hydraulic physical and rheological characteristics of rain triggered lahars at semeru volcano indonesia lahars volcanic debris flows have been responsible for 40 of all volcanic fatalities over the past century mount semeru east java indonesia is a persistently active composite volcano that threatens approximately one million people with its lahars and pyroclastic flows despite their regularity the behaviour and the propagation of these rain triggered lahars are poorly understood in situ samples were taken from lahars in motion at two sites in the curah lengkong river on the southeast flank of semeru providing estimates of the particle concentration grain size spectrum grain density and composition this enables us to identify flow sediment from three categories of lahars a hyperconcentrated flow b non cohesive clast and matrix supported debris flow and c muddy flood to understand hyperconcentrated flow sediment transport processes it is more appropriate to sample the active flows than the post event lahar deposits because in situ sampling retains the full spectrum of the grain size distribution rheometrical tests on materials sampled from moving hyperconcentrated flows were carried out using a laboratory vane rheometer despite technical difficulties results obtained on the 63 180 and 400 m fractions of the sampled sediment suggest a purely frictional behaviour importantly and contrary to previous experiments conducted with monodisperse suspensions our results do not show any transition towards a viscous behaviour for high shear rates these data provide important constraints for future physical and numerical modelling of lahar flows copyright 2010 john wiley sons ltd

control on the emplacement of the andesite lava dome of the soufriere hills volcano montserrat by degassing induced crystallization lava solidification is controlled by two mechanisms external cooling and gas exsolution the latter inducing crystallization due to increasing liquidus temperature the andesite lava dome of the soufriere hills volcano montserrat is an extrusion dominated by crystallization caused by gas exsolution where cooling is unimportant in controlling emplacement in the magma chamber the magma has an estimated viscosity of 7 106 pa s during ascent gas exsolution caused the magma to extrude in a highly crystalline state with only 5 15 residual melt viscosities in the range 1013 1014 pa s and mechanical strength 1 mpa deformation can be heterogeneous with extrusion along shear zones rheological stiffening in the upper conduit also causes large overpressures shallow seismicity and cyclic patterns of dome extrusion gas rich porphyritic andesites tend to be the least mobile kind of lava because transition from magma into hot crystalline material was reached during ascent

the magmatic plumbing system of the askja central volcano iceland as imaged by seismic tomography the magmatic plumbing system beneath askja a volcano in the central icelandic highlands is imaged using local earthquake tomography we use a catalog of more than 1300 earthquakes widely distributed in location and depth to invert for the p wave velocity vp and the vp vs ratio extensive synthetic tests show that the minimum size of any velocity anomaly recovered by the model is 4 km in the upper crust depth 8 km below sea level bsl increasing to 10 km in the lower crust at a depth of 20 km bsl the plumbing system of askja is revealed as a series of high vp vs ratio bodies situated at discrete depths throughout the crust to depths of over 20 km we interpret these to be regions of the crust which currently store melt with melt fractions of 10 the lower crustal bodies are all seismically active suggesting that melt is being actively transported in these regions the main melt storage regions lie beneath askja volcano concentrated at depths of 5 km bsl with a smaller region at 9 km bsl their total volume is 100 km3 using the recorded waveforms we show that there is also likely to be a small highly attenuating magmatic body at a shallower depth of about 2 km bsl

non newtonian rheology of igneous melts at high stresses and strain rates experimental results for rhyolite andesite basalt and nephelinite the stress strain rate relationships of four silicate melt compositions high silica rhyolite andesite tholeiitic basalt and nephelinite have been studied using the fiber elongation method measurements were conducted in a stress range of 10 400 mpa and a strain rate range of 10 6 to 10 3 s 1 the stress strain rate relationships for all the melts exhibit newtonian behavior at low strain rates but non newtonian nonlinear stress strain rate behavior at higher strain rates with strain rate increasing faster than the applied stress the decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt the decrease in viscosity observed at the high strain rates of the present study ranges from 0 25 to 2 54 log10 pa s the shear relaxation times of these melts have been estimated from the low strain rate newtonian shear viscosity using the maxwell relationship s g non newtonian shear viscosity is observed at strain rates time 1 equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time brittle failure of the fibers occurs 2 log10 units of time above the relaxation time this study illustrates that the occurrence of non newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate high silica rhyolite melts involved in ash flow eruptions are expected to undergo a non newtonian phase of deformation immediately prior to brittle failure

elastic properties of model basaltic melt compositions at high temperatures 1 to constrain the effect of composition and temperature on the elasticity of glasses and super cooled liquids acoustic velocities of samples in the pseudoternary system anorthite diopside forsterite an di fo were measured by brillouin spectroscopy both the longitudinal and shear wave velocities were measured in the glassy state and into the region of super cooled liquids the glass transformation temperatures tg inferred from the brillouin measurements are equal to those obtained by earlier viscosity and thermal expansion measurements on the same samples within the limits of experimental uncertainties the variation of the elastic properties with temperature is approximately linear both for the glassy state below tg and in the super cooled liquid state above tg the temperature derivative of vibrational contributions to young s e bulk ks and shear g modulus is approximately 6 12 times greater for super cooled liquids than for glasses in the glassy state the elastic moduli and their temperature derivatives are described by ideal mixing of molar properties of oxides the pronounced variations with composition in the elastic and anelastic properties above the glass transformation can be related to changes in configurational contributions the configurational contribution for chemically complex glasses mixtures of the an di fo end members does not affect the overall compressibility at lower temperatures whereas at higher temperatures they dominate the temperature derivatives of the moduli in the super cooled liquid state the temperature dependence of the vibrational elastic moduli for simple end member compositions an di is much higher than for complex compositions on the other hand the configurational contribution to compressibility is higher for complex compositions than extrapolated from end member compositions therefore the density and elastic properties of complex melts in the basaltic anorthite diopside forsterite system cannot be easily approximated from the behavior of pure anorthite or diopside samples our results indicate that with increasing temperature configurations with a higher bond strength were preferentially occupied isothermal relaxation times varying between 0 01 and 1 s at 950 c show a minimum for intermediate anorthite diopside compositions and are related to the maximum in configurational entropy

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

high temperature and pressure seismic properties of a lower crustal prograde shear zone from the kohistan arc pakistan anastomosing shear zones exposed in the lower crust of the kohistan palaeoisland arc in pakistan have parageneses indicating increasing pressure during deformation therefore they represent a rare example of strain localization during crustal thickening we investigated the seismic properties of a sheared gabbro with constant bulk chemistry across one of these shear zones the compressional wave velocity was measured at confining pressures of up to 0 5 gpa and temperatures of up to 600 8c the density the average vp compressional p wave velocity and the acoustic impedance at room temperature increase from the undeformed protolith through the strain gradient to the intensely sheared mylonite the seismic anisotropy is largest for the strain gradient the vp dependence of the velocities on temperature is much higher in the mylonite than in the protolith the acoustic impedance contrast between protolith and mylonite is high enough to generate seismic reflections at low temperatures but not at high temperatures this suggests that the seismic reflectivity may also depend on the temperature consequently ductile shear zones can be detected in reflection profiles of crusts with low geothermal gradients and may be transparent in crusts with high geothermal gradients

magmatic architecture of dome building eruptions at volcan de colima mexico changes in the physical chemical and rheological properties of ascending magma regulate the style of volcanic eruptions volcan de colima s eruptive cycles of lava dome growth and explosions have been thoroughly monitored during the period 1998 2010 and provide a remarkable opportunity for deepening our understanding of the underlying processes responsible for the evolution of magma properties here we integrate direct observation with analytical and experimental data to 1 constrain the configuration of the shallow plumbing system and its influence on eruptive activity 2 describe the rheological behaviour of the magma and 3 assess the conditions that lead to fragmentation and ultimately to explosive eruptions the configuration of the shallow plumbing system was inferred from direct observation of extrusion sites and porosity of the erupted products during the ongoing eruptive phase magma was never extruded from a central vent both explosive and effusive activities were restricted to discrete vents inside the crater extensive field based density measurements on 500 blocks in pyroclastic flow deposits reveal a bimodality of porosity at values of 12 and 26 vol the least porous rocks tend to be altered whereas the more porous rocks are pristine this bimodal distribution combined with the lack of a central vent suggests the presence of a central dense altered plug the fragments of which are entrained during explosive eruptions during effusive periods the plug appears to deflect the ascent of magma at a shallow depth and consequently the site of lava extrusion the rheological properties and deformation induced seismogenic behaviour of the magmas were investigated using a uniaxial deformation apparatus instrumented with acoustic sensors the homogeneity in the physicochemical properties of the erupted magma permits the description of a flow law at eruptive temperature and strain rate conditions the crystal rich magma of volcan de colima exhibits a shear thinning rheology and becomes increasingly brittle at higher strain rates complete failure of magma can be predicted using the material failure forecast method which integrates the acceleration of released acoustic energy throughout the deformation rapid decompression experiments of samples pressurised with argon were performed to assess the fragmentation conditions under which explosive eruptions progress in the absence of gas loss due to permeable flow the pore pressure required to fragment volcanic products is inversely proportional to the porosity at volcan de colima a rapid decompression of 6 mpa is required to fragment magma averaging 26 vol pores and to thereby instigate an explosive eruption analysis of ballistic impacts 4 6 km away from the vent from recent explosive eruptions further requires decompression as great as 20 mpa which is sufficient to disrupt the more porous material as well as a fraction of the denser plug the continuing growth of a lava dome and of a larger more impermeable plug could have consequences for the stability of the edifice and development of stronger and more erratic explosive activity at volcan de colima

quantifying channel development and sediment transfer following chute cutoff in a wandering gravel bed river abstract three dimensional morphological adjustment in a chute cutoff breach alluvial channel is quantified using digital elevation model dem analysis for a ca 0 7 km reach of the river coquet northumberland uk following cutoff in january 1999 channel and bar topography was surveyed using a total station on five occasions between february 1999 and december 2000 analysis of planform change coupled with dem differencing elucidates channel and barform development following cutoff and enables quantification of sediment transfers associated with morphological adjustment within the reach this exercise indicates an initial phase of bed scour followed by a period characterised by extensive bank erosion and lateral channel migration where erosion including bed scour totalled some 15 000 m3 of sediment the channel in the post cutoff disequilibrium state is highly sensitive to relatively low magnitude floods and provision of accommodation space by bank erosion encouraged extensive lateral bar development bar development was further facilitated by infilling of channels abandoned by repeated within reach avulsion and large scale aggradation of sediment lobes deposited by higher magnitude floods calculations indicate that at least 6600 m3 of sediment was deposited on emerging bars within the reach over the survey period and 2300 m3 deposited within the channel sediment losses from the reach may have exceeded 6500 m3

experimental insights on geomorphological processes within dam break outburst floods summary hydraulic behavior and unsteady sediment transport within dam break outburst floods are inherently inter dependent yet poorly constrained this study experimentally determined how the mobility and clast size of channel bed sediments affected the peak flow depth and flow velocities wave propagation and attenuation sediment entrainment and duration of transport flood power energy transfer and geomorphological impact of outburst floods due to our choice of clast size and of a unimodal size distribution the predominant sediment transport mechanism was bedload we found that frontal wave propagation was slower and attenuated faster for flows over a mobile bed versus those over a fixed bed peak flow depth was greater and was attained earlier for flows over a mobile bed and with increased clast size geomorphological power declined logarithmically with time after an initial period where gravitational forces exceeded frictional forces both peak and time to peak geomorphological power varied inversely with clast size peak deposition rates were greatest with coarser bed sediment but time to peak deposition rate was inversely proportional to clast size volume changes down channel were described by an exponential curve which we suggest indicates that sediment transport proceeded in waves via both translation and dispersion mechanisms peak suspended load occurred coincident with peak flow velocity peak bedload occurred coincident with peak flow depth and peak sediment discharge lagged behind peak water discharge these descriptions of kinematic transformation multi phase flow and of geomorphological work due to outburst floods help to provide data for numerical modelling for mitigating outburst flood hazards and for informing on the immediate and longer term geological legacy of outburst floods

geomorphic effects flood power and channel competence of a catastrophic flood in confined and unconfined reaches of the upper lockyer valley southeast queensland australia flooding is a persistent natural hazard and even modest changes in future climate are believed to lead to large increases in flood magnitude previous studies of extreme floods have reported a range of geomorphic responses from negligible change to catastrophic channel change this paper provides an assessment of the geomorphic effects of a rare high magnitude event that occurred in the lockyer valley southeast queensland in january 2011 the average return interval of the resulting flood was similar to 2000 years in the upper catchment and decreased to similar to 30 years downstream a multitemporal lidar derived dem of difference dod is used to quantify morphological change in two study reaches with contrasting valley settings confined and unconfined differences in geomorphic response between reaches are examined in the context of changes in flood power channel competence and degree of valley confinement using a combination of one dimensional 1 d and two dimensional 2 d hydraulic modelling flood power peaked at 9800 w m 2 along the confined reach and was 2 3 times lower along the unconfined reach results from the dod confirm that the confined reach was net erosional exporting similar to 287 000 m 3 of sediment whilst the unconfined reach was net depositional gaining similar to 209 000 m 3 of sediment 70 of the amount exported from the upstream confined reach the major sources of eroded sediment in the confined reach were within channel benches and macrochannel banks resulting in a significant increase of channel width in the unconfined reach the benches and floodplains were the major loci for deposition whilst the inner channel exhibited minor width increases the presence of high stream power values and resultant high erosion rates within the confined reach is a function of the higher energy gradient of the steeper channel that is associated with knickpoint development dramatic differences in geomorphic responses were observed between the two adjacent reaches of contrasting valley configuration the confined reach experienced large scale erosion and reorganisation of the channel morphology that resulted in significantly different areal representations of the five geomorphic features classified in this study c 2013 elsevier b v all rights reserved

studying monogenetic volcanoes with a terrestrial laser scanner case study at croscat volcano garrotxa volcanic field spain erosional processes natural or anthropogenic may partly destroy the relatively small sized volcanic edifices characteristic of monogenetic volcanic zones leaving their internal structure well exposed nevertheless the study of these outcrops may be extremely challenging due to restricted accessibility or safety issues digital representations of the outcrop surface have been lately used to overcome such difficulties data acquired with terrestrial laser scanning instruments using light detection and ranging technology enables the construction of such digital outcrops the obtained high precision 3 d terrain models are of greater coverage and accuracy than conventional methods and when taken at different times allow description of geological processes in time and space despite its intrinsic advantages and the proven satisfactory results this technique has been little applied in volcanology related studies here we want to introduce it to the volcanological community together with a new and user friendly digital outcrop analysis methodology for inexperienced users this tool may be useful not only for volcano monitoring purposes but also to describe the internal structure of exposed volcanic edifices or to estimate outcrop erosion rates that may be helpful in terms of hazard assessment or preservation of volcanic landscapes we apply it to the croscat volcano a monogenetic cone in the la garrotxa volcanic field catalan volcanic zone ne spain quarrying of which leads to a perfect view of its interior but restricts access to its uppermost parts croscat is additionally one of the most emblematic symbols of the la garrotxa volcanic field natural park and its preservation is a main target of the park administration

temperature dependence of elastic p and s wave velocities in porous mt unzen dacite laboratory measurements of elastic properties of volcanic rocks are crucial for the modelling of volcano seismic activity compared to the large database reported in the literature for sedimentary igneous and metamorphic rocks the data set for volcanic rocks is limited and mostly restricted to basalts data for more silica rich rocks are sparse in particular velocity data for silica rich volcanic rocks measured at elevated temperature are lacking we measured the elastic p and s wave velocities and the velocity anisotropy of porous dacitic rocks from unzen volcano japan exhibiting an open porosity of 3 3 to 24 3 vol the measurements were done at temperatures of up to 600 c and confining pressures of 100 mpa corresponding to depths of 3000 4000 m samples with even higher porosities failed at the required pressures the measurements were carried out in a cubic multi anvil pressure apparatus using the pulse transmission technique in contrast to low porosity magmatic and metamorphic rocks the seismic velocities of the investigated volcanic rocks increased and the velocity anisotropies decreased with increasing temperature due to further sample compaction there is a close relationship between velocity density and porosity the higher the density and the lower the porosity the higher are the p and s wave velocities these results can contribute to a better understanding of the propagation of seismic energy through the volcanic edifice

age and geochemistry of granites associated with momineralizations in western bergslagen sweden abstract the bergslagen area south central sweden where large amounts of fe cu zn pb au ag mo and w have been produced for several centuries is one of the oldest mining districts in europe two episodes of magmatism and ore formation can be distinguished 1 an older early svecofennian phase that generated 1890 1850 ma old calc alkaline continental margin volcanic and plutonic units related to the svecofennian orogeny and 2 a younger phase comprising potassiumrich granitoids which intruded over a period extending from 1825 to 1680 ma during the final stage of or subsequent to the regional metamorphism and deformation related to the svecofennian orogeny in recent years considerable confusion has dominated the discussion concerning the timing and setting of the mo w forming granites in western bergslagen in this study one of the most important intrusions of undeformed granite in western bergslagen has been investigated in regard to geochemistry and u pb zircon age the granite skalhojden has a peraluminous silica and potassium rich chemistry as well as a uniformly flat ree pattern with a marked negative eu anomaly the u pb data yielded an age of 1758 8 ma these data show convincingly that the granite is comparable to other 1800 1680 ma mo w bearing granitoids elsewhere in the fennoscandian shield but are in strong conflict with hypotheses on early svecofennian rift related crust and ore forming processes recently proposed for western bergslagen a revision of the models of crustal growth and ore formation in that area is suggested

hazardous processes and events from glacier and permafrost areas lessons from the chilean and argentinean andes glacier and permafrost hazards such as glacial lake outburst floods and rock ice avalanches cause significant socio economic damages worldwide and these processes may increase in frequency and magnitude if the atmospheric temperature rises in the extratropical andes nearly 200 human deaths were linked to these processes during the twentieth century we analysed bibliographical sources and satellite images to document the glacier and permafrost dynamics that have caused socio economic damages in this region in historic time including glacial lake outburst floods ice and rock ice avalanches and lahars to unravel their causes and geomorphological impacts in the extratropical andes at least 15 ice dammed lakes and 16 moraine dammed lakes have failed since the eighteenth century causing dozens of floods some floods rank amongst the largest events ever recorded 5000 106 m3 and 229 106 m3 respectively outburst flood frequency has increased in the last three decades partially as a consequence of long term decades to centuries climatic changes glaciers shrinkage and lake growth short term days to weeks meteorological conditions i e intense and or prolonged rainfall and high temperature that increased meltwater production have also triggered outburst floods and mass movements enormous mass failures of glaciers and permafrost 10 106 m3 have impacted lakes glaciers and snow covered valleys initiating chain reactions that have ultimately resulted in lake tsunamis and far reaching 50 km flows the eruption of ice covered volcanoes has also caused dozens of damaging lahars with volumes up to 45 106 m3 despite the importance of these events basic information about their occurrence e g date causes and geomorphological impact which is well established in other mountain ranges is absent in the extratropical andes a better knowledge of the processes involved can help to forecast and mitigate these events copyright 2014 john wiley sons ltd

evaluation of titan2d modelling forecasts for the 2007 crater lake break out lahar mt ruapehu new zealand abstract following the 1995 1996 eruptions of mt ruapehu the hazard of a dam breakout lahar was immediately recognised because an unstable 7 9 m pile of volcaniclastic ejecta had accumulated over the former stable outlet of the normally 10 106 m3 crater lake prior to the dam breakout lahar of 18 march 2007 a range of flow scenarios down the eastern flanks of mt ruapehu were simulated using the titan2d mass flow numerical code to forecast flow travel times and inundation areas titan2d is a depth averaged code that solves the movement of a granular or two phase mass over digital representations of natural terrains we compared modelled scenarios run before the 18 march 2007 break out lahar of ruapehu to details from the actual event the titan2d models were accurate in predicting both the inundation areas and travel times of the lahar at various key points down the volcano s flanks to 9 km beyond 9 km and a major break in slope the initial model parameters did not cope with the fundamental change that occurred in flow rheology velocity and discharge predicted at a lahar deflection structure the bund at 9 km from the lake were up to 20 less than those of the actual 2007 flow but matched closely those of the largest 1995 lahar at this location predicted paths of flow including sites of avulsion correlated well with those in the march 2007 event in addition the simulations predicted dynamic behaviour such as super elevation of flow in corners and hydraulic ponding that corresponds to real event measurements this application shows that the titan2d model can be used to reliably forecast certain parameters of lahar flow however care must be taken when choosing parameters and flow length scales over which the comparison should be made

localized and distributed erosion triggered by the 2015 hurricane patricia investigated by repeated drone surveys and time lapse cameras at volcan de colima mexico abstract in october 2015 patricia a major category 5 hurricane made landfall in western mexico resulting in 500 mm cumulated rainfall and lahar generation along the southerly directed montegrande valley of volcan de colima we monitored lahar deposition and erosion using time lapse trail cameras and conducted repeated camera drone overflights two days before and after the hurricane using photogrammetric processing we derive a unique dataset of high resolution digital terrain models and study the geomorphologic impacts of a single lahar event results reveal different types of erosion at 8 km distance from the volcano with overland flow and rill networks developing into major erosion gullies exceeding a depth of 4 m as well as bank collapse oversteepening and marginal erosion we find alternating deposition and erosion zones that depend on general slope and valley width and find that the overland flow related erosion is an important contributor to the bulking process of lahars moreover this study shows that camera monitoring is very useful for studying the relationship between volcano landscape evolution and hydrometeorological extremes and for rapid assessment associated with single lahar events

the glass transition in hydrous granitic melts abstract the influence of water on the glass transition temperature of hydrous granitic melts is estimated on the basis of a variety of available sources of data that provide phenomenological data for the liquid glass transition and for which the relaxation timescale can be accurately estimated these sources include a dilatometric micropenetration viscosity determinations b temperature dependent spectroscopic investigations of hydrous melts and c densities of synthetic fluid inclusions in glasses all available evidence on the glass transition temperature of hydrous granitic melts when corrected for equivalent timescales yields a single consistent trend of decreasing tg with increasing water content that has powerful applications in the rheology and kinetics of processes involving late stage silicic intrusives and eruptive products the brittle ductile transition in hydrous silicic liquids can be accurately predicted using this trend combination of the presently derived relationship for the influence of water on the glass transition of granitic melts with presently available data for the high temperature viscosities of such systems permits the estimation of the temperature dependence of the viscosity of hydrous melts over the entire range of temperature relevant to granite petrogenesis such a comparison reveals that the viscosity temperature relationships of hydrous granitic melts are not arrhenian as is assumed by most existing calculational schemes for the prediction of hydrous melt viscosities the increasing deviation of viscosity temperature relationships of hydrous granitic melts from arrhenian with increasing water content is broadly consistent with similar trends accompanying the addition of excess alkalies to metaluminous granitic melt base compositions in detail however the influence of water on the deviation of viscosity temperature relationships of hydrous granitic melts from arrhenian is not as strong as would be predicted from a molar comparison of the effects of h2o vs alkali oxide or alkaline earth oxide added to these melts the answer to this apparent discrepancy may lie in the incomplete dissociation of water in the melt structure

elastic properties of diopside anorthite and grossular glasses and liquids a brillouin scattering study up to 1400 k the compressional vpand shear vs wave velocities of diopside camgsi2o6 anorthite caal2si2o8 and grossular ca3al2si3o12 glasses and liquids have been measured by high resolution brillouin spectroscopy up to 1200 or 1400 k for all three materials marked breaks in the wave velocity temperature relationships are observed at temperatures consistent with the glass transition temperatures observed in viscosity and calorimetry experiments from comparisons between high temperature ultrasonic relaxed vp data and extrapolated brillouin unrelaxed vp and vs values the configurational compressibility of diopside and anorthite liquids has been determined the relative importance of vibrational and configurational contributions can be markedly different for the compressibility and heat capacity of silicate melts

monitoring and modelling morphological change in a braided gravel bed river using high resolution gps based survey recent research in fluvial geomorphology has emphasized the direct monitoring of channel topography as a useful tool to better understand the interrelationship between river form and process and in particular to estimate bedload transport rates and reach scale sediment budgets until recently however this morphometric approach has been limited to comparison of repeatedly surveyed cross sections with the associated problems of low frequency sampling and an emphasis on cross stream as opposed to downstream morphological dynamics recent advances in analytical photogrammetry have however permitted the acquisition of data at sufficient resolutions to represent macroform 101 m and microform 10 m channel geometry in fully three dimensions while inherently spatially distributed the photogrammetric approach to land surveying is however restricted to observable areas of the channel and is thus of limited use in the subaqueous zone especially if flows are turbid or highly coloured this paper presents an alternative approach to the study of three dimensional morphological dynamics of a divided reach of the gravelly river feshie scotland in which topographic survey of both exposed and submerged areas of the reach was undertaken using the global positioning system gps survey results from two field programmes in 1998 and 1999 are presented in which a geotronics geotracer 2000 real time kinematic gps receiving unit was used to survey a 200 80 m reach rapid radial survey methods were employed permitting the collection of 2000 survey points per day giving a mean density over the 13 ha reach of 1 1 points per square metre a detailed assessment of survey errors and dem quality is presented and a limit of detection of c 10 cm proposed as an upper threshold for the identification of significant change between dems preliminary interpretation of channel dynamics in 1998 99 reveals relatively little change to the overall macroscale reach structure dem differencing techniques however highlight important local changes including the progradation of submerged bar fronts bar head aggradation and scour along major channel thalwegs and the erosion of fines from sloughs copyright 2000 john wiley sons ltd

oscillatory rheology measurements of particle and bubble bearing fluids solid like behavior of a crystal rich basaltic magma the rheology of crystal and bubble bearing magmas governs the propagation of seismic waves as well as eruption dynamics here rheology includes viscous and elastic components and their ratio known as attenuation we perform an oscillatory rheology measurements which provide storage elastic component and loss viscous component moduli and attenuation with frequency dependence using particle and bubble bearing fluids whose liquid viscosity is in the range of that of a basaltic melt we find that both the storage and loss moduli dramatically increase with the particle fraction but weakly depend on the bubble fraction solid like behavior equivalent to attenuation 40 vol the shallow conduit of stromboli volcano filled by a crystal rich and low viscosity basaltic magma may be an example where shear waves propagate and brittle fractures occur to cause explosive eruptions because of its high crystallinity

quantifying the geomorphic impacts of a lake breakout lahar mount ruapehu new zealand at 11 18 h new zealand time gmt 12 on 18 march 2007 an impoundment of 0 01 10 6 m 3 of tephra collapsed releasing 1 3 10 6 m 3 of water from crater lake at 2536 m elevation on mount ruapehu the lahar traveled 200 km along the whangaehu river aerial lidar surveys of the upper 62 km of flow path were made before and after the lahar we present here the first large scale quantification of the geomorphic impact of the dam break flood along with the rates and controls on its sediment entrainment and deposition the flood mobilized a net value of 2 5 3 1 10 6 m 3 of boulders gravel and sand over the first 5 km of travel to form a lahar of at least 4 4 10 6 m 3 passing instruments at 6 9 km lidar volume transfer calculations match dynamic measurements made after a logarithmic increase in cumulative net sediment entrainment the lahar appeared to reach its maximum sediment carrying capacity at 22 km patterns of alternating sediment erosion and deposition occurred that dominantly reflect a combination of channel morphology and confinement on the local sediment carrying capacity of the flow

outburst flood evolution at russell glacier western greenland effects of a bedrock channel cascade with intermediary lakes abstract glacial lake outburst floods have produced a distinctive and widespread quaternary record both onshore and offshore via widespread and intense geomorphological impacts yet these impacts remain poorly understood due to a lack of modern analogues this study therefore makes a systematic quantification of the evolution of a bedrock channelled outburst flood channel topography was obtained from digitised aerial photographs a 5 m grid resolution dem and bathymetric surveys flood inundation was measured in the field from dgps measurements flood evolution was analysed with application of a numerical model novel flood metrics including rate of rise to peak and persistence above a value of hydraulics were calculated the key findings were that outburst floods i that enter intermediary lakes are dramatically attenuated in terms of propagation whilst basin filling proceeds to the outlet level dissipated of energy due to considerable flow recirculation during the rising stage of the flood and after overtopping of the outlet are moderated in terms of peak discharge ii can have kinematic waves that are introduced to a flood via hydraulic ponding iii may develop a partitioning of flow regimes for instantaneous peak discharge bed shear stress and froude number due to time transgressive changes in channel cross section specifically between inner channel and overbank regions furthermore normalised change in cross sectional area and normalised change in channel slope can be used to suggest the relative magnitude of instantaneous peak discharge net erosion along a reach can be related to hydraulic persistence above a marker value and net deposition can be related to a time to peak value reconstructions of quaternary outburst floods should consider the importance of including intermediary lakes modern hazard mitigation studies could usefully note the potential use of reservoirs as an outburst flood alleviation resource

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

constraints on melt content of off axis magma lenses at the east pacific rise from analysis of 3 d seismic amplitude variation with angle of incidence we use 3d multichannel seismic data to form partial angle p wave stacks and apply amplitude variation with angle ava crossplotting to assess melt content and melt distribution within two large mid crustal off axis magma lenses oamls found along the east pacific rise from 9 37 5 n to 9 57 n the signal envelope of the partial angle stacks suggests that both oamls are partially molten with higher average melt content and more uniform melt distribution in the southern oaml than in the northern oaml for ava crossplotting the oamls are subdivided into seven 1 km2 analysis windows the ava crossplotting results indicate that the oamls contain a smaller amount of melt than the axial magma lens aml for both oamls a higher melt fraction is detected within analysis windows located close to the ridge axis than within the most distant windows the highest average melt concentration is interpreted for the central sections of the oamls the overall low oaml melt content could be indicative of melt lost due to recent off axis eruptions drainage to the aml or limited mantle melt supply based on the results of this and earlier bathymetric morphological geochemical and geophysical investigations we propose that the melt poor oaml state is largely the result of limited melt supply from the underlying mantle source reservoir with smaller contribution attributed to melt leakage to the aml we hypothesize that the investigated oamls have a longer period of melt replenishment lower eruption recurrence rates and lower eruption volumes than the aml though some could be single intrusion events

the anatomy of a lahar deciphering the 15th september 2012 lahar at volcan de colima mexico abstract volcan de colima is one of the most active volcanoes in mexico where lahars are a common phenomenon since the reactivation of the volcanic activity in 1991 lahars have become more frequent during the june october rainy season in this region therefore volcan de colima represents a natural laboratory ideal for the constant monitoring of lahars and to study factors controlling their origin flow transport and deposition since 2007 the systematic detection of lahars in volcan de colima has been carried out using seismic data from the broadband stations of the resco network the seismological network of colima university along with three rain gauge stations located on the southern ravines of the volcano in 2011 a new monitoring station was built at 2000 m a s l along the montegrande ravine which consists of a geophone a video camera and a rain gauge station coupled with a moisture sensor transmitting in real time to the resco facilities at colima university with all the instrumentation currently installed on the volcano flanks we could monitor and describe the lahar that occurred on 15 th september 2012 along the montegrande ravine and correlate the monitoring data with information gathered by the field campaign conducted two days after the event the high quality of collected data enabled us to describe the anatomy of this lahar the event consisted of a lahar that lasted 40 min triggered by 20 mm of accumulated rainfall with a maximum intensity of 95 mm h the lahar was characterized by three main surges at 4 5 minute intervals that formed an 80 cm thick terrace the first surge was a debris flow with a block rich front followed by the main body that progressively diluted to a hyperconcentrated flow from which a 40 cm thick massive unit was emplaced 33 wt gravel and 60 wt of sand it was followed by a more dilute hyperconcentrated flow that left a massive 10 cm thick sandy layer 80 wt of sand the third surge deposited a 30 cm thick upper massive unit texturally similar to the first laminated layers separate the two first units subsequent surges were confined to the inner portion of the channel by the newly formed terrace based on flow depth estimation and difference in arrival times between geophones a mean velocity of 3 m s and a maximum peak discharge of 48 m 3 s were estimated segregation processes that promote the upwelling of the largest clasts 20 30 cm on the flow surface were also observed resulting in a clast rich levee on top of the depositional units a sedimentation rate of 5 7 cm min was also determined the results here obtained are useful to better understand textural features of lahar deposits from which important information on flow behavior can be interpreted

effects of riparian vegetation on topographic change during a large flood event rio puerco new mexico usa 1 the spatial distribution of riparian vegetation can strongly influence the geomorphic evolution of dryland rivers during large floods we present the results of an airborne lidar differencing study that quantifies the topographic change that occurred along a 12 km reach of the lower rio puerco new mexico during an extreme event in 2006 extensive erosion of the channel banks took place immediately upstream of the study area where tamarisk and sandbar willow had been removed within the densely vegetated study reach we measure a net volumetric change of 578 050 490 000 m3 with 88 3 of the total aggradation occurring along the floodplain and channel and 76 7 of the erosion focusing on the vertical valley walls the sediment derived from the devegetated reach deposited within the first 3 6 km of the study area with depth decaying exponentially with distance downstream elsewhere floodplain sediments were primarily sourced from the erosion of valley walls superimposed on this pattern are the effects of vegetation and valley morphology on sediment transport sediment thickness is seen to be uniform among sandbar willows and highly variable within tamarisk groves these reach scale patterns of sedimentation observed in the lidar differencing likely reflect complex interactions of vegetation flow and sediment at the scale of patches to individual plants

surface height adjustments in pyroclastic flow deposits observed at unzen volcano by jers 1 sar interferometry abstract pyroclastic flows from the 1990 1995 eruption of unzen a dacitic volcano in the southwest of japan descended the mountain along a variety of routes causing widespread damage and loss of life interferograms constructed from jers 1 l band synthetic aperture radar sar images show a number of features related to these pyroclastic flows and their secondary effects the most useful interferogram in this respect is based on images acquired on 22 july 1993 and 1 december 1993 and shows the descent paths for pyroclastic flows occurring in four valley systems within this time window as zones of decorrelation caused by the repeated resurfacing the 22 july 1993 sar image was through considerable good fortune acquired only 2 6 days after a major pyroclastic flow had descended into the mizunashi valley so that in the absence of rainfall the fresh 2 m thick deposits were dry when first imaged the largest differential surface height changes observed in the interferogram represent height decreases in the vertical of 12 cm and significantly lie within a small region of the mizunashi valley which was resurfaced by the pyroclastic flow of 19 july 1993 but not subsequently within this small region radar coherence is higher maximum correlation value of 0 75 in a center valley site where ash but relatively few large boulders are present in a qualitative sense the new ash surfaces exhibit higher levels of radar coherence than the older pre 19 july deposits in other unzen valleys visited by pyroclastic flows smaller differential surface height decreases 4 cm are observed where the surface deposits were emplaced by events taking place between 1 3 months before the acquisition date of the 22 july 1993 image the extra 8 cm of surface height decrease observed in the case of the freshly laid mizunashi deposits must result from a deflationary mechanism or mechanisms operating in a spatially uniform manner in order for radar coherence to be maintained a number of possible causative mechanisms including hydroconsolidation initiated by the seepage of rainwater into a newly deposited ash sheet deflation on gas release basal erosion settlement and substrate relaxation are discussed here given the relatively low emplacement temperatures of the unzen ash 300 500 c it is unlikely that viscous deformation within the body of the fresh ash deposits is responsible for the subsidence comparison of the 22 july 1993 1 december 1993 interferogram with a landsat 4 thematic mapper image of unzen acquired on 10 january 1994 highlights a ribbon like zone of radar decorrelation running along the course of the mizunashi valley which marks the path of debris flows that occurred within the time interval between the two sar images used in the construction of the interferogram overall these results demonstrate the utility of interferometric sar derived surface height and coherence measurements for monitoring the pyroclastic and debris flow regimes of active volcanoes

stability assessment of the crater lake te wai ā moe overflow channel at mt ruapehu new zealand and implications for volcanic lake break out triggers abstract the presence of lakes on active volcanoes gives rise to several unique volcano hydrologic hazards including those directly related to volcanic activity e g phreatic explosions and non volcanic phenomena e g lake outbursts mt ruapehu volcano hosts the 107 m3 crater lake te wai moe in the active summit crater making it prone to lahars due to the abundance of water stored at high elevation apart from eruptive periods when water is commonly ejected from the lake large lahar events can occur when portions of the crater rim fail during quiescent periods leading to partial lake drainage the latter occurred recently in 1953 and 2007 here we investigate the potential of future lahars due to rim failure at the current overflow channel considering several triggering scenarios during non eruptive periods the geomechanical properties of a matrix dominated breccia unit composing part of the overflow channel were analyzed using physical and mechanical laboratory methods these properties combined with previous geomechanical studies of lava units in the overflow channel were used in finite element and limit equilibrium method based groundwater and stability models groundwater models indicate that a low permeability barrier inside the crater rim is preventing water from seeping through the unconsolidated and potentially permeable breccia unit of the overflow channel the removal of this barrier or weathering of a resistive lava cap could cause water to seep through the overflow channel elevating the potential of collapse slope stability models indicate that under certain conditions the overflow channel is below a conservative threshold of stability and can be destabilized with continued mechanical or chemical weathering that reduces strength properties this is also true during high magnitude tectonic or volcanic earthquakes where large ground accelerations could result in several centimeters of displacement at the overflow channel corresponding to high hazard categories of stability in the worst case scenario modeled here full collapse of the overflow channel could result in the release of c 2 4 million m3 of lake water this could drive a lahar substantially larger than well documented historic events including the more common lahars produced during eruptions the identification of key factors affecting stability can be used to inform future monitoring and the risk of these high impact events

age differences between rbsr whole rock and upb zircon ages of syn and postorogenic svecokarelian granitoids in sottunga sw finland abstract the u pb age on pooled data of zircnos from the postorogenic svecokarelian mosshaga granite is 1788 11 ma 2 the corresponding rb sr whole rock age is 1742 34 ma 2 the mosshaga granite intrudes a synorogenic granodiorite which has a u pb zircon age of 1889 10 ma and a rb sr whole rock age of 1850 28 ma the age differences between the u pb zircon ages and rb sr whole rock ages are concluded to be geologically significant it is shown that the mosshaga pluton cooled rapidly and as a consequence the rb sr isotopic system closed at a time very close to the crystallization of the zircons a commonly observed feldspar and biotite alteration in svecokarelian granitoids indicates migration of rb and sr isotopes in the whole rock system which may lead to apparently younger rb sr ages

the role of multiple glacier outburst floods in proglacial landscape evolution the 2010 eyjafjallajokull eruption iceland the 2010 eyjafjallajokull eruption in iceland provided a unique opportunity to quantify the evolution of proglacial geomorphology during a series of volcanogenic jokulhlaups glacial outburst floods 140 events time lapse imagery and repeat terrestrial laser scans before and directly after the eruption show that the jokulhlaup of 14 april 2010 composed 61 of the 57 106 m3 total discharge of the combined events and had the highest peak discharge for the two main flood events but only deposited 18 of the total volume of sediment in front of gigjokull glacier the majority of sediments 67 of a total volume of 17 12 106 m3 were deposited by the 15 april 2010 jokulhlaup and this was followed by extensive reworking by a series of smaller jokulhlaups over the following 29 days that deposited 15 of the total sediment the geomorphological and sedimentary signatures of the two largest jokulhlaups associated with the onset of the eruption have either been reworked by later floods or are buried by later flood deposits consequently the ice proximal posteruption landscape cannot be used to reconstruct the characteristics or magnitudes of either of the two largest jokulhlaups the findings support a complex response model in which peak discharge and the bulk of the sediment transported is decoupled by changing routing mechanisms and water sediment ratios during the eruption

the crustal structure of the arizona transition zone and southern colorado plateau from multiobservable probabilistic inversion the arizona transition zone is a narrow band that separates two of the main and most contrasting tectonic provinces in western us namely the southern colorado plateau and the southern basin and range provinces as such the internal crustal structure and physical state of this transitional zone hold clues for understanding i the amalgamation of these provinces ii the partitioning of deformation due to both past and present day stress fields and iii the role of thermal versus compositional effects in controlling surface observables here we employ and expand a novel multiobservable probabilistic inversion method and jointly invert fundamental mode rayleigh phase velocities receiver functions surface heat flow geoid height and absolute elevation to obtain an internally consistent 3 d model of the temperature density vs and vp of the arizona transition zone and the southern portions of the colorado plateau and basin and range our results confirm a significant crustal thickening from 28 km in the sw of the arizona transition zone and southern basin and range to 48 km beneath the southern colorado plateau inverted temperatures agree well with the location of recent volcanism and indicate that the lithosphere asthenosphere boundary is not deeper than 70 km in most of the region we find that major pre cambrian surface structures and or shear zones separate crustal domains with distinct bulk properties suggesting that the juxtaposed crustal blocks still retain at least in part their original characteristics however widespread intrusions of significant volumes of mafic magmas have affected these blocks at different depths locally overprinting their original compositions and creating highly heterogeneous crustal sections a dominant and large scale internal crustal pattern of sw dipping planes structures is evident in our models coinciding with the orientation of deep faults previously inferred from earthquake focal mechanisms while we cannot categorically corroborate the presence of melt or aqueous fluids within the crust our results are compatible with these scenarios beneath some parts of the basin and range the mogollon datil and springerville volcanic fields

moraine dam breach and glacial lake outburst flood generation by physical and numerical models summary the areas of glacial lakes in the himalayas continue to increase alarmingly due to global warming with consequent risk of glacial lake outburst flood glof the outburst is most common for moraine dammed lakes as a result of a failure of the dam by overtopping and erosion or piping due to seepage in the present context glof events especially for the moraine dam failure process needs to be predicted to assess the drastic and detrimental impacts on the downstream river valley this study focuses on validating an integrated model for simulating the failure of moraine dam by overtopping and erosion using a coupled numerical simulation model the proposed numerical methodology is validated with the data from experiments in laboratory scale physical models the results of the model are compared for both the erosional profiles during collapse of the dam and the resulting outflowing flood hydrograph the primary finding is that the moraine dam height and the volume of the lake upstream of the dam are the most sensitive parameters influencing the glof peak the model is also applied to the field problem of the tangjiashan lake outburst and dam failure and shows reasonably good agreement with observations the validated model is also run for the south lhonak glacial lake in the sikkim himalayas india to obtain the probable flood hydrograph in case of failure of the moraine dam

modelling outburst floods from moraine dammed glacial lakes in response to climatic change the size and number of moraine dammed supraglacial and proglacial lake systems have increased dramatically in recent decades given an appropriate trigger the natural moraine dams that impound these proglacial lakes are breached producing catastrophic glacial lake outburst floods glofs these floods are highly complex phenomena with flood characteristics controlled in the first instance by the style of breach formation downstream glofs typically exhibit transient often non newtonian fluid dynamics as a result of high rates of sediment entrainment from the dam structure and channel boundaries combined these characteristics introduce numerous modelling challenges in this review the historical contemporary and emerging approaches available to model the individual stages or components of a glof event are introduced and discussed a number of methods exist to model the stages of a glof event dam breach models can be categorised as being empirical analytical or numerical in nature with each method having significant advantages and shortcomings empirical relationships that produce estimates of peak discharge and time to peak are straightforward to implement but the applicability of these models is often limited by the nature of the case study data from which they are derived furthermore empirical models neglect the inclusion of basic hydraulic principles that describe the mechanics of breach formation analytical or parametric models simulate breach development using simplified versions of the physically based equations that describe breach enlargement whilst complex physically based codes represent the state of the art in numerical dam breach modelling to date few of the latter have been applied to investigate the moraine dam failure problem despite significant advances in the physical complexity and availability of higher order hydrodynamic solvers the majority of published accounts that have attempted to reconstruct or predict glof characteristics have been limited often by necessity to the use of relatively simplistic models this is in part attributable to the unavailability of terrain models of many high mountain catchments at the fine spatial resolutions required for the effective application of numerically sophisticated codes and their proprietary and often cost prohibitive nature however advanced models are experiencing increasing use in the glacial hazards literature in particular the suitability of emerging mesh free particle based methods for simulating dam breach and glof routing may represent a solution to many of the challenges associated with modelling this complex phenomenon sources of uncertainty in the glof modelling chain have been identified by various workers however to date their significance for the robustness of reconstructive and predictive modelling efforts have been largely unexplored and quantified in detail these sources include the geometric and material characterisation of moraine dam complexes including lake bathymetry and the presence and extent of buried ice initial conditions freeboard precise spillway dimensions spatial discretisation of the down valley domain hydrodynamic model dimensionality and the dynamic coupling of successive components in the glof model cascade

geomorphological evolution of a fluvial channel after primary lahar deposition huiloac gorge popocatepetl volcano mexico abstract popocatepetl volcano 19 02 n 98 62 w 5424 m began its most recent period of volcanic activity in december 1994 the interaction of volcanic and glacier activity triggered the formation of lahars through the huiloac gorge located on the northern flank of the volcano causing significant morphological changes in the channel the most powerful lahars occurred in april 1995 july 1997 and january 2001 and were followed by secondary lahars that formed during the post eruptive period this study interprets the geomorphological evolution of the huiloac gorge after the january 2001 lahar variations in channel morphology at a 520 m long research site located mid way down the gorge were recorded over a 4 year period from february 2002 to march 2005 and depicted in five geomorphological maps scale 1 200 for 14 february and 15 october 2002 27 september 2003 9 february 2004 and 16 march 2006 a gis was used to calculate the surface area for the landforms identified for each map and detected changes and erosion deposition processes of the landforms using the overlay function for different dates findings reveal that secondary lahars and others types of flows like sediment laden or muddy streamflows caused by precipitation rapidly modified the gorge channel following the january 2001 non eruptive lahar a period associated with volcanic inactivity and the disappearance of the glacier once located at the headwall of the gorge field observations also confirmed that secondary flows altered the dynamics and geomorphological development of the channel these flows incised and destroyed the formations generated by the primary lahars 1997 and 2001 causing a widening of the channel that continues today after february 2004 a rain triggered lahar and other flows infilled the channel with materials transported by these flows the deposits on the lateral edges of the channel form terraces a recent lull in lahar activity contrasts with the increasing instability of the edges of the channel and the continuous edification and destruction of recent lahar terraces

coupled fluid dynamics sediment transport modelling of a crater lake break out lahar mt ruapehu new zealand summary lahars and other sudden onset floods are highly dynamic with temporally and spatially evolving sediment loads numerical models of sudden onset flood behaviour particularly those applied to real world events have tended to neglect sediment transport processes this is a serious though perhaps understandable shortcoming given a lack of field measurements on flow bed interactions the extra computational complexity required and the problem of iteratively updating plastic channel boundaries this paper applies a fluid dynamics model with suspended sediment and bedload transport to calculate flow conditions and rapid landscape change due to an initially dilute lahar from mt ruapehu new zealand we take advantage of an unprecedented dataset of net topographic changes determined from pre and post lahar airborne lidar surveys and time series of hydrological measurements to run and validate the model a sensitivity analysis of key controls on water surface elevation and final sediment thickness illustrates how the flow was supply limited in the upper reaches it was capable of transporting a greater volume and calibre of material than that available modelled patterns of net erosion and deposition can replicate those observed r 2 0 79 and are dominantly controlled by channel gradient and topographic

seismic and acoustic signatures of surficial mass movements at volcanoes abstract surficial mass movements such as debris avalanches rock falls lahars pyroclastic flows and outburst floods are a dominant hazard at many volcanoes worldwide understanding these processes cataloging their spatio temporal occurrence and detecting tracking and characterizing these events would advance the science of volcano monitoring and help mitigate hazards seismic and acoustic methods show promise for achieving these objectives many surficial mass movements generate observable seismic and acoustic signals and many volcanoes are already monitored significant progress has been made toward understanding modeling and extracting quantitative information from seismic and infrasonic signals generated by surficial mass movements however much work remains in this paper we review the state of the art of the topic covering a range of scales and event types from individual rock falls to sector collapses we consider a full variety of volcanic settings from submarine to subaerial shield volcano to stratovolcano finally we discuss future directions toward operational seismo acoustic monitoring of surficial mass movements at volcanoes

high resolution interpretative geomorphological mapping of river valley environments using airborne lidar data the availability of airborne lidar data provides a new opportunity to overcome some of the problems associated with traditional field based geomorphological mapping such as restrictions on access and constraints of time or cost the combination of airborne lidar data and gis technology facilitates the rapid production of geomorphological maps of floodplain environments however unfiltered lidar data which include vegetation and buildings are currently more suitable for geomorphological mapping than data that have been filtered to remove these features classification of lidar data according to elevation in a gis enables the user to identify and delineate geomorphological features in a manner similar to field mapping but it is necessary to use a range of classification intervals in order to map the various types of feature that occur within a single reach comparison of a lidar derived geomorphological map with an independently produced field geomorphological map showed a high degree of similarity between the results of the two methods although ground truthing is essential in cases where a high degree of accuracy is required ground truthing of a lidar derived geomorphological map showed that around 80 of features mapped using both methods were identified from the lidar data suggesting that the method is suitable for applications such as production of base maps for use in field mapping and selection of sites for detailed investigation copyright 2007 john wiley sons ltd

seismic properties of lower crustal xenoliths from el hoyazo se spain experimental evidence up to partial melting abstract seismic techniques provide unique tools to investigate the structure and in combination with petrological geochemical and petrophysical study the composition of the lower crust controversies can be solved with comparative study of metamorphic terrains or xenoliths that occur adjacent to areas where seismic refraction reflection data are available xenoliths represent a direct sampling of the inaccessible lower crust at the time of the volcanism whilst exposed crustal sections can only be used as analogue of present day lower crust the present study is focused on the measurements of compressional wave velocities up to conditions exceeding the beginning of melting 950 c at 500 mpa confining pressure on three garnet biotite sillimanite metapelitic xenoliths recovered from the neogene dacites of el hoyazo se spain they preserve widespread interstitial rhyolitic glass as evidence of primary melt extraction and represent the best example of partially molten lower crust in the alboran domain the influence of glass on vp is primarily reflected by anomalous positive dvp dt while heating with velocity increasing at 500 mpa from 4 98 to 5 50 km s 1 at room temperature to 5 85 6 79 km s 1 at 650 700 c this corresponds to the glass transition where all the grain boundaries and most of the pores within the glass are closed after this point the velocity decreases to 6 2 6 5 km s 1 at 950 c where re melting of the glass is achieved and additional partial melt produced on cooling the behavior is normal with negative dvp dt after the thermal treatment velocities are 30 higher 6 07 7 21 km s 1 and reveal that in the presence of intergranular melt velocity measurements at room temperature cannot be extrapolated to high temperatures p waves measured at melting conditions are in agreement with deep seismic refraction data and tomography in the area and corroborate the hypothesis that partial melts are actually present in alboran lower crust

melt to mush variations in crustal magma properties along the ridge crest at the southern east pacific rise the determination of along axis variations in melt properties within the crustal axial magma chamber beneath fast spreading axes is important for understanding melt delivery from the mantle eruption history along the ridge crest and the process of crustal accretion seismic reflection images1 2 3 4 have shown the molten sill to be continuous along the ridge crest for many tens of kilometres with varying widths 250 4 500 m but variations in its seismic properties and thickness have remained elusive despite several attempts to constrain these properties5 6 7 here we report that the melt sill along the southern east pacific rise which is about 50 m thick undergoes abrupt changes in its internal properties ranging from pure melt to mush the 60 km long ridge crest segment near 14 00 s is characterized by three 2 4 km sections containing pure melt embedded within a magma chamber rich in mush these small pure melt pockets may represent a fresh supply of magma from the mantle capable of erupting and forming the upper crust conversely the 80 90 of the magma chamber which is mushy is unlikely to erupt and may influence the lower crustal accretion

seismic evidence for a crustal magma reservoir beneath the upper east rift zone of kilauea volcano hawaii an anomalous body with low vp compressional wave velocity low vs shear wave velocity and high vp vs anomalies is observed at 8 11 km depth beneath the upper east rift zone of kilauea volcano in hawaii by simultaneous inversion of seismic velocity structure and earthquake locations we interpret this body to be a crustal magma reservoir beneath the volcanic pile similar to those widely recognized beneath mid ocean ridge volcanoes combined seismic velocity and petrophysical models suggest the presence of 10 melt in a cumulate magma mush this reservoir could have supplied the magma that intruded into the deep section of the east rift zone and caused its rapid expansion following the 1975 m7 2 kalapana earthquake

defining conditions for bulking and debulking in lahars through measurements at semeru volcano east java we define the conditions under which bulking entrainment of sediment and pore water and debulking dilution and sedimentation occur in rain triggered volcanic floods lahars two observation sites were installed 510 m apart along the curah lengkong river 11 5 km southeast of semeru s summit this 30 m wide box valley with a gravel and lava base represents a real world flume analogy pore pressure sensors provided stage measurements a broad band seismograph gave insight into sediment content and frictional collisional behavior video cameras were used to measure surface velocities and direct bucket samples were taken eight rainfall induced lahars were recorded lasting 1 3 h with heights of 0 5 2 m peak velocities of 3 7 m s and discharges of 25 250 m3 s flows ranged from typical 40 wt sediment to coarse and dense hyperconcentrated flows 50 60 wt sediment multiple distinct flow packets occurred within the complex lahars and were used to determine internal changes between sites from the multiparameter data set at each site volumetric bulking and wave shortening due to portions of the lahar accelerating toward the flow front are identified initial debulking of lahars between sites may reflect drainage into the dry substrate estimates of discharge and volume at each site lead to the quantification of bulking and debulking by these actively flowing lahars along the channel reach from this we observe that bulking can be localized to certain parts of lahars resulting in intraevent increases in peak discharge that are greater than what would occur if bulking was evenly distributed throughout the flow such data are essential for the development of numerical descriptions and hazard models for mass flows

sedimentological processes in lahars insights from optically stimulated luminescence analysis abstract a lahar is a sediment laden flow capable of major destructive impacts on infrastructure and human life how lahars transport sediment is thus a key issue for understanding lahar sedimentology and behavior especially in terms of the lahar s hydraulic and rheological properties which can be substantially altered as the lahar gains or loses material during its travel in this research we analyze lahar entrainment processes by evaluating luminescence signals total photon counts from lahar sediments using blue luminescence signals blsl a portable osl reader that analyzes several grams of polymineral and polygrain size samples was applied we use data from three lahars in the tenenepanco and huiloac gorges on popocatepetl volcano mexico to elucidate the ways in which lahars may gain lose and transport sediment during flow sediment samples for luminescence analysis were taken through the full thickness of the lahar deposits at eight different sites for two lahars 1997 and 2001 and at one site for a lahar that occurred 500 yrs ago mean luminescence values obtained for the 1997 lahar help to evaluate the relationship between the lahar entrainment processes and the drainage at the different sites for the 2001 lahar this relationship was also established taking into account the channel slope the main conclusion is that luminescence signals total photon counts can be used to detect entrained material in the flow because the bulked materials modify the final osl signals the application of this type of luminescence analysis thus has the potential to provide a better understanding of sediment entrainment in these sediment laden flows

the geology and genesis of the proterozoic massive sulfide deposit at garpenberg central sweden the garpenberg deposit of central sweden is a metamorphosed strata bound zn pb cu ag sulfide deposit intercalated in an early proterozoic supracrustal sequence of felsic metavolcanics and subordinate metasedimentary rocks which have been folded metamorphosed and intruded by synorogenic granitoids the magmatism is calc alkaline and most of the volcanic activity occurred as explosive submarine volcanism the garpenberg deposit is emplaced at the contact between metasedimentary and metavolcanic rocks and consists of 32 lens shaped orebodies stratiform zn pb cu mineralization is underlain by cu bearing stockwork ore with an extensive alteration zone of quartz phlogopite rocks with minor chlorite cordierite garnet staurolite and andalusite chemically the altered zone is enriched in magnesium iron ore metals manganese and volatiles and is depleted in sodium and calcium the proposed volcanogenic origin related to calc alkaline magmatism is supported by the morphology wall rock alteration and ore mineralogy the similarity of the garpenberg deposit to the archean massive sulfide deposits of canada and the kuroko deposits of japan supports this theory but also reveals possible differences between the compositions of precambrian and phanerozoic seawater dissimilarities in the metal ratios cu pb zn of the different deposits and their associated lithologies suggest differences in their tectonic setting the garpenberg deposit is thought to have formed in an active continental margin setting rather than in an island arc

sediment entrainment by debris flows in situ measurements from the headwaters of a steep catchment 1 debris flows can dramatically increase their volume and hence their destructive potential by entraining sediment yet quantitative constraints on rates and mechanics of sediment entrainment by debris flows are limited using an in situ sensor network in the headwaters of a natural catchment we measured flow and bed properties during six erosive debris flow events despite similar flow properties and thicknesses of bed sediment entrained across all events time averaged entrainment rates were significantly faster for bed sediment that was saturated prior to flow arrival compared with rates for sediment that was dry bed sediment was entrained from the sediment surface downward in a progressive fashion and occurred during passage of dense granular fronts as well as water rich inter surge flow en massefailure of bed sediment along the sediment bedrock interface was never observed large magnitude high frequency fluctuations in total normal basal stress were dissipated within the upper 5 cm of bed sediment within this near surface layer concomitant fluctuations in coulomb frictional resistance are expected irrespective of the influence of pore fluid pressure or fluctuations in shear stress if the near surface sediment was wet as it was overridden by a flow additional large magnitude high frequency pore pressure fluctuations were measured in the near surface bed sediment these pore pressure fluctuations propagated to depth at subsonic rates and in a diffusive manner the depth to which large excess pore pressures propagated was typically less than 10 cm but scaled as d fi 0 5 in which d is the hydraulic diffusivity and fiis the frequency of a particular pore pressure fluctuation shallow penetration depths of granular normal stress fluctuations and excess pore pressures demonstrate that only near surface bed sediment experiences the full dynamic range of effective stress fluctuations and as a result can be more easily entrained than deeper sediment these data provide robust tests for mechanical models of entrainment and demonstrate that a debris flow over wet bed sediment will be larger than the same flow over dry bed sediment

the viscous brittle transition of crystal bearing silicic melt direct observation of magma rupture and healing magmas may fl ow or break depending on their deformation rate the transition between such viscous and brittle behavior controls the style of volcanic eruptions while the brittle failure of silicate melts is reasonably well characterized the effect of crystals on the viscous brittle transition has not yet been constrained here we examine the effect of suspended crystals on the mechanical failure of magmas using torsion experiments performed at temperatures 600 900 c strain rates 10 4 10 1 s 1 and confi ning pressures 200 300 mpa relevant for volcanic systems we present a relationship that predicts the critical stress and associated strain rate at which magmas fail as a function of crystal fraction furthermore the results demonstrate that the viscous to brittle transition occurs at lower stresses and strain rates when crystals are present the fractures formed during brittle failure of crystal bearing magma originate in the melt phase which enables gas to escape and hence to reduce gas overpressure these degassing pathways heal on relatively short time scales owing to the high confi ning pressure at depth highlighting the possibility that coherent lavas may actually be the healed remains of partially degassed magma parcels that have undergone many cycles of fracturing and healing

fragility and an extremely low shear modulus of high porosity silicic magma abstract the rheology and strength of bubbly magma govern eruption dynamics by determining the possibility of fragmentation of ascending magmas they are also required parameters for understanding seismic monitoring we measured the rheology and strength of high porosity rhyolitic magma at 500 950 c the measured shear modulus and strength are several orders of magnitude lower than bubble free rhyolite melt implying that high porosity magma cannot avoid fracturing during magma ascent the occurrence of fractures is observed in the low temperature magma 800 c in this temperature range the measured attenuation is low that is the elastic energy originated by deformations avoids attenuation and is stored in the bubbly magma until released by fracturing q 1 the newly found porosity dependent strength based on our measurements comprehensively explains three different fragmentation criteria that have been previously proposed independently our measurements also show that the shear modulus becomes lower by increasing porosity which can slow the shear wave velocity these results suggest that knowing the attenuation of the seismic wave is useful to evaluate magma temperature and the possibility of a fragmentation event that may determine subsequent volcanic activities

a new seismic wave attenuation module to experimentally measure low frequency attenuation in extensional mode abstract a seismic wave attenuation module is developed to experimentally measure the attenuation in extensional mode qe 1 and the young s modulus of copper jacketed 60 mm long and 25 4 mm in diameter samples in a gas medium paterson rig the new module is suitable for natural rock samples and was tested under confining pressure up to 50 mpa and room temperature the module is designed to operate at a strain 10 6 for which rocks behave linearly to calculate attenuation both the applied force and the bulk shortening of the sample are measured employing linear variable differential transformers this technique allows measuring samples with a high degree of heterogeneity attenuation at low seismic frequencies 10 2 102 hz is obtained for rocks at dry and various saturation conditions we present a series of measurements on berea sandstone in a room dry condition and saturated with different fluids water and glycerine solutions with viscosities of 10 cp and 22 cp respectively at a confining pressure of 10 mpa and with a pore pressure of 1 mpa the accuracy of the attenuation data expressed as a phase shift is 0 0019 rad

channel floodplain connectivity during an extreme flood event implications for sediment erosion deposition and delivery the term connectivity has emerged as a powerful concept in hydrology and geomorphology and is emerging as an innovative component of catchment erosion modeling studies however considerable confusion remains regarding its definition and quantification especially as it relates to fluvial systems this confusion is exacerbated by a lack of detailed case studies and by the tendency to treat water and sediment separately extreme flood events provide a useful framework to assess variability in connectivity particularly the connection between channels and floodplains the catastrophic flood of january 2011 in the lockyer valley southeast queensland australia provides an opportunity to examine this dimension in some detail and to determine how these dynamics operate under high flow regimes high resolution aerial photographs and multi temporal lidar digital elevation models dems coupled with hydrological modeling are used to assess both the nature of hydrologic and sedimentological connectivity and their dominant controls longitudinal variations in flood inundation extent led to the identification of nine reaches which displayed varying channel floodplain connectivity the major control on connectivity was significant non linear changes in channel capacity due to the presence of notable macrochannels which contained a 3000 average recurrence interval ari event at mid catchment locations the spatial pattern of hydrological connectivity was not straight forward in spite of bankfull discharges for selected reaches exceeding 5600m 3 s 1 data indicate that the main channel boundary was the dominant source of sediment while the floodplains where inundated were the dominant sinks spatial variability in channel floodplain hydrological connectivity leads to dis connectivity in the downstream transfer of sediments between reaches and affected sediment storage on adjacent floodplains consideration of such variability for even the most extreme flood events highlights the need to carefully consider non linear changes in key variables such as channel capacity and flood conveyance in the development of a quantitative connectivity index copyright c 2013 john wiley sons ltd

shear wave attenuation and dispersion in melt bearing olivine polycrystals 2 microstructural interpretation and seismological implications 1 the torsional forced oscillation tests of melt bearing olivine aggregates reported by jackson et al 2004 consistently show a peak in attenuation that is absent from melt free aggregates tested under similar conditions and grain sizes characterization by sem shows that the melt resides in triple junction tubules and larger pockets as previously described tem imaging and eds analysis reveals that olivine olivine grain boundaries are characterized by a region 1 nm wide which is structurally and chemically distinct from olivine grain interiors from the possible mechanisms that can produce an anelastic attenuation peak melt squirt can be eliminated for our samples and experimental conditions we attribute the observed attenuation peak to elastically accommodated grain boundary sliding requiring that the grain boundaries are weak relative to olivine grain interiors but have a significantly higher viscosity than bulk melt while the nanometer scale grain boundary structure in the melt bearing aggregates is essentially the same as for melt free aggregates studied previously elastically accommodated sliding in the latter is apparently inhibited by tight three grain edge intersections the exponentially increasing high temperature background attenuation in both types of aggregate is attributed to diffusionally accommodated grain boundary sliding extrapolation to mantle grain sizes shows that the broad peak may be responsible for nearly frequency independent attenuation in partially molten regions of the upper mantle

effect of partial melting on vp and vs in crustal enclaves from mazarron se spain abstract the combination of compressional and shear wave velocity is an important tool in discriminating rock types and identifying residing melts within the continental crust here we report the laboratory measurements for vp and vs obtained in varying conditions up to those exceeding the beginning of melting 950 c at 500 mpa confining pressure on two residual garnet biotite sillimanite cordierite spinel metapelitic enclaves recovered from the neogene dacites of mazarron se spain the enclaves preserve widespread interstitial rhyolitic glass as evidence of primary melt extraction at 500 mpa the experimental vp ranges from 7 21 7 46 km s 1 at room temperature to 5 44 km s at 950 c the mean vs is 4 5 km s at room temperature with shear wave splitting of 0 25 0 3 km s measured along three mutually orthogonal directions when temperature increases the vs evidences a reversible slope change at about 650 c and the shear wave splitting reduces to zero isotropic material at 850 950 c where the sample vs is 3 0 km s the vp anisotropy is 7 10 up to 700 c increasing to 20 at 950 c while the vs anisotropy continuously decreases with temperature from 5 to 7 at room temperature to zero at 950 c no mineral reactions are observed up to 650 700 c however microstructure equilibrates due to the relaxation of the primary glass at the glass transition temperature between 850 c and 950 c a new melting reaction is observed producing biotite spinel ilmenite plagioclase melt at melting the rock becomes isotropic for vs and poisson s ratio increases to 0 30 our seismic data show that the seismic signature of high grade metapelitic rocks is similar to that of mafic materials the evolution of vp and vs at melting conditions is compatible with the geophysical data of the area supporting the hypothesis of the current existence of anatectic melts at intermediate depths of the alboran domain

energy growth in laharic mass flows lahars debris flows and sediment rich floods are frequent and deadly hazards at all mountain forming volcanoes their hazard potential is traditionally assessed through mass conserving closed system models where peak conversion rates of potential energy to mechanical energy and hence maximum destruction potential are predicted to occur on the steepest volcano flanks this belies evidence of extremely high energy and deadly catastrophes caused by such flows at large distances from volcanoes here we use the first high resolution record of a moving lahar to develop a new model of the temporally and spatially variable mass flow structure we show that bulk flow energy can grow dramatically in such systems over tens to hundreds of kilometers via momentum transfers from the lahar into water and particles along its path we also demonstrate that dynamic transformations of such flows and their ultimate runout are primarily controlled by the mass flow front

changes in whangaehu river lahar characteristics during the 1995 eruption sequence ruapehu volcano new zealand abstract during the 1995 ruapehu eruptive sequence multiple lahars occurred in the whangaehu river which drains ruapehu s crater lake during the earlier phreatic and phreatomagmatic eruptions lahars were generated by expulsion of waters from the lake but once the lake had emptied lahars were formed by remobilisation of seasonal snowpack laden with saturated freshly erupted tephra four types of lahars occurred during the eruptive sequence 1 initial snow slurry lahars composed of granular snow and ice incorporated by eruptively expelled crater lake waters which left behind frozen deposits with 2 5 20 clastic sediment 2 large dilute lahars generated as the volumes of ejected lake water increased and removed much of the readily available snow at least one third of the pre eruption crater lake volume was expelled during one day producing the largest lahars of the series these lahars were hyperconcentrated flows for up to 84 km from source leaving extensive deposits along the channel margins 3 concentrated lahars smaller volume lahars generated as the frequency of eruptions and volumes of expelled water declined these lahars were able to maintain high sediment concentrations measured at 46 52 by volume suspended sediment at 42 km from source their high sediment concentrations were maintained by erosion and incorporation of sand from the deposits of earlier flows which were lining the channel margins 4 remobilised tephra lahars generated following the two largest tephra eruptions of the sequence seasonal snowpack was covered by water saturated tephra warmer spring temperatures and heavy rainfall events caused collapse and remobilisation of snow and tephra producing several lahars in catchments draining eastern ruapehu

non newtonian rheological law for highly crystalline dome lavas volcanic eruption models are hampered by the lack of multiphase magmatic flow laws most rheological models estimate the viscosity of multiphase lavas via the einstein roscoe equation but this simplification cannot be used for high crystallinity and it does not consider the non newtonian strain rate dependence of viscosity we carried out parallel plate experiments on natural samples to simulate multiphase lava deformation under various stresses and strain rates multiphase lavas exhibit an important component of shear thinning and appear to invalidate the adequacy of einstein roscoe based formulations for highly crystalline lava rheology the remarkable singular dependence of viscosity on strain rate yields a novel universal rheology law at eruptive temperatures t i e log 0 993 8974 t 0 543 log our work reveals the importance of considering microcracking and viscous dissipation at very high strain rate 10 3 s 1 explaining the occurrence of seismic swarms along the conduit margins and consequently supporting plug like magma ascent models

composition and microstructure of magma bodies from effective medium theory summary the extent and seismic properties of magma bodies beneath the subsurface are normally ascertained via seismic methods the seismic properties of such bodies depend on the composition and microstructure of both melt and crystals using effective medium theory we assess the effect of microstructure geometry and orientation of melt and crystals on the seismic properties namely p and s wave velocities and anisotropy we find that s wave velocity and anisotropy are key observables in determining the composition and microstructure of magma bodies

upper crustal structure of newberry volcano from p wave tomography and finite difference waveform modeling 1 seismic tomography combined with waveform modeling constrains the dimensions and melt content of a magma body in the upper crust at newberry volcano we obtain a p wave tomographic image by combining travel time data collected in 2008 on a line of densely spaced seismometers with active source data collected in the 1980s the tomographic analysis resolves a high velocity intrusive ring complex surrounding a low velocity caldera fill zone at depths above 3 km and a broader high velocity intrusive complex surrounding a central low velocity anomaly at greater depths 3 6 km this second upper crustal low velocity anomaly is poorly resolved and resolution tests indicate that an unrealistically large low velocity body representing 60 km3of melt could be consistent with the available travel times the 2008 data exhibit low amplitude first arrivals and an anomalous secondary p wave phase originating beneath the caldera two dimensional finite difference waveform modeling through the tomographic velocity model does not reproduce these observations to reproduce these phases we predict waveforms for models that include synthetic low velocity bodies and test possible magma chamber geometries and properties three classes of models produce a transmittedp phase consistent with the travel time and amplitude of the observed secondary phase and also match the observed lower amplitude first arrivals these models represent a graded mush region a crystal suspension region and a melt sill above a thin mush region the three possible magma chamber models comprise a much narrower range of melt volumes 1 6 8 0 km3 than could be constrained by travel time tomography alone

early proterozoic svecofennian volcanism and associated plutonism in enklinge sw finland abstract the c 1 9 ga old enklinge volcano plutonic centre is part of the svecofennian province of sw finland the rocks of the area consist of an early subaquatic extrusion of mafic intermediate to rhyolitic volcanics underlain by marbles graywackes and quartz feldspar rich volcanoclastic sediments the volcanic sequence is deformed and syntectonically intruded by a biotite tonalite accompanied and mixed with coeval basaltic dykes dacitic quartz porphyry dykes and small breccia pipes occur along the margins of the tonalite intrusion contrary to the bergslagen area in sweden no large co magmatic granites can be found in the volcano plutonic complex and the rhyolites are much less voluminous and only slightly mineralized the rocks of the enklinge area are strongly deformed and the tectonic environment differs strongly from that of the almost nonorogenic and more terrestrial bergslagen area w of enklinge

amorphous materials properties structure and durability compositional dependent compressibility of dissolved water in silicate glasses the sound velocities and elastic properties of a series of hydrous rhyolite andesite and basalt glasses have been determined by brillouin scattering spectroscopy at ambient conditions to elucidate the effect of glass composition on the compressibility of dissolved water both the adiabatic bulk k s and shear modulus of the dry glasses decrease with increasing silica content k s basalt k s andesite k s rhyolite and basalt andesite rhyolite for each composition the shear modulus systematically decreases with increasing water content although the addition of up to 14 mol water decreases the k s of andesite and basalt glasses by up to 6 there is no discernable effect of water on the k s of the rhyolite glasses the partial molar k s of dissolved water k s in rhyolite andesite and basalt glasses are 37 5 19 7 and 40 3 gpa corresponding to partial molar isothermal compressibilities t of 0 029 0 005 0 042 0 004 and 0 026 0 002 gpa 1 respectively these results indicate that the compressibility of dissolved water strongly depends on the bulk composition of the glass hence the partial molar volume of water cannot be independent of the bulk composition at elevated pressure if the compressibility of dissolved water also depends on composition in the analog melts at high temperature and pressure these observations will have important consequences for magmatic processes such as magma mixing unmixing and fractional crystallization

the use of multi temporal lidar to assess basin scale erosion and deposition following the catastrophic january 2011 lockyer flood se queensland australia advances in remote sensing and digital terrain processing now allow for a sophisticated analysis of spatial and temporal changes in erosion and deposition digital elevation models dems can now be constructed and differenced to produce dems of difference dod which are used to assess net landscape change for morphological budgeting to date this has been most effectively achieved in gravel bed rivers over relatively small spatial scales if the full potential of the technology is to be realised additional studies are required at larger scales and across a wider range of geomorphic features this study presents an assessment of the basin scale spatial patterns of erosion deposition and net morphological change that resulted from a catastrophic flood event in the lockyer creek catchment of se queensland seq in january 2011 multitemporal light detection and ranging lidar dems were used to construct a dod that was then combined with a one dimensional flow hydraulic model hec ras to delineate five major geomorphic landforms including inner channel area within channel benches macrochannel banks and floodplain the lidar uncertainties were quantified and applied together with a probabilistic representation of uncertainty thresholded at a conservative 95 confidence interval the elevation change distribution ecd for the 100 km2 study area indicates a magnitude of elevation change spanning almost 10 m but the mean elevation change of 0 04 m confirms that a large part of the landscape was characterised by relatively low magnitude changes over a large spatial area mean elevation changes varied by geomorphic feature and only two the within channel benches and macrochannel banks were net erosional with an estimated combined loss of 1 815 149 m3 of sediment the floodplain was the zone of major net deposition but mean elevation changes approached the defined critical limit of uncertainty areal and volumetric ecds for this extreme event provide a representative expression of the balance between erosion and deposition and importantly sediment redistribution which is extremely difficult to quantify using more traditional channel planform or cross sectional surveys the ability of lidar to make a rapid and accurate assessment of key geomorphic processes over large spatial scales contributes to our understanding of key processes and as demonstrated here to the assessment of major geomorphological hazards such as extreme flood events

lead isotopic evidence for the origin of 1 8 1 4 ga ores and granitoids in the southeastern part of the fennoscandian shield abstract new data for the lead isotopic composition of galena from ore deposits related to 1 8 1 4 ga granitoids in the southeastern part of the fennoscandian shield are presented and discussed together with earlier published information on granitoids and associated ore deposits two types of sulphide deposits genetically related to the granites can be recognized based on general metallogenetic features and isotopic composition granite hosted deposits including sn bearing greisen veins in rapakivi granites and peri intrusive deposits including contact metasomatic skarn deposits like pitkaranta and gruvasen in addition epigenetic deposits with a spatial but not a genetic link to the granites occur at various sites an important metallogenetic belt related to 1 7 1 5 ga granitoids can be followed in an east west direction across the shield from lake siljan in sweden to salmi at lake ladoga within this belt a major difference in metal derivation can be recognized ore deposits southwest of the raahe ladoga line i e in areas without archaean basement indicate metal derivation from remelted 1 9 ga svecofennian crust whereas ore deposits in areas underlain by archaean rock units indicate metal derivation from highly metamorphosed archaean sources

petrology of nattanen type granite complexes northern finland abstract the nattanen type granites form a group of post tectonic and post metamorphic 1 77 ga old epizonal multiple granite intrusions in the granulite belt granitic gneiss surroundings in northern finland the granite complexes the tepasto pomovaara and nattanen stocks and the riestovaara batholith in finland and the juvoaivi stock in the u s s r are composed of various slightly peraluminous microcline plagioclasebiotite granites monzogranites that contain sphene and magnetite as typical minor constituents geochemical evolution within the complexes is demonstrated by the increase of sio2 and rb and decrease of tio2 feo mgo cao sr ba and zr from the oldest to the youngest granite varieties molybdenum mineralization is associated with the latest intrusive phases of the tepasto and juvoaivi stocks the isotope geochemical studies indicate a major archaean crustal component in the source of the nattanen stock that is situated within the early proterozoic granulite belt

propagation of p and s waves in magmas with different crystal contents insights into the crystallinity of magmatic reservoirs abstract increasing amount of crystals tends to reduce the mobility of magmas and modifies its elastic characteristics e g caricchi l et al 2007 non newtonian rheology of crystal bearing magmas and implications for magma ascent dynamics earth and planetary science letters 264 402 419 bagdassarov n dingwell d b and webb s l 1994 viscoelasticity of crystal and bubble bearing rhyolite melts physics of the earth and planetary interior 83 83 99 to quantify the effect of crystals on the elastic properties of magmas the propagation speed of shear and compressional waves have been measured at pressure and temperatures relevant for natural magmatic reservoirs the measurements have been performed in aggregates at variable particle fractions 0 0 7 the measurements were carried out at 200 mpa confining pressure and temperatures between 300 k and 1273 k i e across the glass transition temperature tg from glass to melt the specimens were mixtures of a haplogranitic melt containing 5 25 wt h2o and variable amounts of sub spherical alumina particles additional experiments were carried out on a sample containing both crystals and air bubbles the temperature derivatives of the shear dvs dt and compressional wave dvp dt velocities for pure glass and samples with a crystal fraction of 0 5 are different below and above the glass transition temperature for a crystal fraction 0 7 only dvp dt changed above the tg in the presence of gas bubbles vp and vs decrease constantly with increasing temperature the bubble bearing material yields a lower bulk modulus relative to its shear modulus the propagation velocities of compressional and shear waves increase non linearly with increasing crystal fraction with a prominent raise in the range 0 5

modeling the october 2005 lahars at panabaj guatemala an extreme rainfall event in october of 2005 triggered two deadly lahars on the flanks of toliman volcano guatemala that caused many fatalities in the village of panabaj we mapped the deposits of these lahars then developed computer simulations of the lahars using the geologic data and compared simulated area inundated by the flows to mapped area inundated computer simulation of the two lahars was dramatically improved after calibration with geological data specifically detailed field measurements of flow inundation area flow thickness flow direction and velocity estimates collected after lahar emplacement were used to calibrate the rheological input parameters for the models including deposit volume yield strength sediment and water concentrations and manning roughness coefficients simulations of the two lahars with volumes of 240 200 55 400 and 126 000 29 000 m3 using the flo 2d computer program produced models of lahar runout within 3 of measured runouts and produced reasonable estimates of flow thickness and velocity along the lengths of the simulated flows we compare areas inundated using the jaccard fit model sensitivity and model precision metrics all related to bayes theorem these metrics show that false negatives areas inundated by the observed lahar where not simulated and false positives areas not inundated by the observed lahar where inundation was simulated are reduced using a model calibrated by rheology the metrics offer a procedure for tuning model performance that will enhance model accuracy and make numerical models a more robust tool for natural hazard reduction

control of magma flow in dykes on cyclic lava dome extrusion 1 lava dome eruptions are commonly characterized by large fluctuations in discharge rate with cyclic behaviour on time scalesranging from hours to decades examples include bezymianny volcano russia merapi java santiaguito guatemala mt st helens usa mt unzen japan and soufriere hills volcano montserrat previous models have assumed simple cylindrical conduits for magma transport but extrusions are mainly fed by dykes with cylindrical geometries developing only at shallow levels the widths of dykes embedded in an elastic medium are influenced by local magma pressure affecting flow rates and system dynamics strongly we develop a model for magma flow in dykes which predicts intense pulsations of magma extrusion for the case of a constant source pressure the period time scale is determined by the elastic deformation of the dyke walls and the length to width ratio of the dyke the dyke acts like a volumetric capacitor storing magma as pressure increases and then releasing magma in a pulse of extrusion for the soufriere hills volcano cyclic extrusions with time scales of a few weeks are predicted for dykes 300 500 m long and 3 6 m wide matching observations the model explains the sharp onset of tilt pulsations and seismic swarms citation costa a o melnik r s j sparks and b voight 2007 control of magma flow in dykes on cyclic lava dome extrusion geophys res lett 34 l02303 doi 10 1029 2006gl027466

synchrotron based x ray tomographic microscopy for rock physics investigations abstractsynchrotron radiation x ray tomographic microscopy is a nondestructive method providing ultra high resolution 3d digital images of rock microstructures we describe this method and to demonstrate its wide applicability we present 3d images of very different rock types berea sandstone fontainebleau sandstone dolomite calcitic dolomite and three phase magmatic glasses for some samples full and partial saturation scenarios are considered using oil water and air the rock images precisely reveal the 3d rock microstructure the pore space morphology and the interfaces between fluids saturating the same pore we provide the raw image data sets as online supplementary material along with laboratory data describing the rock properties by making these data sets available to other research groups we aim to stimulate work based on digital rock images of high quality and high resolution we also discuss and suggest possible applications and research directions that can be pursued on the basis o

lahar hazard assessment using titan2d for an alluvial fan with rapidly changing geomorphology whangaehu river mt ruapehu abstract rapid changes in small areas at the apex of alluvial fans may have devastating consequences by directing downstream flood or lahar impacts into catchments of widely varying population or infrastructure vulnerability during a series of lahars in 1995 at mt ruapehu new zealand aggradation of the whangaehu fan apex draining the eastern edifice caused the onset of avulsion of flows northward into the highly vulnerable tongariro catchment an earth training dike or bund was constructed to protect this catchment by retaining flows on the southern side and the normal lahar outlet path to the south surveys in 2001 late 2005 and following a major lahar in march 2007 now show net degradation of a channel in the whangaehu fan apex bordered by the bund this indicates a net increase in the channel capacity at this site and shows that the bund remains at its effective design capacity past hydrological modelling used for the bund design provided a large range of discharge estimates but lacked precise constraints on the size and nature of lahars from eruption and lake breakout events new modelling has been carried out using titan2d to examine the impacts of a 6 106 m3 volume granular flow down this catchment this simulates either an eruption or a lake breakout induced lahar with a historically typical volumetric bulking factor of 4 these simulations predict minimum discharges between 1800 and 2100 m3 s at the bund site by comparison the largest 1995 flow at this site was estimated at around 1200 m3 s further any single modelled flow from the normal outlet channel of crater lake could not be induced to overtop the bund because discharge appears to be limited by the narrow upper reaches of the whangaehu gorge theoretical discharge levels required to overtop the bund are estimated to be 6800 m3 s assuming no aggradation of the channel by the decelerating flow maximum potential discharge at the bund site is additionally modified by potential bifurcation of lahars above a certain size threshold at a point 2 5 km upstream of the bund a major side channel the chute effectively diverts part of the flows away to the southern side of the whangaehu fan this potential for splitting of the flow appears to have increased since 1995 from aggradation of lahar deposits and reworked sediment in the area immediately upstream of the divide despite remaining at design capacity for lahar events in the whangaehu erosion of new channels following the 2007 lahar renders the bund vulnerable to undercutting

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

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

lahars of ruapehu volcano new zealand risk mitigation a dam break lahar resulting from the last eruption of ruapehu is expected when crater lake reaches a critical high level probably within the next 1 5 summers a high level of public consultation political decision making and ongoing scientific input has occurred to address the risks decisions about managing lahar risk have taken into account the fact that lahars are common on the active ruapehu volcano 2797 m and in valleys draining the mountain and that most lahars are generated by eruptions about half of which have no useful precursors lahars threaten new zealand s largest ski area and nationally important infrastructure public safety has been the main consideration but the need for long term risk mitigation and reducing impacts on tongariro national park world heritage area have also been important lahar mitigation on ruapehu now includes six lahar warning systems each with active response plans and some infrastructure isolated from or hardened against lahars

dynamic interactions between lahars and stream flow a case study from ruapehu volcano new zealand three lahars were sampled in the whan gaehu river on the eastern flank of ruapehu volcano new zealand at 23 5 and 42 km from the source as they were flowing on september 27 and 29 and october 6 1995 the lahars were generated by water explosively ejected from the highly mineralized crater lake we used the chemical contrast between the lahars and resident stream water in their paths to describe a four phase model of a noncohesive lahar wave in a river channel 1 ambient stream water pushed ahead of the lahar in a process of miscible displacement due to hydrodynamic dispersion 2 a zone of mixing between the stream water and the lahar that increases in length with distance from source 3 a remnant of the original lahar least diluted by stream water that decreases in length and dilutes downstream 4 the tail of the lahar surge peak discharge occurs at the end of phase 1 as water is pushed ahead of the lahar peak sediment concentration occurs at the end of phase 2 where debris entrainment by the flow is at its greatest i e in front of the lahar proper deposits record only phases 2 and 3 of the lahar wave phase 1 flow left only a tide line of organic debris and phase 4 deposits were rapidly eroded by later streamflow downstream dilution by stream water eventually caused transformation of phases 2 and 3 of the lahars from debris flow to hyperconcentrated streamflow and then to normal streamflow as the flows became progressively finer grained and more turbulent

debris flow evolution and the activation of an explosive hydrothermal system te maari tongariro new zealand abstract analysis of the pre and post eruption topography together with observations of the avalanche deposition sequence yields a triggering mechanism for the 6 august 2012 eruption of upper te maari the avalanche was composed of a wedge of c 683 000 774 000 m 3 of coarse breccia spatter and clay rich tuffs and diamictons which slid from the western flanks of the upper te maari crater the failure plane is considered to be a hydrothermally altered clay layer this landslide led to a pressure drop of up to 0 5 mpa enough to generate an explosive eruption from the hydrothermal system below which had been activated over the months earlier by additional heat and gas from a shallow intrusion the landslide transformed after c 700 m into a clay rich cohesive debris flow eroding soils from steep narrow stretches of channel before depositing on intermediate broad flatter reaches after each erosive reach the debris flow contained greater clay and mud contents and became more mobile at c 2 km flow distance however the unsaturated flow stopped due to a lack of excess pore pressure this volume controlled flow deposited thick steep sided lobes behind an outer levee accreting inward and upward to form a series of curved surface ridges

imaging of the magmatic system feeding las tres virgenes geothermal field baja california sur mexico using enhanced seismic tomography abstract the las tres virgenes volcanic field baja california sur mexico hosts one of the five active geothermal power plants operating in mexico the volcanic system is considered still active and has been extensively studied during and after the development of the geothermal activities however the volumes and locations of the magmatic sources as well as the size of the geothermal reservoir are still poorly known in this work we use the records of 177 local earthquakes recorded in 2012 by a temporary local seismic network to characterize compressional vp and shear vs wave seismic velocities of the volcanic system from the surface down to 8 10 km of depth we applied the enhanced seismic tomography method which incorporates the double difference tomography and the post processing weighted average method results describe for the first time that the magmatic source reaches at least 4 5 km of depth beneath la virgen volcano feeding a widespread reservoir confined in the first 2 3 km of depth which is much larger than the currently exploited region