experimental study on non aqueous phase liquid multiphase flow characteristics and controlling factors in heterogeneous porous media enhanced understanding of non aqueous phase liquid napl infiltration into porous media is important for the effective design of remediation strategies six model multi flow experiments in two dimensional polymethyl methacrylate tank were carried out to verify the influences of soil initial water content local low permeability lens lithologic sharp interface and leakage position on light non aqueous phase liquid lnapl and dense on non aqueous phase liquid dnapl transport velocities in soil with diesel and perchlorethylene as lnapl and dnapl respectively the evolutions of the plume were recorded through the transparent side of the tank by ccd camera and the contaminant fronts were traced using gel pen on a plastic film coated on tank wall at appropriate intervals the controlling factors of free napl migration paths and speeds were analyzed thoroughly and capillary pressure equilibrium models of napl water napl air interface and the partition movement theory were put forward results show that the effect of napl types soil initial water content local low permeability lens leakage position and lithologic sharp interface on napl migration paths and velocities are diverse the napl movement principles should be presented in accordance with partitions as related to the initial water content namely dry soil area capillary zone and water saturated zone the vertical movement and lateral extension of napl are interdependent and the vertical migration is dominant in initial leakage stage the vertical migration is hindered by lateral growth when meeting with local low permeability lens lithologic sharp interface or capillary fringe vertical migration rate reduction is mainly caused by the pore resistance napl residual and lateral spreading and the causes of corresponding increase of horizontal expansion speed are the decrease of vertical velocity and the increase of buoyancy the sufficiently short time allows to neglect chemical reactions dissolution and sorption of napl and heterogeneous porous media

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

new tree ring dates for recent eruptions of mount st helens abstract distinctive patterns of growth rings in increment cores from old growth douglas fir pseudotsuga menziesii stands identify a d 1800 as a more precise date for the eruption of tephra layer t by mount st helens washington layer t was previously inferred to date to about a d 1802 growth patterns also establish a d 1480 as the date of eruption of the earlier layer wn previously estimated as dating to about a d 1500 the timing of radial tree growth places a small limitation on the seasonal resolution of these new tree ring dates

preeruption conditions and timing of dacite andesite magma mixing in the 2 2 ka eruption at mount rainier analytical field and experimental evidence demonstrate that the mount rainier tephra layer c 2 2 ka preserves a magma mixing event between an andesitic magma whole rock sio 2 content of 57 60 wt and a dacitic magma whole rock sio 2 content of 65 1 wt the end member andesite a mix of an injected and chamber andesite and dacite can be characterized on the basis of the homogeneity of the matrix glass and phenocryst rim compositions many pumices however contain mixtures of the end members the end member dacite contains a microlite free matrix glass with 74 77 wt sio 2 orthopyroxene rims of mg 57 64 clinopyroxene rims of mg 66 74 and plagioclase rim anorthite contents of an 45 65 the temperature and oxygen fugacity from fe ti oxide compositions are 930 10 c and 0 5 0 75 log units above nno the mixed andesite contains mg 73 84 orthopyroxene rims mg 73 78 clinopyroxene rims an 78 84 plagioclase rims and mg 67 74 amphibole rims the temperature from fe ti oxides hornblendeplagioclase and two pyroxene geothermometry is 1060 15 c and the oxygen fugacity is approximately one log unit above nno for the injected andesite the chamber andesite is estimated to be a magma with a 64 65 wt sio 2 melt at 980 c and a nno oxygen fugacity we conclude that the andesitic and dacitic magmas are from separate magma storage regions at 7 km and 2 4 km due to differences in the bimodal whole rock matrix glass and phenocryst compositions and the presence or absence of stable hornblende the time involved from the mixing event through the eruption is limited to a period of 4 5 days based on fe ti oxide reequilibration phenocryst growth rates and hornblende breakdown the eruption sequence is interpreted as having been initiated by an injection of the 1060 15 c andesitic magma into the 980 c 7 km andesite storage region the mixed andesitic magma then intersected a shallow 2 4 km dacitic storage system on its way toward the surface the eruption became more dacitic over time and the final products some show evidence of partial reequilibration between the andesite and dacite

estimating mean velocity in mountain rivers it is often necessary to estimate the mean velocity in ungaged mountain rivers but the flow resistance equations available for this purpose require further testing and development such rivers are characterized by coarse bed materials steep slopes and low depths for these conditions boulders protrude well into or completely through the flow and bed roughness is said to be large scale recently three equations specifically intended for large scale roughness have been developed to address this problem data from a mountain river were used to test the equations all were prone to errors of the order of 30 the errors were systematic all the equations tending to overestimate mean velocity compared to observed values an investigation of the possible sources of error suggested that sampling error in the knowledge of bed material size was a major source of uncertainty in the predicted velocities but that this and discharge errors could not wholly account for the observed discrepancies boulder shape is not represented in the equations but this was discounted as an important parameter on the basis of a flume study it was concluded that further research is required to produce a reliable process based flow resistance equation for mountain rivers

multiphase flow modeling of a crude oil spill site with a bimodal permeability distribution fluid saturation particle size distribution and porosity measurements were obtained from 269 core samples collected from six boreholes along a 90 m transect at a subregion of a crude oil spill site the north pool near bemidji minnesota the oil saturation data collected 11 years after the spill showed an irregularly shaped oil body that appeared to be affected by sediment spatial variability the particle size distribution data were used to estimate the permeability k and retention curves for each sample an additional 344 k estimates were obtained from samples previously collected at the north pool the 613 k estimates were distributed bimodal lognormally with the two population distributions corresponding to the two predominant lithologies a coarse glacial outwash deposit and fine grained interbedded lenses a two step geostatistical approach was used to generate a conditioned realization of k representing the bimodal heterogeneity a cross sectional multiphase flow model was used to simulate the flow of oil and water in the presence of air along the north pool transect for an 11 year period the inclusion of a representation of the bimodal aquifer heterogeneity was crucial for reproduction of general features of the observed oil body if the bimodal heterogeneity was characterized hysteresis did not have to be incorporated into the model because a hysteretic effect was produced by the sediment spatial variability by revising the relative permeability functional relation an improved reproduction of the observed oil saturation distribution was achieved the inclusion of water table fluctuations in the model did not significantly affect the simulated oil saturation distribution

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

intermittent mixing processes occurring before plinian eruptions of popocatepetl volcano mexico insights from textural compositional variations in plagioclase and sr nd pb isotopes volcan popocatepetl has explosively erupted in plinian style at least five times in the last 23 000 years extreme deviations in composition and the occurrence of dissolution features in plagioclase and pyroxene and the occasional presence of xenocrysts of cr rich fe ti oxides and mg rich olivines and pyroxenes indicate that magma mixing has been a major process affecting the magmatic system the nearly invariant composition of the erupted products andesitic dacitic suggests however that mixing is not acting alone and must be balanced by assimilation and or crystallization to investigate the magmatic processes that have modified the plinian magmas textural and compositional variations and growth rates in plagioclase were used to approximate the frequency of mixing events affecting each magma systematic analysis of sr nd and pb isotopes was carried out on plagioclase pyroxene and pumice matrix glass to constrain the extent of assimilation of upper crustal rocks additionally a series of phase equilibrium experiments were carried out to constrain the depth where such mixing and assimilation occurred we find that magma was stored at one of two different depths beneath popocatepetl with magma mixing acting in both reservoirs mixing frequency and the relative impact on mineral compositions and textures has varied with time assimilation of calcareous rocks underneath popocatepetl has not been pervasive and does not contribute significantly to the evolution of the plinian magmas the similar compositions of magmas with diverse mixing histories suggest that fractional crystallization and possibly assimilation of deep crust takes place at depth and that intermediate magmas ascend into the upper crust already differentiated

compositional and dynamic controls on mafic silicic magma interactions at continental arc volcanoes evidence from cordon el guadal tatara san pedro complex chile

the frictional resistance characteristics of a bedrock influenced river channel much of the published literature relating to reach scale total ow resistance concentrates on alluvial rivers and little mention is made of the more extreme resistance found in bedrock in uenced river systems this paper presents the results of a detailed investigation of total ow resistance variation for ve channel types on the sabie river south africa cohesive mixed anastomosed uncohesive mixed anastomosed mixed pool rapid alluvial braided and alluvial single thread over a range of discharges manning s n and darcy weisbach f resistance coef cients are calculated using barnes methodology h h barnes us geological survey water supply paper 1849 1967 these data are analysed at the scales of channel type and morphologic unit and the resultant resistance values are compared with the literature generally the low ow friction values estimated for the bedrock in uenced channel types are higher than any reported flow resistance quanti cation of the alluvial channel type study sites on the sabie river produced values slightly higher than earlier studies of similar morphologies in situations where signi cant areas of irregular bedrock are exposed cohesive mixed anastomosed and mixed pool rapid channel types the high ow resistance coef cients at low discharges probably re ect energy dissipation due to hydraulic jumps and internal distortions however these values fall as discharge increases to values comparable to those recorded for step pool rivers it is suggested that the slightly elevated resistance coef cients recorded in the alluvial channel types are the result of the vegetation roughness component operating when the macro channel bar features are inundated copyright 2004 john wiley sons ltd

the 23 500 y 14 c bp white pumice plinian eruption and associated debris avalanche and tochimilco lava flow of popocatepetl volcano mexico abstract the white pumice wp is one of the thickest and most voluminous plinian fallouts produced by popocatepetl volcano in central mexico during the late pleistocene holocene its eruption 23 500 14 c y bp 27 800 cal bp was triggered by the catastrophic failure of the sw flank of the volcano the resulting debris avalanche was highly mobile reaching 72 km from the cone with an apparent coefficient of friction l h of 0 06 the deposit covers an area of 1200 km 2 and has a volume of 10 4 km 3 this gigantic landslide characterized by exceptionally large proximal hummocks 400 m provoked the sudden decompression of the hydrothermal and magmatic systems which produced an initial blast followed by the rise of a plinian column that reached an altitude of 33 km the isopach map allows the recognition of a dispersal axis pointing toward the south where an area of 2490 km 2 was covered by 10 cm of pumice and ash the total volume of the pumice fallout was estimated at 1 9 km 3 dre dense rock equivalent pumice clasts are dacitic 62 66 wt sio 2 anhydrous basis highly vesicular 55 88 vol and display a seriate texture with phenocrysts of plagioclase hornblende augite hypersthene oxides ti magnetite and ilmenite apatite as the eruption advanced discharge rates became more intermittent and the height of the column fluctuated and finally collapsed generating pumice and ash flows that were emplaced around the volcano this short but intense activity was followed during subsequent years by rain induced lahars that reached great distances from the volcano at the same time more degassed andesitic dacitic 61 65 wt sio 2 magma was erupted effusively 4 4 km 3 dre in the new horseshoe shaped 5 km wide crater from which the tochimilco lava flow descended toward the sse where it inundated an area of 68 km 2 and reached as far as 22 km from its source since then multiple eruptions have reconstructed the summit cone almost completely obliterating the horseshoe shaped crater during the course of this catastrophic eruption vei 5 a total volume of 6 3 km 3 dre of juvenile magma pumice and lava were emitted and at least an additional 10 km 3 of pre existing rocks debris avalanche mobilized it surpasses in magnitude most other known plinian eruptions from popocatepetl and can be envisaged as an example of a worst case scenario for hazard evaluation purposes it dramatically changed the morphology of the volcano and had profound and far reaching effects beyond its immediate vicinity along rivers draining surrounding plains as well as on the lacustrine basins e g chalco to the ne a repeat of such an eruption in this densely populated area would certainly cause a major calamity of unprecedented dimensions

petrogenesis of mount rainier andesite magma flux and geologic controls on the contrasting differentiation styles at stratovolcanoes of the southern washington cascades quaternary mount rainier washington usa of the cascades magmatic arc consists of porphyritic calc alkaline andesites and subordinate dacites with common evidence for mingling and mixing with less evolved magmas encompassing andesites basaltic andesites and rarely basalts basaltic andesites and amphibole andesites spessartites that erupted from vents at the north foot of the volcano represent some of mount rainier s immediate parents and overlap in composition with regional basalts and basaltic andesites geochemical major and trace elements and isotopic sr nd pb o compositions of mount rainier andesites and dacites are consistent with modest assimilation typically 20 wt of evolved sediment or sediment partial melt sandstones and shales of the eocene puget group derived from the continental interior are exposed in regional anticlines flanking the volcano and probably underlie it in the middle to lower crust accounting for their assimilation mesozoic and cenozoic igneous basement rocks are unsuitable as assimilants due to their high 143 nd 144 nd diverse 206 pb 204 pb and generally high 18 o the dominant cause of magmatic evolution at mount rainier however is inferred to be a version of in situ crystallization differentiation and mixing langmuir 1989 wherein small magma batches stall as crustal intrusions and solidify extensively yielding silicic residual liquids with trace element concentrations influenced by accessory mineral saturation subsequent magmas ascending through the intrusive plexus entrain and mix with the residual liquids and low degree re melts of those antecedent intrusions producing hybrid andesites and dacites mount st helens volcanic rocks have geochemical similarities to those at mount rainier and may also result from in situ differentiation and mixing due to low and intermittent long term magma supply accompanied by modest crustal assimilation andesites and dacites of mount adams isotopically overlap the least contaminated mount rainier magmas and derive from similar parental magma types but have trace element variations more consistent with progressive crystallization differentiation probably due to higher magma fluxes leading to slower crystallization of large magma batches allowing time for progressive separation of minerals from melt mount adams also sits atop the southern projection of a regional anticlinorium so eocene sediments are absent or are at shallow crustal levels and so are cold and difficult to assimilate differences between southwest washington stratovolcanoes highlight some ways that crustal geology and magma flux are primary factors in andesite generation

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

a 1 d morphodynamic model for rill erosion 1 the key objective of this paper is to develop a 1 d hydrodynamic and sediment transport model namely rill1d that handles transcritical flows over abrupt changes e g formation of pool crests and width change in a single rill and also predicts changes in rill bed elevation replication of rill conditions in terms of flow and bed evolution changes necessitated the use of an enhanced tvd maccormack scheme with implementation of tseng s surface gradient method to provide an oscillation free solution over formed pool crests the model at the end of each time step calculates the flow depth velocity and bed shear stress and provides changes in bed elevation and grain size distribution within a cell the hydrodynamic performance of rill1d is evaluated by comparing its results with either analytical solutions or experimental observations from various benchmark tests with rigid bed conditions that include 1 formation of a hydraulic jump in a rectangular channel 2 steady subcritical and transcritical flow without a shock over a hump 3 formation of a hydraulic jump in a converging diverging frictionless channel and 4 flows over step pools it is shown that the enhanced tvd maccormack scheme adequately simulates transcritical flows by preserving the mass conservation and reducing the artificial numerical error the scheme also approximates satisfactorily depth and velocity for a single rill with a fixed bed consisting of steps and pools except near the pool headwalls where a backroller forms with negative velocities the sediment component of rill1d is evaluated by two field investigations of single rills with mobile beds with the field data the code is tested for its ability to reproduce measured values of sediment transport rates a sensitivity analysis is performed to assess the effects of cell size and critical erosional strength in the predictive ability of the model rill1d performs reasonably well in these simulations in terms of sediment prediction rates and fared adequately in terms of replicating rill bed morphology

geochemical characteristics of igneous rocks associated with epithermal mineral deposits a review abstract newly synthesized data indicate that the geochemistry of igneous rocks associated with epithermal mineral deposits varies extensively and continuously from subalkaline basaltic to rhyolitic compositions trace element and isotopic data for these rocks are consistent with subduction related magmatism and suggest that the primary source magmas were generated by partial melting of the mantle wedge above subducting oceanic slabs broad geochemical and petrographic diversity of individual igneous rock units associated with epithermal deposits indicate that the associated magmas evolved by open system processes following migration to shallow crustal reservoirs these magmas evolved by assimilation recharge and partial homogenization these processes contribute to arc magmatism worldwide although epithermal deposits with the largest au and ag production are associated with felsic to intermediate composition igneous rocks demonstrable relationships between magmas having any particular composition and epithermal deposit genesis are completely absent because the composition of igneous rock units associated with epithermal deposits ranges from basalt to rhyolite consequently igneous rock compositions do not constitute effective exploration criteria with respect to identification of terranes prospective for epithermal deposit formation however the close spatial and temporal association of igneous rocks and epithermal deposits does suggest a mutual genetic relationship igneous systems likely contribute heat and some of the fluids and metals involved in epithermal deposit formation accordingly deposit formation requires optimization of source metal contents appropriate fluid compositions and characteristics structural features conducive to hydrothermal fluid flow and confinement and receptive host rocks but not magmas with special compositional characteristics

repeated recharge assimilation and hybridization in magmas erupted from el chichon as recorded by plagioclase and amphibole phenocrysts abstract compositional and isotopic zoning patterns in plagioclase and amphibole phenocrysts from el chichon record multiple cycles of country rock assimilation magma injection hybridization and mixing laser ablation icp ms and electron microprobe analyses of plagioclase crystals from 7 eruptions spanning 3100 years reveal four types of zoning these compositional and isotopic zones are often associated with textural changes observed in the crystals in thin section e g sieved or patchy regions amphiboles are frequently zoned in al and si and in two magmas may have clinopyroxene rims interestingly most plagioclase show multiple and repeated zoning patterns moreover all magmas contain all zoning patterns and textures and crystals with substantially different sequences of zones occur within mm of one another the most reasonable explanation for the origin of these textures is a frequently recharged chamber plagioclase zones with increasing anorthite contents an and decreasing 87sr 86sr ratios record injection by a hotter possibly wetter and more primitive magma lower 87sr 86sr ratio zones with decreasing an and increasing 87sr 86sr ratios record assimilation of country rock and or hybridization of the host and injected magmas injection of hot magma may provide the heat for country rock assimilation changes in an without corresponding changes in 87sr 86sr ratio likely record slight variations in pressure or temperature during crystallization or the far field thermal effects of magma injection variations in 87sr 86sr ratio unaccompanied by anzoning record assimilation of country rock amphibole zoning patterns also record periodic heating events amphibole with clinopyroxene rims record episodes where the magma was heated beyond the amphibole stability field bulk compositional homogeneity and the juxtaposition of many crystals with disparate zoning patterns in single pumice require the magmatic system to be well mixed strontium diffusion rates indicate that the plagioclase zoning patterns cannot have persisted at magmatic pressures and temperatures for more than 500 years thus cycles of injection and assimilation occur on timescales equal to or shorter than the eruption recurrence interval long term compositional and isotopic homogeneity indicate that there is a balance between recharge assimilation and crystallization

feedback between bed load transport and flow resistance in gravel and cobble bed rivers 1 to calculate bed load engineers often use flow resistance equations that provide estimates of bed shear stress in these equations on the basis of the estimate of the appropriate hydraulic radius associated with the bed only the bed roughness ks is commonly set as a constant whatever the bed load intensity however several studies have confirmed the existence of feedback mechanisms between flow resistance and bed load suggesting that a flow dependent bed roughness should be used therefore using a data set composed of 2282 flume and field experimental values this study investigated the importance of these feedback effects new flow resistance equations were proposed for three flow domains domain 1 corresponds to no bed load and a constant bed roughness ks d where d is a representative grain diameter whereas domain 3 corresponds to a high bed load transport rate over a flat bed with a constant bed roughness ks 2 6d between these two domains a transitional domain 2 was identified for which the bed roughness evolved from d to 2 6d with increasing flow conditions in this domain the darcy weisbach resistance coefficient f can be approximated using a constant for a given slope the results using this new flow resistance equation proved to be more accurate than those using equations obtained from simple fittings of logarithmic laws to mean values the data set indicates that distinguishing domains 2 and 3 is still relevant for bed load in particular the data indicate a slope dependence in domain 2 but not in domain 3 a bed load model based on the tractive force concept is proposed finally flow resistance and bed load equations were used together to calculate both shear stress and bed load from the flow discharge the slope and the grain diameter for each run of the data set efficiency tests indicate that new equations implicitly taking a feedback mechanism into account can reduce the error by a factor of 2 when compared to other equations currently in use showing that feedback between flow resistance and bed load can improve field bed load modeling

the origin of mount st helens andesites abstract mount st helens volcano has intermittently produced mainly dacitic products but occasionally erupted a more diverse suite of lavas including basalts and andesites petrogenetic relations between these magmas provide insight into the dynamics of the subjacent magma system mineralogical and geochemical features of representative lavas erupted during the past 2200 years can distinguish three basaltic and three andesitic variants the mafic lavas include a transitional olivine plagioclase basalts with low k 2 o and incompatible trace element abundances b calc alkaline olivine plagioclase clinopyroxene basalts enriched in k 2 o tio 2 and incompatible trace elements and c calc alkaline olivine plagioclase basaltic andesites with incompatible trace element contents transitional between the two basalt types intermediate lavas include a tholeiitic two pyroxene andesites b calc alkaline plagioclase two pyroxenes olivine amphibole mafic andesites 56 59 wt sio 2 and c calc alkaline plagioclase two pyroxenes amphibole high silica andesites 61 62 wt sio 2 eruption of these magmatic variants within the same eruptive phase implies the existence of different petrogenetic lineages and that the plumbing system is sufficiently complex to simultaneously isolate and preserve numerous magma batches it is unlikely that any of the andesites or dacites are derived by fractional crystallization of the recognized basaltic variants formation of the andesites simply by contamination or assimilation fractional crystallization of basaltic magma is also improbable more plausibly the andesites represent mixing between basaltic and dacitic end member magmas each of which may be somewhat heterogeneous or vary in composition with time in this model efficient mixing must occur in some parts of the magma plumbing system while some conduits or storage reservoirs must be effectively isolated

evaluation of flow resistance in gravel bed rivers through a large field data set 1 a data set of 2890 field measurements was used to test the ability of several conventional flow resistance equations to predict mean flow velocity in gravel bed rivers when used with no calibration the tests were performed using both flow depth and discharge as input since discharge may be a more reliable measure of flow conditions in shallow flows generally better predictions are obtained when using flow discharge as input the results indicate that the manning strickler and the keulegan equations show considerable disagreement with observed flow velocities for flow depths smaller than 10 times the characteristic grain diameter most equations show some systematic deviation for small relative flow depth the use of new definitions for dimensionless variables in terms of nondimensional hydraulic geometry equations allows the development of a new flow resistance equation the best overall performance is obtained by the ferguson approach which combines two power law flow resistance equations that are different for deep and shallow flows to use this approach with flow discharge as input a logarithmic matching equation in terms of the new dimensionless variables is proposed for the domains of intermediate and large scale roughness the field data indicate a considerable increase in flow resistance as compared with the domain of small scale roughness the ferguson approach is used to discuss the importance of flow resistance partitioning for bed load transport calculations at flow conditions with intermediate and large scale roughness in natural gravel cobble and boulder bed streams

water velocity and the nature of critical flow in large rapids on the colorado river utah 1 rapids are an integral part of bedrock controlled rivers influencing aquatic ecology geomorphology and recreational value flow measurements in rapids and high gradient rivers are uncommon because of technical difficulties associated with positioning and operating sufficiently robust instruments in the current study detailed velocity water surface and bathymetric data were collected within rapids on the colorado river in eastern utah with the water surface survey it was found that shoreline based water surface surveys may misrepresent the water surface slope along the centerline of a rapid flow velocities were measured with an adcp and an electronic pitot static tube integrating multiple measurements the adcp returned velocity data from the entire water column even in sections of high water velocity the maximum mean velocity measured with the adcp was 3 7 m s the pitot static tube while capable of only point measurements quantified velocity 0 39 m below the surface the maximum mean velocity measured with the pitot tube was 5 2 m s with instantaneous velocities up to 6 5 m s analysis of the data showed that flow was subcritical throughout all measured rapids with a maximum measured froude number of 0 7 in the largest measured rapids froude numbers were highest at the entrance of a given rapid then decreased below the first breaking waves in the absence of detailed bathymetric and velocity data the froude number in the fastest flowing section of a rapid was estimated from near surface velocity and depth soundings alone

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

large woody debris and flow resistance in step pool channels cascade range washington abstract total flow resistance measured as darcy weisbach f in 20 step pool channels with large woody debris lwd in washington ranged from 5 to 380 during summer low flows step risers in the study streams consist of either 1 large and relatively immobile woody debris bedrock or roots that form fixed or forced steps or 2 smaller and relatively mobile wood or clasts or a mixture of both arranged across the channel by the stream flow resistance in step pool channels may be partitioned into grain form and spill resistance grain resistance is calculated as a function of particle size and form resistance is calculated as large woody debris drag combined grain and form resistance account for less than 10 of the total flow resistance we initially assumed that the substantial remaining portion is spill resistance attributable to steps however measured step characteristics could not explain between reach variations in flow resistance this suggests that other factors may be significant the coefficient of variation of the hydraulic radius explained 43 of the variation in friction factors between streams for example large woody debris generates form resistance on step treads and spill resistance at step risers because the form resistance of step pool channels is relatively minor compared to spill resistance and because wood in steps accentuates spill resistance by increasing step height we suggest that wood in step risers influences channel hydraulics more than wood elsewhere in the channel hence the distribution and function not just abundance of large woody debris is critical in steep step pool channels

distribution of volcanoes in active margins we report a comprehensive study of the distribution of volcanoes in 16 active plate margins corresponding to a total of 479 volcanic systems the active volcanic arcs are found to have a ribbon geometry with an average length width ratio of around 10 the shape of the volcanic arc is compared to the shape of the associated trench by projecting one onto the other the projection direction agrees with the direction of plate convergence which shows that plate motion is the main factor constraining magma generation on the lithospheric scale there is no characteristic spacing between volcanoes in each arc the distribution of volcano spacing is best represented by a gamma distribution which corresponds to randomly generated points in the same geometrical conditions in order to explain how such distributions may be generated we have investigated in the laboratory the gravitational instability of a layer of buoyant liquid which is fed at a constant rate at the bottom of denser fluid different dynamic regimes are reached for different values of the viscosity ratio between the two fluids for low viscosity contrasts there is only one initial instability event with buoyant plumes organized in a periodic pattern these plumes are fed continuously by the source even at large times for high viscosity contrasts which is relevant to the geological problem plumes are produced intermittently by individual instability events they take the form of cavity plumes fed by narrow tails once the plumes have reached the surface they continue to be fed from below by material rising through their shrinking tail in successive instability events plume generation is not repeated at the same locations which leads to a complex plan form with time and hence with increasing number of instability events the cumulative distribution of plume spacing changes from periodic to random material from a single plume is able to sustain volcanic eruptions for a period longer than the time between two instability events and hence the distribution of active volcanic centers reflects the cumulative distribution of several instability events this is consistent with the observed distributions

petrologic diversity in mount st helens dacites during the last 4 000 years implications for magma mixing mount st helens has explosively erupted dacitic magma discontinuously over the last 40 000 years and detailed stratigraphic data are available for the past 4 000 years during this last time period the major element composition of the dacites has ranged from mafic 62 64 wt sio2 to felsic 65 67 wt sio2 temperature has varied by about 150 c 770 920 c and crystallinity has ranged between 20 and 55 water content of these dacites has also fluctuated greatly although the source for the dacitic magmas is probably partial melting of lower crustal rocks there is strong physical evidence such as banded pumices thermal heterogeneities in single pumices phenocryst disequilibrium contrasts between compositions of glass inclusions and host matrix glass and amphibole reaction rims that suggests that magma mixing has been prominent in the dacitic reservoir indeed we suggest that the variations in major and trace element abundances in mount st helens dacites indicate that magma mixing between felsic dacite and mafic magma has controlled the petrologic diversity of the dacitic magmas magma mixing has also controlled the composition of andesites erupted at mount st helens and thus it appears that the continuum of magmatic composition erupted at the volcano is controlled by mixing between felsic dacite or possibly rhyodacite and basalt the flux of the felsic endmember to the reservior appears to have been relatively constant whereas the flux of basalt may have increased in the past 4 000 years as suggested by the apparently increased abundance of mafic dacite and andesite erupted in this period

the isotopic and chemical evolution of mount st helens isotopic and major and trace element analysis of nine samples of eruptive products spanning the history of the mt st helens volcano suggest three different episodes 1 40 000 2500 years ago eruptions of dacite with end 5 esr 10 variable 18o 206pb 204pb 18 76 ca sr 60 rb ba 0 1 la yb 18 2 2500 1000 years ago eruptions of basalt andesite and dacite with end 4 to 8 esr 7 to 22 variable 18o thought to represent melting of differing mantle crust reservoirs 206pb 204pb 18 81 18 87 variable ca sr rb ba la yb and high zr 3 1000 years ago to present day eruptions of andesite and dacite with end 6 esr 13 18o 6 variable206pb 204pb ca sr 77 rb ba 0 1 la yb 11 none of the products exhibit eu anomalies and all are lree enriched there is a strong correlation between87sr 86sr and differentiation indices these data are interpreted in terms of a mantle heat source melting young crust bearing zircon and garnet but not feldspar followed by intrusion of this crustal reservoir by mantle derived magma which caused further crustal melting and contaminated the crustal magma system with mafic components since 1000 years ago all the eruptions have been from the same reservoir which has displayed a much more gradual re equilibration of pb isotopic compositions than other components suggesting that pb is being transported via a fluid phase the nd and sr isotopic compositions lie along the mantle array and suggest that the mantle underneath mt st helens is not as depleted as morb sources there is no indication of seawater involvement in the source region

evaluation of paleohydrologic models for terrestrial inverted channels implications for application to martian sinuous ridges abstract fluvial systems can be preserved in inverted relief on both earth and mars few studies have evaluated the applicability of various paleohydrological models to inverted fluvial systems the first phase of this investigation focused on an extensive spanning 12 km inverted paleochannel system that consists of four sandstone capped carbonate cemented sinuous ridges within the early cretaceous cedar mountain formation located southwest of green river utah morphologic and sedimentologic observations of the exhumed paleochannels were used to evaluate multiple numerical models for reconstructing paleofluvial hydrological parameters another objective of the study was to determine whether aerial or orbital observations yield model results that are consistent with those constrained by field data the models yield an envelope of plausible dominant discharge values 100 500 m 3 s reflecting the limitations of the approach and no single model can be used to reliably estimate paleodischarge on mars landforms with attributes consistent with inverted channels have been identified in spite of differences in the formation history between these martian landforms and the terrestrial analog described here including potential differences in cement composition and the erosional agent that was responsible for relief inversion these numerical models can be applied with modification to the martian landforms and yield an envelope of plausible values for dominant discharge

re examination of crystal ages in recent mount st helens lavas implications for magma reservoir processes u series data for recent mount st helens lavas suggest that crystallization preceded eruption by more than 0 5 ka but are complicated by possible evidence of crystal recycling and or addition of radium to the liquid after crystallization we report new ion and electron microprobe trace and major element data for plagioclase and pyroxene in these recent mount st helens lavas and use these data to reassess 226ra 230th crystal ages by taking into account differences in the partitioning behavior of radium and barium and the effects of impurities in mineral separates revised 226ra 230th model crystallization ages are 2 4 ka for plagioclase with the exception of the 1982 dacite and 0 15 5 7 ka for pyroxene in contrast to previous interpretations no late stage addition of ra to the liquid after precipitation of the minerals is required the variability of ba concentrations measured in plagioclase is too large to be consistent with progressive crystallization from the same liquid or with diffusive re equilibration of xenocrysts with a new host liquid ba heterogeneity limits the residence time of the crystals in a magma at high temperatures and also suggests that in most cases ra th ages have not been significantly modified by ra diffusion into or out of the crystals high 226ra ba in plagioclase in the 1982 dacite relative to the host liquid likely reflects crystallization processes that precluded bulk crystal liquid chemical equilibrium one possibility is that of growth entrapment of surface enrichments during rapid crystallization which could lead to less discrimination between ra and ba than predicted by calculated bulk partition coefficients 226ra 230th crystal ages for the castle creek andesite and basalt that are younger than 230th 238u ages of the same crystals could be explained by mixing of crystals into melts with different 230th 232th ratios by combinations of older and younger crystal growth within the same magma or for the basalt by diffusion of ra into crystals at high magmatic temperatures average plagioclase ages in most of the samples of 2 ka imply that some significant mass fraction of the crystals in each flow was present simultaneously beneath the volcano this observation could be consistent either with simultaneous storage of physically distinct magma batches or with incorporation of a population of similarly aged crystals into each successive magma batch

centrifuge modeling of nonaqueous phase liquid movement and entrapment in unsaturated layered soils four geotechnical centrifuge tests with different soil layered systems were performed to investigate the movement and entrapment of water and of light nonaqueous phase liquids lnapls in unsaturated layered soil deposits the tests were performed at 20 g and a vadose zone condition was created during the centrifuge tests by lowering the water table from the initially water saturated condition during the water drainage stage the water distribution within the models and the dynamic air water capillary pressure saturation relationships of the three sands were obtained using tensiometers and resistivity probes after achieving the unsaturated condition a model lnapl soltrol 220 or silicon oil was injected near the soil surface and the movement and entrapment were monitored during the redistribution stage until the lnapl reached the top of the water table complex lnapl preferential flow and entrapment patterns were observed in the layered models with different textural interfaces due to the relative movement of all three phases water nonaqueous phase liquid napl and air the centrifuge tests data coupled with the numerical analyses show that napl properties subsurface soil structures initial water saturation and napl infiltration rate affect the variation in entrapment conditions in heterogeneous unsaturated soil deposits

resistance to flow in steep rough streams a theory of resistance to flow in steep rough streams is developed that takes into account the existence of a highly turbulent wake zone near the bed of a very rough boundary two zones are identified in the flow field the first one close to the top of the bed contains overlapping wakes generated by protruding roughness elements in the second zone located above the first one the velocity distribution is described in terms of a logarithmic profile flume data are used to check the validity of this formulation the compound velocity profile allows for equations to obtain darcy weisbach and chezy factors the proposed approach is compared with the results of four previous theories using data obtained from several mountain rivers although flow in actual mountain rivers is more complicated than the idealized case treated in the study the formulation provides equations that allow accurate prediction of flow resistance with a mean error of 15

short time scales of magma mixing processes prior to the 2011 eruption of shinmoedake volcano kirishima volcanic group japan we estimated time scales of magma mixing processes just prior to the 2011 sub plinian eruptions of shinmoedake volcano to investigate the mechanisms of the triggering processes of these eruptions the sequence of these eruptions serves as an ideal example to investigate eruption mechanisms because the available geophysical and petrological observations can be combined for interpretation of magmatic processes the eruptive products were mainly phenocryst rich 28 vol andesitic pumice sio2 57 wt with a small amount of more silicic pumice sio2 62 63 wt and banded pumice these pumices were formed by mixing of low temperature mushy silicic magma dacite and high temperature mafic magma basalt or basaltic andesite we calculated the time scales on the basis of zoning analysis of magnetite phenocrysts and diffusion calculations and we compared the derived time scales with those of volcanic inflation deflation observations the magnetite data revealed that a significant mixing process mixing i occurred 0 4 to 3 days before the eruptions pre eruptive mixing and likely triggered the eruptions this mixing process was not accompanied by significant crustal deformation indicating that the process was not accompanied by a significant change in volume of the magma chamber we propose magmatic overturn or melt accumulation within the magma chamber as a possible process a subordinate mixing process mixing ii also occurred only several hours before the eruptions likely during magma ascent syn eruptive mixing however we interpret mafic injection to have begun more than several tens of days prior to mixing i likely occurring with the beginning of the inflation december 2009 the injection did not instantaneously cause an eruption but could have resulted in stable stratified magma layers to form a hybrid andesitic magma mobile layer this hybrid andesite then formed the main eruptive component of the 2011 eruptions of shinmoedake

tree ring evidence for a two year interval between recent prehistoric explosive eruptions of mount st helens distinctive annual ring patterns in trees in a forest stand 10 km east of mount st helens indicate that the volcano9s voluminous layer we tephra was erupted after the a d 1481 growth season late in 1481 or early during 1482 combined with earlier research that established a d 1480 as the date of eruption of the underlying similar layer wn tephra the new tree ring data provide evidence that these two major explosive tephra eruptions about 500 yr ago were separated by about 2 yr during that eruptive sequence a voluminous explosive eruption was therefore followed by more than 1 yr of minor explosive activity before another voluminous eruption occurred this record suggests that mount st helens might produce a second large explosive eruption during its current period of activity examinations of the tephra deposits that correlate with narrowring patterns in trees at mount st helens also demonstrate that distinctive ring patterns can form in trees across a large range of tephra layer thicknesses the examinations also suggest that tephra coarseness interacts with tephra layer thickness in determining the effects that tephra fallout will have upon forest trees

the genesis of arc dacites the case of mount st helens wa throughout the last 35 ka mount st helens has been the most active volcano in the cascade arc but the origin of its voluminous dacites remains controversial these dacites were traditionally interpreted as a result of melting metabasaltic lower crust yet recent studies have challenged this view and suggested an origin dominated by differentiation of mafic magmas through assimilation fractional crystallization afc processes to address this discrepancy on the origin of dacites at mount st helens we conduct an interdisciplinary study using a combination of thermal and geochemical modeling our results show that 45 crystallization of a basaltic andesite parent reproduces the compositions of the dacites with a maximum of 20 30 assimilation of lower crustal lithologies amphibole textures and compositions support such a differentiation trend in a polybaric mush system combined with recent geophysical imaging and experimental data we suggest that mount st helens dacites are generated by 1 mantle derived arc magma evolving by afc to intermediate compositions in a lower crustal magma reservoir and 2 ascent of these magmas to a mid to upper crustal reservoir where they reach high crystallinity without significant further chemical differentiation and are subject to frequent recharge that leave a clear mixing mingling overprint

volcanoes interpreting inclusive evidence crystallization of ascending magma may affect the style of volcanic activity pockets of melt incorporated into crystals provide windows on processes that occur several kilometres below earth s surface

cummingtonite and the evolution of the mount st helens washington magma system an experimental study hydrothermal experiments have been conducted on the 3 5 ka cummingtonite bearing yn tephra from mount st helens washington to determine the stability field of cummingtonite in volcanic rocks and to gather additional data on the evolutionary history of the mount st helens magmatic system cummingtonite is not stable in experiments conducted at or above 810 c at pressures 2 o analyses of melt inclusions that yield preeruption melt h 2 o contents of 6 4 wt the yn tephra belongs to a series of cummingtonite bearing dacites that erupted early in the history of mount st helens these early dacites have relatively homogeneous compositions and are characterized by low temperature 800 c high water pressure and high oxygen fugacity nno 1 phenocryst crystallization silicic magmas that erupted after eruption of basaltic andesite at mount st helens 2 3 ka are more heterogeneous in composition and last equilibrated under higher temperatures 900 c lower water pressures and lower oxygen fugacities than the early dacites these changes in the magma chamber conditions appear to have been related to the intrusion of mafic magma into an upper crustal dacitic magma chamber

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

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

emplacement of nonaqueous liquids in the vadose zone the results of experimental and analytical investigations of the movement of lighter than water organic liquids in the vadose zone are presented the experiments consisted of physical model tests simulating nonaqueous phase liquid napl spills in unsaturated two dimensional domain above the water table the evolution of the plume was observed through the transparent side of a tank containing sand and the contaminant front was traced at appropriate intervals visual observations were supplemented with pressure and saturation measurements suitable for quantitative analysis of the process the experiments show that during infiltration the front advances at constant speed area time after spreading comes to a halt the bulk of the contaminant is contained within a pancake shaped lens situated on top of the capillary fringe fluctuations of the phreatic surface result in trapping the napl below the water table and in spreading the contaminant over a larger area in layered samples the behavior is largely geometry dependent although heterogeneities invariably result in extensive horizontal spreading simplified analytical relationships were developed to estimate the spreading rate of the contaminant during infiltration and the thickness of the final immobilized oil lens observed during the experiments these relationships are based on capillary pressure considerations which have to be included in order to model the immobilization of the plume at saturations higher than the residual values which typically occur in vadose zone when the napl encounters the capillary fringe in its downward migration

coarse bedload transport in a mountain river coarse bedload transport dynamics are investigated utilizing hydrodynamic and sediment transport data obtained in an extensively instrumented study reach located in squaw creek montana usa during 1991 and 1992 a number of discrete bedload transport events associated with the daily rise and fall in stream discharge were investigated data show that initiation of sediment transport was accompanied by a reduction in bed roughness and by changes in bulk hydraulic parameters for larger discharges coarser fractions of the bed material mobilized and bedload transport rates and average hydraulic parameters stabilized as discharge reduced mobile coarse particles became less frequent and deposited fine particles were removed resulting in an increase in bed roughness these observations are attributed to the downstream translation of bar sediments during the passage of a hydrograph bedload pulses were aperiodic but spatially variable flow turbulence and velocity profile data obtained during low flows allowed comparison between average bed shear stress and apparent bed roughness estimates obtained using different approaches 1998 john wiley sons ltd

slope area discharge gaging in mountain rivers tests of the slopearea gaging technique at 16 sites in gravel and boulderbed rivers with slopes of 0 44 in upland britain show that the field measurements must include detailed surveys of bed cros

some consequences of volcanic edifice destruction for eruption conditions abstract destruction of a volcanic edifice by landslides or phreatic explosions unloads the upper crust induced changes of stress field around and of magmatic pressure within a magma reservoir are investigated with an analytical model for the deformation of a liquid filled cavity within an elastic half space unloading affects the reservoir pressure and hence the net result depends on how the liquid filled reservoir responds to a change of remote stress magma compressibility is taken into account and may dampen changes of internal pressure in small volatile rich reservoirs the main consequence of edifice destruction is a decrease of magmatic pressure and stresses on the reservoir walls in some cases this may be responsible for dyke closure at the reservoir walls which stops magma withdrawal and may prevent eruption if an eruption does occur edifice destruction affects the volume of magma erupted depending on edifice size magma reservoir size and depth the erupted volume may be smaller or larger than that which would be erupted with no damage to the edifice these results suggest that major phreatic explosions may prevent magmatic eruptions

time scales of magma formation ascent and storage beneath subduction zone volcanoes there is now sucient information to attempt an integrated model for melt gener ation transfer and storage beneath subduction zone volcanoes fluid release from the subducting oceanic crust into the mantle wedge may occur over a period ranging from a few hundred kyr to as little as less than 1 kyr before eruption this supports models in which uid addition is closely linked to partial melting though there may also be evidence for a component of decompression melting the timing of the onset of uid addition may be linked to the rate of subduction i e water supply rate and the angle of subduction and consequently the thermal structure of the mantle wedge in contrast contributions from subducted sediments to subduction zone lava sources appear to occur some 350 kyr 4 myr before eruption evidence for partial melting of the sediment component combined with the short uid transfer times phenocryst equilibration temperatures and other observations all point to quite high mantle wedge temperatures close to the interface with the subducting plate new 226 ra data permit only a short period of time between uid addition and eruption this requires rapid melt segregation magma ascent by channelled ow and minimal residence time within the lithosphere typically the evolution from basalt to andesite occurs rapidly during ascent or in magma reservoirs inferred from some geophysical data to lie within the lithospheric mantle mineral isochron data suggest that some andesitic magmas subsequently stall in more shallow crustal level magma chambers where they can evolve to dacitic compositions via fractionation typically combined with assimilation on time scales of a few thousand years or less

simulation of three dimensional flow of immiscible fluids within and below the unsaturated zone this paper presents a two phase flow model based on a three dimensional finite difference formulation as three dimensional simulations can require substantial computer effort a numerical technique that takes advantage of vector and parallel processing computer architecture is developed the model is posed in terms of water saturation and nonwetting fluid pressure it uses three phase capillary pressure and relative permeability relationships to permit simulation within or below the unsaturated zone a modified formulation of slice successive overtaxation an iterative matrix solution technique is introduced this technique is designed to use parallel processing capabilities of new computers the model is applied to immiscible fluid flow at two chemical waste landfills near niagara falls new york at both sites denser than water nonaqueous liquids napls are present in the groundwater regimes in relatively large quantities the model applications address several technical concerns at the two sites including the effectiveness of clay as a geologic barrier to napl migration owing to capillary pressure forces the three dimensional aspects of dense napl flow and the sensitivity of napl recovery in pumping wells due to various hydrogeologic and fluid properties the results of the applications show that 1 even under a downward hydraulic gradient natural differences in capillary pressure relationships for different lithologies can prevent downward migration of napl 2 without any lithologic capillary barrier an upward hydraulic gradient induced by a de watering system can prevent downward migration of napl 3 napl recovery at wells is sensitive to relative permeability a relationship that requires field calibration in many settings and 4 the three dimensional aspects of two phase flow and hydrogeologic heterogeneity require explicit treatment in many settings

bar form resistance in gravel bed rivers resistance to flow in unvegetated gravel bed rivers is basically dependent on the skin resistance due to surface bed material and bar form resistance due to accelerations and decelerations in the flow between pools and riffles although flow is generally nonuniform at riffle sections flow is locally uniform it is these sections which principally control the velocity depth characteristics of the reach since hydraulic conditions in the pool result from the backwater effect of the riffle isolating the effect of bar forms on flow resistance is achieved by first establishing the roughness height of the surface bed material on the riffle overall resistance to flow in terms of the total roughness height due to bed forms and grains for equivalent uniform flow is determined from the riffle and reach average flow geometry and the grain roughness height differences between total and grain roughness heights define the bar form effect field data from 62 sites in the united kingdom illustrate that at bankful

estimation of flow through and over armored slopes models developed for the transient routing of intense rainfall on small armored slopes depend on expressions for flow resistance below and above the surface of the armored layer a series of 52 experiments are conducted in two flumes to collect data on the basic relationships of flow resistance crushed rock of 26 155 mm median diameter is placed on embankments with slopes ranging from 0 01 to 0 2 and subjected to steady flow in the flumes flow through the rock layer is found to be approximately proportional to the rock layer porosity the square root of the slope and the mean diameter of the rock and weakly proportional to the stage the portion of flow through the filter layer generally cannot be neglected flow resistance decreases and conveyance greatly increases when the stage exceeds the depth of the rock layer a model for flow both beneath and above the rock surface on an armored slope is synthesized from formulas developed for flow in rubble dams and darcy weisbach formulas developed for flow

the intensity and magnitude of holocene plinian eruptions from mount st helens volcano dispersal characteristics of the t we wn pu ps ye yn and yb plinian fall deposits of mount st helens have been measured at 80 sites downwind of the volcano in order to model eruption dynamics and atmospheric transport isopleth contours for the sizes of maximum pumice and lithic clasts are used to calculate peak eruption column heights and intensities magma discharge based on a theoretical model of tephra dispersal new proximal thickness measurements are combined with an empirical distal extrapolation based on studies of 53 plinian deposits to calculate the magnitude erupted mass of each eruption layer yn 3510 y r b p represents the highest intensity and largest magnitude eruption at mount st helens in post glacial times modeling suggests column height grew to about 31 km before gradually declining at the end of the plinian phase 26 hours several intraplinian surge deposits are present in the upper part of the fall layer close to the volcano and up to 15 km to the northeast of mount st helens peak intensity of the plinian phase was 108 kg s and the total erupted volume was 4 km3 dre of magma small plinian style eruptions are represented by layers such as ps and pu of the pine creek eruptive period 3000 2500 yr b p and have intensities of only 106 kg s when compared with plinian eruptions from other volcanoes the holocene eruptions of mount st helens span from the lower to the middle part of the known range in intensity and magnitude and are typical of events derived from intermediate sized stratovolcanoes there is also a general correlation between the intensity of plinian eruptions within eruptive cycles and the repose period prior to each cycle this relationship may be related to a time dependent process for the accumulation of differentiated and volatile rich magma within the chamber beneath mount st helens

laboratory determined transport properties of core from the salton sea scientific drilling project two cores from the salton sea scientific drilling project have been studied in the laboratory to determine electrical resistivity ultrasonic velocity and brine permeability at pressures and temperatures close to estimated borehole conditions both samples were siltstones the first sample was from 1158 m depth and the other was from 919 m depth a synthetic brine with 13 6 weight percent nacl 7 5 weight percent cacl2 and 3 2 weight percent kcl was used as a pore fluid the dry bulk density of the first sample was 2 44 mg m 3 with an effective porosity of 8 7 the second sample had a dry bulk density of 2 06 mg m 3 with an effective porosity of 22 2 at the midplane of the first sample electrical impedance tomography was used to map the spatial variation of resistivity during the experiment also at the midplane of both samples ultrasonic tomography was used to map the spatial variation of p wave velocity in addition resistivity was measured with six pairs of electrodes along the sample axis both samples showed a strong anisotropy in resistivity and ultrasonic velocity measured perpendicular and parallel to the sample axis the brine permeability of the first sample decreased from 5 d to about 1 6 d during the experiment the second sample permeability had the same trend but the permeability values were about 3 orders of magnitude larger the second sample was subjected to temperatures and pressures exceeding those experienced in situ permeability resistivity and ultrasonic velocity of this sample showed a discontinuous change just beyond these in situ conditions this discontinuity implies a structural change in the rock under conditions which would be found below its origin depth in the borehole a model is proposed to explain the observed velocity anisotropy and variations in velocity electrical resistivity anisotropy and permeability with effective depth when in situ stress is released microcracking may occur along grain boundaries preferentially oriented parallel to bedding this microcracking controls velocity and resistivity anisotropy at room conditions when pressure and temperature are restored competing effects of compaction and thermal softening of the minerals cause a reversal in the anisotropy at temperatures and pressures above those at in situ conditions thermal fracturing or geochemical alteration along grain boundaries causes a discontinuous change in sample physical properties

the acoculco caldera complex magmas genesis evolution and relation with the acoculco geothermal system abstract the acoculco caldera complex acc is located in the eastern part of the trans mexican volcanic belt mexico the acc was formed 2 7 ma and since then volcanic activity has persisted until 0 06 ma through the emission of domes cinder cones fissure lava flows and two ignimbrite eruptions dated at 1 2 and 0 65 ma the pervasive hydrothermal alteration in the central part of the acc has motivated considerable geothermal exploration however none of it assessed the relation between the magmatic heat supply and the evolution of magmas including their reservoir depth magmatic processes were investigated with petrography major oxides trace element geochemistry mineral chemistry and isotopic analysis in addition we performed a series of hydrothermal experiments in order to constrain the storage depth for the magma tapped 1 2 ma during a reactivation of the caldera we investigated the origin of magmas tapped during the eruptive history of the acc and the magmatic processes magma mixing assimilation and crystallization that modified these magmas after the caldera collapse 2 7 ma the local stress field was probably modified and allowed the ascent of peralkaline magmas through new plumbing systems such magmas mixed with calc alkaline magmas and formed the post caldera volcanism influx of new magma is considered as the probable heat supply that maintains the active magmatic system whereas assimilation has been negligible but yields insights about the depth at which processes have occurred our work suggests that there are either shallow storage zones 200 500 bars where magmas crystallize and either erupt or stall and cool or there are intrusive magmas unrelated to the acc suite that have accumulated nearby and heat the reservoir magmas

characterization of transport in an acidic and metal rich mountain stream based on a lithium tracer injection and simulations of transient storage physical parameters characterizing solute transport in the snake river an acidic and metal rich mountain stream near montezuma colorado were variable along a 5 2 km study reach stream cross sectional area and volumetric inflow each varied by a factor of 3 because of transient storage the residence time of injected tracers in the snake river was longer than would be calculated by consideration of convective travel time alone distributed inflows along the stream were a significant source of in stream chemical variations these transport characteristics of the snake river were established on the basis of the assumption of lithium as an ideally conservative tracer and use of simulations of advection dispersion and transient storage evaluations of the validity of this combined tracer and simulation approach lend confidence to the estimation of the physical transport parameters but further development is warranted for methods of onsite transport experimentation in hydrologically complex chemically reactive environments

roughness of loose rock riprap on steep slopes a study was conducted to determine the roughness of rock riprap laid on steep slopes tests were conducted in a 1 07 m wide flume and two 2 74 m wide field scale structures using angular riprap with median diameters d50 ranging from 52 to 278 mm and bed slopes s0 ranging from 0 028 to 0 333 m m empirical relationships were developed to predict the manning roughness coefficient as a function of d50 and s0 the darcy weisbach friction factor was predicted as a function of d d84 the relative submergence newly developed equations are applicable for riprap placed on slopes from 2 8 33 roughness coefficients calculated using the developed equations were compared with roughness coefficients calculated using equations developed from observations on natural mountain streams

unravelling the complexity of magma plumbing at mount st helens a new trace element partitioning scheme for amphibole volcanoes at subduction zones reside above complex magma plumbing systems where individual magmatic components may originate and interact at a range of pressures because whole rock compositions of subduction zone magmas are the integrated result of processes operating throughout the entire plumbing system processes such as mixing homogenisation and magma assembly during shallow storage can overprint the chemical signatures of deeper crustal processes whereas melt inclusions provide an effective way to study the uppermost 10 15 km of the plumbing system challenges remain in understanding magma intrusion fractionation and hybridisation processes in the middle to lower crust 15 30 km depth which commonly involves amphibole crystallisation here we present new insights into the mid crustal plumbing system at mount st helens usa using multiple regression methods to calculate trace element partition coefficients for amphibole phenocrysts and thus infer the trace element compositions of their equilibrium melts the results indicate vertically distributed crystal fractionation dominated by amphibole at higher pressures and in intermediate melts and by plagioclase at lower pressures variations in nb zr and ree concentrations at intermediate sio2 contents suggest repeated scavenging of partially remelted intrusive material in the mid crust and mixing with material from geochemically diverse sources amphibole is an effective probe for deep crustal magmatism worldwide and this approach offers a new tool to explore the structure and chemistry of arc magmas including those forming plutonic or cumulate materials that offer no other constraints on melt composition

petrology and fe ti oxide reequilibration of the 1991 mount unzen mixed magma a dacitic magma 64 5 wt sio2 a mixture of phenocryst rich rhyodacite and an aphyric mafic magma was erupted during the recent 1991 1995 mount unzen eruptive cycle the experimental and analytical results of this study reveal additional details about conditions in the premixing and postmixing magmas and the nature of the mixing process the preeruption rhyodacitic magma was at a temperature of 790 20 c according to fe ti oxide phenocryst cores and at a depth of 6 to 7 km 160 mpa according to al in hornblende geobarometry the mafic magma that mixed with the rhyodacite is found as andesitic 54 to 62 wt sio2 enclaves in the erupted magma and was essentially aphyric when intruded phase equilibria indicate that an aphyric andesite at 160 mpa is 1030 c h2o saturated and possibly as high as 1130 c 2 wt h2o the composition of the rhyodacite which was mixed with the andesite is estimated to lie between 67 and 69 wt sio2 using these compositions and temperatures the temperature of the unzen magma after mixing is estimated to be at least 850 to 870 c the groundmass fe ti oxide microphenocrysts and those in pargasite bearing reaction zones around biotite phenocrysts both give 890 20 c temperatures the oxide oxide contacts give temperatures of 910 20 c the 900 30 c postmixing temperatures are consistent with phase equilibria experiments which show that the magma was not above 930 c at 160 mpa our fe ti oxide reequilibration experiments suggest that the mixing of the two magmas began within a few weeks of the eruption which is a shorter time than is calculated using available diffusion data there is also evidence that some mixing took place much closer to the time of extrusion based on the presence of unrimmed biotite phenocrysts in the magma

experimental constraints on pre eruptive conditions of phonolitic magma from the caldera forming el abrigo eruption tenerife canary islands abstract we have performed phase equilibrium experiments to determine the pre eruptive conditions of the largest caldera forming eruption 20 km 3 of dre that has occurred on tenerife canary islands the abrigo ignimbrite is phonolitic and was erupted during the last caldera forming episode ca 190 ka prior to the construction of the teide pico viejo active central complex the abrigo phonolite contains low amounts of phenocrysts ca 7 vol mainly sanidine biotite clinopyroxene and magnetite with minor amounts of titanite apatite and hauyne we have investigated pressures from 50 to 250 mpa temperatures of 700 900 c water contents in the melt from 1 5 to ca 10 wt and oxygen fugacity f o 2 from 1 log unit above the ni nio solid buffer to quartz magnetite fayalite comparison of the natural and experimental phase proportions and compositions indicates that the phonolite at the roof of the abrigo magma reservoir was at 130 50 mpa corresponding to ca 4 5 km below the surface 825 25 c with 3 1 wt dissolved h 2 o and f o 2 at the ni nio buffer 1 log unit this shows that the magma that produced the largest ignimbrite on tenerife was stored at relatively shallow depths but was water undersaturated and its eruption was probably triggered by input of fresh mafic magma comparison of the abrigo phase equilibrium results with those obtained in other phonolitic magmas e g eifel kerguelen somma vesuvius shows that the major element and probably fluid composition h 2 o cl and s may have a strong effect on the presence or absence of phases and their compositions extrapolating phase equilibria results obtained on a specific phonolite to constrain the pre eruptive conditions of other phonolites should be done with care

resistance equation for large scale roughness a theory of flow resistance for large scale roughness is developed the main points of which are supported by a flume study from which the outline of a process based resistance equation is determined rivers with large scale roughness have steep slopes and depths of the same order of magnitude as the bed material size flow resistance depends on the form drag of the roughness elements and their disposition in the channel theoretical considerations show resistance to be a function of reynolds number froude number roughness geometry and channel geometry these processes are examined using the results of flume experiments based on five different roughness beds and a wide range of flows semi empirical analysis supports the theory and allows the development of a theoretical power law resistance equation which accounts for most of the processes a summary of the data is presented for use in other research studies

summary of pre 1980 tephra fall deposits erupted from mount st helens washington state usa mount st helens has been a prolific source of tephra fall deposits for about 40 000 years these tephra deposits 1 record numerous explosive eruptions 2 form important regional time stratigraphic marker beds and 3 record repeated changes in composition within and between eruptive periods

controls of channel morphology and sediment concentration on flow resistance in a large sand bed river a case study of the lower yellow river abstract accurate estimation of flow resistance is crucial for flood routing flow discharge and velocity estimation and engineering design various empirical and semiempirical flow resistance models have been developed during the past century however a universal flow resistance model for varying types of rivers has remained difficult to be achieved to date in this study hydrometric data sets from six stations in the lower yellow river during 1958 1959 are used to calibrate three empirical flow resistance models eqs 5 7 and evaluate their predictability a group of statistical measures have been used to evaluate the goodness of fit of these models including root mean square error rmse coefficient of determination cd the nash coefficient na mean relative error mre mean symmetry error mse percentage of data with a relative error 50 and 25 p 50 p 25 and percentage of data with overestimated error poe three model selection criterions are also employed to assess the model predictability akaike information criterion aic bayesian information criterion bic and a modified model selection criterion msc the results show that mean flow depth d and water surface slope s can only explain a small proportion of variance in flow resistance when channel width w and suspended sediment concentration ssc are involved the new model 7 achieves a better performance than the previous ones the mre of model 7 is generally

mount st helens potential example of the partial melting of the subducted lithosphere in a volcanic arc mount st helens 50 km to the west of mount adams and the main cascade volcanic chain is only 80 km above the subducting oceanic lithosphere the elevated temperatures off the subducting slab because of the close proximity of the juan de fuca ridge to the trench may induce slab melting at a depth of 80 km dacites from mount st helens have geochemical compositions off magmas that are derived by direct partial melting of metamorphosed basalts at high pressure i e relatively high ai al2o3 15 at 70 sio2 low y and yb because of garnet and amphibole stability in the source low sc and high sr and eu trace element modeling of the partial melting of mid oceanic ridge basalt morb from the juan de fuca ridge that yields a hornblende eclogite residue can reproduce the mount st helens data results off the model are quite distinct from data derived from the mount adams volcanic rocks in contrast mount adams is 135 km above the subducting slab and is associated with normal arc magmatism believed to be derived from the mantle above the subducting plate the cascade are has been active in its present locality because of oblique subduction for the past 7 m y the major volcanoes along the arc have existed for at least 500 ka but mount st helens has existed for 40 ka we suggest that the subducting plate may have reached elevated temperatures because of the approach of north america to the juan de fuca ridge at 40 ka which initiated melting of the slab

drainage network development in the keanakāko i tephra kīlauea volcano hawai i implications for fluvial erosion and valley network formation on early mars 1 a number of studies have attempted to characterize martian valley and channel networks to date however little attention has been paid to the role of lithology which could influence the rate of incision morphology and hydrology as well as the characteristics of transported materials here we present an analysis of the physical and hydrologic characteristics of drainage networks gullies and channels that have incised the keanak ko i tephra a basaltic pyroclastic deposit that occurs mainly in the summit area of k lauea volcano and in the adjoining ka desert hawai i the keanak ko i tephra is up to 10 m meters thick and largely devoid of vegetation making it a good analog for the martian surface although the scales are different the keanak ko i drainage networks suggest that several typical morphologic characteristics of martian valley networks may be controlled by lithology in combination with ephemeral flood characteristics many gully headwalls and knickpoints within the drainage networks are amphitheater shaped which results from strong over weak stratigraphy beds of fine ash commonly bearing accretionary lapilli pisolites are more resistant to erosion than the interbedded coarser weakly consolidated and friable tephra layers because the banks of the gullies and channels are easily eroded widths vary downslope similar to martian valley networks that have been characterized as degraded the floors of the gullies and channels tend to be low relief with few prominent bed forms reflecting the large proportion of sediment transported as bed load in high energy but short lived flood events we calculate that the average flow velocities within the drainage networks are typically 1 m 24 h given some recent modeling of the early martian climate our observations imply that rainfall on early mars could also be associated with large intense events and that martian valley network formation may be related to similar cyclonic storms

excess argon in mount st helens plagioclase as a recorder of magmatic processes excess argon in plagioclase crystals from young 4000 ybp tephra layers from mount st helens washington illustrates the importance of argon isotopes in understanding magmatic processes 40ar 39ar step heating identifies two distinct argon reservoirs in the plagioclase a high cl k low ca k reservoir with atmospheric 40ar 36ar and a low cl k higher ca k reservoir with variable 40ar 36ar the first is probably glass whereas the second is true plagioclase felsic dacite plagioclases have little or no excess argon but those from more mafic layers have significantly higher 40ar 36ar indicating a non atmospheric source these variations are seen within a layer that contains both mafic and felsic dacite and are inconsistent with either xenocrystic or restitic origin for plagioclase the magma chamber exhibits long term open system degassing behavior punctuated by short term fluctuations from influx of high 40ar 36ar basalt the relative timing between mixing and eruption can affect the amount of excess argon recorded in plagioclase

prediction of sediment transport in step pool channels 1 in mountainous drainage networks sediment mobilized on hillslopes must first pass through steep streams before reaching lower gradient channels the bed of steep channels is typically composed of large relatively immobile boulders and finer more mobile gravel most sediment transport equations overpredict sediment flux in steep streams by several orders of magnitude because they do not account for the stress borne by immobile grains and the limited availability of the more mobile sediment we previously developed and tested in flume experiments a sediment transport equation that accounts for these two effects here we modify the parker 1990 bed load equation to include the resistance borne by steps and selective transport of the relatively mobile sediment using a range of hiding functions we test a number of resistance equations and hiding functions combined with our modified and the original parker equations against measured flow and sediment transport in three steep channels our modified sediment transport equation generally predicts the transported sediment volumes to within an order of magnitude of the measured values whereas the unmodified equations do not the most accurate sediment flux predictions were obtained from using our modified equation combined with a hiding function that calculates highly selective transport of the relatively mobile sediment furthermore this hiding function has a critical shields stress that is similar to those reported for lower gradient channels the effects of the immobile steps on flow and sediment transport are not adequately captured by simply increasing the critical shields stress to values reported in steep streams

relationships between water infiltration and oil spill migration in sandy soils abstract this article summarizes a study directed towards the prediction of oil spill migration in sandy soils such a prediction is needed for the design of remedial measures against soil and groundwater contamination the geneal approach in this study is to convert available data concerning water infiltration into equivalent unknown data concerning oil spillage this information is then fed into a numerical model by which the oil spill migration is simulated laboratory measurements including retention curve hydraulic conductivity and infiltration rate were made separately for water and kerosene in order to evaluate and confirm the suggested approach

fe mg and fe mn interdiffusion in ilmenite with implications for geospeedometry using oxides the fe mg and fe mn interdiffusion coefficients for ilmenite have been determined as a function of temperature and crystallographic orientation diffusion annealing experiments were conducted at 1 5 gpa between 800 and 1100 circ hbox c for fe mg interdiffusion each diffusion couple consisted of an ilmenite polycrystal and an oriented single crystal of geikielite the activation energy q and pre exponential factor d 0 for fe mg diffusion in the ilmenite polycrystal were found to be q 188 pm 15 hbox kj mol 1 and text log d 0 6 0 pm 0 6 hbox m 2 hbox s 1 for the geikielite single crystal fe mg interdiffusion has q 220 pm 16 hbox kj mol 1 and text log d 0 4 6 pm 0 7 hbox m 2 hbox s 1 our results indicate that crystallographic orientation did not significantly affect diffusion rates for fe mn interdiffusion each diffusion couple consisted of one ilmenite polycrystal and one mn bearing ilmenite polycrystal for fe mn interdiffusion q 264 pm 30 hbox kj mol 1 and text log d 0 2 9 pm 1 3 hbox m 2 hbox s 1 in the ilmenite we did not find a significant concentration dependence for the fe mg and fe mn interdiffusion coefficients in comparing our experimental results for cation diffusion in ilmenite with those previously reported for hematite we have determined that cation diffusion is faster in ilmenite than in hematite at temperatures 1100 circ hbox c at oxygen fugacities near the wustite magnetite buffer fe and mn diffusion rates are similar for ilmenite and titanomagnetite we apply these experimentally determined cation diffusion rates to disequilibrium observed in ilmenites from natural volcanic samples to estimate the time between perturbation and eruption for the bishop tuff fish canyon tuff mt unzen mt st helens and kimberlites when integrated with natural observations of chemically zoned ilmenite and constraints on pre eruptive temperature and grain size our experimentally determined diffusivities for ilmenite can be used to estimate a minimum time between magmatic perturbation and eruption on the timescale of hours to months