted 34 s values and other minerals mostly sulfates indicating highly acidic conditions we also studied acid rock interaction processes giving rise to widespread corrosion and concomitant replacement by gypsum petrographic and geochemical analyses reveal the presence of a distinctive alteration layer of highly increased porosity at the interface between the host limestone and the secondary gypsum dissolution and replacement of the limestone was fast enough to prevent the development of c and o isotopic alteration halos but resulted in selective leaching of elements this stable isotope signal is thus different from the pronounced isotope gradient commonly observed in co 2 dominated hypogenic caves petrographic observations reveal that the limestone gypsum replacement was a nearly constant volume process

seismic precursors and magma ascent before the april 2011 eruption at axial seamount for volcanoes at submarine rift zones a direct link between seismicity seafloor deformation and magma intrusion has not been demonstrated recordings from ocean bottom hydrophones and bottom pressure recorders map an increasing rate of seismicity at axial seamount northeast pacific over several years before its eruption in april 2011

can we use pyroxene weathering textures to interpret aqueous alteration conditions yes and no pyroxene minerals are a significant component of shergottite nakhlite chassignite snc meteorites e g velbel 2012 and detected across large areas of mars surface e g mustard et al 2005 these minerals are associated with chloride sulfate and perchlorate salts that may represent briny waters present in mars history previous textural analyses by velbel and losiak 2010 comparing pyroxenes and amphiboles from various natural weathering environments showed no correlation between apparent apical angles describing the morphology of denticular weathering textures and mineralogy or aqueous alteration history in relatively dilute solutions however high salinity brines preferentially dissolve surface species potentially leading to different textures dependent on the brine chemistry in this study we performed controlled pyroxene dissolution experiments in the laboratory on a well characterized diopside to determine if aqueous alteration in different high salinity brines representative of potential weathering fluids on mars produce unique textural signatures following two months of dissolution in batch reactors we observed denticles on etch pit margins and pyroxene chip boundaries in all of the solutions investigated ultrapure water 18 m cm 1 a h 2 o 1 low salinity solutions containing 0 35 m nacl a h 2 o 0 99 0 35 m na 2 so 4 a h 2 o 0 98 and 2 m naclo 4 a h 2 o 0 9 and near saturated brines containing 1 7 m na 2 so 4 a h 2 o 0 95 3 m nacl a h 2 o 0 75 and 4 5 m cacl 2 a h 2 o 0 35 no systematic change in denticle length or apical angle was observed between any of the solutions investigated even when altered in brines with significantly different salinity activity of water and anion composition based on these and previous results from natural systems apical angle measurements are not a useful proxy for determining the extent or nature of aqueous alteration however since denticles form relatively slowly during weathering at circum neutral ph denticle length may be a useful proxy for chemical weathering duration all of the experimental solutions produced median denticle lengths 1 m likely due to the brief weathering experiments however perchlorate brines produced a significantly wider range of denticle lengths than those observed in all the other experimental solutions tested since perchlorate is likely a common constituent in martian soils glotch et al 2016 denticle length measurements should be used cautiously as proxies for extent of aqueous alteration on mars particularly in samples that also contain perchlorate

tidal current effects on temperature in diffuse hydrothermal flow guaymas basin a twelve day record of temperature collected from the diffuse flow area of a guaymas basin hydrothermal site exhibits variations from a minimum of 3 05 c to a maximum of 4 87 c whose periodicity is correlated with tides measured at the nearby town of guaymas a simple model based on the hypothesis that temperature variations result as changes in tidal bottom currents induce changes in the height of the thermal boundary layer is in good quantitative agreement with observed temperatures for most of the record the success of this model illustrates that the effects of tidal currents can be strong enough to dominate the time variability of a temperature signal at a fixed point in hydrothermal flow therefore tidal currents must be taken into account when using temperature measurements to estimate time varying heat fluxes from hydrothermal diffuse flow regions

deep sea hydrothermal plumes and their interaction with oscillatory flows 1 the acoustic scintillation method is applied to the investigation and monitoring of a vigorous hydrothermal plume from dante within the main endeavour vent field mef in the endeavour ridge segment a 40 day time series of the plume s vertical velocity and temperature fluctuations provides a unique opportunity to study deep sea plume dynamics in a tidally varying horizontal cross flow an integral plume model that takes into account ambient stratification and horizontal cross flows is established from the conservation equations of mass momentum and density deficit using a linear additive entrainment velocity in the model e um u that is a function of both the plume relative axial velocity um and the relative ambient flow perpendicular to the plume u gives consistent results to the experimental data suggesting entrainment coefficients 0 1 and 0 6 also from the integral model the plume height in a horizontal cross flow ua is shown to scale as 1 8b1 3ua 1 3n 2 3 for 0 01 ua 0 1 m s where b is the initial buoyancy transport and n is the ambient stratification both of which are assumed constant

changing brine inputs into hydrothermal fluids southern cleft segment juan de fuca ridge author s wheat cg zierenberg ra paduan jb caress dw clague da chadwick ww abstract 2020 the authors in 2016 temperature recorders were recovered temperatures were measured and fluid samples were collected from vent 1 a high temperature 338 c hydrothermal discharge site on the southern cleft segment of the juan de fuca ridge coupled with previous sampling efforts this collection represents a 32 year record of discharge from a single chimney structure the longest record to date remarkably the fluid has remained brine dominated for more than three decades this brine formed during phase separation and segregation prior to initial observations in 1984 although the chloride concentration of the discharging fluid has decreased with time the fluid temperature has remained nearly constant for at least 3 3 years and probably for 15 or even 22 years compositions of the discharging fluids are consistent with inputs from a deep sourced brine which was last equilibrated at g400 c at a depth consistent with the base of the sheeted dikes and the brittle ductile transition this brine mixed diffusion or dispersion with a likely non phase separated hydrothermal fluid prior to discharge a survey of hydrothermal endmember fluids with chlorinities in excess of 700 mmol kg shows with the exception of fe a single trend between major ion concentrations and chlorinity even though data are from a range of crustal compositions spreading rates and water and magma depths calculated deep sourced brines from hydrothermal fluid data are similar to data based on fluid inclusions and estimates of brine assimilation in magmas a better understanding of brines is required given their potential duration of discharge and capacity for mobilizing metals

depletion of a brine layer at the base of ridge crest hydrothermal systems the variable salinity of fluid venting from mid ocean ridges is indicative of mixing between hydrothermal seawater and fluids that have undergone supercritical phase separation in order to study the stability of a brine saturated layer that may form in the lowermost part of the hydrothermal system we have performed numerical simulations of a system that has returned into the subcritical regime for typical geological parameters it is shown that the interface between the brine layer and the overlying fluids is not very stable but vanishes by one of two dynamical mechanisms convective breakdown or vertical migration this contradicts the conventional picture of a steady layered convective system in which the brine is depleted only by dispersion and diffusion across the interface the depletion mechanism depends on the fluid dynamical stability of the brine layer convection within the brine layer results either in the convective breakdown for low excess salinity of the brine as compared to seawater or the upward migration of the interface for higher excess salinities consequently the depletion times are much shorter than for models with pure dispersion diffusion across the interface if the brine layer is static high chlorinity liquid is entrained slowly by the convecting overlying fluids leading to downward migration of the interface this gradual depletion of the brine layer results in almost constant vent salinities in agreement with measured salinities of chronic high chlorinity vents fl 2000 elsevier science b v all rights reserved

tide related variability of tag hydrothermal activity observed by deep sea monitoring system and obsh abstract hydrothermal activities were monitored by an ocean bottom seismometer with hydrophone obsh and a composite measuring system manatee including ctd current meter transmission meter and cameras at a small depression on the tag hydrothermal mound in the mid atlantic ridge low frequency pressure pulses detected by the hydrophone with semi diurnal periodicity seem to correspond to cycles of hydrothermal upflow from a small and short lived smoker vent close to the observing site the peaks of pressure pulses are synchronous with the maximum gradient of areal strain decrease due to tidal load release microearthquakes with very near epicenters occur sporadically and do not appear to be directly correlatable to hydrothermal venting temporal variations in bottom water temperature also have semi diurnal periodicity but are more complicated than the pressure events temperatures may be affected both by upwelling of hot water and by lateral flow of the bottom current changing its directions with ocean tide

acid alteration in the fumarolic environment of usu volcano hokkaido japan abstract the last eruptive activity of usu volcano in 1977 78 involved the development of high temperature 550 710 c fumaroles the gases emitted were h2o rich 95 99 mol with cl s 0 05 0 9 f cl 0 3 0 2 and with rh 2 5 close to the rock buffer feo feo1 5 cooling and oxidation of the high temperature gases resulted in the formation of acidic condensates ph 1 6 that interacted with the wall rock complete leaching of the cations ca na mg al and fe from the primary minerals and matrix glass occurred leaving in place only silica these mobilized cations precipitated as secondary minerals from acidic fluids that circulated in microcracks sem study shows mineral associations reflecting increasing fluid oxidation a al fluorides such as ralstonite namgalf6 h2o pyrite and anhydrite gypsum b an al hydroxide hematite gypsum and amorphous silica or cristobalite c al sulfates such as hydronium alunite h3o al3 so4 2 oh 6 alunite kal3 so4 2 oh 6 amorphous silica cristobalite hematite and anhydrite gypsum d al sulfates al fluorides amorphous silica cristobalite pyrite and anhydrite gypsum a ti oxide a fe mg sulfate and barite are present in minor amounts clay minerals are absent from the observed assemblages primary phenocrysts and matrix glass undergo a complete transformation to silica enriched in fluorine 1 7 wt this fluorine enrichment in the silicified parts of silicates and in silica incrustations suggests that f may play a role in silica mobilization modeling of the cooling of the high temperature gases was performed with the program gasworks the calculations suggest that 66 of the total sulfur from the gases may be lost by deposition as native sulfur at temperatures below 160 c thermochemical modeling of condensate rock interaction using chiller indicates that the cooling of gases was the source of the altering solutions oxidation by atmospheric o2 of the sulfur reduced species in the volcanic gas condensates resulted in their extreme acidification condensate rock interactions produce supersaturation with respect to the following mineral assemblages at 95 c 1 pyrite native sulfur cristobalite barite anhydrite diaspore log m h 2 s aq 2 32 2 cristobalite anhydrite hematite alunite diaspore log m h 2 s aq gypsum replaces anhydrite at t 25 c the calculated mineral assemblages are in agreement with those observed in the field

chemical variations in the 1998 2011 and 2015 lava flows from axial seamount juan de fuca ridge cooling during ascent lateral transport and flow

high resolution studies of the summit of axial volcano sea beam bathymetry sea marc i side scan 30 khz towed camera and submersible data from axial volcano juan de fuca ridge jdfr have been integrated to produce detailed maps of the volcano s summit region in order to elucidate its volcanic and tectonic evolution the proximity of axial volcano the youngest edifice of the cobb eickelberg seamount chain to the jdfr superposes a hotspot derived radial stress pattern onto the linear stress field of a mid ocean ridge spreading center the morphology of the summit of axial volcano reflects the differing eruptive styles produced from this superposition long rift zones begin at the edges of the caldera and extend as much as 75 km to the north and south axial volcano has a distinct summit plateau similar to those found on many other submarine volcanos the process by which summit plateaus are constructed is illustrated by the lava flows originating from the south rift zone which have partially filled the southern half of the caldera and have smoothed the flanks the summit plateau contains penetrative ne sw fracturing that is approximately parallel to the jdfr the unusual rectangular caldera is 3 8 km in size and its trend is about 160 three possible mechanisms are discussed for the caldera s formation 1 canary island type trapdoor formation 2 overlapping spreading center interaction and 3 magma source migration although none of these models is fully compatible with the present data base the overlapping spreading center model is preferred postcaldera volcanism probably began with the formation of the central caldera eruptive complex which was characterized by relatively low volume high viscosity flows the most recent volcanism has apparently taken place along the northern and southern rift zones which have erupted more fluid lavas resulting in areally extensive flows covering up to 60 of the caldera floor extensive low temperature venting and areas of high temperature venting near the northern and southern rift zones and caldera walls suggest a shallow magmatic source beneath the summit of axial volcano

jarosite dissolution rates and maximum lifetimes in high salinity brines implications for earth and mars abstract jarosite is a ferric sulfate salt k h na fe 3 so 4 2 oh 6 that forms in acidic oxidizing environments on earth and has also been observed in outcrops on mars high chloride concentrations within the outcrops at meridiani planum suggest that jarosite likely interacted with high salinity brines this study examines jarosite dissolution in h 2 o cacl 2 and h 2 o nacl brines activity of water a h 2 o 0 35 and 0 75 respectively to determine the effects of high salinity brines and a h 2 o on jarosite dissolution rates within brines with a h 2 o 0 75 and 0 35 initial k jarosite dissolution rates at 298 k decrease from log r 9 9 to 11 6 mol m 2 s 1 and na jarosite rates decrease from log r 10 6 to 11 2 mol m 2 s 1 respectively in addition k jarosite dissolution in nacl brine at 263 k yielded an average dissolution rate of log r 11 6 mol m 2 s 1 applying a shrinking sphere model to determine 1 mm jarosite particle lifetimes extends the maximum duration of fluid alteration from lifetimes of attack on residual fe 3 left on the surface of jarosite grains if brines on mars became highly concentrated in chlorine ions through sulfate precipitation the dissolution rate of jarosite and perhaps other minerals as well could accelerate with time shortening particle lifetimes and the inferred duration of aqueous diagenesis significantly

in situ measurement of dissolved chloride in high temperature hydrothermal fluids abstract the ability to continuously monitor chemical properties of hydrothermal vent effluents for extended periods of time is essential to understanding dynamic processes responsible for the temporally variable nature of mid ocean ridge hydrothermal systems although instruments do exist for some parameters there has been no sensor capable of measuring the chloride concentration an indicator of possible phase separation on a real time and long term basis in this article we discuss the construction of a novel instrument which measures solution resistance as a proxy for chloride concentration the sensor consists of four gold electrodes embedded in a cylindrical zro 2 ceramic housing it has been successfully deployed in several high temperature vents at the main endeavour field mef on the juan de fuca ridge in the ne pacific and calibrated under simulated hydrothermal conditions ranging up to 380 c and 300 bar the in situ data clearly demonstrate a tidal influence on the effluent from some high temperature vents possibly relating to a subsurface mixing process involving non seawater end members non tidal changes are used to constrain the sequence and type of controls operating on fluids circulating within the subsurface

bottom trapped subinertial motions over midocean ridges in a stratified rotating fluid abstract linear analytical solutions for bottom trapped subinertial oscillatory flow over simple ridge topographies in a stratified two layer rotating fluid are presented results are compared to moored current meter observations of bottom intensified motions over the endeavour segment of juan de fuca ridge in the northeast pacific the solutions reproduce many of the observed features including preferential amplification of the clockwise rotary component of velocity over the ridge and increased velocity amplification with proximity to the ridge crest for a given internal deformation radius the degree of current amplification increases with increased bottom slope ridge height and oscillation frequency amplification decreases with increased width of the ridge relative to the deformation radius

salinity variations in submarine hydrothermal systems by layered double diffusive convection various mechanisms have been proposed to explain the salinity variations in vent fluids of seafloor geothermal systems new experiments reacting diabase and evolved seawater were carried out to reproduce earlier published observations of cl depletions attributed to formation of an ephemeral cl bearing mineral the absence of any cl depletions in the present study suggests that the formation of cl bearing minerals is not sufficiently widespread to account for the observed salinity variations in the vent fluids a re evaluation of both field and laboratory evidence has led to a new model for subseafloor circulation that accounts for salinity variations as well as other chemical and mineralogic observations in place of a simple single pass convection system we propose that the seafloor systems consist of two vertically nested convection cells in which a brine layer at depth heats and drives an overlying seawater cell such layering of salinities a process known in fluid mechanics as double diffusive conve

gradients in the composition of hydrothermal fluids from the endeavour segment vent field phase separation and brine loss hydrothermal fluid samples collected in 1984 1987 and 1988 from a large vent field near 47 57 n on the endeavour segment of the juan de fuca ridge jfr have been analyzed for major and minor elements and gases there are of the order of 100 individual smoker vents on 10 large sulfide structures which are localized along faults and fault intersections across the vent field each sulfide structure has a characteristic fluid composition which varies very little from one vent orifice to the next or from year to year on a given structure however there are large gradients in fluid composition across the vent field with endmember chlorinity increasing from 255 mmol kg in the sw to 505 mmol kg in the ne end member concentrations of major elements are well correlated with chlorinity and endmember volatile concentrations in the lowest chlorinity fluids are approximately twice as high as in the highest chlorinity fluids the gradients in composition across the vent field and measured vent fluid temperatures 400 c are consistent with supercritical phase separation and loss of brine phase below the seafloor the factor of 2 variation in co2 and h2s is larger than expected for loss of a very high chlorinity brine concentrations of iron and manganese are not positively correlated with chlorinity suggesting that temperature and ph are more important in controlling metal solubility elevated ammonia and bromide chloride ratios indicate that there has been subseafloor interaction between the hydrothermal fluids and organic matter and high boron concentrations point to a sedimentary source

superficial alteration mineralogy in active volcanic systems an example of poas volcano costa rica abstract the alteration mineralogy in the crater area of poas volcano costa rica has been studied to constrain acid fluid rock interaction processes and conditions relevant for the formation of sulphate bearing mineral assemblages found on the surface of mars individual sub environments which include the hyperacid lake laguna caliente ephemeral hot springs fumarole vents and areas affected by acid rain and or spray from the lake are marked by distinct secondary mineral associations with sulphates commonly as prevailing component the sulphates occur in a wide mineralogical diversity comprising gypsum anhydrite various polyhydrated al sulphates alunite jarosite group minerals halotrichite voltaite and copiapite group minerals epsomite and romerite depending on the sub environment they are variably associated with clay minerals kaolinite group and smectite group zeolites sio 2 polymorphs fe hydro oxides ti oxides native sulphur sulphides chlorides fluorides phosphates and carbonates geochemical modelling was performed to identify mechanisms responsible for the formation of the secondary minerals found in the field and to predict their possible stability under conditions not seen at the surface the results indicate that the appearance of amorphous silica hematite anhydrite gypsum pyrite anatase and kaolinite is relatively insensitive to the degree of acidity of the local aqueous system on the other hand alunite jarosite group minerals elemental sulphur and al oh so 4 only form under acidic conditions ph 2 sulphates is restricted to olivine bearing rocks exposed to acid rain or brine spray modelling suggests that their formation required a repetitive sequence of olivine dissolution and evaporation in an open system involving limited amounts of fluid the mineral variety in the crater of poas is remarkably similar to sulphate bearing assemblages considered to be the product of acid sulphate alteration on mars the analogy suggests that comparable fluid rock interaction controls operated in martian volcanic environments

hydrogeochemical processes governing the origin transport and fate of major and trace elements from mine wastes and mineralized rock to surface waters abstract the formation of acid mine drainage from metals extraction or natural acid rock drainage and its mixing with surface waters is a complex process that depends on petrology and mineralogy structural geology geomorphology surface water hydrology hydrogeology climatology microbiology chemistry and mining and mineral processing history the concentrations of metals metalloids acidity alkalinity cl f and so 4 2 found in receiving streams rivers and lakes are affected by all of these factors and their interactions remediation of mine sites is an engineering concern but to design a remediation plan without understanding the hydrogeochemical processes of contaminant mobilization can lead to ineffective and excessively costly remediation furthermore remediation needs a goal commensurate with natural background conditions rather than water quality standards that might bear little relation to conditions of a highly mineralized terrain this paper reviews hydrogeochemical generalizations primarily from us geological survey research that enhance our understanding of the origin transport and fate of contaminants released from mined and mineralized areas mobility of potential or actual contaminants from mining and mineral processing activities depends on 1 occurrence is the mineral source of the contaminant actually present 2 abundance is the mineral present in sufficient quantity to make a difference 3 reactivity what are the energetics rates and mechanisms of sorption and mineral dissolution and precipitation relative to the flow rate of the water and 4 hydrology what are the main flow paths for contaminated water estimates of relative proportions of minerals dissolved and precipitated can be made with mass balance calculations if minerals and water compositions along a flow path are known combined with discharge these mass balance estimates quantify the actual weathering rate of pyrite mineralization in the environment and compare reasonably well with laboratory rates of pyrite oxidation except when large quantities of soluble salts and evaporated mine waters have accumulated underground quantitative mineralogy with trace element compositions can substantially improve the identification of source minerals for specific trace elements through mass balances post dissolution sorption and precipitation attenuation reactions depend on the chemical behavior of each element solution composition and ph aqueous speciation temperature and contact time with mineral surfaces for example little metal attenuation occurs in waters of low ph

a model of an atlantic and pacific hydrothermal plume a turbulent entrainment model of a hydrothermal plume was modified to include the effects of vertical structure in the background temperature and salinity fields owing to the stably stratified salinity field in the pacific relatively warm salty water spreads at an equilibrium level where the plume density equals the ambient density in contrast the unstable salinity profile in the atlantic gives the plume added buoyancy and it continues to rise to an equilibrium level where it is relatively cool and fresh these attributes result from the mixing between the plume and the surrounding seawater at each level below the spreading layer the equilibrium temperature anomaly is not directly proportional to the source strength but depends on the mixing and background salinity gradient the net entrainment of surrounding seawater is greater in the atlantic plume model than in the pacific plume model for the same buoyancy flux recent data from the tag hydrothermal field at 26 n on the mid atlantic ridge and data from a vent field on the endeavor segment of the juan de fuca ridge are compared to model results the model predicts the penetration height and s characteristics of the atlantic plume and it explains some of the differences between the observed atlantic and pacific hydrothermal plumes

characteristics of 4 day oscillations trapped by the juan de fuca ridge current meter observations from different studies along the crest of the juan de fuca ridge have been combined to show new features of the relatively large broad spectral peak centered near a period of about 4 days the coherence range of the 4 day oscillations has been extended to the extreme ends of the ridge and the trapped waves appear to propagate northward along the entire length of the ridge at about 1 m s spectral amplitudes are about double on the south end compared to the north end and a recent model for bottom trapped subinertial waves over topography shows this may be due to variations in ridge width allen and thomson 1993 new observations show coherence between temperatures and currents near the south cleft vent field and suggest 4 day oscillations can play a major role in the local advection of hydrothermal plumes these observations combined with earlier results demonstrate that 4 day oscillations are a significant ridge trapped feature and they suggest that other ridges may be important in transmitting energy over much longer distances

circulation hydrography and transport over the summit of axial seamount a deep volcano in the northeast pacific a numerical model of ocean flow hydrography and transport is used to extrapolate observations of currents and hydrography and infer patterns of material flux in the deep ocean around axial seamount a destination node of nsf s ocean observatories initiative s cabled array using an inverse method the model is made to approximate measured deep ocean flow around this site during a 35 day time period in the year 2002 the model is then used to extract month long mean patterns and examine smaller scale spatial and temporal variability around axial like prior observations model month long mean currents flow anti cyclonically around the seamount s summit in toroidal form with maximum speeds at 1500m depth of 10 11 cm s as a time mean the temperature salinity anomaly distribution takes the form of a cold briny dome above the summit passive tracer material continually released at the location of the ashes vent field exits the caldera primarily through its southern open end before filling the caldera once outside the caldera the tracer circles the summit in clockwise fashion fractionally re entering the caldera over lower walls at its north end while gradually bleeding southwestward during the modeled time period into the ambient ocean a second tracer release experiment using a source of only two day duration inside and near the casm vent field at the northern end of the caldera suggests a residence time of the fluid at that locale of 8 9 days

alunite dissolution rates dissolution mechanisms and implications for mars abstract alunite kal 3 so 4 2 oh 6 is a hydrated aluminous sulfate mineral associated with acidic oxidizing aqueous environments on earth additionally orbiting spacecraft and rovers on mars have reported spectral data that indicate a range of mono and polyhydrated sulfate phases and hydroxysulfate phases suggesting such conditions also existed on mars in the past this study examines alunite dissolution rates in aqueous systems with varying ph temperature and solution chemistry conditions alunite dissolution rates in dilute solutions are 2 3 orders of magnitude slower than jarosite dissolution rates measured under analogous conditions similar to jarosite alunite dissolution rates vary as a function of activity of h and oh following the rate law log r mol m 2 s 1 0 133 0 02 ph 10 65 0 07 at ph r 0 194 0 04 ph 12 53 0 26 at ph 5 however minimum alunite dissolution rates are shifted to higher ph 5 5 5 likely due to differences in fe and al speciation alunite and jarosite rates converge in saturated nacl and cacl 2 brines as the activity of water decreases suggesting that differences in water exchange rates with fe 3 and al 3 control dissolution rates in dilute solutions while metal cl complexation occurs at similar rates within the brines particle lifetimes based on measured dissolution rates in dilute solutions show that alunite particles are expected to be preserved two orders of magnitude longer than jarosite particles over a range of ph and temperature conditions in particular alunite is more likely to be preserved in neutral to moderately alkaline systems compared to jarosite which is expected to be preserved in more acidic conditions alunite dissolution produced amorphous al rich alteration products at moderate to high ph unlike jarosite alunite dissolution does not show a clear trend as a function of temperature alunite dissolution rates do not increase with increasing temperature likely due to lower alunite solubility at higher temperature therefore alunite is expected to be more prevalent in hydrothermal systems compared to jarosite

repeat bathymetric surveys at 1 metre resolution of lava flows erupted at axial seamount in april 2011 at frequently active submarine volcanoes it is difficult to distinguish between new and pre existing lava flows a combination of high resolution bathymetric surveys taken before and after an eruption at axial seamount in 2011 allows detailed mapping of the 2011 lava flows and highlights the tendency of new flows to mimic older ones

constrained circulation at endeavour ridge facilitates colonization by vent larvae understanding how larvae from extant hydrothermal vent fields colonize neighbouring regions of the mid ocean ridge system remains a major challenge in oceanic research1 2 among the factors considered important in the recruitment of deep sea larvae are metabolic lifespan the connectivity of the seafloor topography and the characteristics of the currents3 here we use current velocity measurements from endeavour ridge to examine the role of topographically constrained circulation on larval transport along ridge we show that the dominant tidal and wind generated currents in the region are strongly attenuated within the rift valley that splits the ridge crest and that hydrothermal plumes rising from vent fields in the valley drive a steady near bottom inflow within the valley extrapolation of these findings suggests that the suppression of oscillatory currents within rift valleys of mid ocean ridges shields larvae from cross axis dispersal into the inhospitable deep ocean this effect augmented by plume driven circulation within rift valleys having active hydrothermal venting helps retain larvae near their source larvae are then exported preferentially down ridge during regional flow events that intermittently over ride the currents within the valley

geothermal heat flux from hydrothermal plumes on the juan de fuca ridge thesis m s massachusetts institute of technology dept of ocean engineering and woods hole oceanographic institution 1991

inflation predictable behavior and co eruption deformation at axial seamount deformation of the ground surface at active volcanoes provides information about magma movements at depth improved seafloor deformation measurements between 2011 and 2015 documented a fourfold increase in magma supply and confirmed that axial seamount s eruptive behavior is inflation predictable probably triggered by a critical level of magmatic pressure a 2015 eruption was successfully forecast on the basis of this deformation pattern and marked the first time that deflation and tilt were captured in real time by a new seafloor cabled observatory revealing the timing location and volume of eruption related magma movements improved modeling of the deformation suggests a steeply dipping prolate spheroid pressure source beneath the eastern caldera that is consistent with the location of the zone of highest melt within the subcaldera magma reservoir determined from multichannel seismic results

1998 eruption of axial volcano multibeam anomalies and sea floor observations lava flows erupted during the january february 1998 seismic swarm at axial volcano on the juan de fuca ridge have been identified by differencing of pre and post event multibeam bathymetric surveys and by seafloor observations a sheet flow more than 3 km in length and 500 800 m wide erupted from the uppermost south rift is the site of a robust hydrothermal system 1998 lavas occur over about 9 km of the upper south rift zone or about 20 of the along axis length of the seismicity event 50 km the estimated volume of lava erupted is 18 76 106 m for the extrusion and 100 106 m for the intrusion the total volume is consistent with the volume from modeling of seafloor strain measurements recorded during the event

entrainment and bending in a major hydrothermal plume main endeavour field juan de fuca ridge 1 we measure expansion rate and bending in a 23 hour time series of acoustic images of the lower 25 m section of a buoyant hydrothermal plume rising from grotto vent in the main endeavour field juan de fuca ridge we then calculate entrainment coefficient the constant of proportionality relating mean inflow velocity at the plume edge to maximum mean upward velocity within the plume the plume section alternately bends southwest at relatively high inclinations 37 and northeast at lower inclinations at irregular intervals twice during this time period apparently driven by current reversals in the mixed semi diurnal tidal cycle the measured expansion rates 0 11 0 25 m m and calculated entrainment coefficients 0 07 0 18 are directly proportional to the degree of bending r2 0 75 the loss of buoyancy flux related to enhanced mixing in a stratified environment during bending may contribute to reduction of potential rise height consistent with predicted 400 m and measured 300 350 m plume tops

how long was meridiani planum wet applying a jarosite stopwatch to determine the duration of aqueous diagenesis jarosite dissolution rates can be used to determine the duration of water at meridiani planum and other environments containing this ephemeral metastable ferric sulfate salt the maximum duration of aqueous fluids in the region is calculated based on the dissolution rate of jarosite under varying temperature and ionic strength conditions jarosite lifetimes predicted in this study range from 1 5 a in warm dilute environments to 100 ka in nacl saturated brines at 250 k the preservation of jarosite within rocks at meridiani planum requires that aqueous fluids were active over a small fraction of the billions of years since jarosite formed or was deposited in the region limiting the probability of life being established in such a temporally restricted system in addition water related features such as hematite spherules and crystal molds must have formed relatively quickly during this geologically short period of aqueous diagenesis

direct observation of a submarine volcanic eruption from a sea floor instrument caught in a lava flow our understanding of submarine volcanic eruptions has improved substantially in the past decade owing to the recent ability to remotely detect such events and to then respond rapidly with synoptic surveys and sampling at the eruption site but these data are necessarily limited to observations after the event in contrast the 1998 eruption of axial volcano on the juan de fuca ridge was monitored by in situ sea floor instruments one of these instruments which measured bottom pressure as a proxy for vertical deformation of the sea floor was overrun and entrapped by the 1998 lava flow the instrument survived being insulated from the molten lava by the solidified crust and was later recovered the data serendipitously recorded by this instrument reveal the duration character and effusion rate of a sheet flow eruption on a mid ocean ridge and document over three metres of lava flow inflation and subsequent drain back after the brief two hour eruption the instrument also measured gradual subsidence of 1 4 metres over the next several days reflecting deflation of the entire volcano summit as magma moved into the adjacent rift zone these findings are consistent with our understanding of submarine lava effusion as previously inferred from seafloor observations terrestrial analogues and laboratory simulations

detection of iron substitution in natroalunite natrojarosite solid solutions and potential implications for mars natroalunite containing substantial amounts of fe occurs as a prominent secondary phase during acid sulfate alteration of pyroclastic basalts in volcanic fumaroles in nicaragua and elsewhere and has been observed in laboratory simulations of acid sulfate alteration as well reaction path models constrained by field and experimental observations predict that fe rich natroalunite should also form as a major secondary phase during alteration of martian basalt under similar circumstances here we evaluate the potential to use spectroscopic methods to identify minerals from the alunite group with chemical compositions intermediate between natroalunite and natrojarosite on the surface of mars and to remotely infer their fe contents x ray diffraction and spectroscopic measurements raman visible near infrared mid infrared mossbauer were obtained for a suite of synthetic solid solutions with a range of fe contents ranging from natroalunite to natrojarosite in the visible near infrared minerals with intermediate compositions display several spectral features not evident in end member spectra that could be used to remotely identify these minerals and infer their composition in addition raman spectra mid infrared spectra and x ray diffraction peaks all show systematic variation with changing fe content indicating that these methods could potentially be used to infer mineral compositions as well the results suggest that alunite group minerals with intermediate fe compositions may be able to account for some visible near infrared and mossbauer spectral features from mars that had previously been unidentified or attributed to other phases overall our findings indicate that consideration of solid solutions may lead to new identifications of alunite group minerals on the surface of mars and raise the possibility that minerals with compositions intermediate between natroalunite and natrojarosite may be widely distributed on the planet

evaluation of the rate of dissolution of secondary sulfate minerals for effective acid and metalliferous drainage mitigation abstract the presence of latent acidity in the form of the jarosite alunite mineral group complicates assessment of the rates of acid and metalliferous drainage amd generation from potentially acid forming waste rocks and tailings to enable better prediction of the contributions from these secondary sulfate minerals the relationships between ph and the rate of dissolution for natrojarosite and alunite for comparison with pyrite have been determined in single mineral unstirred systems the dissolution rates of natrojarosite and alunite in the ph range 2 7 were in the range of 10 14 to 10 13 mol m 2 s 1 and were found to be slowest at ph 3 4 and 5 5 respectively at ph above these respective minima alunite and natrojarosite dissolution results in acid release the surface area normalised dissolution rates of both minerals were 2 3 orders of magnitude slower than that of pyrite under the same conditions and were 2 4 orders of magnitude slower than the rates of stirred dissolution of synthetic jarosite and alunite reported in the literature in mixed mineral mini column dissolution tests pyrite oxidation proceeded at almost the same rate in the longer term 50 days regardless of the presence or absence of natrojarosite or alunite as the presence of these secondary sulfate minerals does not impact significantly on pyrite oxidation their contributions to amd can be taken into account separately enabling accurate calculation of the neutralisation rates needed to effectively manage amd

on the rise of turbulent plumes quantitative effects of variable entrainment for submarine hydrothermal vents terrestrial and extra terrestrial explosive volcanism 1 the maximum height reached by a turbulent plume rising in a stratified environment is a key tool to estimate the flux released at its source particularly for large scale flows because flux can often be very hard to measure directly this height is known to be mainly controlled by the stratification of the ambient fluid source buoyancy flux and the efficiency of turbulent mixing between the plume and the external fluid the latter effect has been only superficially explored in spite of its fundamental control on the dynamics here we show that commonly used one dimensional models incorporating a constant entrainment coefficient do not provide satisfying predictions we propose a new model allowing for variable entrainment which gives excellent predictions of maximum heights reached by laboratory plumes in stratified environments we then apply our formalism to natural plumes produced by explosive volcanic eruptions under terrestrial paleo martian and venusian conditions and by submarine hydrothermal activity at mid ocean ridges source mass discharge rates deduced from maximum volcanic column heights for terrestrial eruptions are found to be greater than those estimated with the commonly used constant entrainment parameterization by a factor of 2 in the paleo martian atmosphere existing models overestimate plume heights by 14 27 in the current atmosphere of venus the maximum height reached by a volcanic plume is also found to be smaller than previously estimated for large eruption rates the source heat flux released by the tag field atlantic ocean deduced from several submarine hydrothermal plumes is found greater by a factor 3 with our model

unique event plumes from a 2008 eruption on the northeast lau spreading center the creation of ocean crust by lava eruptions is a fundamental earth process involving immediate and immense transfers of heat and chemicals from crust to ocean this transfer creates event plumes megaplumes massive ellipsoidal eddies with distinctive and consistent chemical signatures here we report the discovery of unique event plumes associated with a 2008 eruption on the northeast lau spreading center instead of a large plume hundreds of meters thick we detected at least eight individual plumes each 50 m thick and apparently only 1 3 km in diameter yet still rising 200 1000 m above the eruption site low and uniform 3he heat 0 041 10 17 mol j and dissolved mn heat 0 04 nmol j ratios in water samples were diagnostic of event plumes high h2 concentrations up to 9123 nm and basalt shards confirmed extensive interactions between molten lava and event plume source fluids remote vehicle observations in 2009 mapped a new small 1 5 5 8 106 m3 lava flow our results suggest that event plumes are more variable and thus perhaps more common than previously recognized small event plumes may be preferentially associated with small or sheet flow eruptions and massive event plumes with slowly extruding pillow mounds 25 75 m thick despite this correlation and high h2 concentrations existing theory and seafloor observations argue that cooling lava cannot transfer heat fast enough to create the buoyancy flux required for event plumes the creation of event plumes under a broad range of eruption conditions provides new constraints for any theory of their formation

paleoclimate of mars as captured by the stratigraphic record in gale crater a kilometers thick sedimentary sequence in gale crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale the sequence is divided into two formations where the lower formation exhibits a net transition in mineralogy from clay sulfate to sulfate oxide assemblages and is separated from the overlying upper formation by an erosional unconformity superposition and crater counts suggest strata in the lower formation lie along the noachian hesperian time stratigraphic boundary whereas beds in the upper formation which lack signatures indicative of clay minerals or sulfates are thinner more regularly spaced and clearly younger the observed stratigraphic trends are consistent with the rocks at gale crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts

near inertial motions over a mid ocean ridge effects of topography and hydrothermal plumes we investigate the spatial structure of near inertial motions in the vicinity of the endeavour segment of juan de fuca ridge approximately 48 n 129 w in the northeast pacific ocean on the basis of time series current and water property data collected from september 1984 to september 1987 near inertial motions are ubiquitous features of the 2200 m water column with root mean square rms current speeds comparable to those of the dominant m2 tidal currents within the lower 1000 m of the water column where most of the observations were obtained near inertial oscillations have rms current speeds of o 1 cm s and vertical isotherm displacements of o 10 m the fluctuations are confined to the frequency band 0 966 1 079 f f is the local coriolis parameter and have characteristic event durations of 1 week although the spectra of subsurface motions are dominated by the blue shifted superinertial band significant spectral peaks are found also in the subinertial and inertial frequency bands marked alteration of the near inertial current amplitudes occurs over two well defined depth zones within the study region within the 200 m zone immediately above the 2100 m ridge crest current amplitudes are amplified by a factor of 1 2 1 7 because of bottom reflection and or scattering of the downward propagating energy evidence that the amplification may be linked to bottom reflection rather than to scattering is provided by flattening and cross slope rotation of the near inertial current ellipses with increased proximity to the top of the ridge reflection would occur at grazing angles of less than 1 and would be associated with surface generated waves originating at distances of over 100 km from the observational site in contrast to the enhanced amplitudes immediately above the top of the ridge near inertial currents within the 1600 to 1800 m depth range undergo pronounced attenuation and frequency alteration amplitude attenuation is especially pronounced for motions in the superinertial band and may arise through critical layer absorption of downward propagating waves as they encounter increased vertical shear in the background flow the increased shear is most likely associated with buoyancy induced flow formed by the extensive hydrothermal plume emanating from vent sites in the axial valley along the ridge crest but it could also be related to bottom trapped oscillations over the steep ridge topography near inertial motions are estimated to have vertical coherence scales of the order of 10 100 m while horizontal coherence scales exceed the 50 km separation between the mooring locations minimum vertical and horizontal coherences are found for the depth zone 1600 1800 m while maximum correlation occurs for near bottom motions immediately above the crest of the ridge weak near inertial motions are observed within the 100 m deep axial valley

tidally driven effluent detected by long term temperature monitoring at the tag hydrothermal mound mid atlantic ridge abstract during aug 13 21 1994 temperatures and current velocity were simultaneously monitored on the tag hydrothermal mound three giant kelps gks vertical thermistor arrays of 50 m height were moored on the periphery of the central black smoker complex cbc a manatee multi monitoring system including current velocity was deployed 50 m east of cbc four daibutsu geothermal probes penetrated the sediment south to west of cbc compilation of all data revealed semi diurnal variations in water temperatures and current velocity and allowed us to discuss the source of these anomalies temperature anomalies of gks correlate well with current velocity and are interpreted to be caused by the main plume from cbc that was bent over by the tidal current we identified two types of asymmetric periodic temperature variations at daibutsu probes 2 and 8 located 20 m to the south of cbc by comparing temperatures and current velocity they are attributed to non buoyant effluents laterally advected by the tidal current the source of one variation is located east to ese of the probes and the source of the other is located to the north on aug 31 a new periodic anomaly emerged on probe 2 with its amplitude up to 0 8 c the 6 h offset between the new anomaly and the previous one suggests that the source of the new anomaly lies to the west of probe 2 the heat flux of these non buoyant effluents is estimated to range from 30 to 100 kw m 2 which is of the same order as direct estimates of diffuse flow at the tag mound it suggests that a significant amount of diffuse effluent is laterally advected by the prevailing current near the seafloor

layers of insect echoes near a thunderstorm and implications for the interpretation of radar data in terms of airflow insects can serve as useful radar targets for determining aspects of the structure and kinematics of the atmosphere but it is necessary sometimes to know more about insect behaviour in order to have confidence in the meteorological interpretations a variety of meteorological radars situated at chilbolton in southern england have been used to investigate the nature of multiple shallow clear air echo layers that were detected at heights between 1 0 and 2 5 km in the vicinity of an elevated daytime thunderstorm mesoscale convective system multi wavelength and polarization measurements were used to confirm that the layers were due in large part to insects the layers were within potentially warm air near the top of a cold undercurrent of surface air the convective updraught of the thunderstorm was fed by air from just above the cold undercurrent some of the insect layers were within air destined to ascend into the storm s convective updraught and some were within undercurrent air that was forced to ascend only temporarily as the storm approached initially the layer echoes ascended with the airflow but then close to the storm their intensity weakened despite continuing updraughts mainly as a result of the insects dropping downwards far ahead of the storm the insects showed a strong preference to remain within their individual shallow layers but even close to the storm where they started dropping out insects still retained a preference to be within these layers as a result some layers continued to be discernible as they followed the ascending airflow towards the storm thereby continuing to serve as useful meteorological tracers of the perturbed flow in the vicinity of the thunderstorm copyright 2011 royal meteorological society

comparative planetary mineralogy implications of martian and terrestrial jarosite a crystal chemical perspective abstract the importance of the discovery of jarosite at the meridiani planum region of mars is discussed terrestrial studies demonstrate that jarosite requires a unique environment for its formation crystallizing from highly acidic ph 2 that reacted with aqueous solutions in shallow aquifers or on the martian surface this interaction forms both h 2 so 4 and h 2 s a martian oxidant must be identified to both oxidize h 2 s to produce the required acidity of the fluid and to oxidize fe 2 to fe 3 we suggest that reactions involving both sulfur and the reduction of co 2 to co may provide part of the answer the jarosite crystal structure is truly remarkable in terms of its tolerance for the substitution of a large number of different cations with different ionic radii and charges the structure accommodates hydrogen oxygen and sulfur the stable isotope systematics of which are strong recorders of low temperature fluid rock atmosphere interactions jarosite has been proven to be a robust chronometer for ar ar and k ar dating techniques and there is every reason to believe that u pb rb sr and nd sm techniques for older jarosite from mars will also be robust although the discovery of jarosite on mars alone with no other analytical measurements on the phase has given us insights to martian surficial processes the true power of jarosite can not be exploited until jarosite is sampled and returned from mars mars sample return is a long way off but until then we should be vigilant about examining martian meteorites for alteration assemblages that contain jarosite a suite of jarosite samples representing a significant time span on mars may hold the key to reading the record of martian atmospheric evolution

detection of an unusually large hydrothermal event plume above the slow spreading carlsberg ridge nw indian ocean about 90 of earth s volcanism occurs along the global mid ocean ridge system here sporadic volcanic and tectonic activity is thought to cause cataclysmic release of hydrothermal fluids forming event plumes each plume often contains as much hydrothermal effluent and heat as chronic hydrothermal venting from a typical vent site discharges during a year to date only a few event plumes have been detected and only above intermediate rate spreading ridges in the pacific here we report the first evidence for an unusually large event plume that originated from the slow spreading 3 cm yr full rate carlsberg ridge in the nw indian ocean at 70 km long up to 4540 km3 in volume and with up to 24 1016 j of excess heat this event plume was substantially larger than previous ones and demonstrates that dispersion of hydrothermal heat and biological products from slow spreading ridges may be more significant and effective than hitherto imagined

deep ocean circulation and transport where the east pacific rise at 9 10 n meets the lamont seamount chain 1 we report the first 3 d numerical model study of abyssal ocean circulation and transport over the steep topography of the east pacific rise epr and adjoining lamont seamount chain in the eastern tropical pacific we begin by comparing results of hydrodynamical model calculations with observations of currents hydrography and sf6 tracer dispersion taken during larval dispersal on the deep east pacific rise ladder field expeditions in 2006 2007 model results are then used to extend observations in time and space regional patterns are pronounced in their temporal variability at m2 tidal and subinertial periods mean velocities show ridge trapped current jets flowing poleward west and equatorward east of the ridge with time varying magnitudes weekly average maximum of 10 cm s 1 that make the jets important features with regard to ridge originating particle larval transport isotherms bow upward over the ridge and plunge downward into seamount flanks below ridge crest depth the passage p1 between the epr and the first lamont seamount to the west is a choke point for northward flux at ridge crest depths and below weekly averaged velocities show times of anticyclonic flow around the lamont seamount chain as a whole and anticyclonic flow around individual seamounts results show that during the ladder tracer experiment sf6 reached p1 from the south in the western flank jet a short lived change in regional flow direction just at the time of sf6 arrival at p1 started the transport of sf6 to the west on a course south of the seamounts as field observations suggest approximately 20 days later a longer lasting shift in regional flow from west to sse returned a small fraction of the tracer to the epr ridge crest

iron and aluminum hydroxysulfates from acid sulfate waters acid sulfate waters are produced mostly by the oxidation of common sulfide minerals such as pyrite chalcopyrite pyrrhotite and marcasite in rocks soils sediments and industrial wastes this spontaneous process of mineral weathering plays a fundamental role in the supergene alteration of ore deposits the formation of acid sulfate soils and the mobilization and release of acidity and metals to surface and ground waters the purely natural process of acid rock drainage is often intensified by human activities related to mining mineral processing construction soil drainage and dredging geochemical reaction rates are accelerated because physical disturbance gives greater exposure of mineral surfaces to air and water and to microbes that catalyze the reaction process large quantities of reactive sulfides are also concentrated and exposed to air as a result of mining and mineral processing acid sulfate waters produce a number of fairly insoluble hydroxysulfate and oxyhydroxide minerals that precipitate during oxidation hydrolysis and neutralization the objective of this chapter is to describe the formation properties fate and environmental implications of the nano to microphase hydroxy sulfates of fe and al that are precipitated from acid sulfate waters these minerals are commonly of poor crystallinity and difficult to characterize much remains to be learned about their occurrence formation and properties mine drainage the best known examples of acid sulfate waters are those released from mines where coal and metallic sulfide ores have been exploited ash et al 1951 barton 1978 nordstrom 1982a rose and cravotta 1998 nordstrom and alpers 1999 there may be as many as 500 000 inactive or abandoned mine sites in the united states alone lyon et al 1993 although most of these pose no immediate water quality problem kleinmann 1989 estimated that about 19 300 km of streams and more than 72 000 ha of lakes and reservoirs have been

numerical simulation of hydrothermal vent induced circulation at endeavour ridge hydrothermal venting at endeavour ridge is focused at five major vent fields spaced at 2 km intervals along a narrow 1 km wide north south trending rift valley a princeton ocean model with an axially symmetric rift valley centered within a rotating full depth 2400 m stratified ocean is used to simulate the circulation and associated temperature and salinity fields generated by vertical heat fluxes from the five vent fields steady seafloor heat fluxes are introduced instantaneously to a quiescent ocean using the model provision for boundary fluxes the model achieves a quasi steady state in about 80 days results are consistent with observation in particular buoyant plumes emanating from the larger vent fields rise to trapping depths as shallow as 1850 m 350 m above bottom and spread laterally with the vent induced circulation plume anomalies remain confined to within several kilometers of the ridge except to the west where anomalies extend more than 10 km off axis as with observations modeled currents within the valley consist of a strong 10 cm s 1 poleward inflow within roughly 75 m of the bottom and an equally strong equatorward counterflow above that depth weak 1 cm s 1 equatorward flow develops over the flank of the west ridge and weak poleward flow over the flank of the east ridge cyclonic relative vorticity dominates the model circulation within the valley while anticyclonic vorticity prevails above the depth of neutral plume buoyancy findings support the notion that turbulent entrainment by buoyant plumes forces a mean poleward flow within the confines of the endeavour ridge axial valley

in situ ground deformation measurements from the summit of axial volcano during the 1998 volcanic episode since september 1987 seafloor instrumentation monitoring ground deformation has been maintained on the summit of axial volcano on the central juan de fuca ridge during a january 1998 volcanic episode pressure records from the central caldera showed a significant increase in pressure indicating caldera subsidence of over 3 m this observed subsidence is interpreted to represent volcanic deflation as magma is erupted and or injected into the volcanic flanks temperature anomalies of nearly 0 45 c were also observed a comparison of the subsidence record with hydroacoustic recordings indicates a continuous volcanic tremor signal coincident with the subsidence event the time coincidence of subsidence of the summit caldera with migration of epicenters into the volcanic rift zones confirms that during the 1998 episode the volcanic flanks were supplied by lateral dike injection from a central magma body rather than locally derived magma sources

multi sensor observations of a wave beneath an impacting rear inflow jet in an elevated mesoscale convective system observations of a wave generated below and propagating with an elevated mesoscale convective system mcs are presented the mcs and the wave tracked directly across the 90 km extent of the observational network deployed for the convective storm initiation project csip and maintained a coherent structure and velocity during this 1 5 hour period the rear inflow jet of the mcs was observed to impact upon but not penetrate the stable undercurrent that was located beneath the mcs apparently constricting the depth of the undercurrent which did not participate in the main convective updraught the wave crest was located approximately 15 km ahead of this constriction the overall wave led to between 200 and 1000 m of ascent and approximately 1500 m of descent however undulations were superimposed on the overall wave with a wavelength of approximately 7 km and a crest totrough amplitude of approximately 1000 m these undulations were associated with double maxima in surface pressure and the elevation of the observed low level wind anomaly where low level winds were backed by more than 90 t hese winds were never at rest relative to the system and the wave was therefore a gravity wave without stagnation the hydrostatic effect expected from the observed lifting in the wave was broadly consistent with the observed surface pressure perturbation of 2 hpa no cold pool outflow was ever observed instead the observed surface cooling of approximately 4 c was shown to be consistent with reduced solar insolation the generation of the observed wave structure and its implications for the maintenance of the mcs and numerical modelling of the system are discussed copyright c

seismic constraints on caldera dynamics from the 2015 axial seamount eruption seismic observations in volcanically active calderas are challenging a new cabled observatory atop axial seamount on the juan de fuca ridge allows unprecedented real time monitoring of a submarine caldera beginning on 24 april 2015 the seismic network captured an eruption that culminated in explosive acoustic signals where lava erupted on the seafloor extensive seismic activity preceding the eruption shows that inflation is accommodated by the reactivation of an outward dipping caldera ring fault with strong tidal triggering indicating a critically stressed system the ring fault accommodated deflation during the eruption and provided a pathway for a dike that propagated south and north beneath the caldera s east wall once north of the caldera the eruption stepped westward and a dike propagated along the extensional north rift

establishing a new era of submarine volcanic observatories cabling axial seamount and the endeavour segment of the juan de fuca ridge abstract at least 70 of the volcanism on earth occurs along the 65 000 km network of mid ocean ridge mor spreading centers within these dynamic environments the highest fluxes of heat chemicals and biological material from the lithosphere to the hydrosphere occur during volcanic eruptions however because underwater volcanoes are difficult and expensive to access researchers are rarely if ever in the right place at the right time to characterize these events therefore our knowledge is limited about the linkages among hydrothermal chemical and biological processes during seafloor formation and crustal evolution to make significant advancements in understanding the evolution of mor environments the united states and canada have invested in the first plate scale submarine cabled observatory linked through the global internet spanning the juan de fuca tectonic plate these two networks include 1700 km of cable and 14 subsea terminals that provide 8 10 kw power and 10 gbs communications to hundreds of instruments on the seafloor and throughout the overlying water column resulting in a 24 7 365 presence in the oceans data and imagery are available in real to near real time the initial experimental sites for monitoring volcanic processes include the mor volcanoes called axial seamount and the endeavour segment that are located on the juan de fuca ridge axial a hot spot influenced seamount is the most robust volcano along the ridge rising nearly 1400 m above the surrounding seafloor and it has erupted twice in the last 15 years in contrast the endeavour segment is characterized by more subdued topography with a well defined axial rift and it hosts one of the most intensely venting hydrothermal systems known a non eruptive spreading event lasting 6 years was documented at endeavour between 1999 and 2005 hydrothermal venting intensity chemistry and temperature as well as associated biological communities at both sites were significantly perturbed by the magmatic and intrusive events this paper presents the similarities and differences between the axial and endeavour volcanic systems and identifies reasons why they are ideal candidates for comparative studies the u s has made a 25 year commitment for sustained observations using the cabled infrastructure the highly expandable nature of submarine optical networking will allow for the future addition of novel experiments that utilize ever evolving advancements in computer sciences robotics genomics and sensor miniaturization comprehensive modeling of the myriad processes involved will continue to assimilate and integrate growing databases yielding a new understanding of integrated processes that create the seafloor in the global ocean basins

seafloor deformation and forecasts of the april 2011 eruption at axial seamount the axial seamount submarine volcano exhibits an inflation deflation cycle comparable to similar volcanoes on land measurements of ocean bottom pressure document the entire inflation deflation cycle between eruptions at axial seamount in 1998 and 2011 and imply that the timing of submarine eruptions could be more predictable than that of their subaerial counterparts

geochemistry of hydrothermal fluids from axial seamount hydrothermal emissions study vent field juan de fuca ridge subseafloor boiling and subsequent fluid rock interaction hydrothermal fluids collected from the ashes vent field in 1986 1987 and 1988 exhibit a very wide range of chemical composition over a small area 60 m in diameter compositions range from a 300 c gas enriched 285 mmol kg co2 low chlorinity 33 of seawater fluid to a 328 c relatively gas depleted 50 mmol kg co2 high chlorinity 116 of seawater fluid the entire range of measured compositions at ashes is best explained by a single hydrothermal fluid undergoing phase separation while rising through the ocean crust followed by partial segregation of the vapor and brine phases other mechanisms proposed to produce chlorinity variations in hydrothermal fluids precipitation dissolution of a chloride bearing mineral or crustal hydration cannot produce the covariation of chlorinity and gas content observed at ashes there is good agreement of the measured fluid compositions with compositions generated by a simple model of phase separation in which gases are partitioned according to henry s law and all salt remains in the liquid phase significant enrichments in silica lithium and boron in the low chlorinity fluids over levels predicted by the model are attributed to fluid rock interaction in the upflow zone depletions in iron and calcium suggest that these elements have been removed by iron sulfide and anhydrite precipitation at some time in the history of the low chlorinity fluids the distribution of low and high chlorinity venting is consistent with mechanisms of phase segregation based on differential buoyancy or relative permeability the relatively shallow depth of the seafloor 1540 m and the observed chemistry of ashes fluids are consistent with phase separation in the sub critical or near critical region

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

modeling the effects of tidal loading on mid ocean ridge hydrothermal systems 1 tidal signals are observed in numerous time series measurements obtained from mid ocean ridge hydrothermal systems in some instances these tidal signals are clearly the result of ocean currents but in other instances it appears that the signals may originate in the subseafloor formation in order to explore the effect of ocean tidal loading on mid ocean ridge hydrothermal systems we apply a one dimensional analytical model of tidal loading on a poroelastic half space and develop a two dimensional numerical model of tidal loading on a poroelastic convection cell the one dimensional models show that for a reasonable range of fluid elastic and hydrological properties the loading efficiency may vary from near zero to near unity and the diffusive penetration depth for tidal pressure signals may vary from tens of meters to kilometers the two dimensional models demonstrate that tides may generate significant vertical and horizontal pressure gradients in mid ocean ridge hydrothermal systems as a result of spatial variations in fluid temperatures and the elastic and hydrological properties of the crust these continuum models predict that outflow temperature perturbations will be very small 10 4 c but in real systems where the continuum hypothesis does not always apply the perturbations may be on the order of 0 1 c the models predict relatively large perturbations to fluid velocity at the seafloor for high temperature vents the outflow perturbations normalized to the mean flow velocity increase as the permeability decreases flow reversals at the seafloor are predicted in some regions of net low temperature outflow and net inflow during the tidal cycle in the subseafloor tidally induced flow perturbations are likely to significantly enhance mixing and fluid exchange below the seafloor in regions of slow flow and in regions where there are strong gradients in temperature or in the mechanical and hydrological properties of the crust tidally enhanced mixing and fluid exchange may significantly influence the extent and character of microbial production in the subseafloor

mantle echoes associated with deep convection observations and numerical simulations abstract finescale radar observations of intense thermals starting plumes during the early stages of precipitation formation were collected by an airborne doppler radar on two separate days the radar data were recorded as the aircraft flew underneath the developing echoes mantle echoes echoes that often appear as an inverted u shape were observed on both days striking in one of the scans was the resemblance of the echo to a mushroom cloud resulting from a nuclear explosion numerical simulations using a two dimensional cloud resolving model were run to augment the interpretation of the observations one of the important conclusions was the proposed modification to the default bulk microphysical scheme used in the model the default scheme yields a rush to precipitation leading to the early establishment of large precipitation contents which is not supported by the observations suggested modifications to the scheme are presented

geologic history of the summit of axial seamount juan de fuca ridge 1 multibeam 1 m resolution and side scan data collected from an autonomous underwater vehicle and lava samples radiocarbon dated sediment cores and observations of flow contacts collected by remotely operated vehicle were combined to reconstruct the geologic history and flow emplacement processes on axial seamount s summit and upper rift zones the maps show 52 post 410 ce lava flows and 20 precaldera lava flows as old as 31 2 kyr the inferred age of the caldera clastic deposits 1 2 m thick accumulated on the rims postcaldera between 31 ka and 410 ce there are no known lava flows near the summit the oldest postcaldera lava 410 ce is a pillow cone se of the caldera two flows erupted on the w rim between 800 and 1000 ce from 1220 to 1300 ce generally small eruptions of plagioclase phyric depleted mafic lava occurred in the central caldera and on the east rim larger post 1400 ce eruptions produced inflated lobate flows of aphyric less depleted and less mafic lava on the upper rift zones and in the n and s caldera all caldera floor lava flows and most uppermost rift zone flows postdate 1220 ce activity shifted from the central caldera to the upper s rift outside the caldera to the n rift and caldera floor and then to the s caldera and uppermost s rift where two historical eruptions occurred in 1998 and 2011 the average recurrence interval deduced from the flows erupted over the last 800 years is statistically identical to the 13 year interval between historical eruptions

is the south pacific helium 3 plume dynamically active it is suggested that the hydrothermal vents of the south pacific rise produce a beta governed circulation at mid depth and that perhaps the associated plume of excess3he lupton and craig 1 points westward because of the dynamics of this circulation rather than as a passive tracer

the 1998 eruption of axial seamount new insights on submarine lava flow emplacement from high resolution mapping 1 axial seamount an active submarine volcano on the juan de fuca ridge at 46 n 130 w erupted in january 1998 along 11 km of its upper south rift zone we use ship based multibeam sonar high resolution 1 m bathymetry sidescan sonar imagery and submersible dive observations to map four separate 1998 lava flows that were fed from 11 eruptive fissures these new mapping results give an eruption volume of 31 106 m3 70 of which was in the northern most flow 23 in the southern most flow and 7 in two smaller flows in between we introduce the concept of map scale submarine lava flow morphology observed at a scale of hundreds of meters as revealed by the high resolution bathymetry and an interpretive model in which two map scale morphologies are produced by high effusion rate eruptions inflated lobate flows are formed near eruptive vents and where they drain downslope more than 0 5 1 0 km they transition to inflated pillow flows these two morphologies are observed on the 1998 lava flows at axial a third map scale flow morphology that was not produced during this eruption pillow mounds is formed by low effusion rate eruptions in which pillow lava piles up directly over the eruptive vents axial seamount erupted again in april 2011 and there are remarkable similarities between the 1998 and 2011 eruptions particularly the locations of eruptive vents and lava flow morphologies because the 2011 eruption reused most of the same eruptive fissures 58 of the area of the 1998 lava flows is now covered by 2011 lava

tapping into the sub seafloor examining diffuse flow and temperature from an active seamount on the juan de fuca ridge abstract a unique sampling strategy involving the cementing of a permanent fluid sampler directly to the seafloor on axial seamount juan de fuca ridge has recently allowed the first long term direct coupling to a low temperature hydrothermal vent on a mid ocean ridge using the hydrologically sealed sampler direct measurement of fluid volume and heat flux from a diffuse hydrothermal vent on the seafloor was obtained over a period of 206 days enhanced variance at both tidal and lower frequencies was recorded with a high coherence between the temperature and flow data we estimate a volume flux of 48 m 3 yr and a heat flux of 260 w m 2 for the square meter of seafloor sampled by the instrument measurement of the darcy flow velocities of the effluent fluid are approximately 1 5 10 6 m s and indicate fluid velocities within cracks in the substrate of 1 4 m day with an effective upper crustal permeability of 10 11 10 12 m 2 while the measured variability in fluid flow is driven primarily by changes in the thermal buoyancy of upwelling fluid there is also a significant above hydrostatic pressure gradient contribution to the measured flux this overpressure produces roughly four times the driving force compared to that attributed to thermal buoyancy alone small variations in the volume flux and the effluent fluid temperature 1 5 10 8 m s and 0 5 c respectively also occurred on approximately tidal time scales and appear to be related to poroelastic control of the velocity of hydrothermal fluid through the seafloor boundary i e tidal pumping

compositional stratigraphy of clay bearing layered deposits at mawrth vallis mars phyllosilicates have previously been detected in layered outcrops in and around the martian outflow channel mawrth vallis crism spectra of these outcrops exhibit features diagnostic of kaolinite montmorillonite and fe mg rich smectites along with crystalline ferric oxide minerals such as hematite these minerals occur in distinct stratigraphic horizons implying changing environmental conditions and or a variable sediment source for these layered deposits similar stratigraphic sequences occur on both sides of the outflow channel and on its floor with al clay bearing layers typically overlying fe mg clay bearing layers this pattern combined with layer geometries measured using topographic data from hirise and hrsc suggests that the al clay bearing horizons at mawrth vallis postdate the outflow channel and may represent a later sedimentary or altered pyroclastic deposit that drapes the topography

alunite on mars identification of minerals on the surface of mars is critical to understanding the geological history of our neighbor planet in this issue of american mineralogist ehlmann et al report their discovery of alunite kal 3 so 4 2 oh 6 in cross crater on mars because terrestrial alunite forms from al rich acid sulfate waters these results strongly suggest the past presence of al rich acid saline martian waters