flowgo a kinematic thermo rheological model for lava flowing in a channel we present a kinematic self adaptive numerical model to describe the down flow thermal and rheological evolution of channel contained lava as our control volume of lava advances down a channel it cools and crystallizes an increasingly thick and extensive surface crust grows and its heat budget and rheology evolve by estimating down flow heat and velocity loss our model calculates the point at which the control volume becomes stationary giving the maximum distance lava flowing in the channel can extend modeled effusion rates velocities widths surface crust parameters heat budget cooling temperature crystallinity viscosity and yield strength all compare well with field data collected during eruptions at mauna loa k lauea and etna modeled lengths of 25 27 2 5 5 7 and 0 59 0 83 km compare with measured lengths of 25 27 4 and 0 75 km for the three flows respectively over proximal flow portions we calculate cooling crystallization viscosity and yield strength of 1 10 c km 1 0 001 0 01 volume fraction km 1 103 104 pa s and 10 3 102 pa respectively at the flow front cooling crystallization viscosity and yield strength increase to 100 c km 1 0 1 volume fraction km 1 106 107 pa s and 103 104 pa respectively all of which combine to cause the lava to stop flowing our model presents a means of a analyzing lava flow thermo rheological relationships b identifying important factors in determining how far a channel fed flow can extend c assessing lava flow hazard and d reconstructing flow regimes at prehistoric unobserved or remote flows

field and experimental constraints on the rheology of arc basaltic lavas the january 2014 eruption of pacaya guatemala we estimated the rheology of an active basaltic lava flow in the field and compared it with experimental measurements carried out in the laboratory in the field we mapped sampled and recorded videos of the 2014 flow on the southern flank of pacaya guatemala velocimetry data extracted from videos allowed us to determine that lava traveled at 2 8 m s on the steep 45 slope 50 m from the vent while 550 m further downflow it was moving at only 0 3 m s on a 4 slope estimates of effective viscosity based on jeffreys equation increased from 7600 pa s near the vent to 28 000 pa s downflow in the laboratory we measured the viscosity of a representative lava composition using a concentric cylinder viscometer at five different temperatures between 1234 and 1199 c with crystallinity increasing from 0 1 to 40 vol the rheological data were best fit by power law equations with the flow index decreasing as crystal fraction increased and no detectable yield strength although field based estimates are based on lava characterized by a lower temperature higher crystal and bubble fraction and with a more complex petrographic texture field estimates and laboratory measurements are mutually consistent and both indicate shear thinning behavior the complementary field and laboratory data sets allowed us to isolate the effects of different factors in determining the rheological evolution of the 2014 pacaya flows we assess the contributions of cooling crystallization and changing ground slope to the 3 7 fold increase in effective viscosity observed in the field over 550 m and conclude that decreasing slope is the single most important factor over that distance it follows that the complex relations between slope flow velocity and non newtonian lava rheology need to be incorporated into models of lava flow emplacement

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

east pacific rise from siqueiros to orozco fracture zones along strike continuity of axial neovolcanic zone and structure and evolution of overlapping spreading centers we have used the sea beam multibeam echo sounding system to survey the east pacific rise epr from 8 20 n to 18 30 n obtaining complete coverage of the epr axial neovolcanic zone and all intervening transform faults here we focus on the epr neovolcanic zone and the definition of overlapping spreading centers ocs s between the orozco and siqueiros transform faults the neovolcanic zone is narrow 0 5 2 0 km and continuous along strike and occurs within and near a strike continuous axial summit graben the neovolcanic zone and summit graben reside along the crest of a volcanic axial high which is 2 10 km wide and which continues uninterrupted along strike for 40 140 km within 20 50 km of an intersection with a transform fault the axial neovolcanic zone narrows and deepens and within only 3 6 km of the intersection the neovolcanic zone turns sharply into the transform valley at seven locations between the siqueiros and orozco transform faults the axial neovolcanic zone is discontinuous and is laterally offset a short distance 1 15 km in contrast with a classic ridge transform ridge plate boundary however offset rise terminations overlap each other by a distance approximately 3 times greater than their offset they curve toward each other and often one merges into the other along strike separating the osc s is an elliptical overlap basin up to 600 m deep whose long axis is subparallel to the adjacent spreading centers the overlap basin is characterized by volcanic constructional edifices a key difference between these offsets and small transform faults in the atlantic is that there are no transform fault structures in the overlap basin which link the offset rise axes a continuous axial depth profile reveals a long wavelength 20 60 km undulation of the rise axis which may be associated with variations in the magmatic budget along strike the lowest points in the axial depth profile occur near transform faults and at osc s suggesting that these features are associated with along strike minima in the magmatic budget we suggest that major phases of volcanic activity propagate episodically along the axis away from centers of magmatic inflation and that osc s develop where magmatic pulses fail to meet due to misalignment of fracture systems sinuous bends in the rise axis or other heterogeneities transform faults fail to develop on fast spreading centers where the lateral offsets are small 15 km because the lithosphere is too thin and weak to maintain a classic rigid plate ridge transform fault pattern the osc geometry is unstable and evolves rapidly and the overlapping rises may propagate at rates faster than the local spreading rate one of the two osc s prevails while the other is abandoned while the locations of osc s may not be fixed relative to the rise axis they may tend to recur near the same place creating scars in older lithosphere which resemble fracture zones but whose fine scale structure is quite different there is excellent agreement between the observed structure of osc s and laboratory studies of osc s using wax models photoelastic studies of overlapping cracks and boundary element modeling of overlapping cracks seismic refraction and reflection near two osc s suggests that large offset osc s have separate magma chambers beneath the offset rise axes while small offset osc s may share a single axial magma chamber three dimensional inversion of magnetic anomalies suggests that significant petrologic anomalies may occur near some osc tips waxing and waning of overlapping magma chambers may give rise to the eruption of highly fractionated feti basalts and associated magnetic anomalies

multiple generation folding and non coaxial strain of lava crusts viscoelastic strain in lava flows is commonly expressed as gravity driven buckling of the lava crust this surface folding process creates the well known ropy p hoehoe texture of basaltic lavas and the ogives and surface ridges of more compositionally evolved lava flows previous work has shown that surface fold wavelengths are proportional to the viscosity contrast between the lava crust and core and to the thickness of the crust thus fold analysis can be an important tool for understanding lava flow rheology we analyze fold wavelength patterns of solidified natural lava flows from the myvatn lava fields iceland piton de la fournaise la reunion and experimental lava flows from the syracuse university lava project in each case lava flows exhibited two dominant wavelengths consistent with multiple generations of coaxial folding the ratio of the two dominant wavelengths for basalt iceland la reunion is 5 1 whereas the wavelength ratio for basaltic andesite syracuse is 3 1 suggesting a compositional control on deformation as proposed by previous studies video analysis of incrementally folded syracuse lava crusts reveals significant non coaxial strain which violates the assumptions of plane strain used in crustal buckling models these results show that interpreting lava rheology from finite strain requires careful consideration of complex three dimensional strain fields despite these complexities the correlation between fold wavelength ratios and lava flow composition persists and may provide important insight into flow characterization

the influence of topographic roughness on lava flow emplacement a quantitative understanding of the factors controlling lava flow emplacement is critical for both hazard assessment and mitigation and for the interpretation of past flow emplacement conditions the influence of topography with a vertical amplitude smaller than flow thickness i e substrate roughness is currently not accounted for in most flow emplacement models and hazard estimates here we measure the effect of substrate roughness on flow emplacement through experiments using analog fluids and molten basalt complementing recent work on the interaction of lava flows with obstacles taller than flow thickness we present results from three sets of analog experiments in which corn syrup polyethylene glycol and molten basalt were each extruded onto a sloping plane covered with a series of beds of varying grain sizes we find that flow front advance rates are impacted by bed roughness for all materials with decreases in average velocities by up to 50 with increases of substrate grain sizes by 5 100 times ranges analogous with topographic variations found in nature these decreases in flow front advance velocities are equivalent to up to an order of magnitude increase in fluid viscosity we interpret this velocity decrease to be caused by the movement of material into void spaces between substrate grains and by enhanced cooling through heat conduction to the substrate due to increased surface contact area the difference in advance velocity with increasing grain size diminishes with time after initial emplacement as a basal boundary layer is established additionally the experimental flow geometry measured by the complexity of the flow external perimeter became increasingly complex with increasing substrate grain size this effect will act to both slow the forward advance of lava flows and to create irregular emplacement paths of flows moving over rough surfaces we propose that flow emplacement models should be modified possibly through a calibrated effective viscosity term to account for bed roughness to increase accuracy in flow prediction and hazard estimation models

the chengwatana volcanics wisconsin and minnesota petrogenesis of the southernmost volcanic rocks exposed in the midcontinent rift the southernmost exposed rocks of the north american midcontinent rift system 1100 ma consist of 3000 m of mafic volcanic flows and minor interflow sediment exposed along the st croix river in minnesota and wisconsin the flows are mostly high fe tholeiitic basalt with plagioclase phenocrysts and ophitic to subophitic clinopyroxene abundant secondary chlorite epidote and actinolite indicate the group was metamorphosed to greenschist facies 350 c low sodium m4 site and tetrahedral aluminum aliv contents of actinolite indicate low pressure metamorphism 0 25 gpa and imply a geothermal gradient of 45 50 c km low magnesium mg 0 37 0 58 and ni contents 36 185 ppm indicate the basalts have undergone significant fractionation and are not primary mantle melts incompatible element abundances are inversely correlated with mg and most samples plot within either high or low trace element groups e g ti p zr the basalts are enriched in the light rare earth elements and th and are v

effects of heterogeneities and anisotropy on sonic and ultrasonic attenuation in rocks we compare the attenuation obtained by the resonant bar technique in the sonic frequency range 3 10 khz with that obtained by the pulse transmission technique in the ultrasonic frequency range 500 khz on a set of 30 rocks including sandstones and limestones the sonic and ultrasonic measurements were performed under high effective pressure on adjacent water saturated samples from each rock block compressional ultrasonic attenuation was typically larger than extensional sonic attenuation particularly in limestones this is attributed to the presence of density heterogeneities that can be seen on x ray scanner imagery heterogeneities at the scale of the ultrasonic wavelength produce diffraction of the waves and as a consequence high attenuation values at ultrasonic frequencies large apparent shear attenuation values compared to compressional attenuation values are explained by shear wave splitting

textural and rheological evolution of basalt flowing down a lava channel the muliwai a pele lava channel was emplaced during the final stage of mauna ulu s 1969 1974 eruption kilauea hawaii the event was fountain fed and lasted for around 50 h during which time a channelized flow system developed in which a 6 km channel fed a zone of dispersed flow that extended a further 2 6 km the channel was surrounded by initial rubble levees of a a capped by overflow units of limited extent we sampled the uppermost overflow unit every 250 m down the entire channel length collecting and analyzing 27 air quenched samples bulk chemistry density and textural analyses were carried out on the sample interior and glass chemistry and microlite crystallization analyses were completed on the quenched crust thermal and rheological parameters cooling crystallization rate viscosity and yield strength were also calculated results show that all parameters experience a change around 4 5 km from the vent at this point there is a lava surface transition from pahoehoe to a a lava density microlite content viscosity and yield strength all increase down channel but vesicle content and lava temperature decrease cooling rates were 6 7 c km with crystallization rates increasing from 0 03 c km proximally to 0 14 c km distally modeling of the channel was carried out using the flowgo thermo rheological model and allowed fits for temperature microlite content and channel width when run using a three phase viscosity model based on a temperature dependent viscosity relation derived for this lava the down flow velocity profile suggests an initial velocity of 27 m s declining to 1 m s at the end of the channel down channel lava underwent cooling that induced crystallization causing both the lava viscosity and yield strength to increase moreover lava underwent degassing and a subsequent vesicularity decrease this aided in increasing viscosity with the subsequent increase in shearing promoting a transition to a a

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

rheological behavior of bubble bearing magmas abstract the vesiculation of the rising magma in a volcanic conduit results in a large change in the viscosity of magma understanding the effect of bubbles on the viscous behavior of bubble melt mixtures over a wide range of bubble volume fractions is essential for accurate modeling of the volcanic processes in this study new equations for the relative viscosity of concentrated bubble bearing suspensions are developed using a differential scheme along with the solution of an infinitely dilute suspension of bubbles out of the four models developed in the paper two models predict the relative viscosity to be a function of only two variables capillary number and volume fraction of bubbles there are no adjustable parameters in these models the remaining two models include an additional parameter that is the maximum packing volume fraction of bubbles the proposed models are evaluated using published numerical and experimental data on the relative viscosity of concentrated suspensions of bubbles the viscosity models for bubble bearing suspensions developed in this study are useful in modeling of the volcanic processes

linear volcanoes along the pacific cocos plate boundary 9 n to the galapagos triple junction abstract a seabeam based reconnaissance of the 500 km of the east pacific rise crest between 7 n and 2 40 n shows that the axial ridge is segmented by four 4 13 km non transform offsets into an en echelon string of distinctively different linear volcanoes these axial volcanoes are oriented orthogonal to relative plate motion except where their overlapping ends veer 15 toward each other and where small intra volcano offsets of their crestal rift zones create abrupt kinks longitudinal gradients of the crestlines are less than 5 m km except where they plunge at rift zones overlapped ends and where they rise locally to small axial peaks transverse profiles vary from trapezoidal to triangular with a steep shield shaped cross section being most common conventional sounding data indicate that this pattern continues to the 140 km offset siqueiros transform fault system at 8 2 n within this fault system is a short spreadingcenter volcano contained in a rift valley that links two strike slip fault zones immediately to the north is the shallow 9 0 8 3 n axial volcano with unusual relief mapped by a deeply towed instrument package at the southern end of the plate boundary as the rise crest enters the region of the pacific cocos nazca triple junction the axial ridge narrows deepens and acquires a more irregular long profile south of 2 30 n the rise crest has a 15 km wide rift valley that contains multiple volcanic ridges with north south strikes structural hypotheses suggested or supported by these morphologic observations include a point source magma supply to the spreading center from mantle diapirs the along strike continuity of axial magma chambers on fast spreading rises even across small rift zone offsets and the importance of magma intrusion as well as eruption for building the axial ridge hypotheses inconsistent with the new data include magma supply and long distance dispersal from a few widely spaced plumes primary control of the topographic volcanic and tectonic characteristics of the rise crest by distance from transform faults and localization of triple junctions over major mantle upwellings

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

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

how shear helps lava to flow understanding the thermo rheological regime and physical character of lava while it is flowing is crucial if we are to adequately model lava flow emplacement dynamics we present measurements from simultaneous sampling and thermal imaging across the full width of an active channel at piton de la fournaise la reunion france our data set involves measurements of flow dynamics at three sites down channel from the vent quantification of flow velocities cooling rates sample texture and rheology allows all thermo rheological parameters to be linked and down as well as cross channel variations to be examined within 150 m from the vent we recorded an unexpected velocity increase from 0 07 to 0 1 m s in spite of cooling rates of 0 19 to 0 29 degree sign c m and constant slope this change requires a switch from a newtonian dominated regime to a bingham plug dominated regime sample analysis reveals that the plug comprises foam like lava and the shear zones involve vesicle poor low viscosity lava with distance from the vent shear zones develop carrying the vesicular plug between them this causes flow to initially accelerate helped by bubble shearing in narrow lateral shear zones until cooling takes over as the main driver for viscosity increase and hence velocity decrease

the memory of the accreting plate boundary and the continuity of fracture zones a detailed aeromagnetic anomaly map of the mesozoic seafloor spreading lineations southwest of bermuda reveals the dominant magnetic grain of the oceanic crust and the character of the accreting boundary at the time of crustal formation the magnetic anomaly pattern is that of a series of elongate lobes perpendicular to the fracture zone flowline trends the linear sets of magnetic anomaly peaks and troughs have narrow regions of reduced amplitude anomalies associated with the fracture zones during the period of mesozoic geomagnetic polarity reversals when 1200 km of central north atlantic seafloor formed the atlantic accreting boundary consisted of stationary elongate spreading center cells that maintained their independence even though sometimes only minor spatial offsets existed between cells normal oceanic crustal structure was formed in the spreading center cells but structural anomalies and discontinuities characteristic of fracture zones were formed at their boundaries which parallel flowlines of mesozoic relative plate motion in the central north atlantic we suggest that the memory for a stationary pattern of independent spreading center cells resides in the young brittle lithosphere at the accreting boundary where the lithosphere is weakest here each spreading center cell independently goes through its cylce of stress buildup stress release and crustal accretion after which its memory is refreshed the temporal offset between the peaks of the accretionary activity that takes place within each cell may provide the mechanism for maintaining the independence of adjacent spreading center cells through times when no spatial offset between the cells exists

dynamics and viscosity of a a and pahoehoe lava flows of the 2012 2013 eruption of tolbachik volcano kamchatka russia the 2012 2013 flank eruption of tolbachik volcano kamchatka lasted 9 months and produced 0 54 km3 of basaltic trachyandesite lava thus becoming one of the most voluminous historical lava effusions of basic composition in subduction related environments globally from march to july 2013 the volcano monotonously erupted lava of constant composition sio2 52 wt with a nearly stable effusion rate of 18 m3 s despite the uniform eruptive and emplacement conditions the dominant style of lava propagation throughout that time gradually changed from a a to pahoehoe we report results of instrumental field measurements of the a a and pahoehoe flow dynamics documented with time lapse cameras as well as the lava viscosity determined by flow rate and shear stress using penetrometer methods maximal propagation velocities of the a a fronts ranged from 2 to 25 mm s and those of the pahoehoe from 0 5 to 6 mm s the flow front velocities of both lava types experienced short period fluctuations that were caused by complex flow mechanics of the advancing flow lobes minimal viscosities of lava of the a a lobes ranged from 1 3 105 to 3 3 107 pa s flow rate method and those of the pahoehoe from to 5 103 to 5 104 pa s shear stress method our data include the first ever measured profiles of viscosity through the entire thickness of actively advancing pahoehoe lava lobes we have found that both the a a and pahoehoe flows were fed by identical parental lava which then developed contrasting rheological properties owing to differences in the process of lava transport over the ground surface the observed transition from the dominant a a to the dominant pahoehoe propagation styles occurred due to gradual elongation and branching of the lava tube system throughout the course of the eruption such evolution became possible because the growing lava field composed of semisolidified flows provided an environment for shallow subsurface intrusions and internal migrations of lava that with time developed into branches of the lava tube system based on our data we propose phenomenological models of the a a and pahoehoe flow mechanics

investigating lava flow rheology using video analysis and numerical flow models abstract lava rheology is a major control on lava flow behavior and a critical parameter in flow simulations but is very difficult to measure at field conditions or correctly extrapolate from the lab scale we present a new methodology for investigating lava rheology through a combination of controlled experiments image analysis and numerical forward modeling our experimental setup part of the syracuse university lava project http lavaproject syr edu includes a large furnace capable of melting up to 450 kg of basalt at temperatures well above the basalt liquidus the lava is poured onto either a tilted bed of sand or a steel channel to produce meter long flows this experimental setup is probably the only facility that allows such large scale controlled lava flows made of natural basaltic material we document the motion of the lava using a high resolution video camera placed directly above the flows and the temperature using infrared probes and cameras after collecting the footage we analyze the images for lava deformation and compare with numerical forward models to constrain the rheological parameters and laws which best describe the flowing lava for the video analysis we employ the technique of differential optical flow which uses the time variations of the spatial gradients of the image intensity to estimate velocity between consecutive frames an important benefit for using optical flow compared with other velocimetry methods is that it outputs a spatially coherent flow field rather than point measurements we demonstrate that the optical flow results agree with other measures of the flow velocity and estimate the error due to noise and time variability to be under 30 of the measured velocity our forward models are calculated by solving the stokes flow equations on an unstructured finite element mesh defined using the geometry of the observed flow itself we explore a range of rheological parameters including the lava s apparent viscosity the power law exponent m and the thermal activation energy our measurements of apparent viscosity agree well with predictions of the composition based shaw 1972 and grd model giordano russell and dingwell 2008 we find that for the high temperature portion of the flow a weakly shear thinning or newtonian rheology m 0 7 with an effective activation energy of b 5500 j gives the best fit to the data our methodology is the first time that high resolution optical flow analysis of flowing lava is combined with numerical flow models to constrain rheology the methodology we present here can be used in field conditions to obtain in situ information on lava rheology without physical interaction with the flow and without being limited to point wise low strain rate local measurements currently available through the use of rotational viscometers in the field

rheology of arc dacite lavas experimental determination at low strain rates andesitic dacitic volcanoes exhibit a large variety of eruption styles including explosive eruptions endogenous and exogenous dome growth and kilometer long lava flows the rheology of these lavas can be investigated through field observations of flow and dome morphology but this approach integrates the properties of lava over a wide range of temperatures another approach is through laboratory experiments however previous studies have used higher shear stresses and strain rates than are appropriate to lava flows we measured the apparent viscosity of several lavas from santiaguito and bezymianny volcanoes by uniaxial compression between 1 109 and 1 315 k at low shear stress 0 085 to 0 42 mpa low strain rate between 1 1 10 8 and 1 9 10 5 s 1 and up to 43 7 total deformation the results show a strong variability of the apparent viscosity between different samples which can be ascribed to differences in initial porosity and crystallinity deformation occurs primarily by compaction with some cracking and or vesicle coalescence our experiments yield apparent viscosities more than 1 order of magnitude lower than predicted by models based on experiments at higher strain rates at lava flow conditions no evidence of a yield strength is observed and the apparent viscosity is best approached by a strain rate and temperature dependent power law equation the best fit for santiaguito lava for temperatures between 1 164 and 1 226 k and strain rates lower than 1 8 10 4 s 1 is log eta text app 0 738 9 24 times 10 3 t k 0 654 cdot log dot varepsilon where app is apparent viscosity and dot varepsilon is strain rate this equation also reproduced 45 data for a sample from bezymianny with a root mean square deviation of 0 19 log unit pa s applying the rheological model to lava flow conditions at santiaguito yields calculated apparent viscosities that are in reasonable agreement with field observations and suggests that internal shear heating may be significant ongoing heat source within these flows enabling highly viscous lava to travel long distances

mantle flow at oceanic spreading centers models derived from ophiolites abstract the internal structures of eleven ophiolite complexes have been structurally investigated the attitude of the foliation and the lineation in the peridotites is related to asthenospheric flow in the uppermost mantle at an oceanic spreading center from the orientation of these structures with respect to the paleohorizontal plane two oceanic situations are distinguished the horizontally spreading asthenosphere illustrated by the table mountain massif newfoundland is characterized by 1 a homogeneous regular and sub horizontal plastic flow pattern over large distances 2 b flat paleo mono and absence of large scale folding 3 c rare economical chromite deposits and depleted mantle the diapirically spreading asthenosphere illustrated by the acoje type philippines displays 1 a inhomogeneous and sub vertical plastic flow pattern 2 b deformed paleo moho and large scale folds 3 c important economical chromite deposits and less depleted mantle presumably due to secondary magmatic impregnation this leads to vogt s model of asthenospheric flow beneath an oceanic ridge the direction of which being equated with the dike swarm in this model the horizontally spreading asthenosphere is derived from the diapirically spreading one in the following way the vertical mantle flow at the diapir center diverges horizontally in every direction including that parallel to the ridge at about 50 km from the diapir center the mantle flow becomes progressively perpendicular to the ridge due to the damming effect of transform faults an important economical consequence of this model is that large chromite deposits are expected preferentially in the diapiric type of ophiolite because chromite is preferentially precipitated at the diapir center from pristine magma

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

the effect of bubbles on the rheology of basaltic lava flows insights from large scale two phase experiments abstract bubbles are known to have a dramatic effect on lava rheology but their impact on lava flow run out distance has not been extensively investigated to quantify bubble effects on basaltic lava flow emplacement we conducted a series of large scale two phase melt bubbles experiments at the syracuse university lava project facility in this study nine basaltic lava flows with low to intermediate vesicle contents approximately 3 24 vol were emplaced over gently sloping 4 9 dry sand surfaces their velocities were measured by particle image velocimetry and their bulk viscosities were calculated using jeffreys equation comparison with melt only viscosities calculated through the grd model allowed the isolation of the effect of bubbles on the viscosity of the experimental flows we find that within the investigated range of vesicularities bubbles increase the relative viscosity of the experimental flows by up to an order of magnitude the increase appears to be steeper for sheet flows than for lobate and toey flows our results which quantitatively assess the effect of bubbles on the rheology of basaltic lava flows will provide a basis for the refinement of models for multi phase flows that are fundamental to accurately forecasting the emplacement of lava flows

transient phenomena in vesicular lava flows based on laboratory experiments with analogue materials realistic lava flow models require a comprehensive understanding of the rheological properties of lava under a range of stress conditions previous measurements have shown that at typical eruption temperatures lavas are non newtonian this is commonly attributed to the formation and destruction of crystal networks in the present study the effects of bubbles on the time dependent non newtonian properties of vesicular melts are investigated experimentally using analogue materials the shear thinning behaviour of bubbly liquids is shown to be dependent on the previous shearing history this thixotropic behaviour which was investigated using a rotational vane viscometer is caused by delayed bubble deformation and recovery when subjected to changes in shear stress the viscoelastic transition and the transient flow behaviour of analogue fluids were studied using both a rotational vane viscometer and oscillatory shear apparatus these experiments have shown that vesicular suspensions are viscoelastic fluids with a yield strength power law rheology and a non zero shear modulus these properties are also found in polymer fluids commonly used as analogue materials for lava such as gum rosin we show that when materials with this rheology are accelerated in channels they may be fragmented and when they flow through a narrowing conduit pulsating flow can develop as a consequence of a transition from slip to non slip conditions at the conduit wall this has important implications both for effusive and explosive volcanic eruptions

interactions between deformation and fluids in the frontal thrust region of the nantroseize transect offshore the kii peninsula japan results from iodp expedition 316 sites c0006 and c0007 integrated ocean drilling program iodp expedition 316 sites c0006 and c0007 examined the deformation front of the nankai accretionary prism offshore the kii peninsula japan in the drilling area the frontal thrust shows unusual behavior as compared to other regions of the nankai trough drilling results integrated with observations from seismic reflection profiles suggest that the frontal thrust has been active since 0 78 0 436 ma and accommodated 13 to 34 of the estimated plate convergence during that time the remainder has likely been distributed among out of sequence thrusts further landward and or accommodated through diffuse shortening unlike results of previous drilling on the nankai margin porosity data provide no indication of undercompaction beneath thrust faults furthermore pore water geochemistry data lack clear indicators of fluid flow from depth these differences may be related to coarser material with higher permeability or more complex patterns of faulting that could potentially provide more avenues for fluid escape in turn fluid pressures may affect deformation well drained sand rich material under the frontal thrust could have increased fault strength and helped to maintain a large taper angle near the toe recent resumption of normal frontal imbrication is inferred from seismic reflection data associated decollement propagation into weaker sediments at depth may help explain evidence for recent slope failures within the frontal thrust region this evidence consists of seafloor bathymetry normal faults documented in cores and low porosities in near surface sediments that suggest removal of overlying material overall results provide insight into the complex interactions between incoming materials deformation and fluids in the frontal thrust region

constraining tephra dispersion and deposition from three subplinian explosions in 2011 at shinmoedake volcano kyushu japan constraining physical parameters of tephra dispersion and deposition from explosive volcanic eruptions is a significant challenge because of both the complexity of the relationship between tephra distribution and distance from the vent and the difficulties associated with direct and comprehensive real time observations three andesitic subplinian explosions in january 2011 at shinmoedake volcano japan are used as a case study to validate selected empirical and theoretical models using observations and field data tephra volumes are estimated using relationships between dispersal area and tephra thickness or mass area a new cubic b spline interpolation method is also examined magma discharge rate is estimated using theoretical plume models incorporating the effect of wind results are consistent with observed plume heights 6 4 7 3 km above the vent and eruption durations estimated tephra volumes were 15 34 106 m3 for explosions on the afternoon of 26 january and morning of 27 january and 5 0 7 6 106 m3 for the afternoon of 27 january magma discharge rates were in the range 1 2 106 kg s for all three explosions clast dispersal models estimated plume height at 7 1 1 km above the vent for each explosion the three subplinian explosions occurred with approximately 12 h reposes and had similar mass discharge rates and plume heights but decreasing erupted magma volumes and durations

channel networks within lava flows formation evolution and implications for flow behavior new high resolution maps of hawaiian lava flows highlight complex topographically controlled channel networks network geometries range from distributary systems dominated by branching around local obstacles to tributary systems constricted by topography we combine 2 d network analysis tools developed for river systems and neural networks with 3 d lidar morphologic analysis and historical records of flow emplacement to investigate both the origins of channel networks and their influence on flow morphology and behavior we find that network complexity is a function of underlying slope and that the degree of flow branching network connectivity and longevity of individual channels all influence the final flow morphology flow and channel widths and levee heights furthermore because channel networks govern the distribution of lava supply within a flow changes in the channel topology can dramatically alter the effective volumetric flux in any one branch which affects both flow length and advance rate specifically branching will slow and shorten flows while merging can accelerate and lengthen them consideration of channel networks is thus important for predicting lava flow behavior and mitigating flow hazards with diversion barriers observed relationships between network geometry flow parameters and morphology also offer insight into the interpretation of these features elsewhere on earth and other terrestrial planets

insights on lava ice snow interactions from large scale basaltic melt experiments quantitative measurements of interactions between lava and ice snow are critical for improving our knowledge of glaciovolcanic hazards and our ability to use glaciovolcanic deposits for paleoclimate reconstructions however such measurements are rare because the eruptions tend to be dangerous and not easily accessible to address these difficulties we conducted a series of pilot experiments designed to allow close observation measurements and textural documentation of interactions between basaltic melt and ice here we report the results of the first experiments which comprised controlled pours of as much as 300 kg of basaltic melt on top of ice our experiments provide new insights on 1 estimates for rates of heat transfer through boundary layers and for ice melting 2 controls on rates of lava advance over ice snow 3 formation of lava bubbles i e limu o pele by steam from vaporization of underlying ice or water and 4 the role of within ice discontinuities to facilitate lava migration beneath and within ice the results of our experiments confirm field observations about the rates at which lava can melt snow ice the efficacy with which a boundary layer can slow melting rates and morphologies and textures indicative of direct lava ice interaction they also demonstrate that ingestion of external water by lava can create surface bubbles i e limu and large gas cavities we propose that boundary layer steam can slow heat transfer from lava to ice and present evidence for rapid isotopic exchange between water vapor and melt we also suggest new criteria for identifying ice contact features in terrestrial and martian lava flows