experiments on piping in sandy gravels tests on internally unstable sandy gravels show that a significant proportion of the sand content is washed out by piping at hydraulic gradients far lower than the critical gradient given by a classical theory the probable explanation is that a major part of the overburden load is carried on a framework of gravel particles leaving the sand under relatively small pressures by contrast piping of the sand from stable sandy gravels occurs at approximately the full theoretical gradient the tests broadly confirm kenney s criterion for the internal stability of granular materials des essais realises sur des graves sableuses a instabilite interne importante montrent qu une proportion non negligeable du sable est lessivee pour des gradients hydrauliques bien inferieurs au gradient critique donne par les theories classiques l explication la plus probable est que la majeure partie de la surcharge des couches subjacentes est transmise au reseau des particules graveleuses le sable n etant alors plus soumis qu

a rapid mechanism to remobilize and homogenize highly crystalline magma bodies the largest products of magmatic activity on earth the great bodies of granite and their corresponding large eruptions have a dual nature homogeneity at the large scale and spatial and temporal heterogeneity at the small scale this duality calls for a mechanism that selectively removes the large scale heterogeneities associated with the incremental assembly of these magmatic systems and yet occurs rapidly despite crystal rich viscous conditions seemingly resistant to mixing here we show that a simple dynamic template can unify a wide range of apparently contradictory observations from both large plutonic bodies and volcanic systems by a mechanism of rapid remobilization unzipping of highly viscous crystal rich mushes we demonstrate that this remobilization can lead to rapid overturn and produce the observed juxtaposition of magmatic materials with very disparate ages and complex chemical zoning what distinguishes our model is the recognition that the process has two stages initially a stiff mushy magma is reheated from below producing a reduction in crystallinity that leads to the growth of a subjacent buoyant mobile layer when the thickening mobile layer becomes sufficiently buoyant it penetrates the overlying viscous mushy magma this second stage rapidly exports homogenized material from the lower mobile layer to the top of the system and leads to partial overturn within the viscous mush itself as an additional mechanism of mixing model outputs illustrate that unzipping can rapidly produce large amounts of mobile magma available for eruption the agreement between calculated and observed unzipping rates for historical eruptions at pinatubo and at montserrat demonstrates the general applicability of the model this mechanism furthers our understanding of both the formation of periodically homogenized plutons crust building and of ignimbrites by large eruptions

ti diffusion in quartz abstract we have measured ti diffusion in quartz under dry 1 atm conditions experiments were performed using synthetic and natural quartz and a tio2 powder source with ti profiles obtained by rutherford backscattering spectrometry rbs over the temperature range 700 1150 c the following arrhenius relation was obtained for diffusion parallel to 001 d ti 7 10 8 exp 273 12 kj mol 1 r t m 2 sec 1 similar diffusivities were obtained for both synthetic and natural quartz and for a range of ti source materials including natural titanite powder and rutile quartz single crystal diffusion couples although ti diffusion appears slightly slower in the direction normal to c this difference is not great using these diffusion parameters calculations indicate that distances over which diffusional alteration of ti concentrations in quartz could occur in a million years would be on order of 500 m at 800 c and 15 m at 600 c the arrhenius relation above should be broadly applicable and may find application in constraining metamorphic histories under conditions where the ti in quartz geothermometer can be reasonably applied this relation can also be used to constrain peak temperatures and cooling histories from observations of exsolved rutile needles in quartz and the width of the ti depleted zone that develops around the growing needles finally these findings may find utility in evaluating crystal residence times in magmatic systems when coupled with observations of the sharpness of zoning patterns in quartz

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

ti diffusion in quartz inclusions implications for metamorphic time scales quartz inclusions in garnet from samples collected from the staurolite zone in central new england are zoned in cathodoluminescence cl the cl intensity is interpreted to be a proxy for ti concentration and the zoning attributed to ti diffusion into the quartz grains driven by ti exchange between quartz and enclosing garnet as a function of changing temperature the cl zoning has been interpreted using a numerical diffusion model to constrain the time scales over which the diffusion has occurred temperature time histories are sensitive to the presumed peak temperature but not to other model parameters the total time of the metamorphic heating and cooling cycle from around 450 c to the peak temperature 550 600 c back to 450 c is surprisingly short and encompasses only 0 2 2 million years for peak temperatures of 600 550 c the metamorphism was accompanied by large scale nappe and dome formation and it is suggested that this occurred as a consequence of in sequence thrusting resulting in a mid crustal ductile duplex structure

time scales of porphyry cu deposit formation insights from titanium diffusion in quartz porphyry dikes and hydrothermal veins from the porphyry cu mo deposit at butte montana contain multiple generations of quartz that are distinct in scanning electron microscope cathodoluminescence sem cl images and in ti concentrations a comparison of microprobe trace element profiles and maps to sem cl images shows that the concentration of ti in quartz correlates positively with cl brightness but al k and fe do not after calibrating cl brightness in relation to ti concentration we use the brightness gradient between different quartz generations as a proxy for ti gradients that we model to determine time scales of quartz formation and cooling model results indicate that time scales of porphyry magma residence are 1 000s of years and time scales from porphyry quartz phenocryst rim formation to porphyry dike injection and cooling are 10s of years time scales for the formation and cooling of various generations of hydrothermal vein quartz range from 10s to 10 000s of years these time scales are considerably shorter than the 0 6 m y overall time frame for each porphyry style mineralization pulse determined from isotopic studies at butte montana simple heat conduction models provide a temporal reference point to compare chemical diffusion time scales and we find that they support short dike and vein formation time scales we interpret these relatively short time scales to indicate that the butte porphyry deposit formed by short lived episodes of hydrofracturing dike injection and vein formation each with discrete thermal pulses which repeated over the 3 m y generation of the deposit

crystallization stages of the bishop tuff magma body recorded in crystal textures in pumice clasts the bishop tuff is a giant silicic ignimbrite erupted at 0 76 ma in eastern california usa five pumice clasts from the late erupted bishop tuff aeolian buttes were studied in an effort to better understand the pre and syn eruptive history of the bishop magma body and place constraints on the timescales of its existence this study complements and expands on a previous study that focused on early erupted bishop tuff pumice clasts bulk densities of pumice clasts were measured using an immersion method and phenocryst crystal contents were determined using a sieving and winnowing procedure x ray tomography was used to obtain qualitative and quantitative textural information particularly crystal size distributions csds we have determined csds for crystals ranging in size from approx 10 to approx 1000 micro m for three groups of mineral phases magnetite ilmenite pyroxene biotite quartz feldspar similar to early erupted pumice late erupted pumice bulk density and crystal contents are positively correlated and comparison of crystal fraction vs size trends suggests that the proportion of large crystals is the primary control on crystallinity porosity is negatively correlated with crystal content which is difficult to reconcile with closed system crystallization magnetite and pyroxene biotite size distributions are fractal in nature often attributedmore to fragmentation however crystals are mostly whole and euhedral such that an alternative mechanism is necessary to explain these distributions quartz feldspar size distributions are kinked with a shallow sloped log linear section describing large crystals 140 micro m and a steep sloped log linear section describing small crystals 140 micro m we interpret these two crystal populations as resulting from a shift in crystallization regime we suggest that the shallow sloped section describes a pre eruptive quartz feldspar growth dominated regime whereas the steep sloped section represents a population that grew during a nucleation dominated regime that began as a result of decompression at the onset of eruption timescales of quartz growth calculated from the slopes of these two segments of the size distributions indicate that the pre eruptive crystal population grew on timescales on the order of millennia and may describe the timescale of crystallization of the bishop magma body the syn eruptive population gives timescales of 1 2 years but possibly much less and probably marks the onset of eruptive decompression less

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

laboratory study on subgrade fluidization under undrained cyclic triaxial loading a long term issue that has hampered the efficient operation of heavy haul tracks is the migration of fluidized fines from the shallow soft subgrade to the overlying ballast i e mud pumping this

titaniq recrystallized experimental confirmation of the original ti in quartz calibrations several studies have reported the p t dependencies of ti in quartz solubility and there is close agreement among three of the four experimental calibrations new experiments were conducted in the present study to identify potential experimental disequilibrium and to determine which ti in quartz solubility calibration is most accurate crystals of quartz rutile and zircon were grown from sio2 tio2 and zrsio4 saturated aqueous fluids in an initial synthesis experiment at 925 c and 10 kbar in a piston cylinder apparatus a range of quartz crystal sizes was produced in this experiment both large and small examples were analyzed by electron microprobe to determine whether ti concentrations are correlated with crystal size cathodoluminescence images and epma measurements show that intercrystalline and intracrystalline variations in ti concentrations are remarkably small regardless of crystal size the average ti in quartz concentration from the synthesis experiment is 392 1 ppmw ti which is within 95 confidence interval of data from the 10 kbar isobar of wark and watson contrib mineral petrol 152 743 754 2006 and thomas et al contrib mineral petrol 160 743 759 2010 as a cross check on the ti in quartz calibration we also measured the concentration of zr in rutile from the synthesis experiment the average zr in rutile concentration is 4337 32 ppmw zr which is also within the 95 confidence interval of the zr in rutile solubility calibration of ferry and watson contrib mineral petrol 154 429 437 2007 the p t dependencies of ti solubility in quartz and zr solubility in rutile were applied as a thermobarometer to the experimental sample the average ti in quartz isopleth calculated from the calibration of thomas et al contrib mineral petrol 160 743 759 2010 and the average zr in rutile isopleth calculated from the calibration of tomkins et al j metamorph geol 25 703 713 2007 cross at 9 5 kbar and 920 c which is in excellent agreement with the p t conditions of the synthesis experiment separates of the high ti quartz from the initial synthesis experiment described above were used as starting material in subsequent experiments at 20 kbar at which pressure the solubility of ti in quartz is expected to be significantly lower in the recrystallized quartz these recrystallization experiments were conducted under wet and dry conditions at 925 c and under wet conditions at 850 c both wet and dry recrystallization experiments produced polycrystalline quartzites rutile occurs as inclusions in quartz and as individual crystals dispersed along quartz grain boundaries quartz that grew during the recrystallization experiments has dark cathodoluminescence indicating substantially lower ti concentrations the average ti concentrations in quartz from the recrystallization experiments are within the 95 confidence interval of a linear fit to the 20 kbar data of thomas et al contrib mineral petrol 160 743 759 2010 collectively the results from the synthesis and recrystallization experiments confirm that the ti in quartz concentrations used to calibrate the p t dependencies of ti in quartz solubility in thomas et al s contrib mineral petrol 160 743 759 2010 calibration represent the equilibrium concentrations of ti in quartz

the bishop tuff new insights from eruptive stratigraphy the 0 76 ma bishop tuff from long valley caldera in eastern california consists of a widespread fall deposit and voluminous partly welded ignimbrite the fall deposit f exposed over an easterly sector below and adjacent to the ignimbrite is divided into nine units f1 f9 with no significant time breaks except possibly between f8 and f9 maximum clast sizes are compared with other deposits where accumulation rates are known or inferred to estimate an accumulation time for f1 f8 as ca 90 hrs the ignimbrite ig is divided into chronologically and or geographically distinct packages of material earlier packages ig1 were emplaced mostly eastward are wholly intraplinian coeval with fall units f2 f8 lack phenocrystic pyroxenes and contain few or no glass mountain derived rhyolite lithic fragments earlier packages ig2 were erupted mostly to the north and east are at least partly intraplinian interbedded with fall unit f9 to the east contain pyroxenes and have lithic fractions rich in g

rapid remobilization of magmatic crystals kept in cold storage we lack thermal histories for magma reservoirs but here the magma under mount hood oregon usa is shown to have been too cold to mobilize for most of the time it has been stored which implies that magma mobilizes at which point it can be imaged geophysically very quickly prior to eruption this paper presents a novel approach to constraining the thermal history of the subsurface magma bodies that feed eruptions by combining temporal information from a variety of sources kari cooper and adam kent combine timescales derived from uranium series disequilibria textural information and trace element zoning in crystals they show that at mount hood oregon only a small fraction of the total storage duration has been spent at temperatures above the critical crystallinity the point at which magma is easily mobilized they conclude that largely liquid bodies that could be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption the processes involved in the formation and storage of magma within the earth s upper crust are of fundamental importance to volcanology many volcanic eruptions including some of the largest result from the eruption of components stored for tens to hundreds of thousands of years before eruption1 2 3 although the physical conditions of magma storage and remobilization are of paramount importance for understanding volcanic processes they remain relatively poorly known4 5 eruptions of crystal rich magma are often suggested to require the mobilization of magma stored at near solidus conditions6 7 8 however accumulation of significant eruptible magma volumes has also been argued to require extended storage of magma at higher temperatures7 8 9 what has been lacking in this debate is clear observational evidence linking the thermal and therefore physical conditions within a magma reservoir to timescales of storage that is thermal histories here we present a method of constraining such thermal histories by combining timescales derived from uranium series disequilibria crystal sizes and trace element zoning in crystals at mount hood oregon usa only a small fraction of the total magma storage duration at most 12 per cent and probably much less than 1 per cent has been spent at temperatures above the critical crystallinity 40 50 per cent at which magma is easily mobilized partial data sets for other volcanoes also suggest that similar conditions of magma storage are widespread and therefore that rapid mobilization of magmas stored at near solidus temperatures is common magma storage at low temperatures indicates that although thermobarometry calculations based on mineral compositions may record the conditions of crystallization they are unlikely to reflect the conditions of most of the time that the magma is stored our results also suggest that largely liquid magma bodies that can be imaged geophysically will be ephemeral features and therefore their detection could indicate imminent eruption

rapid cooling and cold storage in a silicic magma reservoir recorded in individual crystals silicic volcanic eruptions pose considerable hazards yet the processes leading to these eruptions remain poorly known a missing link is knowledge of the thermal history of magma feeding such eruptions which largely controls crystallinity and therefore eruptability we have determined the thermal history of individual zircon crystals from an eruption of the taupo volcanic zone new zealand results show that although zircons resided in the magmatic system for 103 to 105 years they experienced temperatures 650 to 750 c for only years to centuries this implies near solidus long term crystal storage punctuated by rapid heating and cooling reconciling these data with existing models of magma storage requires considering multiple small intrusions and multiple spatial scales and our approach can help to quantify heat input to and output from magma reservoirs

soil failure modes in undrained cyclic loading the failure modes of saturated sand in undrained cyclic loading are explored a typical soil element subject to dynamic load exists initially under a nonhydrostatic state of stress anisotropically consolidated samples in triaxial tests with a superimposed cyclic deviator stress represent such elements except for the rotation of principal stress directions during cycling the response of these samples depends on the degree of anisotropy and whether shear stress reversal occurs for isotropically consolidated undrained tests on saturated sand samples the pore pressure increases with each cycle thus decreasing the effective confining stress the axial cyclic strain also increases as the effective stresses approach the failure state however the static axial strain should remain close to zero for anisotropically consolidated undrained tests with no shear stress reversal the pore pressure generally but not always increases in this case the static axial strain will increase with each cycle and the cyclic strain will remain smaller than the static strain

in situ u pb ages of zircons from the bishop tuff no evidence for long crystal residence times ion microprobe u pb isotope analyses of zircons from fallout and intercalated ash flow deposits of the early most chemically evolved bishop tuff east central california yield a weighted mean age of 823 11 ka mean square of weighted deviates mswd 0 8 n 22 a similar mean age of 839 36 ka mswd 0 6 n 15 obtained on unpolished zircon rims suggests that the difference between these ages and that of 760 ka for the bishop tuff obtained by recent ar isotope determinations may be largely analytical in origin considerations based only on the effect of 230 th 234 u disequilibria on the u pb ages yield an apparent maximum mean crystal residence time for zircon of 100 k y the zircon residence times are significantly shorter than those inferred from previous estimates for the timing of phenocryst growth and suggest that once evolved the early bishop tuff rhyolite was not stored for long before erupting

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

assessment of the liquefaction susceptibility of fine grained soils observations from recent earthquakes and the results of cyclic tests indicate that the chinese criteria are not reliable for determining the liquefaction susceptibility of fine grained soils fine grained soils that liquefied during the 1994 northridge 1999 kocaeli and 1999 chi chi earthquakes often did not meet the clay size criterion of the chinese criteria cyclic testing of a wide range of soils found to liquefy in adapazari during the kocaeli earthquake confirmed that these fine grained soils were susceptible to liquefaction it is not the amount of clay size particles in the soil rather it is the amount and type of clay minerals in the soil that best indicate liquefaction susceptibility thus plasticity index pi is a better indicator of liquefaction susceptibility loose soils with pi 0 85 were susceptible to liquefaction and loose soils with 12 0 8 were systematically more resistant to liquefaction soils with pi 18 tested at low effective confining stresses

beginning of melting in the granite system qz or ab an h2o the beginning of melting in the system qz or ab an h2 o was experimentally reversed in the pressure range p text h text 2 text o 2 15 kbar using starting materials made up of mixtures of quartz and synthetic feldspars with increasing pressure the melting temperature decreases from 690 c at 2 kbar to 630 c at 17 kbar in the an free alkalifeldspar granite system qz or ab h2o in the granite system qz or ab an h2o the increase of the solidus temperature with increasing an content is only very small in comparison to the alkalifeldspar granite system the solidus temperature increases by 3 c 7 c if albite is replaced by plagioclase an 20 an 40 the difference between the solidus temperatures of the alkalifeldspar granite system and of quartz anorthite sanidine assemblages system qz or an h2o is approximately 50 c

geophysical signatures of fracture traces in a karst aquifer florida u s a abstract numerous studies have shown that photolinears are associated with zones of increased fracture density porosity and permeability in carbonate terranes increased solution along the fractures leads to pronounced surface expressions of subsurface fracture zones such as sags sinks and linear depressions such features often have several meters of relief and may be as much as 200 300 m wide r r parizek and others have shown that well yields up to 100 times that of adjacent strata are associated with narrow zones within the surface expressions of the photolinears these zones are seldom more than a few tens of meters wide and often only a few meters wide a study conducted at cross bar ranch wellfield pasco county florida demonstrates that several surface geophysical techniques can be used to delineate zones of higher yield within the wider surface expression of photolinears seismic refraction and d c electrical resistivity proved to be the most useful techniques the geophysical signatures result from the effect of increased karstic solution on overburden thickness and stratigraphy over the inferred fracture zone microgravimetry also appears to be an effective technique showing a distinctive and linearly consistent gravity low of 0 1 0 3 mgal over the inferred fracture zone the geophysical signatures of these methods appear to delineate zones of increased fracture density even where overburden thicknesses exceed 20 m however due to the density of data needed to delineate these zones these methods may be practical only in areas where the locations of such zones are critical and not as a reconnaissance tool

strain degradation of saturated clay under cyclic loading soil degradation is studied from the point of view of cyclic axial strain through stress controlled triaxial tests on hangzhou normally consolidated clay different influence factors on strain such as cyclic stress ratio overconsolidation ratio and frequency are studied degradation index is redefined according to the tests a mathematical model for strain degradation is presented and verified key words cyclic loading saturated clay strain degradation mathematical model

behaviour of clayey sands under undrained cyclic triaxial loading the response of two clayey sands to undrained cyclic triaxial loading is described both the stress history and the cyclic stress level have been varied the behaviour is compared with that observed for the clayey sands tested under monotonic loading effective stress paths for the normally consolidated soils loaded monotonically in triaxial compression and extension are shown to form a hounding envelope which determines the pattern of behaviour under cyclic loading a threshold strain is identified below which cyclic straining results in stable behaviour above the threshold strain pore pressures and strains accumulate under cyclic loading at a rate that increases as the effective stress state approaches the bounding envelope on reaching the bounding envelope in triaxial compression the clayey sands strain soften on reaching the bounding envelope in triaxial extension there is liquefaction l article decrit la reponse de deux sables argileux au chargement triaxial cyclique non draine on a fait vari