principles of early development of karst conduits under natural and man made conditions revealed by mathematical analysis of numerical models numerical models of the enlargement of primary fissures in limestone by calcite aggressive water show a complex behavior if the lengths of the fractures are large and hydraulic heads are low as is the case in nature dissolution rates at the exit of the channel determine its development by causing a slow increase of water flow which after a long gestation time by positive feedback accelerates dramatically within a short time span mathematical analysis of simplified approximations yields an analytical expression for the breakthrough time when this happens in excellent agreement with the results of a numerical model this expression quantifies the geometrical hydraulic and chemical parameters determining such karst processes if the lengths of the enlarging channels are small but hydraulic heads are high as is the case for artificial hydraulic structures such as dams it is the widening at the entrance of the flow path which determines the enlargement of the conduit within the lifetime of the dam this can cause serious water losses this can also be explained by mathematical analysis of simplified approximations which yield an analytical threshold condition from which the safety of a dam can be judged thus in both cases the dynamic processes of karstification are revealed to gain a deeper understanding of the early development of karst systems as a further important result one finds that minimum conditions below which karstification cannot develop do not exist

an experimental study of the kinetics of decompression induced crystallization in silicic melt 1 experiments were conducted to study the temporal evolution of feldspar crystallization kinetics during isothermal decompression pinatubo dacite was held at 780 c 220 mpa fo2 nno 2 h2o saturated conditions for an equilibration period decompressed to final pressures pf ranging from 175 to 5 mpa and then held for 0 3 931 hours according to the plagioclase liquidus curve in ph2o t space for the relevant melt composition these decompressions impose effective undercoolings teff of 34 266 c growth of preexisting phenocrysts and newly formed sparse microlites dominate crystallization at 75 pf 150 mpa teff 34 93 c and equilibrium crystal modes are achieved in 168 hours microlite nucleation is the dominant transformation process for 10 pf 50 mpa teff 125 241 c and chemical equilibrium is not attained by 168 hours under these conditions slow steady decompressions typically produced normally zoned euhedral and planar faceted feldspar crystals although anhedral morphologies were produced at very low pf contrary to expectation slowly decompressed samples were usually further from chemical equilibrium than rapidly decompressed samples after similar durations below the initial pressure although counterintuitive these trends are consistent with new constraints on the relative rates of feldspar nucleation and growth controlled by teff and melt viscosity experienced during each decompression path analysis of liquid to solid transformation kinetics using ttt style diagrams shows that crystallization occurs most rapidly at 100 mpa by a crystal growth mechanism the next most efficient crystallization conditions are at 25 mpa in a crystal nucleation dominated regime

sizing up crystals and their melt inclusions a new approach to crystallization studies a correlation between melt inclusion composition and host crystal size has been discovered in a basaltic ash deposit from a volcanic arc setting least evolved melt inclusions featuring high h2o co2 saturation pressures are found in large olivine crystals melt inclusion compositions become more evolved and volatile saturation pressures decrease as host crystal size decreases this trend is interpreted as reflecting crystal nucleation and growth during decompression of a magma saturated with h2o and co2 in general melt inclusion compositions show large incompatible element enrichment and modest major element variation consistent with in situ crystallization crystal size is used to temporally constrain the formation age of melt inclusions and the decompression path of the magma an estimated crystal growth rate of 10 8 cm s 1 yields an initial average magma ascent rate of 4 8 km yr 1 at mid crustal depths at shallower depths the ascent rate was roughly an order of magnitude greater

multiple levels of magma storage during the 1980 summer eruptions of mount st helens wa transitions in eruptive style explosive to effusive sustained to pulsatory are a common aspect of volcanic activity and present a major challenge to volcano monitoring efforts a classic example of such transitions is provided by the activity of mount st helens wa during 1980 where a climactic plinian event on may 18 was followed by subplinian and vulcanian eruptions that became increasing pulsatory with time throughout the summer finally progressing to episodic growth of a lava dome here we use variations in the textures glass compositions and volatile contents of melt inclusions preserved in pyroclasts produced by the summer 1980 eruptions to determine conditions of magma ascent and storage that may have led to observed changes in eruptive activity five different pyroclast types identified in pyroclastic flow and fall deposits produced by eruptions in june 12 july 22 and august 7 1980 provide evidence for multiple levels of magma storage prior to each event highly vesicular clasts have h2o rich 4 5 5 5 wt melt inclusions and lack groundmass microlites or hornblende reaction rims characteristics that require magma storage at p 160 mpa until shortly prior to eruption all other clast types have groundmass microlites ph20 estimated from both h2o bearing melt inclusions and textural constraints provided by decompression experiments suggest pre eruptive storage pressures of 75 40 and 10 mpa the distribution of pyroclast types within and between eruptive deposits can be used to place important constraints on eruption mechanisms fall and flow deposits from june 12 1980 lack highly vesicular microlite free pyroclasts this eruption was also preceded by a shallow intrusion on june 3 as evidenced by a seismic crisis and enhanced so2 emissions our constraints suggest that magma intruded to a depth of 4 km beneath the crater floor fed the june eruption in contrast eruptions of july and august although shorter in duration and smaller in volume erupted deep volatile rich magma if modeled as a simple cylinder these data require a step wise decrease in effective conduit diameter from 40 50 m in may and june to 8 12 m in july and august the abundance of vesicular intermediate to deep clast types in july and august further suggests that this change was effected by narrowing the shallower part of the conduit perhaps in response to solidification of intruded magma remaining in the shallow system after the june eruption eruptions from july to october were distinctly pulsatory transitioning between subplinian and vulcanian in character as originally suggested by scandone and malone 1985 a growing mismatch between the rate of magma ascent and magma disruption explains the increasingly pulsatory nature of the eruptions through time recent fragmentation experiments spieler et al 2004 suggest this mismatch may have been aided by the multiple levels at which magma was stored and degassed prior to these events

origin and morphology of limestone caves limestone caves form along ground water paths of greatest discharge and solutional aggressiveness flow routes that acquire increasing discharge accelerate in growth while others languish with negligible growth as discharge increases a maximum rate of wall retreat is approached typically about 0 01 0 1 cm yr determined by chemical kinetics but nearly unaffected by further increase in discharge the time required to reach the maximum rate is nearly independent of kinetics and varies directly with flow distance and temperature and inversely with initial fracture width discharge gradient and pco2 most caves require 104 105 yr to reach traversable size their patterns depend on the mode of ground water recharge sinkhole recharge forms branching caves with tributaries that join downstream as higher order passages maze caves form where 1 steep gradients and great undersaturation allow many alternate paths to enlarge at similar rates or 2 discharge or renewal of undersaturation is uniform along many alternate routes flood water can form angular networks in fractured rock anastomotic mazes along low angle partings or sponge work where intergranular pores are dominant diffuse recharge also forms networks and spongework often aided by mixing of chemically different waters ramiform caves with sequential outward branches are formed mainly by rising thermal or h2s rich water dissolution rates in cooling water increase with discharge co2 content temperature and thermal gradient but only at thermal gradients of more than 0 01 c m can normal ground water co2 form caves without the aid of hypogenic acids or mixing artesian flow has no inherent tendency to form maze caves geologic structure and stratigraphy influence cave orientation and extent but alone they do not determine branch work versus maze character

the nature and occurrence of discrete zoning in plagioclase from recently erupted andesitic volcanic rocks montserrat abstract recently erupted rocks from montserrat lesser antilles were found to be coarsely porphyritic including plagioclase magnesio hornblende orthopyroxene titano magnetite and rare quartz phenocrysts zonations within plagioclase show three distinct periods within the evolution of the andesitic magmas initial steady state oscillatory overgrowths an49 54 represent an early period of growth within a confined andesitic magma chamber interaction with an intruding more mafic hotter magma resulted in thick zones of dissolution features that cut through these early growth layers the dissolution zones and crystal fragments are overgrown by thin calcic an86 plagioclase rims a plagioclase growth rate of 10 7cm s suggests that the calcic plagioclase rims were formed in approximately 10 h consistent with the idea that mineral growth may increase magma viscosity inducing conduit plugging and shallow pressurization resulting in cycles of dome inflation eruption and explosive activity thermodynamic modeling of heating and mixing of the andesitic magma with a basaltic liquid produces plagioclase of composition an79 not the observed composition of the late plagioclase an86 we conclude that the final plagioclase grew under non equilibrium conditions as a result of the mixing event

magmatic conditions and magma ascent as indicated by hornblende phase equilibria and reactions in the 1995 2002 soufriere hills magma a study of amphiboles and associated minerals in samples of soufri ere hills andesite erupted from 1995 to 2002 shows significant compositional variations within hornblende phenocrysts a separate set of small pargasitic crystals in the groundmass and two types of reaction rims on the phenocrysts the composition of the amphiboles and coexisting phases defines the thermal history of the erupting magma as many as seven zones 5200 mm wide in the hornblende phenocrysts begin with a sharp increase in mg and si and then change gradually to a more feand al rich hornblende a transition that is consistent with a temperature rise analyses of the hornblende phenocrysts and associated fe ti oxides verify previous conclusions that the pre eruption magma was at 130mpa and 830 10 c but was variably heated before eruption the heating occurred within 30 days of eruption for all magmas erupted based on the width of ti rich rims on titanomagnetite phenocrysts experimental phase equilibria for the andesite confirm that the natural hornblende phenocrysts would be stable between 825 and 855 c at a ph2o of 130mpa and would be even more al rich if crystallized at higher pressure pargasite is not stable in the andesite and its presence along with high an plagioclase microphenocrysts requires mafic magma mingling and hybridization with pre existing andesite experimental melts of the andesite at 130mpa and 830 and 860 c compare well with melt inclusions in quartz and plagioclase respectively reaction rims on a few hornblende crystals in each andesite sample are rich in high ca pyroxene and are produced experimentally by heating the andesite above the stability limit for hornblende decompression induced breakdown rims occur in some samples and the rate of this reaction has been experimentally calibrated for isothermal andesite magma ascent at 830 860 c the average ascent rate of magma during much of the 1995 2002 eruption has been40 02 m s the rate that allows hornblende to erupt free of decompression induced reaction rims

remarkable cyclic ground deformation monitored in real time on montserrat and its use in eruption forecasting telemetered high resolution tiltmeters were installed in montserrat in summer of 1995 in december 1996 and in may 1997 the 1995 installations several km from the soufriere hills vent were too distant to yield useful data however the 1996 and 1997 installations on the crater rim revealed 6 14 h inflation cycles caused by magma pressurization at shallow depths 0 6 km below the base of dome the tilt data correlated with seismicity explosions and pyroclastic flow activity and were used to forecast times of increased volcanic hazard to protect scientific field workers and the general public

a model of the early evolution of karst aquifers in limestone in the dimensions of length and depth a new model of the early evolution of limestone karst aquifers in the dimensions of length and depth is presented in its initial state the aquifer consists of a rock massive with evenly spaced fractures of about 50 mm aperture widths with an hydraulic conductivity of 10 27 ms 21 in addition to this a coarser network of prominent fractures with aperture widths of several 100 mm is also present boundary conditions of constant recharge 450 mm year or constant head from the input of allogenic streams are imposed first the position of the water table in the aquifer is calculated then dissolutional widening during a time step in all the fractures below the water table is found by use of the well known nonlinear dissolution kinetics of limestone this is iterated and the position of the water table as well as the fracture widths are found as a function of time in the case of constant recharge to a karst plateau the water table in any case drops to base level and conduits there propagate from the spring headwards if constant head conditions are valid the position of the water table remains almost stable and conduits propagate along the water table from the input towards the spring there is competition between conduit evolution along prominent fractures and along tight fissures close to the water table in any case under constant head conditions one of these pathways wins and early karst evolution is terminated by a breakthrough event with an explosive increase of the flow through the aquifer until constant head conditions break down depending on the boundary conditions of constant head or constant recharge or a combination of both it is possible to describe models of cave genesis which have been derived from field evidence such as the water table models of swinnerton geol soc am bull 34 1932 662 and rhoades and sinacori j geol 49 1941 785 as well as the four state model by ford and ewers can j earth sci 15 1978 1783 q 2001 elsevier science b v all rights reserved

implications for karst hydrology from 3d geological modeling using the aquifer base gradient approach we use the gradient of the aquifer base to investigate the hydrology of mature shallow karst systems we first present a 3d geological model of the gempen plateau nw switzerland that reveals the geometry of aquifers and aquitards and their displacement at faults then transfer the 3d geological model to a hydrological model the transformation is based on a conceptual karst model approximating subsurface flow in mature shallow karst systems to open surface flow on the top of the uppermost aquitard or aquifer base the gradient of this surface is expected to mainly influence regional groundwater flow patterns we use the hydrological model to delineate spring catchment areas the discharge areas and corresponding catchment areas of the model are compared with the occurrence of springs in the study area and with hydraulic links confirmed by tracer tests we also describe the way in which the hydrological model contributes to identifying flow processes the proposed aquifer base gradient approach enhances vulnerability assessment in mature shallow karst regions by 1 localizing catchment areas as a precondition of source protection strategies and 2 indicating dominant flow processes associated with individual springs

high resolution quantitative imaging of plagioclase composition using accumulated backscattered electron images new constraints on oscillatory zoning oscillatory zoning in plagioclase is investigated at small scale 10 m using accumulated backscattered electron bse images as high resolution imaging method combined with electron microprobe quantitative analysis gray value profiles across these images can be calibrated for an content with a resolution of 0 5 mol an applied to oscillatory zoned crystals this new application of bse imaging allows better characterization of zoning patterns along a profile and quantification of wavelength amplitude and shape of the oscillations we also obtain high resolution information on the morphology of growth zones boundaries this approach allows us to better classify the different types of oscillations and concentric zoning dissolution is more frequent than usually recognized major resorption surfaces crosscut several growth zones irregular 5 10 m saw tooth zones are delimited by faint wavy dissolution surfaces and must be distinguished from small scale oscillations 1 3 m with straight boundaries this suggests at least two mechanisms for the formation of these zoning patterns faint oscillations are probably caused by local kinetic control whereas wavy dissolution surfaces involve magma chamber dynamics

abrupt change in magma liquidus temperature because of volatile loss or magma mixing effects on nucleation crystal growth and thermal history of the magma the liquidus temperature of magma that reaches shallow levels introduction during its ascent may change abruptly as a result of the release of on its way from the source region into the earth s volatiles or through magma mixing or a combination of both crust or even onto the earth s surface magma travelling immediately after this abrupt change of the liquidus temperature through the mantle and crust evolves and one of the occurs a disequilibrium is observed in the melt and here it is shown goals in petrology is to characterize the various processes that the melt rapidly re equilibrates to its thermodynamic equilibrium that occur during this passage of special interest in the a quantitative model for cooling and crystallization of a simple framework of this study are shallow level processes such two component model melt is used to investigate such re equilibration as magma crust interaction magma mixing deprocesses the relaxation time defined as the time required for the volatilization and depressurization that change the geosystem to re equilibrate after varying degrees of liquidus temperature chemical signature of the melt its crystal content its perturbations is found to be 3 or significantly less than the liquidus temperature its flow behaviour and its erupttime it takes to crystallize 40 of the melt regardless of the ability whereas crustal contamination of magma can be amplitude of the perturbation associated with the re equilibration traced through for example trace element and isotope process is an increase in crystal fraction that can easily reach studies e g wilson 1989 and is discussed extensively 10 depending on the amplitude of the perturbation during the in the other papers of this special volume cooling compensation of the liquidus temperature perturbation the temdepressurization and possibly magma mixing strongly perature of the melt remains nearly constant or may even increase slightly depending on the latent heat budget possibly heat of mixing affect the thermal history of magma rising in the mantle and heat absorbed during volatile exsolution which suggests and crust for example any pressure decrease in volatilecrystallization of the melt without cooling saturated systems not uncommon in natural systems especially for more evolved compositions will lead to volatile exsolution and consequent increased liquidus temperature and change in the melting range one of the major consequences of such behaviour is isothermal crystallization which was recognized almost 40 years ago by tuttle bowen 1958 pp 67 and 68 and the

differential weathering in ultramafic rocks of new caledonia the role of infiltration instability abstract ultramafic rocks of new caledonia present extensive pseudokarstic features undulations of the base of the weathering profile fractures enlarged by dissolution dolines possible influence of the infiltrative instability on differential weathering of ultramafic rocks in tropical climate is investigated here starting from the tiebaghi case for which a groundwater model is available infiltration instability is governed by non dimensional numbers i e the damkohler and peclet numbers and by the permeability contrasts between the bedrock and the different layers of the weathering profile these numbers are firstly estimated for the tiebaghi case and secondly a sensitivity study of the weathering style is achieved through numerical modeling computations are firstly carried out without the impervious laterite cover and then the effect of this cover is considered the characteristic time constant for weathering of peridotites is directly estimated at around 7 yrs from the thickness of the weathering front and the fluid velocity the results show that a permeability contrast of at least 100 between the most pervious layer in the weathering front and bedrock and a diffusivity of chemical species lower than 2 5 10 8 m 2 s are required to allow instability the tiebaghi case lies at the limit of instability and dissolution fingers develop in a time lapse of 1 ma however this requires the infiltration of nearly 800 mm of rainfall yearly which is not the case presently the development of dissolution fingers is promoted by any initial pervious zone such as fracture concentration around a faulted zone and the characteristic time for instability development drops to 0 1 0 3 ma extension of these results to other peridotite massifs in the tropical zone submitted to different temperatures and rainfalls is finally discussed

groundmass crystallization of mount st helens dacite 1980 1986 a tool for interpreting shallow magmatic processes the 1980 1986 eruption of mount st helens volcano provides an unprecedented opportunity to observe the evolution of a silicic magma system over a short time scale groundmass plagioclase size measurements are coupled with measured changes in matrix glass plagioclase and fe ti oxide chemistry to document increasing groundmass crystallinity and thus to better constrain proposed physical models of the post may 18 1980 magmatic reservoir measurements of plagioclase microlite and microphenocryst sizes demonstrate that relatively rapid growth approximately 10 9 cm s of groundmass plagioclase occurred immediately subsequent to may 18 relatively rapid plagioclase growth continued through the end of 1980 at an average rate of 3x10 11 cm s plagioclase growth rates then decreased to 1x10 11 cm s through 1986 changes in groundmass crystallinity are reflected in changes in both matrix glass and plagioclase microphenocryst rim chemistry although the matrix glass composition appears to have remained approximately constant from 1981 1986 after a rapid compositional change from may 18 until the end of 1980 plagioclase microphenocrysts show increasingly more complex zoning patterns with time microphenocryst core compositions are commonly positively correlated with crystal size both of these observations indicate continuous groundmass plagioclase growth through 1986 magmatic temperatures estimated from fe ti oxide pairs are approximately constant through 1981 at eruption temperatures of 930 c and at log fo2 of 10 8 by 1985 1986 oxide temperatures decreased to 870 c chemical and textural changes can be explained by 1 rapid degassing and crystallization in response to the intrusion of magma into a shallow 4 5 km reservoir toward the end of the may 18 1980 eruption 2 continued crystallization at a much reduced rate through 1986 due to slow cooling of the shallow magma reservoir growth rates and consequent chemical changes appear to decrease at the end of 1980 this is coincident with the change in eruption style from explosive eruptions sometimes followed by dome growth to solely extrusive dome building events and can be explained by the expected viscosity increase of both degassing and increasing crystallinity the model of twostage crystallization of magma in a shallow reservoir is consistent with conclusions from gas studies casadevall et al 1983 gerlach and casadevall 1986 a b patterns of crater deformation chadwkck et al 1988 and post 1980 seismicity endo et al 1990 although it does not explain the experimental data of hill and rutherford 1989 on the growth rate of amphibole reaction rims textural measurements on mount st helens dacite can also be used to evaluate crystallization kinetics in silicic magmas systems for which experimental data is almost non existent plagioclase growth rates are 5 10 times slower than estimated plagioclase growth rates in basaltic systems a result consistent with the higher viscosity of a more silicic melt furthermore patterns of textural change both average crystal size and number density are similar to those observed during the 1984 mauna loa eruption by lipman and banks 1987 suggesting that the only modification to the crystallization behavior of plagioclase required in extrapolation from basaltic systems is a moderate decrease in rates such that the rate of crystallization scales with the melt viscosity

magma emplacement and remobilization timescales beneath montserrat insights from sr and ba zonation in plagioclase phenocrysts received november 22 2001 accepted december 12 2002since 1995 the soufri ere hills volcano on montserrat lesserantilles island arc has erupted crystal rich andesite magmathat is geochemically very similar to the volcanic products of atleast the last 174 3kyr 1s nomarski images of plagio clase phenocrysts from six andesites erupted between 151 4ka 1s and

vapor transfer prior to the october 2004 eruption of mount st helens washington dome lavas from the 2004 eruption of mount st helens show elevated li contents in plagioclase phenocrysts at the onset of dome growth in october 2004 these cannot be explained by variations in plagioclase melt partitioning but require elevated li contents in coexisting melt a fact confirmed by measurements of li contents as high as 207 g g in coexisting melt inclusions similar li enrichment has been observed in material erupted prior to and during the climactic may 1980 eruption and is likewise best explained via pre eruptive transfer of an exsolved alkali rich vapor phase derived from deeper within the magma transport system unlike 1980 however high li samples from 2004 show no evidence of excess 210pb 226ra implying that measurable li enrichments may occur despite significant differences in the timing and or extent of magmatic degassing diffusion modeling shows that li enrichment occurred within 1 yr before eruption and that magma remained li enriched until immediately before eruption and cooling this short flux time and the very high li contents in ash produced by phreatomagmatic activity prior to the onset of dome extrusion suggest that vapor transfer and accumulation were associated with initiation of the current eruption overall observation of a high li signature in both 1980 and 2004 dacites indicates that li enrichment may be a relatively common phenomenon and may prove useful for petrologic monitoring of mount st helens and other silicic volcanoes lithium diffusion is also sufficiently rapid to constrain vapor transfer on similar time scales to short lived radionuclides

linking petrology and seismology at an active volcano many active volcanoes exhibit changes in seismicity ground deformation and gas emissions which in some instances arise from magma movement in the crust before eruption an enduring challenge in volcano monitoring is interpreting signs of unrest in terms of the causal subterranean magmatic processes we examined over 300 zoned orthopyroxene crystals from the 1980 1986 eruption of mount st helens that record pulsatory intrusions of new magma and volatiles into an existing larger reservoir before the eruption occurred diffusion chronometry applied to orthopyroxene crystal rims shows that episodes of magma intrusion correlate temporally with recorded seismicity providing evidence that some seismic events are related to magma intrusion these time scales are commensurate with monitoring signals at restless volcanoes thus improving our ability to forecast volcanic eruptions by using petrology

karst aquifer evolution in fractured porous rocks the evolution of flow in a fractured porous karst aquifer is studied by means of the finite element method on a two dimensional mesh of irregularly spaced nodal points flow within the karst aquifer is driven by surface recharge from the entire region simulating a precipitation pattern and is directed toward an entrenched river as a base level during the early phase of karstification both the permeable rock matrix modeled as triangular elements and fractures within the rock matrix modeled as linear elements carry the flow as the fractures are enlarged with time by chemical dissolution within the system calcite carbon dioxide water flow becomes more confined to the fractures this selective enlargement of fractures increases the fracture conductivity by several orders of magnitude during the early phase of karstification thus flow characteristics change from more homogeneous pore controlled flow to strongly heterogeneous fracture controlled flow we study several scenarios for pure limestone aquifers mixed sandstone limestone aquifers and various surface recharge conditions as well as the effect of faulting on the aquifer evolution our results are sensitive to initial fracture width faulting of the region and recharge rate

tof sims and electron microprobe investigations of zoned magmatic orthopyroxenes first results of trace and minor element analysis with implications for diffusion modeling zoned phenocrysts in volcanic rocks potentially provide an archive of magmatic processes as a crystal grows and comes into contact with different melt batches the chemical and textural signature of this journey is recorded within its crystal lattice the timescale of some magmatic processes can be investigated through the relaxation of chemical gradients across crystal growth zones through the application of diffusion modeling techniques one of the current limitations to diffusion modeling is the spatial and analytical resolution of the chemical profile that conventional techniques such as electron probe microanalyzer epma dynamic secondary ion mass spectrometry sims and laser ablation inductively coupled plasma mass spectrometry la icpms can achieve here for the first time we present time of flight tof sims tof sims data for zoning of orthopyroxene crystals from the may 1982 eruption of mount st helens volcano u s a and cross calibrate these data between backscattered electron images and epma tof sims has the advantage of being able to achieve micrometer to nanoscale spatial resolution of major elements as well as analyses of light elements such as li and trace and minor elements na k and ni at concentrations that cannot be achieved by epma provided that convolution overlap effects and polyatomic mass inferences are carefully considered with tof sims analyses we identified zoning of li on a spatial scale ca 5 10 m that would be inaccessible to most other conventional analytical techniques preliminary results indicate that li a fast diffusing element may be introduced to the crystals in the minutes hours or days prior to eruption and may provide insights into pre eruptive magmatic processes thus tof sims has the potential to be a powerful tool for obtaining minor and trace element profiles across compositional interfaces within crystals at high spatial resolution

early development of karst systems 2 turbulent flow a simulation model developed to explore patterns of fracture enlargement within incipient limestone karst aquifers has been extended to turbulent flow in contrast to the highly selective passage enlargement that occurs early in cave network development under laminar flow the transition to turbulent flow results in more general passage enlargement leading to maze networks when initial fractures are large and hydraulic gradients are high these results support previously published hypotheses for the development of maze patterns including formation within structural settings that have created initially large fractures or within flow systems periodically inundated by flooding maze development is also favored under turbulent flow when passages are entirely water filled and where the groundwater flow system is long lived by contrast branched patterns are most common when passages become free surface subterranean streams because depression of the piezometric surface along main passages downcutting along main passages and possible infilling with sediment of side passages limit the sharing of discharge among interconnected fractures or bedding planes that promote maze development

using amphibole phenocrysts to track vapor transfer during magma crystallization and transport an example from mount st helens washington abstract in order to evaluate and further constrain models for volatile movement and vapor enrichment of magma stored at shallow levels amphibole phenocrysts from 2004 2005 mount st helens dacite were analyzed for major and selected trace elements li cu zn mn and ree and li isotopes several recent studies have examined fluid mobile trace element abundances in phencryst phases and melt inclusions as a means of tracking volatile movement within subvolcanic magmatic systems and high li contents in plagioclase phenocrysts from 1980 and 2004 mount st helens dacites have been interpreted as evidence that shallow magma was fluxed by a li bearing vapor phase prior to eruption in amphibole phenocrysts zn and mn behave compatibly correlating to feo and al 2 o 3 and show no systematic change with time in contrast li and cu abundances in amphibole vary by up to 3 orders of magnitude 7 6 1140 g g and 1 7 to 94 g g respectively and do not generally correlate with either major or trace elements however they do correlate moderately well r 2 0 54 95 confidence with each other and show systematic temporal variations that are opposite to those observed for plagioclase precluding a simple 1 step diffusion model for li enrichment we propose a diffusion crystallization multi stage dcms model to explain the temporal variations and co variations of li and cu in early erupted dacite october december 2004 profiles of li isotopes in conjunction with measured 7 li intensities and core to rim increases in li concentration are characteristic of li diffusion into the amphiboles consistent with prior models of plagioclase enrichment in amphiboles from 2005 dacite average li and cu concentrations are high 260 660 g g and 29 45 g g respectively and in contrast to amphiboles from earlier erupted dacite correlate weakly with al 2 o 3 wt amphibole al 2 o 3 concentrations are an indicator of pressure with high al amphiboles crystallizing at higher pressures and we suggest that li and cu are partitioned into a fluid phase during ascent and crystallization of the magma so that amphiboles crystallizing at lower pressure have correspondingly lower li and cu concentrations however low li and cu in amphiboles from the dacite at the start of the eruption also require crystallization from a low li cu bearing melt or residence times long enough for amphiboles to re equilibrate with a li cu depleted melt estimated residence times suggest that amphiboles in early dacite could have been present since the end of the 1980 1986 eruptive episode at mount st helens

the role of dissolution kinetics in the development of karst aquifers in limestone a model simulation of karst evolution to model the development of karst aquifers from primary fissures in limestone rock a numerical model of solutional widening of such fractures by calcite agressive water is suggested the geological setting determines relevant geometrical parameters i e length of the fracture its initial width and the hydraulic gradient driving water from the input to the output to simulate the solutional widening as it proceeds in time the solution rates must be known as a function of concentration c of dissolved calcite they are given as a first order kinetic rate law for c leq k cdot c eq as f 1 alpha 0 c c eq for c k cdot c eq close to equilibrium a fourth order rate law becomes dominant f 4 beta cdot c c eq 4 the parameters alpha 0 beta and k depend on the chemistry of the carbonate system and rock chemistry the saturation concentration c eq with respect to calcite depends on the initial co 2 concentration of the inflowing solution

early development of karst aquifers on percolation networks of fractures in limestone we have modeled flow and dissolution processes within percolation networks representing stochastic primary fracture systems in limestone at the beginning of karstification flow is evenly distributed on all fractures available as the system develops by dissolutional widening of the fractures preferred flow pathways evolve which attract more and more flow until at breakthrough the total flow rate increases dramatically these breakthrough times have been investigated with regard to their dependence on the initial fracture aperture width the dimension of the evolving karst aquifer hydraulic gradients connectivity of the percolation network and the chemical parameters such as higher order rate constants and exponents and equilibrium concentration they exhibit a behavior similar to that of breakthrough times for one dimensional conduits dreybrodt 1996 our results show that the structure of the evolving karst aquifer is determined by the initial geological setting however the final conduits are selected from competing pathways with potential breakthrough times close to each other whereby the details of the distribution of undersaturation with respect to calcite play an important role

timescales of mixing and mobilisation in the bishop tuff magma body perspectives from diffusion chronometry we present two feldspar thermometry and diffusion chronometry from sanidine orthopyroxene and quartz from multiple samples of the bishop tuff california to constrain the temperature stratification within the pre eruptive magma body and the timescales of magma mixing prior to its evacuation two feldspar thermometry yields estimates that agree well with previous fe ti oxide thermometry and gives a 80 c temperature difference between the earlier and later erupted regions of the magma chamber using the thermometry results we model diffusion of ti in quartz and ba and sr in sanidine as well as fe mg interdiffusion in orthopyroxene to yield timescales for the formation of overgrowth rims on these crystal phases diffusion profiles of ti in quartz and fe mg in orthopyroxene both yield timescales of 150 years for the formation of overgrowth rims in contrast both ba and sr diffusion in sanidine yield nominal timescales 1 2 orders of magnitude longer than these two methods the main cause for this discrepancy is inferred to be an incorrect assumption for the initial profile shape for ba and sr diffusion modelling i e growth zoning exists utilising the divergent diffusion behaviour of ba and sr we place constraints on the initial width of the interface and can refine our initial conditions considerably bringing ba and sr data into alignment and yielding timescales closer to 500 years the majority of which are then within uncertainty of timescales modelled from ti diffusion in quartz care must be thus taken when using ba in sanidine geospeedometry in evolved magmatic systems where no other phases or elements are available for comparative diffusion profiling our diffusion modelling reveals piecemeal rejuvenation of the lower parts of the bishop tuff magma chamber at least 500 years prior to eruption timescales from our mineral profiling imply either that diffusion coefficients currently used are uncertain by 1 2 orders of magnitude or that the minerals concerned did not experience a common history despite being extracted from the same single pumice clasts introduction of the magma initiating crystallisation of the contrasting rims on sanidine quartz orthopyroxene and zircon was prolonged and may be a marker of other processes that initiated the bishop tuff eruption rather than the trigger itself

timescales of magmatic processes at ruapehu volcano from diffusion chronometry and their comparison to monitoring data abstract recent eruptions from mt ruapehu have been difficult to predict despite the presence of a multi parametric monitoring network as a result it is necessary to assess precursory signals prior to an eruption and align those to magmatic processes at depth fortuitously scoria from all historical ruapehu eruptions contains pyroxene crystals that are strongly reversely zoned in the form of a thin 2 to 3 m outermost rim these crystals therefore preserved changes in the magmatic system soon before their eruption we used experimentally determined diffusion coefficients to assess the timescales of magma magma interaction and compared those to the monitoring record four of the five eruptions analysed 1969 1971 1977 1995 gave diffusion timescales 3 to 5 months before their eruption with an increased number of crystals recording timescales within 1 month of eruption pyroxene crystals from the 1996 eruption record events that occurred prior to and during the 1995 eruption suggesting that the bulk of the 1996 crystals was derived from the 1995 magma these diffusion timescales do not compare well to a change in any monitoring signal before historical eruptions however an examination of recent seismicity 2005 2013 since a significant upgrade both in number of stations and type of seismometers showed that two phreatic eruptions in 2006 and 2007 were preceded by a seismic swarm from 5 to 15 km depth 3 to 5 months before each eruption consistent with the diffusion timescales based on this correlation deep seismic swarms likely indicate a period of pressurisation in the magmatic system which may lead to gas rich phreatic eruptions

water transfer during magma mixing events insights into crystal mush rejuvenation and melt extraction processes many plutons preserve evidence of magma mixing between hydrous mafic magmas and resident felsic crystal rich mushes to investigate water transfer processes in such systems following thermal equilibration we conducted 24 h experiments to establish the petrological evolution of a water undersaturated 4 wt h 2 o in the interstitial melt quartz bearing dacite crystal mush 0 5 0 8 in crystal fraction intruded by a water saturated 6 wt h 2 o initially crystal free andesite magma at 950 c and 4 kbar 12 km depth our results show isothermal undercooling resulting from a change in liquidus temperatures of the interacting magmas due to their changing water content specifically mafic samples dramatically crystallize during water escape into the felsic end members and consequent increase in liquidus temperature conversely the addition of water to the felsic mush reduces the liquidus temperature leading to an increase in melt fraction the experiments provide insights into how volatiles contribute to crystal mush rejuvenation i e increase of melt fraction however h 2 o diffusion alone is not sufficient to promote melt extraction from short and long lived mushes in the earth s crust

modeling three dimensional karst aquifer evolution using different matrix flow contributions summary we have developed the program package karstaquifer which simulates flow and transport in a three dimensional transient karst aquifer consisting of fractures and matrix elements the fractures can be enlarged by chemical dissolution of calcite increasing the secondary permeability of the karst aquifer boundary conditions for our model setup are guided by published benchmark models for karst aquifer evolution in two dimensions length and width with a 100 m high hydraulic head difference across the model domain responsible for relatively fast evolution of the aquifer we are interested in the effect of the third dimension on the evolution of the karst aquifer especially the effect of matrix flow with a matrix defined either as porous medium or as fine fracture system or both we first discuss our model results using a pseudo 3d setup to be able to directly compare results to the 2d benchmark scenarios published we then discuss real 3d models with a prominent fault located in the central part of the aquifer connecting input and output regions finally we replace the prominent fault with a statistical fracture diameter distribution our results compare well with existing 2d scenarios and the additional third dimension offers new insights into the evolution of karst aquifers especially the role of matrix flow under fixed head boundary conditions in their early phases can be studied in more detail

modelling unsaturated flow in an evolving karst aquifer a two dimensional cross section of a karst aquifer in which chemical dissolution enlarges fractures with time is studied the karst aquifer is recharged by precipitation and drains towards a resurgence the initial aquifer has low conductivities both in the rock matrix and the fracture network and the initial water table is high as the enlargement of fractures by dissolution increases the fracture conductivity the water table drops until it reaches a steady state along the level of the resurgence several parameterisations are discussed for flow in the unsaturated zone above the water table it is shown that different approaches result in similar cave passage patterns with a large water table cave draining the recharge towards the resurgence however flow patterns in the unsaturated zone can be very different for the different parameterisations

cave development in the swabian alb south west germany a numerical perspective summary the formation of phreatic cave conduits in the carbonate aquifer of the swabian alb south west germany is discussed by means of numerical simulations three active cave conduit systems the blautopf cave the aachtopf cave and the wimsener cave have been partially explored by divers and exhibit a continuous conduit flow path with phreatic loops down to 50 m below the average water table these three systems drain catchments between 50 and 280 km2 and largely follow the dip of the jurassic limestone beds we use the numerical model karst karst aquifer simulation tool to explore the possibility of structural control of the conduit evolution we show that both the dip of the bedding and the frequency of major bedding partings is likely to result in numerical drainage paths which are similar to the observed cave systems

early development of karst systems 1 preferential flow path enlargement under laminar flow modeling of flow and solutional processes within networks of interconnected conduits in limestone aquifers indicates that enlargement occurs very selectively during the early stages of karst aquifer development under laminar flow if initial flow paths are uniform in size almost all enlargement occurs along a single set of connected conduits that lie along a direct path between recharge and discharge locations and are aligned along the hydraulic gradient with a sufficiently large variation in initial aperture widths enlargement occurs along the flow path offering the least resistance to flow but since flow rates in laminar flow are proportional to the fourth power of diameter but only linearly proportional to hydraulic gradient the preferentially enlarged set of fractures may follow an indirect path results disfavor earlier suggestions that nonselective cave patterns result from artesian flows at least under laminar flow conditions and that all passages should be competitive until the onset of turbulent flow

influence of aperture variability on dissolutional growth of fissures in karst formations the influence of aperture variability on dissolutional growth of fissures is investigated on the basis of two dimensional numerical simulations the logarithm of the fissure aperture before dissolution begins is modeled as a gaussian stationary isotropic random field the initial phase of dissolutional growth is studied up to the time when turbulent flow first occurs at a point within the fissure the breakthrough time the breakthrough time in variable aperture fissures is smaller than that in uniform fissures and decreases as the coefficient of variation of the aperture field increases in comparing uniform and variable aperture fissures in limestone the breakthrough time with 0 1 is about a factor of 2 smaller than that in a uniform fissure the breakthrough time is reduced by about an order of magnitude with 2 0 the mechanism leading to reduced breakthrough times is the focusing of flow into preferential flow channels which are enlarged at a faster rate than the surrounding regions of slower flow dissolution channels are narrower and more tortuous as increases investigations of the influence of reaction rate reveal that the influence of aperture variability is more pronounced in rapidly dissolving rock in uniform fissures in rapidly dissolving minerals breakthrough times are very long since water becomes saturated with respect to the mineral within a short distance of the entrance to the flow path however in variable aperture fissures breakthrough occurs rapidly because of selective growth along preferential flow channels which progressively capture larger fractions of the total flow these results partly explain why conduits develop rapidly in gypsum although previous one dimensional studies suggest that conduit growth will not occur

a model of early evolution of karst conduits affected by subterranean co2 sources in investigating early karstification of one dimensional conduits by computer models so far one has assumed that the co2 content of the calcite aggressive water stems entirely from the surface subterranean sources of co2 however can rejuvenate the solutional power of water already close to equilibrium with respect to calcite and boost dissolution rates in a first scenario we have investigated the influence of a punctual source of co2 as the most simple case of release of co2 into a karstifiable fracture at some position kl from its entrance of the widening joint with length l k 1 the results show that only a small increase of the pco2 in the solution to about 0 01 atm is sufficient to reduce the breakthrough times to about 0 3 with respect to the case where no co2 is delivered other sources of co2 are due to the metabolic activity of microorganisms the existence of such diverse subterraneous microbial life in karst systems is demonstrated whether situated on the fissure surfaces or free floating in the karst water one basic product of their metabolism is co2 this contributes over the whole flow path to the pco2 of the karst water therefore in a second scenario we assumed a constant rate of co2 input along parts of the fracture as could be delivered by the activity of aerobic bacteria dwelling at its walls such a scenario also applies to an extended diffuse co2 migration from volcanic activity deep underground in this case drastic reductions of the breakthrough time by about one order of magnitude are observed these reductions are enhanced when the fracture aperture width of the initial fracture decreases the physicochemical mechanisms of enhancement of karstification are discussed in detail by considering the evolution of the fracture aperture width and of the dissolution rates in space and time

controls on the surface chemical reactivity of volcanic ash investigated with probe gases increasing recognition that volcanic ash emissions can have significant impacts on the natural and human environment calls for a better understanding of ash chemical reactivity as mediated by its surface characteristics however previous studies of ash surface properties have relied on techniques that lack the sensitivity required to adequately investigate them here we characterise at the molecular monolayer scale the surfaces of ash erupted from eyjafjallajokull tungurahua pinatubo and chaiten volcanoes interrogation of the ash with four probe gases trimethylamine tma n ch3 3 trifluoroacetic acid tfa cf3cooh hydroxylamine ha nh2oh and ozone o3 reveals the abundances of acid base and redox sites on ash surfaces measurements on aluminosilicate glass powders as compositional proxies for the primary constituent of volcanic ash are also conducted we attribute the greater proportion of acidic and oxidised sites on ash relative to glass surfaces evidenced by comparison of tma tfa and ha o3 uptake ratios in part to ash interaction with volcanic gases and condensates e g h2o so2 h2so4 hcl hf during the eruption the strong influence of ash surface processing in the eruption plume and or cloud is further supported by particular abundances of oxidised and reduced sites on the ash samples resulting from specific characteristics of their eruptions of origin intense interaction with water vapour may result in a higher fraction of oxidised sites on ash produced by phreatomagmatic than by magmatic activity this study constitutes the first quantification of ash chemical properties at the molecular monolayer scale and is an important step towards better understanding the factors that govern the role of ash as a chemical agent within atmospheric terrestrial aquatic or biotic systems

karst aquifer evolution in fractured rocks we study the large scale evolution and flow in a fractured karst aquifer by means of a newly developed numerical method a karst aquifer is discretized into a set of irregularly spaced nodal points which are connected to their set of natural neighbors to simulate a network of interconnected conduits in two dimensions the conduits are allowed to enlarge by solutional widening the geometric flexibility of this method along with a simplified model for the dissolution kinetics within the system water carbon dioxide calcite enables us to study both laminar and turbulent flow in a karst aquifer during its early phase of evolution a sensitivity analysis is conducted for parameters such as conduit diameter hydraulic pressure differences and recharge conditions along the surface of the aquifer and shows that passage evolution depends strongly on the recharge condition and the amount of water available under fixed hydraulic head boundary conditions an early single passage system develops under laminar conditions and is transformed into a maze like passage system after the onset of turbulence fixed recharge boundary conditions are more likely to result in a branchwork like passage system although the addition of distributed recharge may lead to a maze like system of secondary passages

the 22 july 2009 total solar eclipse modeling d region ionosphere using narrowband vlf observations we present d region ionospheric response to 22 july 2009 total solar eclipse by modeling 19 8 khz signal from nwc very low frequency vlf navigational transmitter located in the australia nwc vlf signal was received at five stations located in and around eclipse totality path in the indian east asian and pacific regions nwc signal great circle paths to five stations are unique having eclipse coverage from no eclipse to partiality to totality regions and the signal is exclusively confined in the low and equatorial regions eclipse induced modulations in nwc signal have been modeled by using long wave propagation capability code to obtain d region parameters of reflection height h and sharpness factor long wave propagation capability modeling showed an increase in h of about 2 3 km near central line of totality 3 0 km in the region near to totality fringe and 2 4 to 3 0 km in the region under partial eclipse using h and wait ionosphere electron density ne profile at the daytime altitude of 75 km showed a decrease in ne by about 58 at a station near totality central line whereas at totality fringe and in partial eclipse region decrease in the ne was between 63 and 71 with respect to normal time values the eclipse associated variations in the h and ne are less in low latitude region as compared to midlatitude the study contributes to explain observations of wave like signature in the d region during an eclipse and difference in the eclipse effect in the different latitude longitude sectors

looping caves versus water table caves the role of base level changes and recharge variations in cave development abstract the vertical organisation of karst conduit networks has been the focus of speleogenetic studies for more than a century the four state model of ford and ewers 1978 which still is considered as the most general relates the geometry of caves to the frequency of permeable fissures the model suggests that the water table caves are common in areas with high fissure frequency which is often the case in natural settings however in alpine karst systems water table caves are more the exception than the rule alpine speleogenesis is influenced by high uplift valley incision rates and irregular recharge to study the potential role of these processes for speleogenesis in the dimensions of length and depth we apply a simple mathematical model based on coupling of flow dissolution and transport we assume a master conduit draining the water to the spring at a base level incision of the valley triggers evolution of deeper flow pathways which are initially in a proto conduit state the master conduit evolves into a canyon following the valley incision while the deep pathways evolve towards maturity and tend to capture the water from the master conduits two outcomes are possible a deep pathways evolve fast enough to capture all the recharge leaving the master conduit dry or b the canyon reaches the level of deep pathways before these evolve to maturity we introduce the loop to canyon ratio lcr which predicts which of the two outcomes is more likely to occur in certain settings our model is extended to account for transient flow conditions in the case of an undulating master conduit floodwater is stored in troughs after the flood retreat this water seeps through sub vertical fractures soutirages connecting the master conduit with the deep pathways therefore the loops evolve also during the dry season and the lcr is considerably increased although the model is based on several approximations it leads to some important conclusions for vertical organisation of karst conduit networks and stresses the importance of base level changes and transient recharge conditions it therefore gives an explanation of speleogenesis that relies much more on the dynamic nature of water flow than on the static fracture density

strontium diffusion kinetics in plagioclase feldspars abstract a pronounced systematic variation by a factor of 104 in strontium tracer diffusion kinetics has been measured in four feldspar specimens that span the range of plagioclase compositions the experiments were carried out in air using isotopically enriched 86sr and analyzed with an ion microprobe the arrhenius relations for strontium diffusion are plagioclase ab d 0 m 2 s q kj g atom sr temperature range c albite 98 1 05e 279 550 1080 oligoclase 73 7 4e 7 261 750 1100 labradorite 36 1 1e 6 295 800 1300 anorthite 4 5 7e 9 267 900 1300 no difference was found within the measurement uncertainty between these results and those for albite under hydrothermal conditions at one kbar 100 mpa strontium diffusion rates parallel to and normal to the albite twin lamellae are the same there is no effect on the strontium diffusion rate in albite between an oxygen partial pressure of 0 2 bar air and 10 19 bar graphite buffer a relation is developed that permits calculation of the strontium diffusion arrhenius parameters for any normal plagioclase composition the large variation in diffusion rate with composition has a major effect on the ease of strontium isotope exchange at high temperatures between plagioclases and coexisting phases in rocks which may prove useful in determining thermal histories

reflection height of daytime tweek atmospherics during the solar eclipse of 22 july 2009 1 we report multipoint observations of daytime tweek atmospherics during the solar eclipse of 22 july 2009 sixteen and sixty three tweek atmospherics were observed at moshiri and kagoshima japan where the magnitudes of the solar eclipse were 0 458 and 0 966 respectively this was the first observation of tweek atmospherics during a low magnitude eclipse 0 458 the average and standard deviation of the reflection height were 94 9 13 7 km at moshiri and 87 2 12 9 km at kagoshima the reflection height at moshiri was almost the same as that for normal nighttime conditions in july 96 7 12 6 km in spite of the low magnitude of the eclipse the reflection height at kagoshima seems be divided into two parts propagation across the total solar eclipse path and propagation in the partial solar eclipse path during the eclipse we also observed the phase variation in the lf transmitter signals the average change in the phase delay of the lf signals was 109 for the paths that crossed the eclipse path and 27 for the paths that did not cross the eclipse path assuming a normal daytime height for lf waves of 65 km a ray tracing analysis indicates that the variations in phase correspond to a height increase of 5 6 km for the paths across the eclipse and 1 2 km for partial eclipse paths the wide range of estimated tweek reflection heights at kagoshima also suggests a difference in electron density in the lower ionosphere between total and partial solar eclipses

low mid latitude d region ionospheric perturbations associated with 22 july 2009 total solar eclipse wave like signatures inferred from vlf observations we present first report on the periodic wave like signatures wls in the d region ionosphere during 22 july 2009 total solar eclipse using jji japan very low frequency vlf navigational transmitter signal 22 2 khz observations at stations allahabad varanasi and nainital in indian sector busan in korea and suva in fiji the signal amplitude increased on 22 july by about 6 and 7 db at allahabad and varanasi and decreased by about 2 7 3 5 and 0 5 db at nainital busan and suva respectively as compared to 24 july 2009 normal day the increase decrease in the amplitude can be understood in terms of modal interference at the sites of modes converted at the discontinuity created by the eclipse intercepting the different transmitter receiver great circle paths the wavelet analysis shows the presence of wls of period 16 40 min at stations under total eclipse and of period 30 80 min at stations under partial eclipse 85 54 totality with delay times between 50 and 100 min at different stations the intensity of wls was maximum for paths in the partially eclipsed region and minimum in the fully eclipsed region the features of wls on eclipse day seem almost similar to wls observed in the nighttime of normal days e g 24 july 2009 the wls could be generated by sudden cutoff of the photo ionization creating nighttime like conditions in the d region ionosphere and solar eclipse induced gravity waves coming to ionosphere from below and above the present observations shed additional light on the current understanding of gravity waves induced d region ionospheric perturbations

karstification beneath the birs weir in basel switzerland a 3d modeling approach we present a three dimensional model describing the evolution of a gypsum karst aquifer along the birs river near basel in switzerland here a small dam site was built in 1890 to generate hydro electric power after subsidence of a nearby highway geophysical and geological field studies have been carried out and a detailed hydrogeological model has been developed these observations identified a karstified weathered zone as the reason for the subsidence to prevent any further damage remedial construction measures have been carried out we employ our numerical model karstaquifer which simulates the temporal evolution of a karst system by dissolution increasing the porosity in the aquifer we used results from geological and geophysical investigations as a priori information for implementing the initial boundary conditions into our three dimensional numerical model our model accounts for topography precipitation and geology and especially for the anisotropy of the local bedrock it can successfully reproduce the weathered zone in its current horizontal and vertical extent we cm also simulate the possible evolution of the aquifer following a remedial construction phase therefore taken together with the geophysical and geological observations and the groundwater model our three dimensional karst aquifer evolution model enhances the understanding of the development of this heterogeneous karst aquifer system c 2012 elsevier b v all rights reserved hydrogeologie der nordwestschweiz grundwasser

textural and chemical variation in plagioclase phenocrysts from the 1980 eruptions of mount st helens usa this study presents major and trace element chemistry of plagioclase phenocrysts from the 1980 eruptions of mount st helens volcano despite the considerable variation in textures and composition of plagioclase phenocrysts distinct segments have been cross correlated between crystals the variation of sr and ba concentration in the melt as calculated from the concentration in the phenocrysts using partition coefficients suggests the cores and rims crystallised from compositionally different melts offset by the plagioclase crystallisation vector in both of these melts sr and ba are correlated despite the abundance of plagioclase in the 1980 dacites we propose that rapid crystallisation of plagioclase upon magma ascent caused a shift in melt composition towards lower sr and higher ba as documented in the rims of the phenocrysts although the cores of the phenocrysts crystallised at relatively shallow depths they preserve the sr and ba of the deep seated melts as they ascended from a deeper region further magma ascent resulted in microlite nucleation which is responsible for a similar shift to even lower sr concentration as observed in the groundmass of post 18 may 1980 samples

modelling karst vadose zone hydrology and its relevance for paleoclimate reconstruction abstract understanding past climatic changes allows us to better understand how our planet will evolve in the future one important source of information on paleoclimate is the analysis of speleothems that develop in karst caves and conduits due to the dissolution and precipitation of calcite however there are many uncertainties in paleoclimatic reconstruction with speleothems one of them being hydrological variability up to now only few studies have considered the impact of hydrological variability on speleothem formation and composition this review paper will provide an introduction to hydrological processes that have the potential to affect speleothem composition and the hydrological modelling approaches that are able to account for them it presents the current state of knowledge on paleoclimatic reconstruction using speleothems and shows that many important flow and transport processes have not yet been included in the interpretation of these archives mostly due to a lack of field information to parametrize them possible directions of future research efforts therefore include a better exploration of karst vadose zone processes and new approaches to incorporate this information into simulation models finally we foresee the exciting advances in reconstructing paleohydrology using karst hydrology models combined with speleothem growth rate and geochemical composition to understand how past climate changes affected the hydrological cycle and water availability

geochemical precursors to volcanic activity at mount st helens usa the importance of the interplay between degassing and crystallization before and after the eruption of mount st helens washington usa in 1980 is well established here we show that degassing occurred over a period of decades to days before eruptions and that the manner of degassing as deduced from geochemical signatures within the magma was characteristic of the eruptive style trace element lithium and short lived radioactive isotope lead 210 and radium 226 data show that ascending magma stalled within the conduit leading to the accumulation of volatiles and the formation of lead 210 excesses which signals the presence of degassing magma at depth

contrasting plagioclase textures and geochemistry in response to magma dynamics in an intra caldera rhyolite system okataina volcano abstract the changing magmatic dynamics of the rhyolite caldera volcano okataina volcanic centre new zealand is revealed in plagioclase growth histories crystals from the 0 7 ka kaharoa eruption are characterized by resorbed cores displaying a cellular texture of high an 40 zones partially replaced by low an 50 20 elevated an fe mg sr and ti follow the resorption surface and display rimward depletion trends accompanied by ba and ree enrichment the zonation is consistent with fractional crystallization and cooling the cores display wide trace element diversity pointing to crystallization in a variety of melts before transport and mixing into a common magma where the rims grew plagioclase from the 36 ka hauparu eruption display several regrowth zones separated by resorption surfaces which surround small resorbed cores with a spongy cellular texture of variable an content an 40 50 the crystals display step wise regrowth of successively higher an fe mg and ti content consistent with progressive mafic recharge two crystal groups are distinguished by trace element chemistry indicating growth in separate melts and co occurrence via magma mingling for plagioclase in both eruption deposits partition coefficients d estimated from crystal rim groundmass glass analyses produce melt compositions similar to the array of rock and glass compositions erupted and are consistent with the processes of fractional crystallization and recharge however d values estimated from some published formulations based on an content and temperature produce unrealistic melts the contrasting zoning patterns in plagioclase correspond to the evolutionary history of magmatism at okataina emptying of the magma reservoir following caldera eruption at 46 ka reduced barriers to mafic magma ascent this is recorded by the frequent resorption and recharge episodes in hauparu crystals subsequent redevelopment of a more silicic reservoir zone post 26 ka dampened thermal and mass perturbations resulting in simpler growth histories of the kaharoa crystals the plagioclase lack features associated with rapid decompression events that are common in andesite systems this reflects the rapid ascent of the rhyolite magmas and lack of precursory eruptions that could decompressed the system

coupled caal nasi diffusion in plagioclase feldspar experiments and applications to cooling rate speedometry abstract the rate of caal nasi interdiffusion in plagioclase feldspar was determined under 1 atm anhydrous conditions over the temperature range 1400 to 1000 c in calcic plagioclase an80 81 by homogenizing coherent exsolution lamellae the dependence of the average interdiffusion coefficient on temperature is given by the expression d 10 99 cm 2 sec exp 123 4 kcal mol rt t in k this value is for diffusion perpendicular to the 03 1 interface of the lamellae caal nasi interdiffusion is 4 to 5 orders of magnitude slower than oxygen diffusion in the temperature range 1400 to 1200 c and possibly 10 orders of magnitude slower at subsolidus temperatures the large differences in diffusion rates explain the apparent contradiction posed by the plagioclases of large layered intrusions e g the skaergaard which retain delicate ca na compositional zoning profiles on the micron scale but have undergone complete oxygen isotopic exchange with heated meteoric groundwater from the surrounding wall rocks caal nasi diffusion is slow the closure temperature is high within the solidus liquidus interval and ca na zoning is preserved oxygen diffusion is faster the closure temperature is lower 350 400 c and the feldspars exchange oxygen with the low temperature hydrothermal fluids the complex micron scale oscillatory zones in plagioclase can also be used as cooling rate speedometers for volcanic and plutonic plagioclase cooling histories typical of large mafic intrusions e g the stillwater are slow begin at high initial temperatures 1200 c and result in homogenization of oscillatory zones on the scale of 10 microns the oscillatory zones found in the plagioclase of granodioritic plutons are preserved because cooling is initiated at a lower temperature 1000 c limiting diffusion to submicron length scales despite the slow cooling rate of the intrusion

zircon reveals protracted magma storage and recycling beneath mount st helens current data and models for mount st helens volcano washington united states suggest relatively rapid transport from magma genesis to eruption with no evidence for protracted storage or recycling of magmas however we show here that complex zircon age populations extending back hundreds of thousands of years from eruption age indicate that magmas regularly stall in the crust cool and crystallize beneath the volcano and are then rejuvenated and incorporated by hotter young magmas on their way to the surface estimated dissolution times suggest that entrained zircon generally resided in rejuvenating magmas for no more than about a century zircon elemental compositions refl ect the increasing infl uence of mafi c input into the system through time recording growth from hotter less evolved magmas tens of thousands of years prior to the appearance of mafi c magmas at the surface or changes in whole rock geochemistry and petrology and providing a new time correlated record of this evolution independent of the eruption history zircon data thus reveal the history of the hidden long lived intrusive portion of the mount st helens system where melt and crystals are stored for as long as hundreds of thousands of years and interact with fresh infl uxes of magmas that traverse the intrusive reservoir before erupting

karstification of aquifers interspersed with non soluble rocks from basic principles towards case studies abstract we have developed a numerical model able to describe the karstification of aquifers in fractured rocks containing soluble limestone or gypsum and insoluble layers when water is flowing along fractures crossing the soluble layers it is able to dissolve the material there to increase the aperture width of the conduit and consequently to increase the local hydraulic conductivity depending on the thickness and the distribution of these layers the dissolution can be active only for limited periods or during the whole evolution time fractures located in insoluble layers do not change at all we are interested in the integral effect of these local processes and study four simplified scenarios of karstification along a prominent wide conduit crossing a fractured limestone block we keep the initial and the boundary conditions the same for all scenarios and vary only in the amount and the distribution of the soluble material we demonstrate that aquifers in 100 limestone without any insoluble layers develop along areas with high hydraulic conductivities and high hydraulic gradients creating channel like pathways on the other hand aquifers containing soluble layers with limited thickness develop faster and exhibit diffuse patterns determined by the chemical properties of the rock the second part of the paper is a step towards modeling of real karst systems we present the evolution of an aquifer located in the vicinity of a large hydraulic structure all initial and boundary conditions except the amount and the distribution of the soluble rock remain the same for all scenarios as a material example for the bedrock we chose gipskeuper from an aquifer along the birs river in switzerland this rock consists of soluble gypsum layers and insoluble clays and marls with typical layer thickness in the range of millimeters to centimeters the basic processes discussed in the first part of the paper remain valid we demonstrate that large insoluble zones can impair the karstification process and even completely block it while areas with thin soluble layers can provide a preferential pathway and decrease the evolution times considerably finally we show that the evolution of the leakage rates and the head distribution within the aquifer can sometimes reveal misleading information about the stage of karstification and the safeness of the dam our model can be used not only to study simplified geological settings and basic processes but also to address some of the complications arising when modeling real aquifers

plagioclase residence times at two island arc volcanoes kameni islands santorini and soufriere st vincent determined by sr diffusion systematics the diffusive relaxation of trace element profiles in plagioclase phenocrysts may provide important constraints on magma residence times in crustal magma chambers initial trace element profiles in plagioclase phenocrysts are governed by variations in the concentration of a trace element in the melt and by the plagioclase melt partition coefficient trace element diffusion will subsequently act to modify this initial profile and given enough time produce a profile that is in equilibrium with the anorthite variations within the crystal we argue that the trace element partition coefficient da b between two parts a and b of a plagioclase crystal of variable anorthite content is equal to the ratio of their crystal liquid partition coefficients and that the equilibrium profile of the crystal can be calculated the time required to establish diffusive equilibrium is dependent on the wavelength and amplitude of the initial trace element concentration range and on the diffusivity of the trace element in plagioclase strontium plagioclase melt partition coefficients and diffusivities are calculated for a range of magmatic temperatures and plagioclase compositions a one dimensional diffusion model is developed that describes the diffusive destruction of oscillatory trace element zoning with time and allows the calculation of upper limits for plagioclase crystal residence times in a magma reservoir the model is tested using major and trace element concentrations measured along crystal traverses of plagioclase phenocrysts from the kameni island dacites santorini and from the 1979 soufriere andesite st vincent three out of eight plagioclase phenocrysts have sr concentration profiles that are not in diffusive equilibrium for these the diffusion model is employed to calculate maximum crystal residence times from incomplete diffusive equilibration of trace element zoning in plagioclase maximum crystal residence times range from 100 to 450 years this is in good agreement with estimates from crystal size distribution and from ra th disequilibrium studies for the kameni islands for soufriere however such short residence times are incompatible with u th mineral errorchron data that suggest residence times of 40 ka in a thermally buffered magma reservoir to reconcile these apparently different ages we invoke a more complicated magmatic history for soufriere where an initially buffered magma reservoir is disturbed by magma mixing and suffers limited additional crystal fractionation prior to eruption

karst aquifer evolution in a changing water table environment 1 a vertical cross section through a karst aquifer is modeled by means of the finite element method to study the evolution of fractures and flow in the aquifer the karst aquifer receives a constant recharge along the top boundary by precipitation and drains toward a resurgence assumed to be the base level in a valley flow is allowed both in the permeable rock matrix and the fracture network and the fractures are enlarged with time by chemical dissolution hence during the early evolution of the karst aquifer the conductivity increases over several orders of magnitude and the initially high water table drops to a steady state base level niveau as a consequence fractures above the final water table change from phreatic to vadose flow conditions a systematic parameter study is carried out to investigate the aquifer evolution over a wide range of parameters such as recharge rate initial fracture width and density and initial calcium concentration the numerical models cover a wide range of drainage patterns from phreatic water table caves to deep bathyphreatic caves to vadose river caves the models suggest that a single theoretical approach is capable of explaining most common cave passage patterns

alkali diffusion in plagioclase feldspar tracer diffusion kinetics at 1 atm pressure under dry conditions using 6li 41k and 87rb in four plagioclase feldspars have been determined diffusion profiles were measured using an ion microprobe sims the arrhenius parameters and 2 uncertainties for li k and rb respectively in albite are pre exponential factor log do 3 8 1 0 3 4 1 4 and 5 8 3 8 in m2 s and activation energies 146 14 296 30 and 283 85 kj mol the diffusion rate of k in albite at 700 c and 100 mpa water pressure equals that at 1 atm dry suggesting that diffusion of k is not dependent on water fugacity between 0 004 and 100 mpa the k diffusion rate depends on plagioclase anorthite content and is approximately 20 times slower in labradorite than albite li diffusion rates in albite and anorthite are identical a linear relation between log d for the alkalis measured and their ionic radius squared permits an estimate of cs diffusion kinetics diffusion rates are isotropic or nearly so in albite

an eruption chronometer based on experimentally determined h li and h na diffusion in quartz applied to the bishop tuff abstract the diffusion of hydrogen in natural hydrothermal quartz crystals was studied between 657 956 c at atmospheric pressure and various oxygen fugacity f o 2 conditions single crystals of oh bearing quartz were dehydrated in the presence of li or na enriched powders to induce li h or na h exchange with the resulting diffusion profiles measured by both fourier transform infrared ftir spectroscopy and laser ablation inductively coupled plasma mass spectrometry la icp ms diffusion parallel to 0001 i e the crystallographic c axis is described by log 10 d m 2 s 1 6 5 0 3 100 4 5 2 kj mol 1 2 303 rt where log10d is the base 10 logarithm of the diffusion coefficient r is the gas constant and t is the temperature in kelvins and uncertainties are 1 diffusion is not affected by f o 2 in this system diffusion perpendicular to 0001 is consistently slower but quantitative constraints cannot be obtained from our data given experimental limitations this diffusivity is primarily associated with h li or h na na li exchange where the h and li are charge balanced by tetrahedrally coordinated al3 a faster mechanism may also exist where the monovalent cations are charge balanced by excess oxygen the final defect population as imaged by ftir spectroscopy and la icp ms likely results from a combination of diffusion and inter site rearrangement of the monovalent cations regardless of such complexities the determined arrhenius relationship should be applicable for natural volcanic quartz crystals from the bishop tuff california wherein h is associated with al3 and h loss from quartz preceding and or accompanying the eruption is charge balanced by li gain without al movement li and h profiles from an example quartz crystal suggest that it experienced eruption cooling timescales of just 16 minutes to 2 4 hours showing the considerable promise of using frozen h diffusion profiles in quartz to extract timescales and thus elucidate the last moments of such explosive silicic eruptions

dynamic plumbing system beneath volcanoes revealed by kinetic modeling and the connection to monitoring data an example from mt etna abstract our ability to monitor volcanoes using seismic signals ground deformation gas fluxes or other ground and satellite based observations as well as our understanding of melt reservoirs that feed eruptions have evolved tremendously in recent years the complex plumbing systems that are thought to feed eruptions are however difficult to relate to the monitoring signals here we show that the record preserved in compositional zoning of erupted minerals may be used to reconstruct sections of the plumbing system kinetic modeling of such zoning can yield information on the residence time of magma in different segments of the plumbing systems this allows a more nuanced evaluation of the link between observed monitoring signals or eruption styles and the magmatic processes and movement of batches of melts at depth the approach is illustrated through a study of the compositional zoning recorded in olivine crystals from the 1991 1993 se flank eruption products of mt etna sicily the zoning patterns in crystals reveal that the plumbing system of the volcano consisted of at least three different magmatic environments between which magma was transported and mixed in the year or two preceding the start of eruption quantification of this history indicates that two main pathways of melt migration and three timescales dominated the dynamics of the system combination of this information with the timing of observation of various monitoring signals allows a reconstruction of the dynamic evolution of this section of the plumbing system during the early stages of the 1991 1993 eruption it is seen for example how the migration of melt through the same sections of the plumbing system can cause pre eruptive triggering enhance strombolian activity and through the ensuing eruption cleanse and flush the plumbing system different kinds of mixing occur simultaneously at different sections of the plumbing system on different timescales a few days up to two years

the effect of crystal plastic deformation on isotope and trace element distribution in zircon combined bse cl ebsd feg empa and nanosims study plastically deformed zircon grains from granulite facies ivrea verbano zone southern alps italy and amphibolite facies tauern window eastern alps austria shear zones have been investigated the main focus was on the effects of crystal plastic deformation on the distribution of trace elements and their isotopes zircon grains reveal crystal plastic deformation patterns in form of i gradual bending of the lattice high density of free dislocations ii highly deformed margins revealing a combination of low and high angle boundaries and gradual bending of the lattice and iii a low angle boundary lab network chemical and isotopic maps and profiles show that trace elements in zircon are re distributed in all plastically deformed domains changes in trace element composition along labs are sometimes revealed by brighter cl and darker bse signal labs and domains of high free dislocation density have depletion in u y yb and enrichment in ce la and nd while ti and p are either enriched depleted or remain unaffected and hf demonstrates stability y and yb are decreased in concentration across labs and have oscillating concentration in domains of high free dislocation density our observations confirm that crystal plastically deformed domains in zircon act as effective pathways for trace cations the pb isotopic system is disturbed by crystal plastic deformation microstructures as indicated by relative 207 pb 206 pb ages showing significant discordance in plastically deformed zircon domains in deformed domains a positive correlation between dislocation density and the degree of isotopic age distortion is observed fractured or porous domains and domains with high density of sub grain boundaries are enriched in common pb from the matrix and thus show significantly older relative 207 pb 206 pb ages than pristine domains in contrast pb loss occurs in domains with high free dislocation density at a distance of 5 10 m from the grain boundary caused by out diffusion of radiogenic pb this study adds to a growing database on the consequences of crystal plastic deformation for trace elements and isotopic systems in zircon we provide additional evidence that such deformation cannot be neglected and may have important implications for zircon geochronology and geochemistry

hornblende dehydration reactions during magma ascent at soufriere hills volcano montserrat hornblende phenocrysts in recent andesites of the soufriere hills volcano display reaction rims of microcrystalline plagioclase pyroxene fe oxides and interstitial glass formed by decompression during magma ascent mass balance calculations give the following reactions with mineral proportions in agreement with modal abundances begin aligned 100 0 text hbl to 49 8 text cpx 27 6 text opx 18 2 text plag 4 5 text ti mag 100 0 text hbl to 53 9 text cpx 24 4 text opx 18 1 text plag 1 9 text ilm 1 7 text mag end aligned these reactions require an open chemical system with exchange of selected components with surrounding melt volatiles tio2 and alkalis are expelled and sio2 and feot are consumed matrix glasses fall into two compositional groups glasses in pumice are relatively rich in cao and poor in k2o and na2o compared to glasses in dome samples the former glasses formed by moderate amounts of groundmass crystallisation of plagioclase associated with rapid magma ascent in explosive eruptions the later glasses evolved in response to hornblende breakdown groundmass crystallisation and mixing of melts from different levels during slow magma ascent and extended residence time in the dome interstitial glass compositions in reaction rims reflect the compositions of the surrounding matrix glasses but show variable compositional differences mostly consistent with the proposed open system reactions

d region ionosphere response to the total solar eclipse of 22 july 2009 deduced from elf vlf tweek observations in the indian sector 1 observations of tweeks with higher harmonics n 1 at low latitude stations allahabad and nainital in the indian sector during the total solar eclipse on 22 july 2009 are presented allahabad and nainital stations were in 100 and 85 of the totality paths observations suggest that about 30 40 obscuration of solar disc can lead to the tweeks occurrence which otherwise occur only in nighttime a total of 148 tweeks at allahabad and 20 tweeks at nainital were recorded with some of them up to 3rd harmonics the world wide lightning location network data indicated that tweeks observed were generated by lightning s located in the partial eclipse area of asia oceania region the changes in d region ionospheric vlf reflection height and electron density 22 23 cm 3 during eclipse have been estimated from the first cut off frequency of the tweeks the reflection height increased from 89 km from the first occurrence of tweek to about 91 92 km at the totality and then decreased to 87 km at the end of the eclipse suggesting a change of about 5 km in the reflection height during eclipse the reflection heights are lower by 2 3 km as compared to normal nighttime tweek reflection heights the above increase in the reflection height indicate that the partial nighttime condition is created during eclipse as the main d region ionizing radiation lyman is blocked but solar soft x ray and euv radiations originating from the limb solar corona are not totally blocked which produce some of ionization in the d region

minimum hydrochemical conditions allowing limestone cave development early theoretical investigations into initiation of limestone cave development suggested that water entering small fractures approaches saturation within a short distance and thus appeared to be unable to produce much further enlargement of these fractures the answer to this problem seems to be white s 1977 kinetic trigger idea emphasizing the precipitous drop in dissolution rates as equilibrium is approached however minimum conditions of flow rate passage geometry and initial co2 concentration may exist below which the waters will so nearly achieve saturation that caves will be unable to develop modeling results indicate that under geologically reasonable pco2 and head gradient values the minimum initial aperture widths in which caves will develop is of the order of 100 m initial apertures wider than about 500 m will form passages very easily even under low head gradients there will thus be strong differential selection among initial flow paths with regard to cavern passage development

evaluation of the effects of 3d diffusion crystal geometry and initial conditions on retrieved time scales from fe mg zoning in natural oriented orthopyroxene crystals abstract volcano petrologists and geochemists increasingly use time scale determinations of magmatic processes from modeling the chemical zoning patterns in crystals most determinations are done using one dimensional traverses across a two dimensional crystal section however crystals are three dimensional objects with complex shapes and diffusion and re equilibration occurs in multiple dimensions given that we can mainly study the crystals in two dimensional petrographic thin sections the determined time scales could be in error if multiple dimensional and geometrical effects are not identified and accounted for here we report the results of a numerical study where we investigate the role of multiple dimensions geometry and initial conditions of fe mg diffusion in an orthopyroxene crystal with the view towards proper determinations of time scales from modeling natural crystals we found that merging diffusion fronts i e diffusion from multiple directions causes additional diffusion that has the greatest influence close to the crystal s corners i e where two crystal faces meet and with longer times the affected area widens we also found that the one dimensional traverses that can lead to the most accurate calculated time scales from natural crystals are along the b crystallographic axis on the ab plane when model inputs concentration and zoning geometry are taken as measured rather than inferred from other observations more specifically accurate time scales are obtained if the compositional traverses are highly symmetrical and contain a concentration plateau measured through the crystal center on the other hand for two dimensional models the ab and ac planes are better suited if the initial pre diffusion concentration and zoning geometry inputs are known or can be estimated although these are a priory unknown and thus may be difficult to use in practical terms we also found that under certain conditions a combined one dimensional and two dimensional model performed on the ab section can reveal the initial pre diffusional concentration and thus offer a unique opportunity to recover lost petrologic information the influence of three dimensional diffusion on the one dimensional two dimensional model estimates is the combined result of the crystal shape in particular the presence of facets and somewhat of the aspect ratio our study focuses on fe mg in orthopyroxene but many of the effects we report are also applicable to other minerals and elements

chronometry and speedometry of magmatic processes using chemical diffusion in olivine plagioclase and pyroxenes the magmatic processes that fuel volcanism crustal growth ore formation and discharge of volcanic gases and aerosols to the atmosphere occur across a range of timescales from millions of years to just a few seconds for example the production of new oceanic crust at mid ocean ridges is a near continuous process that can operate in any one ocean basin on timescales of more than 100 m y however the driving force for such processes is the spreading of the ocean plates that happens on a cm yr timescale at the other end of the spectrum explosive volcanic eruptions involve the ascent and fragmentation of magma at velocities of the order of 100 m s such that the journey from a magma chamber to an ash cloud may take place in a matter of minutes in this case the driving force is the rapid expansion of magmatic gas in response to changes in pressure at intermediate timescales magmatic processes may give rise to hydrothermal ore deposits on timescales of less than a million years for an individual deposit while growth of giant granite batholiths may require piecemeal assembly of magma batches on timescales of a few million years although each of these processes has a characteristic time averaged timescale on which it operates this is typically the end result of one or more natural processes that operate on much shorter timescales for example mid ocean ridges do not extrude magma continuously onto the ocean floor mineralising fluids do not discharge continuously through the shallow crust and granitic magmas do not dribble continuously into evolving batholithic chambers in some cases it is the long term timescales that are important for example the spreading rate of ocean basins in others it is the short term timescales that are important for example the episodic growth of lava domes at active volcanoes although

geochemical variations in late stage growth of volcanic phenocrysts revealed by sims depth profiling in the petrologic and geochemical study of volcanic rocks microlites have become an important tool with which to determine magma decompression rate and ascent path prior to eruption however studies in experimental petrology and kinetic modeling indicate that growth of pre existing phenocrysts will occur over a much wider range of decompression induced undercoolings than microlite nucleation consequently we have developed a method using secondary ion mass spectrometry sims depth profiling to measure geochemical trends recorded during the final stage of phenocryst growth to test and demonstrate the new method we examined explosive and effusive eruptive products collected from soufriere hills volcano montserrat plagioclase feldspar crystals were removed from clasts of pyroclastic deposits phenocrysts were individually selected on the basis of euhedral morphology and a relatively homogeneous distribution of surface contamination such as volcanic glass crystals were cleaned embedded in in and analyzed by sims in depth profiling mode we used an o 2 primary ion beam which provides a faster sputtering rate than the typically utilized o primary beam a normal incidence electron gun is used for charge compensation ten isotopes were examined over 2 10 h periods and the resulting crater depth was determined data show variable trends in an k and fe that we interpret to represent late stage physical variations within the magma prior to eruption the continuous chronology of geochemical data obtained from the sims analyses presented here provide information with unprecedented 0 1 m resolution allowing researchers to determine physical conduit conditions during magma ascent from the chamber to eruption at the surface

time scales of magmatic processes from modeling the zoning patterns of crystals the advent of polarized light microscopy in the middle of the 19th century allowed mineralogists and petrologists interested in igneous rocks to recognize the widespread occurrence of fine scale heterogeneities in the optical properties of minerals e g see young 2003 for details the interpretation of mineral zoning patterns as archives of magmatic processes has been with us for some time e g larsen et al 1938 tomkeieff 1939 the development of the electron microprobe in the 1960 s allowed mineral zoning profiles to be quantitatively analyzed and modeled e g bottinga et al 1966 moore and evans 1967 enhanced textural observations permitted recognition of many kinds of detailed structures during the growth and dissolution of magmatic minerals fig 1 e g anderson 1983 pearce and kolisnik 1990 and these processes were also explored using experimental and numerical models e g albarede and bottinga 1972 lofgren 1972 kirkpatrick et al 1976 loomis 1982 major element zoning patterns are routinely measured and with the arrival of the ion microprobe the identification of heterogeneous distribution of trace elements opened the window for more realistic and sophisticated scenarios and models fig 1 e g kohn et al 1989 blundy and shimizu 1991 singer et al 1995 we now measure abundances of naturally occurring isotopes at the scale of tens of micrometers e g davidson et al 2007a ramos and tepley 2008 and this allows in situ dating of crystals e g cooper and reid 2008 figure 1 a nomarski dic image of a plagioclase crystal from a gabbroic xenolith of volcan san pedro costa et al 2002 the crystal shows a well defined core and a rim separated by an oscillatory zoned interval ion microprobe analysis pits and the trace of the electron microprobe traverse between the pits are evident b major

bang month scale eruption triggering at santorini volcano the time lag between intrusion of fresh hot magma and an ensuing eruption is of critical importance in both understanding the triggering and mitigating the consequences of volcanic eruptions this work looks at material erupted during 1925 28 at the nea kameni volcanic center in santorini greece to determine this time scale by exploiting fe mg diffusion in olivine crystals we constrained the intrusion to eruption time lag to between 3 and 10 weeks these techniques have potential application at many volcanic centers previously erupted material can be used to calibrate records of the short time scale processes common to many volcanic centers

causes and consequences of pressurisation in lava dome eruptions abstract high total and fluid pressures develop in the interior of high viscosity lava domes and in the uppermost parts of the feeding conduit system as a consequence of degassing two effects are recognised and are modelled quantitatively first large increases in magma viscosity result from degassing during magma ascent strong vertical gradients in viscosity result and large excess pressures and pressure gradients develop at the top of the conduit and in the dome calculations of conduit flow show that almost all the excess pressure drop from the chamber in an andesitic dome eruption occurs during the last several hundred metres of ascent second microlites grow in the melt phase as a consequence of undercooling caused by gas loss rapid microlite growth can cause large excess fluid pressures to develop at shallow levels theoretically closed system microlite crystallization can increase local pressure by a few tens of mpa although build up of pressure will be countered by gas loss through permeable flow and expansion by viscous flow microlite crystallization is most effective in causing excess gas pressures at depths of a few hundred metres in the uppermost parts of the conduit and dome interior some of the major phenomena of lava dome eruptions can be attributed to these pressurisation effects including spurts of growth cycles of dome growth and subsidence sudden onset of violent explosive activity and disintegration of lava during formation of pyroclastic flows the characteristic shallow level long period and hybrid seismicity characteristic of dome eruptions is attributed to the excess fluid pressures which are maintained close to the fracture strength of the dome and wallrock resulting in fluid movement during formation of tensile and shear fractures within the dome and upper conduit

nanoscale characterisation of crystal zoning abstract advances in analytical techniques are fundamental to the enhanced understandings of many geological processes zoned volcanic crystals have been analysed by low 5 kv field emission gun electron probe micro analyser feg epma and nanosims to obtain sub micrometre chemical profiles and compared to time of flight sims tof sims and high 15 20 kv epma profiles plagioclase and orthopyroxene crystals have been analysed by feg epma at accelerating voltages of 5 kv providing a spatial resolution step size of 350 nm the resolution of the lowest energy x ray for orthopyroxene crystals using a 30 nm beam and ca 750 nm for plagioclase crystals which at low voltages are unstable and require a 500 nm defocused beam step sizes are comparable in size to interaction volumes analytical protocols are detailed that permit quantitative major and minor element compositions to be acquired at similar precision and accuracy as traditional epma analyses at 15 20 kv nanosims analysis of the same crystals provides a greater spatial resolution of up to 200 nm and allows the measurement of li also the nanosims profiles however cannot currently be quantified the ability to analyse crystals at sub micrometre scales is demonstrated by the good agreement between nanosims feg epma conventional epma and tof sims data feg epma nanosims and tof sims techniques have broad applications within the earth sciences in petrologic studies for example these methods have the ability to analyse small crystals in experimental charges and provide chemical profiles of crystal zoning at a spatial resolution of ca 200 300 nm such profiles are important in crystal forensics and diffusion chronometry studies the implications for the latter application are that timescales of volcanic processes that occur in the days years immediately prior to the eruption can now be studied

short magmatic residence times of quartz phenocrysts in patagonian rhyolites associated with gondwana breakup a key parameter in the study of magma evolution is the time scale on which magmatic processes occur using nanoscale secondary ion mass spectrometry nanosims sims and cathodoluminescence cl analyses we have measured titanium ti diffusion profiles in quartz phenocrysts from a jurassic rhyolite of the el quemado complex patagonia argentina providing new insights into the time scales of the associated volcanic processes cl imaging of quartz phenocrysts reveals oscillatory magmatic zoning we determined ti concentrations with sims and acquired multiple nanosims profiles across growth zones from core to rim all transects show sharp changes in the ti 48 si 29 ratio which correlate reasonably well with changes in cl intensity diffusion modeling of ti in quartz yields a surprisingly short time scale for quartz crystallization of 5 6 2 2 yr and a rapid crystal growth rate of 2 3 x 10 12 m s based on the observed quartz textures we suggest that the rhyolite erupted shortly after initial onset of crystallization followed by decompression driven quartz dissolution during fast magma ascent we further argue that the observed oscillatory zoning and the variation of the ti concentration of the quartz phenocryst does not reflect temperature pressure or titanium activity a ti changes of the magmatic system but rather is the result of growth kinetics which has important implications for the ti in quartz thermometry

ascent driven crystallisation of dacite magmas at mount st helens 1980 1986 we introduce a novel scheme that enables natural silicic glasses to be projected into the synthetic system qz ab or h2o in order to relate variations in volcanic glass chemistry to changing pressure p and temperature t conditions in the sub volcanic magma system by this means an important distinction can be made between ascent driven and cooling driven crystallisation under water saturated or undersaturated conditions in samples containing feldspar and a silica phase quartz or tridymite quantitative p t estimates of the conditions of last equilibrium between crystals and melt can be made formation of highly silicic melts i e 77 wt sio2 is a simple consequence of the contraction of the silica phase volume with decreasing pressure such that high silica glasses can only form by crystallisation at low pressure resorption of quartz crystals appears to be a further diagnostic feature of decompression crystallisation groundmass and inclusion glasses in dacites from the 1980 1986 eruption of mount st helens volcano wa span a wide range in sio2 68 80 wt anhydrous the compositions of the least evolved sio2 poor inclusions in amphibole phenocrysts record entrapment of silicic liquids with 5 4 wt water corresponding to a water saturation pressure of 200 mpa at 900 c the compositions of more evolved higher sio2 plagioclase hosted inclusions and groundmass glasses are consistent with extensive ascent driven fractional crystallisation of plagioclase oxide and orthopyroxene phenocrysts and microlites to low pressures during this polybaric crystallisation plagioclase phenocrysts trapped melts with a wide range of dissolved water contents 3 5 5 7 wt magmas erupted during the plinian phase of the 18 may 1980 eruption were derived from a large reservoir at depths of 6 km subsequent magmas ascended to varying depths within the sub volcanic system prior to extraction from glass chemistry and groundmass texture two arrest levels have been identified at depths of 0 5 1 and 2 4 km a single dome sample from february 1983 contains groundmass plagioclase tridymite and quartz testifying to temperatures of at least 885 c at 11 mpa these shallow storage conditions are comparable to those in the cryptodome formed during spring 1980 the corresponding thermal gradient 0 2 c mpa 1 is consistent with near adiabatic magma ascent from 8 km we argue that the crystallisation history of mount st helens dacite magma was largely a consequence of decompression crystallisation of hot magma beyond the point of water saturation this challenges the conventional view that phenocryst crystallisation occurred by cooling in a large magma chamber prior to the 1980 1986 eruption because the crystallisation process is both polybaric and fractional it cannot be simulated directly using isobaric equilibrium crystallisation experiments however calculation of the phase proportions in water saturated 910 15 c experiments by rutherford et al 1985 over the pressure range 220 125 mpa reproduces the crystallisation sequence and phenocryst modes of mount st helens dacites from 18 may 1980 by allowing for the effects of fractional versus equilibrium crystallisation entrained residual source material and small temperature differences between nature and experiment phase compositions can also be matched to the natural samples we conclude that decompression of water saturated magma may be the dominant driving force for crystallisation at many other silicic volcanic centres

partitioning of lithophile trace elements between h 2 o and h 2 o co 2 fluids and topaz rhyolite melt experiments have been conducted with h 2 o and h 2 o co 2 bearing fluids and melts of a cl f and lithophile trace element enriched vitrophyre associated with topaz rhyolite from spor mountain utah the starting material is mildly peraluminous and contains 1 25 wt percent f and 1 500 ppm cl the experiments were conducted with f sub o 2 controlled near ni nio at pressures of 0 5 to 4 kbars and at temperatures of 770 degrees to 950 degrees c fluid melt trace element distribution coefficients d i were calculated for li be b rb sr y zr nb cs ba ce th and u after ion microprobe analysis of starting material and run product glasses the concentration of element i in the fluid was calculated by mass balance and the fluid melt distribution coefficient d i was calculated as ppm by weight of i in fluid ppm by weight of i in melt the partitioning of li rb sr y nb cs and ce between aqueous fluids and melts of topaz rhyolite composition depends strongly on temperature and pressure at 0 5 kbars li rb sr y nb cs and ce concentrate in the fluid at temperatures or 900 degrees c at 2 kbars this same group of lithophile elements except for sr concentrate in the fluid at t or 900 degrees c be b and ba partition in favor of the melt at 0 5 and 2 kbars and at all temperatures of this study in the presence of co 2 free aqueous fluids at 4 kbars and at temperatures of 770 degrees to 950 degrees c all lithophile elements partition in favor of the melt this behavior for lithophile elements mimics that of published data on the partitioning of pb and zn between rhyolitic melts and cl bearing fluids previous studies have demonstrated an equivalent effect of pressure on the distribution of chalcophile trace elements between granitic melts and cl bearing aqueous fluids fluid melt distribution coefficients for the lithophile trace elements are significantly smaller for topaz rhyolite melts in equilibrium with mixed co 2 h 2 o fluids than for topaz rhyolite melts plus co 2 free aqueous fluids there is no evidence for co 2 complexing with the lithophile trace elements at pressures 6 m the data imply that the alkali elements m dissolve into the fluid as mcl 0 complexes and that ce dissolves into the fluid as a cecl 0 3 complex water saturated magmas of topaz rhyolite composition may become differentiated with respect to li cs and rb or ce y and nb if an aqueous fluid phase is evolved and moves through the magma under the influence of a temperature gradient that has a maximum temperature of at least 850 degrees to 900 degrees c

decadal to monthly timescales of magma transfer and reservoir growth at a caldera volcano caldera forming volcanic eruptions are low frequency highimpact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days with devastating effects on local and global scales1 because no such eruption has been monitored during its long build up phase the precursor phenomena are not well understood geophysical signals obtained during recent episodes of unrest at calderas such as yellowstone usa and campi flegrei italy are difficult to interpret and the conditions necessary for large eruptions are poorly constrained2 3 here we present a study of pre eruptive magmatic processes and their timescales using chemically zoned crystals from the minoan caldera formingeruption of santorini volcano greece4 which occurred in the late 1600s bc the results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption5 6 despite the large volume of erupted magma4 40 60 cubic kilometres and the 18 000 year gestation period between the minoan eruption and the previous major eruption most crystals in the minoan magma record processes that occurred less than about 100 years before the eruption recharge of the magma reservoir by large volumes of silicic magma and some mafic magma occurred during the century before eruption and mixing between different silicicmagmabatches was still taking place during the final months final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period with major growth phases immediately before eruption these observations have implications for the monitoring of long dormant but potentially active caldera systems

mg diffusion in anorthite implications for the formation of early solar system planetesimals we have measured the self diffusion coefficients of mg ca and sr in anorthitic plagioclase in order to assess the potential of mg isotopic heterogeneities in early solar system planetesimals to survive thermal metamorphism diffusion couples were constructed from polished single crystals of natural anorthite and synthetic isotopically enriched anorthite glass couples were annealed at atmospheric pressure and 1200 1400 c and isotopic concentration profiles were measured with an ion microprobe the results show that mg diffusion in anorthite is surprisingly fast with d mg being over 2 orders of magnitude greater than d sr this indicates that the diffusion coefficient of mg in anorthite cannot be approximated with that for sr mg diffusion in the c direction is also slightly faster than in the b direction while ca and sr diffusion appear to be isotropic the results provide important constraints on the thermochronological history of anorthite bearing mineral assemblages that preserve radiogenic 26 mg excesses in a planetesimal heated by the decay of 26 al the temperature at any point depends on the planetesimal size time of formation thermal conductivity and depth within the planetesimal given sufficient heating 26 mg heterogeneities produced by the in situ decay of 26 al in ca al rich inclusions cais and chondrules will be erased by diffusive equilibration using the self diffusion coefficient for mg in anorthite measured in this study we show that the common occurrence of 26 mg excesses in these inclusions requires that they must be stored in small 15 km bodies or the outermost rims of larger bodies for the first 1 2 million years of the solar system s history for early formed bodies larger than 15 km most of the mass will have been heated sufficiently for any radiogenic 26 mg to have been diffusively homogenized in the mg rich planetary environment

using the continuum approach to model unsaturated flow in fractured rock the appropriateness of using the continuum approach for simulations of unsaturated flow through fractured rock is examined in a numerical study of water seepage into an underground opening a continuum model is calibrated against data generated with a high resolution model that created discrete flow and seepage behavior probabilistic predictions of injection data and seepage rates are then compared to the values from the discrete model the study shows that reasonable results can be obtained with a calibrated continuum model even for fractured systems in which the underlying flow processes are discrete calibration is a crucial step in this approach because it yields effective model related and process specific parameters the impact of discretization on the estimated parameters is discussed prediction uncertainty is evaluated by means of monte carlo simulations including both the impact of parameter uncertainties and the effect of local heterogeneity in this paper the advantages and limitations of the continuum approach are discussed from a practical perspective which includes a critical examination of project objectives data needs robustness of assumptions and prediction uncertainty

petrologic evidence for pre eruptive pressure temperature conditions and recent reheating of andesitic magma erupting at the soufriere hills volcano montserrat w i the recent eruption of the soufriere hills volcano in montserrat july 1995 to present september 1997 has produced an andesitic dome sio 2 59 61 wt the eruption has been caused by invasion of mafic magma into a preexisting andesitic magma storage region p 130 mpa 5 km depth the composition of the andesite has remained essentially constant throughout the eruption but heating by the mafic magma increased the andesite temperature from 830 c to 880 c prior to being heated the stable mineral assemblage in the andesite was plagioclase amphibole orthopyroxene titanomagnetite ilmenite quartz the rise in temperature from 830 c to 880 c fo 2 1 log unit above nno has caused quartz to become unstable and has also caused changes in silicate and fe ti oxide mineral compositions the andesitic magma is likely saturated with an h 2 o rich vapor phase in the upper part of the magma storage region melt h 2 o content is 4 7 wt

diffusion coupling between trace and major elements and a model for calculation of magma residence times using plagioclase residence times of plagioclase crystals in magma reservoirs can be determined by modeling the compositional zoning of trace elements in these crystals we present a formulation to model diffusion of trace elements in plagioclase paying special attention to certain thermodynamic and kinetic aspects in particular we account for the compositional dependence on anorthite content of the chemical potential and diffusion coefficients of trace elements e g mg the choice of suitable boundary conditions and potential effects of diffusion in more than one dimension we show that contrary to intuition diffusive fluxes of trace elements may be coupled to major element concentration gradients and ignoring such coupling can lead to incorrect estimates of timescales we illustrate application of the model using plagioclase crystals from a suite of gabbroic xenoliths from a holocene dacitic lava flow of volcan san pedro chilean andes 36 s the inferred timescale for metasomatism of the xenoliths by evolved liquids is on the order of 100 30 to 148 yr and serves to illustrate how trace element zoning in plagioclase provides a window into timescales of magmatic processes inaccessible by isotopic or other methods

high resolution la icp ms trace element mapping of igneous minerals in search of magma histories we report experiments on optimisation of la icp ms mapping as a tool for visualising and quantifying internal structure of trace element concentration in igneous minerals the experimental design was refined with maps on clinopyroxene and amphibole macrocrysts mainly antecrysts from a porphyritic lamprophyre in ne spain as well as on a high precision metal wire grid in terms of spatial resolution we demonstrate with scanning electron microscope and white light interferometry that a full ablation removes between 0 4 and 0 7 mu m of material depending on ablation parameters maps were produced with square laser beam spots of 12 and 24 mu m it was found that complexities can be resolved in the sample even though they are smaller than the beam diameter e g 7 10 mu m discontinuities using 12 mu m laser beam resolution in x and y was found to be identical probably reflecting the fast washout of the two volume ablation cell and the short total dwell time of the analyte menu selected due to the excellent stage reproducibility and the limited ablation depth it is feasible to re ablate the identical map area many times employing different instrument parameters or analyte menus on the magmatic crystals la icp ms maps define very sharp compositional zoning in trace elements highlighting complex crystallisation histories where normal magmatic fractionation is not the only process events of mafic recharge are easily recognised as zones enriched in compatible metals such as cr ni or sc further trace element maps reveal complexities in mineral zoning previously undetectable with petrography or major element data these include resorbed primitive cores and oscillatory zoning within apparently homogeneous mineral zones therefore la icp ms mapping opens a new window of opportunity for analysis of magmatic histories the wide combination of instrumental parameters such as laser beam size scan speed and repetition rate make it possible to carry out experiments at different levels of detail we recommend a two step approach to mapping the initial step involves rapid maps to gain an overview of potential complexities in the sample this enhances representativeness of the analysed materials as a large number of crystals and trace elements can be tested in little time subsequently detailed maps can be carried out on areas of interest an additional functionality is to create 1d profiles from 2d maps the potential of the technique to unveil compositional complexities efficiently and at greater detail than traditional microanalysis will help to improve our understanding of processes in the magmatic environment and beyond c 2015 elsevier b v all rights reserved