experimental modelling of ground deformation associated with shallow magma intrusions abstract active volcanoes experience ground deformation as a response to the dynamics of underground magmatic systems the analysis of ground deformation patterns may provide important constraints on the dynamics and shape of the underlying volcanic plumbing systems nevertheless these analyses usually take into account simplistic shapes sphere dykes sills and the results cannot be verified as the modelled systems are buried in this paper i present new results from experimental models of magma intrusion in which both the evolution of ground deformation during intrusion and the shape of the underlying intrusion are monitored the models consisted of a molten vegetable oil simulating low viscosity magma injected into cohesive fine grained silica flour simulating the brittle upper crust oil injection resulted is sheet intrusions dykes sills and cone sheets the initial topography in the models was flat while the oil was intruding the surface of the models slightly lifted up to form a smooth relief which was mapped through time after an initial symmetrical development the uplifted area developed asymmetrically at the end of the experiments the oil always erupted at the steepest edge of the uplifted area after the experiment the oil solidified the intrusion was excavated and the shape of its top surface mapped the comparison between the uplifted zone and the underlying intrusions showed that 1 the complex shapes of the uplifted areas reflected the complex shapes of the underlying intrusions 2 the time evolution of the uplifted zone was correlated with the evolution of the underlying intrusion and 3 the early asymmetrical evolution of the uplifted areas can be used to predict the location of the eruption of the oil the experimental results also suggest that complex intrusion shapes inclined sheet cone sheet complex sill may have to be considered more systematically in the analyses of ground deformation patterns on volcanoes

the new athena alpha particle x ray spectrometer for the mars exploration rovers 1 the new alpha particle x ray spectrometer apxs is part of the athena payload of the two mars exploration rovers mer the apxs sensor head is attached to the turret of the instrument deployment device idd of the rover the apxs is a very light weight instrument for determining the major and minor elemental composition of martian soils rocks and other geological materials at the mer landing sites the sensor head has simply to be docked by the idd on the surface of the selected sample x ray radiation excited by alpha particles and x rays of the radioactive sources is recorded by a high resolution x ray detector the x ray spectra show elements starting from sodium up to yttrium depending on their concentrations the backscattered alpha spectra measured by a ring of detectors provide additional data on carbon and oxygen by means of a proper calibration the elemental concentrations are derived together with data from the two other athena instruments mounted on the idd the samples under investigation can be fully characterized key apxs objectives are the determination of the chemistry of crustal rocks and soils and the examination of water related deposits sediments or evaporates using the rock abrasion tool attached to the idd issues of weathering can be addressed by measuring natural and abraded surfaces of rocks

recent outgassing from the lunar surface the lunar prospector alpha particle spectrometer 1 the lunar prospector alpha particle spectrometer aps was designed to detect characteristic energy alpha particles from the decay of rn 222 po 218 and po 210 and to therefore map sites of radon release on the lunar surface these three nuclides are radioactive daughters from the decay of u 238 hence the background level of alpha particle activity is a function of the lunar crustal uranium distribution radon reaches the lunar surface either at areas of high soil porosity or where fissures release the trapped gases in which radon is entrained once released the radon spreads out by bouncing across the surface on ballistic trajectories in a random walk process the half life of rn 222 allows the gas to spread out by several hundred kilometers before it decays depositing approximately half of the po 218 recoil nuclides on the lunar surface and allows the aps to detect gas release events up to several days after they occur the long residence time of the pb 210 precursor to po 210 allows the mapping of gas vents which have been active over the last approximately 60 years the aps found only a faint indication of po 218 alpha particles however the rn 222 alpha particle map shows that radon gas was emanating from the vicinity of craters aristarchus and kepler at the time of lunar prospector the po 210 alpha particle distribution reveals a variability in time and space of lunar gas release events po 210 and rn 222 detections are associated with both thorium enhancements and lunar pyroclastic deposits

evolution of magma conduits during the 1998 2000 eruptions of piton de la fournaise volcano reunion island 1 at basaltic volcanoes magma is transported to the surface through dikes magma filled fractures but the evolution of these dikes as eruptions proceed is rarely documented in march 1998 after five and a half years of quiescence piton de la fournaise volcano reunion island entered into a new eruptive phase characterized by intense eruptive activity coeruptive displacements recorded by interferometric synthetic aperture radar insar for the first five eruptions of the cycle are analyzed using 3 d boundary element models combined with a monte carlo inversion method we show that the eruptions are associated with the emplacement of lateral dikes rooted at depths of less than about 1000 m except for the first march 1998 event where an additional deeper source is required the dikes are located above preeruptive seismic swarms this is consistent with nearly isotropic stress caused by repeated dike intrusions and low confining pressure enhanced by the presence of pores in the shallowest 1000 m of the edifice the volumes of the modeled dikes represent 17 of the volume of emitted lava showing that exogenous growth plays a major role in building the volcano by taking into account the preeruptive seismicity and tilt data together with the results of insar data modeling we find that dikes first propagate vertically from a source region below sea level before being injected laterally at shallow depth this behavior is consistent with the presence of levels of neutral buoyancy at shallow depth in the edifice

intrusion and deformation at campi flegrei southern italy sills dikes and regional extension 1 the campi flegrei volcanic district in southern italy has been uplifted since 1968 by a net maximum of 3 m during the intervals 1968 1972 and 1982 1984 the uplift represents a permanent deformation against a background rate of subsidence of about 17 mm a 1 previous models have reproduced the observed vertical deformation but not the full pattern of horizontal movements the 1982 1983 deformation is here reanalyzed in terms of a penny shaped sill on its own with a tabular surface protrusion or in an extensional stress field it can be explained best by the intrusion of a sill of 0 03 0 04 km3 at a depth of 2 75 km in a crust that is being stretched ese wnw at a strain rate of about 5 6 10 5 a 1 the sill s volume is similar to the common volumes of campi flegrei s eruptions since the neapolitan yellow tuff nyt caldera was formed 15 6 ka ago this similarity and the permanent nature of the uplift favor magmatic intrusion as the primary source of unrest sill formation may thus reflect the spreading of magma at a level of neutral buoyancy or along lateral discontinuities in the crust the southern part of the caldera has been shielded from post nyt eruptions despite some 33 m of permanent uplift since roman times precursors to eruptions may thus be related not to caldera wide uplift but to the preceding conditions that determine whether magma ascends beneath the southern part of the caldera favoring sill intrusion or elsewhere favoring an eruption

dynamic dyke propagation deduced from tilt variations preceding the march 9 1998 eruption of the piton de la fournaise volcano during the hour preceding the march 9 1998 eruption of the piton de la fournaise volcano the deformation network of the observatory recorded some large deformations in the summit area a broadband seismic station of the geoscope global network rer is located about 8 km away from the summit of the volcano signals from that station may be interpreted as tilt changes the combination of the above two kinds of signals allows by using a tensile fault model to constrain the geometry as well as some characteristics volume propagation velocity of the dyke that intruded the summit area during the hour preceding the beginning of eruptive activity

determination of the chemical composition of martian soil and rocks the alpha proton x ray spectrometer the alpha proton x ray spectrometer apxs for the mars pathfinder mission is designed to provide a complete and detailed analysis of chemical elements in martian soil and rocks near the landing site the apxs instrument is carried on the pathfinder microrover which will provide transportation to places of interest on the martian surface it consists of a complex sensor head mounted on a simple but sophisticated apxs deployment mechanism adm outside the warm electronics box web of the microrover and the instrument electronics mounted inside the web the adm permits the instrument sensor head to be placed against soil and rock samples in arbitrary positions ranging from horizontal to vertical in order to perform in situ analysis the possibility to transport the apxs to an arbitrary location preselected on earth and to perform in situ analysis there constitutes one of the most exciting aspects of the pathfinder mission the principle of the apxs technique is based on three interactions of alpha particles from a radioisotope source with matter simple rutherford backscattering production of protons from p reactions on light elements and generation of characteristic x rays upon recombination of atomic shell vacancies created by a bombardment measurement of the intensities and energy distributions of these three components yields information on the abundance of chemical elements in the sample in terms of sensitivity and selectivity data are partly redundant and partly complementary alpha backscattering is superior for light elements c o while proton emission is mainly sensitive to na mg al si s and x ray emission is more sensitive to heavier elements na to fe and beyond a combination of all three measurements enables determination of all elements with the exception of h and he present at concentration levels above typically a fraction of 1

crustal deformation and source models of the yellowstone volcanic field from geodetic data 1 geodetic observations comprising interferometric synthetic aperture radar insar global positioning system gps and precision leveling measurements are used to infer volume change in the subsurface associated with the dynamics of the yellowstone volcanic system we focus primarily on the yellowstone caldera and its related magmatic hydrothermal and fault systems it appears that known faults play a significant role in controlling crustal volume increases and decreases due to the migration of volcanic and hydrothermal fluids for example over 5 cm of subsidence from 1992 to 1995 is associated with source volume changes 6 10 km beneath the nw trending elephant back fault zone and a north trending fault cutting across the caldera furthermore we are able to image an episode of fluid intrusion near the northern edge of the caldera the intrusion is elongated in the north south direction and is parallel to the north trending volume decrease the primary intrusion and related hydrothermal activity occurred between 1996 and 2000 though the volume changes appear to have continued shallowed and changed shape between 2000 and 2002 there is evidence that the intrusive activity influenced extensional faults to the north of the caldera

lunar surface geochemistry global concentrations of th k and feo as derived from lunar prospector and clementine data abstract accurate estimates of global concentrations of th k and feo have an important bearing on understanding the bulk chemistry and geologic evolution of the moon we present empirical ground truth calibrations transformations for lunar prospector gamma ray spectrometer data k and th and a modified algorithm for deriving feo concentrations from clementine spectral reflectance data that incorporates an adjustment for tio 2 content the average composition of soil samples for individual landing sites is used as ground truth for remotely sensed data among the apollo and luna sites apollo 12 and 14 provide controls for the incompatible element rich compositions apollo 16 and luna 20 provide controls for the feldspathic and incompatible element poor compositions and apollo 11 15 and 17 and luna 16 and 24 provide controls for fe rich compositions in addition to these apollo and luna sample data we include the composition of the feldspathic lunar meteorites as a proxy for the northern farside highlands to extend the range of the calibration points thus providing an additional anorthositic end member composition these empirical ground truth calibrations for lunar prospector th and k provide self consistency between the existing derived data and lunar sample data clementine spectral reflectance data are used to construct a tio 2 sensitive feo calibration that yields higher feo concentrations in areas of high fe low ti mare basalt rich surfaces than previous feo algorithms the data set so derived is consistent with known sample compositions and regolith mixing relationships

the great eucrite intrusion of ardnamurchan scotland reevaluating the ring dike concept ring dikes are cylindrical sheet intrusions that develop at a subvolcanic level due to ascent of magma along steep outward dipping ring fractures magma ascent is triggered by central block subsidence and fully formed ring dikes are composed of a flat lying sill like roof as well as steeply outward dipping walls on all sides the great eucrite of the ardnamurchan paleocene igneous complex nw scotland is a spectacular gabbro intrusion that has been cited as one of the classic examples of a ring dike for the past 70 yr we combine field observations detailed structural measurements of primary magmatic features and anisotropy of magnetic susceptibility data in a reinvestigation of this intrusive body magmatic layering and macroscopic planar crystal arrangements dip inward and magnetic lineations plunge consistently toward the center of the intrusion in contrast to what would be expected for a ring dike we propose that the great eucrite ring dike is in fact a lopolithic intrusion with an overall funnel shape geometry this conclusion brings into question the presence of three individual foci of activity in ardnamurchan purported to have shifted throughout the development of the complex it also has significant implications for the status and structural evolution of other igneous complexes of the british paleocene igneous province which contain layered mafic intrusions currently regarded as ring dikes

evidence of 210po on martian dust at meridiani planum 1 since the surveyor and apollo missions and up to the recent lunar prospector mission 222rn and 210po have been key isotopes for understanding gas release events and their spatial and temporal variations on the moon comparatively these isotopes have drawn much less attention on mars if any despite the wealth of information it could bring on the uppermost meters of the regolith the exchange of volatiles at the surface and the atmospheric aerosol cycle here we present a statistical analysis of the high energy end of alpha spectra obtained by the alpha particle x ray spectrometer onboard mars exploration rover opportunity and report evidence of 210po a decay product of 222rn attached to atmospheric dust the 210po surface activity on rocks and soils at the landing site is lower than 3 1 10 4 bq cm 2 but analysis of spectra obtained on the dust capture magnet reveals a 210po activity of 4 6 2 4 10 3 bq cm 2 2 this difference is due to the very low dust cover index at the landing site owing to frequent dust devils regional and global dust storms that mobilize substantial amounts of dust and homogenize the dust surface layer we infer that the global average 222rn exhalation rate is significantly greater on mars than on the moon this comparison supports the hypothesis that on mars radon emanation could be comparatively enhanced by the presence of water in the surficial soil analysis of atmospheric spectra yields a radon activity upper limit of 16 5 bq m 3 during nighttime at the landing site

atmospheric imaging results from the mars exploration rovers spirit and opportunity a visible atmospheric optical depth of 0 9 was measured by the spirit rover at gusev crater and by the opportunity rover at meridiani planum optical depth decreased by about 0 6 to 0 7 per sol through both 90 sol primary missions the vertical distribution of atmospheric dust at gusev crater was consistent with uniform mixing with a measured scale height of 11 56 0 62 kilometers the dust s cross section weighted mean radius was 1 47 0 21 micrometers mm at gusev and 1 52 0 18 mm at meridiani comparison of visible optical depths with 9 mm optical depths shows a visible to infrared optical depth ratio of 2 0 0 2 for comparison with previous monitoring of infrared optical depths

effective radium 226 concentration in meteorites the analysis of noble gases in meteorites provides constraints on the early solar system and the pre solar nebula this requires a better characterization and understanding of the capture production and release of noble gases in meteorites the knowledge of transfer properties of noble gases for each individual meteorite could benefit from using radon 222 radioactive daughter of radium 226 the radon 222 emanating power is commonly quantified by the effective radium 226 concentration ecra the product of the bulk radium 226 concentration and of the emanation coefficient e which represents the probability of one decaying radium 226 to inject one radon 222 into the free porous network owing to a non destructive high sensitivity accumulation method based on long photomultiplier counting sessions we are now able to measure ecra of meteorite samples which usually have mass smaller than 15 g and ecra 0 5 bq kg 1 we report here the results obtained from 41 different meteorites based on 129 measurements on 70 samples using two variants of our method showing satisfactory repeatability and a detection limit below 10 2 bq kg 1 for a sample mass of 1 g while two meteorites remain below detection level we obtain for 39 meteorites heterogeneous ecra values with mean min max range of ca 0 1 0 018 1 30 bq kg 1 carbonaceous chondrites exhibit the largest ecra values and eucrites the smallest such values are smaller than typical values from most terrestrial rocks but comparable with those from archean rocks mean of ca 0 18 bq kg 1 an end member of terrestrial rocks using uranium concentration from the literature e is inferred from ecra for all the meteorite samples values of e for meteorites mean 40 4 are higher than e values for archean rocks and reported values for lunar and martian soils exceptionally large e values likely suggest that the 238u 226ra pair would not be at equilibrium in most meteorites and that uranium and or radium are most likely not uniformly distributed ecra of meteorites is correlated with e and seems to mainly reflect the gas permeability of the meteorite which could be one important property preserved in the meteorite of its parent body characterizing its history in space possibly modified by alteration shock metamorphism and eventually weathering on earth larger radon emanation values are associated with larger concentrations of the heaviest noble gases argon krypton xenon and larger 20ne 22ne and 36ar 38ar ratios suggesting earth s atmosphere contamination or solar wind implantation and probably a similar carrier phase such as q phase an unclear correlation is observed with 40ar which may rule out a purely radiogenic effect on radon emanation thus larger radon emanation suggests a larger capacity of collecting solar and terrestrial gases which should imply higher loss of gases generated in the meteorite and larger dispersion of pb u ratios for age determination this study provides the first quantification of natural radon 222 loss from meteorites and opens promising perspectives to quantify the relationship between pore space connectivity and the transfer properties for noble gases in meteorites and other extraterrestrial bodies

scaled experiments of volcanic spreading experiments were conducted to study the spreading of volcanic constructs volcanoes are simulated by a sand cone and the volcanic substratum is simulated by a sand layer brittle substratum overlying a silicone layer ductile substratum similarity conditions between natural volcanoes and experimental prototypes led to the definition of dimensionless numbers experiments determine values which predict whether or not spreading takes place of particular importance are the ratio between the thickness of the brittle substratum and the height of the volcano 2 and the brittle ductile ratio of the substratum 3 2 indicates that the volcano must be large enough to break the substratum before spreading occurs whereas 3 controls the style of deformation during spreading these dimensionless numbers change with time reaching values that tend toward those observed for stable configurations experimental values are compared with those from well constrained natural examples it is found that an essential requirement for volcanic spreading is the presence of a low viscosity layer within the substratum flow of the weak layer away from the excess load is responsible for the spreading the overlying edifice displays radial intersecting grabens due to concentric stretching dissected summit areas concentric zones of thrusts and folds form in the substratum around the edifice and diapirs of the ductile substratum rise within the fault zones

early cenozoic saucer shaped sills of the faroe islands an example of intrusive styles in basaltic lava piles abstract the early cenozoic igneous activity of the north atlantic igneous province that generated widespread sill complexes in sedimentary basins at the nw european margins also generated various intrusive systems in the contemporaneous basaltic lava pile of the faroe islands the faroe island basalt group comprises seven formations with a total thickness of about 6 5 km of which four major formations are built up of tholeiitic lava flows each being several hundred metres thick and three thinner formations are mostly built up of volcaniclastic lithologies each being a few metres to a few tens of metres thick the largest sills are exposed as partly saucer shaped bodies in the three uppermost formations where inner gently dipping basal sill sections gradually give way to more steeply inclined discordant outer rims that commonly cut several hundred metres into overlying lava flows numerous subvertical and moderately inclined dykes ranging in thickness from c 0 5 to c 4 0 m intersect the areas affected by sill intrusion but only inclined dykes or sheets have been positively identified as sill feeders locally controlled rotations of least principal stress axes 3 during initial sill intrusion or propagation may have been an important contributing factor in determining the overall geometry of the investigated intrusions

soils of eagle crater and meridiani planum at the opportunity rover landing site the soils at the opportunity site are fine grained basaltic sands mixed with dust and sulfate rich outcrop debris hematite is concentrated in spherules eroded from the strata ongoing saltation exhumes the spherules and their fragments concentrating them at the surface spherules emerge from soils coated perhaps from subsurface cementation by salts two types of vesicular clasts may represent basaltic sand sources eolian ripples armored by well sorted hematite rich grains pervade meridiani planum the thickness of the soil on the plain is estimated to be about a meter the flatness and thin cover suggest that the plain may represent the original sedimentary surface

the opportunity rover s athena science investigation at meridiani planum mars the mars exploration rover opportunity has investigated the landing site in eagle crater and the nearby plains within meridiani planum the soils consist of fine grained basaltic sand and a surface lag of hematite rich spherules spherule fragments and other granules wind ripples are common underlying the thin soil layer and exposed within small impact craters and troughs are flat lying sedimentary rocks these rocks are finely laminated are rich in sulfur and contain abundant sulfate salts small scale cross lamination in some locations provides evidence for deposition in flowing liquid water we interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water followed by evaporation exposure and desiccation hematite rich spherules are embedded in the rock and eroding from them we interpret these spherules to be concretions formed by postdepositional diagenesis again involving liquid water

geometrical constraints of the 1980 mount st helens intrusion from analogue models the 1980 mount st helens cryptodome intrusion has been simulated by scaled experiments silicone used as a magma analogue was intruded into a cohesive cone that models the edifice measuring surface deformation features associated with variations of injection rate and depth of cryptodome initiation revealed linear relationships with the intrusion characteristics scaled to mount st helens dimensions the 1980 cryptodome is found to have had a maximum e w width of 850 m an initial depth of 680 to 835 m it had an ascending velocity of 5 7 7 3 m day that corresponds to a vertical displacement of 330 380 m toward the surface within the two months of deformation this brought the intrusion to less than 250 m below the crater floor at the point when the north flank failed on may 18 1980

small area thorium features on the lunar surface 1 using an improved understanding of the lunar prospector gamma ray spectrometer lp grs spatial footprint we have derived a new map of global thorium abundances on the lunar surface this map has a full width half maximum spatial resolution of 80 km 2 and is mapped on the lunar surface using 0 5 0 5 pixels this map has allowed the identification and classification of 42 small area 3 g g in southwestern mare tranquillitatis near the apollo 11 landing site with our better understanding of the lp grs spatial footprint we have been able to constrain the surface thorium abundance at the compton belkovich thorium anomaly to 40 55 g g which is higher than any other measured location on the lunar surface and higher than most samples finally using 1 km pixel feo abundances from clementine and lp grs spatial footprint information we have been able to obtain plausible thorium distributions around kepler crater at a resolution of 1 km pixel the materials around kepler crater appear to be a relatively simple mixing of thorium rich mib compositions and high thorium mare basalts

influence of a variable thermal conductivity on the thermochemical evolution of mars 1 the influences of variations in thermal conductivity due to composition temperature and pressure in mantle and crust on the thermochemical evolution of mars have been examined with parameterized convection models we use a temperature and pressure dependent thermal conductivity in the mantle and column averaged values between 1 5 and 4 wm 1k 1 for the crust with 2 wm 1k 1 as the representative value for a basaltic crust the major characteristic of the models is a slower cooling of the upper mantle with a long existing global partial melt zone and a stronger crustal production late in the evolution compared to earlier models which assume a constant thermal conductivity of 4 wm 1k 1 to explain the observed crustal thickness and the early crustal formation on mars the formation of an enriched primordial crust is required recent volcanism can be explained by lateral temperature variations that are caused by thickness variations of the low conducting crust these melt zones which occur underneath thicker than average crust may be the source region for the observed longstanding volcanism in tharsis and elysium instead of plumes rising from the core mantle boundary the evolution of the elastic lithosphere is characterized by a transition at which the elastic strength is first provided by the crust and later also by the upper mantle this finding may explain the estimated elastic lithosphere thickness of less than 16 km in the noachian and more than 100 km in the hesperian and amazonian

structure of a sheet laccolith system revealing the interplay between tectonic and magma stresses at stardalur volcano iceland abstract this paper provides detailed structural data on the faults and intrusions of the eroded stardalur volcano in the esja peninsula at the sw margin of the icelandic rift and new lithostratigraphic data on the host rocks a swarm of centrally dipping sheets emplaced with a fan shaped geometry in section view depicts an ellipse in plan view with an about e w major axis sheet intensity reaches 80 in one 100 m transect near the central portion of the swarm where sheets strike e w with sub vertical dip a 200 m thick multiply intrusive body forms a laccolith in the middle of the centrally dipping sheet swarm at a higher altitude individual intrusive units within this laccolith are sub vertical and strike e w in the center acquiring a sill like geometry outwards and were emplaced in a stress field locally dominated by a n s directed least principal stress 3 within the inclined sheet swarm the stress tensor rotated in response to an excess magma pressure probably linked to an underlying magma chamber which interacted with the tectonic stresses crosscutting relationships between the various intrusions and with the host rock indicate that the activity in the central zone of the stardalur volcano ended with the emplacement of the laccolith later eruptions if they occurred at all were fed by centrally dipping sheets in the final stage nne striking regional vertical dykes and normal faults cut the previous structures in response to dominant regional plate tectonic stresses with a wnw ese directed 3 and a nne ssw directed intermediate principal stress 2

martian dust storms 1999 mars orbiter camera observations the mars orbiter camera on board the mars global surveyor from march 9 1999 ls 107 where ls is the areocentric longitude of the sun measured in degrees from mars northern spring equinox to december 31 1999 ls 274 has obtained 7 5 km pixel 1 daily global maps of the martian surface in two wavelength bands blue 400 450 nm and red 575 625 nm visual inspection of these maps during the 1999 dust storm season has resulted in the detection of 783 dust storms ranging in size from local 102 km2 to regional 1 6 106 km2 no global storms were observed the difference in the numbers of dust storms occurring in the two hemispheres north 343 south 440 was not statistically significant fifty percent of the regional size dust storms formed as a result of the merger of two or more smaller local storms the regional storms from ls 207 to ls 223 were observed to move from the northern hemisphere into the southern hemisphere between 30 w and 50 w longitude this cross equatorial transport of dust suggests the location of the low lying southward flowing branch of the hadley circulation observations show that dust storms occur in several regions on mars at the two polar cap edges at the base of high elevation regions in the northern hemisphere near the polar hood during northern fall and at mid latitudes in both hemispheres specific regions such as solis planum and hesperia which were regions of significant dust activity in the past showed almost no dust storm activity in 1999 suggesting that regional dust sources are variable over a 20 year time frame one region of exceptional activity not noted previously was the arcadia amazonis border however other regions such as near elysium mons acidalia chryse hellas noachis argyre cimmeria and sirenum again were active dust storm regions relative dust opacities were modeled for 117 red wavelength events and ranged from 0 54 diffuse haze to 2 13 concentrated local events from the dust opacities we estimated the north polar sedimentation rate to be 6 0 10 10 4 g cm 2 yr 1 a factor of 40 smaller than previous estimates from the two 1977 global dust storms pollack et al 1979 along with the global dust mass loading 2 6 4 0 10 4 g cm 2 and cross equatorial dust mass loading 3 6 10 4 g cm 2 the 1999 cross equatorial mass dust loading suggests that the southern hemisphere subtropical latitudes require at least 2 3 martian years to replenish their dust sources before global storms can form

rise and emplacement of magma during horizontal shortening of the brittle crust insights from experimental modeling 1 magmatic activity tends to concentrate at plate margins at divergent margins extensional tectonics provide steep conduits for magma to reach the surface at rapidly convergent margins such as the andes one might imagine that horizontal compression prevents the rise of magma nevertheless volcanoes are also common in order to study the mechanisms by which magma rises in a compressional context we resorted to laboratory experiments in which a brittle crust was shortened while magma was intruding our model materials were 1 cohesive fine grained silica powder representing brittle crust and 2 molten low viscosity vegetable oil representing magma in general horizontal shortening and injection were coeval but independent processes thrust faults accommodated the shortening while overpressured oil formed hydraulic fractures in those experiments where there was no shortening injection resulted in a saucer shaped intrusive body in the other experiments where there was shortening oil formed a basal sill before rising along thrust faults once in place the sill lubricated the base of the model so that arcuate thrusts formed at the leading edge of a plateau uplift of the plateau promoted further intrusion of oil at depth in general the pattern of deformation and intrusion depended on the kinematic ratio r between rates of shortening and injection the lengths of the basal sill and plateau increased with decreasing r on the basis of these results we have reexamined two natural examples of magmatic complexes which were emplaced in compressional tectonic settings tromen volcano in argentina and the boulder batholith of montana

widespread uplift and trapdoor faulting on galapagos volcanoes observed with radar interferometry volcanic uplift caused by the accumulation of magma in subsurface reservoirs is a common precursor to eruptions1 2 but for some volcanoes uplift of metres or more has not yet led to an eruption3 here we present displacement maps of volcanoes in the galapagos islands constructed using satellite radar interferometry that might help explain this dichotomy we show that all but one of the seven volcanoes on the islands of isabela and fernandina deformed during 1992 99 cerro azul and fernandina erupted4 5 6 during the observation period and show evidence of inflation co eruptive deflation and shallow dyke intrusion in contrast the largest volcano sierra negra has not erupted yet exhibits spatially and temporally variable deformation with a maximum uplift of 2 7 m between 1992 and 1999 which can be modelled by a shallow inflating sill inflation during 1997 98 however was accompanied by trapdoor faulting on a steeply dipping fracture system within the caldera repeated trapdoor faulting over geological time has formed an arcuate intra caldera ridge within sierra negra and may have acted to relax stresses above the magma chamber inhibiting summit eruptions similar processes may help explain large uplift unaccompanied by eruptive activity at other volcanoes

geostatistical characterization of soil moisture and chloride distribution in deep vadose profiles of the badain jaran desert northwestern china geostatistical analysis of soil moisture and ion accumulation can provide a deep understanding of aspects of a region s hydrology such as recharge rates and flow paths by combining this approach with detrended canonical correspondence analysis the present study investigated the vertical and spatial variation of soil moisture and chloride cl in vadose profiles of megadunes near lakes in the southeastern badain jaran desert northwestern china soil moisture varied vertically within the dune profiles following exponential logarithmic or log normal distributions at different sites as a result of regulation by different local controls the main local controls for cl concentration were slope and orientation of the dune cl was not affected by local controls at depths 5 m sills of spatial variation in soil moisture and cl in the variogram analysis were highly sensitive to local controls in the top 4 m of the profiles and the values were three times those at depths 4 m the lag for soil moisture was insensitive to local controls and was 50 60 m in the top 4 m of the profiles and 20 m in deeper layers whereas the lag for cl was about 20 m at all depths the results demonstrate that understanding recharge rates using factors such as cl accumulation requires a careful survey to ensure that the local controls that regulate these factors are adequately accounted for

sequence of rifting in afar manda hararo rift ethiopia 2005 2009 time space evolution and interactions between dikes from interferometric synthetic aperture radar and static stress change modeling thirteen dike intrusions in the manda hararo rift afar ethiopia from september 2005 to june 2009 studied using an extensive interferometric synthetic aperture radar insar data set provide insight into the mechanics of a major active rift kinematic inversions of insar data reveal that dikes opened by 0 8 3 5 m at an average 5 km depth with volumes of 0 04 0 2 km 3 with up to 12 m opening and a volume greater than 1 km 3 for the september 2005 megadike dikes have their source in a midsegment magma reservoir which induces a local shallowing of the brittle ductile boundary presumably due to thermal weakening of the lithosphere the smaller dikes in 2006 2009 were emplaced in regions of minimum opening of the september 2005 megadike above the central magma reservoir in contrast the most voluminous dike intrusions in 2006 2009 occurred near the locus of the peak of maximum opening of the september 2005 megadike 10 km north of the magma source this may suggest that tension on the plate boundary was highest there both prior to 2005 and possibly also after 2005 evolution and distribution of normal stress on the plate boundary throughout the rifting episode may indicate that tension near to the magma reservoir is lower than toward segment ends average relief of normal stresses of tectonic origin coeval to dike intrusions is comparable with shear stress drops for earthquakes presumably because dikes in the manda hararo rift are intruded at low magma pressure and high tectonic stress time space evolution and interactions between dikes from interferometric synthetic aperture radar and static stress change modeling

three dimensional modeling of the 1983 1984 eruption at piton de la fournaise volcano reunion island displacement vectors on 125 points over a 6 km 2 area were calculated zlotnicki et al 1990 for piton de la fournaise volcano reunion island from photogrammetric surveys conducted in september 1981 and again in september 1984 an eruptive crisis with two episodes occurred during the 3 years between the surveys we modeled the displacements from the photogrammetric surveys using a three dimensional mixed boundary element method the model shows that both eruptive episodes were fed by a single dike oriented 165 from north as the dike approached the ground surface it divided into segments that rotated into an en echelon pattern the model that best fits all observations suggests that the stress state within the volcano is quasi isotropic such that horizontal stresses equal the overburden these high horizontal stresses are incompatible with an elastic edifice loaded merely by gravitational forces however they may be attributed to the cumulative effect of repeated dike intrusions

use of vegetable oil and silica powder for scale modelling of magmatic intrusion in a deforming brittle crust in the upper crust intrusive bodies adopt different configurations depending on the tectonic setting this paper describes a new technique for analogue modelling of such intrusions specifically of low viscosity magma into a deforming brittle crust proper dynamic scaling is an important consideration if the crust has a coulomb failure envelope the model material should have a cohesion c of 40 pa to 7500 pa if the intruding magma is highly mobile the model fluid should have a viscosity of 4 10 9 pa s to 75 pa s for the model crust we have used crystalline silica powder si crystal siliceous microspheres si sphere of grain size 30 m and a mixture si mix of both materials the mechanical properties of these powders have been obtained by shear and tension shear tests si crystal powder is cohesive c 300 pa angle of internal friction 45 and represents competent rock si sphere powder is much less cohesive c 10 pa 25 and represents incompetent rock si mix has intermediate properties the model magma is a vegetable oil which solidifies at room temperature its viscosity when molten is 2 10 2 pa s at 50 c using these materials we have done some preliminary experiments to investigate the intrusion of low viscosity magma into sedimentary basins in non deformed settings intrusions were saucer shaped cone sheets in horizontal extension they were steep dykes finally in horizontal shortening intrusions were basal sills that branched into thrust faults

surface deformation and shallow dike intrusion processes at inyo craters long valley california the inyo craters are the two largest of four phreatic craters that lie within a 2 5 km long 500 to 700 m wide n s trend of faults and fissures at the south end of the inyo volcanic chain in eastern california the alignment of these features with dike fed silicic volcanic centers of the same age a few kilometers to the north suggests that they were produced during intrusion of a dike at about 650 550 yr b p e w extension south of south inyo crater is ten to several tens of meters suggesting that the dike is at least that thick to understand how the faults and fissures developed we mapped and studied the fault and fissure pattern used a theoretical boundary element model to determine the surface strain profile above a shallow dike in a purely elastic medium and conducted physical model experiments of fault and fissure growth results of the field studies and experiments indicate that deformation develops according to the following sequence 1 extension fractures and perhaps other inelastic deformation develop immediately above the dike top and on the limbs of a shallow syncline which forms above the dike 2 fissures form along two parallel trends at the surface on opposite sides of the dike plane leaving a relatively unfractured region in between 3 dip slip movement on subsurface fractures and linkage of these fractures with surface fissures produces inward facing normal fault scarps that bound a nested graben above the dike experimental graben widths are up to several times narrower than predicted from the locations of theoretical strain maxima above a dilating crack in a linearly elastic medium this fact is apparently due to the growth of a zone of inelastic deformation above the experimental dike top in the subsurface if the ratio between the depth to the dike top and the distance between the outermost surface fissures at inyo craters is within the range of ratios measured experimentally then the depth to the dike top is between 250 m and several times that a slant hole drilled in the summer of 1987 by the department of energy office of basic energy sciences intersected three breccia bodies of possibly intrusive origin directly below the center of south inyo crater between 550 m and 610 m below the crater rim no intact juvenile igneous rock was intersected suggesting that the hole passed above the magma filled dike top perhaps passing through the zone of inelastic deformation which is inferred to exist from our model results

volcano load control on dyke propagation and vent distribution insights from analogue modeling 1 the spatial distribution of eruptive vents around volcanoes can be complex and evolve as a volcano grows observations of vent distribution at contrasting volcanoes from scoria cones to large shields show that peripheral eruptive vents concentrate close to the volcano base we use analogue experiments to explore the control of volcano load on magma ascent and on vent location results show that the local loading stress field favors eruption of rising magma away from the volcano summit if a central conduit is not established or is blocked two sets of scaled experiments are developed with contrasting rheological properties to analyze similarities and differences in simulated magma rise below a volcano 1 golden syrup magma analogue is injected into a sand plaster mixed layer crust analogue under a cone 2 water or air magma analogues is injected into gelatin under a sand cone rising dykes approaching the cone stress field are stopped by the load compressive stress with continued intrusion dyke overpressure builds up dykes extend laterally until their tips are able to rise vertically again and to erupt in the flank or at the base of the volcano lateral offset of the extrusion point relative to the edifice summit depends on substratum thickness volcano slope and dyke overpressure the 3d geometry of golden syrup intrusions varies with experimental parameters from cylindrical conduits to dyke and sill complexes experimental results are compared with illustrative field cases and with previously published numerical models this comparison enables applications and limitations of the analogue models to be highlighted and allows us to propose a conceptual model for the evolution of vent distribution with volcano growth