the december 2002 july 2003 effusive event at stromboli volcano italy insights into the shallow plumbing system by petrochemical studies abstract on 28 december 2002 the persistent strombolian activity at stromboli was interrupted by the sudden onset of lava emission onto the sciara del fuoco slope a horseshoe shaped depression on the nw flank of the volcano the effusive episode went on until 22 july 2003 and produced a cumulative volume of lavas of 11 106 m3 ranking the event as the largest occurred in the past 30 years the eruptive vents were mainly located in the ne sector of the sciara del fuoco depression at an elevation of 550 600 m a s l on 30 december the eastern portion of the sciara del fuoco collapsed producing a tsunamigenic landslide on 5 april 2003 a paroxysmal eruption occurred at the summit craters during which crystal poor pumiceous products were emitted the paroxysm did not interrupt the lava emission the strombolian activity at the summit craters gradually resumed starting from march 2003 and fully recovered by the end of july periodic sampling of the lava at the active vents was carried out during the entire effusive event all the analysed samples are shoshonitic basalts sio2 48 5 50 4 wt k2o 2 1 2 4 wt in the range of composition observed in the products erupted during the past 20 years they bear about 50 vol zoned crystals of plagioclase an90 60 diopside augite and olivine fo70 73 in a compositionally homogeneous shoshonitic groundmass bulk rock major and trace element contents measured with different methodologies at different laboratories show only minor variations sr and nd isotope ratios are close to those of the crystal rich scoriae erupted in the previous years despite of small compositional variations related to the emptying of the zoned topmost portion of the conduit the data show that the switch from strombolian explosive to effusive activity is not associated with changes of the textures and composition of the erupted products slight but somehow systematic variation of trace elements and isotope ratios between products erupted before and after the 5 april eruption are likely accounted by limited mixing between the fresh volatile rich crystal poor magma erupted as pumice during the paroxysm and the volatile poor crystal rich magma feeding the lava flow the uniform composition of the erupted lava indicates the presence of a large volume of well mixed crystal rich homogeneous magma residing in the shallow plumbing system of the volcano two possible trigger mechanism of the effusive event are here proposed i a discrete input of fresh magma into the lower part of the shallow magmatic system occurred some months before the eruption and was followed by crystallisation degassing and mixing with the crystal rich shallow magma which re homogenised the system these processes eventually led to the rise of the magma at a higher level and failure of the conduit walls ii the onset of the effusion may represent the consequence of a gradual rise of the magma level in the conduits occurred in the past two decades the process of progressive refilling initiated after the 1985 effusive eruption ultimately culminated on 28 december 2002 with the failure of the conduit wall and the opening of vents 100 150 m below the summit craters

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

rheology of porous volcanic materials high temperature experimentation under controlled water pressure abstract we present a suite of 21 high temperature uniaxial deformation experiments performed on 25 by 50 mm unjacketed cores of porous 0 8 sintered rhyolitic ash the experiments were performed at both atmospheric dry and elevated water pressure conditions wet experiments used a constant displacement rate of 2 5 10 6 m s 1 corresponding to a strain rate o of 5 10 5 s 1 a single experiment was run at 2 5 10 5 m s 1 o 5 10 4 s 1 dry experiments were conducted mainly at 900 c but also included a suite of lower temperature experiments at 850 800 and 750 c wet experiments were performed at 650 c under water pressures of 1 2 5 and 5 mpa and at a fixed p h 2 o of 2 5 mpa for temperatures of 385 450 and 550 c during deformation strain is manifest by shortening of the cores reduction of porosity flattening of ash particles and radial increase of the cores the continuous reduction of porosity leads to a dynamic transient strain dependent rheology and requires strain to be partitioned between a volume porosity loss and a shear radial increase component these data demonstrate the effect of porosity on the rheology of dry and hydrous melts the effect of increasing porosity is to expand the window for ductile deformation for dry melts by delaying the onset of brittle deformation by 50 c 875 c to 825 c the effect is more pronounced in hydrous melts 0 67 0 78 wt h 2 o where the ductile to brittle transition is depressed by 140 to 150 c increasing water pressure also delays the onset of strain hardening due to compaction driven porosity reduction these rheological data are pertinent to any volcanic processes involving high temperature porous magmas e g magma flow in conduits welding of pyroclastic materials

rheology of bimodal crystals suspensions results from analogue experiments and implications for magma ascent 1 the effect of crystal size of bimodal suspensions on rheology of magmas at strain rates between 0 and 1 s 1 is studied suspensions consist of silicon oil and two populations of natural crystals with size 63 125 and 250 500 m mixed in different proportions the total solid fraction of the mixtures is between 0 25 and 0 5 at 0 4 finer coarser and bimodal suspensions display comparable viscosities at 0 4 the viscosity of the bimodal suspensions is larger than that of the unimodal ones the bimodal suspension made mainly of finer crystals shows a stronger increase of viscosity with the addition of finer crystals to a suspension of coarser ones produces a more pronounced increase of viscosity with respect to suspensions of coarse or fine crystals alone and of finer crystals with added coarser ones the bimodal suspensions of coarser crystals develops yield stress at 0 25 the others at 0 4 it is modeled the ascent velocity in a 20 m wide dike of magmas with bimodal and unimodal populations of crystals of different size for 0 4 the crystal size has not effects on the ascent velocity of magmas for 0 4 the velocity of a magma with growing phenocrystals decreases as increases less than that of a magma with forming microlites and more of a magma with microlites and growing phenocrystals a magma with phenocrystals and forming microlites has the lowest ascent velocity

resistivity structure of the upper crust in iceland the results of numerous resistivity soundings from all parts of iceland are analyzed the resistivity and the p wave velocity of the uppermost kilometer in the crust show a strong correlation with the geological structure of iceland by estimating porosity from p wave velocity archie s law is found not to be valid in general the temperature dependence of nine water saturated basaltic rock samples was investigated in a laboratory showing stronger temperature dependence than expected from pore fluid conduction these two facts suggest that interface conduction is the most important conduction mechanism a relation between bulk resistivity fracture porosity pore fluid resistivity and temperature is established comparison of regional bulk resistivity with different zeolite zones shows that the resistivity is mainly a function of the maximum depth of burial of the lava pile emphasizing the importance of clay minerals and zeolites for the measured bulk resistivity

the influence of crystal size distributions on the rheology of magmas new insights from analog experiments this study examines the influence of particle size distributions on the rheology of particle suspensions by using analogue experiments with spherical glass beads in silicone oil as magma equivalent the analyses of 274 individual particle bearing suspensions of varying modality uni bi tri and tetramodality as well as of polymodal suspensions with specific defined skewness and variance are the first data set of its kind and provide important insights in the relationship between the solid particles of a suspension and its rheological behaviour since the relationship between the rheology of particle bearing suspensions and its maximum packing fraction m is well established by several theoretical models the results of the analogue experiments of this study reveal that the polydispersity exerts the largest influence on m consequently the estimation of the polydispersity of a particle size distribution is essential for estimating the viscosity of that given suspension

role of conduit shear on ascent of the crystal rich magma feeding the 800 year b p plinian eruption of quilotoa volcano ecuador we have characterized pumice products belonging to the climactic phase of the 800 year b p quilotoa eruption bulk rock compositions petrography mineral and glass chemistry and textural investigations were performed on the three end member pumice types namely white gray and mingled pumices all the investigated pumice clasts are dacites characterized by the same bulk rock composition and mineralogical assemblage but glass compositions and bulk textures change according to different pumice types white pumice has higher crystallinity 48 wt abundant euhedral pheno microphenocrysts no groundmass microlites the most evolved glass compositions 74 78 wt sio2 and heterogeneous vesicle populations marked by deformed and highly coalesced vesicles with thin walls gray pumice exhibits lower crystallinity 29 36 wt abundant broken and or resorbed crystals ubiquitous groundmass phenocryst fragments and microlites the widest range of glass compositions 69 78 wt sio2 and quite homogeneous poorly deformed and coalesced vesicles with thicker walls mingled pumices are characterized by the alternation of bands or patches with white and gray pumice compositional and textural characteristics we attribute heterogeneities in glass compositions and crystal and vesicle textures to processes occurring within volcanic conduits as magma is ascending to the surface in particular the above observations and results are consistent with an origin of a gray magma by heating of the original white magma in a strongly sheared region of the conduit because of a mechanism of viscous dissipation and crystal grinding and resorption at the conduit walls the less viscous gray magma therefore would enable the onset and preservation of a high mass flux of the eruption otherwise difficult to explain for highly viscous crystal rich dacitic magmas

effects of crystal shape and size modality on magma rheology erupting magma often contains crystals over a wide range of sizes and shapes potentially affecting magma viscosity over many orders of magnitude a robust relation between viscosity and the modality of crystal sizes and shapes remains lacking principally because of the dimensional complexity and size of the governing parameter space we have performed a suite of shear viscosity measurements on liquid particle suspensions of dynamical similarity to crystal bearing magma our experiments encompass five suspension types each consisting of unique mixtures of two different particle sizes and shapes the experiments span two orthogonal subspaces of particle concentration as well as particle size and shape for each suspension type thereby providing insight into the topology of parameter space for each suspension type we determined the dry maximum packing fraction and measured shear rates across a range of applied shear stresses the results were fitted using a herschel bulkley model and augment existing predictive capabilities we demonstrate that our results are consistent with previous work including friction based constitutive laws for granular materials we conclude that predictions for ascent rates of crystal rich magmas must take the shear rate dependence of viscosity into account shear rate dependence depends first and foremost on the volume fraction of crystals relative to the maximum packing fraction which in turn depends on crystal size and shape distribution

magma dynamics during the 2007 stromboli eruption aeolian islands italy mineralogical geochemical and isotopic data abstract after the 6 month long effusive event of 2002 2003 a new lava effusion occurred at stromboli between 27 february and 2 april 2007 despite the different durations approximately the same volume of magma was emitted in both eruptions in the order of 107 m3 a paroxysmal eruption occurred at the summit craters in both the 2002 2003 and 2007 episodes during which a significant amount of low porphyritic lp volatile rich magma was erupted in both cases the paroxysm did not interrupt the lava emission here we present compositional data including texture mineralogy chemistry and sr and nd isotope ratios of bulk rock groundmass and separated minerals of lavas erupted in 2007 together with chemistry and sr and nd isotope composition of the pumices emitted during the 15 march paroxysm as a whole the lavas have the same texture and chemistry that characterize the highly porphyritic hp products usually erupted at stromboli during normal strombolian activity and effusive events compared to the previous hp products the 2007 lavas show minor but systematic mineralogical and isotopic variations which are consistent with a modest increase of the magma supply rate of the volcano compositional variations during the entire duration of the event are very modest glass chemistry changes in lavas erupted in the second half of march can be explained by the minor mixing between the volatile rich lp magma rising through the shallow magmatic system during the 15 march paroxysm and the degassed residing hp magma a first conclusion of this study is that there is no compositional evidence supporting major changes in the magma dynamics of the volcano accompanying the effusive activity as also suggested for the 2002 2003 event the activity of stromboli is controlled by a steady state feeding system in which refilling mixing degassing and crystallization at shallow level continuously operate with modest oscillations in the magma supply rate switching between normal strombolian and effusive activity is related to periods of relatively more vigorous refilling of the shallow system leading to progressive pressure increase in the upper conduits associated with only minor compositional variations in the erupted products

high temperature deformation of volcanic materials in the presence of water we describe an experimental apparatus used to perform deformation experiments relevant to the volcanological sciences the apparatus supports low load high temperature deformation experiments under dry and wet conditions on natural and synthetic samples the experiments recover the transient rheology of complex melt porosity solids volcanic materials during uniaxial deformation the key component to this apparatus is a steel cell designed for high temperature deformation experiments under controlled water pressure experiments are run under constant displacement rates or constant loads the range of accessible experimental conditions include 25 1100 c load stresses 0 to 150 mpa strain rates 10 6 to 10 2 1 s and fluid pressures 0 150 mpa the apparatus is calibrated against standard values of viscosity using constant load experiments on cores of nist nbs 717a borosilicate glass we also report results of constant displacement rate 10 6 m s experiments on porous 70 sintered cores of ash from the rattlesnake tuff the cores of volcanic ash were deformed in experiments under ambient dry and elevated water pressures wet dry experiments at 870 c show an increase in effective viscosity 10 9 5 to 10 10 4 pa s with increasing strain 30 due to porosity reduction during compaction experiments under 1 3 mpa p h 2 o recover lower values of apparent viscosity 10 9 2 to 10 9 4 pa s despite being run at lower temperatures 640 665 c the wet experiments also do not show a rise in viscosity with increased strain decreasing porosity as observed in dry experiments rather the presence of an h 2 o fluid phase expands the window of viscous deformation and delays the onset of strain hardening that normally accompanies porosity reduction

in situ thermal characterization of cooling crystallizing lavas during rheology measurements and implications for lava flow emplacement abstract transport properties of natural silicate melts at super liquidus temperatures are reasonably well understood however migration and transport of silicate melts in the earth s crust and at its surface generally occur at sub liquidus temperatures and in settings where the melts undergo crystallization under various cooling and or decompression conditions in such dynamic situations the occurrence of processes such as the release of latent heat during phase changes viscous heating thermal advection and inertia and changing heat capacity all represent potential influences on the state and thereby on the physico chemical behavior of the system to date rheological data at sub liquidus temperatures are scarce and cooling rate dependent disequilibrium rheological data are virtually absent in fact no in situ thermal characterization of liquid or multiphase mixtures during rheological experiments under either static or dynamic thermal conditions has been presented to date here we describe a new experimental setup for in situ thermal characterization of cooling crystallizing lavas during viscosity measurement at temperatures up to 1600 c we use this device to recover in situ real time observations of the combined rheological and thermal evolution of natural re melted lava samples during the transient disequilibrium conditions characteristic of lava flows and shallow crustal magma migration and storage systems in nature we present the calibration procedure and the method employed to recover the thermal evolution of an experimental sample during flow in varying shear regimes assess the experimental uncertainty and show the ability of the apparatus to measure the release of latent heat of crystallization during transient rheological experiments we further report the results from a first experimental study on the rheological and thermal evolution of a basaltic lava undergoing continuous cooling at a series of different cooling rates and discuss the implications of the results for magma migration and lava flow emplacement

the effect of water on the viscosity of a haplogranitic melt under p t x conditions relevant to silicic volcanism the viscosities of hydrous haplogranitic melts synthesized by hydrothermal fusion at 2 kbar pressure and 800 to 1040 c have been measured at temperatures just above the glass transition and at a pressure of 1 bar using micropenetration techniques the micropenetration viscometry has been performed in the viscosity range of 109 pa s to 1012 pa s the samples ranged in water content from 0 4 to 3 5 wt for samples with up to 2 5 wt h2o the water contents have been determined using infrared spectroscopy obtained before and after each viscometry experiment to be constant over the duration of the measurements above this water content a measurable loss of water occurs during the viscometry the viscosity data illustrate an extremely nonlinear decrease in viscosity with added water the viscosity drops drastically with the addition of 0 5 wt of water and then shallows out at water contents of 2 wt an additional viscosity datum point obtained from the analysis of fluid inclusions in a water saturated hpg8 confirms a near invariance of the viscosity with the addition of water between 2 and 6 wt these measurements may be compared directly with the data of hess et al 1995 in press for the effects of excess alkali and alkaline earth oxides on the viscosity of hpg8 also obtained at 1 bar the viscosity of the melts compared on an equivalent molar basis increases in the order h2o li2o na2o k2o rb2o cs2o bao sro cao mgo beo the extraordinary decrease in melt viscosity with added water is poorly reproduced by the calculation scheme of shaw 1972 for the range of water contents investigated here the speciation of water in the quenched glasses can be used to quantify the dependence of the viscosity on hydroxyl content considering only the hydroxyl groups as active fluidizers in the hydrous melts the nonlinearity of the viscosity decrease and the difference with the effects of the alkali oxides becomes larger consequences for degassing calcalkaline rhyolite are discussed

crystalmom a new model for the evolution of crystal size distributions in magmas with the quadrature based method of moments nucleation and growth of crystals and the resulting crystal size distribution play a fundamental role in controlling the physical properties of magmas and consequently the dynamics of the eruptions in the past decades laboratory experiments demonstrated that size and shape of crystals strongly control the physical properties of magma and lava additionally natural and experimental samples are usually characterized in terms of their crystal size distribution to link it with physical processes that are not directly observable such as cooling or decompression mechanisms in this paper we present crystalmom a new predictive model based on the quadrature based method of moments developed for studying the kinetic of crystallization in volcanic systems the quadrature based method of moments well established in the field of chemical engineering represents a mesoscale modelling approach that rigorously simulates the space time evolution of a distribution of particles by considering its moments the method is applied here for the first time for studying the equilibrium disequilibrium crystallization in magma modelling the temporal evolution of the moments of a crystal size distribution the model verified against numerical and experimental data represents a valuable tool to infer the cooling and decompression rates from the crystal size distribution observed in natural samples

methods of determining the rheological properties of magmas at sub liquidus temperatures non vesicular basaltic melts behave as newtonian fluids at temperatures above their liquidus and their viscosities can be calculated using a method developed by shaw 1972 and bottinga and weill 1972 because many igneous processes involve the flow of silicates at sub liquidus temperatures numerous attempts have been made to calculate the interactive effects of the crystal phase however current methods are appropriate only for relatively low crystal concentrations and they assume newtonian behaviour we argue that this assumption is invalid when bubble or crystal concentrations exceed 30 at higher concentrations factors other than concentration become increasingly important these include particle shape and size distribution a method which takes these factors into account is tested on a range of suspensions including magmas at sub liquidus temperatures and rheological properties calculated using this method agree closely with the measured values we also demonstrate that an equation which was introduced to explain large differences in measured apparent viscosities during the cooling and crystallisation of mount st helens dacite murase et al 1985 and which is currently used to calculate the rheological properties of crystallising lavas generates viscosities which may be in error by several orders of magnitude this difference is argued to be caused by a combination of factors including the ten orders of magnitude range in the strain rates utilised during the mount st helens measurements causing orders of magnitude difference in the resulting apparent viscosities rheological data on crystallising silicic melts are reinterpreted taking into account the non newtonian rheology of the magmas and changes in activation energy of flow during crystallisation

onset of the persistent activity at stromboli volcano italy stromboli known worldwide as the lighthouse of the mediterranean is commonly believed to have been in a state of persistent activity for the past 2000 2500 years however historical sources older than 1000 a d are not accurate enough to assess if the activity of the volcano was exactly the same as we see at present in order to attempt to identify the onset of the present eruptive regime and assess if it has been maintained with the same characteristics through time stratigraphic and radiometric studies of the recent tephra deposits were undertaken up to 4 m deep stratigraphic trenches dug at a height of approximately 500 m on the ne flank of the volcano exposed a conformable tephra pile containing charcoal fragments one of the most interesting finds was the discovery of a 7 cm thick weathered bed rich in organic matter thin palaeosol approximately 3 m below the surface the sequence underneath the palaeosol consists of decimetre thick lapilli fallout beds alternating with ash deposits bearing small charcoals with calibrated ages of between the fourth century b c and the first century a d the sequence above the palaeosol is charcoal free and consists of coarse ash deposits with discrete centimetre thick lapilli fallout beds composed of crystal poor golden pumice and subordinate crystal rich black scoriae similar to scoria pumice pairs emitted during the more energetic explosions of the present day activity the data collected indicate that between the third and seventh centuries a d after a period of quiescence the activity resumed with an eruptive style identical to the present one we conclude that the lighthouse of the mediterranean actually began its activity in a period much later than previously thought

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

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

dynamics and time evolution of a shallow plumbing system the 1739 and 1888 90 eruptions vulcano island italy abstract in this work we analyze the morphology of latitic enclaves occurring in the rhyolitic lava flow of pietre cotte island of vulcano italy we show that enclave morphology is a feature inherited from the shallow plumbing system of the volcano during the invasion of the latitic magma into the rhyolitic magma the complexity of enclave morphology is quantified by fractal analyses using the empirical relationship given by perugini et al 2005 relating the fractal dimension and viscosity ratio the range of viscosity ratios that developed during the injection of the latitic magma into the rhyolitic one is estimated thermodynamical and rheological modeling indicates that the most plausible scenario to explain the variability of observed viscosity ratios is represented by a plumbing system where a large volume of latitic magma intruded a smaller volume of rhyolitic magma the comparison of volume proportions of magmas on the outcrop with those estimated by the modeling allows us to infer that most of the latitic magma remained in the plumbing system after the ending of the 1739 eruptive cycle the strong similarity of compositions from the pietre cotte lava flow and products erupted during the last volcanic activity of vulcano 1888 1890 is interpreted as the reactivation of the latitic magma that possibly evolved through fractional crystallization to produce trachy rhyolitic compositions during the 1888 1890 eruptive cycle we suggest that the methodological approach presented here can represent a further tool for hazard mitigation in volcanic areas in particular it allows obtaining information about the dynamics of plumbing systems of active volcanoes and their time evolution

dynamics of magma mixing and degassing recorded in plagioclase at stromboli aeolian archipelago italy crystal rich materials scoriae and lava flows emitted during the 1985 2000 activity of stromboli were taken into consideration for systematic study of bulk rock matrix glass chemistry and in particular for the study of chemical and textural zoning of plagioclase the most abundant mineral phase over the considered time period bulk rock composition remained fairly constant in both major sio2 49 2 50 9 wt and k2o 1 96 2 18 wt and trace elements the quite constant chemistry of matrix glasses also indicates that the degree of crystallization of magma was maintained at around 50 vol plagioclase ranges in composition between an62 and an88 and is characterized by alternating 10 100 m thick bytownitic and labradoritic concentric layers although the dominant and representative plagioclase of scoriae is an68 the labradoritic layers an62 70 show small scale 1 5 m oscillatory zoning are free of inclusions and appear to record episodes of slow crystal growth in equilibrium with a degassed liquid having the composition of the matrix glass in contrast the bytownitic layers an70 an88 are patchy zoned show sieve structure with abundant micrometric glass inclusions and voids and are attributed to rapid crystal growth

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

shear viscosity of rhyolite vapor emulsions at magmatic temperatures by concentric cylinder rheometry abstract the viscosity of natural rhyolitic melt from lipari aeolian islands and melt bubble emulsions 30 50 vol porosity generated from lipari rhyolite have been measured in a concentric cylinder rheometer at temperatures and shear rates in the range 925 1150 c and 10 3 10 1 2 s 1 respectively in order to better understand the dependence of emulsion shear viscosity on temperature and shear rate in natural systems bubble free melt exhibits newtonian arrhenian behavior in the temperature range 950 1150 c with an activation energy of 395 30 kj mol the shear viscosity is given by log m 8 320 20624 t suspensions were prepared from natural rhyolite glass to which small amounts of na2so4 were added as a foaming agent reasonably homogeneous magmatic mixtures with an approximate log normal distribution of bubbles were generated by this technique suspension viscosity varied from 106 1 to 108 37 pa s and systematically correlates with temperature and porosity in the shear stress range 104 26 105 46 pa of the experiments the viscosity of melt bubble emulsions is described in terms of the relative viscosity r e m where e is the emulsion viscosity and m is the viscosity of melt of the same composition and temperature the dependence of relative viscosity on porosity for magmatic emulsions depends on the magnitude of the capillary number ca g rb 1 m 1 the ratio of viscous forces acting to deform bubbles to interfacial forces resisting bubble deformation for inviscid bubbles in magmatic flows three regimes may be identified for ca 10 an asymptotic regime is reached in which relative viscosity decreases with increasing porosity and is independent of ca our experiments were carried out for 30

rheological properties of basaltic lavas at sub liquidus temperatures laboratory and field measurements on lavas from mount etna models of many magmatic processes require accurate data on the rheological properties of lava at sub liquidus temperatures laboratory measurements of the rheological properties of basalts erupted on mount etna in 1983 were made at various crystal concentrations in a specially designed furnace using a haake rotovisco viscometer attached to a spindle designed to eliminate slippage at the melt spindle interface measurements were made at strain rates between 0 3 and 5 s 1 over the range of eruption temperatures on mount etna 1084 1125 c at temperatures above 1120 c the 1983 lava behaves as a newtonian fluid at lower temperatures the lava is a thixotropic pseudoplastic fluid with a maximum yield strength of 78 pa at a temperature of 1087 c in view of its low yield strength over this temperature range the theological behaviour of the lava approximates to that of a power law fluid apparent viscosities at unit shear strain rates increase from 150 pa s at 1125 c to 3000 pa s at 1084 c unit strain rate apparent viscosities measured in the field using a rotating vane viscometer range from 1385 pa s to 1630 pa s these values are in close agreement with those measured at the same temperature in the laboratory and with those calculated theoretically from the physico chemical properties of the lava

rheological properties of dome lavas case study of unzen volcano abstract transitions between effusive and explosive styles of lava dome eruptions are likely accompanied by changes in lava rheology the common presence of crystals in dome lavas produces a complex non newtonian rheology thus models of such complex rheology are essential for volcanic eruption models here we have measured the rheology of natural unzen lavas with a compressive uniaxial press operating at stresses between 1 and 70 mpa and temperatures between 940 and 1010 c crystal rich unzen lavas are characterised by two essential rheological features which produce non newtonian effects the first is an instantaneous response of the apparent viscosity to applied stress which requires that the magma be described as a visco elastic fluid that exhibits shear thinning the second effect takes the form of a time dependence of the viscosity at moderate to high stress 10 mpa in this regime the apparent viscosity slowly decreases as increasing fracturing of the phenocrysts and the groundmass occurs fragmentation of crystals and alignment of crystal fragments are observed to produce flow banding effects which in turn lower the apparent viscosity of natural dome lavas ultimately deformation may lead to complete rupture of the lava if the stress is sufficient cracking thus stands as an important process in natural dome lava rheology the ubiquitous non newtonian rheology of dome lavas observed experimentally here needs to be adequately treated in order to generate appropriate eruption models

a model for the rheology of particle bearing suspensions and partially molten rocks an edited version of this paper was published by agu copyright 2009 american geophysical union

experimental investigation of magma rheology at 300 mpa from pure hydrous melt to 76 vol of crystals the rheological behaviour of synthetic crystal bearing magmas containing up to 75 vol of crystals 0 s 0 75 has been investigated experimentally at a confining pressure of 300 mpa and temperatures between 475 and 600 c at shear rates between 10 4 and 2x10 3 s 1 starting hydrated crystal bearing glasses were synthesized from a dry haplogranitic glass qz36ab39or29 and 2 5 wt water mixed with 0 pure hydrous melt 16 34 54 65 or 75 vol of al2o3 sieved 45 o 90 m crystals shear viscosity measurements were performed in torsion in a paterson gas medium apparatus for each composition the rheological data were fitted to a power law of the form 1 where is shear rate is shear stress t is temperature r is the gas constant and a n and q are empirical parameters defined as the preexponential term the stress exponent and the activation energy respectively the rheology is found to be newtonian n 1 for pure hydrated melt and 16 vol of crystals at higher crystal contents the magmas behave as pseudoplastic materials and exhibit shear thinning behaviour with stress exponents of 1 3 1 9 and 2 8 for 34 54 and 65 vol of crystals respectively the activation energy seems to be nearly independent of crystal fraction and has a mean value of 231 kj mol 1 the einstein roscoe equation adequately estimates viscosities of the crystal bearing magmas at low crystal contents s 0 25 but progressively deviates from the measured viscosities with increasing crystal content as the rheological behaviour becomes non newtonian a modified power law formulation incorporating crystal content as a variable allows a fit to the experimental data set over the whole range of conditions

the rheology of two phase magmas a review and analysis abstract we consider the current state of our understanding of the rheology of two phase magmas that is suspensions of either bubbles or crystals in a viscous silicate melt the discussion is restricted to strain rates at which the suspending melt can be considered newtonian we start by considering the range of textures found in magmas and the bubble deformation and particle motions caused by shearing we then review proposed models for suspensions focussing on those functions of the form r f or f that have been most widely used to describe magmatic systems r is the relative apparent viscosity of the suspension is the volume fraction of the suspended phase is the driving stress and is the strain rate both theoretical and empirical methods are presented and then compared against the available analogue i e non magmatic and magmatic data the paper contains new data and significant re analysis of previously published data we present a new semi empirical constitutive model for bubble bearing magmas that is valid for steady and unsteady flow and large strains and strain rates this equation utilises a new parameter the capillarity cx that encapsulates the combined effect of shearing and unsteadiness on bubble suspensions we also present a new scheme for dealing with polydispersivity of bubble suspensions new data on the rheology of particle suspensions undergoing forced oscillations are presented these data show that the cox merz rule only holds for dilute particle suspensions 0 25 a re analysis of all available experimental data that relate rheology to particle aspect ratio provides distinct curves of maximum packing as a function of aspect ratio for smooth and rough particles with magmatic data lying on the curve appropriate for rough particles we analyse several rheological datasets of crystal bearing basaltic magmas and find that they are in good agreement with the constitutive equations derived from analogue data by contrast the same equations do not agree well with data for high viscosity haplogranitic melts this may be an effect of fracturing or viscous dissipation within these samples the paper concludes with a practical rheological recipes section giving a step by step method for calculating a constitutive equation for a two phase magmatic suspension and assessing its likely accuracy

dissolution crystallization kinetics recorded in the 2002 2003 lavas of stromboli italy on 28 december 2002 new vents opened on the flanks of stromboli just below the summit craters interrupting the persistent activity of the volcano with a 7 month long effusive eruption we here report on the plagioclase size distribution plgsd in lava samples collected following the chronology of the 2002 2003 eruption data reveal a linear plgsd similar to that found in samples of normal stromboli activity indicating that the switch from strombolian explosive to effusive activity is not associated with changes in texture nevertheless the crystal size distribution slopes and intercepts exhibit slight sinusoidal temporal variations that are here ascribed to a magma supply mechanism able to induce resonance in the crystal size distribution with an amplitude that depends on the supply rate

effect of stirring on crystallization kinetics of basalt texture and element partitioning isothermal crystallization experiments on basalt have been carried out using an infrared heating furnace to investigate the effect of stirring when stirring was not applied static experiment the results agreed well with previous experiments but when stirring was applied and a flow of reynolds number 10 3 4 was present dynamic experiment considerably different results were obtained especially in respect to the nucleation rate and the morphology of crystals at t 25 c essentially similar results were obtained on the nucleation rates and morphologies of crystals in both static and dynamic experiments however at supercoolings larger than 45 c nucleation density increased drastically in dynamic experiments reaching up to ten times as large as that in static experiments crystals of plagioclase and clinopyroxene were small and adapted acicular morphology regardless of t in dynamic experiments and hyalopilitic textures were formed a ttt diagram shows that the nucleation incubation time is shorter in dynamic experiments than in static experiments no compositional difference in major elements was found in plagioclase and clinopyroxene produced in both static and dynamic experiments however minor element concentrations e g mg in plagioclase and ti al in clinopyroxene were found to increase with both t and flow velocity all these results imply that although chemical diffusion in the melts did not play an important role in the dynamic experiments interface kinetics were important it is suggested that hyalopilitic texture commonly seen in natural basalt is mainly due to flow in magma

the viscosity of hydrous phonolites and trachytes the 1 atm viscosities of hydrated synthetic iron free phonolite and trachyte melts are reported between 108 4 and 1013 1 pa s for water contents between 0 and 5 wt these show a very strong reduction with increasing water content particularly at low contents empirical formulae are derived for the dependence of viscosity on temperature and water content at magmatic temperatures of about 1100 k and water contents of 5 wt viscosities are about 910 pa s for the phonolite and 1120 pa s for the trachyte comparisons with data on peralkaline rhyolites show that the effects of dissolved water are similar even though the viscosities of the different compositions vary this indicates that the mechanism by which water reduces the viscosities of partially depolymerized aluminosilicate liquids is independent of the alkali alkaline earth element ratio in addition no major change in this pattern is observed whether water dissolves primarily as oh or molecular h2o this suggests that a third water dissolution mechanism may be important in these compositions in addition to si o si bond breaking and dissolution of molecular water

thermo rheological magma control on the impact of highly fluid lava flows at mt nyiragongo 1 in january 2002 mount nyiragongo erupted foiditic lavas that covered the southern volcano flank devastating vast urban areas lava flows originated from vents at different heights on the eruptive fissure displayed different velocities from tens of km h at the highest vents to slow advance 0 1 1 km h in goma town several km away from the volcano to understand the different behavior of lava flows and their threat to the local population we undertook a multidisciplinary study involving textural and rheological measurements and numerical simulations of heat transfer during magma ascent we demonstrate that pre eruptive cooling and syn eruptive undercooling of magma determined the different rheological behavior of lava flows erupted from vents at diverse heights venting at lower altitudes is expected to produce viscous slowly advancing lavas although development of fluid faster flows should be included among possible future eruptive scenarios

viscosity of andesite melts and its implication for magma mixing prior to unzen 1991 1995 eruption abstract the viscosity of an iron bearing melt with composition similar to unzen andesite was determined experimentally in the high 10 9 10 10 5 pa s and low 5 1000 pa s viscosity range using a parallel plate viscometer and the falling sphere method respectively falling sphere experiments were carried out in an internally heated argon pressure vessel and in a piston cylinder apparatus at 1323 to 1573 k and 200 to 2000 mpa creep experiments were performed in the temperature range of 747 845 k at 300 mpa the water content of the melt varies from nominally dry to 6 2 wt h 2 o the fe 2 fe tot ratio was determined for each sample in the quenched glass using a colorimetric method pressure has minor influence on the viscosity compared with the effect of temperature water content main compositional parameter controlling the viscosity or with the fe 2 fe tot ratio especially important at low water content of the melt based on our new viscosity data and literature data with measured fe 2 fe tot ratio we propose a new empirical equation to estimate the viscosity in pa s of andesitic melts as a function of temperature t in k water content w in wt and fe 2 fe tot ratio the derived relationship reproduces the experimental data 87 in total in the viscosity range from 10 0 5 to 10 13 pa s with a 1 standard deviation of 0 17 log units however application of this calculation model is limited to fe 2 fe tot fe tot 0 3 and to temperatures above t g moreover in the high viscosity range the variation of viscosity with water content is constrained only by few experimental data and needs verification by additional measurements the viscosity data are used to interpret mixing processes in the unzen magma chamber prior to 1991 1995 eruption we demonstrate that the viscosities of the rhyolite and andesite melts from the two end member magmas are nearly identical prior and during mixing enabling efficient magma mixing

the rheology of crystal bearing basaltic magmas from stromboli and etna abstract our ability to forecast volcanic hazards at active volcanoes stems from our knowledge of parameters affecting eruption dynamics persistent activity displayed by basaltic volcanic systems such as etna and stromboli is governed mainly by the textural evolution and rheological properties of eruptive products here we investigate the high temperature 1131 c

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

an expanded non arrhenian model for silicate melt viscosity a treatment for metaluminous peraluminous and peralkaline liquids we present new viscosity measurements for melts spanning a wide range of anhydrous compositions including rhyolite trachyte moldavite andesite latite pantellerite basalt and basanite micropenetration and concentric cylinder viscometry measurements cover a viscosity range of 10 1 to 10 12 pas and a temperature range from 700 to 1650 c these new measurements combined with other published data provide a high quality database comprising 800 experimental data on 44 well characterized melt compositions this database is used to recalibrate the model proposed by giordano and dingwell giordano d dingwell d b 2003a non arrhenian multicomponent melt viscosity a model earth planet sci lett 208 337 349 for predicting the viscosity of natural silicate melts the present contribution clearly shows that 1 the viscosity temperature relationship of natural silicate liquids is very well represented by the vft equation log a b t c over the full range of viscosity considered here 2 the use of a constant high t limiting value of melt viscosity e g a is fully consistent with the experimental data 3 there are 3 different compositional suites peralkaline metaluminous and peraluminous that exhibit different patterns in viscosity 4 the viscosity of metaluminous liquids is well described by a simple mathematical expression involving the compositional parameter sm but the compositional dependence of viscosity for peralkaline and peraluminous melts is not fully controlled by sm for these extreme compositions we refitted the model using a temperature dependent parameter based on the excess of alkalies relative to alumina e g ae sm the recalibrated model reproduces the entire database to within 5 relative

non newtonian behavior of plagioclase bearing basaltic magma subliquidus viscosity measurement of the 1707 basalt of fuji volcano japan abstract laboratory measurements of viscosity were done for basalt erupted in 1707 ad from fuji volcano japan using a concentric cylinder rotational viscometer at temperatures of 1297 1157 c 1 atm pressure and fo 2 near the ni nio buffer on cooling elongated plagioclase crystals with a mean length width ratio of ca 8 5 appeared at 1237 c followed by olivine at 1157 c at progressively lower temperatures the total crystal volume fraction increased monotonously to ca 0 25 viscosity increased from 38 9 to 765 pa s at a shear strain rate of 1 s 1 this basalt magma behaves as a newtonian fluid at temperatures greater than 1217 c but shear thinning behavior occurs at temperatures less than 1197 c because of the suspended plagioclase crystals this behavior is well approximated as a power law fluid at the onset of shear thinning the crystal volume fraction was between 0 06 and 0 13 which is attributed to the pronounced lath shape of plagioclase crystals the relative viscosity increases monotonously with increase of crystal volume fraction at a constant shear strain rate and with decrease of shear strain rate at a constant crystal volume fraction a modified form of the krieger dougherty equation is introduced herein it enables us to describe the dependencies of relative viscosity on both the crystal volume fraction and shear strain rate and consequently the onset of shear thinning behavior

viscosity measurements of subliquidus magmas alkali olivine basalt from the higashi matsuura district southwest japan abstract we carried out viscosity measurements and sampling of a crystal suspension derived from alkali olivine basalt from the matsuura district sw japan at subliquidus temperatures from 1230 c to 1140 c under 1 atm with nno oxygen buffered conditions viscosity increased from 31 to 1235 pa s with a decrease in temperature from 1230 to 1140 c on cooling olivine first appeared at 1210 c followed by plagioclase at 1170 c the crystal content of the sample attained 31 vol at 1140 c plagioclase 22 olivine 9 non newtonian behaviors including thixotropy and shear thinning were pronounced in the presence of tabular plagioclase crystals the cause of such behavior is discussed in relation to shear induced changes in melt crystal textures relative viscosities r s m where s and m are the viscosities of the suspension and the melt respectively were obtained by calculating melt viscosities from the melt composition and temperature at 1 atm using the equation proposed by giordano and dingwell giordano d dingwell d b 2003 non arrhenian multicomponent melt viscosity a model earth and planetary science letters 208 337 349 the obtained relative viscosities are generally consistent with the einstein roscoe relation which represents r for suspensions that contain equant and equigranular crystals even though the crystal suspension analyzed in the present experiments contained tabular plagioclase and granular olivine of various grain sizes this consistency is attributed to the fact that the effect of crystal shape was counterbalanced by the effect of the dispersion of crystal size the applicability of the einstein roscoe equation with respect to crystal shape is discussed on the basis of the present experimental results our experiments and those of sato sato h 2005 viscosity measurement of subliquidus magmas 1707 basalt of fuji volcano journal of mineralogical and petrological sciences 100 133 142 show that the relationship between relative viscosity and crystal fraction is consistent with the einstein roscoe relationship for axial ratios that are smaller than the critical value of 4 6 5 but discrepancies occur for higher ratios

the yield strength of subliquidus basalts experimental results yield strength is an important property of particle fluid suspensions in basaltic lavas that crystallize during flow emplacement the onset of yield strength may result in threshold transitions in flow behavior and flow surface morphology however yield strength crystallinity relations are poorly known particularly in geologic suspensions where difficulties of experimental and field measurements have limited data acquisition in the subliquidus temperature range here we describe two complementary experimental approaches designed to examine the effect of particle shape on the low shear yield strength of subliquidus basalts the first involves melting cubes of holocrystalline basalt samples with different initial textures to determine the temperature crystallinity at which these samples lose their cubic form these experiments provide information on the minimum crystal volume fractions 0 20 0 35 required to maintain the structual integrity of the cube the second set of experiments uses suspensions of corn syrup and neutrally buoyant particles to isolate the effect of particle shape on yield strength development from these experiments we conclude that the shape is important in determining the volume fraction range over which suspensions exhibit a finite yield strength as anisotropic particles may orient during flow the effect of particle shape will be controlled by the orientation distribution of the constituent particles we find that the so called excluded volume can be used to relate results of experiments on anisotropic particles to those of suspensions of spherical particles recent measurements of yield strength onset in basaltic melts at crystal volume fractions near 0 25 are consistent with our observations that crystal frameworks develop at low to moderate crystal volume fractions when crystals are anisotropic e g plagioclase we further suggest that conditions leading to yield strength onset at low crystallinities include rapid cooling increased crystal anisotropy heterogeneous nucleation which promotes extensive crystal clustering and large cluster anisotropy and static conditions random crystal orientations

intra grain sr isotope evidence for crystal recycling and multiple magma reservoirs in the recent activity of stromboli volcano southern italy over the last several hundred years stromboli has been characterized by steady state strombolian activity the volcanic products are dominated by degassed and highly porphyritic hp magma black scoria bombs lapilli and lava flows of basaltic shoshonitic composition periodically about one to three events per year more energetic explosive eruptions also eject light coloured volatile rich pumices with low phenocryst content lp magma that have more mafic compositions than the hp magma an in situ major and trace element and sr isotope microanalysis study is presented on four samples chosen to characterize the different modes of activity at stromboli a lava flow 1985 1986 effusive event a scoria bomb from the normal present day activity of stromboli april 1984 and a scoria and coeval pumice sample from a recent more explosive eruption september 1996 plagioclase an

textural effects of steady state behaviour of the stromboli feeding system abstract the exceptionally persistent activity of stromboli volcano has lasted for at least 1400 years the normal strombolian activity is periodically interrupted by more energetic explosions 1 2 per year and by sporadic effusive episodes every 10 20 years normal activity and effusive episodes are characterized by crystal rich high k to shoshonitic basalts issuing from a volatile poor shallow system crystal poor pumice are emitted only during more violent explosions and are thought to derive from deep pulses of volatile rich magma shallow level degassing induces massive crystallization of deep pulses of feeding magma that continuously mixing with the resident one produces the crystal rich shoshonite of the persistent activity we examined the crystallization history of the crystal rich shallow reservoir using plagioclase crystal size distribution csd analysis of scoriae and lavas emitted in the past twenty years csds show a linear dependence from crystal size in the size interval 0 06 1 2 mm number density of larger crystals is biased by right hand truncation effects csds slopes and intercepts are quite constant during the whole considered time span revealing a system that is close to the equilibrium also from a kinetic point of view the linear crystal size distribution are reached by the system through episodes of growth and resorption respectively occurring in the degassed and undegassed magma during the continuous mixing in the feeding system plagioclase net growth rate 2 10 11 cm s results from a balance of growth 10 10 cm s and resorption episodes which induce spectacular zoning and resorption textures in crystals larger than 200 m csds of mafic phases cannot be accurately acquired on each single sample due to poor counting statistics the evaluation of pyroxene and olivine csd on the whole data set however confirms the conclusions acquired from plagioclase csds

viscosity of high crystal content melts dependence on solid fraction 1 the rheological properties of suspensions containing high solid fractions are investigated attention is focused on viscosity of silicate and magmatic melt systems a general empirical equation which describes the relative viscosity of suspensions as a function of suspended solid fraction is proposed in the limit of very dilute solid concentrations it reduces to the einstein equation the proposed relationship is satisfactorily applied to reproduce available experimental data relative to silicate melts moreover the extrapolation of the model to very high concentrations is compared with experimental observations on partially melted granite

early diagnesis of carbohydrates in the marine environment ii composition and origin of carbohydrates in skagerrak sediments abstract the distribution and composition of carbohydrates were determined for the upper 15 cm of four cores from the southern slope of the skagerrak high concentrations were found in the upper bioturbated layers rapidly decreasing at sediment depths 3 cm total contents appear to be controlled by bioturbation application of various biomarker criteria suggests that carbohydrates originated from terrestrial macroalgal and planktonic sources input from these sources might be by episodic events rather than by continuous sedimentation as can be hypothesised from the irregular occurrence of marine and terrestrial signals

water and the viscosity of andesite melts the viscosity of a synthetic andesite like melt has been measured between 1010 and 1014 p for water contents in the range 0 3 5 wt the very slow kinetics of water exsolution over this viscosity range allowed the measurements to be made at 1 bar with a high precision after a steep viscosity decrease of 5 orders of magnitude for 1 wt h2o an additional 2 5 wt h2o causes a further viscosity decrease of only 2 orders of magnitude these viscosity decreases are qualitatively similar to those observed previously for more silica rich compositions the new data join smoothly with available high temperature measurements made at high pressures on water bearing andesite melts because the intrinsic effects of pressure are as small for water bearing as for water free samples the depressing effect of water on the viscosity of natural andesite melts can be estimated changes in water speciation as a function of either temperature or pressure do not seem to have marked effects on the viscosity although quantitative applications are not yet possible the configurational entropy theory accounts qualitatively for these features

rheological properties of magma from the 1538 eruption of monte nuovo phlegrean fields italy an experimental study abstract the rheology of natural partially crystallized samples from monte nuovo 1538 ad eruption have been investigated using a high temperature high pressure internally heated pressure vessel within the temperature interval of investigation the samples exhibited newtonian rheology at deformation strain rates up to 10 4 s 1 at higher strain rates a decrease of viscosity with increasing strain rate shear thinning eventually terminating in a sudden viscosity drop stress weakening was observed stress weakening occurred at higher applied strain rates and stresses with increasing temperature the microstructural analyses of the samples revealed that stress weakening resulted from strain localization which occurred in brittle and viscous regimes at the lowest and highest temperatures investigated respectively the different rheological behaviors of the investigated material is likely responsible for the changes in the dynamics of magma ascent within the volcanic conduit during the eruption of monte nuovo volcano we infer that the occurrence of syn eruptive decompression driven crystallization observed in previous studies induced strong variations in the rheological properties of magma which in turn was responsible for the changes of eruptive style observed during the monte nuovo eruption

role of heat advection in a channeled lava flow with power law temperature dependent rheology 1 the cooling of a lava flow both in the transient and the steady state is investigated considering that lava rheology is pseudoplastic and dependent on temperature lava exits from the vent with constant velocity and flows down a slope under the effect of gravity force inside a channel of rectangular cross section we consider that cooling of lava is caused by thermal radiation into the atmosphere and thermal conduction at the channel walls and at the ground the heat equation is solved numerically in a 3 d computational domain and the solution is tested to evaluate the numerical errors we study the steady state and the initial transient period of lava cooling results indicate that the advective heat transport significantly modifies the cooling rate of lava slowing down the cooling process since the lava velocity depends on temperature the cooling rate depends on the effusion temperature velocity profiles are modified during cooling showing two marginal static zones where the crust can form and remain stable the fraction of crust coverage is calculated under the assumption that the solid lava is a plastic body with temperature dependent yield strength we numerically confirm that heat advection cannot be neglected in the mechanism of formation of lava tubes

an analytical model for gas overpressure in slug driven explosions insights into strombolian volcanic eruptions strombolian eruptions common at basaltic volcanoes are mildly explosive events that are driven by a large bubble of magmatic gas a slug rising up the conduit and bursting at the surface gas overpressure within the bursting slug governs explosion dynamics and vigor and is the main factor controlling associated acoustic and seismic signals we present a theoretical investigation of slug overpressure based on magma static and geometric considerations and develop a set of equations that can be used to calculate the overpressure in a slug when it bursts slug length at burst and the depth at which the burst process begins we find that burst overpressure is controlled by two dimensionless parameters v which represents the amount of gas in the slug and a which represents the thickness of the film of magma that falls around the rising slug burst overpressure increases nonlinearly as v and a increase we consider two eruptive scenarios 1 the standard model in which magma remains confined to the vent during slug expansion and 2 the overflow model in which slug expansion is associated with lava effusion as occasionally observed in the field we find that slug overpressure is higher for the overflow model by a factor of 1 2 2 4 applying our model to typical strombolian eruptions at stromboli we find that the transition from passive degassing to explosive bursting occurs for slugs with volume 24 230 m 3 depending on magma viscosity and conduit diameter and that at burst a typical strombolian slug with a volume of 100 1000 m 3 has an internal gas pressure of 1 5 bars and a length of 13 120 m we compare model predictions with field data from stromboli for low energy puffers mildly explosive strombolian eruptions and the violently explosive 5 april 2003 paroxysm we find that model predictions are consistent with field observations across this broad spectrum of eruptive styles suggesting a common slug driven mechanism we propose that paroxysms are driven by unusually large slugs large v

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

review of ten years of volcano deformations recorded by the ground based insar monitoring system at stromboli volcano a tool to mitigate volcano flank dynamics and intense volcanic activity abstract stromboli volcano southern italy is one of the most monitored volcano in the world with a surveillance network that includes a permanently sited ground based sar interferometer gbinsar this work is the review of the gbinsar data gained from the last decade of monitoring activity the analysis of the entire dataset of gbinsar measurements allowed the assessment of the deformation field of the northern part of the summit crater area and the sciara del fuoco depression in detail the main displacements recognized can be related to different factors 1 the inflation deflation respectively immediately before and after each new effusive event 2 the bulging of localized sectors of the volcano involved in the vent opening 3 the gravitational sliding of the sciara del fuoco infill 4 the movement of lava flows accelerations in this sector are related to sheet intrusions while the possibility of vent opening associated with small sliding or catastrophic flank failure are related to highly overpressurized sheets able to produce high displacement rate in the sciara del fuoco in the summit crater area the increases in the displacement rate are related to the pressurization of the shallow conduit system as the consequence of the variation in the magma level magmastatic pressure or to the lateral magma migration lateral conduit expansion or dike intrusion in response to the increase of the overpressure component fluctuations in the displacement rate in the summit crater area can be related to the magma overturning within the conduit with the increases in displacement rate during the upwelling of less dense magma while displacement rate decreases as the degassed magma column is pushed out from the conduit lava flows or overflows instead the decrease in the displacement rate without coeval lava outpouring could be related to the sink of the degassed magma due to density contrast between the gas poor and the gas charged magmas using the displacement rate in the summit crater area as a proxy for the variation in the pressure condition in conduit both magmastatic and overpressure components thresholds for the crises characterized by the occurrence of overflows eventually associated with major explosions and flank effusions eventually associated with paroxysmal explosions are identified small conduit overpressure will produce overflows sometimes associated with crater rim collapses while large magma overpressure will laterally expand the conduit forming ne sw striking sheets feeding eruptive vents at the base of the summit crater area and within the sciara del fuoco generating conditions of instability that can evolve into catastrophic collapse of the instable flank

the effect of particle size on the rheology of liquid solid mixtures with application to lava flows results from analogue experiments 1 we investigate the effect of crystal size on the rheology of basaltic magmas by means of a rheometer and suspensions of silicon oil with natural magmatic crystals of variable size from 63 to 0 5 mm and volume fraction from 0 03 to 0 6 at constant finer suspensions display higher viscosities than coarser ones shear thinning flow index n 0 1 0 2 and is more pronounced stronger departure from the newtonian behavior in finer suspensions maximum packing and average crystal size displays a nonlinear positive correlation while yield stress develops at 0 2 0 3 irrespective of the crystal size we incorporate our results into physical models for flow of lava and show that with respect to lava flows containing coarser crystals those with smaller crystals are expected to 1 flow at lower velocity 2 have a lower velocity gradient and 3 be more prone to develop a region of plug flow our experimental results explain the observation that phenocryst bearing and microlite bearing lavas at etna volcano italy show smooth pahoehoe and rough aa surfaces respectively

the viscosity of shoshonitic melts vulcanello peninsula aeolian islands italy insight on the magma ascent in dikes abstract the viscosity of shoshonitic melts and glasses from vulcanello peninsula vulcano island italy was experimentally determined at temperatures between 733 k and 1673 k the water content of the melts varies from 0 03 to 4 75 wt h 2 o the micropenetration technique was employed at ambient pressure in the high viscosity range 10 9 10 12 pa s falling sphere s experiments were performed at 500 and 2000 mpa in the low viscosity range 10 0 5 10 3 pa s results show a decrease of about 2 orders of magnitude in viscosity if 3 wt of water is added to the dry melt at 1300 k at high temperature the viscosity of vulcanello melts is intermediate between that of andesitic and basaltic melts in contrast at low temperatures 1050 k the shoshonitic melt is characterized by a lower viscosity with respect to the two previous melts the general viscosity models of giordano et al giordano d mangiacapra a potuzak m russell j k romano c dingwell d b di muro a 2006 an expanded non arrhenian model for silicate melt viscosity a treatment for metaluminous peraluminous and peralkaline liquids chemical geology 229 42 56 for dry silicate melts is in good agreement with the experimental data in the high temperature range less than 0 3 log units but shows significant differences in the low temperature range up to 1 1 log units the calculation model for hydrous silicate melts from huy and zhang huy h zhang y 2007 toward a general viscosity equation for natural anhydrous and hydrous silicate melts geochimica et cosmochimica acta 71 403 416 reproduces the new viscosity data in the high temperature range within 0 6 log units but shows as well large discrepancies in the low t range for hydrous melts deviations up to 2 log units thus we propose a specific calculation model to predict the viscosity of the shoshonitic melts as a function of temperature and water content this model reproduces the experimental data 24 measurements with a 1 standard deviation of 0 17 log units the viscosity data are used to constrain the ascent velocity of shoshonitic magmas from vulcanello within dikes using petrological data temperature and crystal content of the magma and volcanological information geometrical parameters of the eruptive fissure and depth of magma storage we estimate the time scale for the ascent of magma from the main reservoir to the surface results show time scales in the order of hours to few days we conclude that the rapid ascent of poorly evolved melts from moho depths should be taken into account for the hazard assessment of vulcano island

recycling and re hydration of degassed magma inducing transient dissolution crystallization events at stromboli italy abstract intrusive degassing and recycling of degassed and dense magma at depth have been proposed for a long time at stromboli the brief explosive event that occurred at the summit craters on 9 january 2005 threw out bombs and lapilli that could be good candidates to illustrate recycling of shallow degassed magma at depth we present an extensive data set on both the textures and the mineral bulk rock and glassy matrix chemistry of the 9 jan products the latter have the common shoshonitic basaltic bulk composition of lavas and scoriae issued from typical strombolian activity in contrast they differ by the heterogeneous chemistry of their matrix glasses and their crystal textures that testify to crystal dissolution event s just prior magma crystallization upon ascent and eruption comparison between mineral paragenesis of the natural products and experimental phase equilibria suggest water induced magma re equilibration we propose that mineral dissolution is related to water enrichment of the recycled degassed magma via differential gas bubble transfer and to some extents its physical mixing with volatile rich magma blobs however all these features illustrate transient processes even though evidence of mineral dissolution is ubiquitous at stromboli its effect on the bulk magma chemistry is minor because of the subtle interplay between mineral dissolution and crystallization in magmas having comparable bulk chemistry

glass forming ability and crystallisation behaviour of sub alkaline silicate melts abstract the intrinsic solidification behaviour and glass forming ability gfa of natural sub alkaline silicate melts have been experimentally quantified via cooling induced solidification approach gfa is measured by the critical cooling rate rc the rate at which a melt solidifies 2 area of crystals cooling rates of 9000 1800 180 60 7 and 1 c h have been run between 1300 c super liquidus region and 800 c quenching temperature at air f o 2 and ambient p for six silicate melts with compositions ranging from basalt b to rhyolite r i e b 100 b 80 r 20 b 60 r 40 b 40 r 60 b 20 r 80 and r 100 and water contents comprised between 53 b 100 and 384 b 20 r 80 ppm the ranges of cooling rates and chemical compositions used in this study are the broadest ever investigated in the earth sciences the phase proportions area were determined by image analysis on about 500 back scattered electron images collected over different magnifications phases are glass clinopyroxene cpx spinel sp and plagioclase plg sp is ubiquitous with abundance of few area and nucleates earlier than silicate crystals cpx solidifies in all runs except in r 100 and its abundance follows asymmetric broad gaussian like trends with tails towards low rates as a function of cooling rate moving from b 100 to b 40 r 60 these trends conserve their shape but shift progressively to lower cooling rates and mineral abundances plg crystallises only at low cooling rates and in sio 2 poor compositions run products with low amounts of crystals 5 area clearly show that cpx preferentially nucleates on surfaces of sp whereas a significant crystallisation of cpx 5 area is observed with decreasing cooling rate and with changing composition from b 100 to b 20 r 80 the crystallisation of silicate crystals is related to the chemical diffusivity of components in the melt also the initial crystallisation of plg occurs preferentially on cpx in general the amount of crystals decreases as the cooling rate increases however in some cases the amount of crystals remains constant or even decreases for b 80 r 20 with decreasing cooling rate rc values change over 5 orders of magnitude being 100 b 20 r 80 b 40 r 60 b 60 r 40 and b 80 r 20 and b 100 respectively the variation of rc can be modelled through nbo t nonbridging oxygen per tetrahedron parameter by the following equation rc a 1 e nbo t b c where a b and c are fitting parameters equal to 9214 0 297 and 0 040 respectively similarly to other glass forming liquids network metallic and molecular systems rc for natural sub alkaline silicate melts is inversely related to the reduced glass transition parameter trg trg tg tm and can be quantified with the equation rc a trg b where a and b are 1 19 10 4 and 28 7 respectively these results may be used to retrieve the solidification conditions of aphyric degassed and oxidised lavas in addition our data provide general constrains on the crystallisation kinetics of natural crystal bearing silicate melts erupted on earth e g lavas with phenocrysts the relationship between crystal content and cooling rate suggests that the solidification path induced by degassing can be also complex and nonlinear the growth of crystals with size up to 1 mm from a nearly anhydrous superheated silicate melt indicates that variable cooling conditions of lavas have to be accounted to discriminate among minerals formed before during and after eruptions moreover our results can be used to design glass ceramics from naturally available easy to find low cost starting materials

the influence of trace amounts of water on the viscosity of rhyolites as a major volatile in volcanic systems water has a significant influence on the rheological properties of silicic magmas this is especially so at minor water contents relevant to the emplacement of silicic lavas to investigate the influence of water on the viscosity of natural rhyolitic obsidians a novel strategy has been adopted employing parallel plate and micropenetration techniques viscosities have been determined on three types of material a raw water bearing obsidians b remelted 1650 c 1 atm degassed glasses of the obsidians and c hydrothermally hydrated 1300 c 3 kbar obsidians ten natural rhyolitic obsidians peraluminous calc alkaline and peralkaline were employed seven originated from lava flows and contained 0 2 wt h2o two samples were f rich from pyroclastic successions and one was an obsidian cobble with 1 5 wt water also associated with pyroclastic units melt compositions and water contents were stable during viscometry the measured decreases in activation energies of viscous flow and viscosity with small amounts of water are much greater than the shaw calculation scheme predicts in addition a marked non linear decrease in exists with increasing water content in contrast to the case for peralkaline rhyolites 0 1 0 2 wt water decreases activation energies significantly up to 30 for calc alkaline compositions these results have important implications for the ease of near surface degassing of silicic magmas during emplacement and permit the testing of calculational models for viscosity largely based on synthetic systems

volcanic dilemma flow or blow volcanic eruptions can be either slow outpourings of lava or explosive ejections of fragmented rock in his perspective dingwell discusses the physical and chemical properties of magma that lead to these two styles of eruption new experiments and computer simulations are pointing to the involvement of solidlike behavior of liquid magma when it makes a transition to a glass

rheology of melts from the colli albani volcanic district italy a case study in this study the first viscosity measurements in the glass transition range of melts from highly explosive large volume eruptions from the colli albani volcanic district cavd are presented the magmas are ultrapotassic rich in iron and cao and characterised by a low silica content 45 wt melt compositions range from tephri phonolitic to foiditic the colli albani eruptions appear anomalous since they produced a large volume of erupted material in spite of their silica undersaturated compositions the viscosity of the colli albani melt changes as the melt composition evolves from the original melt to a country rock contaminated melt to a crystal bearing melt with a permanent decrease in liquid viscosity conventional estimations of viscosities assume these magmas to have a low viscosity the presented data show that the melt viscosities are higher than expected taking into account further chemical or rheological features of a melt the investigated cavd melts are not that striking as assumed in comparison with other large volume eruptions consequently considering the alkaline earth to alkaline ratio together with the sio2 content could provide an alternative when comparing large volume eruptions

magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallization basaltic eruptions are the most common form of volcanism on earth and planetary bodies the low viscosity of basaltic magmas inhibits fragmentation which favours effusive and lava fountaining activity yet highly explosive hazardous basaltic eruptions occur the processes that promote fragmentation of basaltic magma remain unclear and are subject to debate here we used a numerical conduit model to show that a rapid magma ascent during explosive eruptions produces a large undercooling in situ experiments revealed that undercooling drives exceptionally rapid in minutes crystallization which induces a step change in viscosity that triggers magma fragmentation the experimentally produced textures are consistent with basaltic plinian eruption products we applied a numerical model to investigate basaltic magma fragmentation over a wide parameter space and found that all basaltic volcanoes have the potential to produce highly explosive eruptions the critical requirements are initial magma temperatures lower than 1 100 c to reach a syn eruptive crystal content of over 30 vol and thus a magma viscosity around 105 pa s which our results suggest is the minimum viscosity required for the fragmentation of fast ascending basaltic magmas these temperature crystal content and viscosity requirements reveal how typically effusive basaltic volcanoes can produce unexpected highly explosive and hazardous eruptions volcanoes that typically erupt effusively can generate highly explosive eruptions of basaltic lava under specific temperature and viscosity conditions suggest crystallization experiments combined with numerical models of magma fragmentation

constraining pre eruptive magma conditions and unrest timescales during the monte nuovo eruption 1538 ad campi flegrei southern italy integrating textural and csd results from experimental and natural trachy phonolites we present crystallization experiments representing a broad range of growth conditions of alkali feldspar and sodalite in a trachy phonolite magma composition during later stages of evolution our results include i textural data and mineral assemblages of synthetic samples ii feldspar nucleation kinetics and growth rate estimates and iii textural data mineral abundances and crystal size distribution measurements on samples representative of the monte nuovo eruption 1538 ad the last eruption of campi flegrei southern italy experiments reproduced the texture and feldspar content of natural products indicating that kinetic data can provide insights into processes within the volcanic system shortly before and during this small magnitude eruption and particularly about magma ascent timescale we suggest that the groundmass crystallization of monte nuovo magma started between 4 and 7 km depth 100 200 mpa at a temperature between 825 and 840 c close to the liquidus of alkali feldspar the crystallization kinetics of alkali feldspar and the absence of sodalite in most of the natural samples indicate that magma ascent rate increased in the shallow part of the conduit from about 3 km depth to the quenching level possibly fragmentation point 30 mpa during the first phases of the eruption the crystallization time of the magma requires that it ascended from pre eruptive storage to the quenching level in several hours to a few days we also observe that a small decrease in pressure can induce a dramatic increase in crystallinity with associated rheological changes leading to changes in the eruption style and such changes could occur on timescales of hours to several days the products from the later phases of the monte nuovo eruption are more crystalline and contain sodalite in response to the decrease in magma ascent rate which in turn allowed for more degassing during ascent resulting in more time spent at very shallow depths

crystallization kinetics and rheology of leucite bearing tephriphonolite magmas from the colli albani volcano italy abstract we have investigated the rheology of liquid and crystal bearing tephriphonolite magmas from the colli albani volcanic district high 1124 1569 c and low 690 800 c temperature anhydrous liquid viscosities were determined by a combination of concentric cylinder 101 0 to 103 6 pa s and micropenetration 109 2 to 1012 1 pa s viscometry comparison with literature data reveals that at high temperatures viscosity seems to be related to the melts degree of polymerization nbo t while at low temperatures the dependency is not linear with values of viscosity higher than expected subliquidus isothermal crystallization experiments and viscosity determinations were carried out at high temperature 1150 1240 c in air using a concentric cylinder apparatus at constant shear strain rate 0 1 s 1 the overall crystal fraction varies between 0 06 at 1240 c leucite and 0 34 at 1150 c leucite 0 32 plagioclase 0 02 with a direct linear increase of crystal content with decreasing temperature which parallels the viscosity increase the inspection of products quenched at the end of the crystallization stage defined when viscosity reaches a constant value reveals strong evidence of leucite clustering after the first segment of the experiment performed at a constant shear rate a second stage of experiments at variable shear rate was performed comprised of an up ramp 0 1 s 1 0 9 s 1 and a down ramp 0 9 s 1 0 1 s 1 segment at the end of the down ramp leucite crystals appear sub spherical and unclustered for the same applied shear rate the viscosity values of the up ramp are not recovered within the experimental time scale indicating strain and strain rate dependent rheology for these suspensions while the down ramp viscosity data are shown to be in perfect agreement with literature models discrepancies between the up ramp data and pre existing predicting models have been observed we suggest that this complex behavior is related to the clustering of leucite crystals during the crystallization process and their breakage during the higher shear rate viscosity measurements the kinetics of crystallization in terms of nucleation and growth rates seems to be strongly affected by the degree of undercooling and dynamic stirring conditions we conclude that any modeling of tephriphonolite magma flow either in conduit or subaerial should take into account the effects of strain strain rate and internal textures i e clustering

shear rate dependent disequilibrium rheology and dynamics of basalt solidification magmas and lavas undergo a range of shear rates during transport and emplacement further transport of magma and lava occurs at subliquidus conditions where the melt crystallizes at varying temperature pressure and oxygen fugacity transport efficiency and eruption style are governed by magma rheology which evolves during cooling crystallization and degassing quantification of magma rheology rests almost exclusively on experimentation at constant temperature and shear rate we present the first study on the effect of shear rate on subliquidus basalt rheology at conditions relevant to lava flows and shallow magmatic systems the results reveal that basalts reach their rheologic death or cutoff temperature t cutoff i e the point at which the sample rheologically solidifies and flow stops at higher temperatures when flowing faster whereas crystallization is suppressed when the shear rate is low we explore the implications of shear enhanced crystallization for modeling and forecasting of lava flow hazards and our understanding of magma and lava transport storage systems plain language summary natural magmatic processes span several orders of magnitude in deformation rate the presented approach is the first to systematically document the resulting effects on the magma lava transport properties our paper presents an experimental study on the shear rate dependence of the crystallization solidification dynamics and rheology of basalts at experimental conditions that mimic the natural environment these were made possible through application of a newly developed experimental apparatus and method the measurements show that at a specific subliquidus temperature the so called rheological cutoff temperature the effective viscosity of basalts increases dramatically leading to solidification of the melt systematic investigation of this rheological cutoff shows a drastic previously unrecognized dependence on shear rate cooling rate and composition high deformation rates result in more intense crystallization at higher temperatures whereas crystallization is suppressed to lower temperatures in the absence of deformation the presented results open an entirely new field of studies in magma rheology and have important implications for the forecasting of natural hazards lava flow emplacement and the understanding of magma and lava storage and transport systems in general we discuss the implications of the experimental results for lava flow emplacement magma migration and for the computational modeling of lava flows for hazard assessment