numerical simulations of radiative cooling beneath the anvils of supercell thunderstorms abstract numerical simulations of supercell thunderstorms that include parameterized radiative transfer and surface fluxes are performed using the advanced regional prediction system arps to investigate the effects of anvil shadows on the near storm environment if the simulated storm is nearly stationary the maximum low level air temperature deficits within the shadows are about 2 k which is roughly half the cooling found in some previous observations it is shown that the extinction of downwelling shortwave radiation by the anvil cloud creates a differential in the flux of downwelling shortwave radiation between the sun and the shade that is at least an order of magnitude greater than the differential of any other term in either the surface radiation or the surface energy budgets the loss of strong solar heating of the model surface within the shaded regions leads to a reduction of surface temperatures and stabilization of the model surface layer beneath the anvil the reduction in vertical mixing

permian triassic red stained albitized profiles in the granitic basement of ne spain evidence for deep alteration related to the triassic palaeosurface extensive areas of the variscan granitic basement in ne spain display profiles of red stained albitized facies characterized by albitization of ca plagioclase chloritization of biotite and microclinization of orthoclase along with the alteration of igneous quartz to secondary cl dark quartz these profiles have a geopetal structure beneath the triassic unconformity with a very intense and pervasive alteration in the upper part that progressively decreases with depth to 150 200 m where the alteration is restricted to the walls of fractures the red albitized facies contains secondary maghemite and hematite that indicate oxidizing conditions dating of microclinized orthoclase and secondary monazite that have formed in the red stained albitized facies yielded k ar and u th pbtotal ages of 240 and 250 ma respectively suggesting that the alteration developed during the permian triassic period the geopetal disposition of the red albitized profile with respect to the triassic unconformity its large regional extent and the fracture controlled alteration in the lower part of the profile indicate groundwater interaction the 18o values of albitized plagioclase 11 microclinized orthoclase 13 and secondary cl dark quartz 12 suggest that the alteration temperature was about 55 c this low temperature suggests that the alteration occurred during interaction of the granitic rocks with na rich fluids below a surficial weathering mantle on the permian triassic palaeosurface the latter is possibly related to triassic evaporitic environments in long lasting stable landscapes in which na rich solutions infiltrated deep regional groundwaters

topographic variability on mars implications for lava flow modeling 1 a new data analysis technique is presented for quantifying topographic variability on the surface of mars directly from mars orbiter laser altimeter mola precision experiment data record pedr elevation data the statistic expressing the degree of variability is the mean standard deviation of the residuals resulting from regressions on mola pedr elevation profiles this topography statistic is determined for ten volcanic areas on the basis of thousands of data points from 181 pedrs the topography statistic varies considerably exhibiting a strong correlation to volcanic area despite the correlation with volcanic area the correlation between topographic variability and slope is weak lava flow thickening behavior is quantified with two statistics that are in turn used as a rough measure of rheologic change there is a strong significant correlation between both flow thickening statistics and topographic variability these results suggest that the influence of local topographic variability is more important than previously thought in modeling lava flows on mars

the pretornadic phase of the goshen county wyoming supercell of 5 june 2009 intercepted by vortex2 part i evolution of kinematic and surface thermodynamic fields abstractthe authors analyze the pretornadic phase 2100 2148 utc tornadogenesis began at 2152 utc of the goshen county wyoming supercell of 5 june 2009 intercepted by the second verification of the origins of rotation in tornadoes experiment vortex2 the analysis relies on radar data from the weather surveillance radar 1988 doppler wsr 88d in cheyenne wyoming kcys and a pair of doppler on wheels dow radars mobile mesonet observations and mobile sounding observations the storm resembles supercells that have been observed in the past for example it develops a couplet of counter rotating vortices that straddle the hook echo within the rear flank outflow and are joined by arching vortex lines with the cyclonic vortex becoming increasingly dominant in the time leading up to tornadogenesis the outflow in the hook echo region where sampled has relatively small virtual potential temperature deficits during this stage of evolution a few kilometers upstream north of the location of maxim

influence of volatile loss on thickness and density profiles of active basaltic flow lobes a bulk density increase due to degassing during emplacement may have a significant influence on the thickness of a lava flow and the rate at which it advances we present a theoretical model of a lava flow that loses enough volatiles to cause density changes along the path of the flow we assume that the flow is emplaced as a single isolated unit and the bulk rheology e g viscosity is a function of distance from the vent this type of model is applicable to solitary lobes of basaltic aa and isolated sheets of pahoehoe that advance as a fluid continuum with bulk lava density changes as a function of distance along the flow path equations for the flow thickness and the bulk density profiles are derived from mass and volume conservation formulas are tabulated for thickness and density profiles for various combinations of flow rates rheologic changes and degassing rate functions we also tabulate formulas for estimating parameters associated with the form and rate of degassing from field data the mauna loa 1984 1 flow is a typical example of a flow showing evidence of a bulk density increase and is used to estimate the model parameters thickness and density profiles are then computed for a range of plausible lava densities two different rate functions for the loss of volatiles and two different models of viscosity change results indicate that the thickness profile of a lava flow can be significantly affected when there is a large difference between the density at the vent and at the flow front for relatively high rates of degassing the flow profile has a maximum thickness located progressively closer to the vent as the rate of degassing increases for depth dependent degassing an increase in viscosity acts to thicken the flow which increases the rate of degassing thus mitigating the thickening influence of the increasing viscosity degassing while a flow is active can increase the duration of emplacement by as much as 60 we find that the flow thickness profiles are sensitive to the choice of flow rate and the initial density regardless of the form of the degassing function the nature of the flow rate can significantly affect the shape of the profile as well as the flow front thickness when the rate of volatile loss depends on the flow thickness the density profile depends explicitly on the way the rheology changes along the flow path in all cases density increases during emplacement counter the tendency of a flow to thicken due to increases in viscosity or resistance to flow with distance thus the parameters that define the rate of degassing and the consequent density change along the path of a flow emerge as important variables for a quantitative understanding of flow emplacement

a concentrated outbreak of tornadoes downbursts and microbursts and implications regarding vortex classification abstract a remarkable case of severe weather occurred near springfield illinois on 6 august 1977 aerial and ground surveys revealed that 17 cyclonic vortices an anticyclonic vortex 10 downbursts and 19 microbursts occurred in a limited 20 km 40 km area associated with a bow shaped radar echo about half of the vortices appeared to have occurred along a gust front some of the other appear to have occurred within the circulation of a mesocyclone accompanying the bow echo but these vortices seem to have developed specifically in response to localized boundary layer vorticity generation associated with horizontal and vertical wind shears on the periphery of microbursts some of these vortices and other destructive vortices in the literature do not qualify as tornadoes as defined in the glossary of meteorology a moon pragmatic definition of a tornado is suggested

very recent and wide spread basaltic volcanism on mars new spacecraft data provide increasing evidence for a dynamic environment on presenta day mars exogenic processes such as impact cratering mass wasting processes and active dune migration have all been observed to modify the surface no traces of current endogenic activity have been found yet but some studies point to very localized volcanism in the last few millions of years however no systematic study of young volcanic surfaces had been performed so far we present absolute model age determinations of plains volcanism on mars as derived from impact crater sizefrequency distributions extended areas in tharsis the largest volcanoa tectonic region on mars have been resurfaced by lava flows in the last few tens of millions of years we also present results on the rheologic properties of these lava flows inferred from morphometric measurements yield strengths are in the range of 100a 300 pa and viscosities reach values of 10 2 to 10 3 pa s indicating basaltic compositions the results imply that mars retained until recently and probably still retains enough internal heat to produce widea spread plaina style volcanism producing lowa viscosity lava flows throughout large parts of tharsis

bow echo mesovortices part ii their genesis abstract this two part study examines the damaging potential and genesis of low level meso scale mesovortices formed within bow echoes this was accomplished by analyzing quasi idealized simulations of the 10 june 2003 saint louis bow echo event observed during the bow echo and mesoscale convective vortex experiment bamex in part ii of this study mesovortex genesis was investigated for vortices formed at different stages of convective system evolution during the early cellular stage cyclonic mesovortices were observed the cyclonic mesovortices formed from the tilting of baroclinic horizontal vorticity acquired by downdraft parcels entering the mesovortex as the convective system evolved into a bow echo cyclonic anticyclonic mesovortex pairs were also observed the vortex couplet was produced by a local updraft maximum that tilted baroclinically generated vortex lines upward into arches the local updraft maximum was created by a convective scale downdraft that produced an outward bulge in th

bow echo mesovortices part i processes that influence their damaging potential abstract this two part study examines the damaging potential and genesis of low level meso scale mesovortices formed within bow echoes this was accomplished by analyzing quasi idealized simulations of the 10 june 2003 saint louis bow echo event observed during the bow echo and mesoscale convective vortex experiment bamex this bow echo produced both damaging and nondamaging mesovortices a series of sensitivity simulations were performed to assess the impact of low and midlevel shear cold pool strength and coriolis forcing on mesovortex strength by analyzing the amount of circulation maximum vertical vorticity and number of mesovortices produced at the lowest grid level it was observed that more numerous and stronger mesovortices were formed when the low level environmental shear nearly balanced the horizontal shear produced by the cold pool as the magnitude of deeper layer shear increased the number and strength of mesovortices increased larger coriolis forcing and stronger cold pools als

the pretornadic phase of the goshen county wyoming supercell of 5 june 2009 intercepted by vortex2 part ii intensification of low level rotation abstractthe dynamical processes responsible for the intensification of low level rotation prior to tornadogenesis are investigated in the goshen county wyoming supercell of 5 june 2009 intercepted by the second verification of the origins of rotation in tornadoes experiment vortex2 the circulation of material circuits that converge upon the low level mesocyclone is principally acquired along the southern periphery of the forward flank precipitation region which is a corridor characterized by a horizontal buoyancy gradient thus much of the circulation appears to have been baroclinically generated the descending reflectivity core drc documented in part i of this paper has an important modulating influence on the circulation of the material circuits a circuit that converges upon the low level mesocyclone center prior to the drc s arrival at low levels approximately the arrival of the 55 dbz reflectivity isosurface in this case loses some of its previously acquired circulation during the final f

tornado like vortexgenesis in a simplified numerical model abstract a novel approach to the modeling of tornado like vortexgenesis has been developed and is used to articulate the sequence of events that leads to tornadogenesis the pseudostorm is an idealized thunderstorm representation and emulates the storm relative flow into an updraft of the horizontal streamwise vorticity that is baroclinically generated in cold air outflow by not explicitly simulating the morphology of a tornadic thunderstorm but instead concentrating on the development of low level rotation and tornado scale vortices the authors are able to transcend many of the experimental limitations encountered by cloud modelers intense near ground cyclonic vortices which are classified herein as tornado like evolve solely from horizontal streamwise vorticity due to buoyancy gradients and friction if present at the lower boundary regardless of the lower boundary condition none of the vortices exceed the thermodynamic speed limit based on the vertically integrated buoyancy or convect

authigenic albite in carbonate rocks a tracer for deep burial brine migration euhedral post depositional albite from the eastern and western alps the western carpathians and some greek islands was examined petrographically and geochemically to gain insights into the nature of feldspar reactions in carbonate rocks this study focuses on coarsely crystalline homogeneously nucleated albite in order to avoid problems related to the presence of inseparable detrital material in fine grained albite varieties all albite samples show a very restricted compositional variability and are typically 99 mol ab component unit cell parameters determined by rietveld analysis are slightly more variable than previously accepted but confirm high al si ordering characteristic of low albite the oxygen isotopic composition of albite ranges from 19 4 to 28 3 vsmow there is no direct relationship between the 18o value and the inferred temperature of albite formation nor is there one with stoichiometry the coarse crystal size up to several millimetres in diameter petrographic evidence showing albite cross cutting stylolites greater abundance of albite in carbonate rocks subject to high grade diagenetic or weak metamorphic overprinting and available fluid inclusion data suggest that albite precipitation is favoured at higher temperatures in carbonates than in sandstones pore fluids were invariably brines as suggested by the inferred high positive 18ofluid values the common association of albite bearing carbonates and evaporites and reports of saline fluid inclusions in albite the presence of authigenic albite may thus be a useful tracer of palaeobrine carbonate reactions particularly in deep burial and incipient metamorphic settings

explosive volcanic eruptions from linear vents on earth venus and mars comparisons with circular vent eruptions 1 conditions required to support buoyant convective plumes are investigated for explosive volcanic eruptions from circular and linear vents on earth venus and mars vent geometry linear versus circular plays a significant role in the ability of an explosive eruption to sustain a buoyant plume on earth linear and circular vent eruptions are both capable of driving buoyant plumes to equivalent maximum rise heights however linear vent plumes are more sensitive to vent size for analogous mass eruption rates linear vent plumes surpass circular vent plumes in entrainment efficiency approximately when lo 3ro owing to the larger entrainment area relative to the control volume relative to circular vents linear vents on venus favor column collapse and the formation of pyroclastic flows because the range of conditions required to establish and sustain buoyancy is narrow when buoyancy can be sustained however maximum plume heights exceed those from circular vents for current atmospheric conditions on mars linear vent eruptions are capable of injecting volcanic material slightly higher than analogous circular vent eruptions however both geometries are more likely to produce pyroclastic fountains as opposed to convective plumes owing to the low density atmosphere because of the atmospheric density profile and water content on earth explosive eruptions enjoy favorable conditions for producing sustained buoyant columns while pyroclastic flows would be relatively more prevalent on venus and mars these results have implications for the injection and dispersal of particulates into the planetary atmosphere and the ability to interpret the geologic record of planetary volcanism

reliability of k ar dating of clays and silicifications associated with vein mineralizations in western europe k ar ages were determined on fine fractions and one massive silicification associated with vein mineralizations in uranium barium fluorine and related base metals in western europe the reliability of the potassic materials analysed once the mineralogical and geochemical relationships to the low temperature mineralization have been established is demonstrated the isotopic ages are concentrated between nearly 190 and 170 ma this epoch corresponds to that of the rifting of the future atlantic and tethys oceans this type of low temperature mineralization thus seems to be better explained by extensional phenomena

new statistics for estimating the bulk rheology of active lava flows puu oo examples downstream changes in lava rheology due to cooling crystallization and vesiculation have a strong influence on the final length and morphology of a lava flow three statistics are proposed to estimate the change in lava rheology with distance along the path of an active flow these statistics correspond to three separate models of the volumetric flow rate dependence on the thickness of the flow each statistic is based on flow dimensions and topographic data that are often available from field measurements or remote sensing one model assumes an elementary laminar newtonian flow a second empirical model often used to describe the flow of complex geologic materials such as lahars sediment laden floods and debris flows is also investigated for comparison a new volume loss model is also proposed to account for stationary components such as levees and stagnant areas the three statistics derived from these flow rate models are applied and interpreted for two well defined lobes from episodes 2 and 18 of the 1983 1984 puu oo eruption the power law dependence of the first two models results only in modest differences in the estimates of rheologic change along the flow path however the removal of lava from the active flow to construct stationary components produces significant differences in both the magnitude of computed rheologic changes and the ability to discern trends in rheologic changes along the path of the flow

studies of lava flows in the tharsis region of mars using sharad the tharsis region of mars is covered in volcanic flows that can stretch for tens to hundreds of kilometers radar measurements of the dielectric properties of these flows can provide information regarding their composition and density sharad shallow radar a sounding radar on the mars reconnaissance orbiter detects basal interfaces beneath flows in some areas of tharsis northwest and west of ascraeus mons with additional detections south of pavonis mons comparisons with 12 6 cm ground based radar images suggest that sharad detects basal interfaces primarily in dust or regolith mantled regions we use sharad data to estimate the real relative permittivity of the flows by comparing the measured time delay of returns from the subsurface with altimetry measurements of the flow heights relative to the surrounding plains in cases where the subsurface interface is visible at different depths spanning tens of meters it is also possible to measure the loss tangent tan of the material the permittivity values calculated range from 7 6 to 11 6 with an average of 9 6 while the mean loss tangent values range from 7 8 10 3 to 2 9 10 2 with an average of 1 0 10 2 these permittivity and loss tangent estimates for the flows northwest of ascraeus mons west of ascraeus mons and south of pavonis mons are consistent with the lab measured values for dense low titanium basalt

high winds generated by bow echoes part i overview of the omaha bow echo 5 july 2003 storm during bamex abstract an analysis of a bow echo that produced damaging winds exceeding f1 in intensity on the fujita scale near omaha nebraska is shown part i of this study presents a combination of airborne doppler derived wind syntheses with a comprehensive damage survey in order to document the generation of strong winds at the surface a detailed kinematic analysis of the evolution of a quasi linear convective system into a bow shaped and subsequently a spearhead echo is shown for the first time it is hypothesized that a large cyclonic bookend vortex 70 80 km in diameter north of the bow apex enhanced the rear inflow jet and initiated the bowing process a hook shaped echo and mesovortex formed at the apex of a bowed segment of the convective line and was located to the north of the swath of strong damage rated greater than f1 in damage intensity the peak single doppler radial velocity recorded by the tail radar was 43 m s 1 in the low level outflow near the apex of the bow echo the regions of the str

vortex lines within low level mesocyclones obtained from pseudo dual doppler radar observations abstract vortex lines passing through the low level mesocyclone regions of six supercell thunderstorms three nontornadic three tornadic are computed from pseudo dual doppler airborne radar observations obtained during the verification of the origins of rotation in tornadoes experiment vortex in every case at least some of the vortex lines emanating from the low level mesocyclones form arches that is they extend vertically from the cyclonic vorticity maximum then turn horizontally usually toward the south or southwest and descend into a broad region of anticyclonic vertical vorticity this region of anticyclonic vorticity is the same one that has been observed almost invariably to accompany the cyclonic vorticity maximum associated with the low level mesocyclone the vorticity couplet straddles the hook echo of the supercell thunderstorm the arching of the vortex lines and the orientation of the vorticity vector along the vortex line arches compared to the orientation of the ambient barotrop

dielectric properties of lava flows west of ascraeus mons mars 1 the sharad instrument on the mars reconnaissance orbiter detects subsurface interfaces beneath lava flow fields northwest of ascraeus mons the interfaces occur in two locations a northern flow that originates south of alba patera and a southern flow that originates at the rift zone between ascraeus and pavonis montes the northern flow has permittivity values estimated from the time delay of echoes from the basal interface between 6 2 and 17 3 with an average of 12 2 the southern flow has permittivity values of 7 0 to 14 0 with an average of 9 8 the average permittivity values for the northern and southern flows imply densities of 3 7 and 3 4 g cm 3 respectively loss tangent values for both flows range from 0 01 to 0 03 the measured bulk permittivity and loss tangent values are consistent with those of terrestrial and lunar basalts and represent the first measurement of these properties for dense rock on mars

the bertholene uranium deposit mineralogical characteristics and upb dating of the primary u mineralization and its subsequent remobilization consequences upon the evolution of the u deposits of the massif central france abstract in the southern part of the massif central france u ores of the rouergue area are spatially related to the unconformity of the permian carboniferous sedimentary terranes overlying the variscan basement the bertholene uraniferous orebody is located in the palanges precambrian orthogneiss close to the unconformity and in the vicinity of a highly deformed part of the orthogneiss massif marked by the occurrence of mylonitic bands for which a variscan age is assumed the u ore is mainly expressed as coffinite but primary u oxide was also identified hydrothermal alteration stages have been defined a first albitization stage is expressed on a regional scale and successive stages of argillization silicification and lastly carbonate crystallization have been described in the mining district the u oxide formation followed the silicification stage u pb systematics were used on coffinite and u oxide to define the evolution of the bertholene deposit 1 1 primary u oxide was found to be 173 9 ma old this phase of u concentration or remobilization has also been dated in the two other u deposits of the southern part of the massif central lodeve pierres plantees as well as in deposits located in limousin and morvan france the event which mobilized the u in these deposits is related to the consequences of the liassic pre rifting phase that preceded the opening of ligurian ocean during malm times 2 2 complex phenomena have affected the coffinite u pb system u pb and pb pb data show that 2 1 a unsupported isotopically heterogeneous radiogenic pb was in the coffinites during their genesis and may reflect the role of primary u oxide as their source 2 2 b in some coffinites rn loss phenomena controlled mainly the evolution of the u pb system two main types of coffinites were identified and the u pb data indicate that the coffinitization event occurred during oligocene times 40 30 ma or from the oligocene to actual times

triassic magnetic overprints related to albitization in granites from the morvan massif france the morvan massif located in the northern part of the french massif central shows widespread unusual deep alteration profiles in the palaeozoic basement rocks gneisses granites and rhyolites they are characterised by overall albitization chloritisation and haematisation albite and chlorite constitute their characteristic mineral paragenesis haematite pigmentation comes with this paragenesis and gives an overall pink coloration to the weathered rocks a paleomagnetic analysis was conducted after detailed petrographical and mineralogical studies of the alteration that lead to the albitized profiles special attention was devoted to the occurrence of haematite the main paleomagnetism carrier with the though to date this palaeoweathering event petrographical checking after heating treatments showed that deshydroxylation of chlorite also led to the formation of secondary haematite this haematite formed by recrystallization acquired remanence properties and thus superimposed and hided the original magnetic signal this problem has prevented the extraction of the original magnetic signal especially in the sections made up of rhyolites virtual geomagnetic poles vgps obtained from the characteristic directions carried by haematite have been compared to the european apparent polar wander path apwp an early triassic magnetic overprint has been recorded in the albitized basement rocks of the morvan massif the age obtained for this albitization phenomena strengthens the hypothesis that albitization developed in relation with palaeoweathering processes linked with the triassic palaeosurface therefore large scale continental weathering could be the main mechanism for late permian early triassic remagnetizations which are widespread throughout the palaeozoic formations of western europe as far as we know this is the first time that deep palaeoweathering phenomena affecting hard and non disaggregated weathered rocks of the basement have been directly dated palaeomagnetism appears as a precious tool to date alteration events developed in widely and long lasting emerged areas of the basement

the light toned stratified sedimentary rock exposures in western juventae chasma mars in context abstract juventae chasma an isolated depression northeast of the valles marineris trough system hosts four mounds of light toned layered materials these are erosional remnants interpreted to consist of sedimentary rocks the geological setting of juventae chasma is a complex amalgamation of terrains and surfaces of different morphologies ages and structures most previous published studies assumed or interpreted that the light toned mound forming materials were deposited in the chasm after it opened or began to open here we use detailed observations of the geologic setting the nature of chasm wall rocks and the distribution and nature of the contacts of the light toned materials with adjacent geologic materials to argue that the light toned mounds in juventae chasma are more likely remnants of light toned materials that existed in the subsurface before the chasm opened up the rock cut by the chasm was not a monolithic unit e g lava flows and might have included both light toned and dark toned sedimentary rocks bearing a range of diagenetic properties the light toned materials were deposited as clasts precipitates or both within craters or depressions that were filled buried lithified and then exposed when juventae chasma formed because the sedimentary rock types and stratal package properties differ from one mound to the next the buried craters or depressions could have existed at different times and provide sedimentary records of different environments that existed at different times during the planet s early history noachian period upon exposure these materials as well as chasm wall rocks and chaotic terrain blocks underwent differential erosion as a function of rock physical properties to produce the geomorphic expressions observed today

the effect of mesoscale heterogeneity on the genesis and structure of mesovortices within quasi linear convective systems abstract this study examines the structure and evolution of quasi linear convective systems qlcss within complex mesoscale environments convective outflows and other mesoscale features appear to affect the rotational characteristics and associated dynamics of these systems thus real data numerical simulations of two qlcs events have been performed to i identify and characterize the various ambient mesoscale features that modify the structure and evolution of simulated qlcss and then to ii determine the nature of interaction of such features with the systems with an emphasis on the genesis and evolution of low level mesovortices significant low level mesovortices develop in both simulated qlcss as a consequence of mechanisms internal to the system consistent with idealized numerical simulations of mesovortex bearing qlcss and not as an effect of system interaction with external heterogeneity however meso scale order of 10 km heterogeneity in the form of a convective outflow boundary is su

an igneous origin for features of a candidate crater lake system in western memnonia mars the association of channels inner terraces and delta like features with martian impact craters has previously been interpreted as evidence in favor of the past existence of crater lakes on mars however examination of a candidate crater lake system in western memnonia suggests instead that its features may have formed through igneous processes involving the flow and ponding of lava accumulations of material in craters and other topographic lows throughout much of the study region have characteristics consistent with those of volcanic deposits and terraces found along the inner flanks of some of these craters are interpreted as having formed through drainage or subsidence of volcanic materials channels previously identified as inlets and outlets of the crater lake system are interpreted instead as volcanic rilles these results challenge previous interpretations of terrace and channel features in the study region and suggest that candidate crater lakes located elsewhere should be reexamined

influence of a great plains urban environment on a simulated supercell abstractthe effect of urban areas on weakly forced precipitation systems has been studied extensively however interactions between urban areas and strongly forced convection such as supercells remain relatively unexamined the present study uses simulations of a supercell to quantify the impacts of a large plains urban area on the evolution and strength of a supercell an initial ensemble of simulations ctrle of a supercell over homogeneous land use is performed using the wrf arw model additionally 108 simulations are conducted in which the land use pattern of dallas ft worth texas is placed inside the model domain with the city center shifted to be in or near the path of the supercell simulations with urban areas are compared to ctrle with the aid of hierarchical clustering analysis to form statistically similar groups of simulations clustering analyses identify groups of ensemble members with closely located urban areas that have similar patterns of 0 1 km updraft helicity and near surfac

low level mesovortices within squall lines and bow echoes part i overview and dependence on environmental shear this two part study proposes fundamental explanations of the genesis structure and implications of lowlevel meso g scale vortices within quasi linear convective systems qlcss such as squall lines and bow echoes such mesovortices are observed frequently at times in association with tornadoes idealized simulations are used herein to study the structure and evolution of meso g scale surface vortices within qlcss and their dependence on the environmental vertical wind shear within such simulations significant cyclonic surface vortices are readily produced when the unidirectional shear magnitude is 20 m s 21 or greater over a 0 2 5 or 0 5 km agl layer as similarly found in observations of qlcss these surface vortices form primarily north of the apex of the individual embedded bowing segments as well as north of the apex of the larger scale bow shaped system they generally develop first near the surface but can build upward to 6 8 km agl vortex longevity can be several hours far longer than individual convective cells within the qlcs during this time vortex merger and upscale growth is common it is also noted that such mesoscale vortices may be responsible for the production of extensive areas of extreme straight line wind damage as has also been observed with some qlcss surface vortices are also produced for weaker shears but remain shallow weak and short lived although similar in size and strength to mesocyclones associated with supercell storms and also sometimes producing similar hooklike structures in the rain field it is also shown that the present vortices are quite distinct structurally and dynamically most critically such vortices are not associated with long lived rotating updrafts at midlevels and the associated strong dynamically forced vertical accelerations as occur within supercell mesocyclones

plateaus and sinuous ridges as the fingerprints of lava flow inflation in the eastern tharsis plains of mars abstract the tharsis montes rift aprons are composed of outpourings of lava from chaotic terrains to the northeast and southwest flank of each volcano sinuous and branching channel networks that are present on the rift aprons suggest the possibility of fluvial processes in their development or erosion by rapidly emplaced lavas but the style of lava flow emplacement throughout rift apron development is not clearly understood to better characterize the style of lava emplacement and role of fluvial processes in rift apron development we conducted morphological mapping of the pavonis mons southwest rift apron and the eastern tharsis plains using images from the high resolution imaging science experiment hirise mars orbiter camera moc context camera ctx thermal emission imaging system themis and high resolution stereo camera hrsc along with the mars orbiter laser altimeter mola precision experiment data records pedrs and gridded data our approach was to 1 search for depositional fans at the slope break between the rift apron and adjacent low slope plains 2 determine if there is evidence that previously formed deposits might have been buried by plains units 3 characterize the tharsis plains morphologies east of pavonis mons and 4 assess their relationship to the rift apron units we have not identified topographically significant depositional fans nor did we observe evidence to suggest that plains units have buried older rift apron units flow features associated with the rift apron are observed to continue across the slope break onto the plains in this area the plains are composed of a variety of small fissures and low shield vents around which broad channel fed and tube fed flows have been identified we also find broad flat topped plateaus and sinuous ridges mixed among the channels tubes and vents flat topped plateaus and sinuous ridges are morphologies that are analogous to those observed on the coastal plain of hawai i where lava flows have advanced from the volcano s several degree flank onto the nearly zero degree coastal plain when local volumetric flow rates are low flow fronts tend to spread laterally and often thicken via endogenous growth or inflation of the sheet like flow units if flow advance is restricted by existing topography into narrow pathways inflation can be focused into sinuous elongate ridges the presence of plateaus and ridges emplaced from the rift zones across the plains to the east of pavonis mons and a lack of fan like features or evidence for their burial are consistent with rift apron lavas crossing a slope break with low local volumetric flow rates that led to inflation of sheet like and tube fed lava flows

rheology of a long lava flow at pavonis mons mars 1 dimensions of lava flows can be used to unravel the relative roles of viscosity changes and concurrent formation of levees stationary margins and stagnant zones this approach is applied to data derived from the mars orbiter laser altimeter mola experiment for a long lava flow on the plains north of pavonis mons mars we obtain a formula for the relative change in viscosity on the basis of a steady state newtonian flow rate our approach features a new length scale that describes the transfer of lava from the active advancing component to passive components this length scale can be determined from planetary image and topographic data by estimating the volume fraction of lava contained in flow margins relative to the total flow volume we find only modest changes in viscosity over the distal 175 km of the pavonis flow allowing the flow to also lose volume through degassing resulting in a density increase does little to affect the overall viscosity change thickening and widening of the flow with distance are as expected for a single coherent isothermal viscous flow this dynamic regime features a balance between the formation of an outer skin and shedding of lava into stationary zones requirements for attaining such a regime include a thick flow shallow slopes over extended distances and preexisting surface roughness that is small compared to flow thickness this style of emplacement may explain why many of the long thick sheet like flows on the plains of mars often exhibit an unexpected lack of thickening with distance

metallogenesis of the french part of the variscan orogen part ii time space relationships between u au and snw ore deposition and geodynamic events mineralogical and upb data abstract mineralogical geochemical structural and isotopic u pb studies were carried out on representative uranium and gold deposits from the french part of the variscan orogen results are compared with complementary data from the literature in order to propose a reconstruction of the metallogenesis in the variscan terranes with a particular emphasis on u deposits the data show that the early metal concentrations or pre enrichments in the terranes are affected by successive metallogenic stages which caused significant metal transport and deposition thus the significant geodynamic events which affected the variscan terranes were responsible for multistage metal deposition or alteration of the early concentrations and for the superimposed features of the metal deposits u pb geochronological results complemented by a compilation of geochronological data on u and pb zn ba f deposits show that three major stages of u deposition took place in western europe in the periods 325 300 ma 290 260 ma and 190 170 ma in addition small uranium mineralization events have been dated at 425 ma 90 110 ma and as tertiary about 40 ma the permo stephanian stage is associated with late brittle deformation associated with major shear zone movements and constitutes the major stage of u concentration the jurassic phase has a prominent part in the hydrothermal remobilization of uranium and in f ba pb zn deposition throughout western europe especially in the eastern part of the massif central other stages correspond to subordinate uranium migration within variscan terranes during earlier or later geodynamic phases the silurian metamorphism in vendee and the mesozoic to tertiary tectonic movements related to the pyrenean or alpine orogenies in the south eastern part of the massif central and in the alps data available on au and sn w as sb deposits have been considered for comparison with the u metallogenesis stages related to the deposition of such metals display significant similarities with those related to uranium deposition they occurred mostly during visean to permian events related to the intrusion of the late visean sn w and late carboniferous sn w li f granitoids and to the late brittle deformation stages which affected the hercynian basement in the vicinity of major shear zones au as sb however the significant discrepancies between the physical chemical conditions of solubilization transport and deposition of the metal led to distinct deposit location independently of the metal source location within the terranes

dimensions of pu u o o lava flows on mars longitudinal thickness profiles are simulated for lava flows on mars erupted under conditions identical to those of episodes 2 and 18 of the pu u o o eruption at kilauea volcano hawaii three separate approaches are used to estimate the change in the newtonian viscosity along the length of these flows the first approach assumes that all parts of the flow are in uniform motion and the volumetric flow rate is conserved at all stations along the flow path the second approach assumes the same newtonian flow model but takes advantage of independently acquired advance rate data the third approach uses a recent model for the conservation of lava volume this model apportions the flow rate into an active advancing component and a separate component that is stationary e g levees stagnant zones stationary margins viscosity changes for all three approaches are compared with new insights into the rheologic changes in the pu u o o flows the three approaches to flow emplacement are used as a basis for scaling the terrestrial flow thickness profiles to account for the difference in mars gravity for the same volumetric effusion rate and identical topography explicit scaling for the lower gravity affects the initial flow thickness and advance rate more subtle is the implicit influence of the lower gravity on the viscosity change along the flow path differences in viscosity change estimated by all three models are magnified when applied to lava flows on mars to illustrate the sensitivity of relative viscosity estimates on the assumed flow rate model we also estimate viscosity increases for lava flows at ascraeus mons elysium planitia and alba patera we show that the third model consistently predicts significantly greater increases in viscosity and must be considered when analyzing channelized flows where significant volumes of material have been lost to stagnant margins during emplacement

ages k ar des mineralisations de brioude massiac w au as sb pb zn pontgibaud pb ag sn et labessette as pb sb au place de ces districts dans l evolution geotectonique du massif central francais de nombreuses mineralisations filoniennes polymetalliques recoupent le socle metamorphique et granitique varisque du massif central trois de ces districts notamment brioude massiac w as au as sb au pontgibaud as sn et pb ag et labessette as sb pb au ont recemment fait l objet d etudes sur les condition thermodynamiques du depot des minerais et sur les sources potentielles de leurs elements metalliques une succession d episodes hydrothermaux de haute moyenne et basse temperature developpe une intense alteration phyllosilicatee a muscovite phengite illite et kaolinite dominantes

reconciling channel formation processes with the nature of elevated outflow systems at ophir and aurorae plana mars 1 many hesperian outflow channels head at elevations compatible with aquifer recharge beneath the martian south polar cap and such channels are widely interpreted as the products of this recharge some outflow channels head at greater elevations that are inconsistent with southern recharge including three systems located in aurorae planum and eastern ophir planum these three systems have previously been interpreted as having formed through aqueous outbursts from local aquifers recharged by the meltwaters of ancient upland glaciers to the west however the viability of this interpretation is weakened by the lack of a geomorphic record supportive of past meltwater flow from western uplands inconsistencies between hypothesized processes and the nature of regional topography and mineralogy and the absence of satisfactory analog processes for catastrophic aqueous flow from the subsurface in contrast a volcanic origin for the ophir and aurorae systems appears to be in accord with the basic characteristics of constituent channels and associated landforms the volcanotectonic nature of the valles marineris system and adjacent upland plains and the nature of available analog landforms and processes though numerous uncertainties remain a volcanic interpretation of these outflow systems can more simply account for the existence of component channels the attributes of other elevated outflow systems on mars similarly appear to be most consistent with volcanic origins if the ophir and aurorae systems formed volcanically thermal considerations imply minimum erupted lava volumes of 6 4 103 km3 for allegheny vallis and 6 2 104 km3 for elaver vallis

tornadogenesis in a simulated mesovortex within a mesoscale convective system abstractthe advanced regional prediction system arps is used to simulate a tornadic mesovortex with the aim of understanding the associated tornadogenesis processes the mesovortex was one of two tornadic mesovortices spawned by a mesoscale convective system mcs that traversed southwestern and central oklahoma on 8 9 may 2007 the simulation used 100 m horizontal grid spacing and is nested within two outer grids with 400 m and 2 km grid spacing respectively both outer grids assimilate radar upper air and surface observations via 5 min three dimensional variational data assimilation 3dvar cycles the 100 m grid is initialized from a 40 min forecast on the 400 m grid results from the 100 m simulation provide a detailed picture of the development of a mesovortex that produces a submesovortex scale tornado like vortex tlv closer examination of the genesis of the tlv suggests that a strong low level updraft is critical in converging and amplifying vertical vorticity associated with the mesovortex

a major late jurassic fluid event at the basin basement unconformity in western france 40ar 39ar and k ar dating fluid chemistry and related geodynamic context the malm lower cretaceous period is often considered to represent a period of time markedly devoid of crustal deformations and of heat and mass transfers in western france although numerous evidences of such transfers are reported in varied basins from western iberia to western africa migrating evaporitic derived brines and seawater interacted with both the sedimentary cover and the basement in the poitou high located at the boundary between aquitaine and paris basins occurring after sedimentation this activity induced significant alterations of the sediments by dolomitization and silicification and the basement by adularization and locally by concentration of f ba pb zn assemblages that are typical of carbonate hosted metal deposits thus metals were leached from metamorphic granitic basement already weathered and peneplaned during triassic time and were redeposited by brines during this main fluid event the main objective of this study was to decipher the timing of this major fluid heat mass transfer on the basis of 40ar 39ar and k ar dating of epigenetic minerals having similar paragenetic and geochemical signatures over an extended area from the atlantic ocean coast to the french massif central a late jurassic fluid stage 146 156 ma significantly younger than what is generally reported in western europe was obtained this fluid event occurred within a segment of a continental margin that was located away from main rift zones and far more than 500 km from major deformation areas such as the main rift or orogenic zones all over western europe these results yield a new concept based on wide wavelength relationships between fluid movements and geodynamic events affecting both the sedimentary basins and their basements

petrographie et datations k ar des transformations minerales affectant le gite uranifere de bertholene aveyron france la mineralisation uranifere de bertholene est encaissee dans un orthogneiss a proximite de sa couverture permo carbonifere les variations de facies observees dans la zone du gisement trahissent d importantes transformations mineralogiques des roches l etude petrographique revele deux stades majeurs 1 important phenomene d albitisation obliterant localement la texture et la mineralogie initiale de l orthogneiss 2 phenomenes plus tardifs d hydrolyse de l albite et d argilisation la mineralisation uranifere est mise en place lors de ce dernier stade les datations k ar de fraction fines et de phases minerales separees permettent de preciser l ge des transformations 1 les phenomenes d albitisation sont dates a 200 210 ma 2 l ge des phenomenes d argilisation et de la mise en place des mineralisation est fixe a 170 175 ma ces deux ges deja connus en plusieurs autres points du sud du massif central comme episodes de metamorphisme de diagenese ou de mise en place de mineralisations diverses apparaissent d une grande importance regionale

albitisation related to the triassic unconformity in igneous rocks of the morvan massif france the carboniferous morvan massif in the northern part of the french massif central consists of granite and some rhyolite a triassic erosional unconformity has developed on the massif which is covered by mesozoic sediments of the paris basin the igneous rocks of the morvan massif show a strong alteration with pseudomorphic replacement of the primary plagioclases into albite pseudomorphic replacement of primary biotite into chlorite and minor precipitation of neogenic minerals like albite chlorite apatite haematite calcite and titanite the geometry and arrangement of these alterations give significant constraints about their development some of the altered facies develop in a pervasive manner others are restricted to centimetric to metric wide joints that imply fluid flow phenomena moreover the alteration facies are arranged in a clear succession with strongly altered facies at the top and weakly altered facies towards the depth which point to a genetic relationship with the triassic unconformity regional distribution of the alterations which affect the carboniferous igneous and volcanic formations beneath the jurassic sedimentary cover also leads to associate these alterations with the triassic unconformity dating of the alterations provides even a further constraint alterations are of triassic age that means the same age as the unconformity taking into account all these geological constraints it is proposed that albitisation of the morvan massif was developed under low temperature subsurface conditions in relation to the triassic palaeosurface

a hybrid model for leveed lava flows implications for eruption styles on mars 1 many channelized lava flows on the plains of mars have substantial embanking margins and levees inferred to have been stationary while the central channel was active levee formation can be attributed to two end member processes during emplacement construction during passage of the flow front and growth along the entire length of the flow while it is active it is shown here that the amount of lava that can be deposited by the flow front alone is limited estimates of the levee volume for many mars plains flows exceed this limit and must have formed by processes that continued after the passage of the front experimental studies of analogous laboratory flows also indicate a combination of both modes of emplacement a model that combines both modes of levee formation is presented including a method for estimating volumetric flow rate eruption duration and viscosity six lava flows on the plains of the tharsis volcanic province are used as illustrative examples crustal thicknesses for the six flows examined range from 9 to 23 m estimated emplacement times required to cool crusts of these thicknesses range from 1 year to 10 years corresponding viscosities are on the order of 105 106 pa s effusion rates range from 25 to 840 m3 s 1 and are all within the range of terrestrial observations therefore the large leveed plains flows on mars are not dramatically different in eruption rate or lava viscosity from large terrestrial analogs

the long lava flows of elysium planita mars viking orbiter images are used to study the distribution and morphology of 59 lava flows in the elysium planitia region of mars average widths for these flows range from 3 to 16 km and many of the flows exceed 100 km in length the aspect ratio flow length to average width is highly variable 40 1 to 294 km from the summit of elysium mons an unusual attribute of five flows is their segmented nature with up to 13 individual segments on a single flow which each have a surface area from 25 to 250 km2 photoclinometry is used to derive an average thickness of 40 60 m for these flows indicating that individual flow volumes range from 17 7 to 68 1 km3 plausible values for the effusion rate 101 104 m3 s 1 suggest that individual eruptions could have lasted for a few months to several decades and could have injected between 1 36 and 2 04 1012 kg of water vapor into the atmosphere assuming a 1 wt water content for the parental magma a total volume for all 59 flows is estimated to be 817 1226 km3 which would have released 2 04 3 01 1013 kg of water vapor into the atmosphere or 0 2 of the amount previously calculated plescia 1993 as the amount released from the cerberus flows in se elysium planitia

geologically recent water flow inferred in channel systems in the ne sulci gordii region mars a series of fluid carved channels in the sulci gordii region of mars were investigated numerous channel networks exist in sulci gordii part of the olympus mons aureole and this area comprises some of the youngest volcanic terrain on mars the channels ranged in length from 43 to 155 km with widths of 128 288 m the morphology of the channels was analysed assuming both lava and water as possible agents for three of the four channels studied water appears to be the likely agent while one channel is probably lava formed for the water formed channels discharge rates were estimated at 8000 36 000 m3 s 1 the lava channel was probably formed from short lived episodic activity by a low viscosity lava the age of the channels and surrounding area was estimated using crater counting to be 100 ma water has appeared to have flowed for almost 150 km under the climatic conditions at this time there is some evidence for later tectonic activity possibly as recent as 10 ma but crater dating accuracy was limited by the lack of high resolution images of some areas sulci gordii is therefore a dynamic site with evidence of hydrological and volcanic activity extending into the recent geological past

morphology and emplacement of a long channeled lava flow near ascraeus mons volcano mars 1 channeled lava flows hundreds of kilometers long are common on the lower flanks of the tharsis montes on mars our analysis of a 690 km long lava flow along the southwest perimeter of ascraeus mons shows that it was emplaced on low local slopes 100 km in length but the maximum effusion rates necessary on earth are essentially the minimum for martian flows on the basis of our calculated effusion rates the eruption duration was 3 to 7 earth months assuming a constant effusion rate and continuous eruption the morphology of the ascraeus mons flow shows similarities to terrestrial and simulated channeled flows downstream changes in morphology resemble those observed in the 1907 flow mauna loa volcano hawaii and channeled polyethylene glycol peg flows braided sections of the channel in the ascraeus mons flow contain islands which are hundreds of meters across and resemble features observed in the 1907 and 1984 flows on mauna loa volcano crosscutting relationships suggest islands in the proximal section were shaped by thermal and mechanical erosion whereas islands in the medial section are inferred to be material rafted by surges of lava through the channel overall understanding the morphology of long lava flows on mars is essential to the interpretation of their emplacement and constraining eruption conditions in the saddle regions of the tharsis volcanoes

damaging surface wind mechanisms within the 10 june 2003 saint louis bow echo during bamex abstract detailed radar and damage survey analyses of a severe bow echo event that occurred on 10 june 2003 during the bow echo and mesoscale convective vortex mcv experiment are presented a bow echo formed just east of saint louis missouri and produced a continuous straight line wind damage swath approximately 8 km in width and 50 km in length along with five f0 f1 tornadoes careful superposition of the damage survey analysis and weather surveillance radar 1988 doppler wsr 88d data from saint charles missouri klsx showed that the primary straight line wind damage swath was not collocated with the bow echo apex as has been suggested in previous studies rather the primary damage swath was found north of the bow apex collocated with a low level vortex that formed on the leading edge of the bow echo much of the primary damage swath appeared to have been created by the low level vortex moreover most of the surface straight line wind damage was generated during the early stages of bow echo mo

tornado resolving ensemble and probabilistic predictions of the 20 may 2013 newcastle moore ef5 tornado abstractan ensemble of 10 forecasts is produced for the 20 may 2013 newcastle moore ef5 tornado and its parent supercell using a horizontal grid spacing of 50 m nested within ensemble forecasts wi

young lava flows on the eastern flank of ascraeus mons rheological properties derived from high resolution stereo camera hrsc images and mars orbiter laser altimeter mola data 1 we report on estimates of the rheological properties of late stage lava flows on the eastern flank of ascraeus mons mars from previous studies it is known that the dimensions of flows reflect rheological properties such as yield strength effusion rates and viscosity our estimates are based on new high resolution images obtained by the high resolution stereo camera hrsc on board the european space agency s mars express spacecraft in combination with mars orbiter laser altimeter mola data compared to earlier studies the high spatial resolution of the hrsc and mola data allowed us to map 25 late stage lava flows and to measure their dimensions as well as their morphological characteristics in greater detail our estimates of the yield strengths for these flows range from 2 0 102 pa to 1 3 105 pa with an average of 2 1 104 pa these values are in good agreement with estimates for terrestrial basaltic lava flows and are comparable to previous estimates derived for a small number of lava flows on ascraeus mons our investigation indicates that the effusion rates for the studied ascraeus mons flows are on average 185 m3 s 1 ranging from 23 m3 s 1 to 404 m3 s 1 these results are higher than earlier findings that indicate effusion rates of 18 60 m3 s 1 with an average of 35 m3 s 1 however our effusion rates are similar to terrestrial effusion rates of kilauea and mauna loa and other martian volcanoes on the basis of our estimates of the effusion rates and the measured dimensions of the flows we calculated that the time necessary to emplace the flows is on average 26 days viscosities were estimated on the basis of yield strengths and effusion rates yielding average values of 4 1 106 pa s and ranging from 1 8 104 pa s to 4 2 107 pa s on the basis of newly available data sets e g hrsc mola we are now able not only to identify possible differences in eruptive behavior between ascraeus mons and elysium mons but also to study such differences over time

continental basinal origin of ore fluids from southwestern massif central fluorite veins albigeois france evidence from fluid inclusion and stable isotope analyses the most important fluorspar mining district in france is located in the palaeozoic basement of the albigeois in southwestern french massif central the massive fluorite is hosted within large e w striking fractures crosscutting cambro ordovician clastics associated with large zones of hypersilicified tectonic breccia which form the wall of the mined deposits fluid inclusion data for pre fluorite and fluorite stage fluids have salinities between 20 26 wt nacl equiv with homogenisation temperatures between 85 170 c furthermore low first ice melting temperatures around 50 c indicates the presence of significant cacl2 and possibly mgcl2 together with nacl calculated fluid 18o for pre fluorite quartz ranges from 9 1 to 5 2 with d between 55 to 64 placing the data directly on the present day meteoric water line fluorite stage fluids have 18o between 0 1 to 3 2 and d ranging from 53 to 75 indicating an interacted meteoric fluid origin combining the fluid inclusion and stable isotope data illustrates that the main fluorite depositing fluid has characteristics typical of a basinal brine the authors have no evidence that a magmatic system was involved in the deposit genesis the proposed model highlights that mineralisation was related to major mesozoic extensional events coinciding with the gradual opening of the atlantic and tethys oceans in order to account for the chemistry of the fluids and the siting of the deposits the authors postulate a genetic relationship with local continental evaporite bearing basins coincident with and controlled by the e w fractures

crystallization history of the 1984 mauna loa lava flow during a 3 week eruption in 1984 mauna loa produced vent lavas that increased in crystallinity from 1 to 30 and 27 km long flows that increased in crystallinity as they moved downstream we examined the crystallization history of these lavas using crystal size distribution csd analysis to study the rates of crystallization viscosity increase and latent heating typical average growth and nucleation rates were 5 10 9 cm s 1 and 5 cm 3 s 1 for microphenocrysts 20 to 500 m size crystals nucleated in the rift zone and 5 10 8 cm s 1 and 5 104 cm 3 s 1 for microlites 1 to 20 m size crystals nucleated in the channel these crystallization rates are high compared with those found in other csd studies of igneous rocks probably due to highly nonequilibrium conditions brought on by rapid degassing in the rift zone and cooling in the lava channel growth and nucleation rates decreased with time at the vent and with distance downstream the maximum downstream total crystallinity measured is 39 25 microlites 14 microphenocrysts in a quenched sample 14 km from the vent growth and nucleation rates cannot be calculated for postemplacement samples but they place upper limits of 53 58 on the amount of crystallization in the channel 9 20 km from the vent crystallization could have been mostly responsible for the 105 fold downstream increase in apparent viscosity although degassing and increasing incorporation of solid lava fragments also contributed another effect of crystallization on the lava flow was the sizeable latent heating 0 01 j g 1 s 1 over the first half of the flow length if the crystallinity of downstream quench samples is representative of the hot fluid core which may have been counteracted by entrainment of cooler material measurements of crystallization are shown to be crucial in the study of lava flow emplacement dynamics

lava flows at arsia mons mars insights from a graben imaged by hirise abstract hirise has imaged a graben wall on the western flank of arsia mons volcano mars this graben is 3 16 km in plan view size and is oriented almost perpendicular to the general volcano slope we have identified 1318 individual sub horizontal layers which we interpret to be lava flows in the 885 m high nearly vertical eastern wall of this graben the average and median outcrop widths of each layer are 149 and 85 m respectively no layers extend 1 72 km across the width of the section arguing against these being either areally extensive ash or paleo glacial deposits which has implications for the reoccurrence interval of glacial events and or the long term magma production rate of the volcano measurements n 118 made at a 100 m spacing across the width of the section reveal that there are on average 17 3 layers at each location this implies an average layer thickness of 51 m locally however as many as 7 layers can be counted within a 70 m high part of the section implying if these layers are indeed lava flows that arsia mons occasionally erupted flows that were only 10 m thick

radar and damage analysis of severe bow echoes observed during bamex abstract this study examines damaging wind production by bow shaped convective systems commonly referred to as bow echoes recent idealized numerical simulations suggest that in addition to descending rear inflow at the bow echo apex low level mesovortices within bow echoes can induce damaging straight line surface winds in light of these findings detailed aerial and ground surveys of wind damage were conducted immediately following five bow echo events observed during the bow echo and mesoscale convective vortex mcv experiment bamex field phase these damage locations were overlaid directly onto weather surveillance radar 1988 doppler wsr 88d images to i elucidate where damaging surface winds occurred within the bow shaped convective system in proximity to the apex north of the apex etc and then ii explain the existence of these winds in the context of the possible damaging wind mechanisms the results of this study provide clear observational evidence that low level mesovortices wit

vortex structure and evolution within bow echoes part i single doppler and damage analysis of the 29 june 1998 derecho abstract single doppler radar along with damage observations are examined to investigate the structural evolution of vortices observed within the 29 june 1998 derecho event that propagated through southeastern iowa into central and eastern illinois a total of 13 meso scale vortices observed primarily at low levels 0 3 km agl along the leading edge of the convective system were detected by the weather surveillance radar 1988 doppler wsr 88d radars at davenport iowa and lincoln illinois all but one of the vortices formed after the system evolved into a bow echo ten of the vortices formed north of the apex while three formed south of the apex seven of the vortices produced tornadoes that created f0 f1 surface damage none of the vortices exhibited appreciable upscale growth careful analysis of the radar data suggests that it may be possible to discern between the tornadic and nontornadic vortices the tornadic vortices tended to be stronger longer lived and deeper than their nontornadic count

observations of near surface vertical wind profiles and vertical momentum fluxes from vortex se 2017 comparisons to monin obukhov similarity theory abstractobservations of near surface vertical wind profiles and vertical momentum fluxes obtained from a doppler lidar and instrumented towers deployed during vortex se in the spring of 2017 are an

lava flows as kinematic waves a recently proposed model for the emplacement of lava flows is reinterpreted as a kinematic wave theory for the depth of the flow with this interpretation the longitudinal profile of an advancing flow is considered to be a propagating waveform with its length limited continuously by the amount of lava extruded the application of kinematic wave formalism provides new insights into the effects of time dependent source behavior on the shape and extent of the wave eruption behavior with a period of increasing flow depth at the source is shown to produce so called breaking points in the depth profile where the kinematic wave model itself could be invalid two models of such eruption behavior are investigated and this is shown not to be the case specifically when the conservation of lava volume is imposed the breaking points always reside beyond the front of the wave in general it is found that source behavior propagates downstream faster than the flow advances thus only a fraction of the source time dependence is reflected in the shape of the kinematic wave the remainder of the time dependent source effects must be deposited in the flow front lateral margins or solidifying crust or be dissipated irretrievably by processes not included in the model the fraction of eruption history contained in the advancing waveform depends crucially on the nature of the flow rate flow depth relation for the lava distal surface waves budding at the nose of the flow distal levee collapse and other volcanological observations may be manifestations of time dependent source behavior that advanced beyond the kinematic wave front

design and field experiments of a ground penetrating radar for mars exploration 1 we developed a wideband low power lightweight prototype ground penetrating radar gpr for subsurface exploration for mars the transmitter and receiver subsystems were constructed using a commercially available radio frequency rf and digital integrated circuits connectorized components and evaluation boards the transmit receive system antennas laptop controller and batteries are all accommodated on a 2 5 m sled field experiments were conducted in kansas and alaska the experiments in kansas tested the operation of the system the primary objective of the alaska experiments was to investigate the ability of a gpr to detect and distinguish between subsurface deposits of ice and ice cemented soils the investigation depths of these experiments ranged from 1 m to 30 m and the subsurface geology included near surface thaw discontinuous permafrost water saturated soils and lenses of pure ice dielectric contrasts within the ground were detected with near meter resolution however identifying the geologic context of an interface was difficult due to ambiguities associated with reflection data these investigations demonstrate some of the difficulties associated with inverting reflection data to obtain dielectric properties of the subsurface fortunately previous geophysical investigations such as drilled cores and seismic surveys helped to constrain the geology and numerical simulations provided an additional resource for the interpretations on mars additional geological context will be limited and numerical simulations will become extremely important for data interpretation due to these difficulties we demonstrate in one experiment how dielectric information can be obtained directly from bistatic measurements with a fixed transmitter and mobile receiver finally a comparison with a commercially available geophysical survey systems inc gssi radar system is presented and we discuss how the system can be modified and improved for future exploration on mars

the arcadia oklahoma storm of 17 may 1981 analysis of a supercell during tornadogenesis abstract on 17 may 1981 an extensive dataset was collected for a supercell thunderstorm that produced an f2 tornado near arcadia in central oklahoma coordinated dual doppler scans of the storm by 10 cm research radars were collected at approximately 5 min intervals from 30 min before the tornado touched down until 15 min after the tornado had dissipated the arcadia storm was also well sampled by a 444 m tall instrumented tower the low level inflow updraft mesocyclone and rear precipitation core of the supercell all passed across the tower a comparison of the instrumented tower measurements with a dual doppler synthesis reveals that the latter qualitatively resolved the low level flow however the magnitudes of the low level horizontal winds and updraft speed were underestimated in addition the vertical shear of the horizontal wind in the lowest kilometer was unresolved in the doppler winds in the storm environment horizontal vorticity was strong 1 5 10 2 s 1 and approximately streamwise

multi stage fluid incursion in the palaeozoic basement hosted saint salvy ore deposit nw montagne noire southern france abstract the saint salvy vein hosted zn ge deposit occurs in an e w fault system which flanks the southern margin of the late variscan sidobre granite and cross cuts cambrian black shales of the palaeozoic basement comprehensive mineralogical and geochemical studies of vein samples have revealed four mineralizing events m1 m4 related to late and post variscan tectonic events a further late stage event may be related to weathering m1 skarn deposits and m2 patchily mineralized quartz veinlets are associated with granite emplacement quartz contains low salinity h2o co2 nacl dominated fluids 6wt nacl equiv of relatively high temperature 300 580 c trapped under moderate to high pressure estimated m1 fluid d and calculated fluid 18o plot within the metamorphic water field there appears to be no involvement of magmatic fluids by contrast m3 barren quartz and m4 zinciferous economic mineralization stages have h2o co2 nacl cacl2 fluid inclusions with high salinities 23 25 wt nacl equiv and low temperatures 80 140 c which were trapped under low pressure conditions the high salinity and nacl cacl2 content of both m3 and m4 indicates that their parent fluids leached evaporitic salts m3 fluids are meteoric water dominated falling close to the meteoric water line d and 18o averaging 64 and 8 respectively m4 fluids have highly distinctive d averaging 101 and calculated fluid 18o varying from 1 2to 7 1 the unusually low d composition of m4 suggests the involvement of organic fluids in which h is derived directly or indirectly from organic matter the relatively high 18o of m4 fluids indicates that considerable isotopic exchange with sedimentary material took place displacing the 18o from the meteoric water line the data imply interaction of meteoric waters with evaporite and hydrocarbon bearing sedimentary sequences most probably the adjacent aquitain basin the main economic mineralization m4 stage took place during a tensional event probably coincident with the lias dogger transition calculated 34sh2s of m4 sulphide 5 4to 8 2 is almost identical to 34s of local cambrian sulphides 4 7to 9 4 suggesting a genetic link abundant siderite associated with m4 sphalerite has 13c ranging from 2 6to 4 4 indicating that carbon was sourced from sedimentary carbonate mobilized by or equilibrated with the hydrothermal fluid late stage sulphides exhibit extraordinary and highly distinctive 34s sphalerite has extremely low 34s 42 5to 50 5 whereas pyrite has an extraordinary large range from 33 2 to 74 3 closed system sulphate reduction is held to be responsible for the extremely high 34s whereas more open system reduction produces the very low values the coincidence of isotopically low 13c 7 6to 11 9 for co genetic calcite suggests the involvement of organic matter in the reduction process

a self replication model for long channelized lava flows on the mars plains 1 a model is presented for channelized lava flows emplaced by a self replicating levee building process over long distances on the plains of mars such flows may exhibit morphologic evidence of stagnation overspills and upstream breakouts however these processes do not inhibit the formation and persistence of a prominent central channel that can often be traced for more than 100 km the two central assumptions of the self replication model are 1 the flow advances at the average upstream velocity of the molten core and 2 the fraction of the lava that travels faster than the average upstream velocity forms stationary margins in the advancing distal zone to preserve the self replication process for an exemplary 300 km long flow north of pavonis mons the model indicates that 8 m of crust must have formed during emplacement as determined from the channel and levee dimensions when combined with independent thermal dynamic estimates for the crustal growth rate relatively narrow constraints are obtained for the flow rate 2250 m3 s 1 emplacement duration 600 d and the lava viscosity of the molten interior 106 pa s minor transient overspills and breakouts increase the emplacement time by only a factor of 2 the primary difference between the prodigious channelized martian flows and their smaller terrestrial counterparts is that high volumetric flow rates must have persisted for many hundreds of days on mars in contrast to a few hours or days on earth

new observations of volcanic features on mars from the themis instrument 1 images obtained by the themis instrument on mars odyssey permit the identification of many new volcanic features on mars several new types of vent systems including fissure vents within the tharsis region flank vents on olympus mons and ascraeus mons and lava shields on the floor of arsia mons have been found the valley networks on hecates tholus are seen to be more complex than previously believed extending from the caldera rim to the base of hecates tholus volcano individual valleys change width and depth in apparent response to local topography valley formation spanned the time period during which lava flows from elysium mons embayed the southern flank of hecates tholus as demonstrated by the burial of some valleys by the lava flows and the formation of sediment fans on top of adjacent parts of the flows themis images now allow new constraints to be placed on the dynamics of lava flow emplacement with the identification of flows with well defined lava channels on the northern flank of ascraeus mons as well as an enigmatic braided lava channel three previously unreported collapse events 3 7 to 4 3 km in diameter are identified within the caldera of ascraeus mons details of the mode of formation of parts of the olympus mons aureole can also be identified supporting the idea that the aureole had a landslide origin themis images show that parts of the aureole have been modified by water discharged to the east of olympus mons

time dependent profiles of lava flows this work investigates the combined effects of a time dependent effusion rate and a spatially varying viscosity on the thickness profile of a flowing lava we formulate relatively simple governing equations as a primitive dynamical model for these two influences on lava flow morphology free boundary solutions for the profile of the flow and its extent are presented and analyzed for different boundary conditions at the source of the flow and several models for the spatial dependence of the viscosity the results presented here suggest that time dependence in the flow depth at the source and the form of the viscosity variation are significant influences on the morphology and dimensions of lava flows moreover this analysis implies that time dependent source conditions may contribute to the scatter in plots of eruption rate versus flow length and disparities between field and laboratory estimates of lava viscosity

high winds generated by bow echoes part ii the relationship between the mesovortices and damaging straight line winds airborne radar analysis of a mesovortex that developed near the apex of a bow echo is presented the mesovortex was shown to play a critical role in determining the location of intense straight line wind damage at the surface the perturbation pressure gradient force in natural coordinates along the parcel path accelerated the horizontal winds however intense mesovortices modified the low level outflow and largely determined the locations where the strongest winds occurred regions of maximum winds are accounted for as a superposition of the vortex and the flow in which it is embedded the strongest winds occur on the side of the vortex where translation and rotation effects are in the same direction this model explains the observed tongue of high wind speeds that were confined to the periphery of the mesovortex the origin of the mesovortex is also examined similarities and differences of this bow echo event with recent modeling studies are presented

trends in effusive style at the tharsis montes mars and implications for the development of the tharsis province 1 we mapped lava flows on the tharsis montes arsia mons pavonis mons and ascraeus mons using high resolution stereo camera images that centrally transect each shield from north to south covering 20 of each shield s surface these data were co registered to mars orbiter laser altimeter thermal emission imaging system and mars orbiter camera data enabling lava flow structures and vents to be consistently differentiated across each volcano lava flow and vent abundances and relationships are used to provide new insight into the late amazonian eruptive history of the tharsis montes the volcanoes are divided into their main flanks rift aprons and small vent fields where present on the main flanks channel fed flows always embay tube fed flows indicating a change from long lived stable tube forming eruption conditions to shorter lived less stable channel forming eruption conditions superposition relationships suggest that main flank and rift apron development were likely separated by an eruptive hiatus the rift aprons as compared to the main flanks show higher abundances of tube and channel fed flows and embayment of tube fed flows by channel fed flows is less consistent several trends from the arsia mons to ascraeus mons southwest rift aprons and small vent fields were identified including increased tube abundance median slope and number of satellitic eruptive vents and a decrease in channel to tube fed flow ratios apron volumes and maximum apron elevations these trends suggest that the most recent volcanic activity at the tharsis montes might have originated from a single shared magma source possibly marking a change in magma production style from main flank construction

rheologic inferences from the levees of lava flows on mars 1 a new methodology is presented for estimating the rate of levee growth for channelized lava flows on the basis of spatial changes in the dimensions of the channels and levees the rate of levee growth can then be used to describe the decrease in flow rate as a function of distance along the flow and subsequently to constrain rheologic behavior along the flow length one terrestrial mauna loa 1984 1a and two martian one on the plains north of pavonis mons one near the summit of ascraeus mons examples are shown a linear levee building rate function adequately describes levee growth for all three examples with the overall magnitude of the rate function inversely correlated with the total volume of material in the levees theoretical levee widths based on these linear functions are consistent with those measured in the field or from planetary images assuming newtonian rheologies the viscosity increases for the mauna loa and pavonis mons lava flows are about an order of magnitude greater than when the levee building process is ignored application to the mauna loa 1984 1a flow shows that the model provides results more consistent with independent petrologic studies as well as field observations of the levee formation process viscosity changes at ascraeus mons are similar to those estimated previously zimbelman 1985 because of the constant thickness of the flow

on the use of advection correction in trajectory calculations abstractan advection correction procedure is used to mitigate temporal interpolation errors in trajectory analyses constructed from gridded in space and time velocity data the procedure is based on a technique introduced by gal chen to reduce radar data analysis errors arising for the nonsimultaneity of the data collection experiments are conducted using data from a high resolution cloud model 1 cm1 numerical model simulation of a supercell storm initialized within an environment representative of the 24 may 2011 el reno oklahoma tornadic supercell storm trajectory analyses using advection correction are compared to traditional trajectory analyses using linear time interpolation backward trajectories are integrated over a 5 min period for a range of data input time intervals and for velocity pattern translation estimates obtained from different analysis subdomain sizes box widths and first guess options the use of advection correction reduces trajectory end point position errors for a large m

the influence of cross sectional channel geometry on rheology and flux estimates for active lava flows lava rheology and effusion rate are critical factors in determining the evolution of lava flows however direct and accurate field measurements are difficult to carry out and estimates are usually based on measurements of the flow s surface velocity and assumptions of sub surface geometry using numerical flow models we show that the potential for error due to geometry uncertainty is minimized if a semi elliptical cross sectional channel shape is assumed flow is simulated for isothermal newtonian temperature dependent newtonian and isothermal power law rheology lavas for isothermal newtonian lava we find that the error in channel shape alone can make apparent viscosity estimates 3 5 times too large e g for inappropriate use of the jeffreys equation on a narrow semi elliptical channel for a temperature dependent rheology using an analytical approximation for newtonian flow in a semi elliptical geometry yields apparent viscosity and flux values that are more accurate than estimates which assume a rectangular geometry for all channel shapes considered including rectangular channels viscosity calculations for real channels on mauna loa and mount etna show that for a newtonian rheology a semi elliptical analytical solution gives an approximation three times closer to the actual viscosity than a rectangle with the same depth while if the lava is shear thinning power law exponent m 0 6 a rectangular approximation is 15 more accurate our results can be used to bracket possible viscosity and flux estimates when channel topography is poorly constrained

low level mesovortices within squall lines and bow echoes part ii their genesis and implications this two part study proposes a fundamental explanation of the genesis structure and implications of lowlevel meso g scale vortices within quasi linear convective systems qlcss such as squall lines and bow echoes such mesovortices are observed frequently at times in association with tornadoes idealized experiments with a numerical cloud model show that significant low level mesovortices develop in simulated qlcss especially when the environmental vertical wind shear is above a minimum threshold and when the coriolis forcing is nonzero as illustrated by a qlcs simulated in an environment of moderate vertical wind shear mesovortexgenesis is initiated at low levels by the tilting in downdrafts of initially crosswise horizontal baroclinic vorticity over a 30 min period the resultant vortex couplet gives way to a dominant cyclonic vortex as the relative and more notably planetary vorticity is stretched vertically hence the coriolis force plays a direct role in the low level mesovortexgenesis a downward directed vertical pressure gradient force is subsequently induced within the mesovortices effectively segmenting the previously nearly continuous convective line in moderate to strong environmental shear the simulated qlcss evolve into bow echoes with straight line surface winds found at the bow echo apex and additionally in association with and in fact induced by the lowlevel mesovortices indeed the mesovortex winds tend to be stronger more damaging and expand in area with time owing to a mesovortex amalgamation or upscale vortex growth in weaker environmental shear in which significant low level mesovortices tend not to form damaging surface winds are driven by a rear inflow jet that descends and spreads laterally at the ground well behind the gust front

formation of hrad vallis mars by low viscosity lava flows abstract hrad vallis is a martian outflow channel previously interpreted as a product of aqueous outbursts from the subsurface possibly involving mudflows associated with lahar like events however an alternative volcanic hypothesis for the development of the system is worthy of consideration on the basis of 1 the nature of landforms preserved along component channels and adjacent uplands and 2 similarities between the basic properties of this system and large volcanic channels of the inner solar system hrad vallis commences on the distal flanks of the elysium mons shield volcano terminates within extensive volcanic plains is associated with landforms typical of large volcanic channels and shows evidence for having been a conduit for large volumes of lava the properties of this system are consistent with incision by low viscosity lava crude thermal estimates suggest that this system could have formed through effusion of as little as 10 900 km 3 of magma to the surface or 6 of the volume of the terrestrial columbia river basalt group incision rates of up to several meters per day are estimated for mechanical and thermal processes involving lava flows with depths of 5 20 m and dynamic viscosities of 1 pa s flow of lava within the hrad vallis system is predicted to have been fully turbulent and characterized by discharges as great as 865 000 m 3 s predicted flow conditions are consistent with those previously determined for athabasca valles which also formed as a result of the expulsion of flows from structures associated with elysium mons

the effect of inflation on the morphology derived rheological parameters of lava flows and its implications for interpreting remote sensing data a case study on the 2014 2015 eruption at holuhraun iceland abstract morphology derived lava flow rheology is a frequently used tool in volcanology and planetary science to determine rheological parameters and deduce the composition of lavas on terrestrial planets and their moons these calculations are usually based on physical equations incorporating 1 lava flow driving forces gravity slope and flow rate and 2 morphological data such as lava flow geometry flow width height or shape of the flow outline all available methods assume that no geometrical changes occur after emplacement and that the measured flow geometry reflects the lava s apparent viscosity and or yield strength during emplacement it is however well established from terrestrial examples that lava flows may inflate significantly after the cessation of flow advance this inflation affects in turn the width to height ratio upon which the rheological estimates are based and thus must result in uncertainties in the determination of flow rheology as the flow height is one of the key parameters in the morphology based deduction of flow properties previous studies have recognized this issue but to date no assessment of the magnitude of this error has been presented this is likely due to a lack of digital elevation models dems at sufficiently high spatial and temporal resolution the 2014 15 holuhraun eruption in central iceland represents one of the best monitored large volume 1 5 km3 lava flow fields 85 km2 to date an abundance of scientific field and remote sensing data were collected during its emplacement moreover inflation plays a key role in the emplacement dynamics of the late stage of the lava field here we use a time series of high resolution dems acquired by the tandem x satellite mission prior during and after the eruption to evaluate the error associated with the most common methods of deriving lava flow rheology from morphological parameters used in planetary science we can distinguish two dominant processes as sources of error in the determination of lava flow rheology from morphology 1 wholesale inflation of lava channels and 2 post halting inflation of individual lava toes these result in a 2 4 to 17 fold overestimation of apparent viscosity and a 0 7 to 2 4 fold overestimation of yield strength when applied in planetary sciences this overestimation in rheological parameters translates directly to an overestimation of the respective lavas silica content we conclude that although qualitatively informative morphological analysis is insufficient to discern lava rheology and composition instead in situ analysis together with high resolution remote sensing data is needed to properly constrain the compositions involved in planetary volcanism

fissure eruptions in tharsis mars implications for eruption conditions and magma sources the tharsis region has been the focus of many studies of volcanism on mars not only are the largest volcanoes on the planet located here but also many of the youngest volcanic features are found within tharsis comparatively little attention has been given to understanding the origin of the smaller volcanoes within tharsis and these smaller structures may provide important information on both the regional tectonics of the area and the availability of magma from the shallow or deep crust we have identified six separate but physically close vent systems in eastern tharsis just to the east of the volcano jovis tholus these vents are typically linear fissures a few to 20 km in length that have built small shields rising to 50 85 m above the level of the surrounding topography the maximum length of individual lava flows from these fissures is 30 km but more typical lengths are 15 20 km mapping of the vent complexes reveals that smooth material interpreted to be spatter from fire fountaining is located on the rims of some of the fissures this spatter then formed either short 5 km flows or merged close to the fissure to form the longer flows there appears to have been some temporal evolution of the flow field as the oldest parts of the basement at each center are built from a series of compound flows that cannot be subdivided into individual flows we find evidence of frozen lava ponds and channelized flows from central vents photoclinometric profiles are constructed across one of the longer flows to confirm an unusual attribute originally identified by mouginis mark and christensen mouginis mark p j christensen p r 2005 new observations of volcanic features on mars from the themis instrument j geophys res 110 e8 doi 10 1029 2005je002421 of the flows from the central vent complex they are all 5 m thick which is a factor of 8 15 thinner than flows elsewhere on mars to investigate the unusual eruption conditions limited total volume of the construct and of individual flows we model the lava rheology the duration of emplacement the subsurface conditions that may have led to these eruptions and the volatile content of the magma we find lava viscosities and yield strengths to be 100 pa s and 100 pa respectively eruption rates to be 5000 m3 s 1 flow speeds to be 1 2 m s 1 durations of emplacement of individual flow units to be 5 h and the equivalent magma water content to be 0 1 0 2 mass these eruption conditions are consistent with a wide range of possible depths of the magma reservoirs feeding the eruptions small vents such as the ones studied here have also been identified in other parts of eastern tharsis so that the eruptions described here may characterize a common style of volcanism on mars that can only be identified now that image spatial resolution in the range 1 20 m pixel is available it is therefore possible that additional searches of other volcanic areas syrtis planum elysium planitia and hesperia planum may also show greater diversity of activity than is currently accepted