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

transport capacity of pyroclastic density currents experiments and models of substrate flow interaction 1 one of the more distinctive features of many ignimbrites is the presence of large lithics some greater than meter scale and pumices that have been transported great distances 10 km from the eruptive vent sometimes over steep terrain and expanses of water in many cases these particles have been transported much further than can be explained by aerodynamic forces and ballistic trajectories we examine the forces responsible for transport of large clasts and examine in detail the momentum transfer occurring when particles interact with their boundaries we performed a suite of experiments and numerical simulations to quantify the mass and momentum transfer that occurs when particles interact with a pumice bed substrate and with water substrate two geologically motivated flow end members we find that clasts transported in dilute currents are particularly sensitive to the nature of the boundary and while large particles can skip several times on a water substrate they travel less far than particles that impact pumice bed substrates all else being equal large particles in dense pyroclastic density currents are themselves relatively insensitive to the details of their boundaries however one of the most important ways boundary conditions influence large particles is not through direct interaction but by changing the local concentration of fine particles momentum transfer from fine particles to large particles appears to be required to transport large clasts great distances if initially dense flows become dilute during transport then the transport capacity of large particles in the flow is substantially decreased

thermohydraulic explosions in phreatomagmatic eruptions as evidenced by the comparison between pyroclasts and products from molten fuel coolant interaction experiments 1 thermohydraulic explosions were produced by molten fuel coolant interaction mfci experiments using remelted shoshonitic rocks from vulcano italy the fragmentation history and energy release were recorded the resulting products were recovered and analyzed with the scanning electron microscope fine particles from experiments show shape and surface features that result from melt fragmentation in brittle mode these clasts relate to the thermohydraulic phase of the mfci where most of the mechanical energy is released they are here called active particles the total surface area of such particles is proportional to the energy of the respective explosions other particles from experiments show shape and surface features that result from melt fragmentation in a ductile regime these fragments called passive particles form after the thermohydraulic phase during the expansion phase of the mfci in order to verify thermohydraulic explosions in volcanic eruptions we compared experimental products with samples from phreatomagmatic base surge deposits of vulcano ash particles from the experiments show features similar to those from the deposits suggesting that the experiments reproduced the same fragmentation dynamics to achieve discrimination between active and passive particles we calculated shape parameters from image analysis the mass of active particles in base surge deposits was calculated as the material properties for the natural samples are identical to the experimental ones the energy measurements and calculations of the experiments can be applied for a single phreatomagmatic eruption at vulcano a maximum mechanical energy release of 2 75 1013 j was calculated representing a tnt analogue of 6 5 kt

mechanisms of hydrovolcanic pyroclast formation grain size scanning electron microscopy and experimental studies pyroclasts produced by explosive magma water interactions are of various sizes and shapes data from analysis of over 200 samples of hydrovolcanic ash are interpreted by comparison with experimentally produced ash grain size and scanning electron microscopy sem reveal information on the formation of hydrovolcanic pyroclasts strombolian explosions result from limited water interaction with magma and the pyroclasts produced are dominantly centimeter sized with increasing water interaction hydrovolcanism increases in explosivity to surtseyan and vulcanian activity these eruptions produce millimeter to micron sized pyroclasts the abundance of fine ash 63 m diameter increases from 5 to over 30 percent as water interaction reaches an explosive maximum this maximum occurs with interactions of virtually equal volumes of melt and water five dominant pyroclast shape types determined by sem result from hydrovolcanic fragmentation 1 blocky and equant 2 vesicular and irregular with smooth surfaces 3 moss like and convoluted 4 spherical or drop like and 5 plate like types 1 and 2 dominate pyroclasts greater than 100 m in diameter types 3 and 4 are typical of fine ash type 5 pyroclasts characterize ash less than 100 m in diameter resulting from hydrovolcanic fragmentation after strong vesiculation fragmentation mechanisms observed in experimental melt water interactions result from vapor film generation expansion and collapse fragments of congealed melt are products of several alternative mechanisms including stress wave cavitation detonation waves and fluid instability mixing all result in rapid heat transfer these mechanisms can explain the five observed pyroclast shapes stress wave fracturing cavitation of the melt results from high pressure and temperature gradients at the melt water interface simultaneous brittle fracture and quenching produces type 1 pyroclasts type 2 develops smooth fused surfaces due to turbulent mixing with water after fracture and before quenching fluid instabilities promote turbulent mixing of melt and water and produce fine ash this kind of fragmentation occurs during high energy explosions the increased melt surface area due to fine fragmentation promotes high efficiency heat exchange between the melt and water shapes of resulting pyroclasts are determined by maximum surface area type 3 and surface tension effects type 4 type 5 pyroclasts result from nearly simultaneous vesicle burst and melt water fragmentation

thermoelastic properties of the rotokawa andesite a geothermal reservoir constraint abstract knowledge of the thermal properties of geothermal reservoir rocks is essential to constraining important engineering concerns such as wellbore stability reservoir forecasting and stimulation procedures the thermo mechanical evolution of geological material is also important to assess when considering natural processes such as magmatic dyke propagation contact metamorphism and magma lava emplacement and cooling effects to better constrain these properties in the geothermal reservoir thermal measurements were carried out on core samples from production wells drilled in the rotokawa andesite geothermal reservoir located in the taupo volcanic zone new zealand linear thermal expansion testing thermogravimetric analysis and differential scanning calorimetry were used employing experimental heating rates of 2 5 and 20 c min thermal property analyses can elucidate whether thermal expansion values measured under varied heating and cooling rates are rate dependent and if thermo chemical reactions influence the resultant expansivity measured thermal expansion coefficients of the rotokawa andesite are shown not to be heating rate dependent we have also found that significant thermochemical reactions occur during heating above 500 c resulting in non reversible changes to the thermomechanical properties the combined thermogravimetric calorimetric and thermomechanical analysis allows insight to the reactions occurring and how the thermomechanical properties are affected at high temperature we incorporated results of tensile strength testing on the rotokawa andesite to apply our thermal property measurements to a one dimensional thermal stress model the developed model provides a failure criterion for the rotokawa andesite under thermal stress the importance of this study is to further understand the critical heating and cooling rates at which thermal stress may cause cracking within the rotokawa reservoir thermal cracking in the reservoir can be beneficial in reservoir stimulation procedures but also poses potential risk to wellbore stability so constraining the conditions at which this can occur can be beneficial to resource utilization

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

thermal properties of vesicular rhyolite abstract thermal diffusivity of rhyolite melt and rhyolite foam 70 80 porosity has been measured using the radial heat transfer method cylindrical samples length 50 55 mm diameter 22 mm of rhyolite melt and foam have been derived by heating samples of little glass mountain obsidian using available data on heat capacity and density of rhyolite melt the thermal conductivity of samples has been determined the difference in thermal conductivity between rhyolite melt and foam at igneous temperatures 1000 c is about one order of magnitude the effect of thermal insulation of magmas due to vesiculation and foaming of the top layer is discussed in terms of the data obtained using a simple illustrative model of magma chamber convection

particle water heat transfer during explosive volcanic eruptions 1 thermal interaction between volcanic particles and water during explosive eruptions has been quantified using a numerical heat transfer model for spherical particles the model couples intraparticle conduction with heat transfer from the particle surface by boiling water in order to explore heat loss with time for a range of particle diameters the results are combined with estimates of particle settling times to provide insight into heat removal during eruption from samples of volcanic particles produced by explosive eruption heat removal is restricted by resistance to heat transfer from the volcanic particles with intraparticle thermal conduction important for large particles and surface cooling by boiling dominating for small particles in most cases volcanic particles approach thermal equilibrium with the surrounding fluid during an explosive eruption application of the results to a sample from the gjalp 1996 iceland eruption indicates that relative to 0 c 70 80 of the heat is transferred from the particles to boiling water during the settling time before burial in the stratigraphic succession the implication is that for subglacial explosive eruptions much of the heat content of the magma is coupled into melting ice extremely rapidly if all particles of the gjalp 1996 deposit were cooled to the local boiling point by the end of the eruption then approximately 78 of the initial heat content was removed from the erupting magma during the eruption this is consistent with calorimetric calculations based on volumes of ice melted during and after the eruption

in situ production of ash in pyroclastic flows 1 abrasion and comminution of pumice clasts during the propagation of pyroclastic flows have long been recognized as a potential source for the enhanced production of volcanic ash however their relative importance has eluded quantification the amount of ash produced in situ can potentially affect runout distance deposit sorting the volume of ash introduced in the upper atmosphere and internal pore pressure we conduct a series of laboratory experiments on the collisional and frictional production of ash that may occur during different regimes of pyroclastic flow transport ash produced in these experiments is predominately 10 100 microns in size and has similar morphology to tephra fall ash from plinian events we find that collisional ash production rates are proportional to the square of impact velocity frictional ash production rates are a linear function of the velocity of the basal particle enriched bed load region of these flows using these laboratory experiments we develop a subgrid model for ash production that can be included in analytical and multiphase numerical procedures to estimate the total volume of ash produced during transport we find that for most flow conditions 10 20 of the initial clasts comminute into ash with the percentage increasing as a function of initial flow energy most of the ash is produced in the high energy regions near the flow inlet although flow acceleration on steep slopes can produce ash far from the vent on level terrain collisionally and frictionally produced ash generates gravity currents that detach from the main flow and can more than double the effective runout distance of these flows ash produced at the frictional base of the flow and in the collisional upper regions of the flow can be redistributed through the entirety of the flow although frictionally produced ash accumulates preferentially near its source in the bed load flows that descend steep slopes produce the majority of their ash in the collisonally dominant flow head and flow snouts likely develop subangular to rounded pumice during this process

subaqueous eruption and emplacement of the shinjima pumice shinjima moeshima island kagoshima bay sw japan abstract the shinjima pumice is a fines depleted pumice lapilli tuff emplaced several thousands years ago at about 100 140 m below sea level this 40 m thick deposit comprises many poorly defined flow units which are 1 10 m thick diffusely stratified and showing upward coarsening of pumice clasts with a sharp to transitional base parallel to wavy diffuse stratifications are commonly represented by alignment of pumice clasts especially in the lower half of the flow units pumice clasts of block to coarse lapilli size commonly have thermal contraction cracks best developed on the surfaces demonstrating that they were hot but cooled down to the ambient temperatures prior to their emplacement these features are suggestive of the direct origin of the shinjima pumice from subaqueous eruptions a theoretical consideration on the behavior of subaqueous eruption plumes and hot and cold pumice clasts suggests that subaqueous eruption plumes commonly collapse by turbulent mixing with the ambient water and are transformed into water logged mass flows

identifying magma water interaction from the surface features of ash particles the deposits from explosive volcanic eruptions those eruptions that release mechanical energy over a short time span1 are characterized by an abundance of volcanic ash2 3 this ash is produced by fragmentation of the magma driving the eruption and by fragmenting and ejecting parts of the pre existing crust host rocks interactions between rising magma and the hydrosphere oceans lakes and ground water play an important role in explosive volcanism4 5 because of the unique thermodynamic properties of water that allow it to very effectively convert thermal into mechanical energy although the relative proportion of magma to host rock fragments is well preserved in the pyroclastic rocks deposited by such eruptions it has remained difficult to quantitatively assess the interaction of magma with liquid water from the analysis of pyroclastic deposits2 3 4 5 here we report the results of a study of natural pyroclastic sequences combined with scaled laboratory experiments we find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water the abundance of such ash grains can then be related to the water magma mass ratios during their interaction

contrasting mechanisms of magma fragmentation during coeval magmatic and hydromagmatic activity the hverfjall fires fissure eruption iceland growing evidence for significant magmatic vesiculation prior to magma water interaction mwi has brought into question the use of diagnostic features such as low vesicularities and blocky morphologies to identify hydromagmatic pyroclasts we address this question by quantifying co variations in particle size shape and texture in both magmatic and hydromagmatic deposits from the hverfjall fires fissure eruption iceland overlapping vesicularity and bubble number density distributions measured in rapidly quenched magmatic and hydromagmatic pyroclasts indicate a shared initial history of bubble nucleation and growth with substantial vesiculation prior to mwi hydromagmatic fragmentation occurred principally by brittle mechanisms where the length scale and geometry of fracturing was controlled by the bubble population this suggests that the elevated fragmentation efficiency of hydromagmatic deposits is driven at least in part by brittle disintegration of vesicular pyroclasts due to high thermal stress generated during rapid cooling in this way the shape and size distributions of hydromagmatic pyroclasts both critical input parameters for ash dispersion models are strongly influenced by the dynamics of vesiculation prior to mwi this result underlines the need to analyse multiple grain size fractions to characterise the balance between magmatic and hydromagmatic processes during the hverfjall fires eruption the external water supply was sufficient to maintain mwi throughout the eruption with no evidence for progressive exhaustion of a water reservoir we suggest that both the longevity and the spatial distribution of mwi were determined by the pre existing regional hydrology and represent continuous interaction between a propagating dike and a strong groundwater flow system hosted within permeable basalt lavas

the fracture behaviour of volcanic glass and relevance to quench fragmentation during formation of hyaloclastite and phreatomagmatism quench fragmentation is a non explosive process that occurs when molten magma is super cooled to glass upon contact with ambient water this occurs when coherent lavas are erupted subaqueously when they flow into water when magma intrudes into water saturated sediments and when magma and water interact explosively during phreatomagmatism quench fragmentation also occurs alongside explosive phreatomagmatic activity although products of quench fragmentation hyaloclastite sensu stricto have been discussed qualitatively in the volcanological literature compared to explosive fragmentation processes very little is known about the exact dynamics of quench fragmentation of magma and how this relates to the rheology and physical properties of volcanic glass based on literature from materials engineering we present a detailed review of the processes by which glass forms the properties of glass and the fracture mechanics that cause it to fragment non explosively we also consider how this can be applied to understanding the dynamics behind the volcanological processes of in situ glass fragmentation during quenching in wet environments and phreatomagmatism important parameters for the occurrence of quench fragmentation are the temperature difference between the magma and the ambient water and how much the ambient water is superheated above its leidenfrost temperature the geometry of the lava or magma intrusion the thermal conductivity and the thermal expansion are also of great importance the resistance of the magma against fragmentation can be increased with the presence of crystals provided the thermal expansion of the crystals does not greatly exceed that of the glass vesicles have the opposite effect unless the magma is highly vesicular this overview then provides a solid basis for further quantitative study of quench fragmentation and hyaloclastite formation

effects of thermal quenching on mechanical properties of pyroclasts contact with water can promote magma fragmentation obsidian chips and glass spheres typically crack when quenched vesicular pyroclasts are made of glass so thermal quenching by water may damage them if water enters eruption columns or if pyroclastic density currents interact with water hot pumice can be quenched we performed a set of experiments on air fall pumice from medicine lake california we made quenched samples by heating natural clasts to 600 c quenching them in water at 21 c drying them at 105 c and then cooling them to room temperature we compare these samples with untreated air fall pumice from the same deposit hereafter referred to as regular pumice we tested whether quenched pumice would 1 shatter more easily in collisions and 2 abrade faster we also tested whether individual clasts lose mass upon quenching and whether they increase in effective wet density two measurements which may help characterize the magnitude of clast damage during quenching we also compare pre quenching and post quenching textures using x ray microtomography xrt images results from collision experiments show no clear difference between quenched pumice and regular pumice quenched pumice abraded faster than regular pumice on average 0 3 of mass may have been lost during quenching effective wet density increased 1 5 on average as measured after 5 minutes of immersion in water overall we find modest differences between quenched pumice and regular pumice in experiments and measurements the experimental results imply that quenching may damage small parts of a clast but tends not to cause cracks that propagate easily through the clast post quenching xrt imaging shows no obvious change in clast texture this is in stark contrast to non vesicular glass that develops large cracks on quenching we present four factors that explain why pumice is resistant to damage from thermal quenching thin glass films experience lower transient thermal stresses many internal surfaces are initially vapor cooled vesicles can arrest cracks and cracks from thermal quenching may not occur in the locations most susceptible to fracture in later collisions

velocity profile in shallow coastal waters in a series of field measurements the mean velocity profiles were measured during the acceleration and deceleration phases of tidal currents off the east and south coasts of england salinity temperature profiles were also measured the sites have simple geometries and the beds were covered with sand the measured velocity profiles consist of an outer region encompassing 90 of the boundary layer thickness an inner region adjacent to the bed and an overlap region between the outer and inner regions the velocity profiles in the outer and overlap regions obey the defect law and the usual log law respectively the coefficient of the skin friction was high mainly due to bed forms

statistical analysis of textural data from complex pyroclastic sequences implications for fragmentation processes of the agnano monte spina tephra 4 1 ka phlegraean fields southern italy the agnano monte spina eruption 4 1 ka generated pyroclastic deposits with complex internal stratigraphy that reflects variations in eruptive style to obtain constraints on the fragmentation processes we analysed grain size and scanning electron microscopy sem data by means of multivariate statistical techniques of the cluster and factor analysis types the results allow the identification of end member deposits related to either pure magmatic activity or pure phreatomagmatic activity in addition some deposits show evidence of the contemporaneous operation of both end member fragmentation modes the presence of the two contrasting fragmentation processes during the various phases of explosive activity is tentatively interpreted to be a function in inhomogeneities in gas exsolution processes within the magma column that feeds the eruption

ash from the eyjafjallajokull eruption iceland fragmentation processes and aerodynamic behavior 1 the fragmentation process and aerodynamic behavior of ash from the eyjafjallajokull eruption of 2010 are investigated by combining grain size scanning electron microscopy sem and quantitative particle morphology ash samples were collected on land in iceland at 3 55 km distance from the volcanic vent and represent various phases of the pulsating eruption the grain size is fine even for deposits close to the vent suggesting that the parent particle population at fragmentation consisted of a substantial amount of fine ash sem investigation reveals that ash produced during the first phase of the eruption consists of juvenile glass particles showing key features of magma water interaction suggesting that phreatomagmatism played a major role in the fragmentation of a vesicle poor magma in the last phase of the eruption fragmentation was purely magmatic and resulted from stress induced reaction of a microvesicular fragile melt the shape of ash as determined by quantitative morphology analysis is highly irregular rendering the settling velocity quite low this makes transportation by wind much easier than for other more regularly shaped particles of sedimentary origin we conclude that the combination of magma s fine brittle fragmentation and irregular particle shape was the main factor in the extensive atmospheric circulation of ash from the mildly energetic eyjafjallajokull eruption

the influence of conduit processes on changes in style of basaltic plinian eruptions tarawera 1886 and etna 122 bc basaltic volcanism is most typically thought to produce effusion of lava with the most explosive manifestations ranging from mild strombolian activity to more energetic fire fountain eruptions however some basaltic eruptions are now recognized as extremely violent i e generating widespread phreatomagmatic subplinian and plinian fall deposits we focus here on the influence of conduit processes especially partial open system degassing in triggering abrupt changes in style and intensity that occurred during two examples of basaltic plinian volcanism we use the 1886 eruption of tarawera new zealand the youngest known basaltic plinian eruption and the only one for which there are detailed written eyewitness accounts and the well documented 122 bc eruption of mount etna italy and present new grain size and vesicularity data from the proximal deposits these data show that even during extremely powerful basaltic eruptions conduit processes play a critical role in modifying the form of the eruptions even with very high discharge and presumably ascent rates partial open system behaviour of basaltic melts becomes a critical factor that leads to development of domains of largely stagnant and outgassed melt that restricts the effective radius of the conduit the exact path taken in the waning stages of the eruptions varied in response to factors which included conduit geometry efficiency and extent of outgassing and availability of ground water but a relatively abrupt cessation to sustained high intensity discharge was an inevitable consequence of the degassing processes

charcoal reflectance as a proxy for the emplacement temperature of pyroclastic flow deposits hot pyroclastic flow deposits often entomb and preserve vegetation as charcoal when studied in polished section this charcoal is highly reflective novel data from experimentally charred woods demonstrate that reflectance increases with both temperature and time at temperatures above 250 c reflectance rises rapidly for the first hour effectively stabilizing after 4 h for temperatures below 400 c however for higher temperatures reflectance only stabilizes after 24 h charcoalified woods from block and ash flow deposits generated by the soufriere hills volcano in montserrat have yielded interpreted deposit temperatures based on reflectance data of 325 525 c these temperatures compare favorably with directly measured data 365 640 c from the same deposits indicating that charcoal reflectance is useful as a temperature proxy for ancient pyroclastic flow deposits particularly where magnetic or mineral data are absent for this purpose however caution should be exercised as only a minimum temperature can be inferred where the heating duration of the deposit is unknown unlike magnetic or mineral data temperature data from charcoalified woods can be obtained from reworked deposits providing a valuable means of validating observations made about the style of eruption of volcanoes in ancient settings

granular disruption during explosive volcanic eruptions volcanic eruptions can inject hazardous ash clouds into the atmosphere numerical simulations and experiments on volcanic rock samples show that clasts initially formed deep in the volcanic conduit break up during collisions in the conduit thus generating fine grained clouds of ash

breaking news on the formation of volcanic ash fracture dynamics in silicate glass abstract in explosive volcanic eruptions magmatic melts behave like brittle solids under rapid loading volcanic ash particles predominantly are generated by brittle fragmentation induced within pre stressed magma in volcanic conduits here we present straightforward measurements of fracture area velocity i e surface generation rates in analog materials under volcanic time and deformation rates using a high resolution high speed camera at up to 2 5 million frames per second surface generation rates are directly linked to energy dissipation and can be related to pyroclast formation during explosive volcanism according to our findings pre existing stress fields play a crucial role for the evolution of cracks control the dynamics of fracture area growths during fragmentation and thus strongly modify the production of volcanic ash

vertical segregation in granular mass flows a shear cell study 1 non fluidised dry granular mass flows are obtained with rock fragments located on a rough rotating disk in these flows that develop a quasi rigid upper layer and a basal layer of colliding particles dense clasts sink whereas light ones rise when surrounded by particles with intermediate density our experiments demonstrate that the presence of a quasi rigid upper layer in granular mass flows does not prevent vertical segregation and that the formation of coarse tail grading in pyroclastic flows does not require fluidising gases high speed videos reveal that vertical segregation in granular mass flow of rock fragments is generated by inertia differences between segregating clasts and matrix when they are both pushed upward by collisions with the basal layer coarse tail grading occurs because the average segregation velocity of smaller clasts is smaller than that of larger clasts

pumice pumice collisions and the effect of the impact angle 3 in nature particles have irregular shapes and their collisions are not necessarily normal to surfaces thus we present here the studies of oblique collisions of pumice cylinders on flat pumice surfaces cylinders were used to increase the complexity of the particle shape compared to that of a sphere the purpose of these experiments is to understand the effect of the impact angle on the rebound features and provide an example of their variability that can be useful in modelling pumice pumice collisions in geophysical flows the rebound features are the rebound angles the ratios of the components of velocities and the energy losses our results reveal a complexity which suggests that the description of pumice pumice impacts using a constant coefficient of restitution is an oversimplification 4 here we do not refer to the coefficient of restitution also because it applies to collisions where the energy losses are only due to plastic deformations and vibrations in geophysical flows the collisions are more complex because of for example erosion shattering and comminution of the rock fragments the coefficient of restitution e purports to describe the degree of plasticity in collisions of two bodies and is generally defined as the ratio of the final to initial components of the relative velocities normal to the contact surface goldsmith 2001 this coefficient can be measured by dropping a non rotating particle onto the horizontal surface of a large rigid body if the particle has been dropped from the height h1 and rebounds to the height h2 then e is equal to ffiffiffiffiffiffiffiffiffiffiffiffi

physical weathering and modification of a rhyolitic hyaloclastite in iceland fragmental volcanic glass or hyaloclastite is a common glaciovolcanic eruption product that is formed in large abundance during basaltic andesitic and rhyolitic subglacial eruptions the physical weathering of rhyolitic hyaloclastites differs notably from basaltic hyaloclastites due to differences in cementation and edifice consolidation as rhyolitic glasses are also much rarer comparatively little is known about their physical weathering and fracturing characteristics in the presented study we provide a process oriented analysis of the physical modification of subglacially erupted rhyolitic hyaloclastites from the blahnukur edifice in torfajokull iceland frost weathering experiments were performed to determine how vesicular glass particles fragment to finer particle sizes the surficial porosity of the glass drives such frost weathering through the process of pore pressurisation and was quantified using high pressure mercury intrusion uniaxial compression experiments were carried out to understand how the glass structure responds to the application of external stress the observed fracturing in both experimental treatments was found to adhere to fractal statistics which allowed the compression experiments to be used in conjunction with the frost weathering experiments for inferring the fracturing characteristics of rhyolitic volcanic glasses transport processes by wind and gravity were simulated by long duration abrasion experiments in rock tumblers through granular avalanching but these low energy particle interactions were not found to significantly abrade particles a notable result from our fragmentation experiments was the production of 10 m particles this size range is considered respirable and illustrates how physical weathering can continuously create potentially harmful ash textures a process which is often overlooked in health hazard assessments after volcanic eruptions fragmentation by post eruptive weathering can lead to overestimations of the fine ash fraction produced by syneruptive fragmentation and granulometric studies therefore need to be appreciative of the effects of such secondary fracturing processes

garnet compositions and their use as indicators of peraluminous granitoid petrogenesis southeastern arabian shield garnet an uncommon accessory mineral in igneous rocks occurs in seven small peraluminous granitoid plutons in the southeastern arabian shield textural equilibrium between garnet and other host granitoid minerals indicates that the garnets crystallized from their host magmas compositions of the garnets form three groups that reflect host granitoid compositions which in turn reflect source compositions and tectonic regimes in which the host magmas were generated garnets from the seven plutons have almandine rich cores and spessartine rich rims this reverse zoning depicts host magma compositional evolution i e rimward spessartine enrichment resulted from progressive host magma manganese enrichment the garnets are heavy rare earth element enriched lu la n ranges from 13 to 355 and one of the garnets contains spectacularly elevated abundances of y ta th u zn zr hf sn and nb involvement of garnets with these trace element characteristics in magma genesis or evolution can have dramatic effects on trace element signatures of the resulting magmas other researchers suggest that mn enriched magmas are most conducive to garnet nucleation although the garnetiferous granitoids discussed here are slightly mn enriched other genetically similar peraluminous arabian granitoids lack garnet mn enrichment alone does not guarantee garnet nucleation the presence of excess alumina in the magma may be a prerequisite for garnet nucleation

authigenic mineral texture in submarine 1979 basalt drill core surtsey volcano iceland author s jackson md couper s stan cv ivarsson m czabaj mw tamura n parkinson d miyagi lm moore jg abstract 2019 american geophysical union all rights reserved micrometer scale maps of authigenic microstructures in submarine basaltic tuff from a 1979 surtsey volcano iceland drill core acquired 15 years after eruptions terminated describe the initial alteration of oceanic basalt in a low temperature hydrothermal system an integrative investigative approach uses synchrotron source x ray microdiffraction microfluoresence micro computed tomography and scanning transmission electron microscopy coupled with raman spectroscopy to create finely resolved spatial frameworks that record a continuum of alteration in glass and olivine microanalytical maps of vesicular and fractured lapilli in specimens from 157 1 137 9 and 102 6 m depths and borehole temperatures of 83 93 9 and 141 3 c measured in 1980 respectively describe the production of nanocrystalline clay mineral zeolites and al tobermorite in diverse microenvironments irregular alteration fronts at 157 1 m depth resemble microchannels associated with biological activity in older basalts by contrast linear microstructures with little resemblance to previously described alteration features have nanocrystalline clay mineral nontronite and zeolite amicite texture the crystallographic preferred orientation rotates around an axis parallel to the linear feature raman spectra indicating degraded and poorly ordered carbonaceous matter of possible biological origin are associated with nanocrystalline clay mineral in a crystallographically oriented linear microstructure in altered olivine at 102 6 m and with subcircular nanoscale cavities in altered glass at 137 9 m depth although evidence for biotic processes is inconclusive the integrated analyses describe the complex organization of previously unrecognized mineral texture in very young basalt they provide a foundational mineralogical reference for longitudinal time lapse characterizations of palagonitized basalt in oceanic environments

stress induced brittle fragmentation of magmatic melts theory and experiments 1 the release of kinetic energy during explosive volcanic eruptions is a key parameter for hazard assessment and civil defense the explosive production of volcanic ash by intensive fragmentation of magma and host rocks represents a substantial part of this energy for cases of explosive eruption where predominantly host rock was fragmented phreatomagmatic eruptions to form the major part of volcanic ash rock mechanical parameters could be measured and fragmentation energies assigned in cases where most of the produced ash is of juvenile origin magmatic eruptions a general method for the determination of fragmentation energy is still lacking in this article we introduce a thermodynamic approach that relates grain size data of the produced ash deposits to shear rates acting during the deformation of magma with the use of a standardized fragmentation experiment the physical parameters needed to determine the specific fragmentation energy and deformation history were measured the experiment was calibrated and tested with two case histories of the campi flegrei volcanic field southern italy both eruptions are classified as most probable worst case scenarios during the next period of activity to be expected within the next 10 100 years using the experimentally determined specific fragmentation energies the total mass of produced ash of each eruption and assuming an energy dissipation as observed in the experiments the total kinetic energy release of the worst case campi flegrei eruptive events to come were calculated with 25 and 40 kt tnt equivalent