estimating groundwater exchange with lakes 1 the stable isotope mass balance method groundwater inflow and outflow contributions to the hydrologic budget of lakes can be determined using a stable isotope 18o 16o mass balance method the stable isotope method provides a way of integrating the spatial and temporal complexities of the flow field around a lake thereby offering an appealing alternative to the traditional time and labor intensive methods using seepage meters and an extensive piezometer network in this paper the method is applied to a lake in northern wisconsin demonstrating that it can be successfully applied to lakes in the upper midwest where thousands of similar lakes exist inflow and outflow rates calculated for the wisconsin lake using the isotope mass balance method are 29 and 54 cm yr respectively which compare well to estimates derived independently using a three dimensional groundwater flow and solute transport model of 20 and 50 cm yr such a favorable comparison lends confidence to the use of the stable isotope method to estimate groundwater exchange with lakes in addition utilization of stable isotopes in studies of groundwater lake systems lends insight into mixing processes occurring in the unsaturated zone and in the aquifer surrounding the lake and verifies assumed flow paths based on head measurements in piezometers

mount st helens 1980 and mount pelee 1902 flow or surge the far reaching directed blast of mount st helens and the devastating nuees ardentes of mount pelee produced deposits that in many places consist of three main layers a basal gravelly or sandy layer 1 a massive or bedded ash layer 2 and a capping ash cloud layer 3 these thin and in part landscape mantling deposits are generally ascribed to pyroclastic surges and the dune bedding seen in parts of layer 2 has reinforced this interpretation there are several reasons however for preferring a pyroclastic flow origin 1 much of layer 2 is unequivocal pyroclastic flow 2 the tripartite subdivision and landscape mantling habit is similar to that displayed by ignimbrites of the low aspect ratio type 3 the deflation of a pyroclastic surge and the subsequent deposition of particulate material will tend not to conserve the fine ash and dust that are abundant in valley ponded parts of layer 2 and cannot explain the observed tendency for layer 2 to show stronger fines depletion on ridges than in valley bottoms and 4 the coarseness and the variance of grain size found within dune bedded bed sets in mount st helens layer 2 are like those of very weak pyroclastic surges and the dune bedding most likely resulted from local minor turbulence as could have been caused by surface roughness in a mountainous terrain littered with tree stumps and fallen trees in a thin depositing pyroclastic flow the directed blast and nuees ardentes at mount st helens and mount pelee are interpreted to have been violently emplaced pyroclastic flows producing deposits of low aspect ratio type the characteristics of which stem from an exceptionally high flow velocity

stratigraphy chronology and character of the 1976 pyroclastic eruption of augustine volcano alaska the chronology of deposits of the 1976 eruption of augustine volcano which produced pyroclastic falls pyroclastic flows and lava domes is determined by correlating the stratigraphy with published records of seismicity plume observations and distant ash falls three thin air fall ash beds unit a1 a2 and a3 correlate with events near the beginning of the 1976 eruption on 22 and 23 january on 24 january a small volume ash cloud surge deposit unit s accumulated over the north half of augustine island a series of pumiceous pyroclastic flows represented by the lobate pumiceous deposits unit f occurred on 24 january and locally melted the snowpack to cause small pumice laden floods a thin ash bed unit a4 was deposited on 24 january and the main plinian eruption unit p occurred on 25 january in middle to late february and again in mid april lava domes were extruded at the summit accompanied by incandescent block and ash flows down the north flank a hut near the north coast of the island was mechanically and thermally damaged by the small volume ash cloud surge of unit s before the eruption of the pumice flow of unit f the metal roof was then penetrated by lithic fragments of the plinian fall of 25 january explosive eruptions in the early stage of an eruption like that which deposited unit s are important hazards at augustine island as are infrequent debris avalanches and attendant tsunamis

the eruptive rate and history of kuju volcano in japan during the past 15 000 years abstract the eruptive history of kuju volcano on kyushu japan during the past 15 000 years has been determined by tephrochronology and 14c dating kuju volcano comprises isolated lava domes and cones of hornblende andesite together with aprons of pyroclastic flow deposits on its flanks kuju volcano produced tephras at roughly 1000 yr intervals during the past 5000 years and 70 of the domes and cones have formed during the past 15 000 years the youngest magmatic activity of kuju volcano was the 1 6 km3 andesite eruption about 1600 years ago which emplaced a lava dome and block and ash flow kuju volcano shows a nearly constant long term eruption rate 0 7 0 4 km3 for 1000 years during the past 15 000 years this rate is within the range of estimated average eruption rates of late quaternary volcanoes in the japanese arc but is about one order of magnitude higher than the eruption rate of unzen volcano kuju volcano has been in phreatic eruption since october 1995 the late quaternary history of kuju indicates that it poses a significant volcanic hazard primarily due to block and ash flows from collapsing lava domes

groundwater recharge and discharge dynamics in an arid zone ephemeral lake system australia the coongie lakes are a series of ephemeral freshwater lakes on the lower reaches of cooper creek a large intermittent river of the arid lake eyre basin australia hydrogeological chemical and isotopic observations in conjunction with numerical modeling of groundwater responses to lake inundation events have been used to identify the dominant processes linking shallow unconfined groundwater with the hydrology of the lakes during wet and dry periods the lakes are predominantly zones of net groundwater recharge during inundation events however soil profile data suggests that drying of some of these lakes allows evaporative groundwater discharge to occur through the soil profile of the dry lake beds resulting in salinization of the soil profile of the more ephemeral lakes the occurrence of young high salinity groundwater is best explained by variations in soil profile flushing in response to wet and dry interannual periods of river discharge during interannual drier phases when filling of previously dry lakes is more common recharge is mostly via macropore flow during the rising stage of the inundation increased salinization of the lake bed sediments occurs during longer dry periods due to transport of solutes to the near surface from lake bed evaporation and limited flushing of the soil profile because of the macropore dominated flow during recharge during wet periods recharge is more likely dominated by matrix flow that results in leaching of the soil profile and increased export of solutes into the alluvial aquifer

isotopic tracing of the source water for cedar bog in west central ohio usa abstract cedar bog a boreal fen in west central ohio is home for many endangered plants and animals the whereabouts of the water source that sustains cedar bog has been the subject of several investigations in the past two decades some of these studies indicated that a recharge area lies to the east and northeast of the bog using environmental isotopes of oxygen and hydrogen the present study positively identifies a major recharge area located northeast of the bog and enclosed by two small tributaries of the mad river oxygen isotopic composition and tritium contents of ground water suggest that the bog water is only a few years old

oblique reflections in the mars express marsis data set stable density structures in the martian ionosphere the mars advanced radar for subsurface and ionospheric sounding marsis onboard the european space agency s mars express mex spacecraft routinely detects evidence of localized plasma density structures in the martian dayside ionosphere such structures likely taking the form of spatially extended elevations in the plasma density at a given altitude give rise to oblique reflections in the active ionospheric sounder data these structures are likely related to the highly varied martian crustal magnetic field in this study we use the polar orbit of mex to investigate the repeatability of the ionospheric structures producing these anomalous reflections examining data taken in sequences of multiple orbits which pass over the same regions of the martian surface under similar solar illuminations within intervals lasting tens of days presenting three such examples or case studies we show for the first time that these oblique reflections are often incredibly stable indicating that the underlying ionospheric structures are reliably reformed in the same locations and with qualitatively similar parameters the visibility or lack thereof of a given oblique reflection on a single orbit can generally be attributed to variations in the crustal field within the ionosphere along the spacecraft trajectory we show that within these examples oblique reflections are generally detected whenever the spacecraft passes over regions of intense near radial crustal magnetic fields i e with a cusp like configuration the apparent stability of these structures is an important feature that must be accounted for in models of their origin

observations of the latitude dependence of the location of the martian magnetic pileup boundary 1 we report observations that show the dependence of the altitude of the magnetic pileup boundary mpb at mars on planetary latitude as seen by the mars global surveyor magnetometer electron reflectometer instrument the mpb is further away from mars on average at southern latitudes than at northern latitudes the data are consistent with a mpb distance mapped to the terminator plane that does not vary with latitude in the northern hemisphere but increases with increasing southern latitude in the southern hemisphere we also report increased variability in the mpb distance within the longitude range 90 270 e longitude in the southern hemisphere which is the region that contains the strongest crustal magnetic fields these trends are most obvious in a planet fixed coordinate system indicating a planet fixed driver of the mpb location the proposed mechanism is the local diversion of shocked solar wind flow by crustal magnetic fields

cooling degassing and compaction of rhyolitic ash flow tuffs a computational model previous models of degassing cooling and compaction of rhyolitic ash flow deposits are combined in a single computational model that runs on a personal computer the model applies to a broader range of initial and boundary conditions than riehle s earlier model which did not integrate heat and mass flux with compaction and which for compound units was limited to two deposits model temperatures and gas pressures compare well with simple measured examples the results indicate that degassing of volatiles present at deposition occurs within days to a few weeks compaction occurs for weeks to two to three years unless halted by devitrification near emplacement temperatures can persist for tens of years in the interiors of thick deposits even modest rainfall significantly chills the upper parts of ash deposits but compaction in simple cooling units ends before chilling by rainwater influences cooling of the interior of the sheet rainfall does however affect compaction at the boundaries of deposits in compound cooling units because the influx of heat from the overlying unit is inadequate to overcome heat previously lost to vaporization of water three density profiles from the matahina ignimbrite a compound cooling unit are fairly well reproduced by the model despite complexities arising from numerous cooling breaks uncertainties in attempts to correlate in detail among the profiles may be the result of the non uniform distribution of individual deposits regardless it is inferred that model compaction is approximately valid thus the model should be of use in reconstructing the emplacement history of compound ash deposits for inferring the depositional environments of ancient deposits and for assessing how long deposits of modern ash flows are capable of generating phreatic eruptions or secondary ash flows

the 1883 and late prehistoric eruptions of augustine volcano alaska abstract the eruptive history of augustine volcano has been characterized by cycles of growth and destruction of the volcano repeated failure of 5 10 of the edifice has produced mobile debris avalanches that reached the sea on all sides high lava extrusion rates rapidly restore the volcano to its pre failure configuration this equilibrium between constructive and destructive processes has resulted in a relatively low lava dome complex surrounded by an apron of volcaniclastic debris three times the volume of the dome complex the most recent edifice collapse occurred in 1883 producing the 0 3 km3 burr point debris avalanche deposit three major slide blocks extended the shoreline up to 2 km and produced a tsunami that swept across cook inlet hummock morphologies change from a proximal radial orientation to a dominantly transverse alignment reflecting deceleration and compression of the avalanches as they enter the sea the breached crater formed by collapse was then largely filled by a 0 09 km3 lava dome and a 0 04 km3 lava flow travelled down the north flank lithic block and ash flows and pyroclastic surges reached the coast the burr point avalanche deposit partially overlaps the rocky point debris avalanche deposit to the west that was probably emplaced 200 400 years b p a major collapse event at ca 1540 110 a d produced the west island debris avalanche ending a period of expansion of the western side of the island an accompanying lateral blast overtopped the avalanche covering a 40 sector of the west flank the plinian tephra layer b may also have been erupted at the time of the west island eruption today augustine volcano has rebuilt itself to a size similar to that which preceded the last edifice failure in 1883 the frequency of past collapses three in the last 500 years suggests that summit collapse is a possibility during any future eruption the next major collapse is expected to involve 0 1 0 5 km3 of the summit the ensuing debris avalanche would likely reach the coast producing a tsunami that could impact populated areas of the kenai peninsula the largest tsunami would result from collapse in directions other than to the north or west tsunami magnitude is contingent on failure volume direction and timing with respect to tides

determination of groundwater flow through regimes of shallow lakes and wetlands from numerical analysis of stable isotope and chloride tracer distribution patterns a numerical model previously developed to systematically examine groundwater flow in vertical section near shallow surface water bodies such as lakes wetlands and ponds is further developed to include simulation of the distribution patterns of hydrogeochemical and stable isotopic tracers in relation to the surface water body and the geometry of distribution patterns of the tracers in the groundwater release zone of the lake many different possible flow regimes are identified however in this paper attention is focused on flow through water bodies as these are the flow regimes observed in field validation two shallow lakes on the swan coastal plain of south west western australia are the subject of field studies where hydrogeochemical and stable isotopes are used to validate the flow through groundwater flow regime predicted by the modelling confirming the validity of the approach the flow regime transition diagrams introduced in earlier papers are extended to include consideration of the hydrogeochemical and stable isotopic indices cl l cl and 1000 l 1000 these ratios are introduced as an additional two of nine non dimensional ratios that are necessary to analyse the problem the ratios represent the chloride and isotopic composition ci l and l respectively in the groundwater release zones of the lakes relative to these parameters in the groundwater capture zone cl and for the lake field data from the case studies plotted on appropriately configured transition diagrams demonstrates the overall validity of the modelling approach and its underlying assumptions it is concluded that isotopic and hydrogeochemical data are invaluable in interpreting the interaction between lakes or wetlands and regional aquifers as it is very difficult to make physical or hydraulic measurements in the field that allow an understanding of lake aquifer interaction the tools and concepts developed that are summarized in the presented transition diagrams are invaluable starting points for the consideration and analysis of other case specific examples of groundwater surface water interaction and will improve the scientific basis of decision making concerning lake and wetland management and groundwater interaction by water resource and environmental managers

a proxy for determining solar wind dynamic pressure at mars using mars global surveyor data 1 we develop a method to infer the upstream solar wind pressure at mars using data from the mars global surveyor mgs magnetometer instrument the method assumes magnetic field pressure in the magnetic pileup region balances the incident solar wind dynamic pressure newtonian pressure balance conditions are imposed for positions off of the subflow point proof of concept exists from the mapping phase of the spacecraft mission when the orbital geometry at a constant altitude allows fits to magnetic field data as a function of solar zenith angle during the elliptical orbit phase of mgs when the spacecraft passes through a large range of altitudes such fits are not possible however the measured magnetic pressure in the magnetic pileup region is scaled by the same means as derived for the mapping orbits and reasonable upstream solar wind pressure is obtained we compare the distribution of solar wind pressure calculated using mgs data with the solar wind pressure measured upstream of the earth during the same time period and find good agreement further supporting this algorithm as a valid proxy for the incident solar wind pressure the response of the position of the magnetic pileup boundary to the inferred solar wind pressure also validates the method high solar wind ram pressure depresses the altitude of the magnetic pileup boundary

surface height adjustments in pyroclastic flow deposits observed at unzen volcano by jers 1 sar interferometry abstract pyroclastic flows from the 1990 1995 eruption of unzen a dacitic volcano in the southwest of japan descended the mountain along a variety of routes causing widespread damage and loss of life interferograms constructed from jers 1 l band synthetic aperture radar sar images show a number of features related to these pyroclastic flows and their secondary effects the most useful interferogram in this respect is based on images acquired on 22 july 1993 and 1 december 1993 and shows the descent paths for pyroclastic flows occurring in four valley systems within this time window as zones of decorrelation caused by the repeated resurfacing the 22 july 1993 sar image was through considerable good fortune acquired only 2 6 days after a major pyroclastic flow had descended into the mizunashi valley so that in the absence of rainfall the fresh 2 m thick deposits were dry when first imaged the largest differential surface height changes observed in the interferogram represent height decreases in the vertical of 12 cm and significantly lie within a small region of the mizunashi valley which was resurfaced by the pyroclastic flow of 19 july 1993 but not subsequently within this small region radar coherence is higher maximum correlation value of 0 75 in a center valley site where ash but relatively few large boulders are present in a qualitative sense the new ash surfaces exhibit higher levels of radar coherence than the older pre 19 july deposits in other unzen valleys visited by pyroclastic flows smaller differential surface height decreases 4 cm are observed where the surface deposits were emplaced by events taking place between 1 3 months before the acquisition date of the 22 july 1993 image the extra 8 cm of surface height decrease observed in the case of the freshly laid mizunashi deposits must result from a deflationary mechanism or mechanisms operating in a spatially uniform manner in order for radar coherence to be maintained a number of possible causative mechanisms including hydroconsolidation initiated by the seepage of rainwater into a newly deposited ash sheet deflation on gas release basal erosion settlement and substrate relaxation are discussed here given the relatively low emplacement temperatures of the unzen ash 300 500 c it is unlikely that viscous deformation within the body of the fresh ash deposits is responsible for the subsidence comparison of the 22 july 1993 1 december 1993 interferogram with a landsat 4 thematic mapper image of unzen acquired on 10 january 1994 highlights a ribbon like zone of radar decorrelation running along the course of the mizunashi valley which marks the path of debris flows that occurred within the time interval between the two sar images used in the construction of the interferogram overall these results demonstrate the utility of interferometric sar derived surface height and coherence measurements for monitoring the pyroclastic and debris flow regimes of active volcanoes

chemical evolution of groundwater near a sinkhole lake northern florida 1 flow patterns age of groundwater and influence of lake water leakage leakage from sinkhole lakes significantly influences recharge to the upper floridan aquifer in poorly confined sediments in northern florida environmental isotopes oxygen 18 deuterium and tritium chlorofluorocarbons cfcs cfc 11 ccl3f cfc 12 ccl2f2 and cfc 113 c2cl3f3 and solute tracers were used to investigate groundwater flow patterns near lake barco a seepage lake in a mantled karst setting in northern florida stable isotope data indicated that the groundwater downgradient from the lake contained 11 67 lake water leakage with a limit of detection of lake water in groundwater of 4 3 the mixing fractions of lake water leakage which passed through organic rich sediments in the lake bottom were directly proportional to the observed methane concentrations and increased with depth in the groundwater flow system in aerobic groundwater upgradient from lake barco cfc modeled recharge dates ranged from 1987 near the water table to the mid 1970s for water collected at a depth of 30 m below the water table cfc modeled recharge dates based on cfc 12 for anaerobic groundwater downgradient from the lake ranged from the late 1950s to the mid 1970s and were consistent with tritium data cfc modeled recharge dates based on cfc 11 indicated preferential microbial degradation in anoxic waters vertical hydraulic conductivities calculated using cfc 12 modeled recharge dates and darcy s law were 0 17 0 033 and 0 019 m d for the surficial aquifer intermediate confining unit and lake sediments respectively these conductivities agreed closely with those used in the calibration of a three dimensional groundwater flow model for transient and steady state flow conditions

observations stratigraphy and eruptive processes of the 1990 eruption of kelut volcano indonesia the february 10 1990 eruption of kelut volcano eastern java reportedly began with seven discrete short lived explosions between 11 41 and 12 35 local times deposits of this initial phreatomagmatic stage include a basal ash fall layer unit a1 widespread pumice surge deposits unit s and related pisolitic ash layer unit a2 the main plinian phase of the eruption lasted about 4 hours from 12 35 and produced pumice flow deposits unit pf overlain by a pumice fallout layer distributed mainly to the southwest unit p and intra plinian scoria flow deposits unit sf uppermost scoria rich ash fall layers unit a3 likely relate to late discrete eruptive pulses a few small explosions resumed on february 11 and 12 leaving no recognizable deposit an embryonic lava dome had formed in the crater bottom by april then was submerged by the new crater lake destruction of the summit area resulted from emplacement of the pre plinian pumice surge up to 4 5 km on the south and west flanks and of the early plinian pumice flows up to 1 2 km radially from the crater before these were channelized in the main valleys to further travel 3 km most of the 32 human deaths resulted from roof collapse under the load of fallout tephra beyond the devastated area which had been evacuated before the eruption began the eruption produced 0 13 km3 of tephra of which 0 12 km3 represent the products of the plinian phase the average eruptive rate of the plinian phase is estimated to have been 7 5 106 kg s magma dre the pumice flows are interpreted to have been formed due to unsteadiness and low velocity of the eruptive column at the beginning of the plinian phase the intra plinian scoria flows incorporate either more degassed or colder juvenile magma they were presumably erupted at the edge of the column due to fluctuations in the mass flux and in pressure in the conduit

magnetic resonance sounding evidence shows that shallow groundwater discharge maintains the lake landscape in the hunshandake sandy land north china the hunshandake sandy land hsl is a well known water rich sandy region in china that is home to many lakes most of these lakes are sustained by groundwater inflow however due to the limited hydrogeological survey data the mechanism by which the lakes interact with groundwater is not well understood magnetic resonance sounding mrs is a geophysical method that has emerged in recent years that can directly detect the distribution of groundwater and determine the lithology of the aquifer medium compared with drilling this method is convenient rapid and inexpensive in this study to determine how the lakes are recharged by groundwater a field experiment using mrs was conducted on haoletuyin lake which is located in the central hsl the results showed that compared with borehole data the mrs derived aquifer depth has an uncertainty of 6 88 additionally the lithology of the media derived from the mrs is consistent with that derived from the borehole data this finding suggests that the mrs derived results are highly accurate based on the mrs derived results two hydrogeological profiles were plotted and they show that the lake in the experimental area is recharged primarily by shallow groundwater and not by deep groundwater this study is significant because it not only reveals the mechanism by which haoletuyin lake is maintained but also proves that mrs is an excellent tool for studying lake groundwater relations in desert sandy land regions with limited hydrogeological survey data

pressure gradients driving ion transport in the topside martian atmosphere an edited version of this paper was published by agu copyright 2019 american geophysical union

hydrogeochemistry and isotope techniques to determine water interactions in groundwater dependent shallow lakes wet pampa plain argentina this paper gives an account of the implementation of hydrochemical and isotopic techniques to identify and explain the processes that govern solute exchange in two groundwater dependent shallow lakes in the southeastern pampa plain of argentina water samples lakes streams spring water and groundwater for hydrochemical and stable isotopic determination were collected and the main physical chemical parameters were measured the combination of stable isotope data with hydrogeochemical techniques was used for the identification of sources and preferential recharge areas to these aquatic ecosystems which allowed the explanation of the lake water origin the hydrochemical processes which explain los padres lake water chemistry are evaporation from groundwater co2 input calcite dissolution na release by ca2 and mg2 exchange and sulfate reduction the model that best aligns with la brava lake hydrochemical constraints includes mixing co2 and calcite dissolution cationic exchange with na release and mg2 adsorption and to a lesser extent ca na exchange this model suggests that the fractured aquifer contribution to this water body is greater than 50 an isotopic specific fingerprint for each lake was identified finding a higher evaporation rate for la brava lake compared to los padres lake isotopic data demonstrate the importance of these shallow lakes as recharge areas to the regional aquifer becoming areas of high groundwater vulnerability the tandilia range system considered in many hydrogeological studies as the impermeable bedrock of the pampean aquifer acts as a fissured aquifer in this area contributing to low salinity waters and with a fingerprint similar to groundwater isotopic composition

surface water groundwater interaction near shallow circular lakes flow geometry in three dimensions steady flow regimes for three dimensional lake aquifer systems are studied via idealized mathematical models that are extensions of earlier simplified vertical section models of interaction between shallow lakes and underlying aquifers the present models apply to a shallow circular lake at the surface of a rectangular aquifer of finite depth yielding a truly three dimensional representation of the resulting flow system flux boundary conditions are applied at the ends of the aquifer with net vertical recharge or evapotranspiration at the water table the lake is defined by a region with constant head by determining and visualizing solutions to the discretized saturated flow equations a range of possible flow regimes is identified and their topological properties are studied tools for analyzing flow regimes are described including a method for locating and mapping three dimensional dividing surfaces within steady flow fields results show strong similarities between two and three dimensional systems including a large number of flow through recharge and discharge regimes and reverse flow cells flow lines calculated on a vertical plane through the middle of a lake resemble but are not identical to two dimensional streamlines for a range of aquifer flow and recharge conditions estimates of the widths and depths of capture and release zones for various lake aquifer geometries are asymptotic to earlier results for two dimensional systems numerical predictions are compared with analytical results for certain limiting flow regimes

marsis observations of the martian nightside ionosphere dependence on solar wind conditions despite the absence of solar radiation on the martian nightside a weak irregular and variable ionosphere is produced there the nightside ionosphere is thought to be maintained by two main sources dayside nightside plasma transport and electron precipitation observations by mars express mex and mars global surveyor mgs have shown that these plasma sources are either hindered or favored by the presence of strong crustal magnetic fields and that these effects are modulated by external parameters such as the solar wind dynamic pressure and the orientation of the interplanetary magnetic field imf these external drivers are expected to influence the supply of plasma to the nightside and thus the formation of the irregular nightside ionosphere we here present a statistical study of the martian ionosphere at solar zenith angle greater than 107 from november 2005 to may 2006 using remote measurements of ionospheric echoes with the mars advanced radar for subsurface and ionospheric sounding marsis radar sounder onboard mex and using mgs based proxies for the solar wind dynamic pressure and the imf clock angle we find that the peak densities increase with the dynamic pressure and also that cases of very high peak density are almost always associated with westward imf orientation we find that using mex aspera 3 electron data these cases often seem to be linked to accelerated electrons plasma transport is known to be important in the near nightside on the other hand electron precipitation prevails when the dynamic pressure is high enough to compress the ionosphere and in vertical field regions where the imf orientation matters

influence of regional setting on the interaction between shallow lakes and aquifers 1 interaction between surface water and groundwater depends on the position of a lake within the regional flow system the approach in this paper is to nest a local scale two dimensional 2 d lake aquifer model within a 1 d regional aquifer model to examine the effect of the regional setting on surface water groundwater interaction this extends previous steady state flow modeling which is presented in earlier publications the results indicate that the type of regional setting and position of the lake within that setting impose constraints on the near field flow geometry only nine of 39 previously identified flow regimes are possible in the regional flow system considered flow through lakes are dominant and can occur anywhere within the regional flow recharge and discharge lakes are more likely to occur near the groundwater divide where regional hydraulic gradients are flattest and can be counteracted by local forcing in and near the lake

first measurements of the ionospheric plasma escape from mars before the phobos mission the magnetosphere of mars was relatively unexplored basically all data on the charged particle environment of mars had come from the soviet mars missions mars 2 3 4 and 5 here we report the results of an ion composition experiment on board the soviet phobos 2 spacecraft which allowed us to determine the loss of plasma from the ionosphere of mars because mars has a very small intrinsic magnetic field the ion outflow had been expected to be similar to that of venus surprisingly there were many similarities between the ionospheric outflow from mars and the earth the ion loss from mars results from both ion pick up that results from mass loading of the solar wind in the martian boundary layer and ionospheric o beams of energies up to several kev possibly from upward acceleration processes similar to those observed above the earth s auroral oval a preliminary estimate of the ionospheric outflow from mars indicates that the planet is losing oxygen at a rate of 3 x 1025 ions s 1 this corresponds to an evacuation of its present total atmospheric oxygen content contained in co2 and o2 in less than 100 million years

plasma intrusion above mars crustal fields mars express aspera 3 observations abstract using data of the aspera 3 instrument on board the european mars express spacecraft we investigate the effect of the martian crustal fields on electrons intruding from the magnetosheath for the crustal field strength we use published data obtained by the mars global surveyor mag er instrument for a fixed altitude of 400 km we use statistics on 13 months of 80 100 ev electron observations to show that the electron intrusion altitude determined by a probability measure is approximately linearly dependent on the total field strength at 400 km altitude we show that on the dayside the mean electron intrusion altitude describes the location of the magnetic pile up boundary mpb such that we can quantify the effect of the crustal fields on the mpb on the nightside we quantify the shielding of precipitating electrons by the crustal fields

magnetic field and plasma observations at mars initial results of the mars global surveyor mission the magnetometer and electron reflectometer investigation mag er on the mars global surveyor spacecraft has obtained magnetic field and plasma observations throughout the near mars environment from beyond the influence of mars to just above the surface at an altitude of 100 kilometers the solar wind interaction with mars is in many ways similar to that at venus and at an active comet that is primarily an ionospheric atmospheric interaction no significant planetary magnetic field of global scale has been detected to date 2 1021 gauss cubic centimeter but here the discovery of multiple magnetic anomalies of small spatial scale in the crust of mars is reported

magnetic reconnection in the ionosphere of mars the role of collisions this is an excel data file for an analysis of nasa maven date looking at magnetic reconnection in the ionosphere it will accompany a later paper in the j geophysical research on this topic

transient hydrogeological controls on the chemistry of a seepage lake a solute mass balance method was used to estimate groundwater inflow and outflow rates for nevins lake michigan a seepage lake in the upper peninsula that historically has shown extremely variable water chemistry compared with most other seepage lakes a 4 year study 1989 1992 of the hydrology and geochemistry of nevins lake and its contiguous groundwater system revealed that changes in the mass of dissolved solutes are the result of annual hydraulic gradient reversals a pronounced acidification of nevins lake from 1986 to 1988 was likely caused by drought induced diminished groundwater inflow rates in this study dissolved calcium the major cation in water of nevins lake groundwater and precipitation was used for estimating mass flow rates during the 1989 1992 period nevins lake showed a reproducible annual cycle in calcium mass immediately following spring snowmelt and the resulting hydraulic gradient reversal the mass of dissolved calcium in the lake increases rapidly and then it decreases steadily throughout the summer and early fall at which time the lake becomes hydraulically mounded and receives no groundwater inflow groundwater flow rates estimated by the solute mass balance method are sensitive to assumed solute concentrations in discharging groundwater pore water samples from the lake bed are shown to be more representative of water discharging to the lake than are samples from piezometers near the lake shore but spatial and temporal variability in pore water chemistry must be considered stable isotope analyses 18o and 2h of lake water groundwater and pore water samples show that water discharging to nevins lake in the spring is entirely recycled lake water and no groundwater derived from terrestrial recharge reaches the lake the conceptual model formulated during this study linking lake chemistry and the contiguous groundwater system and general groundwater flow patterns surrounding highly transient lake systems are likely transferable to other similar systems

the interaction of lakes with variably saturated porous media numerical simulation of variably saturated porous media indicates that groundwater recharge is variable in time and space depending on the thickness of the unsaturated zone through which infiltrating water must move the resulting complex transient groundwater flow systems have significant impact on contiguous surface water in very permeable media small local closed groundwater flow systems can develop and dissipate within a few weeks to several months after major recharge these have a direct effect on contiguous surface water by alternately causing seepage to and seepage from the surface water the transient nature of these flow systems indicates that reversals of the direction of groundwater flow may be common in less permeable media the same complex flow systems may occur but the time for development and dissipation is much greater for example it is conceivable that small local flow systems may exist for many months or years as a result of major recharge therefore directions of flow in such systems are more stable and the effect on contiguous surface water also is more stable the findings of this study indicate that wells and groundwater quality sampling sites need to be carefully located to define accurately water table configuration groundwater recharge direction of seepage through the beds of surface water bodies and complex geochemical processes related to changing directions of groundwater flow

tsunamis generated by eruptions from mount st augustine volcano alaska during an eruption of the alaskan volcano mount st augustine in the spring of 1986 there was concern about the possibility that a tsunami might be generated by the collapse of a portion of the volcano into the shallow water of cook inlet a similar edifice collapse of the volcano and ensuing sea wave occurred during an eruption in 1883 other sea waves resulting in great loss of life and property have been generated by the eruption of coastal volcanos around the world although mount st augustine remained intact during this eruptive cycle a possible recurrence of the 1883 events spurred a numerical simulation of the 1883 sea wave this simulation which yielded a forecast of potential wave heights and travel times was based on a method that could be applied generally to other coastal volcanos

the 1986 eruption of mount st augustine field test of a hazard evaluation the 1986 eruption of mount st augustine an island volcano in cook inlet of southcentral alaska provided a good test of previously prepared volcanic hazard models for that volcano the 1986 eruption was generally similar to other historic eruptions an initial vent clearing explosive eruptive phase in late march of 1986 removed part of the dome emplaced at the end of the last eruption 1976 pyroclastic flows reached the sea during this phase and airborne ash spread over much of cook inlet including anchorage the initial explosive phase was followed by dome growth which continued over much of the spring and late summer of 1986 pyroclastic flows much less intense than those of march 1986 accompanied dome growth volcanic hazards from the 1986 eruption were generally within the limits set by previous hazard studies pyroclastic flows were confined to a very high hazard zone on and immediately surrounding augustine island airborne ash and volcanic gases presented a moderate hazard over much of cook inlet and presented a serious hazard to aircraft encountering the ash plume the potential for a large debris avalanche that could enter cook inlet and result in a tsunami existed during the 1986 eruption previous work on mount st augustine underestimated the landslide related hazard and more work is needed to assess fully the potential of this hazard these new data when incorporated into existing hazard assessments will improve an already successful hazard evaluation for mount st augustine assuming that augustine island will never be developed far field hazards associated with ashfalls and tsunamis are the most serious real time satellite and radar imagery can potentially provide adequate warnings about ash plumes but the warning time for tsunami hazards is short improvements in the tsunamis warning system are needed to reduce the hazard

estimating groundwater exchange with lakes 2 calibration of a three dimensional solute transport model to a stable isotope plume a three dimensional groundwater flow and solute transport model was calibrated to a plume of water described by measurements of 18o and used to calculate groundwater inflow and outflow rates at a lake in northern wisconsin the flow model was calibrated to observed hydraulic gradients and estimated recharge rates calibration of the solute transport submodel to the configuration of a stable isotope 18o plume in the contiguous aquifer on the downgradient side of the lake provides additional data to constrain the model a good match between observed and simulated temporal variations in plume configuration indicates that the model closely simulated the dynamics of the real system the model provides information on natural variations of rates of groundwater inflow lake water outflow and recharge to the water table inflow and outflow estimates compare favorably with estimates derived by the isotope mass balance method krabbenhoft et al this issue model simulations agree with field observations that show groundwater inflow rates are more sensitive to seasonal variations in recharge than outflow

the influence of a mini magnetopause on the magnetic pileup boundary at mars 1 3d single fluid non ideal mhd simulations are used to predict positions for the bow shock and magnetic pileup boundary mpb the positions are in agreement with those calculated from mars global surveyor data the simulations were run with the strong southern magnetic anomalies facing into the solar wind and the imf in either the northward or southward direction the simulations show that the strong southern magnetic anomalies create a magnetopause like structure i e a mini magnetopause in place of an mpb but plasma signatures for both types of boundaries are similar distinguishing characteristics include the magnetic field orientation pressure and the current the current regions associated with a mini magnetopause are larger in scale and greater in magnitude than those at the mpb the simulations also show that including non ideal mhd physics is important in resolving both the magnetic pileup boundary and the mini magnetopause