seasonal thermal inertia variations at gale crater role of active surface deposition phenomena abstract thermal inertia has been found to play a significant role in planetary remote sensing applications forming the basis of potentially all major lithological discriminations of the planetary surface it has always been visualised to serve as a distinctive thermal property of the surface with its values remaining fairly constant at least for a short time period unless the surface undergoes extensive and rapid degradation thermal inertia for mars has been previously calculated from point spectrometer orbiter and rover measurements and they have been successfully used for surface geologic interpretations the present study computes surface thermal inertia over 12 sols along curiosity s traverse at gale crater using thermal infrared imaging system themis and rover environmental monitoring station rems observations and attempts to analyse the same on a seasonal timescale we find that surface thermal inertia at gale follows a seasonal sinusoidal behaviour with the surface exhibiting maximum and minimum thermal inertia values during southern autumn and spring respectively the difference between them of the order of 300 to 400 t i u we have attempted here to illustrate that the seasonal behaviour seen in surface thermal inertia may be the result of active surface deposition processes localised to gale in this regard we have also explored the potential role of seasonal dust and water ice deposition in contributing to these observed variations effectively concluding that seasonal dust deposition could be a highly likely cause to which these seasonal thermal inertia changes can be attributed to

valles marineris dune sediment provenance and pathways abstract although low albedo sand is a prevalent component of the martian surface sources and pathways of the sands are uncertain as one of the principal present day martian sediment sinks the valles marineris vm rift system hosts a diversity of dune field populations associated with a variety of landforms that serve as potential sediment sources including spur and gully walls interior layered deposits ilds and landslides here we test the hypothesis that vm dune fields are largely derived from a variety of local and regional intra rift sediment sources results show several dune fields are superposed on ancient wall massifs and ilds that are topographically isolated from extra rift sand sources spectral analysis of dune sand reveals compositional heterogeneity at the basinal dune field and dune scales arguing for discrete relatively unmixed sediment sources in coprates and melas chasmata mapping is consistent with the principle sand source for dunes being noachian aged upper and lower wall materials composed of primary igneous minerals and glasses some of which show evidence for alteration in contrast dune fields in capri juventae and ganges chasmata show evidence for partial sediment derivation from adjacent early hesperian aged hydrated sulfate bearing ild units this finding indicates that these ilds act as secondary sand sources dunes containing soft secondary minerals e g monohydrated sulfate are unlikely to have been derived from distant sources due to the physical weathering of sand grains during transport isolated extra rift dune fields sand sheets and sand patches are located on the plateaus surrounding vm and the adjoining areas but do not form interconnected networks of sand pathways into the rift if past wind regimes with respect to directionality and seasonality were consistent with more recent regimes inferred from morphological analysis i e dune slip faces wind streaks and were sufficient in strength and duration small dune populations within aurorae chaos and north of eastern vm might have resulted from extended sand pathways into vm however we favor local and regional derivation of dune sand from a variety of intra rift lithologic sources for most cases dune sand sources and the mechanism by which the sand is liberated are discussed in the context of findings described herein but are broadly applicable to analysis of sediment production elsewhere on mars

controls on sand ramp formation in southern namibia sand ramps have the potential to provide rich palaeoenvironmental information in dryland regions wherein proxy records are typically scarce however current knowledge of the geomorphic controls and processes of sand ramp formation is limited this study provides a data rich examination of the key factors controlling sand ramp formation the location and morphology of 75 sand ramps in southern namibia are examined the sediments and chronologies of 10 sand ramps are studied in detail using 51 osl dates and 83 grain size and loi samples heavy mineral assemblages are used to determine the provenance of 10 samples and osl sensitivity is used to explore geomorphic processes of 8 samples sand ramp morphology can be grouped into one of four classes of increasing size and complexity and is closely linked to the available accommodation space heavy mineral assemblages indicate local sediment sources and all 75 studied sand ramps are within 4 km of a large ephemeral river channel or within 5 5 km of a dune field therefore accommodation space and sediment supply are identified as the primary controls of sand ramp formation sedimentology and osl sensitivity suggest a complex interplay of aeolian fluvial and colluvial processes contribute to sand ramp formation with large variability observed between ramps three of the ten dated sand ramps have been present in the namibian landscape for 100 ka eight sand ramps show episodic deposition between 75 12 ka and five show evidence of surface reworking over the past 2 ka environmental sensitivity is likely to be linked to the size and availability of the accommodation space therefore individual sand ramps are expected to reflect local environmental conditions recording when an abundant sediment supply coincided with available accommodation space whilst a regional analysis of multiple sand ramps with chronometric data offers the potential to identify larger scale palaeoenvironmental controls of sediment supply

origin of volcanic gases discharging from a cooling lava dome of unzen volcano japan abstract chemical and isotopic compositions were measured for volcanic gases discharged from the recently erupted heisei shinzan dome of unzen volcano the volcanic gases are largely mixed with the air whose content ranges from 60 to 90 chemical and isotopic compositions of the gases are corrected for the air mixing accounting not only for the major air components but also for contribution of the atmospheric moisture and co 2 the variation of the corrected composition revealed that these gases are derived from various sources including 1 the air circulating through the lava domes 2 the local meteoric water at various degrees of evaporation and vapor loss 3 the magmatic co 2 likely originated from a deep source and 4 the gases discharged from the cooling lava dome the gases discharged from the cooling lava dome are characterized by the oxygen and hydrogen isotopic composition typical of the subduction type volcanoes but with high cl content and high cl s and f s ratios in contrast discharges of co 2 with the magmatic 13 c values are not correlated with discharge of heat or acid gas species suggesting the ascent of co 2 rich fluids from a deep source possibly through the volcanic conduit

climbing and falling dunes in valles marineris mars 1 multiple occurrences of wall dunes are found several kilometers above the valles marineris canyon floor dune slip face orientation and bed form morphologies indicate transport direction and whether the wall dunes are climbing dunes or falling dunes on earth these types of dunes form in a unidirectional wind regime and are strongly controlled by the local topography newly acquired mars reconnaissance orbiter mro images and topography of the walls of valles marineris show similar sand dune morphologies as wind blown sediment has interacted with local and regional topography primarily found in melas and coprates chasmata these climbing and falling dunes are relevant for understanding aeolian sediment flux sediment sources and wind directions falling dunes show photogeologic and thermophysical evidence of their sand being provided by adjacent outcrops

inverse maximum gross bedform normal transport 2 application to a dune field in ganges chasma mars and comparison with hirise repeat imagery and mrams abstract inverse maximum gross bedform normal transport imgbnt analysis has been applied to context camera ctx images of the largest dune field in ganges chasma on mars the dune field was selected for its position in a likely complex multi directional wind regime results indicate that four main winds are responsible for simultaneous construction of the dune field including along chasma winds from the ese winds blowing down a nearby re entrant from the ne winds blowing down the adjacent chasma wall from the nw and chasma floor winds from the sw each wind represents a transport vector that dominates dune morphology at its respective edge of the dune field such that the central axis of the dune field reflects the convergence of the three most prominent winds ese nw and sw the mars regional atmospheric modeling system mrams was run at twelve times throughout the martian year to provide context for the local wind patterns potential sand fluxes calculated from mrams output show that three major air flows from the ene e nne ne and nnw n converge near the location of the dune field these flows likely correspond to the ese ne and nw winds identified from imgbnt analysis respectively mrams output shows that the flows with major northerly components are produced by larger scale hadley return flow constructively combining with nighttime downslope winds the flow with a major easterly component is likely produced by equatorial easterly trade winds constructively combining with the diurnal tide and or local topography although the model correctly predicts the major elements of the local wind pattern some aspects are either over or underrepresented demonstrating the value of using aeolian morphological analysis to conclusively constrain the major sand moving winds on mars overlapping high resolution imaging experiment hirise images of barchanoid dunes at the northernmost edge of the dune field indicate that these dunes are currently migrating southward at 5 m mars year 2 6 m earth year the direction of migration is consistent with both mrams predictions in this location and the nw ne winds found from imgbnt analysis dune morphology suggests that sand in the northwestern part of the dune field is likely to be derived from the adjacent chasma wall to the north and northwest and sand in the southeastern part of the dune field was probably transported from farther east along the main chasma floor

multidisciplinary observations of the 2011 explosive eruption of telica volcano nicaragua implications for the dynamics of low explosivity ash eruptions we present multidisciplinary observations of the march june 2011 vei 2 eruptive episode of the basalticandesite telica volcano nicaragua which allow for a comprehensive study of the eruption mechanics of low explosivity eruptions at persistently active volcanoes the observations are from a dense network of seismic and gps instrumentation augmented by visual observations of the eruptive episode geochemical and petrologic analysis of eruptive products plume so2 measurements and temperature measurements of fumaroles inside and outside the active vent the 2011 eruptive episode was telica s most explosive since 1999 and consisted of numerous vulcanian explosions with maximum column heights of 1 5 2 km above the crater rim depositing a low volume of dominantly hydrothermally altered ash based on observed variations in seismicity temperature and so2 flux the lack of deformation of the edifice the non juvenile origin of and predominance of accretionary lapilli in the ash we propose that temporary sealing of the hydrothermal system between similar to 0 5 and 2 km depth allowed pressure to build up prior to vulcanian explosions making this a phreatic eruptive episode

local recharge processes in glacial and alluvial deposits of a temperate catchment summary this study demonstrates that the composition and structure of quaternary deposits and topography significantly influence rates of recharge and distribution of diffuse agricultural pollution at the hillslope scale analyses were made of vertical profiles of naturally occurring chloride and nitrate and artificially introduced bromide in unsaturated and saturated sections of borehole cores of glacial till and alluvium under different land uses in the upper eden valley uk estimates of local potential recharge were made based on chloride mass balance and nitrate peak methods persistent chloride bulges below the root zone were observed and are interpreted to result from filtration processes at lithological boundaries changes in the shape of chloride profiles downslope corroborated by nitrate profiles indicate the roles of surface or near surface runoff and runon and the existence of lateral subsurface flows at depth these findings have implications for estimation of recharge rates through unsaturated zones in quaternary deposits and the interpretation of potential hot spots of diffuse agrochemicals particularly nitrates moving through quaternary deposits into groundwater

passive infrared remote sensing evidence for large intermittent co2 emissions at popocatepetl volcano mexico abstract passive infrared ftir and correlation spectrometer cospec measurements were conducted at popocatepetl volcano during february 10 to 26 1998 from sites 4 to 17 km distant from the summit volcano behavior was relatively quiet and so 2 flux averaged 1670 1420 t day 51 measurements relatively small for popocatepetl concurrent hcl so 2 and hf so 2 ratios were 0 17 0 01 and 0 031 0 003 respectively about the same as ratios measured from 1994 to 1997 the amount of co 2 in the volcanic plume was quantified using fascode in which atmospheric co 2 is numerically subtracted from the total infrared spectrum to obtain the residual magmatic co 2 surprisingly co 2 so 2 mass ratios rose dramatically to values as high as 140 about 30 times higher than typical values of 2 to 8 measured from 1994 to 1996 these excursions in high co 2 so 2 ratios were short lived lasting no longer than about 0 5 to 3 0 h but co 2 flux occasionally exceeded 100 000 t day we estimate that the average co 2 so 2 ratio for the period was about 23 yielding an average co 2 flux of roughly 38 000 t day chemical and petrographic analyses of lava and pumice erupted during explosions on june 30 1997 and january 1 1998 show conclusively that popocatepetl produces mixed products formed by injection of mafic magma into a more silicic chamber at temperatures and pressures of roughly 1040 c and 5 kbar in addition popocatepetl eruptive products include xenoliths of metamorphosed carbonate rocks containing wollastonite and other calc silicate minerals indicating reaction of magma with cretaceous limestone underlying the volcano using a normal co 2 so 2 ratio of 4 for reference we calculate an average excess co 2 production of 32 000 t day for 17 days this would require assimilation of only 5 10 4 km 3 of limestone an amount easily accessible in the 3 km thick cretaceous section beneath the volcano we also examine two scenarios in which excess co 2 is produced by degassing of subjacent basalt magma but these explanations seem less plausible to us because many other volcanoes are underlain by carbonate sequences short duration bursts of co 2 flux and increased co 2 so 2 ratio might be observed at other sites if simultaneous real time measurements of major gas species are made

high resolution thermal inertia derived from the thermal emission imaging system themis thermal model and applications 1 thermal inertia values at 100 m per pixel are determined using nighttime temperature data from the thermal emission imaging system themis on the mars odyssey spacecraft producing the highest resolution thermal inertia data set to date themis thermal inertia values have an overall accuracy of 20 a precision of 10 15 and are consistent with both thermal emission spectrometer orbital and miniature thermal emission spectrometer surface thermal inertia values this data set enables the improved quantification of fine scale surface details observed in high resolution visible images in the tharsis region surface textures and crater rims observed in visible images have no corresponding variation in the themis thermal inertia images indicating that the dust mantle is pervasive at themis scales and is a minimum of a few centimeters and up to 1 2 m thick the thermal inertia of bed form material indicates particle diameters expected for aeolian sediments and these materials are likely currently saltating variations in the thermal inertia within interior layered deposits in hebes chasma can be distinguished and the thermal inertia is too low to be consistent with bedrock or a lava flow thus a secondary emplacement of volcanic material or a volcanic ash deposit is a more likely method of formation higher resolution themis thermal inertia enables the identification of exposed bedrock on the martian surface in nili patera and ares vallis bedrock material corresponds to distinct compositional and morphologic surfaces indicating that a specific unit is exposed and is likely currently being kept free of unconsolidated material by aeolian processes

monitoring active volcanoes and mitigating volcanic hazards the case for including simple approaches abstract simple approaches to problems brought about eruptions and their ensuing hazardous effects should be advocated and used by volcanologists while awaiting more sophisticated remedies the expedients we advocate have all or many of the following attributes only locally available materials are required no extensive training of operators or installation is necessary they are affordable and do not require foreign aid or exports they are often labor intensive and are sustainable without outside assistance where appropriate the involvement of local residents is advocated examples of simple expedients which can be used in forecasting or mitigating the effects of crises emphasize the relative ease and the less elaborate requirements with which simple approaches can be activated emphasis is on visual observations often by untrained observers simple meteorogical measurements observations of water level in lakes temperature and chemistry of springs and fumaroles new springs and collapse areas and observations of volcanic plumes simple methods are suggested which can be applied to mitigating damage from mudflows nuees ardentes tephra falls and gas discharge a review in hindsight at ruiz includes the use of both chemical indicators and simple mudflow alarms simple expedients are sufficiently effective that any expert volcanologist called to aid in a crisis must include them in the package of advice offered simple approaches are a critical and logical complement to highly technical solutions to hazardous situations

chemical variations of tephra fall deposit leachates for three eruptions from popocatepetl volcano abstract leachates from ash samples of the popocatepetl eruptions of april 30 1996 may 12 1997 and october 17 1998 settled at different distances from the crater were analyzed for anions so 4 2 cl f and some metals this study is aimed at determining the causes of the compositional variations of the leachates to assist the assessment of water soil and crop contamination due to ash deposits different behavior was observed in the ion concentrations with distance for the three eruptions on april 30 1996 so 4 2 and f concentrations increased with distance and cl remained almost constant on may 12 1997 concentrations of the three anions decreased with distance on october 17 1998 f cl and so 4 2 increased more than three fold with distance tephra size distributions were also different for the three eruptions the observed trends of the leachates anion concentrations may have different causes the type and intensity of the eruptions the distribution of the tephra sizes the degree of interaction of the tephras with volcanic gases humidity static charge the original characteristics of the solid material the transport time from the crater to the site of settling and the relative angle between the wind direction and the sampling line enrichment factors and concentration trends for metals with distance suggest that co ni cu and pb in the leachates resulted mostly from volcanic gas adsorption

craters as sand traps dynamics history and morphology of modern sand transport in an active martian dune field abstract aeolian transport of sand is abundant on modern day mars as revealed by remote sensing measurements of the motion of dunes and of the meter scale ripples that mantle them we study a large scale natural sand trap within the meroe patera dune field a 1 8 km diameter crater which features a dune free shadow in its lee we compare the volume of sand trapped within this crater to the sand volume that would be expected to cover the area of the crater and its dune free shadow behind it if the crater were not present we find that the crater holds less sand than this missing volume would predict implying that sand escapes from the crater over time modern day imagery shows an apparent lack of sand escaping from the meroe crater however suggesting that changes in the wind regime at the site may have allowed sand to escape in the past the persistence of an altered dune morphology all the way to the far downwind edge of the dune field suggests consistent wind conditions over the time of the crater dune field interaction

microscale chemical heterogeneity in groundwater ronen d magaritz m gvirtzman h and garner w 1987 microscale chemical hetereogeneity in groundwater j hydrol 92 173 178 large variations in the concentration of cl no a and so42 in the upper water layers of a polluted aquifer were found between samples that were vertically separated by as little as 3 cm this was disclosed when a multilayer dialysis cell device was used to obtain undisturbed real time samples from test wells this first time presentation of chemical fine structure provides new insights into mechanisms of contamination of an aquifer by surface inputs and raises the question of the validity of groundwater quality data based on single samples however obtained

context camera investigation on board the mars reconnaissance orbiter 1 the context camera ctx on the mars reconnaissance orbiter mro is a facility instrument i e government furnished equipment operated by a science team not responsible for design and fabrication designed built and operated by malin space science systems and the mro mars color imager team marci ctx will 1 provide context images for data acquired by other mro instruments 2 observe features of interest to nasa s mars exploration program e g candidate landing sites and 3 conduct a scientific investigation led by the marci team of geologic geomorphic and meteorological processes on mars ctx consists of a digital electronics assembly a 350 mm f 3 25 schmidt type telescope of catadioptric optical design with a 5 7 field of view providing a 30 km wide swath from 290 km altitude and a 5000 element ccd with a band pass of 500 700 nm and 7 m pixels giving 6 m pixel spatial resolution from mro s nearly circular nearly polar mapping orbit raw data are transferred to the mro spacecraft flight computer for processing e g data compression before transmission to earth the ground data system and operations are based on 9 years of mars global surveyor mars orbiter camera on orbit experience ctx has been allocated 12 of the total mro data return or about 3 terabits for the nominal mission this data volume would cover 9 of mars at 6 m pixel but overlapping images for stereo mosaics and observation of changes and meteorological events will reduce this area ctx acquired its first instrument checkout images of mars on 24 march 2006

hyperfiltration of sodium chloride through kaolinite membranes under relatively low heads implications for groundwater assessment abstract three relatively low head hyperfiltration experiments were conducted to investigate clay membrane behavior at lower hydraulic heads dilute cl solutions 187 and 336 mg l were forced through thin layers of kaolinite 0 67 1 62 mm under heads ranging between 1 45 and 1 89 m at the end of each experiment there was a cl concentration increase 15 29 within the cell the concentration increase is attributable to solute sieving by the kaolinite calculated final concentration increases at the membrane face ranged between 1 51 and 1 65 times the initial concentration and the calculated values of the reflection coefficient ranged between 0 35 and 0 40 these experiments show that clays are capable of significant hyperfiltration effects at lower pressure heads more typical of natural aquifers consequently hyperfiltration effects may need to be considered in a broad spectrum of shallow subsurface processes in which these effects have been regarded as inconsequential particularly in perched aquifers

experimental support for a predictive osmotic model of clay membranes osmosis has been cited as a mechanism for explaining anomalously high fluid pressures in the subsurface clays and shales act as membranes and osmotic flux across these units may result in pressures sufficiently high to explain these anomalies the theoretical osmotic pressures as calculated solely from solution properties can be quite large however it is not yet resolved whether these geologic membranes are sufficiently ideal to generate such pressures

gas and ash emissions associated with the 2010 present activity of sinabung volcano indonesia abstract sinabung volcano sumatra indonesia awoke from over 1200 years of dormancy with multiple phreatic explosions in 2010 after a period of quiescence sinabung activity resumed in 2013 producing frequent explosions lava dome extrusion and pyroclastic flows from dome and lava flow collapses becoming one of the world s most active volcanoes and displacing over 20 000 citizens this study presents a compilation of the geochemical datasets collected by the indonesian center for volcanology and geological hazard mitigation cvghm from 2010 current 2016 which provides insights into the evolution of the eruption based on observations of so2 emissions ash componentry ash leachate chemistry and bulk ash geochemistry the eruption can be split into six distinct geochemical phases the initial stage of phreatic summit explosions phase a occurred from august september 2010 during which background so2 emissions averaged 550 180 t d 1 s d an eruptive pause phase b starting in october 2010 abruptly ended in september 2013 with a resumption of conduit clearing eruptions phase c this third phase had a relatively modest background so2 emission rate avg 430 310 t d and produced ash consisting of accidental ejecta with high s cl leachate molar ratios 12 0 8 2 max 34 suggestive of deep sourced magma and or the incorporation of hydrothermal sulfur bearing phases lava extrusion at the summit phase d began in mid december 2013 and was accompanied by relatively low so2 emission rates 360 200 t d and lower but variable s cl leachate ratios 6 3 8 5 the most intense phase of the eruption phase e occurred from mid january to late february 2014 following a major lava dome collapse this period included increased lava extrusion rates dozens of large eruptions per day high so2 emission rates average 1680 1070 t d peak 3800 t d and a dramatic drop in s cl ash leachates to ratios average 1 4 0 5 consistent with increased degassing from shallow magma and the clearing out of sulfurous phases from the old hydrothermal system from march 2014 through the time of writing september 2016 sinabung settled into a relatively steady state of lower activity phase f ash emissions now consist of dominantly juvenile andesitic dacitic material with low s cl leachate ratios average 1 1 0 6 in august 2016 so2 emissions started being measured in a continuous manner using a network of permanent scanning doas instruments background so2 emission rates average 450 290 t d for the entirety of phase f but have been progressively decreasing to an average of 250 300 t d since june 2016 this long term gradual decline in so2 emission rates at sinabung since early 2014 is consistent with an apparent decrease in magma supply and lava effusion rates our conceptual degassing model suggests that large explosions and pyroclastic flows could continue in the near term owing to conduit plugging and dome collapses remaining a major threat until the magma supply rate decreases further and the eruption ends

assessment of leachable elements in volcanic ashfall a review and evaluation of a standardized protocol for ash hazard characterization abstract volcanic ash presents a widespread and common hazard during and after eruptions complex interactions between solid ash surfaces and volcanic gases lead to the formation of soluble salts that may be mobilized in aqueous environments a variety of stakeholders may be concerned about the effects of ash on human and animal health drinking water supplies crops soils and surface runoff as part of the immediate emergency response rapid dissemination of information regarding potentially hazardous concentrations of soluble species is critical however substantial variability in the methods used to characterize leachable elements makes it challenging to compare datasets and eruption impacts to address these challenges the international volcanic health hazard network www ivhhn org organized a two day workshop to define appropriate methods for hazard assessment the outcome of this workshop was a consensus protocol for analysis of volcanic ash samples for rapid assessment of hazards from leachable elements which was subsequently ratified by leading volcanological organizations the purpose of this protocol is to recommend clear standard and reliable methods applicable to a range of purposes during eruption response such as assessing impacts on drinking water supplies and ingestion hazards to livestock and also applicable to research purposes where possible it is intended that the methods make use of commonly available equipment and require little training to evaluate method transferability an interlaboratory comparison exercise was organized among six laboratories worldwide each laboratory received a split of pristine ash and independently analyzed it according to the protocol for a wide range of elements collated results indicate good repeatability and reproducibility for most elements thus indicating that the development of this protocol is a useful step towards providing standardized and reliable methods for ash hazard characterization in this article we review recent ash leachate studies report the outcomes of the comparison exercise and present a revised and updated protocol based on the experiences and recommendations of the exercise participants the adoption of standardized methods will improve and facilitate the comparability of results among studies and enable the ongoing development of a global database of leachate information relevant for informing volcanic health hazards assessment

meteorological predictions for 2003 mars exploration rover high priority landing sites 1 the mars regional atmospheric modeling system is used to predict meteorological conditions that are likely to be encountered by the mars exploration rovers at several proposed landing sites during entry descent and landing seven areas five of which contain specific high priority landing ellipses are investigated hematite two sites isidis planitia elysium planitia two sites valles marineris and gusev crater the last two locations are in regions of extreme topography and the local and regional thermal circulations that result are equally extreme horizontal wind speeds near the floor of valles marineris exceed 50 ms 1 vertical velocities near the walls exceed 40 ms 1 and penetrate 10 km in altitude above the rim of the canyon thermal convection is suppressed within valles marineris by subsidence that forms in response to the upslope flows along the canyon walls wind magnitudes at gusev crater are approximately one third of those at the canyon but horizontal wind shear is greater deep convective thermals are noted at the relatively flat hematite site where 10 ms 1 updrafts rising to heights of 5 km are not uncommon during the midafternoon linearly organized convective updrafts superimposed on upslope circulations dominate over most of isidis planitia hexagonal and linearly organized convection predominates at elysium planitia afternoon circulations at all sites pose some risk significant risk in some cases to entry descent and landing most of the atmospheric hazards are not evident in current observational data and general circulation model simulations and can only be ascertained through mesoscale modeling of the region

the adsorption of hcl on volcanic ash understanding the interaction between volcanic gases and ash is important to derive gas compositions from ash leachates and to constrain the environmental impact of eruptions volcanic hcl could potentially damage the ozone layer but it is unclear what fraction of hcl actually reaches the stratosphere the adsorption of hcl on volcanic ash was therefore studied from 76 to 150 c to simulate the behavior of hcl in the dilute parts of a volcanic plume finely ground synthetic glasses of andesitic dacitic and rhyolitic composition as well as a natural obsidian from vulcano italy served as proxies for fresh natural ash hcl adsorption is an irreversible process and appears to increase with the total alkali content of the glass adsorption kinetics follow a first order law with rate constants of 2 13 10 6 s 1 to 1 80 10 4 s 1 in the temperature range investigated for dacitic composition the temperature and pressure dependence of adsorption can be described by the equation ln c 1 26 0 27ln p 715 3 t where c is the surface concentration of adsorbed hcl in mg m2 t is temperature in kelvin and p is the partial pressure of hcl in mbar a comparison of this model with a large data set for the composition of volcanic ash suggests that adsorption of hcl from the gas phase at relatively low temperatures can quantitatively account for the majority of the observed cl concentrations the model implies that adsorption of hcl on ash increases with temperature probably because of the increasing number of accessible adsorption sites this temperature dependence is opposite to that observed for so2 so that hcl and so2 are fractionated by the adsorption process and the fractionation factor changes by four orders of magnitude over a temperature range of 250 k the assumption of equal adsorption of different species is therefore not appropriate for deriving volcanic gas compositions from analyses of adsorbates on ash however with the experimental data provided here the gas compositions in equilibrium with the ash surfaces can be calculated in particular for dacitic composition the molar ratio of s cl adsorbed to the ash surface is related to the molar s cl ratio in the gas phase according to the equation ln s cl adsorbed 2855t 1 0 28ln s cl gas 11 14 our data also show that adsorption on ash will significantly reduce the fraction of hcl reaching the stratosphere only if the initial hcl content in the volcanic gas is low 1 mol for higher initial hcl concentrations adsorption on ash has only a minor effect while hcl scavenging by hydrometeors may remove a considerable fraction of hcl from the eruption column recent models suggest that this process is much less efficient than previously thought our experimental data therefore support the idea that the hcl loading from major explosive eruptions may indeed cause severe depletions of stratospheric ozone

cementing halite in triassic bunter sandstone tonder southwest denmark as a result of hyperfiltration of brines abstract samples of cores from the bunter sandstone formation of the tonder structure have been carefully prepared without access of fresh water the presence of cementing halite has been proven by chemical analysis and microscopic studies of these samples computer log analysis combined with core analysis show the cementing halite to exist mainly in the sandstone layers of the upper bunter sand unit the depositional environments of the bunter sandstone formation of the tonder structure are outlined it is argued that the cementing halite formed as a result of hyperfiltration of the saturated formation brines through low permeable layers of shale this process took place during the emplacement of nitrogen gas in the upper bunter sand unit late in the diagenetic history of the sandstone

experimental and numerical modeling of chemical osmosis in the clay samples of the aquitard in the north china plain this study focuses on addressing the existence of chemical osmosis in the clay samples of the aquitard in the north china plain ncp for this purpose chemical osmotic experiments in the clay samples collected from the aquitard in the ncp were implemented to estimate the reflection coefficient or chemico osmotic efficiency in clayey sediments more specifically under a certain chemical potential gradient the reflection coefficients were respectively achieved by measuring the osmotic flow and the induced pressure in terms of the two sets of undisturbed clay core samples and their remolded clay samples equipped in a rigid wall permeameter the measured reflection coefficient is the value of 0 023 for in situ clay sample much smaller than that of 0 098 for remolded sample also the constant head tests for determining the hydraulic conductivity of clay samples were conducted before and after the osmotic tests it is indicated that the permeability of the remolded sample is smaller than the undisturbed sample in both periods moreover a chemical osmosis continuum model was used to fit the evolution of the osmotically driven hydraulic pressure in the clay samples where more intrinsic parameters of the samples were calibrated additional analysis demonstrates the sensitivity of the osmosis pressure to the different parameters input to the model for the in situ clay sample this study could provide a reliable basis for further evaluating the role of clay sediments in the desalination of shallow saline groundwater and salinization of deeper fresh groundwater in the ncp

aeolian sediment transport pathways and aerodynamics at troughs on mars 1 interaction between wind regimes and topography can give rise to complex suites of aeolian landforms this paper considers aeolian sediment associated with troughs on mars and identifies a wider range of deposit types than has previously been documented these include wind streaks falling dunes lateral dunes barchan dunes linear dunes transverse ridges sand ramps climbing dunes sand streamers and sand patches the sediment incorporated into these deposits is supplied by wind streaks and ambient planitia sources as well as originating within the trough itself notably from the trough walls and floor there is also transmission of sediment between dunes the flow dynamics which account for the distribution of aeolian sediment have been modeled using two dimensional computational fluid dynamics the model predicts flow separation on the upwind side of the trough followed by reattachment and acceleration at the downwind margin the inferred patterns of sediment transport compare well with the distribution of aeolian forms model data indicate an increase of wind velocity by 30 at the downwind trough margin this suggests that the threshold wind speed necessary for sand mobilization on mars will be more frequently met in these inclined locations

mt st helens evidence of increased magmatic gas component abstract this paper presents measurements of so 2 flux and ash leachate chemistry from mt st helens volcano during the period may 18 to july 22 which are in contrast to similar data from before may 18 comparison of post 18 may so 2 data with similar data from other volcanoes leads to the conclusion that between 15 and 25 may the so 2 flux reached typical magmatic levels ash leachate chemistry from the eruption of 18 may 22 june and 22 july also indicate a large magmatic gas component concentrations of cl and so 2 4 on may 18 ash increase with distance from the volcano and decrease with time leachate chemistry is used to estimate that a minimum of 2 4 10 5 tons of s were released on may 18 low f concentrations on the ash though increasing present to health hazards

volcanic ash leachate compositions and assessment of health and agricultural hazards from 2012 hydrothermal eruptions tongariro new zealand abstract after almost 80 years of quiescence the upper te maari vent on mt tongariro erupted suddenly at 2352 h nz time on 6 august 2012 the short lived hydrothermal eruption distributed a fine ash of minor volume 5 10 5 m 3 over 200 km from source the threat of further eruptions prompted an investigation of the possible health and agricultural impacts of any future eruptions from this volcano particularly since the most recent large scale ash falls in new zealand in 1995 1996 had generated significant agricultural problems including livestock deaths deposited ash was sampled between 5 and 200 km from the volcano as soon as possible after the eruption two sub lobes of ash were identified from different vent areas and displayed subtly different leaching properties the first was an initial small lobe directed nne likely formed from drifting low level clouds associated with the initial lateral explosive blast and surges the main fall lobe directed eastward was sourced from a short lived vertical plume that rose up to c 8 km ash from the initial fall lobe had higher concentrations of f and al in single step leaches as well as in the totals of three sequential extractions further the initial lobe showed a higher proportion of soluble f and al extracted in the first leach compared to totals a linear relationship between concentrations of al and f in single leaches from the 6 august eruption was highly significant pearson correlation coefficient r 0 987 for 1 20 leaching ratios and r 0 971 for 1 100 suggesting the presence of soluble alumino fluoride complexes alf x 3 x an even more significant 1 1 ratio is displayed for the largest concentration leached ions of ca and so 4 which correspond to the presence of crystalline gypsum throughout the newly excavated hydrothermal system although no fresh magma was erupted in this event a shallow intrusion prior to the hydrothermal explosion apparently provided significant contents of volcanic gas that was dissolved within the hydrothermal fluids and adhering to ejected particles this and the ubiquitous presence of gypsum dominated the soluble components of these ash deposits leading to a complex leaching profile the leaching study carried out here showed that agricultural and human health hazard assessment particularly of f and s is not straightforward particularly because f solubility may be complex and not well characterised by simple leaching studies in the case of s which is agriculturally important saturation effects are apparent using normal leaching protocols and also imply a need for modification of standard methods

hyperfiltration of nickel sulphate solutions through silty sandstone and its effect on hydraulic conductivity abstract hyperfiltration reverse osmosis and subsequent precipitation of minerals from the hyperfiltrated solution are processes that potentially decrease the hydraulic conductivity of porous media these processes were demonstrated by hyperfiltrating niso4 solutions through fine grained sandstone the mineral precipitates occur in very small mm sized layers at the high pressure side of the samples where they create zones of lowered hydraulic conductivity 2 3 orders of magnitude lower than initial the total amount of precipitates is very small compared to the dissolved mass which was passed through the membrane hyperfiltration induced precipitates and the resulting lowering of hydraulic conductivities were observed at solute saturations as low as 10 nevertheless at saturations higher than 50 the conductivity reduction strongly increased full reversibility of the hydraulic conductivity reduction by extensive re flushing with water was only obtained at low initial solute saturations 10 this indicates that precipitated minerals in many pores are susceptible only to very slow diffusion controlled re dissolution

geologic context of recurring slope lineae in melas and coprates chasmata mars one of the major mars discoveries of recent years is the existence of recurring slope lineae rsl which suggests that liquid water occurs on or near the surface of mars today these dark and narrow features emerge from steep rocky exposures and incrementally grow fade and reform on a seasonal basis and are detected in images from the high resolution imaging science experiment camera rsl are known to occur at scattered midlatitude and equatorial sites with little spatial connection to one another one major exception is the steep low albedo slopes of melas and coprates chasmata in valles marineris where rsl are detected among diverse geologic surfaces e g bedrock and talus and landforms e g inselbergs and landslides new images show topographic changes including sediment deposition on active rsl slopes midwall locations in coprates and melas appear to have more areally extensively abundant rsl and related fans as compared with other rsl sites found on mars water budget estimates for regional rsl are on the order of 105 to 106 m3 of fluid for depths of 10 to 100 mm and suggest that a significant amount of near surface water might be present many rsl are concentrated near local topographic highs such as ridge crests or peaks which is challenging to explain via groundwater or ice without a recharge mechanism collectively results provide additional support for the notion that significant amounts of near surface water can be found on mars today and suggest that a widespread mechanism possibly related to the atmosphere is recharging rsl sources

chemistry of ash leachates to monitor volcanic activity an application to popocatepetl volcano central mexico abstract monitoring volcanic activity and assessing volcanic risk in an on going eruption is a problem that requires the maximum possible independent data to reduce uncertainty a quick relatively simple and inexpensive method to follow the development of an eruption and to complement other monitoring parameters is the chemical analysis of ash leachates particularly in the case of eruptions related to dome emplacement here the systematic analysis of so 4 2 cl and f concentrations in ash leachates is proposed as a valuable tool for volcanic activity monitoring however some results must be carefully assessed as is the case for s cl ratios since eruption of hydrothermally altered material may be confused with degassing of incoming magma sulfur isotopes help to identify so4 produced by hydrothermal processes from magmatic so2 lower s isotopic values correlated with higher f percentages represent a better indicator of fresh magmatic influence that may lead to stronger eruptions and emplacement of new lava domes additionally multivariate statistical analysis helps to identify different eruption characteristics provided that the analyses are made over a long enough time to sample different stages of an eruption

chlorine 36 dating of very old groundwater 2 milk river aquifer alberta canada the milk river aquifer in southern alberta canada consists of sandstone interbedded between thick shale units the groundwater is confined and discharges by both upward and downward leakage through the shales the concentration of cl increases by about 2 orders of magnitude downgradient through the aquifer this cl increase complicates 36cl dating of the system climatic changes flushing of connate water introduction of cl from older water below the aquifer and ion filtration have been proposed as possible explanations for the increase the 36cl data show a consistent decrease of the 36cl cl ratio downgradient but an increase in the 36cl concentration downgradient in certain parts of the aquifer dates calculated from the 36cl cl ratio show a reasonable distribution in light of the hydraulic controls on the system whereas dates calculated from the 36cl concentration give negative ages this suggests that ion filtration is responsible for the cl increase and that the 36cl cl dates are to be preferred we estimate water ages to be more than 2 m y near the distal end of the aquifer

apparent thermal inertia and the surface heterogeneity of mars abstract thermal inertia derivation techniques generally assume that surface properties are uniform at horizontal scales below the footprint of the observing instrument and to depths of several decimeters consequently surfaces with horizontal or vertical heterogeneity may yield apparent thermal inertia which varies with time of day and season to investigate these temporal variations we processed three mars years of mars global surveyor thermal emission spectrometer observations and produced global nightside and dayside seasonal maps of apparent thermal inertia these maps show broad regions with diurnal and seasonal differences up to 200 j m 2 k 1 s 1 2 at mid latitudes 60 s to 60 n and 600 j m 2 k 1 s 1 2 or greater in the polar regions we compared the seasonal mapping results with modeled apparent thermal inertia and created new maps of surface heterogeneity at 5 resolution delineating regions that have thermal characteristics consistent with horizontal mixtures or layers of two materials the thermal behavior of most regions on mars appears to be dominated by layering with upper layers of higher thermal inertia e g duricrusts or desert pavements over fines prevailing in mid latitudes and upper layers of lower thermal inertia e g dust covered rock soils with an ice table at shallow depths prevailing in polar regions less common are regions dominated by horizontal mixtures such as those containing differing proportions of rocks sand dust and duricrust or surfaces with divergent local slopes other regions show thermal behavior that is more complex and not well represented by two component surface models these results have important implications for mars surface geology climate modeling landing site selection and other endeavors that employ thermal inertia as a tool for characterizing surface properties

geochemistry of ash leachates from the 1993 lascar eruption northern chile implication for recycling of ancient evaporites abstract volcanic formations in the central andes overlie extensive amounts of ancient evaporites of cenozoic age recycling of buried salts in present closed basins through the hydrological cycle is a well known process another salt recycling process through volcanic activity has been detected in a recent eruption of the lascar volcano in northern chile about 10 9 metric tons of air fall tephra was deposited over the surrounding closed basins leaching experiments were carried out on ashes deposited near the summit and in a lower neighbouring valley summit ash leachates are almost pure caso 4 solutions whereas the valley ashes leachates are enriched in minor components leachates of the summit ash are near neutral whereas those of the valley ash have ph as high as 10 5 sulfur isotope composition of the leached sulfate is consistent with the volcanic recycling of tertiary gypsum present in the sedimentary section beneath the volcanic cordillera as a rough estimate about 700 000 tons of easily soluble caso 4 were added in only three days to the surrounding closed basins the high ph of the valley ash leachates is due to the hydration of alkali and alkaline earth metal oxides formed during pyrolysis of vegetation by hot ash efflorescent salts encrusted on plants and dissolution of volcanic glass provided some of the minor components the almost pure caso 4 composition of the leach waters is compositionally distinct from any present inflow waters in the central andes addition of caso 4 may explain some of the differences between the observed brine compositions and those predicted by simulating the evaporation of regular inflows the recycling of sedimentary gypsum is probably not restricted to lascar volcano the recycling of ancient salts and possibly also the pyrolysis of vegetation may have been crucial processes in the salt balance of closed basins during the intense volcanic activity of the tertiary

mars global digital dune database and initial science results 1 a new mars global digital dune database mgd3 constructed using thermal emission imaging system themis infrared ir images provides a comprehensive and quantitative view of the geographic distribution of moderate to large size dune fields area 1 km2 that will help researchers to understand global climatic and sedimentary processes that have shaped the surface of mars mgd3 extends from 65 n to 65 s latitude and includes 550 dune fields covering 70 000 km2 with an estimated total volume of 3 600 km3 this area when combined with polar dune estimates suggests moderate to large size dune field coverage on mars may total 800 000 km2 6 times less than the total areal estimate of 5 000 000 km2 for terrestrial dunes where availability and quality of themis visible vis or mars orbiter camera narrow angle moc na images allow we classify dunes and include dune slipface measurements which are derived from gross dune morphology and represent the prevailing wind direction at the last time of significant dune modification for dunes located within craters the azimuth from crater centroid to dune field centroid referred to as dune centroid azimuth is calculated and can provide an accurate method for tracking dune migration within smooth floored craters these indicators of wind direction are compared to output from a general circulation model gcm dune centroid azimuth values generally correlate to regional wind patterns slipface orientations are less well correlated suggesting that local topographic effects may play a larger role in dune orientation than regional winds

ultrahigh resolution topographic mapping of mars with mro hirise stereo images meter scale slopes of candidate phoenix landing sites 1 the objectives of this paper are twofold first to report our estimates of the meter to decameter scale topography and slopes of candidate landing sites for the phoenix mission based on analysis of mars global surveyor mgs mars orbiter camera moc images with a typical pixel scale of 3 m and mars reconnaissance orbiter mro high resolution imaging science experiment hirise images at 0 3 m pixel 1 and second to document in detail the geometric calibration software and procedures on which the photogrammetric analysis of hirise data is based a combination of optical design modeling laboratory observations star images and mars images form the basis for software in the u s geological survey integrated software for imagers and spectrometers isis 3 system that corrects the images for a variety of distortions with single pixel or subpixel accuracy corrected images are analyzed in the commercial photogrammetric software socet set bae systems yielding digital topographic models dtms with a grid spacing of 1 m 3 4 pixels that require minimal interactive editing photoclinometry yields dtms with single pixel grid spacing slopes from moc and hirise are comparable throughout the latitude zone of interest and compare favorably with those where past missions have landed successfully only the mars exploration rover mer b site in meridiani planum is smoother moc results at multiple locations have root mean square rms bidirectional slopes of 0 8 4 5 at baselines of 3 10 m hirise stereopairs one per final candidate site and one in the former site yield 1 8 2 8 slopes at 1 m baseline slopes at 1 m from photoclinometry are also in the range 2 3 after correction for image blur slopes exceeding the 16 phoenix safety limit are extremely rare

aeolian processes in proctor crater on mars sedimentary history as analyzed from multiple data sets 1 proctor crater is a 150 km diameter crater in noachis terra within the southern highlands of mars the analysis leading to the sedimentary history incorporates several data sets including imagery elevation composition and thermal inertia mostly from the mars global surveyor mission the resulting stratigraphy reveals that the sedimentary history of proctor crater has involved a complex interaction of accumulating and eroding sedimentation aeolian features spanning much of the history of the crater interior dominate its surface including large erosional pits stratified beds of aeolian sediment sand dunes erosional and depositional streaks dust devil tracks and small bright bed forms that are probably granule ripples long ago up to 450 m of layered sediment filled the crater basin now exposed in eroded pits on the crater floor these sediments are probably part of an ancient deposit of aeolian volcaniclastic material since then some quantity of this material has been eroded from the top layers of the strata small bright dune forms lie stratigraphically beneath the large dark dune field relative to the large dark dunes the bright bed forms are immobile although in places their orientations are clearly influenced by the presence of the larger dunes their prevalence in the crater and their lack of compositional and thermal distinctiveness relative to the crater floor suggests that these features were produced locally from the eroding basin fill dust devil tracks form during the spring and summer following a west southwesterly wind early in the spring the dust devils are largely restricted to dark patches of sand as the summer approaches dust devil tracks become more plentiful and spread to the rest of the crater floor indicating that the entire region acquires an annual deposit of dust that is revealed by seasonal dust devils the dark dunes contain few dust devil tracks suggesting that accumulated dust is swept away directly by saltation rather than by the passage of dust devils spectral deconvolution indicates that the dark dunes have infrared spectra consistent with basalt like materials the average thermal inertia calculated from thermal emission spectrometer bolometric temperatures is 277 17 j m 2 s 0 5 k 1 leading to an effective grain size of 740 170 mm which is consistent with coarse sand and within the range expected for martian sand the coarse sand that composes the large dune field may have originated from outside the crater saltating in from the southwest most of the transport pathway that delivered this sand to the dune field has since been eroded away or buried the sand was transported to the east center of the crater floor where beneath the present day dunes a 50 m high mound of sand has accumulated dune slip faces indicate a wind regime consisting of three opposing winds some of these wind directions are correlated with the orientations of dust devil tracks and bright bed forms the combination of a tall mound of sand and three opposing winds is consistent with a convergent wind regime which produces the large reversing transverse and star dunes that dominate the dune field the dark dunes have both active slip faces and seemingly inactive slip faces suggesting that the dunes vary spatially in their relative activity nevertheless the aeolian activity that has dominated the history of proctor crater still continues today index terms 5415 planetology solid surface planets erosion and weathering 5470 planetology solid surface planets surface materials and properties 5410 planetology solid surface planets

chemical osmosis reverse chemical osmosis and the origin of subsurface brines abstract calculations using recently tabulated values of density and osmotic coefficient for nacl h2o indicate that overpressuring is more than adequate to overcome chemical osmosis and drive reverse chemical osmosis in sedimentary sequences the best demonstrated overpressuring mechanism is the rapid deposition of fine grained sediments the dehydration of gypsum contributes to overpressuring for brief time intervals at shallow depths whereas water evolved during the protracted conversion of smectite to illite is probably a subordinate but continuing contributor to overpressuring at greater depth occurrences of overpressuring in sedimentary sections older than cretaceous indicate that post depositional mechanisms such as tectonic compression and aquathermal pressuring must also operate the latter may be of major importance in geothermal areas with adequate low permeability seals and a nontrivial contributor in areas of normal geothermal gradient because of shales that sharply decrease normal fluid flow the strongest arguments for the importance to present day brine compositions of membrane concentration of sea water solutes are 1 1 the correlation of d values of water molecules of pore fluid with those of local meteoric water 2 2 the need for major sources of mg2 and cl in apparently evaporite free basins even where dissolution of halite is a major contributor of solute reverse chemical osmosis still operates to leak relatively dilute water of the associated diagenetic chemical reactions that of mg2 with limestone to form dolomite is particularly effective in generating concentrated cl brines rich in ca2 it decreases the concentration of mg2 increases that of ca2 and decreases those of both so42 and co32 by precipitating caco3 and caso4 because of the ca2 common ion effect

geochemical surveillance of magmatic volatiles at popocatepetl volcano mexico surveillance of popocatepetl volcanic plume geochemistry and so 2 flux began in early 1994 after fumarolic and seismic activity increased significantly during 1993 volatile traps placed around the summit were collected at near monthly intervals until the volcano erupted on december 21 1994 additional trap samples were obtained in early 1996 before the volcano erupted again emplacing a small dacite dome in the summit crater abundances of volatile constituents ppm day of cl s total f co 2 hg and as varied but most constituents were relatively high in early and late 1994 however ratios of these constituents to cl were highest in mid 1994 34 s s total in trap solutions ranged from 1 5 to 6 4 lowest values generally occurred during late 1994 13 c co 2 of trap solutions were greatly contaminated with atmospheric co 2 and affected by absorption kinetics when trap data are combined with so 2 flux measurements made through november 1996 popocatepetl released about 3 9 mt so 2 16 mt co 2 0 75 mt hcl 0 075 mt hf 260 t as 2 6 t hg and roughly 200 mt h 2 o near vent gas concentrations in the volcanic plume measured by correlation spectrometer cospec and fourier transform infrared ftir commonly exceed human recommended exposure limits and may constitute a potential health hazard volatile geochemistry combined with petrologic observations and melt inclusion studies show that mafic magma injection into a preexisting silicic chamber has accompanied renewed volcanism at popocatepetl minor assimilation of cretaceous wall rocks probably occurred in mid 1994

electrolyte induced solute permeability effects in compacted smectite membranes abstract experiments suggest that increasing electrolyte flux into a compacted smectite membrane may result in greater permeability of the membrane to the electrolyte the influx of electrolyte into the membrane pores decreases the double layer thickness therefore reducing the clay s ability to exclude anions as a result solute previously accumulated in the concentration polarization layer cpl may be able to dissipate through the membrane producing a temporary situation where the effluent is more concentrated than the feed solution of course at some juncture the cpl will diminish sufficiently so that the effluent concentration will be the same as that of the feed solution and a true state will be reached the fact that increasing electrolyte concentration within the clay membrane decreases the membrane efficiency implies that the result of solute accumulation in geological basins even though a portion of such accumulation is attributable to the solute filtering ability of low permeability rocks is the ultimate cessation of membrane effects at the start of the cycle shale membranes have low solute concentrations and thus high rejection capabilities the largest amount of solute accumulates deep in the basin center where vertical flux rates are high because of greater solute concentration within the aquifer the solute concentration in the centrally located membranes rises more quickly than that of those located near the basin margins therefore the cessation of membrane effects occurs first in the deep center of the basin and gradually moves upward and outward toward the basin margins the fact that membrane efficiency decreases as pore solute concentration increases might help explain why conclusive trends attributable to membrane effects have not been more commonly observed in the subsurface

mean airflow patterns upwind of topographic obstacles and their implications for the formation of echo dunes a wind tunnel simulation of the effects of windward slope 1 secondary airflow plays an important role in dune formation and development in the case of the echo dunes that form upwind of an obstacle it introduces considerable complexity because both the initiation and development processes are influenced by airflow patterns in this study we measured the variations of airflow in front of obstacles with different windward stoss slope angles by means of particle image velocimetry in a series of wind tunnel tests the windward slope angle was the key factor in determining the secondary airflow patterns the horizontal velocities decreased and the vertical velocities increased as the airflow approached perpendicular to the obstacle and a vortex of reversed flow formed in front of obstacles with a stoss slope of 60 or steeper the positions of airflow separation and of the core of the reversed vortex were a function of the windward slope angle depending on the position of the reverse vortex and its significance for the formation of echo dunes the windward slope could be divided into three groups 65 or less 70 75 and 80 or more the horizontal velocity profiles deviated from a log linear distribution resulting in five airflow regions with different rates of change of horizontal velocity we discuss the significance of these velocity variations for sand accumulation and the effects of each airflow region on echo dune formation

hyperfiltration induced precipitation of calcite abstract hyperfiltration is sometimes cited as a mechanism to explain high degrees of calcite cementation at shale sandstone contacts to test this cementation mechanism a series of experiments were performed in which solutions undersaturated with respect to calcite were hydraulically forced through a ca bentonite at different flow rates calcite precipitate was observed on the bentonite membrane from hyperfiltrated stock solutions having initial calcite saturation indices of 0 91 and 0 59 supersaturation conditions at the clay s high pressure interface are likely provided by establishment of a concentration polarization layer in the subsurface the driving force for hyperfiltration is a differential hydraulic pressure gradient acting across a shale membrane this hydraulically induced flux of solution causes a build up of solute at the shale s high pressure interface to levels that may exceed saturation indices of common cementing minerals like calcite although the source of the hydraulic pressure is likely due to compaction within the sedimentary pile directional flow constraints suggest that hyperfiltration induced precipitation of calcite occurs at sand shale boundaries away from areas of active compaction

volcanic sulfate aerosol formation in the troposphere the isotopic composition of volcanic sulfate provides insights into the atmospheric chemical processing of volcanic plumes first mass independent isotopic anomalies quantified by 17o and to a lesser extent 33s and 36s in sulfate depend on the relative importance of different oxidation mechanisms that generate sulfate aerosols second the isotopic composition of sulfate 34s and 18o could be an indicator of fractionation distillation condensation processes occurring in volcanic plumes here we present analyses of o and s isotopic compositions of volcanic sulfate absorbed on very fresh volcanic ash from nine moderate historical eruptions in the northern hemisphere most of our volcanic sulfate samples which are thought to have been generated in the troposphere or in the tropopause region do not exhibit any significant mass independent fractionation mif isotopic anomalies apart from those from an eruption of a mexican volcano coupled to simple chemistry model calculations representative of the background atmosphere our data set suggests that although h2o2 a mif carrying oxidant is thought to be by far the most efficient sulfur oxidant in the background atmosphere it is probably quickly consumed in large dense tropospheric volcanic plumes we estimate that in the troposphere at least more than 90 of volcanic secondary sulfate is not generated by mif processes volcanic s bearing gases mostly so2 appear to be oxidized through channels that do not generate significant isotopically mass independent sulfate possibly via oh in the gas phase and or transition metal ion catalysis in the aqueous phase it is also likely that some of the sulfates sampled were not entirely produced by atmospheric oxidation processes but came out directly from volcanoes without any mif anomalies

geomorphology and sediments of sand ramps in the mojave desert abstract sand ramps are amalgamated accumulations of aeolian fluvial and talus deposits they have developed as a result of the interactions of wind blown sand and desert piedmont processes adjacent to mountain ranges in the mojave desert and occur next to regional and local sand transport corridors sand ramps are dominated by aeolian sand that was deposited as sand sheets against the mountain front but also include significant fluvial units periods of geomorphic stability are represented by paleosols and talus accumulations the sand ramps provide a record of the response of aeolian processes to climatic change in the mojave desert most are now relict features and accumulated in periods of higher sediment supply from fluctuating and or desiccating paleolakes during the late pleistocene and early holocene

low head hyperfiltration through intact burlington limestone and jefferson city dolomite discs abstract hyperfiltration is the ability of a membrane to retard the passage of a solute under a hydraulic head in excess of osmotic pressure disaggregated and recompacted shales mudstones clays and tuff have been shown to exhibit hyperfiltration induced membrane effects in past experiments however limestone and dolomite have not previously been tested therefore eight hyperfiltration experiments were performed on intact burlington limestone and jefferson city dolomite to assess the membrane properties of these lithologies four experiments were conducted on each lithology using 0 0050 and 0 0100 m cl solutions at heads of 0 50 and 1 00 m reflection coefficients a measure of osmotic efficiency ranged from 0 34 to 0 39 for the burlington limestone and 0 32 to 0 40 for the jefferson city dolomite at the end of the hyperfiltration experiments cl was concentrated within the cell above input concentrations by 85 95 for the burlington limestone and 79 105 for the jefferson city dolomite an additional experiment passed 0 0020 m dissolved silica solution through the burlington limestone at a head of 0 965 bar 14 psi the final concentration of silica within the cell was 0 0043 m dissolved silica at steady state a concentration 114 higher than the original input solution concentration the reflection coefficient for this experiment was calculated to be 0 33 the results of these experiments suggest that membrane properties in these lithologies may be worthy of consideration in some geologic scenarios including 1 shallow or perched aquifers bounded by thin limestone or dolomite strata 2 overpressured aquifers bounded by limestone or dolomite 3 limestone or dolomite bounded aquifers with significant vertical components of flow and 4 facies changes with significant lateral component of flow bounded by either lithology furthermore the results suggest that silica cementation may be possible even under relatively low head conditions cementation due to hyperfiltration even at shallow depths and low pressures should be further investigated similarly other low permeability lithologies lacking a charged surface could potentially function as geologic membranes