experiments on magma mixing 1 the arrival of a new hot batch of magma changes the thermal and the chemical state of a volcanic plumbing system formation of hybrid magma by chemical dilution liquid miscibility model of different magma batches is generally accepted observations of drop like domains of less evolved newer magma in more evolved host magma point to the contribution of a mechanical mixing process liquid immiscibility the interplay of both mechanisms seems to control the time scale from the dormant to the active state of a volcano we carried out laboratory experiments using melts from natural volcanic rock compositions with the aim to validate model calculations for shear rate dependent domain sizes the results confirmed the model and also the importance of hydro mechanically mixing for chemical dilution the key process however that is able to change the state of a magma reservoir on a critical time scale is hydrodynamic magma mixing

flow behaviour and runout modelling of a complex debris flow in a clay shale basin identification of debris flow hazard areas necessitates the knowledge of the flow thickness and the runout distance both have been investigated using a numerical runout model on the faucon stream south french alps representative of clay shale basins results of various rheological tests and numerical experiments are presented and discussed the calibration of the model was undertaken using the results of both geomorphological surveys and sedimentological analyses rheological tests using either a parallel plate rheometer a coaxial rheometer slump tests and an inclined plane were carried out on several samples results have shown that the flow behaviour could be described by an herschel bulkley constitutive equation the rheological responses of several natural suspensions collected from surficial deposits sandstones moraines weathered black marls were also investigated in order to model the runout of the flow the model bing was used the model describes well the influence of each type of sediment on the behaviour runout distance deposit thickness of the flow although the velocities were significantly overestimated different risk scenarios are tested and discussed copyright 2005 john wiley sons ltd

submarine silicic caldera at the front of the izu bonin arc japan voluminous seafloor eruptions of rhyolite pumice myojin knoll caldera a submarine rhyolitic center 400 km south of tokyo is one of nine silicic calderas along the northern 600 km of the izu bonin ogasawara arc and the first anywhere to receive detailed submersible based study the caldera slightly smaller than the crater lake structure in oregon is 6 7 km in diameter its inner walls are 500 900 m high and it has a remarkably flat floor at 1400 m below sea level mbsl the caldera collapse volume is 18 km 3 suggesting that more than 40 km 3 of pumiceous tephra may have been erupted at the time the caldera formed precaldera seafloor eruptions built a broad volcanic edifice consisting of overlapping composite volcanoes made of rhyolitic lavas shallow intrusions and a variety of volcaniclastic deposits including thick accumulations of rhyolitic pumice erupted at 900 500 mbsl the caldera forming eruption produced a 150 200 m deposit of nonwelded fines depleted pumice that resembles a colossal layer of popcorn at the top of the caldera wall freshly erupted pumice behaved as sinkers or floaters depending on the environment in which it cooled the pumice clasts deposited proximally and exposed in the caldera wall were likely quenched in eruption columns that remained below sea level this pumice ingested seawater and sank as gases filling its vesicles cooled particularly as steam in its vesicles condensed to liquid water some eruption columns may have broken through the sea surface and entered the air especially during vigorous phases of the caldera forming eruption these pumices had the opportunity to ingest air as they cooled becoming floaters as they fell back to the sea these could have been carried distally on the sea surface by the combined effects of ocean currents and wind the age of the caldera is unknown but it may be as young as several thousand years its magmatic system at depth retains sufficient heat to sustain an actively growing intracaldera kuroko type polymetallic sulfide deposit rich in gold and silver and topped by chimneys emitting fluids as hot as 278 c sufficient time has elapsed however for a 250 m high postcaldera dome to grow on the caldera floor and for the caldera rim to be deeply scalloped by slumping

subaqueous explosive eruption and welding of pyroclastic deposits silicic tuffs infilling an ancient submarine caldera at mineral king in california show microscopic fabrics indicative of welding of glass shards and pumice at temperatures 500 degrees c the occurrence indicates that subaqueous explosive eruption and emplacement of pyroclastic materials can occur without substantial admixture of the ambient water which would cause chilling intracaldera progressive aggradation of pumice and ash from a thick fast moving pyroclastic flow occurred during a short lived explosive eruption of approximately 26 cubic kilometers of magma in water 150 meters deep the thickness high velocity and abundant fine material of the erupted gas solids mixture prevented substantial incorporation of ambient water into the flow stripping of pyroclasts from upper surfaces of subaqueous pyroclastic flows in general both above the vent and along any flow path may be the main process giving rise to buoyant convective subaqueous eruption columns and attendant fallout deposits

large scale rhyolite peperites jurassic southern chile development of a jurassic volcano tectonic rift basin in the southern andes created a setting in which thick rhyolitic volcaniclastic sequences accumulated in submarine environments and were penetrated by hypabyssal intrusions during or shortly after deposition in the ultima esperanza district of southern chile extensive masses of peperite were produced when rhyolite magma underwent quenching disruption and commingling with wet unconsolidated sediments during intrusion at shallow levels beneath the sea floor the peperite forms discordant intrusive masses with volumes of up to several cubic kilometers in which large widely spaced coherent rhyolite feeder pods are surrounded by and grade into closely packed and dispersed peperite closely packed peperite consists of tightly fitting clasts separated by sediment filled fractures in dispersed peperite the sediment forms a matrix surrounding large masses of fractured rhyolite and smaller more widely separated rhyolite clasts evidence of in situ quench fragmentation is well preserved on both outcrop and thin section scales thin sections show that clast margins and in some cases entire small clasts underwent cooling contraction granulation releasing shards of quenched rhyolite and fragments of phenocrysts into the adjacent sediment interaction between magma and wet sediment was non explosive and involved fluidization of the host sediments creating space for the intruding magma and causing pervasive injection of highly mobile sediment along thermal contraction cracks in quench fragmented rhyolite the ability of the magma to undergo complex intermixing with large volumes of sediment with widespread preservation of in situ fragmentation textures is interpreted to reflect a relatively low magma viscosity presumably caused by retention of volatiles in the magma at the ambient pressures involved beds of redeposited peperite within the rift basin fill indicate that some of the intrusive peperite masses reached the sea floor undergoing slumping and mass flow the peperites were thus an important local source of coarse grained debris during the evolution of the basin

emplacement textures in late palaeozoic andesite sills of the flechtingen roslau block north of magdeburg germany

analysis of debris flow surges using the theory of uniformly progressive flow coarse debris flows develop surges with distinct longitudinal sorting although highly unsteady such flow often appears to attain a steady state condition moving over long distances with approximately constant velocity and maximum depth typically a steep bouldery front is followed by an accumulation of liquid slurry which in turn decays into a dilute tail such sorting has long been recognized by field workers but its influence on the dynamic behaviour of debris flow surges has not yet been fully clarified by analysis a simple model is presented using the theory of uniformly progressive flow and incorporating zoned longitudinal variation in rheology it is shown that non homogeneity can cause very significant magnification of the peak discharge depending on the slope angle and on the length of the frontal boulder concentration the shape of the surge flow profiles is determined not only by the rheology of the retained material but by the longitudinal variation of material characteristics as a result excessive reliance on laboratory derived rheological constitutive relationships is not advisable models of debris flow surges should be non homogeneous and able to incorporate zones of contrasting rheology copyright 2000 john wiley sons ltd

the 1891 submarine eruption offshore pantelleria island sicily channel italy identification of the vent and characterization of products and eruptive style high resolution bathymetry and seafloor sampling have been used to characterize the 1891 submarine eruption of the pantelleria volcanic complex this submarine eruption has been documented mainly by historical reports describing basaltic scoria bombs floating on the sea surface i e lava balloons in this study the 1891 eruptive vent has been identified as a small cone volume of 700 000 m3 rising 90 m from 350 m w d and located within a newly discovered submarine volcanic field covering a wide area offshore from the nw coast of pantelleria recently kelly et al 2012 confirmed this location by a multibeam and rov survey pyroclasts from the 1891 eruption crop out directly on the seafloor and are fresh scoria clasts i e small bombs bomb fragments and lapilli and glass ash sized grains both have been characterized in their morphology textures and geochemistry the distinctive vesicularity and crystallization characteristics displayed by the scoriaceous pyroclasts reflect modes of degassing in both syn and posteruptive regimes these characteristics along with the distribution of deposits suggest for the strongest eruptive phase of the 1891 eruption a style analogous to hawaiian fountaining glass grains from a buoyant plume were dispersed northward from the vent up to distances of 1 5 km redirected by the levantine intermediate water the identification of the 1891 submarine eruptive vent offshore pantelleria as well as the features of erupted pyroclasts improve our knowledge of submarine explosive eruptions that occur at shallow intermediate depths and among these of the rare eruptions producing lava balloons

volcano sedimentary characteristics in the abu treifiya basin cairo suez district egypt example of dynamics and fluidization over sedimentary and volcaniclastic beds by emplacement of syn volcanic basaltic rocks abstract this paper describes the neogene lava sediment mingling from the abu treifiya basin cairo suez district egypt the lava sediment interactions as peperites have been identified for the first time at the study area and can be used as paleoenvironmental indicators the identification of peperite reflects contemporaneous time relationship between volcanism and sedimentation and this finding is of primary importance to address the evolutional reconstruction of the abu treifiya basin characterization of the facies architecture and textural framework of peperites was carried out through detailed description and interpretation of their outcrops the peperites and sedimentary rocks are up to 350 m thick and form a distinct stratigraphic framework of diverse lithology that is widespread over several kilometers at the study area lateral and vertical facies of the peperites vary from sediment intercalated with the extrusive intrusive basaltic rocks forming peperitic breccias to lava sediment contacts at a large to small scales respectively peperites encompass five main facies types ascribed to i carbonate sediments hosted fluidal and blocky peperites ii lava flow hosted blocky peperites iii volcaniclastics hosted fluidal and blocky peperites iv sandstone siltstone rocks hosted blocky peperites and iv debris flows hosted blocky peperites soft sediment deformation structures vesiculated sediments sediments filled vesicles and fractures in lava flows indicate that lava flows mingled with unconsolidated wet sediments all the peperites in this study could be described as blocky or fluidal but mixtures of different clast shapes occur regardless of the host sediment the presence of fluidal and blocky juvenile clasts elucidates different eruptive styles reflecting a ductile and brittle fragmentation the gradual variation from fluidal to blocky peperite texture producing the vertical grading is affected by influencing factors e g the viscosity magma temperature confining pressure sediment fluidization and vapor film at the magma sediment interactions peperites in the study area record deposition within a shallow marine and fluvio lacustrine environment accumulated in a rift related basin developed during pre to syn rift phase respectively the facies transitions peperites in this area resulted from the explosive and sediment depositional processes which were mingled separately by volcanism under contrast geological conditions the development of such contrast in the depositional sequences reflects variation in the accommodation to sediment supply in the same accumulation space inside the depocenters during the rifting of the abu treifiya basin hydrothermal mineralizations comprising quartz and carbonate are restricted to peperites and lava flows

subaqueous basaltic magmatic explosions trigger phreatomagmatism a case study from askja iceland abstract sequences of basaltic pillow lavas that transition upward with systematic gradation from pillow fragment breccias to fluidal bomb bearing breccias to bomb bearing lapilli tuffs are common at askja volcano iceland based on the detailed textural investigation of three of these sequences we argue that they record temporally continuous transitions from effusive to explosive products that were erupted from and deposited at or near a single subaqueous vent the recognition of such sequences is important as they provide evidence for controls on the onset of explosive activity in subaqueous environments such investigations are complicated by the interplay of magmatic gas expansion and phreatomagmatic and mechanical granulation fragmentation mechanisms in the subaqueous eruptive environment all of the sequences studied at askja have textural componentry and sedimentological characteristics suggestive of a close genetic and spatial relationship between the pillow lavas and all of the overlying glassy clastic deposits the identification of magma fragmentation signatures in pyroclasts was accomplished through detailed textural studies of pyroclasts within the full range of grain sizes of a given deposit i e bomb blocks lapilli and fine ash these textural characteristics were compared and evaluated as discriminators of fragmentation in pyroclastic deposits the presence of angular vitric clasts within the breccia and lapilli tuff displaying fragile glassy projections indicates little or no post depositional textural modification a shift in vesicle and clast textures between the pillow lavas and the large concentration of fluidal bombs in the breccia indicates that the phreatomagmatic explosions were initially triggered by magmatic vesiculation the initial magmatic gas expansion may have been triggered by depressurization caused by the drainage of the ice confined lake surrounding askja the fuel coolant interactions fcis of the more efficient phreatomagmatic explosions were enabled by the increase in the surface area to volume ratio of the fluidal bombs in the water producing a premix of magma and water the onset and increasing influence of phreatomagmatic fragmentation is preserved in the presence of very fine blocky ash particles and diminished presence of larger particles such as fluidal bombs the textural sedimentological and environmental characteristics of these deposits suggest that phreatomagmatic explosions can be triggered by initial magmatic gas expansion but that it is likely one of many mechanisms for triggering such explosions

unravelling carbonatite silicate magma interaction dynamics a case study from the velay province massif central france mechanisms of interaction between a carbonatite magma and a silicate magma are inferred on the basis of the textural and geochemical features of a carbonate bearing tuff from the massif central characterized by the presence of carbonatite globules within a silicate glass matrix a two fluid dynamical model is proposed in order to constrain the formation of the carbonatite globules that underwent no geochemical re equilibration with the trachyte magma due to rapid thermal re equilibration and crystallization of dolomite it is suggested that a viscous fingering instability occurred simultaneously with the injection of a carbonatite magma into a chamber filled with a more viscous trachytic magma instantaneous fragmentation of the fingers induced by the action of gradient stresses resulted in the formation of a magmatic emulsion the replenishment event triggered immediate evacuation of the magma chamber such that interaction between the two magmas occurred over a short time scale and large scale mixing was prevented the exsolution of volatiles perhaps as a consequence of the recharge event shortly before the eruption drove a metasomatic event that produced the subtle chemical variations observed at the interface between carbonatite globules and silicate matrix

the saturation behaviour of pumice and some sedimentological implications abstract caldera forming explosive eruptions from rhyolitic volcanoes typically produce huge quantities of pyroclastic material blanketing the landscape and triggering long term voluminous and widespread sedimentary responses pumice is a major component of such eruptions but its behaviour in the sedimentary environment is little understood its most notable feature is its very low density which frequently enables pumice to float on water for long periods of time before eventually waterlogging enough to sink once fully saturated pumice behaves in a broadly similar way to normal clastic material in terms of its hydrodynamic behaviour modified by its lower density however relatively little is known about its earlier behaviour in the sedimentary environment and in particular the manner and rate by which initially dry pumice absorbs water in this paper we develop a mathematical model which predicts that the time required for a pumice clast to saturate is proportional to the square of its radius tests on samples of real pumice accord with predicted trends and match lacustrine pumiceous facies observed in the field the ability to predict the time required for large pumice clasts to sink may provide a tool for estimating the timescales over which certain rapid post eruptive sedimentary processes operate

large volume rhyolite ash flow eruptions and submarine caldera collapse in the lower mesozoic sierra nevada california the mineral king roof pendant in the southern sierra nevada california provides a view of a triassic and early jurassic submarine caldera complex which was tilted to vertical and intruded by middle cretaceous granitoids an estimated 90 km3 of rhyolitic and 10 km3 of andesitic volcanic rocks are interstratified with marine sandstones siltstones limestones and conglomerates periods of volcanotectonic activity alternated with periods of marine sedimentation volcanic eruptions at mineral king resulted in 1 deposition of widespread very thick sheets of rhyolite ash flow tuff and 2 construction of small 1 8 km3 andesitic stratocones growth faults fault talus aprons slide blocks slumps and debris flows found in association with these volcanic deposits indicate that the eruptive phases represent periods of great seismic activity interuptive phases were periods of volcanic and tectonic quiescence during which sequences of shallow to deep marine sediments were deposited four different times at mineral king eruption of large volumes of rhyolite ash flow tuff resulted in catastrophic caldera collapse and ponding of single ash flow tuffs to thicknesses greater than 0 5 km only minimum volumes can be estimated for three of these intracaldera tuffs because they are truncated by younger granites volumes are estimated to be at least 25 km3 each placing these tuffs in the lower size range of epicontinental ring structures the fourth caldera the vandever mountain caldera is entirely preserved in the roof pendant the vertically dipping strata of the vandever mountain caldera provide an unusual opportunity to examine a submarine caldera in cross section evidence for caldera subsidence during the eruption of the vandever mountain rhyolite ash flow tuff includes the following 1 the great thickness of the ash flow tuff and the rapid accumulation of the tuff during progressive draw down of a compositionally zoned magma chamber 2 high angle faults which pond the ash flow tuff and offset underlying but not overlying stratigraphy and 3 megabreccia and slide blocks up to 0 5 km long that were derived from the caldera wall and floor and incorporated into the ash flow tuff as it filled the caldera disruption of the caldera floor was intense near the caldera margin but negligible along most of its length owing to pistonlike subsidence of an intact cylinder of crust small volume ash flow eruptions occurred along an incipient leaky ring fracture zone prior to the caldera forming eruption of the vandever mountain ash flow tuff the vandever mountain caldera was not affected by resurgent doming or late stage rhyolite magmatism in the cross sectional view provided by the mineral king roof pendant

subsurface structure of a large basaltic maar volcano examined using geologically constrained potential field modelling lake purrumbete maar newer volcanics province southeastern australia abstract lake purrumbete maar lpm is situated in the late cenozoic intraplate basaltic newer volcanics province southeastern australia it is one of the largest maar volcanoes in the world with a near circular crater that is up to 2800 m in diameter containing a 45 m deep lake gellibrand marl accidental lithics which occurs to a maximum depth of 250 m below lpm represent the deepest excavated host rock unit present in the volcanic succession irregular clast shapes and peperitic textures observed in marl lithics suggest the host rock was poorly consolidated during the eruption high resolution lake and land based gravity and magnetic data were collected to conduct forward and inverse modelling of the subsurface architecture of the maar this is done to test the assumption based on lithics that the diatreme is limited to 250 m depth and identify the reasons behind lpm s large size the collection of gravity data presented a unique challenge due to the nature of measuring small changes in gravitational forces

quenching of steam charged pumice implications for submarine pyroclastic volcanism abstract huge quantities of silicic pumice have been deposited in intra oceanic convergent margin settings throughout earth s history the association of submarine silicic calderas with thick proximal accumulations of pumice lapilli suggests that these pyroclasts were deposited as a direct result of submarine eruptions yet when first erupted these highly vesicular gas filled clasts had densities significantly less than seawater experiments carried out 1 atm on heated pumice samples whose vesicles were charged with steam the dominant component of magmatic volatiles show that buoyancy of freshly erupted submarine pumice is transient upon quenching the phase change of steam to liquid water creates strong negative pore pressures within the pumice vesicles that accelerate the absorption of surrounding water generating high density pumice and promoting rapid clast sinking variations in the physical properties of steam with temperature and pressure have important implications for submarine pyroclastic eruptions firstly highly vesicular pumice can be deposited on the seafloor at temperatures elevated significantly above ambient if they are erupted at sufficient depths to remain wholly submarine 200 m and either the fluid in which they cool contains heated water and or they only absorb sufficient water to sink secondly the rapid increase in density of the eruption column caused by condensation and the transition from buoyant gas filled to denser water saturated pumice lapilli together with turbulent mixing with the surrounding seawater favour collapse and transport of pyroclasts in water supported gravity currents finally this mixing of the ejecta with seawater and the ease of water ingestion into permeable pumice clasts suggest that water supported transport mechanisms can operate as primary dispersal processes in explosive submarine eruptions

a progressive entrainment runout model for debris flow analysis and its application abstract a progressive entrainment model has been incorporated into an energy based runout model to calculate the kinematic characteristics of debris flow the progressive entrainment model considers both rolling and sliding motions of erodible material to study the effect of the controlling parameters in the entrainment model sensitivity analyses have been carried out by varying model parameters such as the internal friction angle of the debris the basal friction angle of the channel the turbulent flow coefficient and the mean value of the probabilistic density function pdf for the resting angle the results are evaluated by calculating the change of the maximum entrainment rate the maximum frontal velocity the final total volume the longitudinal length of deposition the maximum debris flow height and the runout distance of the debris the progressive entrainment runout model is sensitive to the characteristic particle size basal friction angle and turbulent coefficient measurements from the 1990 tsingshan debris flow hong kong china are used to validate the model velocities at different channel sections estimated using the super elevation method and entrainment depth are used to evaluate the simulation results comparing the results between simulated and observed maximum velocity and entrainment depth indicate that the progressive entrainment model together with the runout model can capture the erosion characteristics of the granular material the results are also compared with that using a dynamic entrainment model the results demonstrate that the progressive entrainment model provides a more realistic calculation of entrainment for this case compared with the dynamic entrainment model

coordinated spectral and xrd analyses of magnesite nontronite forsterite mixtures and implications for carbonates on mars 1 mineral detection on mars largely relies on laboratory data of minerals and mineral mixtures the objective of this study is to provide reflectance spectra in the visible near infrared vnir and mid ir regions x ray diffraction xrd data and mossbauer spectra of a suite of carbonate phyllosilicate and olivine mixtures in order to facilitate identification and characterization of these minerals on mars remote sensing observations indicate that combinations of these minerals are present in ancient rocks on mars around the isidis basin and in gusev crater magnesite nontronite and forsterite size fractions 125 m were selected for this study results of the vnir reflectance analyses illustrate the complexity of vnir spectra of mixtures analyses of the nir band depths near 2 3 2 5 3 4 and 4 m showed clear trends with carbonate abundance although the data are not linear mixtures of magnesite and nontronite exhibited a band near 2 3 m much closer to that observed for nontronite than that for magnesite vnir analyses of the mixtures indicated that a small amount of forsterite in any of the mixtures contributed a large increase in the broad 1 m band and hence the red slope characteristic of fe2 bearing minerals mid ir mixture spectra were dominated by magnesite and forsterite and nontronite was much more difficult to detect by mid ir spectra in the mixtures this could be related to why phyllosilicates are detected in many locations on mars using data collected by the compact reconnaissance imaging spectrometer for mars but not detected using data collected by the thermal emission spectrometer mossbauer spectroscopy is well suited for analyses of fe2 and fe3 bearing minerals and modeling of the peak areas gave well correlated trends for nontronite and forsterite abundances where abundant fe was present xrd full pattern fitting analyses were performed on the magnesite forsterite series giving results within 6 wt of the actual values with a mean difference between actual and calculated values of 2 4 wt this study provides important laboratory data for characterizing the spectral and xrd properties of mineral mixtures that will facilitate mineral identification on mars carbonates in particular have been primarily observed at low abundances and in small outcrops and they are frequently found mixed with other minerals through analyses of mineral mixtures using multiple data sets this study seeks to provide ground truthing that will enable better coordination of carbonate detections in the dust and rocks of mars

resedimentation of cold pumiceous ignimbrite into water facies transformations simulated in flume experiments deposits and transport processes resulting from the resedimentation of cold unconsolidated ignimbrite into water were simulated by flume experiments the ignimbrite sample used was poorly sorted 2 4 3 fine ash rich 2000 kg m 3 and pumice 500 to ca 1300 kg m 3 as a result of the binding forces of the ash matrix the experiments involved resedimentation from a steep front onto the floor with or without an initial ramp of the water filled tank under both still and wave generated conditions larger discrete collapse events were induced by oversteepening the sample front and by undercutting from wave action the mass of the collapse and proportion of pore space water strongly influenced the style of resedimentation and the deposits initial collapse events were from the top of the steep front and fell onto the floor the largest densest clasts were deposited as a lithic lag in a proximal sediment wedge or rolled down to a break in slope fine ash was transported in dilute turbidity currents and coarse unsaturated pumice clasts floated off moderate collapse events generated high density turbidity currents trapping pumice in the flow causing them to saturate these low density pumice clasts were easily remobilized by wave activity and passing currents and accumulated on the gentle slope at the bottom of the resedimented deposit large collapse events slumped producing poorly sorted mounds similar in texture to the original starting material as the matrix of the ignimbrite sample became saturated with water moderate and large collapse events generated debrisflows and slurries that deposited massive poorly sorted deposits furthermore once more gentle slopes were established between the sample and deposit small cascading grainflows deposited lithic clasts on the upper slopes and levees of pumice at the terminus of low relief ash channels the experiments show that excluding large collapse events and debrisflows resedimenting ignimbrite in water is effective at segregating low density pumice clasts from dense lithic clasts and fine ash experiments using fine ash poor ignimbrite and well sorted quartz sand for comparison formed an inherently unstable initial steep front that immediately collapsed by continuous grain avalanches the grainflow deposits had textures similar to the fines poor starting material

1d numerical model of muddy subaqueous and subaerial debris flows a 1d numerical model of the downslope flow and deposition of muddy subaerial and subaqueous debris flows is presented the model incorporates the herschel bulkley and bilinear rheologies of viscoplastic fluid the more familiar bingham model is integrated into the herschel bulkley rheological model the conservation equations of mass and momentum of single phase laminar debris flow are layer integrated using the slender flow approximation they are then expressed in a lagrangian framework and solved numerically using an explicit finite difference scheme starting from a given initial shape a debris flow is allowed to collapse and propagate over a specified topography comparison between the model predictions and laboratory experiments shows reasonable agreement the model is used to study the effect of the ambient fluid density initial shape of the failed mass and rheological model on the simulated propagation of the front and runout characteristics of muddy debris flows it is found that initial failure shape influences the front velocity but has little bearing on the final deposit shape in the bingham model the excess of shear stress above the yield strength is proportional to the strain rate to the first power this exponent is free to vary in the herschel bulkley model when it is set at a value lower than unity the resulting final deposits are thicker and shorter than in the case of the bingham rheology the final deposit resulting from the bilinear model is longer and thinner than that from the bingham model due to the fact that the debris flow is allowed to act as a newtonian fluid at low shear rate in the bilinear model

experimental interaction of magma and dirty coolants the presence of water at volcanic vents can have dramatic effects on fragmentation and eruption dynamics but little is known about how the presence of particulate matter in external water will further alter eruptions volcanic edifices are inherently dirty places where particulate matter of multiple origins and grainsizes typically abounds we present the results of experiments designed to simulate non explosive interactions between molten basalt and various coolants ranging from homogeneous suspensions of 0 to 30 mass bentonite clay in pure water to heterogeneous and or stratified suspensions including bentonite sand synthetic glass beads and or naturally sorted pumice four types of data are used to characterise the interactions 1 visual video observations 2 grainsize and morphology of resulting particles 3 heat transfer data from a network of eight thermocouples and 4 acoustic data from three force sensors in homogeneous coolants with 20 sediment heat transfer is by forced convection and conduction and thermal granulation is less efficient resulting in fewer blocky particles larger grainsizes and weaker acoustic signals many particles are droplet shaped or and vesicular containing bubbles filled with coolant both of these particle types indicate significant hydrodynamic magma coolant mingling and many of them are rewelded into compound particles the addition of coarse material to heterogeneous suspensions further slows heat transfer thus reducing thermal granulation and variable interlocking of large particles prevents efficient hydrodynamic mingling this results primarily in rewelded melt piles and inefficient distribution of melt and heat throughout the coolant volume our results indicate that even modest concentrations of sediment in water will significantly limit heat transfer during non explosive magma water interactions at high concentrations the dramatic reduction in cooling efficiency and increase in mingling help to explain globular peperite and provide information relevant to analyses of premixing associated with highly explosive molten fuel coolant interactions in debris filled volcanic vents

experimental study on the influence of clay minerals on the yield stress of debris flows abstractit is common knowledge that a relationship exists between the volumetric sediment concentration the percentage of clay mineral content and the activity of clay minerals which is related to the clay type and the yield stress of a debris flow mass in this paper the effect of four types of common clay minerals montmorillonite illite chlorite and kaolin on the yield stress of mixtures were investigated in a quantitative way laboratory experiments were carried out with single and mixed clay mineral types various volumetric concentrations and percentages of clay mineral content for the same clay content and same volumetric concentration a decreasing effect was found respectively of montmorillonite illite kaolin on the yield stress of the flow mixture whereas the effect of chlorite was equal to that of kaolin a concept of equivalent clay mineral percentage p0 is introduced in this paper in which the value of 1 is taken as the characteristic coefficient of kaolin in the experiments

gis based cell model for simulating debris flow runout on a fan summary a gis based cell model based on a kinematic approach is proposed to simulate debris flow routing on a fan the sediment water mixture is modeled as a monophasic continuum and the flow pattern is discretized by square cells 1 m in size that coincide with the dem cells flow occurs from cells with a higher mixture free surface to those with a lower mixture free surface a uniform flow law is used if the elevation of the former cell is higher than that of the latter otherwise the flow is simulated using the broad crested weir law erosion and deposition are simulated using an empirical law that is adjusted for a monophasic continuum the sediment concentration in the routing volume is computed at each time step and controls both erosion and deposition the cell model is used to simulate a debris flow that occurred on the rio lazer dolomites north eastern italian alps on november 4th 1966 furthermore the hydrologic and the hydraulic conditions for the initiation of debris flow are simulated providing the solid liquid hydrograph of the resulting debris flow a number of simulations has been carried out with physically reasonable parameters the results are compared with the extension of the debris flow deposition area and the map of observed depths of deposited sediments this comparison shows that the proposed model provides good performance the analysis of sensitivity carried out by systematically varying the model parameters shows that lower performances are associated with parameter values that are not physically reasonable the same event is also simulated using a cellular automata model and a finite volume two dimensional model the results show that the two models provide a sediment deposition pattern less accurate than that provided by the present cell model

diatreme evolution during the phreatomagmatic eruption of the songaksan tuff ring jeju island korea the songaksan tuff ring jeju island korea which erupted ca 3 7 ka bp in a coastal setting provides an unusual opportunity to study the processes of phreatomagmatic eruption and the formation of a diatreme because of the exceptionally well preserved ejecta beds and well known subsurface geology the tuff sequence can be divided into four units a to d which have distinctly different accidental componentry quartz rich vs quartz poor grain surface features abraded and ash coated vs unabraded and uncoated and chemical compositions of juvenile particles the basal tephra bed of unit a which probably erupted after the removal of the relatively hard shallow level 120 m deep accidental grains suggesting that the early erupted tephra had not yet experienced recycling and pre eruption mixing in the diatreme on the other hand the overlying tephra beds of units a b and d contain an abundance of abraded and ash coated juvenile accidental grains suggesting that the tephra comprised significant proportions of recycled or premixed materials from previous eruptions or subsurface explosions which participated in the explosion driven mixing in the diatreme before eventual ejection from the diatreme unit c is unusual in that it comprises extremely rare accidental grains and ash coated juvenile accidental grains we interpret that the supply of solid materials either accidental or juvenile to the diatreme was greatly reduced because of temporary stabilization of the diatreme and the reduction in magma flux to the diatreme the diatreme is therefore envisaged to have been filled with a water saturated slurry in which particle abrasion and adhesion were inhibited we also infer that the diatreme fill was temporarily removed by a powerful explosion before eruption of unit c on the basis of the near absence of the tephra grains from earlier eruptions throughout the tephra beds of unit c the ratio of tachylite to sideromelane grains generally increases up section of the tuff sequence with two abrupt drops across the tuff unit boundaries these variations are coincident with the changes in the chemical composition of juvenile particles suggesting an overall decrease in magma flux punctuated by brief increases in magma flux associated with the arrival of new magma batches the textural and compositional variations of the songaksan tuff ring suggest that there can be significant variability in diatreme processes even during a purely phreatomagmatic eruption of a tuff ring including removal and renewal of the diatreme fill and that there is still much room for further investigation of the diatreme processes from the ejecta beds in order to make the current diatreme model more robust

revised conceptual model for maar diatremes subsurface processes energetics and eruptive products diatremes are debris filled structures beneath maars that result from many magma water phreatomagmatic explosions during a monogenetic volcano s lifetime a long standing model requires deepening explosions due to water table drawdown that eject progressively deeper seated country rock from the explosion sites while the overlying diatreme and its surface crater widen due to subsidence a revised model is proposed wherein explosions can take place at any level within a diatreme at a given time most effectively venting material from near surface explosions deep seated country rock lithics in tephra deposits record stepwise vertical mixing of material by upward directed debris jets and downward subsidence rather than direct ejection from deep explosions juvenile and lithic clasts erupted during a given explosion may have had a complex history within the diatreme and need not directly reflect fragmentation or brecciation during the explosion that ejects them

field observations rheological testing and numerical modelling of a debris flow event debris flows generated from landslides are common processes and represent a severe hazard in mountain regions due to their high mobility and impact energy we investigate the dynamics and the rheological properties of a 90 000 m3 debris flow event triggered by a rapid regressive landslide with high water content field evidence revealed a maximum flow depth of 7 8 m with an estimated peak discharge of 350 400 m3 s 1 depositional evidence and grain size distribution of the debris pose the debris flow in an intermediate condition between the fluid mud and grain flow behaviour the debris flow material has silt clay content up to 15 per cent the rheological behaviour of the finer matrix was directly assessed with the ball measuring system the measurements performed on two samples at 45 63 per cent in sediment concentration by volume gave values of 3 5 577 pa for the yield strength and 0 6 27 9 pa s for the viscosity based on field evidence we have empirically estimated the yield strength and viscosity ranging between 4000 200 pa and 108 134 pa s respectively we used the flo 2d code to replicate the debris flow event we applied the model with rheological properties estimated by means of direct measurements and back analyses the results of these models show that the rheological behaviour of a debris flow mass containing coarse clasts can not be assessed solely on the contribution of the finer matrix and thus neglecting the effects of direct grain contacts for debris flows composed by a significant number of coarse clasts a back analysis estimation of the rheological parameters is necessary to replicate satisfactorily the depositional extent of debris flows in these cases the back estimated coefficients do not adequately describe the rheological properties of the debris flow copyright 2006 john wiley sons ltd

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

an experimental facility for investigating hydromagmatic eruptions at high pressure and high temperature with application to the importance of magma porosity for magma water interaction an experimental facility has been developed to investigate magma water interaction mwi the facility operates in a high pressure and high temperature environment with temperatures up to 1 200 c and pressures up to 200 mpa cylindrical sample holders 20 by 180 mm in size are heated conductively to yield a three phase melt crystals and gas system and then water or other fluid is injected into the sample through a capillary tube diameter 0 5 mm length ca 1 000 mm under controlled conditions pressure volume and temperature changes are continuously recorded during every phase of the experiments to test this facility mwi is studied at subliquidus temperatures 800 and 900 c and pressure 8 mpa using a leucite tephrite sample with two different initial grain sizes because of the grain size dependence of sintering the two starting materials produce magmas with different textures at the same temperature porous magma for large initial grain sizes and dense magma for small initial grain sizes in these experiments 1 5 g of water at room temperature is injected into 6 0 g of partially molten sample at velocities ranging from 1 to 3 m s we find that the extent of fragmentation and transport caused by mwi are mainly controlled by the texture of the interacting sample with explosive interaction occurring only for porous magmas

dynamic modelling of entrainment in rapid landslides entrainment of path material is an important feature of many rapid landslides the associated increases in volume and changes in flow character can significantly influence mobility a simple material entrainment algorithm based on the assumption of natural exponential growth with displacement has been incorporated into a new computer model designed to simulate rapid landslide motion across 3d terrain the user controls the growth rate and can also implement a change in rheology at the onset of entrainment a hypothetical example is used to demonstrate the influence of the mass and momentum transfer assumptions a back analysis of the 1999 nomash river landslide is included to show that the simple model is capable of simulating the bulk characteristics of a complex event involving substantial entrainment key words landslides debris flows rock avalanches entrainment erosion dynamic modelling

variation in peperite textures associated with differing host sediment properties peperites formed by mixing of magma and wet sediment are well exposed along punta china baja california mexico where two sills intrude a section of lava flows limestones and volcaniclastic rocks irregular lobes and dikes extend from the sills several meters into host sediments including highly comminuted flow top breccias lithic lapilli tuff breccias and shelly micrites whereas intrusive contacts with lava flows are sharp and planar where one sill intruded both coarse grained volcaniclastic rock and fine grained limestone textural differences between the hosts produced strikingly different styles of peperite blocky masses of the basaltic intrusions up to 1 m in size were dispersed for distances up to 3 m into host lithic lapilli tuff breccias the blocks consequently underwent in situ fragmentation as they were rapidly quenched the high degree of dispersion resulted from steam explosions as the magma enveloped pockets of water in the coarse grained permeable host elutriation of fine grained material from vertical pipes in tuff breccia above the lower sill provides evidence for meter scale fluidization of the host the contact zone between the basaltic magma and the shelly micrite host resembles a mixture of two viscous immiscible fluids fluidal peperite intrusion occurred behind a stable vapor film which entrained lime mud particles and carried them off grain by grain as magma advanced into the host thin section scale elutriation pipes formed microglobular peperite represents a frozen example of a fuel coolant interaction fci between basaltic magma and fluidized micrite host the intimate intermixing of magma and host at the submillimeter level is attributed to fluid instabilities developed along the magma vapor host interface such intimate intermixing of magma and water bearing fragmental debris is commonly a precursory step toward explosive hydrovolcanism

blocky versus fluidal peperite textures developed in volcanic conduits vents and crater lakes of phreatomagmatic volcanoes in mio pliocene volcanic fields of western hungary abstract volcanic fields in the pannonian basin western hungary comprise several mio pliocene volcaniclastic successions that are penetrated by numerous mafic intrusions peperite formed where intrusive and extrusive basaltic magma mingled with tuff lapilli tuff and non volcanic siliciclastic sediments within vent zones peperite is more common in the pannonian basin than generally realised and may be also important in other settings where sediment sequences accumulate during active volcanism hajagos hegy an erosional remnant of a maar volcano was subsequently occupied by a lava lake that interacted with unconsolidated sediments in the maar basin and formed both blocky and globular peperite similar peperite developed in kissomlyo a small tuff ring remnant where dykes invaded lake sediments that formed within a tuff ring lava foot peperite from both hajagos hegy and kissomlyo were formed when small lava flows travelled over wet sediments in craters of phreatomagmatic volcanoes at sag hegy a large phreatomagmatic volcanic complex peperite formed along the margin of a coherent intrusion all peperite in this study could be described as globular or blocky peperite globular and blocky types in the studied fields occur together regardless of the host sediment

products of neptunian eruptions a common pyroclastic facies in subaqueous volcanic successions comprises massive to graded very thick several to tens of meters laterally extensive several kilometers beds of nonwelded pumice lapilli with volumes ranging to tens of cubic kilometers this facies may be overlain by laminated ash or bimodal ash and giant 1 m pumice clasts and underlain by coarse lithic breccia the association is inferred to be the typical product of sustained magmatic volatile driven explosive eruptions from vents at water depths of 1300 200 m we propose the term neptunian for such eruptions and their products the eruption column rapidly mixes with the surrounding water cools increases in density and collapses while remaining under water lithic clasts that are too heavy to be entrained in the column are deposited close to the source forming a neptunian lithic breccia pumice lapilli are rapidly waterlogged and form the dominant component in the collapsing column and in eruption fed water supported density currents neptunian density currents hot buoyant giant pumice clasts continue to rise and may reach the water surface before being waterlogged and settling along with temporarily suspended ash forming neptunian suspension deposits eruption magnitude fragmentation mechanisms and juvenile pyroclast characteristics especially vesicularity are very similar in neptunian and plinian style eruptions but column behavior differs primarily because of the contrasting physical properties of the ambient fluid water versus air

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

felsic maar diatreme volcanoes a review felsic maar diatreme volcanoes host major ore deposits but have been largely ignored in the volcanology literature especially for the diatreme portion of the system here we use two mexican tuff rings as analogs for the maar ejecta ring new observations from one diatreme and the economic geology literature on four other mineralized felsic maar diatremes to produce an integrated picture of this type of volcano the ejecta rings are up to 50 m thick and extend laterally up to 1 5 km from the crater edge in two mexican examples the lower part of the ejecta ring is dominated by pyroclastic surge deposits with abundant lithic clasts up to 80 at hoya de estrada these deposits display low angle cross bedding dune bedforms undulating beds channels bomb sags and accretionary lapilli and are interpreted as phreatomagmatic rhyolitic juvenile clasts at tepexitl have only 0 25 vesicles in this portion of the ring the upper parts of the ejecta ring sequences in the mexican examples have a different character lithic clasts can be less abundant the grain size is typically coarser and the juvenile clasts can be different in character with some more vesicular fragments fragmentation was probably shallower at this stage the post eruptive maar crater infill is known at wau and consists of reworked pyroclastic deposits as well as lacustrine and other sediments underneath are bedded upper diatreme deposits interpreted as pyroclastic surge and fall deposits the upper diatreme and post eruptive crater deposits have dips larger than 30 at wau with approximately centroclinal attitudes at still lower structural levels the diatreme pyroclastic infill is largely unbedded montana tunnels and kelian are good examples of this at cerro de pasco the pyroclastic infill seems bedded despite about 500 m of post eruptive erosion relative to the pre eruptive surface the contact between the country rocks and the diatreme is sometimes characterized by country rock breccias kelian mt rawdon pyroclastic rocks in the diatreme are typically poorly sorted and ash rich they contain a heterolithic mix of juvenile clasts and lithic clasts from various stratigraphic levels megablocks derived from the ejecta ring or the country rocks are often found in the diatremes evidence for multiple explosions is in the form of steep crosscutting pyroclastic bodies within some diatremes and fragments of pyroclastic rocks within other pyroclastic facies pyroclastic rocks are cut by coherent felsic dikes and plugs which may have been feeders to lava domes at the surface allowing for the difference in magma composition felsic maar diatreme volcanoes have many similarities with their ultramafic to mafic equivalents differences include a common association with felsic domes inside the crater or just outside wau although the domes within the crater may be destroyed during the eruption hoya de estrada tepexitl the dikes and plugs feeding and invading felsic diatremes seem larger the processes of phreatomagmatic explosions involving felsic magmas may be different

basanite glaciovolcanism at llangorse mountain northern british columbia canada the llangorse volcanic field is located in northwest british columbia canada and comprises erosional remnants of miocene to holocene volcanic edifices lava flows or dykes the focus of this study is a single overthickened 100 m thick valley filling lava flow that is middle pleistocene in age and located immediately south of llangorse mountain the lava flow is basanitic in composition and contains mantle derived peridotite xeno liths the lava directly overlies a sequence of poorly sorted crudely bedded volcaniclastic debris flow sediments the debris flow deposits contain a diverse suite of clast types including angular clasts of basanite lava blocks of peridotite coated by basanite and rounded boulders of granodiorite many of the basanite clasts have been palagonitized the presence and abundance of clasts of vesicular to scoriaceous palagonitized basanite and peridotite suggest that the debris flows are syngenetic to the overlying lava flow and sampled the same volcanic vent during the early stages of eruption they may represent lahars or outburst floods related to melting of a snow pack or ice cap during the eruption the debris flows were water saturated when deposited the rapid subse quent emplacement of a thick basanite flow over the sediments heated pore fluids to at least 80 100 c causing in situ palagonitization of glassy basanite clasts within the sediments the over thickened nature of the llangorse mountain lavas suggests ponding of the lava against a down stream barrier the distribution of similar aged glaciovolcanic features in the cordillera suggests the possibility that the barrier was a lower elevation valley wide ice sheet

confort 15 model of conduit dynamics applications to pantelleria green tuff and etna 122 bc eruptions numerical simulations are useful tools to illustrate how flow parameters and physical processes may affect eruption dynamics of volcanoes in this paper we present an updated version of the conflow model an open source numerical model for flow in eruptive conduits during steady state pyroclastic eruptions mastin and ghiorso in a numerical program for steady state flow of magma gas mixtures through vertical eruptive conduits u s geological survey open file report 00 209 2000 in the modified version called confort 15 the rheological constraints are improved incorporating the most recent constitutive equations of both the liquid viscosity and crystal bearing rheology this allows all natural magma compositions including the peralkaline melts excluded in the original version to be investigated the crystal bearing rheology is improved by computing the effect of strain rate and crystal shape on the rheology of natural magmatic suspensions and expanding the crystal content range in which rheology can be modeled compared to the original version conflow is applicable to magmatic mixtures with up to 30 vol crystal content moreover volcanological studies of the juvenile products crystal and vesicle size distribution of the investigated eruption are directly incorporated into the modeling procedure vesicle number densities derived from textural analyses are used to calculate through toramaru equations maximum decompression rates experienced during ascent finally both degassing under equilibrium and disequilibrium conditions are considered this allows considerations on the effect of different fragmentation criteria on the conduit flow analyses the maximum volume fraction criterion porosity criterion the brittle fragmentation criterion and the overpressure fragmentation criterion simulations of the pantelleritic and trachytic phases of the green tuff pantelleria and of the plinian etna 122 bc eruptions are performed to test the upgrades in the confort 15 modeling conflow and confort 15 numerical results are compared analyzing the effect of viscosity decompression rate temperature fragmentation criteria critical strain rate porosity and overpressure criteria and equilibrium versus disequilibrium degassing in the magma flow along volcanic conduits the equilibrium simulation results indicate that an increase in viscosity a faster decompression rate a decrease in temperature or the application of the porosity criterion in place of the strain rate one produces a deepening in fragmentation depth initial velocity and mass flux of the mixture are directly correlated with each other inversely proportional to an increase in viscosity except for the case in which a faster decompression rate is assumed taking into account up to date viscosity parameterization or input faster decompression rate a much larger decrease in the average pressure along the conduit compared to previous studies is recorded enhancing water exsolution and degassing disequilibrium degassing initiates only at very shallow conditions near the surface brittle fragmentation i e depending on the strain rate criterion in the pantelleritic green tuff eruption simulations is mainly a function of the initial temperature in the case of the etna 122 bc plinian eruption the viscosity strongly affects the magma ascent dynamics along the conduit using confort 15 and therefore incorporating the most recent constitutive rheological parameterizations we could calculate the mixture viscosity increase due to the presence of microlites results show that these seemingly low viscosity magmas can explosively fragment in a brittle manner mass fluxes resulting from simulations which better represent the natural case i e microlite bearing are consistent with values found in the literature for plinian eruptions 106 kg s the disequilibrium simulations both for green tuff and etna 122 bc eruptions indicate that overpressure sufficient for fragmentation if present occurs only at very shallow conditions near the surface

disappearance of a crater lake implications for potential explosivity at soufriere volcano st vincent lesser antilles soufriere volcano in st vincent west indies is one of the most active volcanoes in the eastern caribbean with at least six eruptions since 1718 ad the latest of which occurred in 1979 prior to the 1979 eruption the active crater hosted deep water lakes during periods of repose which were always replenished within a few years after the eruptions in 1979 the crater was filled with 108 m3 of fragmental material and despite constant precipitation has remained virtually dry ever since with the exception of a small shallow pond a resistivity survey was conducted in july 2006 to investigate groundwater occurrence in the crater results from the resistivity data inversion on several 2 d profiles show a shallow horizontal conductor across the crater floor consistent with a water saturated aquifer they also show that the post 1979 pond currently present in the crater lake is in fact an outcropping part of the groundwater water reservoir the reservoir water table is 28 m above the pre 1979 lake level and reflects mass equilibrium in the system where constant seepage underground balances the meteoric recharge we suggest that the groundwater body extends at depth to the bottom of the pre 1979 crater lake either due to a significant structural discontinuity or because of a reduction of permeability at depth the estimated maximum volume of water stored underground is 10 30 106 m3 and energy considerations indicate that 2 4 7 3 1010 kg of magma would potentially be sufficient to vaporise the whole groundwater body this amount of magma represents only 13 41 of the mass erupted during the last eruption in 1979 which was the smallest of the past 3 eruptions 1902 1971 72 1979 since explosive phreatic or phreatomagmatic eruptions at soufriere seem to be linked to magma water interaction within confined space the results from this survey suggests that phreatic or phreatomagmatic activity is a distinct possibility during future magma intrusion in the summit area despite the apparent disappearance of water in the summit crater

subaqueous rhyolitic dome top tuff cones a model based on the devonian bunga beds southeastern australia and a modern analogue the relics of two late devonian subaqueous rhyolitic dome top tuff and pumice cone successions are preserved in the bunga beds outlier of the boyd volcanic complex southeastern australia these cone successions and other rhyolitic volcanics of the bunga beds are associated with turbidite and other deep water massflow sedimentary rocks the two cone successions have a generally similar stratigraphy at the base flow banded variably autobrecciated and quench fragmented rhyolite representing an intrusive to extrusive dome is overlain by rhyolitesediment breccia representing extrusion of the dome through the deep water sediment pile and resedimentation down its flanks in the northern cone succession an overlying succession of bedded pumiceous crystal rich to crystal poor tuffs represents the onset of pyroclastic activity and growth of a tuff cone an overyling debris flow deposit represents degradation of part of the cone the topmost unit a stratified pumice succession is thought to represent another cone building eruptive phase and is separated from the underlying strata by a major slide surface the southern cone succession contains less tuff and abundant pumice and is also terminated by a debris flow deposit indicating cone degradation a modern analogue for the inferred eruptive style and sequence is the 1953 1957 rhyolite eruption that formed the tuluman island lava tuff cone complex in the bismarck sea the eruptions were often cyclical consisting of an initial inferred submarine lava forming stage passing into a pumicecone forming stage in some cases a subaeriallava forming stage and a final stage following the cessation of volcanism during which the cones collapsed gravitationally or were destroyed by wave erosion using observations from both the tuluman island eruptions and the preserved stratigraphies of the devonian tuff cones a dynamic model is proposed for the formation of subaqueous rhyolitic dome top tuff and pumice cones

laboratory analysis of mudflow properties a rotational viscometer has been designed for laboratory measurements of the rheological properties of natural mudflow deposits in colorado the mudflow matrices comprised of silt and clay particles are sheared under temperature controlled conditions at volumetric sediment concentrations ranging from 0 10 0 45 this study stresses the importance of conducting rheological measurements at low rates of shear because 1 those are the conditions found in natural channels and 2 they avoid the slippage problems observed at large sediment concentrations at low rates of shear the bingham model is fitted to the measured rheograms and both the viscosity and yield stress increase exponentially with the sediment concentration of the fluid matrix both the yield stress and the viscosity increase by three orders of magnitude as the volumetric concentration of sediments in the fluid matrix changes from 10 to 40 the addition of sand particles does not significantly alter the rheological properties of the matrix unless the volumetric concentration of sands exceeds 0 20

facies architecture of the upper oligocene submarine smrekovec stratovolcano northern slovenia abstract the upper oligocene smrekovec volcanic complex svc represents the remains of a submarine stratovolcano which underwent early miocene tectonic dissection and large scale displacement along the periadriatic line according to the lithofacies architecture abundance and spatial distribution central medial and distal zones of the former volcano edifice have been recognized the zones extend at a distance of 0 2 km 2 5 km and 5 20 km south of the periadriatic line respectively lavas shallow intrusive bodies autobreccia peperite and hyaloclastite deposits occur mainly in the central zone which is extensively altered under hydrothermal conditions characterised by the development of zeolites mainly laumontite prehnite chlorite albite and epidote explosive volcanic activity intensified with the evolution of magma from basaltic andesitic to dacitic gas and water supported eruption fed density flows are assumed their deposits show lithofacies organisation in pyroclastic depositional units pdus similar to either volcaniclastic turbidites type 1 or thin subaqueous ignimbrites type 2 volcaniclastic debris flow deposits are developed as volcaniclastic breccia and sandy debris flow deposits the former occurs in the central and medial zones and the latter occurs in the medial zone only the most widespread lithofacies in the svc are volcaniclastic turbidite deposits three types of sedimentary unit tsu have been distinguished type 1 is 2 5 m thick and dominated by the massive division it mainly occurs in the central zone type 2 is 0 7 3 5 m thick and occurs in the central and medial zones it comprises the massive division bedded fining and thinning upward division and a horizontally wavy and cross laminated division topped by massive fine grained tuff type 3 is 0 1 1 5 m thick and mainly occurs in the distal zone the massive division is absent and thinly bedded and laminated divisions are topped by massive fine grained tuff volcaniclastic turbidites were settled from low density turbidity currents and related suspension clouds mixed volcaniclastic siliciclastic deposits are subordinate in occurrence and restricted to the distal zone they are commonly reworked by bottom currents

simulation of event based landslides and debris flows at watershed level abstract a coupled model has been developed to simulate at watershed level landslides and debris flows induced by a severe typhoon tropical cyclone in taiwan the model comprises a landslide susceptibility model to predict landslide occurrence an empirical model to select debris flow initiation points and a debris flow model to simulate the transport and deposit of failed materials from the identified source areas in raster format with a 10 m spatial resolution the model output includes unstable cells debris flow initiation cells debris flow velocities runout paths and deposition zones the model was first tested and calibrated in a small area where the damage by landslides had been investigated and recorded it was then applied to a watershed and the simulation results were validated by comparing them with a landslide debris flow inventory map prepared from satellite images using a multiple change detection technique model test and validation results confirm the usefulness of the model in predicting the number and size of affected areas landslides and runouts combined runout path and volume of runout deposits it is a common practice in taiwan to separate landslide and debris flow inventories and to study debris flows only in select drainage basins this study suggests that landslide and debris flow should be modeled as a sequential process for efficient watershed management

subterranean fragmentation of magma during conduit initiation and evolution in the shallow plumbing system of the small volume jagged rocks volcanoes hopi buttes volcanic field arizona usa monogenetic volcanoes have limited magma supply and lack long lived sustained magma plumbing systems they erupt once often from multiple vents and sometimes over several years and are rarely or never re activated eruptive behavior is very sensitive to physical processes e g volatile exsolution magma water interaction occurring in the later stages of magma ascent at shallow crustal depths 1 km which yield a spectrum of eruptive styles including weak to moderate explosive activity violent phreatomagmatism and lava effusion jagged rocks complex in the late miocene hopi buttes volcanic field arizona usa exposes the frozen remnants of the feeding systems for one or a few monogenetic volcanoes it provides information on how a shallow magmatic plumbing system evolved within a stable non marine sedimentary basin and the processes by which magma flowing through dikes fragmented and conduits were formed we have identified three main types of fragmental deposits 1 buds which emerge from dikes 2 pyroclastic massifs and 3 diatremes these represent three different styles and intensities of shallow depth magma fragmentation they may develop successively and at different sites during the evolution of a monogenetic volcano the deposits consist of a mixture of pyroclasts with varying degrees of welding and country rock debris in various proportions pyroclasts are commonly welded together but also reveal in places features consistent with phreatomagmatism such as blocky shapes dense groundmasses and composite clasts loaded and cored the extent of fragmentation and the formation of subterranean open space controlled the nature of the particles and the architecture and geometry of these conduit structures and their deposits

intra vent peperites related to the phreatomagmatic 71 gulch volcano western snake river plain volcanic field idaho usa abstract the western snake river plain volcanic field in sw idaho contains up to 400 basaltic vents and centers that produced lava shields pahoehoe lava fields scoria cones and a great variety of phreatomagmatic volcanoes between late miocene and middle pleistocene time tephra deposits produced by phreatomagmatic eruptions are particularly well exposed in the walls of the snake river canyon where thick accumulations of pyroclastic rocks indicate widespread phreatomagmatic eruptive events throughout most of the volcanic history of the region previously many of the phreatomagmatic deposits were considered to be the products of subaqueous eruptions that took place on the floor of one or more large freshwater intra continental lakes recent field based observations confirm the presence of widespread phreatomagmatic pyroclastic rocks however some that had been interpreted as being subaqueous exhibit textural features that are more consistent with subaerial depositional environments intrusive and extrusive magmatic bodies with features associated with peperite formation have also been identified most of these peperites can be attributed to magma sediment mixing in intra crater conduit or vent settings and therefore they can only be used as widespread paleoenvironmental indicators with limitations to demonstrate magma and surface water e g lake non explosive interaction one of the studied sites 71 gulch volcano was previously used to indicate the presence of a shallow lake at this site there is clear field evidence that peperitic feeder dykes contacted muddy sandy siliciclastic sediments forming globular peperite the peperitic feeder dykes transition to pillowed ponded lava up section the ponded lavas are partially surrounded by a 5 m thick unit composed of gently dipping dune bedded volcanic glass shard rich unsorted tuff and lapilli tuff containing abundant impact sags caused by volcanic lithics we suggest that the 3d architecture of the erosional remnant of 71 gulch volcano does not require the presence of a lake at the time of its formation it is equally possible that that it represents a subaerial phreatomagmatic upper conduit crater filling succession this interpretation opens up many questions about the mio pliocene evolution of sw idaho the timing of the volcanism and its association with the evolution of the lacustrine systems in the region in addition re evaluations of the volcanic features in sw idaho have some general implications for the usage of phreatomagmatic pyroclastic rocks for paleoenvironmental reconstruction

pyroclastic density currents resulting from the interaction of basaltic magma with hydrothermally altered rock an example from the 2006 summit eruptions of mount etna italy after 16 months of quiescence mount etna began to erupt again in mid july 2006 the activity was concentrated at and around the southeast crater sec one of the four craters on the summit of etna and eruptive activity continued intermittently for 5 months during this period numerous vents displayed a wide range of eruptive styles at different times virtually all explosive activities took place at vents at the summit of the sec and on its flanks eruptive episodes which lasted from 1 day to 2 weeks became shorter and more violent with time volcanic activity at these vents was often accompanied by dramatic mass wasting processes such as collapse of parts of the cone highly unusual flowage processes involving both old rocks and fresh magmatic material and magma water interaction the most dramatic events took place on 16 november when numerous rockfalls and pyroclastic density currents pdcs were generated during the opening of a large fracture on the se flank of the sec cone the largest pdcs were clearly triggered explosively and there is evidence that much of the energy was generated during the interaction of intruding magma with wet rocks on the cone s flanks the most mobile pdcs traveled up to 1 km from their source this previously unknown process on etna may not be unique on this volcano and is likely to have taken place on other volcanoes it represents a newly recognized hazard to those who visit and work in the vicinity of the summit of etna

premixing of magma and water in mfci experiments experimental studies have been performed to evaluate pre explosive water melt mixes with respect to explosive volcanic molten fuel coolant interaction mfci i e phreatomagmatic explosion remolten ultrabasic volcanic rock was used as a magma simulant measurement of the explosion intensity was used to determine optimal premixing conditions a well defined optimal range was found for the hydrodynamic mixing energy differential flow speed of 4 2 m s as well as for the water melt mass ratio 0 03 to 0 04 under experimental conditions the mass flux of water had a minor influence on the explosion intensity additionally transparent mixing experiments with silicon oil and inked water were carried out they indicate a direct dependence of the pre explosive water melt interface area on the explosion intensity the experimental results show that the contact conditions of water and melt required for explosive mfci may easily be established in natural volcanic systems thus explosive mfci is a probable mechanism of explosive volcanism

complex bombs of phreatomagmatic eruptions role of agglomeration and welding in vents of the 1886 rotomahana eruption tarawera new zealand 1 basaltic bombs ejected from a rotomahana crater during the 1886 tarawera eruption in new zealand are of two fundamental types cored bombs which have single large fragments generally of rhyolite wall rock material as their cores and loaded bombs which contain abundant small fragments dispersed through the bombs similar lithic bearing bombs are common products of other phreatomagmatic eruptions worldwide cored bombs originate when a large wall rock fragment is entrained in basaltic melt and then ejected with an adhering skin of basalt in contrast loaded bombs are constructed by agglomeration of multiple fragments of basalt among which smaller rhyolitic wall rock fragments are dispersed different styles and rates of bomb loading are reflected in the bombs textures and compositions these textures provide insight into the nature of fragmentation during the eruption the processes of recycling that produce multiply ejected clasts versus recapitulated ones those where early formed clasts were reingested in magma and then formed the cores of new bombs the degree and timescale of interaction of magma with vent walls and the timescales over which lithic material from the vent walls is incorporated into complex bombs prior to their ejection because fragments of rhyolitic pumice are readily refused their condition constrains estimates of the timing of fragmentation and agglomeration the presence of nonfused rhyolite pumice within many loaded bombs implies that the processes forming and quenching the bombs cannot have exceeded several seconds in contrast other bombs contain patches of compositionally modified basalt with isolated rhyolite derived feldspar xenocrysts that indicate complete fusing melting and assimilation of entrained rhyolitic debris the bomb population overall indicates that conditions within this rotomahana vent were thermally and physically heterogeneous and that recycling of debris was ubiquitous both as recycling of large individual clasts and by fallback and aggregation of material which was reingested in magma before being reejected as new bombs

the pristine shape of olympus mons on mars and the subaqueous origin of its aureole deposits abstract the tallest volcano in the solar system olympus mons on mars is bordered by at least ten enormous sub circular hummocky deposits forming a welded halo termed the aureole the aureole units or simply aureoles which are the deposits of landslides from olympus mons have dramatically transformed the pristine size and shape of the volcanic edifice topographic data are used to determine the amount of collapsed material and so reconstruct the original outline of olympus mons before the landslides took place under the assumption that the edifice did not start failing until it had reached this maximum size due to post aureole deposition on the eastern and southern flanks and to the uncertainty of the slippage level on the northern side the reconstruction is sufficiently precise along the western and north western olympus mons flank it is more uncertain for the northern flank while it is not feasible around the rest of the volcano it appears that the radius along the western and north western olympus mons before the collapse of the aureole landslides was approximately 200 km longer or more the results show that the volume of the aureoles even if enormous is insufficient to fill the ideal conical edifice which would be obtained prolonging the olympus mons flanks with present slope angles thus an overhang remains in the pre aureole reconstructed olympus mons which would also explain the onset of instability that led to the aureole collapse further a drape deposit blanketing the southern acheron fossae ridge just at the front of the western w aureole landslide deposit and a fan channel system carved on the same w aureole are investigated and it is suggested that these morphologies have been emplaced in subaqueous setting while the drape may indicate a landslide thrust water splash akin to a tsunami deposit caused by the fast travelling w aureole landslide the fan channel system is similar to certain morphologies in the terrestrial oceans a numerical model of the collapse of the western aureole unit in water shows final runouts on both acheron ridge and amazonis planitia compatible with observations provided that the friction angle is extremely small of the order of a tenth of degree simulations indicate that the w aureole could have reached acheron fossae ridge with velocities in excess of 100 m s which would explain the several tens of km long distance reached by the landslide thrust tsunami deposit in short morphological and numerical lines of evidence would indicate a subaqueous origin for the largest w aureole landslide

a miocene basanite peperitic dyke at stanley northwestern tasmania australia abstract a miocene basanite dyke at stanley northwestern tasmania australia displays well preserved peperite texture the dyke is 2 m wide and has intruded basaltic breccia host sediment one contact of the dyke is fluidally shaped and amoeboid apophyses 10 25 cm long extend into the host sediment whereas the other contact is characterized by blocky peperite texture comprising tabular to wedge shaped clasts up to 30 cm across separated by host sediment the clasts have internal spherical fractures and some show splinter texture vesicles are common in the clasts and those intersected by clast margins have been filled with sediment the interior of the dyke comprises close packed blocky peperite consisting of tabular wedge shaped and polyhedral clasts tens of centimetres across separated by host sediment these clasts show well developed jigsaw fit texture the textures and structures in the basanite dyke are inferred to have formed in two stages an earlier hotter apophysis forming stage and a later cooler angular clast forming stage both of which occurred during the intrusion of magma into wet poorly consolidated sediment in a shallow marine environment during the apophysis forming stage the magma had relatively low viscosity and progressively displaced wet sediment the wet sediment around the dyke was partly fluidized by vaporization of pore water the angular clast forming stage reflects a change in the rheological behaviour of the magma from ductile to brittle most likely in response to decreasing temperature the chilled parts of the dyke were subject to stress arising from cooling contraction and also from continued pulsatory movement of hotter still ductile magma in the interior of the dyke resulting in brittle fragmentation brittle fragmentation was accompanied by movement of host sediment into the newly created open spaces forming blocky peperite spherical fractures splinter texture and sediment filled vesicles formed during the angular clast forming stage because the host sediment is texturally identical either side of the dyke increasing magma viscosity as temperature decreased combined with pulsatory intrusion were evidently important in the production of the blocky peperite

a study of a flowslide with significant entrainment in loess areas in china flowslides are a frequent type of natural disaster in loess areas and may result in the significant loss of properties and or casualties the dagou flowslide is a typical event in a loess area and is accompanied by significant sediment entrainment to analyze the mechanisms responsible for flowslides and to obtain the parameters for a runout analysis a field investigation was conducted specimens were sampled on site to carry out laboratory tests including a triaxial test sieve analysis and chemical component analysis the parameters were used in the runout study employing an energy based runout model an analytical entrainment model was adopted to calculate the entrainment after considering physical properties and the mechanism of the entrainment process of the loess finally the entrainment model was incorporated into the runout model to simulate the post failure process of this case energy dissipation due to the deformation of slices was considered as it was thought to be important for a slide with a significant deformation the simulation results were compared with the measurements including runout distance total volume erosion depth deposition height at different sections and velocities at specific locations the results indicate that the energy based runout model together with the entrainment model can capture the kinematic characteristics of the dagou flowslide therefore it is feasible to use this model to predict the runout characteristics of flowslides in similar areas copyright c 2017 john wiley sons ltd

peperite a review of magma sediment mingling the study of peperite is important for understanding magma water interaction and explosive hydrovolcanic hazards this paper reviews the processes and products of peperite genesis peperite is common in arc related and other volcano sedimentary sequences where it can be voluminous and dispersed widely from the parent intrusions it also occurs in phreatomagmatic vent filling deposits and along contacts between sediment and intrusions lavas and hot volcaniclastic deposits in many environments peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal but other shapes occur and mixtures of different clast shapes are also found magma is dominantly fragmented by quenching hydromagmatic explosions magma sediment density contrasts and mechanical stress as a consequence of inflation or movement of magma or lava magma fragmentation by fluid fluid shearing and surface tension effects is probably also important in fluidal peperite fluidisation of host sediment hydromagmatic explosions forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed factors which could influence fragmentation and mingling processes include magma host sediment and peperite rheologies magma injection velocity volatile content of magma total volumes of magma and sediment involved total volume of pore water heated presence or absence of shock waves confining pressure and the nature of local and regional stress fields sediment rheology may be affected by dewatering compaction cementation vesiculation fracturing fragmentation fluidisation liquefaction shear liquification and melting during magma intrusion and peperite formation the presence of peperite intraclasts within peperite and single juvenile clasts with both sub planar and fluidal margins imply that peperite formation can be a multi stage process that varies both spatially and temporally mingling of juvenile clast populations formed under different thermal and mechanical conditions complicates the interpretation of magma fragmentation and mingling mechanisms

highly vesicular pumice generated by buoyant detachment of magma in subaqueous volcanism many submarine caldera volcanoes are blanketed with deposits of highly vesicular pumice typically attributed to vigorous explosive activity1 2 3 4 however it is challenging to relate volcanic products to specific eruptive styles in submarine volcanism5 6 here we document vesicularity and textural characteristics of pumice clasts dredged from the submarine macauley volcano in the kermadec arc southwest pacific ocean we find that clasts show a bimodal distribution with corresponding differences in vesicle abundances and shapes specifically we find a sharp mode at 91 vesicularity and a broad mode at 65 80 subordinate clasts show gradients in vesicularity we attribute the bimodality to a previously undocumented eruptive style that is neither effusive nor explosive the eruption rate is insufficient to cause magma to fragment explosively yet too high to passively feed a lava dome instead the magma foam buoyantly detaches at the vent and rises as discrete magma parcels or blebs while continuing to vesiculate internally the blebs are widely distributed by ocean currents before they disintegrate or become waterlogged this disintegration creates individual clasts from interior and rim fragments yielding the bimodal vesicularity characteristics we conclude that the generation and widespread dispersal of highly vesicular pumice in the marine environment does not require highly explosive activity

contrasting pyroclast density spectra from subaerial and submarine silicic eruptions in the kermadec arc implications for eruption processes and dredge sampling pyroclastic deposits from four caldera volcanoes in the kermadec arc have been sampled from subaerial sections raoul and macauley and by dredging from the submerged volcano flanks macauley healy and the newly discovered raoul sw suites of 16 32 mm sized clasts have been analyzed for density and shape and larger clasts have been analyzed for major element compositions density spectra for subaerial dry type eruptions on raoul island have narrow unimodal distributions peaking at vesicularities of 80 85 whereas ingress of external water wet type eruption or extended timescales for degassing generate broader distributions including denser clasts submarine erupted pyroclasts show two different patterns healy and raoul sw dredge samples and macauley island subaerial emplaced samples are dominated by modes at 80 85 implying that submarine explosive volcanism at high eruption rates can generate clasts with similar vesicularities to their subaerial counterparts a minor proportion of healy and raoul sw clasts also show a pink oxidation color suggesting that hot clasts met air despite 0 5 to 1 km of intervening water in contrast macauley dredged samples have a bimodal density spectrum dominated by clasts formed in a submarine eruptive style that is not highly explosive macauley dredged pyroclasts are also the mixed products of multiple eruptions as shown by pumice major element chemistry and the sea floor deposits reflect complex volcanic and sedimentation histories the kermadec calderas are composite features and wide dispersal of pumice does not require large single eruptions when coupled with chemical constraints and textural observations density spectra are useful for interpreting both eruptive style and the diversity of samples collected from the submarine environment

modelling a cohesive frictional debris flow an experimental theoretical and field based study the rheology of debris flows is difficult to characterize owing to the varied composition and to the uneven distribution of the components that may range from clay to large boulders in addition to water few studies have addressed debris flow rheology from observational experimental and theoretical viewpoints in conjunction we present a coupled rheological numerical model to characterize the debris flows in which cohesive and frictional materials are both present as a first step we consider small scale artificial debris flows in a flume with variable percentages of clay versus sand and measure separately the rheological properties of sand clay mixtures a comparison with the predictions of a modified version of the numerical model bing shows a reasonable agreement between measurements and simulations as application to a field case we analyse a recent debris flow that occurred in fjaerland western norway for which much information is now available the event was caused by a glacial lake outburst flood glof originating from the failure of a moraine ridge in a previous contribution breien et al landslides 2008 5 271 280 we focused on the hydrological and geomorphological aspects in particular we documented the marked erosion and reported the change in sediment transport during the event in contrast to the laboratory debris flows the presence of large boulders and the higher normal pressure inside the natural debris flow requires the introduction of a novel rheological model that distinguishes between mud to clast supported material we present simulations with a modified bing model with the new cohesive frictional rheology to account for the severe erosion operated by the debris flow on the colluvial deposits of fjaerland we also suggest a simple model for erosion and bulking along the slope path numerical simulations suggest that a self sustaining mechanism could partly explain the extreme growth of debris flows running on a soft terrain

linking the ukinrek 1977 maar eruption observations to the tephra deposits new insights into maar depositional processes abstract the ukinrek maars erupted 30 march to 9 april 1977 forming two maars a line of small pit craters and a tephra blanket extending to 2 km from the vents we combine photographic and written observations with stratigraphic analysis to reconstruct the eruption the eruption began with very low a few meters high fountaining from small craters above an inferred east west trending dike creating local scoria spatter agglomerate ramparts with a sandy matrix the eruption very quickly in minutes to hours centered on the west maar the west maar eruption lasted 1 2 days starting and ending with phreatomagmatic explosions with weak phreato strombolian activity in between initial explosions formed a 30 m wide crater enlarged by crater wall collapse and columns as high as 6500 m phreato strombolian activity produced 72 of the erupted volume including a small spatter cone and a scoria blanket around the vent a final explosion series emplaced a lithic rich breccia as ballistic blocks possibly as the northern half of the final crater collapsed into the southern vent area the east maar formed over the last nine days of the eruption and represents 93 of the total volume 4 6 106 m3 of the ukinrek eruption initial explosions were probably shallower than 10 20 m but most of the eruption occurred from explosions at 50 60 m below the pre eruptive surface with evidence of explosions to 90 m depth only at the very end of the eruption the east maar eruption mostly produced columns of lapilli ash and steam and the deposits are mostly fallout winds blew fallout mostly to the north for the first 5 6 days and to the south for the last three days of the eruption wind directed pyroclastic density currents collapsed from the column producing fines rich layers within the coarser fallout sporadic explosions produced weak density currents in the first few days and lithic and juvenile block rich breccias in the last few days of the eruption we interpret that collapse of the crater walls made a slurry that in part provided the water for phreatomagmatic interaction explosions came from depths

fluidization of wet sediments during the emplacement and cooling of various igneous bodies during the emplacement and cooling of igneous bodies fluidization of wet sediment by water vapour may occur by heating or by pressure relief during the opening of fractures momentary fluidization causes sediment reconstitution and local transport continuous fluidization can result in substantial sediment displacement theoretical considerations show that fluidization due to heating is not likely to occur at depths where pressure is much greater than 312 bars studies of the emplacement of sills of andesite ayrshire fluid rhyolite ramsey island and viscous rhyolite moelwyn hills recognize a wide range of phenomena attributable to wet sediment fluidization and in places modify existing interpretations the transgressive bases of the subaqueously welded ash flow tuffs of the capel curig volcanic formation are consistent with emplacement attended by fluidization of the subjacent sediment evidently fluidization is a means by which large volumes of wet sediment can be replaced by igneous material with minimal disturbance of the remaining host also fluidization can result in exceptionally complex contact relationships between sedimentary host and intrusive rocks and can cause fractures formed during cooling to be thoroughly pervaded by sediment fluidization is commonly associated with the formation of peperites

subaqueous pyroclastic flows and ignimbrites an assessment an assessment of the literature on subaqueous pyroclastic flows and their deposits shows that the term pyroclastic flow is frequently used loosely to describe primary hot gas rich pyroclastic flows mass flows which resulted from the transformation of gassupported flows into water supported ones and secondary mass flows carrying redeposited pyroclastic debris based on subaerial pyroclastic flows the term pyroclastic flow should be restricted to demonstrably hot gas rich mass flows of pyroclastic debris using this definition very few examples of subaqueous pyroclastic deposits with evidence for hot emplacement and of having been wholly submerged have been described in the majority of these cases the evidence for a hot state of emplacement and for the subaqueous nature of the host depositional environment is inadequate the only unequivocal cases of hot pyroclastic flow deposits with adequate supporting evidence are the ordovician nearshore shallow marine ignimbrites of ireland and wales and miocene ignimbrites of southwest japan resulting from the passage of subaerially erupted pyroclastic flows into shallow water other possible examples are near vent dense clast deposits in the donzurobo formation of japan possible submarine intra caldera ponded ignimbrite successions in california and wales and near vent pumiceous deposits of ramsay island wales all other purported cases are either clearly the result of water supported mass flow transportation and deposition debris avalanches debris flows turbidity currents or lack adequate supporting evidence regarding the heat state or the palaeoenvironment only the shallow marine ignimbrites of ireland and wales show adequate evidence of welding but even these could have been nearly wholly exposed above sea level when welding occurred we conclude that when pyroclastic flows enter water they are generally disrupted explosively and or ingest water and transform into water supported mass flows and we suggest the various scenarios in which this occurs there is no evidence to suggest that welding in wholly subaqueous environments is common

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

root zone processes in the phreatomagmatic pipe emplacement model and consequences for the evolution of maar diatreme volcanoes abstract the understanding of processes within the root zone of maar diatreme volcanoes is important for the interpretation of the geology volcanology and even hazard assessment of these volcanoes in the phreatomagmatic model of pipe formation the irregularly shaped root zone is the site of the phreatomagmatic explosions and thus functions as the engine for pipe formation in this model the root zone grows over a period of time in a series of many single thermohydraulic i e phreatomagmatic explosions the explosions initially occur close to the surface and with ongoing explosive activity penetrate towards deeper levels the ejection of country rock clasts from the root zone results in a mass deficiency in the root zone that causes the overlying tephra and the adjacent country rocks to subside passively in a sinkhole like fashion into the root zone many phreatomagmatic eruptions consequently result in the formation of a cone shaped diatreme thus with ongoing eruptions the cone shaped diatreme has to grow systematically both in depth and diameter during its growth processes in the lower diatreme levels successively destroy the upper levels of the evolving root zone at the surface the maar crater in turn reacts to the underlying subsidence processes and also grows both in depth and diameter thermohydraulic explosions which fragment both magma and the surrounding country rocks mostly occur within the bottom part of the root zone violent explosions in small pipes may clear the overlying diatreme for a short period of time before tephra fall and collapse of the walls of the new crater refill the small initial diatreme in larger pipes via expansion of the mixture of highly pressurized water vapor juvenile gas phases and explosively produced tephra the confined and expanding eruption cloud has to pierce through the diatreme fill in a feeder conduit in order to erupt diatreme clearing events in large pipes are difficult or impossible to maintain since the explosive force in the root zone is only in exceptional instances strong enough to lift or entrain the entire diatreme tephra knowledge of the genetic relationships between root zones and diatremes is critical to understand pipe growth processes the combination of such processes can lead to substantial variation in volcanic behavior and thus produce fundamentally different volcano and rock types it is the purpose of this paper to outline important features of root zones and suggest their significance for the genesis and evolution of maar diatreme and related volcanoes

oso washington landslide of march 22 2014 dynamic analysis abstractthis paper describes and explains the spectacular mobility of the 2014 oso landslide which was the cause of its fatal consequences a geomorphic interpretation of the site conditions is us

on the formation of deep seated subterranean peperite like magma sediment mixtures abstract in addition to large amounts of fragmented country rocks maar diatreme volcanoes commonly eject juvenile lapilli and cauliflower bombs containing many dispersed xenoliths and or xenocrysts derived from the country rocks surrounding the diatremes formation of these lapilli and bombs is attributed to thermohydraulic explosions in the root zones of the diatremes and their consequences the thermohydraulic explosions release shock waves which are capable of intensely fragmenting the surrounding country rocks vaporisation of water superheated during thermohydraulic explosions and its expansion to lower pressure causes ejection of major parts of the fragmented country rocks surviving sections of fragmented country rocks may collapse or slide into the partially evacuated root zone and thus form a mass flow deposit subsequent to each explosion when prior to a new explosion magma rises from the underlying feeder dyke into the root zone it intrudes this clastic debris inflates it and may mingle with the debris to form a peperite subsequent explosions can fragment and eject fragments of this peperite in the form of juvenile ash grains juvenile lapilli and bombs containing xenoliths or xenocrysts from the country rock debris lack of further explosions but continued rise and intrusion of magma will cause emplacement of such inflated peperite masses as plugs

reconstruction of a destructive debris flow event via numerical modeling the role of valley geometry on flow dynamics debris flows are widespread natural phenomena characterized by high mobility high velocity and long runout distance and impact forces which frequently cause human casualties and significant damage to infrastructure to better understand the dynamics of such events analyzing in particular the effect induced by the valley geometry on flow velocity runout and mobilized volumes in this work we reconstruct a real debris flow event through numerical modeling specifically we used a modified version of the bing model a fluid dynamic depth integrated numerical model for debris flows which has been properly modified to account for width changes along the valley the studied event which occurred in scaletta zanclea messina north eastern sicily italy on october 1 2009 is exceptionally well constrained by field and topographic information in this respect the flow velocity estimated from two specific locations on the basis of field evidence the distribution of erosional and depositional areas along the racinazzo valley based on the comparison of pre and post event digital elevation models dems and the runout distance were used as constraints to calibrate the model furthermore we report a detailed description of the main event characteristics based on hydrological records and witness reports the numerical modeling results are consistent with witness reports and the severe damage recorded in the scaletta marina village and highlight the effect of the valley geometry on both the debris flow velocity and the erosion deposition processes the effect of changing valley width has been also quantified resulting in accelerations of the debris in correspondence of the valley narrowing and stagnations at the plateaus copyright 2015 john wiley sons ltd

the grain size distribution and composition of the touzhai rock avalanche deposit in yunnan china abstract the september 23 1991 rock avalanche that occurred in touzhai zhaotong yunnan province of china claimed 216 lives and caused heavy property losses the touzhai avalanche possesses typical and representative feature of high mobility field surveys are applied in the exploration of the grain size distribution and deposit composition and the lab analyses provide important information about the occurrence mechanism of the rock avalanche flow the touzhai rock avalanche has a volume of 9 million m3 that traveled about 3 4 km along touzhai valley within 3 min with an effective coefficient of friction of 0 22 the deposit of the touzhai rock avalanche contains a wide spectrum of grain sizes 50 cm outcropped in the deposit surface is 0 2 compared with the upper reaches a greater number of boulders are found to exist in the middle and lower reaches of the rock avalanche flow the non uniformity coefficient curvature coefficient and fractal dimension of the deposit

contrasting interactions of two magmas with the same water saturated hosts big bend national park texas abstract rhyolitic and mafic dikes cut lower tertiary sediments tuffs and mafic lavas of the eocene oligocene chisos formation in big bend national park texas two contrasting magmas injected into the same hosts under the same conditions provide a controlled experiment on magma host interaction peralkaline rhyolite dikes are extensive and stand in bold topographic relief on contact surfaces against mudstones close packed spheroids of chilled rhyolite indicate vigorous movement of magma within envelopes of fluid against sandstones the rhyolite dike contacts are more irregular and locally protrude as blunt fingers into the wall rock against mafic lava flows dike contacts are planar and the rhyolite is less altered mafic dikes cut the rhyolite dikes some contacts of these mafic dikes are peperitic indicating intrusion into soft wet sediment and tuff the same hosts of the older rhyolitic dikes must also have been water saturated and unconsolidated higher viscosity and lower temperature prevented rhyolite magma from forming detached bodies or engulfing its host to form peperites estimated pressures and contact temperatures approximate or exceed the critical point of water indicating that the fluid envelopes at rhyolite dike contacts were very unstable because even small temperature fluctuations would have produced wide variations in fluid density around the critical point the resulting volume instability triggered rapid pulsations in the fluid envelope deforming the contacts where permeability of the host was low hot fluid accumulated at contacts but where permeability was high fluid could escape before reaching high temperature

dynamic mingling of magma and liquefied sediments abstract hydrodynamic mingling of magma and liquefied sediments is generally accepted to represent the key process in the formation of some peperites experimental studies on simulant liquids and calculations based on recent empirical findings in the field of polymer research were undertaken to investigate the effectiveness of this process these studies show that for a wide range of shear rates a laminar flow behaviour of the system magma liquefied sediment can be expected i e turbulent mingling is not a realistic scenario formation of peperitic fabrics with grain sizes on a cm scale can hydrodynamically be explained under realistic intrusion velocities in addition to the hydrodynamics cooling processes must also be considered during peperite formation calculations of the cooling history of the juvenile magmatic component under realistic cooling conditions demonstrate a significant limitation of the hydrodynamic mingling time the consequence for peperite formation under normal intrusion conditions is that domains of magmatic melt and domains of liquefied sediment smaller than 10 cm are not probable however as smaller domain sizes peperitic grain sizes exist in nature we conclude that either those peperites represent the products of explosive events or that hydrodynamic mingling was accompanied by additional fragmentation processes

insights into eruption dynamics from textural analysis the case of the may 2008 chaiten eruption the may 2008 chaiten southern chile eruption was characterized by several explosive events each associated with plumes which reached up to about 19 km above sea level on may 6 a study of the textural and physical features of the juvenile clasts erupted during the climactic phase of the 2008 eruption of chaiten is presented pumice clasts show unimodal density distribution main mode at 600 kg m3 average vesicularity of about 69 a glassy groundmass with no microcrystals and vesicles with dimension between 1 m and 2 mm they also show a unimodal vesicle size distribution with most frequent vesicle size in the range 0 05 0 08 mm and an estimated vesicle number density of 1 3 0 5 105 mm 3 related to a rapid nucleation event produced during the late phases of magma rise this is confirmed by the absence of microcrystals that could otherwise have delayed vesicle formation and allowed the magma to maintain a low viscosity and a supersaturation in volatiles vesiculation and fragmentation were triggered by a sudden decompression of the melt associated with the opening of the volcanic conduit 10 mpa s 1

diverse patterns of ascent degassing and eruption of rhyolite magma during the 1 8 ka taupo eruption new zealand evidence from clast vesicularity k lauea hawaii like vesuvius and etna is a frequently active volcano associated with a national park which is a focus for volcano tourism two contrasting summit eruptions at k lauea in 2008 2009 and 1959 emphasize how even small eruptions on populous volcanoes have significant impact on both hawaii volcanoes national park hvnp and the surrounding communities the effects are typically more indirect and social than direct physical but have significant fiscal repercussions the former include both positive benefits and negative impacts as an illustration direct consequences of the 1959 eruption were the rerouting of the major park access road and destruction of a summer camp but benefits included an unprecedented surge in visitor numbers and construction of nature trails that are now the most visited asset in the park both positive and negative impacts have increased in intensity with time due to growth in the resident population and visitor numbers for example the entire park has been evacuated twice during the ongoing 2008 2009 eruption

assessing entrainment of bed material in a debris flow event a theoretical approach incorporating monte carlo method entrainment of underlying bed sediment by a debris flow can significantly increase the debris flow magnitude to study this phenomenon a theoretical approach to assessing bed sediment entrainment is presented the approach is based on a static approximation that bed sediment entrainment occurs when the shearing stress of the flow is sufficiently high to overcome the basal resistance of the bed sediment in order to delineate erodible zones in a channel we analyze the critical condition of this static equilibrium model and subsequently propose a new concept of a critical line to detect the entrainment reaches in a channel considering the spatial and temporal uncertainties of the input parameter the approach is further incorporated within a monte carlo method and the distribution of entrainment zones and post entrainment volumes can be analyzed this approach is illustrated by back analysis of the 2010 yohutagawa debris flow event japan results from 10 000 trials of monte carlo simulation are compared with the in situ surveys it is shown that the present approach can be satisfactorily used to delineate erodible zones and estimate possible entrainment volume of the event discussion regarding the sensitivities and limitations of the approach concludes the paper copyright 2015 john wiley sons ltd

origin and metamorphism of peperite and associated rocks in the devonian elwell formation northern sierra nevada california the late devonian elwell formation is part of a late paleozoic island arc assemblage exposed in the northern sierra nevada california in the 10 km interval from mount elwell plumas county to packer lake sierra county it consists largely of numerous andesitic sills interleaved with phosphatic radiolarian chert and turbidity current and debris flow deposits peperite formed by interaction of intrusive andesitic magma and still moist incompletely lithified chert not far beneath the sea floor occurs sparingly the whole assemblage was thoroughly recrystallized greenschist facies regional metamorphism during the late jurassic nevadan orogeny the phosphatic chert is composed of white fluorapatite rich lenses and nodules enclosed in a black matrix consisting of microgranular quartz and carbonaceous material probably graphite radiolaria family entactiniidae are so abundant that the chert is thought to have originated as radiolarian ooze the phosphatic lenses and nodules probably formed by direct inorganic precipitation of fluorapatite from pore water within decaying radiolarians at the sediment water interface the andesitic sills are generally aphyric and aphanitic original textures varied from hyalopilitic in sill interiors to pilotaxitic at sill margins the andesite was charged with plagioclase now albite microlites and quench morphologies occur where sills intruded the wettest chert relatively thick sills commonly display columnar structure whereas a few originally more viscous sills are flow laminated the top of a sill emplaced essentially at the sediment water interface is pillowed many sills bear xenoliths of phosphatic chert and scarce quartz megacrysts evidently derived from the underlying dacitic sierra buttes formation appear nearly everywhere concentrations of major element oxides and immobile trace elements indicate that the andesite originated as part of the tholeiitic rock association of island arcs rare earth abundance patterns are particularly diagnostic of this paleotectonic setting most peperite has poorly sorted coarse ash to coarse block andesitic fragments uniformly distributed through a voluminous black chert matrix where invaded chert retained the most pore water quenched andesitic magma formed irregularly shaped lapilli and small pillows that initially exhibited ductile behavior rapid cooling below the softening point of glass resulted in brittle fracture of the lapilli during dispersal through the chert by steam explosions steam explosions also incorporated into the peperite rigid clasts of locally dewatered chert and shattered already formed phosphatic nodules where the invaded chert was better lithified freezing sill margins simply granulated quietly in situ by thermal contraction cracking of microlitic glass fluid chert injected widely spaced contraction joints deep within the sills in all cases there was sufficient heated connate water to cause palagonitization and chloritization of andesitic fragments greenschist facies metamorphism produced two mineral assemblages in the interiors of andesitic sills the second perhaps reflecting locally higher pco 2 ph 2 o during metamorphism 1 albite quartz epidote actinolite chlorite ti rich mineral calcite stilpnomelane white mica and 2 albite quartz chlorite ti rich mineral calcite stilpnomelane white mica epidote rich specks occurring sporadically in the sills represent metasomatism on a scale of millimetres to centimetres such specks are mineralogically zoned in andesitic fragments in intensely recrystallized peperite additional examples of local meta somatic activity include syntectonic crystallization of calcite rhombohedra across original vesicle walls in a sill cleavage developed locally during regional metamorphism is parallel to axial planes of closely appressed folds that deformed andesitic fragments in peperite and flow laminae in sills

setting of zn cu au ag massive sulfide deposits in the evolution and facies architecture of a 1 9 ga marine volcanic arc skellefte district sweden the skellefte mining district occurs in an early proterozoic mainly 1 90 1 87 ga svecofennian magmatic province of low to medium metamorphic grade in the baltic shield in northern sweden the district contains over 85 pyritic zn cu au ag massive sulfide deposits and a few vein au deposits and subeconomic porphyry cu au mo deposits the massive sulfide deposits mainly occur within and especially along the top of a regional felsic dominant volcanic unit attributed to a stage of intense extensional continental margin arc volcanism from facies analysis we interpret the paleogeography of this stage to have comprised many scattered islands and shallow water areas surrounded by deeper seas all the major massive sulfide ores occur in below wave base facies associations however some ores occur close to stratigraphic intervals of above wave base facies associations and the summits of some volcanoes that host massive sulfides emerged above sea level intense marine volcanism was superceded at different times in different parts of the district by a stage of reduced volcanism uplift resulting in subregional disconformities and then differential uplift and subsidence resulting in a complex horst and graben paleogeography uplift of the arc is attributed to the relaxation of crustal extension and the emplacement of granitoids to shallow crustal levels a few massive sulfide ores formed within the basal strata of this second stage the horst and graben system was filled by prograding fluvial deltaic sediments and mainly mafic lavas and during this stage the skellefte district was a transitional area between renewed arc volcanism of more continental character to the north and subsidence and basinal mudstone turbidite sedimentation to the south this whole volcanotectonic cycle occurred within 10 to 15 m y we define 26 main volcanic sedimentary and intrusive facies in the skellefte district the most abundant facies are 1 normal graded pumiceous breccias which are interpreted as syneruptive subaqueous mass flow units of pyroclastic debris 2 porphyritic intrusions and 3 mudstone and sandstone turbidites facies associations define seven main volcano types which range from basaltic shields to andesite cones and rhyolite calderas despite this diversity of volcano types most massive sulfide ores are associated with one volcano type subaqueous rhyolite cryptodome tuff volcanoes these rhyolite volcanoes are 2 to 10 km in diameter 250 to 1 200 m thick at the center and are characterized by a small to moderate volume rhyolitic pyroclastic unit intruded by rhyolite cryptodomes sills and dikes massive sulfide ores occur near the top of the proximal near vent facies association the remarkable coincidence in space and time between the ores and this volcano type indicates an intimate genetic relationship between the ores and the magmatic evolution of the volcanoes many of the massive sulfide ores occur within rapidly emplaced volcaniclastic facies and are interpreted to have formed by infiltration and replacement of these facies some of the ore deposits have characteristics of both marine massive sulfides and subaerial epithermal deposits we suggest that massive sulfides in the skellefte district span a range in ore deposit style from deep water sea floor ores to subsea floor replacements to shallow water and possibly subaerial synvolcanic replacements facies models are provided for the mineralized rhyolite volcanoes and volcanological guides are provided for exploration for blind ores within these volcanoes

an upper pliocene coarse pumice breccia generated by a shallow submarine explosive eruption milos greece the filakopi pumice breccia fpb is a very well exposed pliocene volcaniclastic unit on milos greece and has a minimum bulk volume of 1 km3 it consists of three main units a basal lithic breccia 4 8 m mainly composed of angular to subangular andesitic and dacitic clasts up to 2 6 m in diameter b very thickly bedded poorly sorted pumice breccia 16 17 m and c very thick reversely graded grain supported coarse pumice breccia 6 5 20 m at the top the depositional setting is well constrained as shallow marine up to a few hundred metres by overlying fossiliferous and bioturbated mudstone this large volume of fine pumice clasts is interpreted to be the product of an explosive eruption from a submarine vent because 1 pumice clasts are the dominant component 2 the coarse pumice clasts 64 mm have complete quenched margins 3 very large 1 m pumice clasts are common 4 overall the formation shows good hydraulic sorting and 5 a significant volume of ash was deposited together with the coarsest pyroclasts

pre eruptive water content of rhyolitic magmas as determined by ion microprobe analyses of melt inclusions in phenocrysts abstract the ion microprobe was used to analyze trapped melt inclusions in phenocrysts from two rhyolitic eruptions for h2o f and incompatible trace elements eleven melt inclusions from phenocrysts in air fall tephra from obsidian dome near long valley usa gave an average of 4 1 1 2 wt h2o and showed large variations in f and incompatible trace elements reflecting a complex history reported to involve mixing of at least two magma types eight inclusions in phenocrysts from the taupo ultraplinian event new zealand gave 4 5 0 8 wt h2o with small variations in the other elements analyzed measured water contents are similar to earlier estimates of the pre eruptive water contents of these and similar rhyolites and major and trace element analyses of inclusions compare closely with bulk analyses suggesting that the analyses of inclusions represent the chemistry of the magma at the time of entrapment

iblean diatremes 3 volcanic processes on a miocene carbonate platform iblean mountains se sicily a comparison of deep vs shallow marine eruptive processes evolution and magma fragmentation processes of two contrasting well exposed diatreme complexes interbedded with late miocene calcareous marine sediments in distinct sedimentary environments of a carbonate platform iblean plateau sicily are compared with each other the nephelinitic cozzo molino diatreme cmd to the east developed in shallow water 0 80 m water depth the alkali basaltic valle guffari seamount vgs to the west grew on a deeper water carbonate ramp 150 200 m water depth we focus on the dominant boundary conditions inferred to have governed depth of magma fragmentation and subaqueous emplacement mechanisms water depth physical nature of host rocks magma composition and inferred differences in initial volatile concentrations there are gross similarities in the composition of the two moderately evolved magmas the low viscosity magmas in both diatremes were laden with xenoliths originating from mantle to lower crustal sites although similar the eastern shallow water cmd was likely more volatile rich with magma fragmented prior to reaching the surface and the surrounding tephra cone was partly emergent the eruptions of the entirely submarine vgs diatreme complex in the deeper water environment were dominated by interaction of soft sediment and alkali basaltic magma or a pre fragmented volatile particle mixture eruption columns were thus strongly damped and the submarine complex never pierced the water surface

olivine basalt and trachyandesite peperites formed at the subsurface surface interface of a semi arid lake an example from the early miocene bigadic basin western turkey abstract miocene successions in western turkey are dominated by lacustrine fluvial and evaporitic sedimentary deposits these deposits include considerable amounts of volcaniclastic detritus derived from numerous ne trending volcanic centres in western turkey as well as in the bigadic region early miocene syn depositional ne trending olivine basalt and trachyandesite bodies that formed as intrusions and lava flows occur within the bigadic borate basin olivine basalts occur as partly emergent intrusions and trachyandesite dykes fed extensive lava flows emplaced in a semi arid lacustrine environment peperites associated with the olivine basalt and trachyandesites appear to display contrasting textural features although all the localities include a large variety of clast morphologies from blocky to fluidal fluidal clasts mainly globular ameboidal and pillow like varieties are widespread in the peperite domains associated with olivine basalts apparently due to large volume sediment fluidisation in contrast fluidal clasts related to trachyandesites are restricted to narrow zones near the margins of the intrusions and have commonly elongate and polyhedral shapes with digitate margins rather than globular and equant varieties blocky and fluidal clasts in the olivine basalt peperite display progressive disintegration suggesting decreasing temperature and increasing viscosity during fragmentation abundance of blocky clasts with respect to fluidal clasts in the trachyandesite peperite indicates that the fluidal emplacement and low volume sediment fluidisation in the early stages were immediately followed by quench fragmentation due to the high viscosity of the magma size texture and abundance of the blocky and fluidal clasts in the olivine basalt and trachyandesite peperites were mainly controlled by sediment fluidisation pulsatory magma injection and magma properties such as composition viscosity vesicularity and size abundance and orientation of phenocrysts variously combining these contrasting features to varying degrees may form diverse juvenile clast shapes in peperitic domains