petrologic determination of ascent rates for the 1995 1997 soufriere hills volcano andesitic magma the recent eruption of the soufriere hills volcano in montserrat july 1995 to present october 1997 has produced a hornblende bearing andesitic lava dome it is possible to petrologically estimate changes in ascent rates of amphibole bearing magmas for certain rates of decompression a breakdown rim of fine grained anhydrous reaction products forms where amphibole is in contact with melt the thickness of the rim varies with ascent rate most of the amphibole phenocrysts in the magma storage region lack breakdown rims about 10 have 200 400 m thick coarse grained breakdown rims that are interpreted to be relicts of a past heating event study of a time series of new dome andesites showed that ascent rate increased from december 1995 0 001 m s to july 1996 0 008 m s while eruptive style remained extrusive ascent rate increased to 0 012 m s in august 1996 and the first major explosive eruption occurred on 17 18 september 1996

global scatterometer observations of the structure of tropical cyclone wind fields abstracta very large database containing 24 years of scatterometer passes is analyzed to investigate the surface wind fields within tropical cyclones the analysis confirms the left right asymmetry of the wind field with the strongest winds directly to the right of the tropical cyclone center northern hemisphere at values greater than 2 times the radius to maximum winds the asymmetry is approximately equal to the storm velocity of forward movement observed wind inflow angle i e storm motion not subtracted is shown to vary both radially and azimuthally within the tropical cyclone the smallest observed wind inflow angles are found in the left front quadrant with the largest values in the right rear quadrant as the velocity of forward movement increases and the central pressure decreases observed inflow angles ahead of the storm decrease and those behind the storm increase in the right rear quadrant the observed inflow angle increases with radius from the storm center in all other quadrants the observed inflow angle is approximately constant as a function of radial distance

advances in fourier transform infrared spectroscopy of natural glasses from sample preparation to data analysis fourier transform infrared spectroscopy ftir is an analytical technique utilized to measure the concentrations of h and c species in volcanic glasses water and co2 are the most abundant volatile species in volcanic systems water is present in magmas in higher concentrations than co2 and is also more soluble at lower pressures and therefore it is the dominant volatile forming bubbles during volcanic eruptions dissolved water affects both phase equilibria and melt physical properties such as density and viscosity therefore water is important for understanding magmatic processes additionally quantitative measurements of different volatile species using ftir can be achieved at high spatial resolution recent developments in analytical equipment such as synchrotron light sources and the development of focal plane array fpa detectors allow higher resolution measurements and the acquisition of concentration maps these new capabilities are being used to characterize spatial gradients or lack thereof around bubbles and other textural features which in turn lead to new insights into the behavior of volcanic feeder systems here practical insights about sample preparation and analysis of the distribution and speciation of volatiles in volcanic glasses using ftir spectroscopy are discussed new advances in the field of ftir analysis produce reliable data at high spatial resolution that can be used to produce datasets on the distribution dissolution and diffusion of volatiles in volcanic materials

an observational study of a coastal barrier jet induced by a landfalling typhoon abstractin this study the structure and evolution of a coastal barrier jet cbj along the east coast of taiwan is documented using operational doppler radars the formation of the cbj was control

effects of terrain and landmass near fujian province of china on the structure and propagation of a long lived rainband in typhoon longwang 2005 a numerical study

the impact of pre existing gas on the ascent of explosively erupted magma most if not all magmas contain gas bubbles at depth before they erupt those bubbles play a crucial role in eruption dynamics by allowing magma to degas which causes the magma to accelerate as it ascends towards the surface there must be a limit to that acceleration however because gas bubbles cannot grow infinitely fast to explore that limit a series of experiments was undertaken to determine the maximum rate at which bubbly high silica rhyolite can decompress rhyolite melt that was hydrated at 150 mpa with 5 3 wt dissolved water and contained 7 to 18 vol bubbles can degas in equilibrium at 875 c when decompressed at rates up to 1 2 mpa s 1 from 150 to 78 mpa and up to 1 8 mpa s 1 when decompressed further to 42 mpa in contrast that same rhyolite cannot degas in equilibrium at 750 c if decompressed faster than 0 015 0 025 mpa s 1 when combined with other published experiments the maximum rate of decompression for equilibrium degassing is found to increase by a factor of ten for every 50 75 c increase in temperature when compared to predictions from conduit flow models that assume equilibrium degassing it is found that such models greatly over estimate the rate at which relatively cold rhyolite can decompress whereas that assumption is largely correct for hot rhyolite and thus for most other magmas all of which are less viscous than rhyolite in addition most bubbles that were 20 30 m in size at high pressure were lost from the population at low pressure that absence suggests that only relatively large vesicles seen in volcanic pumice may be relics of pre eruptive bubbles even if small bubbles were originally present at depth

diffusion of dissolved co2 and cl in hydrous silicic to intermediate magmas the bulk diffusivity of dissolved co sub 2 in obsidian and dacite melts containing 0 11 wt dissolved water at 800 1 100c and 1 gpa was characterized using a sup 14 c radiotracer technique five values were also obtained for cl in melts containing 8 h sub 2 o carbon dioxide diffusivity d sub co sub 2 in nominally dry molten obsidian is similar to previously reported values for a simple melt in the na sub 2 o al sub 2 o sub 3 sio sub 2 system and for dry basalt indicating little effect of melt composition on bulk co sub 2 diffusion three d sub co sub 2 values for hydrous dacite melt are consistent with this lack of a melt composition effect dissolved water however causes an increase of d sub co sub 2 in molten obsidian by about an order of magnitude for each 5 of added water the activation energy of approximately 18 kcal mol is lower by a factor of approximately 3 than that for diffusion in dry basalt in comparison with existing data for diffusion of water in silicic melts at their typical liquidus temperatures d sub co sub 2 is generally lower unless the melt contains more than about 6 dissolved h sub 2 o in which case d sub co sub 2 approximately d sub h sub 2 0 the few data obtained frommore chlorine diffusion reveal the d sub cl is lower by a factor of 5 10 than d sub co sub 2 in the same melt the overall systematics of the new data on dissolved volatile diffusion indicate that diffusional fractionation effects are likely to be most significant in silicic to intermediate magmas having water contents in the 0 4 range less

doppler profiler and radar observations of boundary layer variability during the landfall of tropical storm gabrielle abstract detailed observations of boundary layer structure were acquired on 14 september 2001 prior to and during the landfall of tropical storm gabrielle the mobile integrated profiling system mips and the shared mobile atmospheric research and teaching radar smart r were collocated at the western florida coastline near venice very close to the wind center at landfall prior to landfall the boundary layer was rendered weakly stable by a long period of evaporational cooling and mesoscale downdrafts within extensive stratiform precipitation that started 18 h before landfall the cool air mass was expansive with an area within the 23 c surface isotherm of about 50 000 km2 east northeasterly surface flow transported this cool air off the west coast of florida toward the convergent warm core of the gabrielle and promoted the development of shallow warm and cold fronts that were prominent during the landfall phase airflow properties of the boundary layer around the coastal zone are examined using

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

the boundary layer winds in hurricanes danielle 1998 and isabel 2003 abstract this paper describes the boundary layer wind structure and dynamics of hurricanes danielle 1998 and isabel 2003 based on the analysis of high resolution global positioning system dropwindsonde data and simulation of the flow by a three dimensional boundary layer model produced by kepert and wang the observations show that the hurricane boundary layer has a complex three dimensional structure with large variability over small distances the analysis emphasizes three aspects the degree of gradient wind balance the radially varying depth of the boundary layer and the strength of the near surface wind speed relative to that at a higher level each aspect is compared both with results obtained in a simulation of the individual storm by kepert and wang s model and with theoretical predictions the observations show that the boundary layer depth decreases toward the center of the storm consistent with theoretical arguments the strongest azimuthal winds occur near the top of but still within

petrology of the 1991 1995 eruption at unzen effusion pulsation and groundmass crystallization abstract effusive eruption of dacite magma 2 1 108 m3 during 1991 1995 formed a lava dome at the summit of unzen volcano japan the effusion rate was highest at the beginning 4 0 105 m3 day 4 6 m3 s and decreased roughly with time to almost zero before this pattern was repeated with a second pulse of magma supply the whole rock chemistry of lavas shows significant variation attributable to variations in phenocryst abundance the more mafic the more abundant the phenocrysts the pattern of chemical variation with time shows some difference from that of the effusion rate all phenocrysts in dacite plagioclase hornblende biotite quartz and magnetite show evidence of disequilibrium with melt although a glomerophyric aggregation of phenocrysts suggests coexistence with each other phenocrysts are isotopically heterogeneous from species to species the calculated initial melt composition was rhyodacite and was nearly constant throughout the activity in contrast the bulk phenocryst population is andesite a model explaining the textures and the isotopic heterogeneity is the capture of diorite fragments or xenocrysts by parental rhyodacite magma it is suggested that when effusion rate was high less viscous crystal poor magma exited from the reservoir groundmass glass and plagioclase microlite rims show temporal chemical variations correlating with the effusion rate the higher the effusion rate the more evolved the compositions groundmass crystallinity increased with decreasing effusion rate from 33 to 50 textures in dome lavas suggest that groundmass crystallization had been mostly completed when magma reached the conduit top the fe ti oxide temperature 880 780 c was low when the crystallinity was high micropumice erupted before dome growth provided a sample recording magmatic foam in the conduit porosity of dome lavas was lower at lower effusion rates collapse of foam magma and simultaneous escape of volatiles through the conduit top were probably responsible for the accompanying low frequency earthquakes phenocrysts were broken and the breakdown rims on hornblende phenocrysts were torn off during collapse and successive compaction when effusion waned degassing and the resultant crystallization proceeded more completely so that the magma became too viscous to flow in the conduit top and behaved as a plug resulting in a temporary halt of effusion in turn groundmass crystallization in magma below the plug increased excess pressure in the upper parts of conduit due to slow cooling the plug was scavenged when rising excess pressure overcame its effective strength then the second pulse of magma supply began strong endogenous growth and extrusion of a lava spine in the later stage probably occurred for the same reason

propagation directions of ocean surface waves inside tropical cyclones abstractsurface wave propagation inside tropical cyclones tcs is complicated and multiple wave systems are frequently observed the directional wave spectra acquired by hurricane hunters are analyzed to quantify its azimuthal and radial variations referenced to the hurricane heading the dominate feature in the front half of the tc coverage area is single wave systems propagating toward left and left front multiple wave systems are generally observed in the back and right quarters outside the radius of maximum wind rmw the directional differences and locations of occurrences of multisystem spectra are gaussian distributed the directional differences of the secondary and tertiary wave systems from the primary system are centered around 60 70 the minor systems are more likely on the left hand side of the primary system than on the right hand side by a 3 to 1 ratio the most likely azimuthal location of multisystem spectra is about 210 counterclockwise from the heading in the right front quarter

directional wind wave coupling in fully coupled atmosphere wave ocean models results from cblast hurricane abstractthe extreme high winds intense rainfall large ocean waves and copious sea spray in hurricanes push the surface exchange parameters for temperature water vapor and momentum into untested regimes the coupled boundary layer air sea transfer cblast hurricane program is aimed at developing improved coupling parameterizations using the observations collected during the cblast hurricane field program for the next generation hurricane research prediction models hurricane induced surface waves that determine the surface stress are highly asymmetric which can affect storm structure and intensity significantly much of the stress is supported by waves in the wavelength range of 0 1 10 m which is the unresolved spectral tail in present wave models a directional wind wave coupling method is developed to include effects of directionality of the wind and waves in hurricanes the surface stress vector is calculated using the two dimensional wave spectra from a wave model with an added short wave s

magma ascent rates from amphibole breakdown an experimental study applied to the 1980 1986 mount st helens eruptions recent 1980 1986 mount st helens dacites contain the phenocryst assemblage plagioclase amphibole low ca pyroxene magnetite ilmenite and rare high ca pyroxene which indicates that they all originated from an 8 km deep reservoir at 900 20 c with xh2o 0 67 in fluid according to experimental data iron titanium oxide phenocryst compositions indicate that all post may 18 dacitic magmas erupted at 900 20 c except for the final lava extrusion in october 1986 the magma reservoir may have cooled to 866 c by october 1986 amphiboles in the post may 18 1980 magma contain one or more amphibole populations characterized by reaction rims of different thicknesses the development of the amphibole reaction rims in these rocks is a response to water loss from the coexisting melt during an approximately adiabatic ascent from a deep reservoir constant p and t and isothermal decompression experiments show that during a 900 c constant rate decompression from 8 km to the surface no reaction rim develops on amphibole in 4 days a 10 m rim develops in 10 days and a 35 m rim develops in 20 days these experimental data and histograms of rim widths in 1980 1986 mount st helens dacites show that post may 18 eruptions are composed in large part of magma represented by a population of thin rimmed amphiboles magma which ascended from the deep 8 km reservoir in 6 to 10 days the remainder of each sample consists of magma containing amphiboles with reaction rims ranging from 14 to 60 m magma which apparently spent from 8 to 25 days along the conduit margins before being mixed thoroughly millimeter scale into the erupting magma the mixing in a viscous slowly ascending dacite may be enhanced by its flow through partially crystallized magma emplaced earlier and by the evolution and loss of a large vesicle population the experimental calibration of amphibole reaction rim width versus decompression time yields average ascent velocities for post may 18 dacites of about 15 30 m h for magma represented by the thick rimmed amphiboles and from 35 to 50 m hr for magma represented by the thin rimmed crystals an ascent rate of 66 m h is indicated for the may 18 1980 eruption which contains amphiboles with no reaction rims the volume of endogenous dome growth which preceded extrusion of magma newly derived from the deep source region suggests that the effective conduit volume beneath mount st helens in 1981 1982 was equivalent to a cylinder 8 km long and 8 9 m in radius

numerical study on the development of asymmetric convection and vertical wind shear during tropical cyclone landfall idealized simulations on an f plane of tropical cyclone tc landfall under a quiescent environment in the southern hemisphere are performed to investigate the effects of land sea surface contrast on precipitation in the control simulation with realistic roughness and moisture over land to the south of the tc the simulated vortex moves toward land due to a land induced steering flow the abrupt decrease increase of tangential wind at the surface leads to convergence divergence on the onshore offshore flow side enhanced convergence at the top of the planetary boundary layer is found on both onshore and offshore sides and is caused by advection from the surface and the enhanced offshore radial wind the boundary layer top convergence pattern is consistent with the rainfall distribution vertical wind shear develops during the landfall process associated with the low and upper level asymmetric flows across the model domain the wavenumber 1 like low level asymmetric flow is introduced by an asymmetric geopotential height field that is generated by the large area of frictionally induced convergence on the onshore side and divergence on the offshore side the upper level asymmetric flow is attributed to asymmetric convection and associated diabatic heating after landfall most rainfall is found in the down shear right quadrant which is consistent with previous studies that focused on the effect of environmental shear although the existence of feedback from the vertical wind shear to rainfall remains an open question the relation between maximum rainfall and vertical wind shear is robust especially when the shear magnitude is large after landfall

cooling rates of plinian fall and pyroclastic flow deposits in the bishop tuff inferences from water speciation in quartz hosted glass inclusions cooling rates inferred from water speciation in rhyolitic glass inclusions in quartz phenocrysts from the bishop tuff california vary over more than 5 orders of magnitude from about 10 to 10 4 c s 1 many of the cooling rates are within the previously published experimentally calibrated range of this technique but the slowest rates 10 4 c s 1 are extrapolated such extrapolation suggests cooling rates as low as 10 8 c s 1 0 3 c year 1 for the interiors of thick pyroclastic flow deposits the temperatures at which oh and molecular h2o species would be in equilibrium range from 400 c for glass inclusions from plinian fall deposits to 250 c for the most slowly cooled glassy inclusions from pyroclastic flow deposits notwithstanding appreciable uncertainties cooling rates correlate with depositional process fall vs flow deposition and distance above the cold ground or below overlying hot pyroclastic flow deposits plinian inclusions within 2 5 m of the cold pre bishop ground cooled at 1 10 c s 1 consistent with thermal modeling of small pumice clasts falling through cold air very slow inferred cooling rates for pyroclastic flow deposits 10 6 to 10 8 c s 1 also agree with thermal conduction models faster cooling rates 10 1 to 10 4 c s 1 for inclusions in the lowermost 0 5 m of pyroclastic flow deposits reflect the effect of quenching against the cold ground at blind spring hill east of long valley caldera intermediate cooling rates 10 3 to 10 6 c s 1 are observed in plinian deposits overlain by and partially interbedded with pyroclastic flow deposits indicating that reheating of rapidly cooled plinian inclusions can reset water speciation melt inclusions in pyroclastic flow deposits are quenched to glass only if the deposit is relatively thin or has a relatively low emplacement temperature in relatively thick or hot deposits inclusions may be quenched to glass at the base of the deposit where it is more rapidly cooled by contact with the pre eruption ground

taltson basement gneissic rocks upb and nd isotopic constraints on the basement to the paleoproterozoic taltson magmatic zone northeastern alberta the taltson magmatic zone is a 300 km long northerly trending belt of archean to paleoproterozoic granitic basement gneiss amphibolite supracrustal gneissic rocks and voluminous paleoproterozoi

inferring magma ascent timescales and reconstructing conduit processes in explosive rhyolitic eruptions using diffusive losses of hydrogen from melt inclusions abstract we integrate field observations with geochemical data from quartz hosted melt inclusions to develop a hydrogen diffusion based method to shed light on timescales and conduit processes during the opening stages of two supereruptions we focus on the initial explosive phases first 5 of the total magma volume erupted from 1 the episodic oruanui eruption taupo nz 530 km3 25 4 ka and 2 the continuous bishop tuff eruption long valley 650 km3 0 765 ma quartz hosted melt inclusions for both eruptions exhibit coherent trends for major and trace elements e g al2o3 sio2 nb u rb however in the first three phases of ten in the oruanui eruption there is significant variability in measured h2o values 2 6 5 8 wt particularly in phases 1 and 3 each of which reflects the opening stages of two respective inferred vent sources phase 3 inclusions also record greater scatter in li concentrations in contrast melt inclusions from the first two bishop tuff fall layers yield a narrower range of h2o concentrations 4 0 5 8 with 90 between 4 5 and 5 8 wt we interpret the scatter in measured h2o concentrations to represent changes during slow magma ascent or partial stalling within the conduit at lower pressures using a diffusion model we estimate that 61 of the oruanui melt inclusions experienced modification of original h2o concentrations due to slow ascent in the conduit system prior to eruptive quenching with the longest timescales 5 days mostly in phase 3 inclusions in contrast only 33 of melt inclusions from the initial bishop fall layer f1 experienced diffusive losses from their starting concentrations implying that most magma spent less than a day ascending from the storage region at the eruption onset similarities between the oruanui and the previously studied huckleberry ridge tuff include comparable extents and distribution of diffusive losses seen as h and li scatter and field evidence for episodic activity our observations imply that in these two systems the first erupted magmas rose from reservoirs with low degrees of overpressure and that magma mobilization was controlled by external factors e g tectonics rather than by strong volatile over pressures in contrast the bishop eruption may well have been initiated by overpressure leading to continuous escalating activity

prolonged ascent and episodic venting of discrete magma batches at the onset of the huckleberry ridge supereruption yellowstone abstract how exceedingly large volcanic supereruptions begin provides crucial information on the storage ascent and release of silica rich magma in catastrophic events initial fall deposits of the 2 08 ma 2500 km 3 huckleberry ridge eruption are multiply bedded and in several places contain reworked intervals indicating time breaks in the opening phases of the eruption a 2 5 m section of these fall deposits was sampled at nine levels below the earliest ignimbrite member a at mount everts mammoth wyoming we analyzed major and trace elements and volatiles in quartz hosted melt inclusions mis reentrants res unsealed melt inclusions and associated obsidian pyroclasts thick walled shards to establish quartz crystallization and storage depths and melt compositional groupings systematic relationships between rb and other incompatible elements u cl b indicate 55 fractional crystallization between the least and most evolved glass compositions in contrast h 2 o concentrations in mis show scattered relationships with trace elements and are interpreted to reflect variable loss of h 2 o by diffusion through the quartz host during magma ascent the wide h 2 o variations 1 0 4 7 wt in mis from individual fall horizons imply as much as 14 days of diffusive loss reflecting highly variable and surprisingly slow decompression conditions water and co 2 gradients in reentrants however are consistent with final ascent times of 0 3 1 5 m s similar to those represented by mis that we infer to have experienced little to no diffusive h 2 o loss the wide range of ascent rates for co erupted crystals mirrors that of intermittent explosive activity at mount st helens in summer 1980 and implies that the huckleberry ridge magma body was not strongly overpressured at eruption onset restored entrapment pressures and geochemical data for mis provide evidence for six distinct populations of quartz that originally crystallized in geochemically distinct magma domains the compositions of res and obsidian pyroclasts by comparison show that by the onset of eruption the quartz had been brought together into three discrete magma bodies which we interpret to have been cupolas on the roof of the main magma body these cupolas were erupted sequentially and episodically from separate vents to generate the fall deposits before escalating activity led to generation of voluminous pyroclastic flows and this pattern of activity suggests that tectonic triggering may have destabilized multiple magma bodies supereruptions as large as the huckleberry ridge event may start hesitatingly if the parental magma bodies are not strongly overpressured with small scale episodic activity that is modulated by external controls that may leave no other geological evidence for their presence

the transition of the hurricane frederic boundary layer wind field from the open gulf of mexico to landfall abstract numerous aircraft ship buoy and land nation data were composited with respect to the center of hurricane frederic for two time periods a 24 h period corresponding to the storm s position in the open gulf of mexico on 12 september 1979 and an 8 h period corresponding to the landfall of frederic near 0400 gmt on 13 september comparison of wind analyses for the two periods indicated a rotation of maximum inflow angles from the southeast to northeast quadrants and a strong frictional decrease of wind speed over land them and other features of the landfall analysis were compared with a model landfall study by moss and jones 1978 the landfall composite wind field was compared with the fujita damage vector analysis to determine the damage time interval and mean wind speed range damage vector directions were found to be well correlated with the surface streamlines with the most severe damage being associated with frederic s northern eyewall ten meter level wind speed data over water vo and

supersaturation nucleation and growth of plagioclase a numerical model of decompression induced crystallization supersaturation nucleation and growth of plagioclase sngplag is a numerical model that predicts the nucleation and growth of plagioclase crystals in a decompressing magma as a function of time the model is written in matlab but is available as a standalone compiled program sngplag uses the melts webservice to determine equilibrium plagioclase mode for a user defined magma composition as a function of pressure and temperature user inputs include decompression path the presence and size distributions of antecrysts and phenocrysts and crystal shape at each time step the model evaluates the difference between the calculated crystallinity and equilibrium crystallinity for a given pressure and temperature to determine the degree of supersaturation which then sets plagioclase nucleation and growth rates growth rates are used to grow the existing crystals whereas nucleation adds new crystals sngplag produces results that can be compared to quantitative textures in natural volcanic rocks including total crystallinity microlite number density microlite crystal size distribution the characteristic size of microlite crystals as well as a time series of crystallinity model results are consistent with the established crystallization theory as expected microlite crystallinity increases as decompression rate slows decompression path greatly affects microlite textures for the same average decompression rate single step paths have higher crystallinities and microlite number densities than multi step decompressions which are in turn more crystalline than continuous paths pre existing crystals damp microlite crystallization as these crystals provide a substrate to accommodate crystal growth and thus reduce supersaturation the size distribution and volume fraction of these pre existing crystals determines the magnitude of the damping sngplag predicts that melt composition and temperature also exert important controls higher temperatures and higher silica contents both reduce microlite crystallization in comparison with the previous studies of decompression rate based on microlite crystallization experiments sngplag generally predicts minimum decompression rates that are up to three to four times slower the difference is likely because those studies applied single or multi step decompression experiments to simulate natural magma ascent which may be better represented by continuous decompression pathways or series of continuous decompression intervals punctuated with pauses previous studies also fail to account for the effects of phenocrysts or antecrysts on microlite nucleation and growth

bnd bubble number density decompression rate meter for explosive volcanic eruptions abstract this decade has been witness to substantial progress in the understanding of bubble dynamics and its role in volcanic eruptions a comparison between the results of experiments and a model for bubble nucleation shows that bubble number density bnd can be calculated as a function of decompression rate for given physical properties such as the diffusivity of water in a silicate melt and interfacial tension within an acceptable margin of error conversely in this paper we propose a method hereafter referred to as bnd decompression rate meter to estimate the decompression rate by using bnd data of natural pumice samples from volcanic eruptions as a result of the application of the bnd decompression rate meter to pumice and scoria from explosive eruptions it is found that the decompression rates increase in the range from 10 6 to 10 8 pa s with the eruption column heights these rates are proportional to the 4th power of the eruption column heights and are linear to the discharge rates the absolute values of the estimated decompression rates are very high and cannot be explained by the existing models of conduit flows in order to explain such high rates of decompression and the correlation with discharge rate we propose a possible model according to which the bubble nucleation propagates downward as a rarefaction shock wave in the conduit

constraints on cooling rates and permeabilities of pumice in an explosive eruption jet from colour and magnetic mineralogy abstract in explosive volcanic eruptions vesicular magma droplets produced by fragmentation are propelled into the atmosphere where they are chilled to form pumices the thermal history of droplets and the permeability of their internal bubble networks determine how much they are deformed in the eruption jet and hence what information pumices record about the state of the magma at fragmentation we study these aspects of the minoan plinian eruption of santorini volcano by quantifying the rate of oxidation reactions that took place when air entered the hot magma fragments in our experiments white minoan pumices were heated for minutes to hours between 600 and 850 c either in air or in an atmosphere with an oxygen fugacity at the ni nio buffer pumices were unchanged by heating at ni nio those heated in air often became pink to dark pink depending on heating time and their curie temperatures as determined by magnetic susceptibility measurements increased we use oxidation rates deduced from these experiments in conjunction with calculations of the rate of conductive cooling and of the rate at which air can enter a pumice to constrain the conditions experienced by pumices during the eruption natural minoan pumices less than about 5 cm in radius are white whereas larger ones often have white rims and pink interiors with curie temperatures higher than those of white material we infer that small pumices were cooled before being oxidized and that oxidation of the interiors of large clasts mostly took place during flight at temperatures within a few tens of degrees of magmatic values white rims of large pumices despite being permeable were cooled before oxidation could occur permeability developed in the liquid state but did not develop early enough with respect to cooling or was not large enough to allow extreme oxidation we give measurements of pumice permeabilities that should be close to magmatic values

the mechanism of volcanic eruptions a steady state approach a theory of a volcanic eruption as a steady magma flow from a magma chamber to the surface is described magma is considered as a two component two phase medium and magma flow is steady one dimensional and isothermal mass and momentum exchange between condensed and gaseous phases is assumed to be in equilibrium with nucleation of bubbles as a fast process at small oversaturations three basic flow structures in a conduit are recognized and three resulting types of eruption are described 1 in the discrete gas separation dgs flow melt with discrete gas bubbles erupts this type includes lava eruptions and strombolian activity 2 in the dispersion regime there is continuous eruption of a gas pyroclastic suspension catastrophic explosive eruptions are included in this type 3 here a partly destroyed foam is erupted with permeable structure that allows gas escape near the surface this structure evolves with an increase in permeability and a decrease in the total porosity this type corresponds to lava dome extrusions a criterion dividing dgs flow from the other two regimes is obtained di u n1 3a c0 where u is the magma ascent velocity is magma viscosity n is number of bubble nuclei in a unit mass of magma a is the solubility coefficient for volatiles in magma and c0 is the volatile content the boundary between the dispersion regime and the partly destroyed foam regime depends on u c0 and particle size dp for the dispersion regime the basic governing parameters are magma chamber depth h conduit conductivity b2 b is the characteristic cross dimension of the conduit and excess pressure in the magma chamber instability of the dispersion regime is investigated numerically the dependence of magma discharge rate on the governing parameters is described as a combination of equilibrium surfaces with cusp catastrophes magma chamber depth is a splitting parameter in most cusps and controls the existence of unstable magma flow with sharp regime changes catastrophic rise of eruption intensity is possible if h hcr the critical chamber depth hcr depends approximately linearly on c0 and is about 15 km at c0 0 05 some scenarios of eruption evolution are described in a steady state approximation and the mechanism of catastrophic explosive eruptions is proposed the theory is applied to well documented eruptions tolbachik 1975 1976 and mount st helens 1980 the theory can also describe changes in a volcanic system such as destruction of the conduit or chamber walls destruction of the edifice changes in magma composition and caldera subsidence due to magma evacuation

cluster analysis of post landfall tracks of landfalling tropical cyclones over china in this paper we apply finite mixture model based clustering algorithms to cluster post landfall tracks of tropical cyclones tcs making landfall over china because existing studies find that landfall surfaces or elevations affect post landfall tc movements we also take account of elevations in addition to time orders in this model our study reveals three clusters with cluster 1 making landfall in hainan province and moving across the western coast of guangdong province most of the tc tracks in cluster 1 move over the ocean and make secondary landfalls over yunnan province of china and vietnam cluster 1 finally dissipates inland and moves westward as a result of the westward shift subtropical high westward steering flow easterly vertical wind shear and strong mountainous blocking cluster 2 makes landfall over guangdong and fujian provinces tcs in cluster 2 subsequently move inland and disappear due largely to westward shift subtropical high easterly steering flow easterly vertical wind shear and relatively strong mountainous blocking cluster 3 makes landfall along the fujian and zhejiang coast and sustains a long period of time recurving mostly to the mid latitude region owing to the surrounding eastward shift subtropical high westerly vertical wind shear weak mountainous blocking and westerly steering flow because cluster 2 is significantly associated with la nina events tcs more likely make landfall over southeastern china coast and move westward or northwestward without recurving cluster 3 sustains a longer time than clusters 1 and 2 in spite of its weak horizontal and vertical water vapor supply tcs in cluster 3 interact actively with westerlies during the post landfall period however we cannot observe any analogous interactions with the mid latitude westerlies in clusters 1 and 2 tcs of clusters 1 and 2 are influenced by summer monsoon flows moreover summer monsoon exerts a greater influence on cluster 1 than cluster 2 the composite 200 hpa divergence of cluster 3 is stronger than that of clusters 1 and 2 this explains to some degree why cluster 3 sustains longer than clusters 1 and 2 after making landfall

fragmentation of magma during plinian volcanic eruptions the ratio of the volume of vesicles gas to that of glass liquid in pumice clasts v g v l reflects the degassing and dynamic history experienced by a magma during an explosive eruption v g v l in pumices from a large number of plinian eruption deposits is shown here to vary by two orders of magnitude even between pumices at a given level in a deposit these variations in v g v l do not correlate with crystallinity or initial water content of the magmas or their eruptive intensities despite large ranges in these variables gas volume ratios of pumices do however vary systematically with magma viscosity estimated at the point of fragmentation and we infer that pumices do not quench at the level of fragmentation but undergo some post fragmentary evolution on the timescale of plinian eruptions pumices with viscosities 109 pa s can expand after fragmentation as long as their bubbles retain gas at a rate inversely proportional to their viscosity once the bubbles connect to form a permeable network and lose their gas expansion halts and pumices with viscosities 105 pa s can collapse under the action of surface tension textural evidence from bubble sizes and shapes in pumices indicates that both expansion and collapse have taken place the magnitudes of expansion and collapse therefore depend critically on the timing of bubble connectivity relative to the final moment of quenching we propose that bubbles in different pumices become connected at different times throughout the time span between fragmentation and quenching after accounting for these effects we derive new information on the fragmentation process from two characteristics of pumices the most important is a relatively constant minimum value of v g v l of 1 78 64 vol vesicularity in all samples with viscosities 105 pa s this value is independent of magma composition and thus reflects a property of the eruptive mechanism the other characteristic is that highly expanded pumices 85 vol vesicularities are common which argues against overpressure in bubbles as a mechanism for fragmenting magma we suggest that magma fragments when it reaches a vesicularity of 64 vol but only if sheared sufficiently strongly the intensity of shear varies as a function of velocity in the conduit which is related to overpressure in the chamber so that changes in overpressure with time are important in controlling the common progression from explosive to effusive activity at volcanoes

ar diffusion in hydrous silicic melts implications for volatile diffusion mechanisms and fractionation the effect of dissolved water on the diffusivity of ar in glasses and melts of rhyolitic and albitic compositions was investigated experimentally at pressures up to 1500 mpa and water contents of 0 1 5 wt the data for water poor rhyolitic composition at 500 mpa can be described in the whole temperature range of 480 1102 c by a simple arrhenius relationship dar 2 14u10 36 m 2 s exp 318 883 t a 4 0 wt increase in water content increases the ar diffusivity by approximately one order of magnitude in both rhyolitic and albitic melts at 1000 c in contrast to viscosity and total water diffusion an exponential dependence of ar diffusivity on water content was observed for the rhyolitic composition in the whole range of water contents for water poor rhyolite ar diffusivity depends on pressure with an apparent activation volume of 13 15 cm 3 mol at pressures up to 800 mpa for water rich rhyolite v5 wt water there is no significant pressure effect at 1000 c in the range 500 1500 mpa combining our data with previous data from carroll m r carroll earth planet sci lett 103 1991 156 168 ar diffusivity in 10 312 m 2 s in rhyolitic melts can be expressed as

polarimetric radar observations of the persistently asymmetric structure of tropical cyclone ingrid abstract tropical cyclone ingrid had a distinctly asymmetric reflectivity structure with an offshore maximum as it passed parallel to and over an extended coastline near a polarimetric weather radar located near darwin northern australia for the first time in a tropical cyclone polarimetric weather radar microphysical analyses are used to identify extensive graupel and rain hail mixtures in the eyewall the overall microphysical structure was similar to that seen in some other asymmetric storms that have been sampled by research aircraft both environmental shear and the land sea interface contributed significantly to the asymmetry but their relative contributions were not determined the storm also underwent very rapid changes in tangential wind speed as it moved over a narrow region of open ocean between a peninsula and the tiwi islands the time scale for changes of 10 m s 1 was of the order of 1 h there were also two distinct types of rainbands observed large scale principal bands with embedded d

radar observations of intense orographic precipitation associated with typhoon xangsane 2000 abstract with measurements from two ground based doppler radars located in northern taiwan this study documents the detailed aspects of intense orographic precipitation associated with typhoon xangsane 2000 as it moved northward immediately off the eastern coast of taiwan bringing strong low level northeasterly to north northeasterly winds impinging on the mountainous northern coast with relatively good persistent coverage of radar echoes on both inland and upstream regions this particular event provides a unique description of the orographic precipitation and its relationship with orographic geometry strong upstream oncoming flow and the precipitation inherently associated with typhoon circulations in this case the heaviest precipitation was observed to occur primarily over two coastal mountain barriers mount da tun dt and the nangang keelung range nkr barrier dt is an approximately 3d mountain barrier and the nkr adjacent to the southeast of dt is a relatively lower narrower 2d moun

the dynamics of boundary layer jets within the tropical cyclone core part i linear theory abstract observations of wind profiles within the tropical cyclone boundary layer have until recently been quite rare the recent massive increase in observations due to the operational implementation of the global positioning system dropwindsonde has emphasised that a low level wind speed maximum is a common feature of the tropical cyclone boundary layer here is proposed a mechanism for producing such a maximum whereby strong inward advection of angular momentum generates the supergradient flow the processes that maintain the necessary inflow against the outward acceleration resulting from gradient wind imbalance are identified as being i vertical diffusion ii vertical advection and iii horizontal advection two complementary tools are used to diagnose the properties and dynamics of the jet the first presented here is a linear analytical model of the boundary layer flow in a translating tropical cyclone it is an extension of the classical ekman boundary layer model as well as of earlier w

hurricane sea surface inflow angle and an observation based parametric model abstractthis study presents an analysis of near surface 10 m inflow angles using wind vector data from over 1600 quality controlled global positioning system dropwindsondes deployed by aircraft on 187 flights into 18 hurricanes the mean inflow angle in hurricanes is found to be 22 6 2 2 95 confidence composite analysis results indicate little dependence of storm relative axisymmetric inflow angle on local surface wind speed and a weak but statistically significant dependence on the radial distance from the storm center a small but statistically significant dependence of the axisymmetric inflow angle on storm intensity is also found especially well outside the eyewall by compositing observations according to radial and azimuthal location relative to storm motion direction significant inflow angle asymmetries are found to depend on storm motion speed although a large amount of unexplained variability remains generally the largest storm relative inflow angles 50 are found in the fas

decompression experiments as an insight into ascent rates of silicic magmas an experimental study of h2o exsolution bubble growth and microlite crystallisation during ascent decompression of silicic magmas in the volcanic conduit is presented isobaric and decompression experiments were performed on a rhyolitic melt at 860 c nno 1 h2o saturation and pressures between 15 and 170 mpa two sets of decompression experiments were performed with decompression rates varying between 0 001 and 960 mpa min 1 from 150 to 50 mpa high pressure decompression and 2 from 50 to 15 mpa low pressure decompression the experiments highlight incomplete h2o exsolution for decompression rates 100 mpa min incomplete bubble growth for decompression rates 0 1 mpa min crystal nucleation time lags and incomplete chemical re equilibration to final pressures the observed crystallisation process i e growth versus nucleation depends on the decompression range indeed decompression induced crystallisation during high pressure decompressions is dominated by growth of existing crystals whereas during low pressure decompressions crystal nucleation is the dominating process this study provides a means to infer magma ascent rates in eruptions of silicic magmas through a combined petrologic and experimental approach

the effect of nonlinear decompression history on h2o co2 vesiculation in rhyolitic magmas magma ascent rate is one of the key parameters that controls volcanic eruption style tephra dispersion and volcanic atmospheric impact many methods have been employed to investigate the magma ascent rate in volcanic eruptions and most rely on equilibrium thermodynamics combining the mixed h2o co2 solubility model liu et al 2005 with the diffusivities of both h2o and co2 for normal rhyolitic melt zhang et al 2007 behrens and zhang 2009 we model the kinetics of h2o and co2 in rhyolitic eruptions that involve non linear decompression rates our study focuses on the effects of the total magma ascent time the non linearity of decompression paths and the influence of different initial co2 h2o content on the post eruptive h2o and co2 concentration profiles around bubbles within the melt our results show that under most circumstances volatile diffusion profiles do not constrain a unique solution for the decompression rate of magmas during an eruption but instead provide a family of decompression paths with a well defined trade off between ascent time and non linearity an important consequence of our analysis is that the common assumption of a constant decompression rate averaged value tends to overestimate the actual magma ascent time

why is the tropical cyclone boundary layer not well mixed abstractplausible diagnostics for the top of the tropical cyclone boundary layer include i the top of the layer of strong frictional inflow and ii the top of the well mixed layer that is the layer over which potential temperature is approximately constant observations show that these two candidate definitions give markedly different results in practice with the inflow layer being roughly twice the depth of the layer of nearly constant here the authors will present an analysis of the thermodynamics of the tropical cyclone boundary layer derived from an axisymmetric model the authors show that the marked dry static stability in the upper part of the inflow layer is due largely to diabatic effects the radial wind varies strongly with height and therefore so does radial advection of this process also stabilizes the boundary layer but to a lesser degree than diabatic effects the authors also show that this differential radial advection contributes to the observed superadiabatic layer ad

statistical location and timing of the convective lines off the mountainous coast of southeastern taiwan from long term radar observations in this study observations from the c band doppler radar on green island which is located off the southeastern coast of taiwan during 1998 2004 were analyzed to investigate the statistical characteristics of the convective lines occurring off the mountainous coast of southeastern taiwan with emphasis on their formative location and timing a total of 211 cases of the lines were identified during the study period it is shown that the lines were clearly a year round phenomenon and five cases occurred per month on average statistical analyses for all identified cases reveal that the formative area of the lines was extended substantially from nearshore regions to at least 100 km offshore with the region of the most frequent formation primarily confined to an elongated zone located 30 km off the coast along coast variations of line formation were also evident and were shown to be closely related to the nearshore terrain features the lines tended to form more frequently during the nighttime hours than the daytime hours with a formative peak between 2000 and 2200 lst minimum formation was found near noon between 1200 and 1400 lst however considerable cases still could be found during the late morning and late afternoon hours more than 70 of the lines 150 cases had a duration of less than 4 h and the mean duration for all lines was calculated to be 3 5 h in addition this study also documented statistical differences in the formative and flow characteristics between the nearshore and offshore lines which are distinguished by offshore distances of formative location that are less or greater than 40 km respectively of particular note the analyses presented strongly suggest that the physical mechanisms contributing to the initiation of the nearshore and offshore lines are fundamentally different

quench rates in air water and liquid nitrogen and inference of temperature in volcanic eruption columns we applya geospeedometer previouslydeveloped in this lab to investigate cooling rate profiles of rhy olitic samples initiallyheld at 720 750 c and quenched in water liquid nitrogen and air for quench of mm size samples in liquid nitrogen and in air the cooling rate is uniform and is controlled byheat transfer in the quench medium instead of heat conduction in the sample the heat transfer coefficient in static air decreases with increasing sample size for quench of mm size samples in water heat transfer in water is rapid and the cooling rate is largelycontrolled byheat conduction in the sample our experimental results are roughlyconsistent with previous calculations for cooling in air and in water although constant heat transfer coefficients were used in these calculations but cooling rate in liquid nitrogen is only1 8 2 3 times that in static air and slower bya factor of 2 than calculated byprevious authors cooling rate in compressed airflow is about the same as that in liquid nitrogen the experimental results are applied to interpret cooling rates of pyroclasts in ash beds of the most recent eruptions of the mono craters cooling rates of pyroclasts are inversely correlated with sample size and slower than those in air the results indicate that the hydrous species concentrations of the pyroclasts were frozen in the eruption column rather than inside ash beds or in flight in ambient air from the cooling rates we infer eruption column temperature in a region where and at a time when hydrous species concentrations in a pyroclast were locked in the temperature ranges from 260 to 570 c for the most recent eruptions of mono craters these are the first estimates of temperatures in volcanic eruption columns the abilityto estimate cooling rates and eruption column temperatures from eruptive products will provide constraints to dynamic models for the eruption columns 2002 elsevier science b v all rights reserved

numerical study of nucleation and growth of bubbles in viscous magmas the nucleation and growth processes of bubbles in viscous magmas with a constant decompression rate have been numerically investigated based on a formation which accounts for effects of viscosity as well as diffusivity interfacial tension and decompression rate the numerical solutions show two regimes in the nucleation and growth process a diffusion controlled regime and a viscosity controlled regime mainly depending on the decompression rate initial saturation pressure and viscosity the basic mechanism common to both regimes is that growth governs nucleation through depletion of degassing components in basaltic eruptions the vesiculation is essentially controlled by diffusion and the viscosity controlled regime is limited to very high decompression rate and very small water content when andesitic magma saturated by water at 10 mpa is decompressed through the propagation of rarefraction wave induced by a landslide as took place in the mount st helens 1980 eruption the vesiculation is controlled by the viscosity up to 100 m depth on the other hand in a rhyolitic magma for the same situation vesiculation is controlled by the viscosity over the whole depth of the magma column in the viscosity controlled regime the vesicularity may be 90 or less as seen in silicic pumice whereas in the diffusion controlledmore regime the vesicularity equals or exceeds 98 such as in reticulite in hawaiian basalt an observed variation of the number density of bubbles by several orders of magnitude in plinian eruptions and the correlation with the sio2 content can be attributed approximately to the dependence of diffusivity of viscosity on sio2 content and temperature assuming the apparent correlation between sio2 content and temperature of magma less

magma decompression rates during explosive eruptions of kīlauea volcano hawaii recorded by melt embayments the decompression rate of magma as it ascends during volcanic eruptions is an important but poorly constrained parameter that controls many of the processes that influence eruptive behavior in this study we quantify decompression rates for basaltic magmas using volatile diffusion in olivine hosted melt tubes embayments for three contrasting eruptions of k lauea volcano hawaii incomplete exsolution of h2o co2 and s from the embayment melts during eruptive ascent creates diffusion profiles that can be measured using microanalytical techniques and then modeled to infer the average decompression rate we obtain average rates of 0 05 0 45 mpa s 1 for eruptions ranging from hawaiian style fountains to basaltic subplinian with the more intense eruptions having higher rates the ascent timescales for these magmas vary from around 5 to 36 min from depths of 2 to 4 km respectively decompression exsolution models based on the embayment data also allow for an estimate of the mass fraction of pre existing exsolved volatiles within the magma body in the eruptions studied this varies from 0 1 to 3 2 wt but does not appear to be the key control on eruptive intensity our results do not support a direct link between the concentration of pre eruptive volatiles and eruptive intensity rather they suggest that for these eruptions decompression rates are proportional to independent estimates of mass discharge rate although the intensity of eruptions is defined by the discharge rate based on the currently available dataset of embayment analyses it does not appear to scale linearly with average decompression rate this study demonstrates the utility of the embayment method for providing quantitative constraints on magma ascent during explosive basaltic eruptions

the extratropical transition of tropical cyclones part i cyclone evolution and direct impacts abstractextratropical transition et is the process by which a tropical cyclone upon encountering a baroclinic environment and reduced sea surface temperature at higher latitudes transforms into an extratropical cyclone this process is influenced by and influences phenomena from the tropics to the midlatitudes and from the meso to the planetary scales to extents that vary between individual events motivated in part by recent high impact and or extensively observed events such as north atlantic hurricane sandy in 2012 and western north pacific typhoon sinlaku in 2008 this review details advances in understanding and predicting et since the publication of an earlier review in 2003 methods for diagnosing et in reanalysis observational and model forecast datasets are discussed new climatologies for the eastern north pacific and southwest indian oceans are presented alongside updates to western north pacific and north atlantic ocean climatologies advances in understanding and in some cases mode

dual doppler derived profiles of the southwesterly flow associated with southwest and ordinary typhoons off the southwestern coast of taiwan abstractthis study used ground based dual doppler observations to explore an understanding of kinematic characteristics of the southwesterly flow associated with the southwest sw and ordinary or typhoons immediately off the southwestern coast of taiwan the sw or typhoon stated herein is referred to as a typhoon with without an obvious combination of its outer circulations and the summer southwesterly monsoon active over the south china sea six typhoon events mindulle 2004 kalmaegi 2008 morakot 2009 talim 2005 jangmi 2008 and fungwong 2008 were chosen for analysis the first latter three listed belong to the family of the sw or typhoons the vertical profiles generated from hourly synthesized winds for these typhoons indicate that intense orographic rainfall tended to occur during the prevalence of the west southwesterly wsw flow that was more perpendicular to the south north orientation of the topography in southern taiwan a unique consistent feature of the wsw flow as

degassing and microlite crystallization of basaltic andesite magma erupting at arenal volcano costa rica abstract volcanoes can erupt explosively in plinian style or effusively as lava flows most models for such ranges in activity are based on silicic magma which may not be appropriate for less viscous basic magma although basic magma erupting at arenal volcano has not varied significantly in bulk composition the volcano has exhibited a full range in eruptive style from plinian activity in 1968 to strombolian bursts to lava flows we examined groundmass textures of samples erupted over that range of activity to investigate the controls on the variability microlite textures in lavas collected both hot rapid quenched and cold show that most samples have textures that are overprinted by crystallization as a result of cooling despite that overprint microlites in the plinian sample have unique crystal morphologies and vesicles that are much smaller and more spherical than those in the other samples we interpret those differences as recording a change in degassing style as a result of changing ascent rate in the conduit to constrain the potential changes in ascent rate a limited number of decompression experiments were run at rates from 0 0013 to 0 25 mpa s crystal textures and morphologies vary greatly as decompression rates change and compared to our observed differences in the natural groundmass it appears that magma erupted in the plinian event decompressed between 0 0013 and 0 025 mpa s whereas magma erupted in non plinian events decompressed slower than 0 0013 mpa s the change in eruptive style from explosive plinian to lava effusion thus resulted from an order of magnitude decrease in magma ascent rate plinian magma probably rose too quickly to allow bubbles to coalesce and allow the magma to degas efficiently whereas at other times magma rose more slowly which allowed bubbles to coalesce and gas to escape leading to less explosive activity

h2o in rhyolitic glasses and melts measurement speciation solubility and diffusion dissolved h2o in silicate melts and glasses plays a crucial role in volcanic eruptions on terrestrial planets and affects glass properties and magma evolution in this paper major progress on several aspects of the h2o melt or glass system is reviewed consistency among a variety of data is investigated discrepancies are evaluated and confusion is clarified on the infrared measurement of total h2o and species concentrations calibration for a variety of glasses has been carried out at room temperature the measurements for h2o in rhyolitic glasses have undergone the most scrutiny resulting in the realization that absorptivities for the near infrared bands depend on total h2o content although the variation of the absorptivities does not seem to significantly affect the determination of total h2o it does affect the determination of molecular h2o and oh species concentrations calibration of the infrared technique for h2o in rhyolitic glasses still needs much improvement especially at high total h2o furthermore it is now almost certain that the molar absorptivities also depend on the measurement temperature in in situ studies hence it will be necessary to carry out calibrations in situ at high temperatures on h2o speciation results from two experimental approaches the quench technique and the in situ technique are very different leading to controversy in our understanding of true speciation a solution is presented to reconcile this controversy it is almost certain that the quench technique does not suffer from a quench problem but interpretation of in situ results suffered from ignoring the dependence of the molar absorptivities on measurement temperature accurate calibration at high temperatures is necessary for the quantitative application of the in situ technique to h2o speciation in silicate melts and glasses on h2o solubility in silicate melts recent experimental work has significantly expanded the t p range of solubility measurements and recent solubility models fill a gap for predicting solubility for a wide range of melt compositions i present a solubility model for rhyolitic and quasi rhyolitic melts over a wide range of t and p 500 1350 c 0 8 kbar by incorporating the role of speciation the solubility model is able to recover the experimental solubility data and has extrapolative value although the partial molar volume of h2o derived from the solubility model differs from that derived from density measurements on h2o diffusion recent studies on h2o diffusion in a quasi rhyolitic melt at 800 1200 c 0 5 5 kbar and up to 7 total h2o not only provide important new diffusion data but are also challenging earlier understanding of h2o diffusion based on data in rhyolitic glasses at 400 550 c 1 bar and 0 2 1 8 total h2o a comparison between the earlier model and recent data is made the recent high temperature diffusivities at total h2o 2 can be predicted by the earlier model however at higher total h2o the earlier model fails new work is under way to understand the diffusion mechanisms at high h2o contents

a multiscale numerical study of hurricane andrew 1992 part ii kinematics and inner core structures despite considerable research understanding of the temporal evolution of the inner core structures of hurricanes is very limited owing to the lack of continuous high resolution observational data of a storm in this study the results of a 72 h explicit simulation of hurricane andrew 1992 with a grid size of 6 km are examined to explore the inner core axisymmetric and asymmetric structures of the storm during its rapid deepening stage based on the simulation a conceptual model of the axisymmetric structures of the storm is proposed most of the proposed structures confirm previous observations the main ingredients include a main inflow outflow in the boundary layer upper troposphere with little radial flow in between a divergent slantwise ascent in the eyewall a penetrative dry downdraft at the inner edge of the eyewall and a general weak subsiding motion in the eye with typical warming drying above an inversion located near an altitude of about 2 3 km the storm deepens as the axes of these features contract it is found that the inversion divides the eye of the hurricane vertically into two parts with a deep layer of warm dry air above and a shallow pool of warm moist air below the air aloft descends at an average rate of 5c m s 21 and has a residency time of several days in contrast the warm moist pool consists of air from the main inflow and penetrative downdrafts offset somewhat by the air streaming in a returning outflow into the eyewall in the lowest 2 km it is subject to the influence of the upward heat and moisture fluxes over the underlying warm ocean the warm moist pool appears to play an important role in supplying high ue air for deep convective development in the eyewall the penetrative downdraft is dry and originates from the return inflow in the upper troposphere and it is driven by sublimative evaporative cooling under the influence of the asymmetric radial inflow of dry cold air in the midtroposphere it penetrates to the bottom of the eye azimuthally downshear with a width often greater than 100 km in a radially narrow zone along the slantwise inner edge of the eyewall it is further shown that all the meteorological fields are highly asymmetric whereas the storm scale flow features a source sink couplet in the boundary layer and dual gyres aloft the inner core structures exhibit alternative radial inflow and outflow and a series of inhomogeneous updrafts and downdrafts all the fields tilt more or less with height radially outward and azimuthally downshear furthermore pronounced fluctuations of air motion are found in both the eye and the eyewall sometimes a deep layer of upward motion appears at the center of the eye all these features contribute to the trochoidal oscillation of the storm track and movement the main steering appears to be located at the midtroposphere 4 5 km and the deep layer mean winds represent well the movement of the hurricane

melt pockets in phenocrysts and decompression rates of silicic magmas before fragmentation 1 a new method is presented to estimate the decompression rate of silicic magma prior to fragmentation and is applicable to rates of 1 100 kpa s this method uses the remaining concentrations of h2o and co2 in bubble free cylindrical melt now glass pockets in phenocrysts that are connected to the surrounding bubbly melt these melt pockets are common in volcanic rocks during magma ascent bubbles grow in the surrounding melt and the concentrations of dissolved h2o and co2 decrease establishing a boundary condition of low volatile concentration at the outlet of the melt pocket in turn volatiles diffuse from the melt pocket into the surrounding bubbly magma and form a gradient that is time dependent the volatile concentration at the inner limit of the melt pocket likewise diminishes with time knowing the diffusivity and solubility of h2o and co2 permits the remaining h2o and co2 contents to be estimated for different decompression rates using diffusion equations we apply this approach to the measured h2o and co2 contents in quartz hosted melt pockets in pumice from the phreatomagmatic 26 5 ka oruanui eruption taupo new zealand a decompression rate of 1 7 kpa s 5 35 cm s was obtained for oruanui magma

bubble nucleation in rhyolitic melts experiments at high pressure temperature and water content abstract we report the first measurement of bubble nucleation in hydrated rhyolitic melts in response to pressure release two rhyolitic obsidians one containing less than 1 of microlites of fe ti oxides and the other about 20 of various crystals were hydrated at 150 mpa and 780 850 c after saturation was reached 5 3 5 5 wt water pressure was lowered and the samples were allowed to nucleate and grow bubbles for various amounts of time before the final rapid quenching of the experiments the results demonstrate the importance of heterogeneous nucleation microlites of fe ti oxides are very efficient as sites for bubble nucleation in their presence modest nucleation was observed even after decompression by 6 10 8 bubbles cm 3 in the absence of microlites no nucleation occurred at p mpa at p 10 mpa bubbles also nucleated on crystals of biotite zircon and apatite modest nucleation 10 3 10 5 cm 3 took place even in crystal free samples but it was still heterogeneous when p exceeded 80 mpa nucleation in crystal free samples became extensive 10 5 10 7 cm 3 the lack of correlation of bubble density with either time or decompression suggests that nucleation was still heterogeneous nucleation rates were controlled mainly by the availability of sites rates were faster than 10 6 cm 3 s 1 when microlites were present and faster than 10 5 cm 3 s 1 in the absence of microlites at p 70 mpa narrow size distributions in most samples suggests that nucleation took place immediately after the pressure drop the experimental data we present here indicate that the presence or absence of efficient nucleation sites can lead to two distinct modes of bubble formation when a large number of efficient sites e g fe ti oxide are present bubble nucleation requires very little supersaturation and to a good approximation gas and magma are in equilibrium in magmas that are crystal free or contain crystals that are inefficient at nucleating bubbles very high degrees of supersaturation are required in order to initiate nucleation these two modes of exsolution may lead to contrasting styles of convection pressure build up and eruption

bubble nucleation in magmas a dominantly heterogeneous process abstract bubble nucleation is at the heart of magma ascent and degassing nucleation kinetics control how easily a magma exsolves its volatiles and thereby its explosivity close to the surface homogeneous nucleation i e without assistance from crystal substrates or other phases often requires attainment of large supersaturation pressures p n 100 mpa the change in pressure required for onset of nucleation while heterogeneous nucleation on pre existing crystals can occur at significantly lower values p n p n given experimental constraints on pressure conditions at the onset of nucleation decompression rate meters e g toramaru 2006 also relate the number density of bubbles in pyroclasts a readily obtained textural characteristic to rates of pressure change dp dt during ascent all these treatments require an explicit or implicit decision as to whether magma degassing was dominated by homogeneous or heterogeneous nucleation which is guided by the choice of surface tension values this contribution exploits the current textural datasets available for eruptions involving a variety of magma compositions to test the assumptions that homogeneous and or heterogeneous nucleation dominate bubble vesiculation in natural melts the comparison between pyroclast textures and those obtained via decompression experiments in the laboratory indicates that supersaturation pressures and decompression rates required for homogeneous nucleation are unrealistically high for natural magmas i review the arguments for and against homogenous nucleation and defend the alternate view that heterogeneous nucleation may dominate in all magma types including rhyolites in order to solve this central debate our focus needs to be shifted towards understanding the pre decompression phase equilibria and textural characteristics of magnetite in addition to the state of the melt structure

experimental constraints on degassing of magma isothermal bubble growth during continuous decompression from high pressure numerical models predict that rapid ascent of hydrous magma can lead to supersaturation of dissolved volatile constituents possibly leading to explosive eruption we have performed controlled decompression experiments to investigate the ascent rates required to maintain bubble melt equilibrium high silica rhyolitic melts were saturated with water at 200 mpa and 825 c decompressed to lower pressures at constant rates of 0 025 0 25 0 5 and 1 0 mpa s 1 and then rapidly quenched isobarically other samples were saturated with water over the pressure range investigated to determine equilibrium water solubility in order to quantify degassing efficiency during decompression at a decompression rate of 0 025 mpa s 1 melt vapor equilibrium was maintained over the entire pressure range examined 200 to 17 5 mpa a single bubble nucleation event occurred in response to decompression and quenched bubble sizes can be modeled by a equilibrium bubble growth model that takes into account the number density of bubbles at decompression rates of 0 25 0 5 and 1 0 mpa s 1 rhyolitic melts could not degas in equilibrium when pressure decreased from 200 mpa to 140 mpa and water supersaturation p in the melt reached up to 60 mpa with higher values at faster decompression rates further pressure release resulted in near equilibrium degassing and p dropped significantly in each case p decreased when bubbles exceeded 10 vol a single heterogeneous bubble nucleation event occurred in each experiment when p 20 mpa no other bubbles nucleated despite p reaching 60 mpa which is probably too low to trigger homogeneous nucleation compared to estimates for magma decompression rates during lava dome eruptions our results indicate that magmas can degas efficiently throughout their ascent to the surface in explosive eruptions decompression rates may exceed those of this study and hence melts may become supersaturated with water such fast decompressions are expected however only when magma is highly vesicular which would aid approach to equilibrium degassing

decompression rate of magma at fragmentation inference from broken crystals in pumice of vulcanian eruption abstract decompression rate of magma at fragmentation immediately before or after fragmentation was determined using broken crystals found in the pumices ejected during the vulcanian explosion of sakurajima volcano japan the combined analysis of textural data obtained from the natural pumice samples and a simple model for the crystal fracturing in vesiculating viscous magma indicated a decompression rate 7 0 10 3 7 8 10 4 pa s for the ejecta produced during the later phase of vulcanian explosion this result suggests that the short duration of the vulcanian explosion is controlled by the rapid decrease of the magma ascent rate to a vent an understanding of the control mechanism of the termination of an eruption by precise prediction of the eruption process is essential for both volcanology and hazard mitigation

coupled effect of magma degassing and rheology on silicic volcanism abstract explosive volcanism such as the 1991 mt pinatubo philippines and the 2008 mt chaiten chile eruptions is caused by violent vesiculation of hydrous magma however gas may efficiently separate from magma owing to the enhancement of gas permeability by shear deformation of magma flowing in a volcanic conduit this makes it difficult to maintain the driving force of explosive volcanism although explosive volcanism is actually common here we propose that shear localization in a volcanic conduit controls the eruption style and explosivity based on deformation experiments of vesicular magma linked with synchrotron radiation x ray radiography and computed tomography we observed for the first time in situ that the shear localization caused magma fracturing and formed a slip plane and thus inhibited deformation and outgassing elsewhere we also observed the compaction of vesicular magma into a dense lava as a result of outgassing when shear localization did not occur in a natural setting shear localizes along the edges of a volcanic conduit where the strain rate is high causing a highly permeable fracturing layer to form at the conduit s edge and leaving less sheared and less outgassed magma at its center the less outgassed magma in the center may ascend rapidly and cause explosive volcanism non explosive lava effusion may occur only when shear localization does not occur effectively this new view explains the rapid ascent of viscous magma and the formation of pyroclasts with contrasting vesicularity pyroclastic obsidian and highly vesiculated pumice

the fragmentation threshold of pyroclastic rocks in response to rapid decompression porous magma may fragment explosively this occurs when the melt can no longer withstand forces exerted upon it due to the overpressure in included bubbles this occurs at a critical pressure difference between the bubbles and the surrounding magma in this study we have investigated this pressure threshold necessary for the fragmentation of magma here we present the first comprehensive high temperature experimental quantification of the fragmentation threshold of volcanic rocks varying widely in porosity permeability crystallinity and chemical composition we exposed samples to increasing pressure differentials in a high temperature shock tube apparatus until fragmentation was initiated experimentally we define the fragmentation threshold as the minimum pressure differential that leads to complete fragmentation of the pressurized porous rock sample our results show that the fragmentation threshold is strongly dependent on porosity high porosity samples fragment at lower pressure differentials than low porosity samples the fragmentation threshold is inversely proportional to the porosity of the other factors permeability likely affects the fragmentation threshold at high porosity values whereas chemical composition crystallinity and bubble size distribution appear to have minor effects the relationship for fragmentation threshold presented here can be used to predict the minimum pressure differential necessary for the initiation or cessation of the explosive fragmentation of porous magma

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

asymmetric distribution of convection associated with tropical cyclones making landfall along the south china coast this study examines the convection distribution associated with 18 tcs that made landfall along the south china coast during 1995 and 2005 cloud top temperatures from high resolution satellite imageries of the geosynchronous meteorological satellite 5 are used as proxy of strong convection it is found that convection tends to be enhanced on the western side of the tc as it makes landfall in 10 of the cases in agreement with the conclusion of some previous studies four cases have stronger convection on the eastern side this deviation from the general rule appears to be related to the tcs being more slow moving or their interaction of the tc with another land surface prior to its making landfall along the south china coast for the remaining cases in which no significant asymmetries in convection can be identified the vertical wind shear appears to enhance convection on the east side

mesoscale air sea interactions related to tropical and extratropical storms in the gulf of mexico data indicate that the climatological vorticity of the lower atmosphere of the northwestern gulf of mexico is relatively strong with monthly means exceeding a rossby number of 3 from october through march with a maximum of 4 6 in december it has been hypothesized that wintertime cyclogenesis over the northwestern gulf is enhanced by this lower level atmospheric vorticity field when it occurs simultaneously with appropriate upper level venting observations from november 1982 to mid february 1983 were studied in which seven significant cyclones were generated in the northwestern gulf it was found that all seven storms occurred when the vorticity correlate of horizontal air temperature difference was 3 5 c above the climatological mean difference although these results corroborate the postulate that such lower level vorticity is related to cyclogenesis the data from mid february through march 1983 were less supportive during those months only two of the six significant storms developed when the horizontal air temperature difference was above the climatological mean surprisingly the location of the most unstable air within the atmospheric boundary layer is not found in the northwestern gulf of mexico but instead along the shelf break relatively strong free convection in the atmospheric boundary layer is found over the loop current and the deep western gulf as expected the unstable regions of the deep gulf can enhance the potential for frontogenesis and cyclogenesis but it is likely that the linear character of the strong shelf break free convection does not enhance cyclogenesis it is shown that a maximum in the frequency of tropical storms within the gulf of mexico exists some 275 km south of the mississippi delta at 27 n 90 w this maximum is a result of only those storms which originate within the gulf two plausible effects of the loop current and its rings on tropical storms are discussed one is that these ocean features are large and consolidated heat and moisture sources from which a nearby slowly moving atmospheric disturbance can extract energy the second is that of the cyclonic vorticity that can be generated in the lower atmosphere by such oceanographic features

heterogeneous bubble nucleation on fe ti oxide crystals in high silica rhyolitic melts the nucleation of h2o bubbles in magmas has been proposed as a trigger for volcanic eruptions to determine how bubbles nucleate heterogeneously in silicate melts experiments were carried out in which high silica rhyolitic melts were hydrated at 740 800 c and 50 175 mpa decompressed by 20 70 mpa and held at the lower pressures for 10 s before being quenched the hydration conditions were subliquidus and all samples contain blocky magnetite needle shaped hematite plagioclase magnetite is abundant at 800 c and high pressures whereas hematite becomes more abundant at lower temperatures and pressures bubbles nucleated in a single event in all samples with the number density nt of bubbles varying between 2 107 and 1 109 cm 3 at low degrees of supersaturation one to a few bubbles nucleate on faces of magnetite but at medium to high degrees of supersaturation multiple bubbles nucleate on single magnetite grains on hematite one to a few bubbles nucleated at the ends of the needle shaped crystals at medium supersaturations but formed along their entire lengths at high supersaturations nt increases as water diffusivity decreases indicating that the number of bubbles nucleated is influenced by their growth which depletes the melt with respect to h2o and lowers supersaturation if volcanic eruptions are triggered by bubble formation in magmas stored in shallow level magma chambers then the supersaturations needed for heterogeneous nucleation suggest that only small amounts of crystallization are needed whereas homogeneous nucleation is unlikely to trigger eruptions

diffusion of dissolved carbonate in magmas experimental results and applications the diffusivity of dissolved carbonate in sodium aluminosilicate 60 sio 2 30 na 2 o 10 al 2 o 3 and iron free basalt melts was measured by a 14 c thin source tracer technique at conditions of combined high temperature and high pressure ranging from 800 c to 1350 c and 0 5 to 18 kbar for the simple melt and 1350 to 1500 c at 15 kbar for the haplobasalt melt the two melts have similar dissolved carbonate transport properties expressed for the simple system at 0 5 kbar by d carbonate 3 559exp 46 600 rt the pressure dependence at 1200 c is given by d carbonate 4 13 10 7 exp 11 02p rt the activation energy of 46 6 kcal mole is low relative to expected values for small highly charged cations suggesting that the actual diffusing species is a larger carbonate anion this interpretation is supported by the 11 cm 3 mole activation volume which corresponds to twice the molar volume of oxygen anions because the 14 c diffusion gradients conform quite well to a constant diffusivity thin source model there can be no strong dependence of carbonate diffusivity upon dissolved carbonate content at least in the 0 0 2 wt range represented by the experimental profiles carbonate diffusion is markedly different from previously determined systematics for water being 1 2 orders of magnitude slower in granitic magmas and considerably faster in basalts this difference can result in diffusional fractionation of co 2 and h 2 o in magmas which may be most significant in small scale processes such as growth of vapor bubbles and formation of some types of glass inclusions in phenocrysts the new data also place constraints on the rate at which co 2 dominated fluid bubbles can actually grow under more or less isothermal conditions at 10 kbar the growth rate is on the order of 1 mm day depending upon the degree of supersaturation in co 2 when combined with knowledge of initial co 2 contents of magmas and observed characteristics of dispersed bubbles e g in ocean floor basalt glasses the diffusivity data may expedite the reconstruction of magma decompression paths

the 26 5 ka oruanui eruption new zealand an introduction and overview abstract the 26 5 ka oruanui eruption from taupo volcano in the central north island of new zealand is the largest known wet eruption generating 430 km3 of fall deposits 320 km3 of pyroclastic density current pdc deposits mostly ignimbrite and 420 km3 of primary intracaldera material equivalent to 530 km3 of magma erupted magma is 99 rhyolite and 90 pdc deposits range from mm to cm thick ultra thin veneers enclosed within fall material to 200 m thick ignimbrite in proximal areas the farthest travelled 90 km most energetic pdcs velocities 100 m s 1 occurred during phase 8 but the most voluminous pdc deposits were emplaced during phase 10 grain size variations in the pdc deposits are complex with changes seen vertically in thick proximal accumulations being greater than those seen laterally from near source to most distal deposits modern lake taupo partly infills the caldera generated during this eruption a 140 km2 structural collapse area is concealed beneath the lake while the lake outline reflects coeval peripheral and volcano tectonic collapse early eruption phases saw shifting vent positions development of the caldera to its maximum extent indicated by lithic lag breccias occurred during phase 10 the oruanui eruption shows many unusual features its episodic nature wide range of depositional conditions in fall deposits of very wide dispersal and complex interplay of fall and pdc activity

experimental constraints on permeable gas transport in crystalline silicic magmas the gas and fluid transport in magmas via permeable flow through interconnected bubble networks controls the rate of outgassing from magmas ascending in volcanic conduits and the fluid transport in the mushy boundary layer of magma reservoirs hence clarifying its mechanism and rate is crucial to understanding the explosivity of volcanic eruptions and the evolution and dynamics of a magma reservoir recent experimental studies have determined the gas permeabilities in crystal free rhyolite and basalt however no experimental study has investigated the effect of the crystal contents on the permeable gas transport in magmas in this study we performed decompression experiments for hydrous rhyolitic melts having crystallinities of 30 and 50 vol to examine the effect of crystals on the bubble microstructure and gas permeability during magma vesiculation size controlled 100 meshed corundum crystals were used as an analog of the phenocrysts in silicic magmas microstructural analyses using x ray ct showed that bubbles coalesce and their connectivity increases with a decrease in the final pressure after the decompression that is an increase in the vesicularity as long as the vesicularities of melt part in the crystal free basis melt vesicularity were similar no clear effect of the crystallinity on the degree of bubble coalescence and connectivity was observed at melt vesicularities 68 vol this result indicates that the permeable fluid transport through a deep volcanic conduit which has been proposed on the basis of the observations of volcanic gases and natural products is so slow that other processes like shear deformation or magma convection may be needed to explain the observations

diffusion obstacles and opportunities in petrochronology many of the approaches in petrochronology are rooted in the assumption of equilibrium diffusion is an expression of disequilibrium the movement of mass in response to chemical potential gradients and isotopes in response to isotopic gradients it is extremely important that we be aware of how the effects of diffusion can place obstacles across our path towards petrochronologic enlightenment conversely the effects of diffusion also provide opportunities for understanding rates processes and conditions experienced by rocks the enormity of the field does not permit us to provide a comprehensive review of either the mathematics of diffusion or quantitative data that have been obtained relevant to the interpretation of diffusive processes in rocks and minerals many resources cover these topics including rimg volume 72 diffusion in minerals and melts zhang and cherniak 2010 and several textbooks crank 1975 glicksman 2000 particularly relevant to the discussion of petrochronology are summaries of the theory and controls on diffusion brady and cherniak 2010 zhang 2010 as well as diffusion rates in feldspar cherniak 2010a accessory minerals cherniak 2010b garnet ganguly 2010 mica pyroxene and amphibole cherniak and dimanov 2010 and melts zhang and ni 2010 zhang et al 2010 rather than duplicate that material our goal is to explore the obstacles and opportunities presented by the effects of diffusion as they inform the rates of petrologic processes to achieve this goal we emphasize key principles and illustrative examples quantitative interpretation of the effects of diffusion assumes predictability of numerous factors that may affect chemical or isotopic transport including temperature initial and boundary conditions water and oxygen fugacities activities of other components multiple mechanisms of diffusion and crystal chemistry coupling of the substitution of elements into different crystallographic sites additionally the extraction of meaningful ages durations of events and temperatures requires

magma ascent rates volcanoes can erupt explosively generating high columns of ash and occasional pyroclastic flows or they can erupt slowly forming lava flows and domes this variation reflects significant differences in mass eruption rate e g wilson et al 1980 mass eruption rates in turn are controlled by the rates of magma ascent through the volcanic conduit and the conduit size the magma ascent rate itself is a function of the pressure in the magma storage region the physical properties of the magma such as its density viscosity and crystallinity and the resistance to flow in the conduit that connects the magma storage zone to the surface papale and dobran 1994 mastin and ghiorso 2001 pinkerton et al 2002 sparks et al 2006 a number of important characteristics of volcanic eruptions are affected or controlled by the rate at which magma ascends from depth for example the bubble content i e vesicularity and the degree of crystallization that develop in the melt phase can be significantly different in rapidly vs slowly ascended magma in fact the inability of rapidly ascending magma to effectively lose exsolved gas may be one factor causing an eruption to change from effusive to explosive behavior as recently documented for the soufriere hills eruption on montserrat in the west indies sparks et al 1998 therefore in order to better understand the processes involved and the changes that occur in volcanic eruptions it is important to quantify the rates at which different magmas rise to the surface the fact that the rate of magma ascent controls a number of reactions that occur in volatile rich magmas suggests several ways to study magma ascent rates using reaction data and theoretical flow models one reaction that is a direct result of magma ascent is the exsolution of volatiles from the melt

magma residence and eruption at the taupo volcanic center taupo volcanic zone new zealand insights from rhyolite melts geobarometry diffusion chronometry and crystal textures the taupo volcanic center tvc taupo volcanic zone tvz new zealand is home to the two most recent silicic caldera forming eruptions in the tvz the giant 530 km3 dre oruanui supereruption and the large 35 km3 dre taupo eruption this offers a unique opportunity to investigate similarities and differences between large and supersized volumes of rhyolitic magma at the tvc and more generally we combine information from crystal textures crystal size distributions crystal compositions ti in quartz diffusion chronometry and glass compositions rhyolite melts geobarometry to investigate the crustal storage conditions longevity and eruption of these magmas results show differences between the storage depths of the oruanui and taupo magmas consistent with the differences in their glass silica contents but strikingly similar short crustal residence times for the final crystal poor eruptible magma bodies decades to centuries differences in groundmass textures between the two systems also likely reflect differences in ascent durations decompression paths and or amounts of undercooling experienced by these systems due to the differences in their storage depths finally comparing the evolution of storage depths and magma compositions at the tvc with those in a preceding central tvz ignimbrite flare up supports the idea that the modern tvc may be flaring up and highlights the evolution of magma storage depths with increasing system maturity in this volcanic region