did magma ascent rate control the explosive effusive transition at the inyo volcanic chain california rhyolitic eruptions often begin explosively and then shift to extrusions of lava it is widely believed that the style of eruption is dependent on magma flow rate within the conduit fast ascent leading to explosive eruption and slow ascent favoring effusive behavior currently the velocity of rhyolite magma flowing in a conduit is unknown and therefore eruption models remain untested against geologic evidence of magma ascent we show that explosively erupted rhyolite magma from the inyo volcanic chain ascended slowly centimeters per second at same rates as the dome building phases we propose that the explosive effusive transition sub plinian rhyolite eruptions is governed by the alleviation of exsolved volatile pressure in the shallow conduit rather than the magma flow rate

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

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

why is the bay of bengal less productive during summer monsoon compared to the arabian sea 1 the bay of bengal is traditionally considered to be a less productive basin compared to the arabian sea we explore the reasons for this in the central bay during summer copious rainfall and river water freshen the upper layers of the bay by 3 7 psu during summer and sst was warmer by 1 5 2 c than in the central arabian sea this leads to a strongly stratified surface layer the weaker winds over the bay are unable to erode the strongly stratified surface layer thereby restricting the turbulent wind driven vertical mixing to a shallow depth of 20 m this inhibits introduction of nutrients from below situated close to the mixed layer bottom into the upper layers while advection of nutrients rich water into the euphotic zone makes the arabian sea highly productive this process is unlikely in the bay of bengal

reconstructing depositional processes and history from reservoir stratigraphy englebright lake yuba river northern california 1 reservoirs provide the opportunity to link watershed history with its stratigraphic record we analyze sediment cores from a northern california reservoir in the context of hydrologic history watershed management and depositional processes observations of recent depositional patterns sediment transport calculations and 137cs geochronology support a conceptual model in which the reservoir delta progrades during floods of short duration days and is modified during prolonged weeks to months drawdowns that rework topset beds and transport sand from topsets to foresets sediment coarser than 0 25 0 5 mm deposits in foresets and topsets and finer material falls out of suspension as bottomset beds simple hydraulic calculations indicate that fine sand 0 063 0 5 mm is transported into the distal bottomset area only during floods the overall stratigraphy suggests that two phases of delta building occurred in the reservoir the first from dam construction in 1940 to 1970 was heavily influenced by annual prolonged 20 m drawdowns of the water level the second built on top of the first reflects sedimentation from 1970 to 2002 when the influence of drawdowns was less sedimentation rates in the central part of the reservoir have declined 25 since 1970 likely reflecting a combination of fewer large floods changes in watershed management and winnowing of stored hydraulic mining sediment

emplacement of the rocche rosse rhyolite lava flow lipari aeolian islands the rocche rosse lava flow marks the most recent rhyolitic extrusion on lipari island italy and preserves evidence for a multi stage emplacement history due to the viscous nature of the advancing lava 108 to 1010 pa s indicators of complex emplacement processes are preserved in the final flow this study focuses on structural mapping of the flow to highlight the interplay of cooling crust formation and underlying slope in the development of rhyolitic lavas the flow is made up of two prominent lobes small 0 2 m scale folding and a channelled geometry foliations dip at 2 4 over the flatter topography close to the vent and up to 30 50 over steeper mid flow topography brittle faults tension gashes and conjugate fractures are also evident across flow heterogeneous deformation is evident through increasing fold asymmetry from the vent due to downflow cooling and stagnation a steeper underlying topography mid flow led to development of a channelled morphology and compression at topographic breaks resulted in fold superimposition in the channel we propose an emplacement history that involved the evolution through five stages each associated with the following flow regimes 1 initial extrusion crustal development and small scale folding 2 extensional strain stretching lineations and channel development over steeper topography 3 compression at topographic break autobrecciation lobe development and medium scale folding 4 progressive deformation with stagnation large scale folding and re folding and 5 brittle deformation following flow termination the complex array of structural elements observed within the rocche rosse lava flow facilitates comparisons to be made with actively deforming rhyolitic lava flows at the chilean volcanoes of chaiten and cordon caulle offering a fluid dynamic and structural framework within which to evaluate our data

explosive origin of silicic lava textural and δd h2o evidence for pyroclastic degassing during rhyolite effusion a long standing challenge in volcanology is to explain why explosive eruptions of silicic magma give way to lava a widely cited idea is that the explosive to effusive transition manifests a two stage degassing history whereby lava is the product of non explosive open system gas release following initial explosive closed system degassing direct observations of rhyolite eruptions indicate that effusive rhyolites are in fact highly explosive as they erupt simultaneously with violent volcanic blasts and pyroclastic fountains for months from a common vent this explosive and effusive overlap suggests that pyroclastic processes play a key role in rendering silicic magma sufficiently degassed to generate lava here we use precise h isotope and magmatic h2o measurements and textural evidence to demonstrate that effusion results from explosion s lavas are the direct product of brittle deformation that fosters batched degassing into transient pyroclastic channels tuffisites that repetitively and explosively vent from effusing lava our measurements show specifically that d h ratios and h2o contents of a broad suite of explosive and effusive samples from chaiten volcano hydrous bombs plinian pyroclasts tuffisite veins and lava define a single and continuous degassing trend that links wet explosive pyroclasts 1 6 wt h2o d 76 4 to dry obsidian lavas 0 13 wt h2o d 145 7 this geochemical pattern is best fit with batched degassing model that comprises small repeated closed system degassing steps followed by pulses of vapour extraction this degassing mechanism is made possible by the action of tuffisite veins which by tapping already vesicular or brecciated magma allow batches of exsolved gas to rapidly and explosively escape from relatively isolated closed system domains and large tracts of conduit magma by giving them long range connectivity even though tuffisite veins render magma degassed and capable of effusing they are nonetheless the avenues of violent gas and particle transport and thus have the potential to drive explosions when they become blocked or welded shut thus the effusion of silicic lava traditionally thought to be relatively benign process presents a particularly hazardous form of explosive volcanism

rheology of bubble bearing magmas the rheology of bubble bearing suspensions is investigated through a series of three dimensional boundary integral calculations in which the effects of bubble deformation volume fraction and shear rate are considered the behaviour of bubbles in viscous flows is characterized by the capillary number ca the ratio of viscous shear stresses that promote deformation to surface tension stresses that resist bubble deformation estimates of ca in natural lava flows are highly variable reflecting variations in shear rate and melt viscosity in the low capillary number limit e g in carbonatite flows bubbles remain spherical and may contribute greater shear stress to the suspension than in high capillary number flows in which bubble deformation is significant at higher ca deformed bubbles become aligned in the direction of flow and as a result contribute less shear stress to the suspension calculations indicate that the effective shear viscosity of bubbly suspensions at least for ca 0 5 is a weakly increasing function of volume fraction and that suspensions of bubbles are shear thinning field observations and qualitative arguments however suggest that for sufficiently large ca ca greater than about 1 the effective shear viscosity may be less than that of the suspending liquid bubbles reach their quasi steady deformed shapes after strains of order one for shorter times the continuous deformation of the bubbles results in continual changes of rheological properties in particular for small strains the effective shear viscosity of the suspension may be less than that of the liquid phase even for small ca results of this study may help explain previous experimental theoretical and field based observations regarding the effects of bubbles on flow rheology

transitions between explosive and effusive eruptions of silicic magmas water rich silicic magmas may erupt explosively giving rise to massive columns of fragmented ash1 5 or effusively as viscous bubbly lavas to form lava domes6 8 complex cycles of explosive and effusive eruptions are often observed8 12 although these two eruption mechanisms have been modelled independently1 8 the conditions under which a volcano exhibits a particular style of eruption are not known and the transitions between eruption styles are poorly understood by modelling the ascent of magma along a permeable conduit we show here that for small magma chamber overpressures the style of eruption explosive or effusive is dependent on the magma flow rate we also identify a critical overpressure above which only explosive eruptions occur complex eruption sequences follow naturally for example if a shallow magmatic system is supplied with magma at an intermediate flow rate the eruption will be slow and effusive until the chamber over pressure becomes too large an explosive eruption then relieves the overpressure and an effusive eruption style resumes we suggest that monitoring of temporal variations in chamber overpressure for example by measuring ground deformation can be used to assess whether a passively effusing volcano has the potential to erupt explosively

weekly observations on dispersal and sink pathways of the terrigenous flux of the ganga brahmaputra in the bay of bengal during ne monsoon the analyses of 64 sequential satellite images october 1999 march 2001 of indian remote sensing satellite irs p4 ocean color monitor ocm bands around 490 555 and 670 nm for total suspended matter tsm synchronous sea truth data acquisition and salinity variations have been used to construct dispersal pathways of the surficial fluvial flux into the northern bay of bengal during the ne monsoon from the spatial extent of the plumes of tsm 160 120 km during october of 1999 and2000 off the mouth of the himalayan rivers the ganga andthe brahmaputra g b it is deduced that fluvial flux does not diminish concurrently with the termination of the southwest sw monsoon as suggestedby time series trap experiments in the northern bay during the ne monsoon the g b plumes move north to south initially off the mouth and thereafter advects sw alongshore in the form of coastal sediment plumes reducing the salinity of the coastal waters along the entire northern bay during october december we have observed a strong relation between enhanced episodic discharges of the ganga brahmaputra g b and augmented coastal turbidity during weekly events it is also observed that even during such short weekly events of very high pulse of tsm discharge by the g b system the fluvial fluxes do not advect offshore into the deeper regions of the northcentral bay but are transportedalongshore andd istributedalong the shelf our results therefore suggest that the reduced recovery of the fluxes in the sediments traps subsequent to the sw monsoon are not linearly related to the magnitude of fluvial flux of the g b but stems from the prevalent dispersal patterns r 2005 elsevier ltd all rights reserved

petrologic and experimental evidence for the movement and heating of the pre eruptive minoan rhyodacite santorini greece hydrothermal experiments combined with petrologic observations form the basis for a new two stage model for the evolution of the pre eruption minoan magma chamber at santorini greece ninety nine percent of the erupted volume is two pyroxene rhyodacitic magma that had been stored at a temperature of 885 c based on magnetite ilmenite and quilf geothermometry the rest of the volume is basaltic to andesitic magma which occurs as 200 mpa in addition the composition of the plagioclase hosts an56 6 of the inclusions require temperatures of 825 25 c at pressures 200 mpa this demonstrates that the minoan rhyodacitic magma underwent a two stage evolution first crystallizing at 825 c and 200 mpa and then rinsing to a shallow 50 mpa storage region with a concomitant rise in temperature to 885 c we suggest that the episodic intrusion of mafic magmas provided the necessary heat and perhaps contributed to the ascent of the magma to shallow crustal depths where it reequilibrated before the cataclysmic eruption phase equilibria suggest that much of the heating of the rhyodacite occurred in the shallow storage region thermal budget calculations suggest that the rhyodacite magma could have been heated by intrusions of basalt rising at reasonable upwelling rates and injected into the storage zone over several hundred years preservation of amphibole in the mafic scoria indicate that injection of mafic magma continued up until days before the cataclysmic eruption perhaps triggering the event

sulfur budget and global climate impact of the a d 1835 eruption of cosiguina volcano nicaragua large explosive volcanic eruptions can inject massive amounts of sulfuric gases into the earth s atmosphere and in so doing affect global climate the january 1835 eruption of cosiguina volcano nicaragua ranks among the americas largest and most explosive historical eruptions but whether it had effects on global climate remains ambiguous new petrologic analyses of the cosiguina deposits reveal that the eruption released enough sulfur to explain a prominent ca ad 1835 sulfate anomaly in ice cores from both the arctic and antarctic a compilation of temperature sensitive tree ring chronologies indicates appreciable cooling of the earth s surface in response to the eruption consistent with instrumental temperature records we conclude that this eruption represents one of the most important sulfur producing events of the last few centuries and had a sizable climate impact rivaling that of the 1991 eruption of mount pinatubo

physicochemical models of effusive rhyolitic eruptions constrained with insar and dem data a case study of the 2011 2012 cordon caulle eruption abstract the 9 month long 2011 2012 eruption of cordon caulle southern andes chile is the best instrumentally recorded rhyolitic eruption to date and the first time that the effusion of a rhyolitic flow has been observed in detail we use interferometric synthetic aperture radar insar with time lapse digital elevation models dems and numerical models to study the dynamics of coupled magma reservoir deflation and lava effusion insar recorded 2 2 2 5 m of subsidence after the first three days of the eruption which can be modeled using a spheroidal magma reservoir at a depth of 5 km 20 km long and with a pressure drop of 20 30 mpa the source is elongated in the nw se direction and its large dimensions imply a large plumbing system active throughout the eruption and spanning neighboring volcanoes with a slight change in the geometry halfway through the effusive phase tandem x and pleiades dems record the extrusion of both the rhyolitic lava flow and the intrusion of a shallow laccolith around the eruptive vent after the third day of the eruption with a total volume of 1 45 km3 dre the laccolith was emplaced during the first month of the eruption during both the explosive and effusive stages of the eruption both the reservoir pressure drop and the extruded volume time series follow quasi exponential trends and can be explained by a model that couples the reservoir pressure decrease time and pressure dependent variations in the magma properties inside of the reservoir and conduit flow this model predicts both the temporal evolution and amplitude of both time series during the effusive phase and a magma compressibility of 10 10 pa 1 half the reported compressibility of the magma of the sub plinian explosive phase further we estimate that the reservoir contained 1 3 wt dissolved h2o at the onset of lava effusion with no exsolved co2 and h2o in the reservoir throughout the effusive phase this implies that the magma was significantly degassed after the explosive phase the remaining volatiles in the magma after the explosive stage might have caused magma fragmentation consistent with the hybrid explosive effusive style observed during the waning of the eruption

equilibration scales in silicic to intermediate magmas implications for experimental studies experimental phase equilibrium studies are increasingly being used for the determination of intensive variables p t fh2o fo2 in silicic to intermediate magmas in contrast silicic igneous bodies are now perceived as open periodically recharged systems involving only limited chemical equilibration thus the use of laboratory determined crystal liquid equilibrium data needs clarification here we review the field petrological and geochemical evidence concerning states and scales of chemical equilibrium in silicic magma bodies it is concluded that total chemical equilibrium is generally not the rule however a subsystem in local equilibrium the reactive magma can be identified equilibration scales in silicic magmas are rate limited either by diffusive flux in crystals dicl regime or by diffusive flux in the melt md regime the recognition that equilibrium in magmas is limited to a reactive subsystem requires phase equilibrium studies to be chemically scaled experiments either of total or partial equilibrium type should aim at a close reproduction of equilibrium states specific to natural systems the laboratory reconstruction of the natural equilibrium states guarantees a precise determination of the pre eruptive parameters and a reliable application of the experimental data to active volcanic systems

storage conditions of the 29 ka rhyolitic guangoche white pumice sequence los azufres volcanic field central mexico abstract rhyolitic magmas in occasions can be related to explosive eruptions in active volcanoes that may not exhibit precursory signals making them very dangerous for the surrounding communities to understand the pre eruptive conditions of such magmas it is important to decipher the mechanisms capable to produce these explosive events in this study we analyzed the pre eruptive conditions of guangoche stratovolcano located to the southwest of the los azufres volcanic field in the central part of the trans mexican volcanic belt during the late pleistocene guangoche generated three plinian subplinian eruptions and some effusive eruptions all of them involving high silica rhyolitic magmas one of these plinian events vei 5 occurred 29 ka and deposited the white pyroclastic sequence wps this eruption ejected 0 7 km3 dre volume of rhyolitic magma and deposited a pumice fallout followed by three pumice rich pyroclastic density currents petrography combined with mineral composition melt inclusions and water saturated phase equilibria experiments were used to determine the evolution of the magma storage of the wps event prior to the eruption the magma was a crystal poor 14 vol rhyolite containing the following mineral assemblage biotite fe ti oxides amphibole sanidine and quartz set in a rhyolitic matrix 77 3 wt sio2 with low ba 121 16 7 ppm eu 0 15 0 02 ppm and sr 37 7 ppm based on fe ti oxythermometers and phase equilibria experiments we determine that the magma was stored between 75 and 100 mpa 3 4 km depth at a temperature of 769 8 c moreover h2o co2 dissolved in quartz melt inclusions and the textural features of the mineral assemblage of the wps products provided insights of the presence of a quartzo feldspathic crystal mush located at minimum depths between 4 3 and 9 5 km 98 218 mpa large sanidine quartz plagioclase and amphibole phenocrysts and mineral clots in the wps rocks represent assimilated parts from this mush by a melt extraction process probably triggered by the arrival of a relatively hotter magma at the base of the crystal mush which in turn caused reheating and partial melting of the quartzo feldspathic crystal mush generating the 29 ka rhyolitic wps magma

using the sediment record in a western oregon flood control reservoir to assess the influence of storm history and logging on sediment yield abstract dorena lake a flood control reservoir with a 686 km2 watershed in the western cascade mountains of oregon contains a 50 year record of sediment deposition by measuring the amount of lake sediment performing 137cs dating and examining the stratigraphy of sediment cores information was obtained about variations in the sediment yield of the watershed the average yield for 50 years is 108 tons km2 year and rates for shorter time periods vary from 42 to 269 tons km2 year depending on the time of average and the occurrence of large storm events a comparison of sediment yield values with timber harvesting rates and with the number of high discharge days during different time periods implies that sediment yield is controlled primarily by flood magnitude and frequency the amplitude of variation in yield that might be produced by changes in logging rates or methods is too small to be detected with the methods used in this study because in large watersheds 1 the effects of localized events tend to be averaged out and 2 sediment delivery ratios are generally low also the reservoir was constructed after a significant portion of the watershed had been logged so the data cannot be compared with pre disturbance sediment yields this study shows that reservoirs in the western cascades are worthy of further study but information is needed to constrain reservoir trap efficiency and problems of scale in large watersheds may hinder the detection of land use influences on sedimentation

recent volcanism in the puyehue cordon caulle region southern andes chile 40 5 s petrogenesis of evolved lavas

influences of tropical monsoon climatology on the delivery and dispersal of organic carbon over the upper gulf of thailand abstract organic carbon cycling in se asia is data sparse and poorly studied although high sediment yield and organic carbon intensity occur in the tropical region in the present study we evaluated the role of tropical monsoon pertaining to fluvial discharge sediment load coastal current and water stratification on seasonal organic carbon dynamics during four sampling campaigns in the upper gulf of thailand ugot this study demonstrates that particulate organic carbon poc is closely correlated with the river influx of suspended sediment which is generally regulated by the local rainfall higher poc is found near the large estuarine section chao phraya river chao during southwest monsoon period and the small estuarine section mae klong river mk during november 2013 when tropical cyclones impacted poc in the estuarine sections is more significantly influenced by the seasonal shift compared with the coastal sections land derived organic matter prevails in the small estuarine and coastal sections while marine derived organic matter dominates in the estuarine sections impacted by chao and mk anthropogenic inputs and dam regulation also influences the river export of organic matter during the high precipitation periods total organic carbon toc however displays less significant seasonal monsoon variations than poc further toc tends to accumulate in the sub silt fraction of sediments which mainly occurs in the small estuarine and eastern coastal sections and is more obviously influenced by marine derived factors toc in sediment of the chao and mk influenced sections however displays more seasonal variations with prevailing river input evidenced by coarser sediment and higher c n ratios moreover the almost year round water stratification across the region acts as the barrier in retaining organic carbon in the estuaries and their vicinities from dispersal into the lower portion of gulf of thailand high sedimentation rate 1 1 cm yr 1 further facilitates the organic carbon burial in the study area the delivery dispersal and burial of organic carbon are closely associated with the climate controlled precipitation and thus the tropical monsoon climatology under the global warming in particular is an important factor influencing the organic carbon in the ugot

magma fragmentation by rapid decompression the processes leading to magma fragmentation and the generation of pyroclastic debris during explosive volcanic eruptions are of fundamental importance in volcanology observations of explosive eruptions1 3 as well as theoretical analyses of the underlying processes4 have raised the question of whether the rapid decompression of highly viscous vesicular magma that results from the collapse of a lava dome or volcanic edifice can in itself produce explosive magma fragmentation and pyroclast formation here we report the results of a laboratory investigation of pyroclast formation following rapid decompression samples of magma from the 1980 eruption of mount st helens when rapidly depressurized from initial pressures of up to 12 mpa and at temperatures in the range 750 825 c fragmented to form pyroclastic products that are in many respects similar to those formed in real eruptions moreover we observe explosive fragmentation at temperatures well below those normally associated with magmatic processes suggesting that even relatively cool magma bodies can be very hazardous when subjected to rapid unloading events

impact of indus river discharge on productivity and preservation of organic carbon in the arabian sea over the twentieth century marine high productivity zones along the continents are of great economic importance and they account for most organic carbon burial the carbon cycle in many coastal zones is influenced by the sediments and dissolved nutrients introduced by rivers however there is little direct evidence for a regional marine response to changes in river dynamics here we present a suite of high resolution records of organic and inorganic paleoceanographic proxies which together demonstrate that past changes in indus river discharge have strongly affected productivity patterns in the coastal northeastern arabian sea anthropogenic activity including the building of dams and irrigation facilities during the past century has drastically decreased the discharge rate of the indus river between a d 1890 and 1998 the period over which this reduction occurred primary productivity off the pakistan coast seems to have decreased by more than one third over the same period the regional oxygen minimum zone weakened increasing the supply of oxygen to the sediments leaving the expected imprint on a suite of redox sensitive elements and reducing the preservation of organic matter

geochemical constraints on the role of tuffisite veins in degassing at the 2008 09 chaiten and 2011 12 cordon caulle rhyolite eruptions abstract hybrid activity during the rhyolitic eruptions of chaiten 2008 09 and cordon caulle 2011 2012 in chile has offered unprecedented insights into the enigmatic and complex degassing processes occurring during eruptions of silicic magma highly permeable transient fracture networks within the conduit can act as outgassing channels their interaction with deeper volatile rich melt can account for both punctuated explosive activity and large scale degassing of the system leading towards predominantly effusive behaviour in this study we characterise trace element concentrations and 210pb 226ra systematics within pyroclastic material from the recent eruptions at chaiten and cordon caulle volcanoes results reveal how gas fluxing from deep volatile rich reservoirs to the surface within magmatic conduits can be recorded by trace elements and 210pb 226ra disequilibria in tuffisite veins tuffisite veins particle filled fracture networks are present in volcanic bombs from both eruptions trace element heterogeneity associated with tuffisites preserves evidence for degassing at chaiten enrichments e g cu and depletions e g mo li and bi are identified in vein material and clasts transported within veins and record multiple degassing events at cordon caulle enrichments of volatiles in an early vein e g tl and bi and depletions in a later vein e g cd in pb and tl reflect interactions between glassy clasts and the carrier gas phase that transported them in contrast 210pb and 226ra which can be fractionated during degassing are mostly in secular equilibrium modelling suggests that the disparity between the signals preserved in these two types of chemical signatures reflects the brevity of degassing events and the relative volumes of tuffisite veins and the bodies of degassing magma that they source gas from the lack of preserved 210pb enrichments in tuffisite veins at both volcanoes places an upper limit on the mass of deeper bubble rich magma outgassed via tuffisites during their lifetime this study shows that both the presence and absence of sample scale geochemical heterogeneity can be used to place constraints on syn eruptive physical processes and underlines the value of analysing a wide suite of trace element species

sediment production from forest road surfaces erosion on roads is an important source of fine grained sediment in streams draining logged basins of the pacific northwest runoff rates and sediment concentrations from 10 road segments subject to a variety of traffic levels were monitored to produce sediment rating curves and unit hydrographs for different use levels and types of surfaces these relationships are combined with a continuous rainfall record to calculate mean annual sediment yields from road segments of each use level a heavily used road segment in the field area contributes 130 times as much sediment as an abandoned road a paved road segment along which cut slopes and ditches are the only sources of sediment yields less than 1 as much sediment as a heavily used road with a gravel surface

rheology of crystal bearing silicate melts an experimental study at high viscosities the viscosity of partially crystallized mg3al2si3o12 melts has been measured under uniaxial compression in the interval 1010 1013 poise as a function of the volume fraction of crystals these inclusions are well rounded spherulites of aluminous enstatite having the same composition as the melt and whose growth rate is negligible at the temperature of the measurements the viscosity increases by less than 1 order of magnitude for crystal fractions of 40 vol and remains newtonian up to the maximum stress exerted namely 1 kbar the einstein roscoe equation 0 1 m n provides very good fits to the measurements only if either the m or n parameter is allowed to depend on temperature for modeling of magmatic processes however the widely recommended constant values m 0 6 and n 2 5 should be adequate the rheology changes abruptly when the clustered spherulites begin to oppose shear deformation at a crystal fraction of about 40 vol the viscosity becomes non newtonian with yield strengths of a few tens of bars at temperatures at which the viscosity of the melt is higher than 1010 poise as long as the crystal fraction remains lower than 70 vol the deformation proceeds in an irregular manner with a nonuniform distribution of crystals and melt the deformation becomes again regular at low stresses with lower melt fractions but samples undergo extensive fracturation along the direction of uniaxial stress similar rheology changes have been observed during the isothermal crystallization of li2si2o5 melts which produces small ellipsoidal inclusions these results suggest that the influence of solid suspensions on the rheology of magmas is primarily determined by the crystal fraction even though additional measurements would be useful to determine the possible influence of other factors such as the size distribution or the shape of the inclusions

erosion in mediterranean mountain landscapes during the last millennium a quantitative approach based on lake sediment sequences iberian range spain abstract land degradation and soil erosion are key environmental problems in mediterranean mountains characterized by both a long history of human occupation and strong seasonality of hydrological regimes experimental monitored catchments have identified main controlling factors on erosion dynamics but because of the short time span of the instrumental measurements they do not integrate the complete temporal and spatial variability of these environments to obtain some long term series of mediterranean landscape evolution we propose a novel strategy based on multi proxy analyses of lake sediments aimed to quantify sediment delivery and erosion dynamics karstic lakes in the iberian range central spain provide an opportunity to reconstruct the depositional evolution of the watersheds and to evaluate the response to both the variable anthropogenic impacts and climate forcings during the last 1000 years the most significant periods of increased sediment delivery 26 483 t km yr 1 in the iberian range sites took place during the 15th 16th and 18th 19th centuries as a result of large land use changes and land clearing positive synergies between increasing human population and more humid periods led to peaks in sediment deliver during some phases of the little ice age recent changes associated with the rural exodus and land abandonment during mid 20th century are more clearly shown in larger watersheds by decreased sediment delivery to the lakes due to the re vegetation of the landscape 6 200 t km yr 1 this new integrated approach based on long term lake sequences provides a longer perspective of erosion processes in mediterranean watersheds and validates the main factors identified in monitoring surveys land cover and surface formations erodibility in both settings lakes and experimental catchments most sediment delivery occurs during flooding events measured and reconstructed values show comparable large ranges underlying the punctuated nature of sediment dynamics in mediterranean landscapes at decadal and centennial scales

a rheological investigation of vesicular rhyolite abstract the rheology of vesiculating rhyolitic systems exerts a strong control on the transport of silicic magmas in the subvolcanic to volcanic environments we present here an investigation of vesiculating and vesiculated rhyolites using dilatometric methods this study examines the effect of vesicle content on the viscosity of a natural supercooled rhyolitic liquid with 0 70 vesicles the experimental samples of rhyolitic glass are derived from fusion of a natural obsidian from little glass butte oregon crystal free rhyolite glasses of varying porosity were prepared by fusing obsidian powder in a pt crucible differing porosities were obtained by varying the temperature 1300 1650 c and duration 0 5 6 h of the fusions cylindrical samples of the resulting vesiculated rhyolites were cored from the crucible using diamond tools and their ends were ground flat and parallel for dilatometry the porosity of each sample was determined from archimedean buoyancy density determinations and comparison with bubble free rhyolite 2 331 g cm 3 porosity 1 p p o the density of foamed samples was determined using their mass volume and regular geometry viscosities were determined in the parallel plate mode at stresses of 5 10 3 to 10 5 pa the viscosimeter was calibrated using nbs 711 glass the bubble contents were microscopically investigated using a video reflected light system and image analysis software distribution functions of the size orientation aspect ratio and surface porosity were obtained the viscosity of rhyolite decreases with increasing bubble content a general relationship of the form 0 1 c describes the effect of porosity in volume fraction on the viscosity where c is a dimensionless constant 22 4 2 9 and log 10 0 10 94 0 04 pa s at 850 c

complex mass wasting response of drainage basins to forest management in coastal british columbia the impacts of logging activities on mass wasting were examined in five watersheds in the coastal mountains of british columbia historical aerial photos were used to document mass wasting events and their occurrence was related to logging activities in the study basins logged and forested areas were compared in terms of mass wasting magnitude and frequency with reference to site characteristics the recovery time of the landscape after logging was assessed bedrock type and basin physiography had no identifiable effect on mass wasting frequency and magnitude mass wasting failure was primarily controlled by slope gradient basin vulnerability increased following clearcutting relative to forested areas in that mass wasting was initiated on gentler slopes the volume of sediment produced from logged slopes is of the same order as that from forested areas which are steeper by as much as 10 in both logged and forested areas the size distribution of mass wasting events follows an exponential distribution however the variability in mass wasting size in forested areas is much higher than that obtained for logged areas the recovery time after forest harvesting is over 20 years which confirms published estimates based on vegetation reestablishment continuous disturbance of the basin however may extend the recovery time for the whole basin well beyond 20 years

clay mineral accumulation rates in the arabian sea during the late quaternary abstract the regional variations in clay mineral concentrations in 39 turbidite free and undisturbed deep sea sediment cores from the arabian sea are compared with distribution patterns of clay mineral accumulation rates during the holocene and the last glaciation dust plumes from the red sea area arabia mesopotamia iran and pakistan can be traced by accumulation rates of mineral specific dust loads during the late quaternary the major proportions of aeolo marine sediments in the western arabian sea were derived from arabia during the summer season the clay mineral assemblage in these dust plumes consists of illite smectite kaolinite chlorite and palygorskite in decreasing order of abundance the distribution pattern of palygorskite in particular reveals that dust transport from southern arabia occurs mainly with northwesterly to westerly winds in the mid troposphere dust plumes from iran and pakistan which are characterized by high chlorite content are dispersed by northwesterly winds over the northwestern arabian sea dust contributions from the red sea area which are rich in smectite and characterized by the occurrence of amphiboles are transported to the gulf of aden the amount of dust related to northeast monsoon winds during the winter season appears to be negligible when compared to the proportions borne on other dust bearing winds in addition to aeolian contributions we distinguish two fluvial contributions a chlorite illite kaolinite and quartz rich assemblage from oman and pakistan into the gulf of oman and a smectite rich assemblage which is dominant off southern india originating from rivers that drain the indian subcontinent the significant difference between the holocene and glacial accumulation rates of wind transported clay minerals consist in the higher abundance of quartz illite and chlorite in the northwestern arabian sea during the last glaciation this pattern indicates intensified dust contributions by northwesterly winds from the persian gulf area which was dry during glacial times

eruptive history geochronology and magmatic evolution of the puyehue cordon caulle volcanic complex chile forty three 40 ar 39 ar age determinations of lava flows domes ignimbrites and dikes plus 14 c dates from seven distal tephra layers combined with stratigraphy geochemistry and sr and th isotope data establish an eruptive chronology for the puyehue cordon caulle volcanic complex at 40 5 s in the andean southern volcanic zone svz the complex preserves 131 km 3 of lava and tephra that erupted from numerous vents widely separated in time and space approximately 80 of the total volume consists of basaltic to andesitic lava that formed two broad shield volcanoes between 314 and 70 ka the modern puyehue stratovolcano was built on the southerly shield during the past 69 k y following a hiatus of 25 k y puyehue has erupted 15 km 3 of basaltic to rhyolitic magma that spans the entire compositional range found in the southern svz and evolved via at least six phases including 1 basaltic andesitic to dacitic lavas between 69 and 32 ka 2 a shift to bimodal magma compositions that is first expressed by a rhyodacite mingled with inclusions of mgo rich basaltic andesite at 34 ka 3 dacitic to rhyolitic flows and domes from 19 to 12 ka 4 basaltic to basaltic andesitic flows between 15 and 12 ka 5 subsequent rhyolitic dome growth in several effusive and explosive stages between 7 and 5 ka followed by 6 a powerful series of phreatomagmatic and sub plinian eruptions at ca 1 1 ka that obliterated the preceding rhyolite domes and formed the present 2 5 km diameter 280 m deep summit crater along the cordon caulle fissure zone 5 km 3 of rhyodacitic to rhyolitic lavas domes and cones have formed during the past 16 5 k y including explosive and effusive eruptions in 1921 1922 and 1960 eruptive rates were nonuniform over time with background growth at 0 04 km 3 k y or less punctuated by spurts at up to 0 90 km 3 k y the time averaged rate 0 42 km 3 k y is nearly double that at the tatara san pedro complex 500 km to the north during the past 300 k y these findings indicate that within a single arc the magmatic and eruptive fluxes at individual frontal volcanoes can be highly variable the last three stratocone building events on puyehue began during periods of deglaciation suggesting a relationship between unloading of ice and ease of magma ascent puyehue basalt exhibits subtle changes in 238 u 230 th 87 sr 86 sr and trace element composition over time that signal shifts in the composition and degree of melting of the mantle wedge or the extent to which basalt was modified by assimilation of heterogeneous crustal melts the complex has become exceptionally bimodal and more explosive over time with recent rhyolites evolving by extreme crystal fractionation of mafic magma and lesser volumes of andesite and dacite created via mixing of rhyolite and basalt despite the high flux of basalt during the past 300 k y no large silicic magma reservoir formed in the upper crust instead 238 u 230 th data favor rapid ascent of several small bodies of basaltic and silicic magma from the lower crust promoted perhaps by conduits that reflect strike slip faulting beneath the complex

rhyolite lava emplacement dynamics inferred from surface morphology abstract the morphology of a silicic lava is created by the fluid dynamic conditions that operated during flow careful analysis of these features can thus be used to reconstruct emplacement processes we used unoccupied aerial system and structure from motion photogrammetry techniques to collect centimeter scale spatial resolution imagery of the surfaces of south coulee and obsidian dome rhyolite lavas mono inyo craters usa we supplement the newly acquired orthomosaics and digital elevation models with existing imagery of other holocene rhyolite lavas from across the western usa including rock mesa dome south sister or newberry flow south sister or obsidian flow newberry or interlake flow newberry or and banco bonito flow valles caldera nm although many morphologic features exist we restrict our quantitative analyses to the recurrent ridges and blocks of loose rubble that are common to the flows ridge spacing and ridge vergence indicate the ridges are likely folds produced by compression during emplacement pressure ridge spacings range from 27 to 45 m at south coulee and 18 to 34 m on obsidian dome spacing generally decreases with distance from the vent across both lavas ridge amplitudes range from 4 to 17 m at both lavas and show little correlation with distance from the vent the vergence of the crest of the ridges in the flow interiors points back to the source vent which provides strong evidence for endogenous flow and the backward rotation of folds produced by undertow of the underlying lava ridges near flow margins verge towards the flow front demonstrating that exogenous flow becomes increasingly important at the point of advance in both south coulee and obsidian dome block sizes are largest near the vent and gradually decrease towards the flow front the gradual decrease in block size with increasing distance from the vent likely reflects decreasing effusion rates from the conduit we interpret our high resolution field measurements under the lens of analytical solutions to fluid dynamic models to estimate emplacement timescales and associated rates we calculate relatively abbreviated eruptive timescales ranging from 1 month to

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

a comparison of the sedimentary records of the 1960 and 2010 great chilean earthquakes in 17 lakes implications for quantitative lacustrine palaeoseismology seismically induced event deposits embedded in the sedimentary infill of lacustrine basins are highly useful for palaeoseismic reconstructions recent well documented great megathrust earthquakes provide an ideal opportunity to calibrate seismically induced event deposits for lakes with different characteristics and located in different settings this study used 107 short sediment cores to investigate the sedimentary impact of the 1960 mw 9 5 valdivia and the 2010 mw 8 8 maule earthquakes in 17 lakes in south central chile i e lakes negra lo encanado aculeo vichuquen laja villarrica calafquen pullinque pellaifa panguipulli neltume rinihue ranco maihue puyehue rupanco and llanquihue a combination of image analysis magnetic susceptibility and grain size analysis allows identification of five types of seismically induced event deposits i mass transport deposits ii in situ deformations iii lacustrine turbidites with a composition similar to the hemipelagic background sediments lacustrine turbidites type 1 iv lacustrine turbidites with a composition different from the background sediments lacustrine turbidites type 2 and v megaturbidites these seismically induced event deposits were compared to local seismic intensities of the causative earthquakes eyewitness reports post earthquake observations and vegetation and geomorphology of the catchment and the lake megaturbidites occur where lake seiches took place lacustrine turbidites type 2 can be the result of i local near shore mass wasting ii delta collapse iii onshore landslides iv debris flows or mudflows or v fluvial reworking of landslide debris on the contrary lacustrine turbidites type 1 are the result of shallow mass wasting on sublacustrine slopes covered by hemipelagic sediments due to their more constrained origin lacustrine turbidites type 1 are the most reliable type of seismically induced event deposits in quantitative palaeoseismology because they are almost exclusively triggered by earthquake shaking moreover they most sensitively record varying seismic shaking intensities the number of lacustrine turbidites type 1 linearly increases with increasing seismic intensity starting with no lacustrine turbidites type 1 at intensities between v and vi and reaching 100 when intensities are higher than vii combining different types of seismically induced event deposits allows the reconstruction of the complete impact of an earthquake

inventory fluxes and residence times from the depth profiles of naturally occurring 210pb in marine sediments of mumbai harbor bay measurements of the vertical concentration profile of deposited 210pb and its parent 226ra in cores of recent marine sediment of mumbai harbor bay mhb were made to determine the various depth distribution parameters sedimentation rate age of sediment total inventory fluxes residence times scavenging rate linear attenuation coefficient and relaxation mass depth overall the profile distributions of 226ra and 210pb showed a decreasing trend with increasing the depth the mean of sedimentation rate in the studied area was obtained to be about 0 76 cm year 1 which corresponds to average age of sediment of about 56 years the average total deposited 210pb for the studied sediment profile was 9 68 k bq m 2 and correspondingly the average value of fluxes of total 210pb and excess 210pb atmospheric flux were 0 59 and 0 32 k bq m 2 year 1 respectively the residence time of 210pb was in the range of 26 226 years throughout the sediment profile and showed generally an increasing trend from top to bottom the mean relaxation mass depth h0 derived from the depth profile of 210pb at the studied area was about 190 kg m 2 the negative association between clay content of cores and the h0 of 210pb indicates that as the clay content increases the penetration depth of deposited 210pb in sediment profile decreases

rhyodacite magma storage conditions prior to the 3430 ybp caldera forming eruption of aniakchak volcano alaska this study presents a pre eruptive magma storage model for the rhyodacite and andesite magmas erupted during the 3430 ybp caldera forming eruption of aniakchak volcano alaska derived from phase equilibria experiments and petrological data the compositions of fe ti oxide pairs from the early erupted plinian rhyodacite pumice yield core temperatures of 871 900 c with rims up to 942 c and fo2 from 10 6 to 11 8 log units melt inclusions entrapped in plagioclase phenocrysts have h2o contents between 3 and 5 wt estimated by ftir and electron microprobe volatiles by difference methods with no detectable co2 assuming water saturation this corresponds to entrapment pressures between 65 and 150 mpa phase equilibria results reproduce the natural phase assemblages at p text h 2 text o of 95 150 mpa at 870 880 c assuming water saturation a mismatch in experimental versus natural glass sio2 and al2o3 and melts models for h2o undersaturated conditions indicate that the rhyodacite may not have been h2o saturated melts models with x text h 2 text o 0 8 and ptotal of 125 150 mpa at 870 880 c reproduce the natural groundmass glass al2o3 composition best indicating the magma may have been slightly h2o undersaturated those pressures correspond to storage at 4 5 5 4 km depth in the crust melts models and vbd estimates from melt inclusions in titanomagnetite grains from the andesite indicate pre eruptive conditions of 1 000 c and 110 mpa corresponding to a minimum residence depth of 4 1 km assuming water saturation or greater if the magma was h2o undersaturated previous geochemical studies indicate separate histories of the two magmas though they retain some evidence that they are ultimately related through fractional crystallization processes analogous to the 1912 novarupta magmas the rhyodacite and andesite presumably originated within the same crystal mush zone beneath the edifice yet were separated laterally and underwent different degrees of crustal assimilation the andesite must have resided in close proximity with ascent occurring in response to movement of the rhyodacite and resulting in extensive syn eruptive mingling

geologic and physiographic controls on bed material yield transport and channel morphology for alluvial and bedrock rivers western oregon the rivers of western oregon have diverse forms and characteristics with channel substrates ranging from continuous alluvial gravel to bare bedrock analysis of several measurable morphologic attributes of 24 valley reaches on 17 rivers provides a basis for comparing nonalluvial and alluvial channels key differences are that alluvial reaches have greater bar area greater migration rates and show systematic correlation among variables relating grain size to bed material transport capacity we relate these differences between channel types to bed material transport rates as derived from a coupled regional analysis of empirical sediment yield measurements and physical experiments of clast attrition during transport this sediment supply analysis shows that overall bed material transport rates for western oregon are chiefly controlled by 1 lithology and basin slope which are the key factors for bed material supply into the stream network and 2 lithologic control of bed material attrition from in transport abrasion and disintegration this bed material comminution strongly affects bed material transport in the study area reducing transport rates by 50 90 along the length of the larger rivers in the study area a comparison of the bed material transport estimates with the morphologic analyses shows that alluvial gravel bed channels have systematic and bounding relations between bed material transport rate and attributes such as bar area and local transport capacity by contrast few such relations are evident for nonalluvial rivers with bedrock or mixed bed substrates which are apparently more influenced by local controls on channel geometry and sediment supply at the scale of western oregon the physiographic and lithologic controls on the balance between bed material supply and transport capacity exert far reaching influence on the distribution of alluvial and nonalluvial channels and their consequently distinctive morphologies and behaviors differences germane for understanding river response to tectonics and environmental perturbations as well as for implementing effective restoration and monitoring strategies

influence of orographically enhanced sw monsoon flux on coastal processes along the se arabian sea 1 the arabian sea has an excess evaporation over precipitation regime the southeast arabian sea is however anomalous because it has 2800 4800 mm rainfall during the southwest monsoon swm despite a high rainfall the fluvial influence on supply of total suspended matter tsm and marine productivity is deemed insignificant and remains unevaluated we evaluated the poorly resolved influence of fluvial influx on shelf processes we documented low salinity stratification high productivity and turbidity over the entire inner shelf chlorophyll a 2 4 mg m 3 po4 3 2 5 m no3 6 8 2 1 m tsm 88 182 mg l 1 salinity near shore region 26 offshore region 33 8 34 6 p s u the deeper regions 40 m however had greatly reduced tsm and nutrient levels no3 po4 3 1 0 m tsm 24 mg l 1 and patches of high chlorophyll a upon cessation of the swm nutrient levels and tsm reduced considerable we identify two processes that contribute to the marine productivity and turbidity during the swm over the deeper regions there is a poor influence of fluvial supply and upwelling regulates productivity over the shallow inner shelf the sequestering of fluvial influx due to the prevalence of strong winds upwelling and equatorward flow is dominant the later processes induced high marine productivity and eutrophication in the near shore region and may have implications for siltation of channels reduced turbidity nutrient and chlorophyll a levels and higher salinity of the coastal waters during rest of the year imply a substantial role of fluvial fluxes on coastal processes

co eruptive subsidence and post eruptive uplift associated with the 2011 2012 eruption of puyehue cordon caulle chile revealed by dinsar abstract the 2011 2012 eruption of the puyehue cordon caulle volcanic complex southern andes chile was associated with complex surface deformation affecting an area of roughly 50 by 50 km we report here differential sar interferometry dinsar results of pre co and post eruptive deformation from envisat asar cosmo skymed and alos 2 palsar scenes acquired between early 2011 and early 2017 no clear pre eruptive deformation is observed during five months before the eruption although some patterns could be interpreted as showing inflation occurring between april and may 2011 co eruptive interferograms show a complex deformation pattern consisting in a major deflation lobe 120 cm los lengthening centered 10 km nw of the eruption vent accompanied by smaller uplift and subsidence regions in the vicinity of the vent re inflation began immediately after the end of the eruption a first pulse lasted 3 years between 2012 and 2015 accumulating 70 cm uplift we detect here a second pulse beginning in june 2016 and still ongoing in february 2017 reaching 12 cm in half a year inverse modeling with spherical cavity and spheroidal sources locates re inflation sources at a depth ranging between 8 and 11 km under the surface it suggests re filling of the reservoir occurring after the draining of a shallow magma chamber during the 2011 2012 eruption

fayalite oxidation processes in obsidian cliffs rhyolite flow oregon this study investigates the oxidation of fayalite fe22 sio4 that is present in lithophysae from a rhyolite flow obsidian cliffs oregon textural chemical and structural analyses of the successive oxidation zones are used to constrain 1 the oxidation processes of olivine and 2 the role of temperature chemical diffusion and meteoric infiltration petrologic analyses and thermodynamic modeling show that the rhyolite flow emplaced at 800 950 c fayalite bearing lithophysae formed only in the core of the lava flow variations in the gas composition inside the lithophysae induced the oxidation of fayalite to a laihunite 1 m zone fe12 fe23 1 sio4 2 this zone is made of nano lamellae of amorphous silica sio2 and laihunite 3 m fe2 1 6fe3 1 6 0 8 sio4 2 hematite fe2o3 it probably formed by a nucleation and growth process in the fayalite fractures and defects and at fayalite crystal edges the laihunite 1 m zone then oxidized into an oxyfayalite zone with the composition fe2 0 52fe3 2 32 1 16 sio4 2 this second oxidation zone is made of lamellae of amorphous silica sio2 and hematite fe2o3 with a possible small amount of ferrosilite fe2 sio3 a third and outer zone composed exclusively of hematite is also present the successive oxidation zones suggest that there may be a mineral in the olivine group with higher fe3 content than laihunite 1 m the transformation of laihunite 1 m to this oxyfayalite phase could occur by a reaction such as formula 1 this would imply that fe3 can also be incorporated in the m1 site of olivine 1 embed mml math 1 gif

historical change in lake sedimentation in lake takkobu kushiro mire northern japan over the last 300 years abstract environmental degradation including shallowing deterioration of aquatic habitat and water pollution has arisen from the inflow of fine sediment to lake takkobu in northern japan the lake has experienced gradual environmental degradation due to agricultural development which has introduced both fine sediment and sediment associated nutrients into the lake we have reconstructed the history of sediment yield to lake takkobu in kushiro mire over the last 300 years and have examined trends with reference to land use development fifteen lake sediment core samples were obtained and various physical variables of lake sediments were analyzed and dated using 137cs and tephrochronology the physical variables showed that all points contained mainly silt except for two points close to the river mouths where the mean diameter was

color change processes of a plinian pumice and experimental constraints of color change kinetics in air of an obsidian colors of plinian pumices were measured by spectrocolorimetry and their quantitative color parameters in the l a b color space were determined a series of heating experiments of obsidian was conducted to simulate the color change processes of rhyolitic glasses in these experiments following three stages of color change processes were observed stage i showed a rapid b yellowishness increase associated with fast dehydration controlled by water diffusivity dwater in stage ii a reddishness increase was accompanied by fe2 decrease both a increase and fe2 decrease can be simulated by a diffusion model obtained diffusivity doxidation were about two orders of magnitude smaller than dwater the a value increase after the oxidation in stage iii appeared to be quasi linear with time indicating the zeroth order reaction corresponding to the formation of hematite like structures in rhyolitic glasses the diffusion limited a increase model in stage ii was applied to a natural plinian pumice fall unit to evaluate time periods of color change processes through oxidation by air of fragmented rhyolitic materials

eruption mechanisms and short duration of large rhyolitic lava flows of yellowstone abstract large volume effusive rhyolite lava flows are a common but poorly understood occurrence from silicic volcanic centers we integrate characterization of lava flow topographic morphology and petrographic textures and zoning of crystals with physical models of viscous fluid flow in order to interpret the eruption durations and discharge rates for the most recent effusive volcanic eruptions from yellowstone these large volume 10 70 km3 crystal poor rhyolite lavas erupted within the yellowstone caldera as 100 200 m thick flows and have a cumulative erupted volume of 650 km3 that is similar to less frequent caldera forming events but occur as individual eruptions spread over 100 ka most of this work is focused on the axisymmetric 124 ka 50 km3 summit lake flow we examined crystallinity major and trace element concentrations oxygen and hydrogen isotopic values and quartz morphology and zoning in samples from the center to margin of this flow water contents down to 0 1 wt and d values of 110 are low and require closed system degassing until near surface lithostatic pressure while major elements are consistent with water undersaturated pre eruptive storage and crystallization at 4 8 km depth we found some evidence for subtle km scale zoning within the lavas but describe significant microscopic scale compositional diversity including sharp boundaries between high ti cores and 200 m thick rims on quartz phenocrysts embayed quartz external morphology and rim growth may be the result of undercooling during coalescence of magma bodies during shallow transport between dikes and sills modeling the emplacement of the lava flow as a simple viscous fluid suggests that emplacement of rhyolite lava at 800 c occurred over 2 to 5 yrs with high discharge rates 100 m3 s such high magma discharge rates are accommodated through 6 km long fissures that allow for slower magma ascent velocities of 10 yr flow durations and significant cooling of the flow front that should result in a more complex compound flow morphology than observed higher temperatures require unrealistically wide 50 m dike widths to accommodate large discharge rates petrographic and isotopic evidence from crystals suggests recharge and merger of individual magma batches occurs on a similar timescale to the eruption duration and may directly cause overpressure and emplacement of these rhyolite lava flows from a shallow ephemeral magma chamber large volume rhyolitic lavas are able to erupt effusively through elongate fissures that utilize preexisting zones of crustal weaknesses such as ring fractures less common explosive eruptions at yellowstone may result when ascending magmas are forced through narrower conduits or when recharge rates are especially high the results of this study provide a unique top down constraint on effusive eruption rates make new interpretations of common petrographic textures and presents a comprehensive model for eruption control

rapid reinflation following the 2011 2012 rhyodacite eruption at cordon caulle volcano southern andes imaged by insar evidence for magma reservoir refill cordon caulle is a large fissural volcano that has erupted rhyodacitic magma of the same composition in its past three historical eruptions in 1921 1960 and 2011 2012 there was significant ground deformation observed before and during the 2011 2012 eruption here we use c and x band insar time series results to document post eruptive uplift up to 0 8 m between march 2012 and may 2015 with los rates up to 45 cm yr that have been largely aseismic along with subsidence in the 2011 2012 lava flow the 2012 uplift rate is one of the largest for silicic systems and was likely produced by the intrusion of 0 125 km3 of magma in the same tectonically controlled plumbing system that has been active during the historical eruptions nevertheless the uplift ended before the reservoir refilled with the erupted volume maybe due to a change in the pressure gradient produced by the 2011 2012 eruption

autopsy of a reservoir facies architecture in a multidam system elwha river washington usa the 2011 2014 removal of two large dams on the elwha river washington state the largest dam removal yet completed globally created extensive cutbank exposures of reservoir sediments allowing the first characterization of the facies architecture of sediments through direct observation in reservoirs worldwide and providing an unparalleled opportunity to assess the relationship between environmental influences such as changes in sediment supply and their expression in the stratigraphic record using a combination of facies description from observation of 49 measured sections and 100 exposures and analysis of digital elevation models and historic aerial photographs we delineated the characteristic depositional zones of each reservoir and mapped the evolution of the subaerial delta over the life span of the reservoir former lake mills the younger upstream reservoir was characterized by a tripartite subaerial gilbert style delta that prograded 1 km into the main reservoir from 1927 to 2011 sediments were composed of coarse grained topset beds steeply dipping foreset beds and a fine grained gently dipping prodelta while individual event horizons were discernible in fine grained sediments of former lake mills their number and spacing did not correspond to known drawdown or flood events former lake aldwell impounded from 1913 to 2011 was initially defined by the rapid progradation of a gilbert style subaerial delta prior to the upstream completion of glines canyon dam however the 1927 closure of glines canyon dam upstream caused the delta to evolve to a fine grained mouth bar type delta indicative of low finer grained sediment this evolution combined with a previously unrecognized landslide deposit into the upper delta plain suggests that understanding the exogenic influences on reservoir sedimentation is critical to interpretation and prediction of the sedimentation within individual systems

a melt viscosity scale for preeruptive magmas a simplified method to estimate preeruptive melt viscosity by using only melt sio2 content groundmass sio2 content is proposed for sub alkaline magmas melt viscosity is controlled by many magmatic properties e g melt composition melt water content and temperature however these properties are linked by phase equilibrium in preeruptive magmas in this study the magmatic properties were investigated by compiling data of phase equilibria experiments performed under preeruptive conditions negative correlations are found between melt sio2 contents and liquidus temperatures and between liquidus temperatures and melt water contents both increasing melt sio2 content and decreasing liquidus temperature have the effect of increasing the melt viscosity producing a linear positive correlation between logarithmic values of melt viscosity and linear values of melt sio2 content for a specific melt sio2 content an increase in liquidus temperature causes a decrease in melt viscosity whereas a decrease in water content causes an increase in melt viscosity as a result of this opposing effect the melt viscosity is strongly correlated with the melt sio2 content the correlation coefficient of 1 based on this relationship an empirical equation predicting logarithmic values of preeruptive melt viscosity is proposed as a linear function of melt sio2 content referred to as the melt viscosity scale the equation reproduces melt viscosities for compiled experimental melts and natural melts with root mean square deviation of 0 4 and 0 5 log units respectively this method provides order of magnitude estimates for preeruptive melt viscosity its strength is in being applicable to examples for which a full dataset of preeruptive magmatic properties is lacking or has large uncertainties e g slowly cooled lavas the simplicity of this method enables us to easily and promptly estimate preeruptive melt viscosity combined with rheological models for multiphase magmas the present method can be applied widely and thus greatly increase the number of case studies which include evidence based estimates of preeruptive magma viscosity

dynamics of wind affected volcanic plumes the example of the 2011 cordon caulle eruption chile the 2011 cordon caulle eruption represents an ideal case study for the characterization of long lasting plumes that are strongly affected by wind the climactic phase lasted for about 1 day and was classified as subplinian with plumes between 9 and 12 km above the vent and mass flow rate mfr on the order of 107 kg s 1 eruption intensity fluctuated during the first 11 days with mfr values between 106 and 107 kg s 1 this activity was followed by several months of low intensity plumes with mfr 106 kg s 1 plume dynamics and rise were strongly affected by wind during the whole eruption with negligible upwind spreading and sedimentation the plumes that developed on 4 6 and 20 22 june can be described as transitional i e plumes showing transitional behavior between strong and weak dynamics while the wind clearly dominated the rise height on all the other days resulting in the formation of weak plumes individual phases of the eruption range between volcanic explosivity indices veis 3 and 4 while the cumulative deposit related to 4 7 june 2011 is associated with veis 4 and 5 crosswind cloud and deposit dispersal of the first few days are best described by a linear combination of gravitational spreading and turbulent diffusion with velocities between 1 and 10 m s 1 downwind cloud velocity for the same days is best described by a linear combination of gravitational spreading and wind advection with velocities between 17 and 45 m s 1 results show how gravitational spreading can be significant even for subplinian and small moderate eruptions strongly advected by wind and with low richardson number and low mfr

3d gravity inversion and thermodynamic modelling reveal properties of shallow silicic magma reservoir beneath laguna del maule chile abstract active large volume silicic magma systems are potentially the most hazardous form of volcanism on earth knowledge of the location size and physical properties of silicic magma reservoirs is therefore important for providing context in which to accurately interpret monitoring data and make informed hazard assessments accordingly we present the first geophysical image of the laguna del maule volcanic field magmatic system using a novel 3d inversion of gravity data constrained by thermodynamic modelling the joint analysis of gravity and thermodynamic data allows for a rich interpretation of the magma system and highlights the importance of considering the full thermodynamic effects on melt density when interpreting gravity models of active magmatic systems we image a 30 km 3 low density volatile rich magma reservoir at around 2 km depth containing at least 85 melt hosted within a broader 115 km 3 body interpreted as wholly or partially crystallised 70 crystal cumulate mush our model suggests a magmatic system with shallow crystal poor magma overlying deeper crystal rich magma even though a large density contrast 600 kg m 3 with the surrounding crust exists the lithostatic load is 50 greater than the magma buoyancy force suggesting buoyancy alone is insufficient to trigger an eruption the reservoir is adjacent to the inferred extension of the troncoso fault and overlies the location of an intruding sill driving present day deformation the reservoir is in close proximity to the 2 0 km 3 nieblas rln eruption at 2 3 ka which we calculate tapped approximately 7 of the magma reservoir however we suggest that the present day magma system is not large enough to have fed all post glacial eruptions and that the location or size of the system may have migrated or varied over time with each eruption tapping only a small aliquot of the available magma the presence of a shallow reservoir of volatile rich near liquidus magma in close proximity to regional scale faulting has important implications for volcano monitoring and hazard mitigation

atmospheric summer circulation and coastal upwelling in the arabian sea during the holocene and the last glaciation accumulation rates of biogenic and lithogenic components were studied in 39 turbidite free well dated sediment cores from the northern indian ocean to define the proportions of fluvial and eolian input and to reconstruct quaternary patterns of coastal upwelling the majority of dust deposited in the western arabian sea during the holocene about 100 106 t yr 1 is advected from arabia by northwesterly winds which overlie the low level southwest monsoon the glacial increase in dust flux to 160 106 t yr 1 culminated in the northern arabian sea most probably due to i entrainment of dust rich in chlorite dolomite and lithogenic carbonate in the then dry persian gulf and ii a southward shift of the mean position of the southwest monsoon during glacial summer this shift is recorded in reduced accumulation rates of biogenic opal and increased rates of marine carbonate off somalia and oman both the terrigenous and biogenic sediment records show that the northwesterly winds and the southwest monsoon persisted over the last 27 000 yr as well as the asian continental summer heat low however the glacial seasonal time span of the southwest monsoon season was much reduced most likely because of a delay in the seasonal onset of the southwest monsoon

intrusion of the bay of bengal water into the arabian sea during winter monsoon and associated chemical and biological response this work was supported by the department of ocean development under the program marine research living resources mr lr jayu narvekar acknowledges the financial support from csir

ash production and dispersal from sustained low intensity mono inyo eruptions recent rhyolitic volcanism has demonstrated that prolonged low intensity ash venting may accompany effusive dome formation we examine the possibility and some consequences of episodes of extended weak ash venting at the rhyolitic mono inyo chain in eastern california we describe ash filled cracks within one of the youngest domes panum crater which provide a textural record of ash venting during dome effusion we use synchrotron based x ray computed tomography to characterize the particles in these tuffisites particle sizes in well sorted tuffisite layers agree well with grain size distributions observed during weak ash venting at soufriere hills volcano montserrat and yield approximate upper and lower bounds on gas velocity and mass flux during the formation of those layers we simulate ash dispersal with ash3d to assess the consequences of long lived mono inyo ash venting for ash deposition and the accompanying volcanic hazards our results highlight the sensitivity of large scale outcomes of volcanic eruptions to small scale processes

a 5000 yr record of climate change in varved sediments from the oxygen minimum zone off pakistan northeastern arabian sea the upper holocene marine section from a kasten core taken from the oxygen minimum zone off karachi pakistan at water depth 700 m contains continuously laminated sediments with a sedimentation rate of 1 2 mm yr and a unique record of monsoonal climatic variability covering the past 5000 years our chronostratigraphy is based on varve counts verified by conventional and ams 14 c dating individual hemipelagic varve couplets are about 0 8 1 5 mm thick with light colored terrigenous laminae a deposited mainly during the winter monsoon alternating with dark colored laminae b rich in marine organic matter coccoliths and fish debris that reflect deposition during the high productivity season of the late summer monsoon august october precipitation and river runoff appear to control varve thickness and turbidite frequency we infer that precipitation decreased in the river watershed indicated by thinning varves after 3500 4000 yr b p this is about the time of increasing aridification in the near east and middle east as documented by decreasing nile river runoff data and lake level lowstands between turkey and northwestern india this precipitation pattern continued until today with precipitation minima about 2200 1900 yr b p 1000 yr b p and in the late middle ages 700 400 yr b p and precipitation maxima in the intervening periods as documented by spectral analysis the thickness of varve couplets responds to the average length of a 250 yr cycle a 125 yr cycle the gleissberg cycle of solar activity 95 yr and a 56 yr cycle of unknown origin higher frequency cycles are also present at 45 39 29 31 and 14 yr the sedimentary gray value also shows strong variability in the 55 yr band plus a 31 yr cycle because high frequency cyclicity in the enso band ca 3 5 and 5 yr is only weakly expressed our data do not support a straightforward interaction of the pacific enso with the monsoon driven climate system of the arabian sea

the origin of volcano tectonic earthquake swarms volcano tectonic vt seismicity is commonly recorded prior to and during eruptions vt seismicity may reflect stresses induced by dike propagation as indicated by propagating hypocenters and fault plane solutions fps reflecting regional stresses or stresses induced by dike inflation indicated by randomly distributed hypocenters and fps with pressure axes rotated 90 to regional maximum compression although numerical models of dike induced stresses indicate that both regimes should occur during dike emplacement this has not yet been observed according to published seismic data instead 90 rotated fps are observed in some cases while propagating hypocenters mark dike formation in other cases we suggest that differences in the seismic expression of upper crustal magma migration may result from differences in the regional tectonic setting and in the nature of magma wall rock interactions ultimately it may be possible to use information contained in vt seismicity to forecast changes in a volcano s behavior by establishing the characteristic stress field response for a given volcano or through a deeper understanding of the complex relationships between vt seismicity local crustal stresses and the physical mechanisms of magma migration

spherulite crystallization induces fe redox redistribution in silicic melt rhyolitic obsidians from krafla volcano iceland record the interaction between mobile hydrous species liberated during crystal growth and the reduction of ferric iron in the silicate melt we performed synchrotron ftir and xanes measurements along a transect extending from a spherulite into optically distinct colorless and brown glass zones measurements show that the colorless glass is enriched in oh groups and depleted in ferric iron while the brown glass shows the opposite relationship the color shift between brown and clear glass is sharp suggesting that the colorless glass zone was produced by a redox front that originated from the spherulite margin and moved through surrounding melt during crystallization we conclude that the most likely reducing agent is hydrogen produced by magnetite crystallization within the spherulite the krafla obsidians dramatically capture redox disequilibrium on the micoscale and highlight the importance of hydrous fluid liberation and late stage crystallization to the redox signature of glassy lavas

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

evaluation of the influence of monsoon climatology on dispersal and sequestration of continental flux over the southeastern arabian sea abstract associated with the coupled land ocean heating cooling seasonal reversal of monsoon winds regulates hydrography precipitation upwelling fluvial influx and a host of biogeochemical processes we evaluate the role of the monsoon winds fluvial discharge and currents on continental flux dynamics from advection magnitude of clays over an anomalous high precipitation regime of the southeastern arabian sea coupled with the intense rains and a high fluvial discharge we archived an elevated content of detrital clays 41 mg l 1 during the southwest monsoon over the 40 m however had much reduced detrital clays

book reviewmoraines and varves origin genesis classification ch schluchter editor a a balkema rotterdam 1979 441 pp dfl 85 00 u s 45 00

estimating accumulation rates and physical properties of sediment behind a dam englebright lake yuba river northern california 1 studies of reservoir sedimentation are vital to understanding scientific and management issues related to watershed sediment budgets depositional processes reservoir operations and dam decommissioning here we quantify the mass organic content and grain size distribution of a reservoir deposit in northern california by two methods of extrapolating measurements of sediment physical properties from cores to the entire volume of impounded material englebright dam completed in 1940 is located on the yuba river in the sierra nevada foothills a research program is underway to assess the feasibility of introducing wild anadromous fish species to the river upstream of the dam possible management scenarios include removing or lowering the dam which could cause downstream transport of stored sediment in 2001 the volume of sediments deposited behind englebright dam occupied 25 5 of the original reservoir capacity the physical properties of this deposit were calculated using data from a coring campaign that sampled the entire reservoir sediment thickness 6 32 m at six locations in the downstream 3 4 of the reservoir as a result the sediment in the downstream part of the reservoir is well characterized but in the coarse upstream part of the reservoir only surficial sediments were sampled so calculations there are more uncertain extrapolation from one dimensional vertical sections of sediment sampled in cores to entire three dimensional volumes of the reservoir deposit is accomplished via two methods using assumptions of variable and constant layer thickness overall the two extrapolation methods yield nearly identical estimates of the mass of the reservoir deposit of 26 106 metric tons t of material of which 64 7 68 5 is sand and gravel over the 61 year reservoir history this corresponds to a maximum basin wide sediment yield of 340 t km2 yr assuming no contribution from upstream parts of the watershed impounded by other dams the uncertainties and limitations of the estimates of overall sediment quantities are discussed implications for watershed management and future reservoir sedimentation studies are also presented

rheology of bubble bearing magmas abstract the physical effects of air or argon bubbles on the rheology of a calcium aluminosilicate melt have been measured at temperatures ranging from 830 to 960 c at 1 bar pressure the melt composition is sio 2 64 al 2 o 3 23 and cao 13 wt while bubble volume fractions are 0 0 06 0 13 0 32 0 41 and 0 47 measured newtonian viscosities range from 10 10 to 10 14 dpa s melts with bubble fractions of 0 06 and 0 13 show with increasing temperature t an increasing relative viscosity for t t 850 c for all bubble fractions the viscosity decreases markedly with temperature the observed maximum decrease of the relative viscosity is 75 for a bubble fraction of 0 47 at 907 c at all bubble fractions the viscosity is independent of the applied stress which ranged from 11 to 677 bars no clear indications were observed of non newtonian rheological behavior under our experimental conditions the relative viscosity of the two phase liquid depends primarily on the bubble fraction physical and volcanological implications of these measurements are discussed

petrological architecture of a magmatic shear zone a multidisciplinary investigation of strain localisation during magma ascent at unzen volcano japan shearing of magma during ascent can promote strain localisation near the conduit margins anymechanical and thermal discontinuities associated with such events may alter the chemical physicaland rheological stability of the magma and thus its propensity to erupt lava spines can record suchprocesses preserving a range of macroscopic and microscopic deformation textures attributed toshearing and friction as magma ascends through the viscous brittle transition here we use a multi disciplinary approach combining petrology microstructures crystallography magnetics and experi mentation to assess the evidence role and extent of shearing across a marginal shear zone of the1994 1995 lava spine at unzen volcano japan our results show that crystals can effectively moni tor stress conditions during magma ascent with viscous remobilisation crystal plasticity and com minution all systematically increasing towards the spine margin accompanying this we find anincrease in mineral destabilisation in the form of pargasitic amphibole breakdown displaying tex tural variations across the shear zone from symplectitic to granular rims towards the spine margin in addition the compaction of pores chemical and textural alteration of interstitial glass and mag netic variations all change systematically with shear intensity the strong correlation between thedegree of shearing crystal deformation and disequilibrium features together with distinct magneticproperties implies a localised thermal input due to shear and frictional processes near the conduitmargin during magma ascent this was accompanied by late stage or post emplacement fluid andgas induced alteration of the gouge as well as oxidation and glass devitrification understandingand recognising evidence for strain localisation during magma ascent may therefore be vital whenassessing factors that regulate the style of volcanic eruptions which may provide insights into thecryptic shifts from effusive to explosive activity as observed at many active lava domes

storage and eruption of near liquidus rhyolite magma at cordon caulle chile the last three eruptions at the cordon caulle volcanic complex chile have been strikingly similar in that they have started with relatively short pre eruptive warning and produced chemically homogeneous rhyolite to rhyodacite magma with glassy to aphyric texture these characteristics collectively call for an understanding of the storage conditions leading to the rise and extraction of crystal poor silicic magma from volcanoes we have analyzed and experimentally reproduced the mineral assemblage and glass chemistry in rhyolite magma produced in the most recent eruption of cordon caulle and we use these to infer magma storage and ascent conditions fe ti oxide mineral geothermometry suggests that the rhyolite was stored at 870 920 c at these temperatures the phenocryst assemblage plag an37 cpx opx mag ilm can be reproduced under h2o saturated conditions of between 100 and 50 mpa corresponding to crustal depths between about 2 5 and 5 0 km the shallow and relatively hot magma storage conditions have implications for the rapid onset degassing efficiency and progression from explosive to mixed pyroclastic effusive eruption style at cordon caulle

landslides affecting sedimentary characteristics of reservoir basin typhoons aere 2004 and matsa 2005 caused high nephelometric turbidity in the shihmen reservoir in northern taiwan jeopardizing the operation of the reservoir for several days and ultimately impacting the living conditions and economy of the downstream residents the torrential rains caused landslides and debris flows in upland areas and flowed into riverbeds likely contributing significantly to the suspended sediment yields in the reservoir this investigation elucidates how upland landslides affect sediment attributes in the reservoir basin study methods including field observations spatial analysis in gis and aerial photo interpretation are adopted to trace the sediment sources and contributing factors to the landslide torrential rains induced landslides and debris flows upland causing river incisions and soil erosion in landslide areas lacking vegetation these factors together with the conditions of the engineered structures and geologic vulnerabilities of the area caused suspended sediment yield in the reservoir the high nephelometric turbidity could potentially reoccur with masses of landslide derived sediment remaining upland and in the riverbed

1500 years of lake sedimentation due to fire earthquakes floods and land clearance in the oregon coast range geomorphic sensitivity to floods during timber harvest period

lava rise plateaus and inflation pits in the mccartys lava flow field new mexico an analog for pāhoehoe like lava flows on planetary surfaces

ocean currents and sea surface heights estimated across the west florida shelf abstract the across shelf structures of the ocean circulation and the associated sea surface height ssh variability are examined on the west florida shelf wfs for the 3 yr interval from september 1998 to december 2001 five sets of characteristic circulation patterns are extracted from 2 day low pass filtered data using the self organizing map extreme upwelling and downwelling structures with strong currents asymmetric upwelling and downwelling structures with moderate currents and a set of transitional structures with weak currents the temporal variations of these structures are coherent with the local winds on synoptic weather time scales on seasonal time scales they are related to both the local winds and the water density variations the circulation is predominantly upwelling during autumn to spring months october april and downwelling during summer months june september coastal sea level fluctuations are related to both the dynamical responses of the inner shelf circulation to meteorol

anomalous inland influx of the river indus gulf of kachchh india the gulf of kachchh is a funnel shaped macrotidal water body located in the arid region of northwestern india with 50 cm annual rainfall and insignificant fluvial input the gulf waters however have high suspended matter time series measurements of total suspended matter tsm and synchronous validated hydrodynamic modeling have been used to decipher the dispersal pathways and the sources of the high turbidity contrary to the prevalent offshore reducing trend for most of the indian coast the gulf is anomalous for having an enhanced turbidity at the mouth with lower concentrations in the inland areas the hydrography of the gulf is dominated by strong alongshore currents at the mouth which move in out during flood ebb and undergo cyclic dynamic changes with tidal phases the flood tidal currents amplify inland with propagating tides pulling in the offshore waters and acting as a feeder of high saline turbid offshore waters into the gulf most of which are trapped inland due to time lag of ebb and flood between the outer and the inner gulf based upon the distribution maps of tsm and clays in the water column it is deduced that a large segment of the gulf is nourished by contributions from the indus river

a high resolution benthic stable isotope record for the south atlantic implications for orbital scale changes in late paleocene early eocene climate and carbon cycling abstract the late paleocene and early eocene were characterized by warm greenhouse climates punctuated by a series of rapid warming and ocean acidification events known as hyperthermals thought to have been paced or triggered by orbital cycles while these hyperthermals such as the paleocene eocene thermal maximum petm have been studied in great detail the background low amplitude cycles seen in carbon and oxygen isotope records throughout the paleocene eocene have hitherto not been resolved here we present a 7 7 million year myr long high resolution orbitally tuned benthic foraminiferal stable isotope record spanning the late paleocene and early eocene interval 52 5 60 5 ma from ocean drilling program odp site 1262 south atlantic this high resolution 2 4 kyr record allows the changing character and phasing of orbitally modulated cycles to be studied in unprecedented detail as it reflects the long term trend in carbon cycle and climate over this interval the main pacemaker in the benthic oxygen isotope 18 o and carbon isotope 13 c records from odp site 1262 are the long 405 kyr and short 100 kyr eccentricity cycles and precession 21 kyr obliquity 41 kyr is almost absent throughout the section except for a few brief intervals where it has a relatively weak influence during the course of the early paleogene record and particularly in the latest paleocene eccentricity paced negative carbon isotope excursions 13 c cies and coeval negative oxygen isotope 18 o excursions correspond to low carbonate caco 3 and coarse fraction cf values due to increased carbonate dissolution suggesting shoaling of the lysocline and accompanied changes in the global exogenic carbon cycle these negative cies and 18 o events coincide with maxima in eccentricity with changes in 18 o leading changes in 13 c by 6 5 kyr in the 405 kyr band and by 3 1 kyr in the higher frequency 100 kyr band on average however these phase lags are not constant with the lag in the 405 kyr band extending from 4 5 kyr to 21 2 kyr from the late paleocene to the early eocene suggesting a progressively weaker coupling of climate and the carbon cycle with time the higher amplitude 405 kyr cycles in the latest paleocene are associated with changes in bottom water temperature of 2 4 c while the most prominent 100 kyr paced cycles can be accompanied by changes of up to 1 5 c comparison of the 1262 record with a lower resolution but orbitally tuned benthic record for site 1209 in the pacific allows for verification of key features of the benthic isotope records which are global in scale including a key warming step at 57 7 ma

magmatic evolution of the puyehue cordon caulle volcanic complex 40 s southern andean volcanic zone from shield to unusual rhyolitic fissure volcanism abstract magmas erupted from quaternary volcanoes of southern andes between 37 and 46 s latitude are mainly basaltic to andesitic however pccvc 40 s shows a singular magmatic evolution due to the abnormal evacuation of rhyolites especially in the last 100 ka in addition pccvc is the result of juxtaposing products from the nw trending alignment of cordillera nevada caldera cordon caulle fissure volcano and the puyehue stratocone using 40 ar 39 ar and 14 c geochronology it can be established that they evolved since ca 500 ka as coeval but separated vents with a first stage of shield volcanism followed by repeated collapses that formed an internal nw elongated graben from ca 100 ka volcanic activity occurred in both a fissure system cordon caulle and a central volcano puyehue holocene explosive eruptions mainly in the puyehue crater accompanied the dome growing along a nw trending fissure system last historical eruptions were in 1921 and 1960 when nw fissures of cordon caulle fed rhyodacitic lava flows in 1960 the fissure eruption was triggered by a remote mw 9 5 thrust earthquake cordillera nevada caldera presents a reduced compositional range 52 63 sio 2 and geochemical features of low pressure magma mixing and assimilation instead cordon caulle and puyehue volcanoes have a wide silica range 48 71 sio 2 and an outstanding affinity which can be modelled with initial high pressure fractional crystallization moderate magma mixing and subsequent low pressure fractional crystallization from a common parental source the exceptional magmatic evolution and eruptive style of pccvc in southern andes could be related with the physics of the plumbing system which in turn can be controlled by external factors as the structure of the continental crust and the ongoing stress regime

rapid reservoir erosion hyperconcentrated flow and downstream deposition triggered by breaching of 38 m tall condit dam white salmon river washington condit dam on the white salmon river washington a 38 m high dam impounding a large volume 1 8 million m3 of fine grained sediment 60 sand 35 silt and clay and 5 gravel was rapidly breached in october 2011 this unique dam decommissioning produced dramatic upstream and downstream geomorphic responses in the hours and weeks following breaching blasting a 5 m wide hole into the base of the dam resulted in rapid reservoir drawdown abruptly releasing 1 6 million m3 of reservoir water exposing reservoir sediment to erosion and triggering mass failures of the thickly accumulated reservoir sediment within 90 min of breaching the reservoir s water and 10 of its sediment had evacuated at a gauging station 2 3 km downstream flow increased briefly by 400 m3 s 1 during passage of the initial pulse of released reservoir water followed by a highly concentrated flow phase up to 32 sediment by volume as landslide generated slurries from the reservoir moved downstream this hyperconcentrated flow analogous to those following volcanic eruptions or large landslides draped the downstream river with predominantly fine sand during the ensuing weeks suspended sediment concentration declined and sand and gravel bed load derived from continued reservoir erosion aggraded the channel by 1 m at the gauging station after which the river incised back to near its initial elevation at this site within 15 weeks after breaching over 1 million m3 of suspended load is estimated to have passed the gauging station consistent with estimates that 60 of the reservoir s sediment had eroded this dam removal highlights the influence of interactions among reservoir erosion processes sediment composition and style of decommissioning on rate of reservoir erosion and consequent downstream behavior of released sediment

petrologic indicators of preeruption magma dynamics new phase equilibria experiments on dacite from the june 1991 eruption of mount pinatubo philippines allow calibration of a geobarometer for matrix glass at pressures of 160 220 mpa comparison with natural glass compositions suggests equilibration at lower water fugacity mathit f h 2 o than inferred from al in hornblende geobarometry the disparity between geobarometric techniques may be explained by a decrease in mathit f h 2 o and consequent crystallization several weeks before eruption a time period too short for hornblende reequilibration reduced mathit f h 2 o could have resulted from processes associated with basalt magma injection including 1 late stage magma ascent under h 2 o saturated conditions or 2 influx of other volatiles co 2 so 2 into the dacite magma system

the iugs systematics of igneous rocks in order to create a sustainable classification of igneous rocks which all geologists might use an international body was set up by the iugs the iugs subcommission on the systematics of igneous rocks in the course of creating the classification the subcommission has established ten principles for its construction and for defining an appropriate nomenclature the principles are 1 use descriptive attributes 2 use actual properties 3 ensure suitability for all geologists 4 use current terminology 5 define boundaries of rock species 6 keep it simple to apply 7 follow natural relations 8 use modal mineralogy 9 if mode not feasible use chemistry 10 follow terminology of other iugs advisory bodies these principles and their rationale have not previously been enunciated the classification separates and individually classifies the pyroclastic carbonatitic melititic lamprophyric and charnockitic rocks before entering the main qapf classification for plutonic and volcanic rocks which is based on the modal mineral proportions of quartz q alkali feldspar a and plagioclase p or of alkali feldspar a plagioclase p and feldspathoids f rocks with mafic content 90 have their own classification if the mineral mode cannot be determined as is often the case for volcanic rocks then a chemical classification of total alkalis versus silica tas is used the nomenclature for these classifications necessitates only 297 rock names out of the c 1500 that exist

hydrologic modeling of flood conveyance and impacts of historic overbank sedimentation on west fork black s fork uinta mountains northeastern utah usa abstract this study assesses historic overbank alluvial sedimentation along a low gradient reach of west fork black s fork in the northern uinta mountains utah in this previously glaciated setting an alluvial floodplain that is approximately 400 m wide by 1500 m long has been modified by the combined effects of valley morphometry and the recent history of clear cut logging during the late 19th and early 20th centuries to quantify the effects on sedimentation and flow conveyance three natural streambank exposures were sampled and analyzed for nuclear bomb fallout 137 cs the distribution of 137 cs within the three profiles suggests that a remnant outwash terrace exerts a first order control over the deposition of overbank alluvium upstream from a constriction in the floodplain caused by the terrace remnant as much as 40 cm of overbank alluvium has been deposited since the beginning of clear cut logging immediately downstream of that constriction no evidence exists for any overbank sedimentation during that same period vibracore samples and oakfield soil probe sampling throughout the study reach quantified the geographic extent and thicknesses of the historic alluvial package flood conveyance through the study area was modeled using the u s army corps of engineers hec ras modeling program model simulations were run for modern conditions using surveyed topography and for prehistoric conditions using the modern topography less the historic alluvial package determined by 137 cs analyses model results indicate that the floodplain constriction caused a significant impediment to flood conveyance at even modest discharges during prehistoric conditions this promoted ponding of floodwaters upstream of the constriction and deposition of alluvium this has increased bank heights upstream of the constriction to the point that under modern conditions 1 to 5 year recurrence interval floods are largely confined within the channel these results confirm the validity of this new approach of combining 137 cs dating of alluvial sediments with hec ras flow modeling to compare flood conveyance along a single stream reach prior to and since an abrupt change in alluvial sedimentation patterns

indian summer monsoon and winter hydrographic variations over past millennia resolved by clay sedimentation 1 reconstruction of century scale indian monsoon and winter hydrography is made from an ams dated core located in the unique region of the southeast arabian sea which lies in the pathways of the low salinity bay of bengal waters advecting during winter northeast monsoon nem based upon clay mineral analyses in seawaters we identify chlorite and kaolinite as specific clays supplied by the bay of bengal waters and local fluvial flux by the southwest monsoon swm precipitation from the peninsular india respectively along the southwest continental margin of india an evaluation of clay flux and 18o in g ruber portrays century scale weaker swm precipitation events during 450 650 yr 1000 yr and 1800 2200 cal yr bp kaolinite wt and flux were found to be low during all these events though chlorite had a persistent or enhanced flux from the enhanced flux of chlorite and reduced kaolinite chlorite ratio during weaker phases of swm we deduce a stronger nem winter hydrography implying an inverse coupling between the summer and the winter monsoon