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

geochemistry of volcanic gas at the 2012 13 new tolbachik eruption kamchatka abstract we report measurements of the chemical and isotopic composition of gas emitted from the lava flow at the 2012 13 new tolbachik eruption gas and condensate samples were taken from two vents over a lava tube in may 2013 the 1030 c gas sample was collected in evacuated giggenbach bottle from a periodically pumping to venting outlet above active lava flow 300 m from naboko cone concentrations of major components in the 1030 gas sample are mol 95 5 h 2 o 0 47 co 2 2 01 so 2 1 18 hcl 0 34 hf that are within a range of gas compositions for subduction zone volcanoes isotopic analysis of he gives a corrected to atmosphere r r a ratio 7 24 he ne ratio 1 41 that is close to morb values the 1030 c condensate contained 9 7 ppm cu 2 5 ppm zn 1 5 ppm tl 20 ppb re and 3 ppb au and can be considered as a representative sample for the metal composition of exsolved magmatic gases at the 2012 13 tolbachik eruption isotopic data on the 1030 c condensate 18 o 6 4 d 32 indicate a magmatic source another condensate sample taken at 690 c was found to be drastically different from the magmatic 1030 c condensate we suggest that the disproportional enrichment in trace elements of this 690 c condensate as compared to the 1030 c condensate could result from evaporation at forced pumping during sampling and possible dissolution of earlier precipitated sublimates in the gas conduit unusual isotopic composition of the 690 c condensate 18 18 9 d 68 5 can be explained by the isotopic exchange between volcanic vapor and atmospheric o 2 18 23 5

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

toothpaste lava characteristics and origin of a lava structural type transitional between pahoehoe and aa toothpaste lava an important basalt structural type which illustrates the transition from pahoehoe to aa is particularly well displayed on the 1960 kapoho lava of kilauea volcano its transitional features stem from a viscosity higher than that of pahoehoe and a rate of flow slower than that of aa viscosity can be quantified by the limited settling of olivine phenocrysts and rate of flow by field observations related to the low angle slope on which the lava flowed much can be learned about the viscosity rheologic condition and flow velocity of lavas long after solidification by analyses of their structural characteristics and it is possible to make at least a semiquantitative assessment of the numerical values of these parameters

viscoelastic behaviour of basaltic lavas the rheological properties of basaltic lavas from etna hawai i and vesuvius have been investigated at temperatures between 500 and 1150 c using a small strain oscillatory shear the viscoelastic response of the lavas to small forced sinusoidal torques 109 pa s could be measured at strain rates less than 10 2 10 1 s 1 at 800 c temporal variations in complex shear modulus and internal friction suggest that over durations of up to 120 h structural adjustments were occurring within some of the samples this time varying behaviour of lava samples may be attributed to the slow closing healing of microcracks and small pore spaces resulting in the apparent stiffening of lava samples under annealing thus those parts of lava flows that undergo slow cooling will have more elastic properties regions that cool faster possess smaller shear moduli and higher internal friction due to thermal microcracking and less cohesion between crystals and the bulk glassy matrix

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

a 14 000 year record of fire climate and vegetation from the bear river range southeast idaho usa the vegetation and fire history of the bear river range brr southeast idaho has been reconstructed from pollen plant macrofossils and macroscopic charcoal from lacustrine sediments overall the brr record shows independent responses of vegetation and fire regime to climate variation the reconstructions suggest strong seasonal bias from the proxies evaluated with the pollen record most sensitive to insolation driven summer temperature trends and the charcoal based fire record more sensitive to winter snowpack variability together the proxies suggest that the early holocene experienced larger than average snowpacks but very warm summers warmer than modern summer temperatures were maintained through much of the mid holocene but snowpacks decreased dramatically creating the most extreme xeric conditions in the holocene between 7100 and 6000 bp after 6000 bp summers began to show a consistent cooling trend winter precipitation remained low until 4400 bp after which higher than average snowp

dynamics and energetics of bubble growth in magmas analytical formulation and numerical modeling we have developed a model of diffusive and decompressive growth of a bubble in a finite region of melt which accounts for the energetics of volatile degassing and melt deformation as well as the interactions between magmatic system parameters such as viscosity volatile concentration and diffusivity on the basis of our formulation we constructed a numerical model of bubble growth in volcanic systems we conducted a parametric study in which a saturated magma is instantaneously decompressed to one bar and the sensitivity of the system to variations in various parameters is examined variations of each of seven parameters over practical ranges of magmatic conditions can change bubble growth rates by 2 4 orders of magnitude our numerical formulation allows determination of the relative importance of each parameter controlling bubble growth for a given or evolving set of magmatic conditions an analysis of the modeling results reveals that the commonly invoked parabolic law for bubble growth dynamics r t1 2 is not applicable to magma degassing at low pressures or high water oversaturation but that a logarithmic relationship r log t is more appropriate during active bubble growth under certain conditions a second aspect of our study involved a constant decompression bubble growth model in which an initially saturated magma was subjected to a constant rate of decompression model results for degassing of initially water saturated rhyolitic magma with a constant decompression rate show that oversaturation at the vent depends on the initial depth of magma ascent on the basis of decompression history explosive eruptions of silicic magmas are expected for magmas rising from chambers deeper than 2 km for ascent rates 1 5 m s 1

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

pāhoehoe a ā and block lava an illustrated history of the nomenclature lava flows occur worldwide and throughout history various cultures and geologists have described flows based on their surface textures as a result surface morphology based nomenclature schemes have been proposed in most languages to aid in the classification and distinction of lava surface types one of the first to be published was likely the nine class italian language description based classification proposed by mario gemmellaro in 1858 by far the most commonly used terms to describe lava surfaces today are not descriptive but instead are merely words specifically the hawaiian words a rough brecciated basalt lava and p hoehoe smooth glassy basalt lava plus block lava thick brecciated lavas that are typically more silicic than basalt a and p hoehoe were introduced into the western geological vocabulary by american geologists working in hawai i during the 1800s they and other nineteenth century geologists proposed formal lava type classification schemes for scientific use and most of them used the hawaiian words in 1933 ruy finch added the third lava type block lava to the classification scheme with the tripartite system being formalized in 1953 by gordon macdonald more recently particularly since the 1980s and based largely on studies of lava flow interiors a number of sub types and transitional forms of all three major lava types have been defined this paper reviews the early history of the development of the p hoehoe a and block lava naming system and presents a new descriptive classification so as to break out the three parental lava types into their many morphological sub types

channel overflows of the pōhue bay flow mauna loa hawai i examples of the contrast between surface and interior lava a number of overflows from a large lava channel and tube system on the southwest rift zone of mauna loa were studied initial overflows were very low viscosity gas rich p hoehoe evidenced by flow unit aspect ratios and vesicle sizes and contents calculated volumetric flow rates in the channel range between 80 and 890 m3 s and those of the overflows between 35 and 110 m3 s after traveling tens to hundreds of meters the tops of these sheet like overflows were disrupted into a surface composed of clinker and p hoehoe fragments after these a overflows came to rest lava from the interiors was able to break out on to the surface as p hoehoe the surface structure of a lava flow records the interaction between the differential shear rate usually correlated with the volumetric flow rate and viscosity induced resistance to flow however the interior of a flow being better insulated may react differently or record a later set of emplacement conditions clefts of toothpaste lava occurring within fields of clinker on proximal type a flows also record different shear rates during different times of flow emplacement the interplay between viscosity and shear rate determines the final morphological lava type and although no specific portion of lava ever makes a transition from a back to p hoehoe parts of a flow can appear to do so

heat transfer in volcano ice interactions on earth the very high temperature contrast between magma lava and water ice commonly leads to the assumption that significant melting will take place immediately upon magma lava ice contact yet observations of active flows show little evidence of voluminous melting upon contact we use analytical thermal models to reassess the efficiency with which heat can be transferred from magma to ice in three situations lava flows erupted on top of glacial ice sill intrusions beneath glacial ice evolving into subglacial lava flows and dyke intrusions into the interiors of glaciers we find that the maximum ratios of thickness of ice that can be melted to the thickness of magmatic heat source are likely to be 2 5 for subaerial lava flows encroaching onto glaciers 6 7 for subglacial lava flows and 10 for dykes intruded into glacial ice rates of ice melt production are not linear functions of time and flow thickness however and this may account for the observations of minimal immediate water release from beneath advancing lava flows field observations during future eruptions should be directed at measuring the temperature of released water

longitudinal deformation of a lava flow the influence of bingham rheology abstract the behaviour of a lava flow is reproduced by a two dimensional model of a bingham liquid flowing down a slope the liquid is described by two parameters viscosity and yield stress both strongly temperature dependent assuming liquidus temperature at the eruption vent the temperature decrease due to the heat loss by radiation produces changes in the rheological parameters and consequently in velocity strain and strain rate along the flow velocity compressive strain strain rate and stress along the flow direction are computed as functions of the distance from the vent and of time for different kinds of lava flows basic and acidic and are compared with corresponding results for a newtonian liquid the model shows that in connection with the pronounced velocity decrease occurring at a certain distance from the vent the compressive strain strain rate and stress also show a strong variation a greater compressive strain is in fact induced in a bingham flow cooling by radiation than in a newtonian flow this behaviour may explain the presence of folds which are commonly observed at the surface of cooled lava flows

the evolution of high alumina basalts of the klyuchevskoy volcano kamchatka russia based on microprobe analyses of mineral inclusions abstract the origin of calc alkaline high alumina basalts hab of the klyuchevskoy volcano kamchatka was examined using electron microprobe analyses of phenocrysts and mineral phases included in the phenocrysts continuous trends on major element variation diagrams suggest the hab were derived from high magnesia basalt hmb by fractional crystallization phenocrysts in the hab are strongly zoned olivine mg 91 64 clinopyroxene wo45 38en40 51fs5 20 and chrome spinel magnetite inclusions in them cr2o3 45 0 wt tio2 0 5 11 microprobe analyses of minerals included in the phenocrysts provide additional constraints on the mineral crystallization trends in the hab fe mg partitioning data when applied to the phenocrysts cores show they crystallized from a hmb the similarity of phenocryst core compositions in hab with those in hmb strongly suggests a genetic relationship between the two magma types

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

pulsed inflation of pahoehoe lava flows implications for flood basalt emplacement abstract dilated fractures in hawaiian pahoehoe lava flows contain three zones that show the kinematics of inflation the upper columnar zone forms through thermal contraction prior to inflation the middle planar zone reflects inflation induced tension and the lower banded zone contains evidence of brittle and ductile deformation the formation of the lower banded zone requires varying strain rates during fracture propagation and is best explained by a model where small pulses of lava inject beneath the cooled flow crust through a network of preferred pathways we demonstrate via simple models of pipe flow that this inflation mechanism is incapable of producing areally extensive continental flood basalts on earth although it may explain related features on large martian volcanoes

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

thermal infrared spectral character of hawaiian basaltic glasses multispectral thermal infrared remote sensing of hawaiian basalts younger than a few hundred years old can be used to discriminate basalt lava flows that are difficult to map with visible and near infrared images laboratory thermal infrared reflectance spectra of the exposed surfaces of mauna loa and kilauea basalts show systematic changes with age fresh glass collected from active lava flows shows a broad reflectance feature between 8 and 12 m indicative of a strong degree of disorder after a few weeks of exposure to the environment the spectra of the top surfaces of samples begin to exhibit spectral features suggestive of ordering into silicate chainlike and sheetlike units with progressive aging features of apparent sheetlike structures become the preferred mode as soon as 3 years after emplacement a silica rich coating can begin to develop on the surfaces adding another spectral feature to the laboratory reflectance measurements the thermal infrared multispectral scanner tims with six channels between 8 and 12 m has been used to take advantage of these spectral differences in basalts to map flows in hawaii remote sensing instruments with increased spectral resolution in the thermal infrared would aid in further discrimination of basalts with more subtle differences in age quenching and weathering histories

mafic crystal distributions viscosities and lava structures of some hawaiian lava flows the distribution patterns of mafic phenocrysts in some hawaiian basalt flows are consistent with simple in situ gravitational settling we use the patterns to estimate the crystal settling velocity and hence viscosity of the lava which in turn can be correlated with surface structures numerical modeling generates theoretical crystal concentration profiles through lava flow units of different thicknesses for differing settling velocities by fitting these curves to field data crystal settling rates through the lavas can be estimated from which the viscosities of the flows can be determined using stokes law lavas in which the crystal settling velocity was relatively high on the order of 5 10 4 cm sec show great variations in phenocryst content both from top to bottom of the same flow unit and from one flow unit to another such lava is invariably pahoehoe flow units of which are usually less than 1 m thick lavas in which the crystal settling velocity was low show a small but measurable variation in phenocryst content these lavas are part of a progression from a rough pahoehoe to toothpaste lava to a a toothpaste lava is characterized by spiny texture as well as the ability to retain surface grooves during solidification and flow units are usually thicker than 1 m in the thickest of hawaiian a a flows those of the distal type no systematic crystal variations are observed and high viscosity coupled with a finite yield strength prevented crystal settling the amount of crystal settling in pahoehoe indicates that the viscosity ranged from 600 to 6000 pa s the limited amount of settling in toothpaste lava indicates a viscosity greater than this value approaching 12 000 pa s we infer that distal type a a had a higher viscosity still and also possessed a yield strength

the importance of pahoehoe abstract pahoehoe lava flows are common in every basaltic province and their submarine variants pillow lavas and sheet flows cover the bulk of the earth pahoehoe flows are emplaced by inflation the injection of molten lava underneath a solidified crust only in the past few years has an understanding of the inflation process and the ability to recognize ancient inflated lava flows been achieved all large terrestrial basaltic flow fields studied to date including flood basalts were emplaced as thermally efficient inflated compound pahoehoe sheet flows this leads us to propose that this is the standard way of emplacing large lavas the swell hypothesis the atmospheric impact of such flood basalt eruptions could have been protracted and severe providing a plausible link between flood basalt eruptions and mass extinctions

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

the initial cooling of pahoehoe flow lobes in this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows the accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation this model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not an empirical fit to field data we find that the only significant processes are a heat loss by thermal radiation b heat loss by atmospheric convection c heat transport within the flow by conduction with temperature and porosity dependent thermal properties and d the release of latent heat during crystallization the numerical model is better able to reproduce field measurements made in hawai i between 1989 and 1993 than other published thermal models by adjusting one parameter at a time the effect of each of the input parameters on the cooling rate was determined we show that a the surfaces of porous flows cool more quickly than the surfaces of dense flows b the surface cooling is very sensitive to the efficiency of atmospheric convective cooling and c changes in the glass forming tendency of the lava may have observable petrographic and thermal signatures these model results provide a quantitative explanation for the recently observed relationship between the surface cooling rate of pahoehoe lobes and the porosity of those lobes jones 1992 1993 the predicted sensitivity of cooling to atmospheric convection suggests a simple field experiment for verification and the model provides a tool to begin studies of the dynamic crystallization of real lavas future versions of the model can also be made applicable to extraterrestrial submarine silicic and pyroclastic flows

lava effusion rate definition and measurement a review measurement of effusion rate is a primary objective for studies that model lava flow and magma system dynamics as well as for monitoring efforts during on going eruptions however its exact definition remains a source of confusion and problems occur when comparing volume flux values that are averaged over different time periods or spatial scales or measured using different approaches thus our aims are to 1 define effusion rate terminology and 2 assess the various measurement methods and their results we first distinguish between instantaneous effusion rate and time averaged discharge rate eruption rate is next defined as the total volume of lava emplaced since the beginning of the eruption divided by the time since the eruption began the ultimate extension of this is mean output rate this being the final volume of erupted lava divided by total eruption duration whether these values are total values i e the flux feeding all flow units across the entire flow field or local i e the flux feeding a single active unit within a flow field across which many units are active also needs to be specified no approach is without its problems and all can have large error up to 50 however good agreement between diverse approaches shows that reliable estimates can be made if each approach is applied carefully and takes into account the caveats we detail here there are three important factors to consider and state when measuring giving or using an effusion rate first the time period over which the value was averaged second whether the measurement applies to the entire active flow field or a single lava flow within that field and third the measurement technique and its accompanying assumptions

structure and origin by injection of lava under surface crust of tumuli lava rises lava rise pits and lava inflation clefts in hawaii tumuli are positive topographic features that are common on hawaiian pahoehoe lava flow fields particularly on shallow slopes and 75 measured examples are presented here to document the size range tumuli form by up tilting of crustal plates without any crustal shortening and are thus distinguished from pressure ridges which are up buckled by laterally directed pressure the axial or star like systems of deep clefts that characterize tumuli are defined here as lava inflation clefts their tips advanced into red hot lava and they widened as uplift proceeded and while the lava crust was thickening flat surfaced uplifts formed like tumuli by injection of lava under a surface crust were previously called pressure plateaus but lava rise is proposed instead the pits that abound among lava rises previously attributed to collapse or subsidence are generally formed because the lava around them rose and the name lava rise pit is proposed unique examples of tumuli and lava rises from which lava drained out under a surface crust 1 5 to 2 5 m thick are described from kilauea caldera these examples show that in tumuli and lava rises the crust floats on considerable bodies of fluid lava and is able to do so because of its higher vesicle content the fluid lava loses many of its gas bubbles during residence beneath the crust the bulk densities of samples from tumuli show a general downward increase the form of the density profile is consistent with the relationship that for any given crustal thickness the density of fluid lava closely matched the average density of that crust suggesting that the lava was stably density stratified it is inferred that stable stratification was regulated by out flows of the more vesicular lava fractions loss of bubbles through the lava inflation clefts and entry of injected lava at its level of neutral buoyancy below the uppermost meter the downward decrease in vesicularity closely conforms with that expected by compression of a uniform mass of gas per unit mass of lava

effect of slope on development of pahoehoe flow fields evidence from mount etna abstract we describe and compare two types of pahoehoe on mount etna one similar to an hawaiian inflated flow field consisting of tumuli lava rises and lava rise pits and the other a coalescing complex of rootless centres of ephemeral boccas fed from lava tubes and superimposed on an initial a a flow field the former we define as a primary pahoehoe field that results from relatively slow advance rate of lava over an almost horizontal surface the latter is a result of an eruption of long enough duration to allow tube formation over a substantial portion of the flow field over steeper slopes at breaks in slope in the underlying topography centres of ephemeral boccas develop giving rise to low effusion rate pahoehoe lavas covering the original channelled a a surface these we refer to as secondary pahoehoe flow fields

observations on lava snowpack and their interactions during the 2012 13 tolbachik eruption klyuchevskoy group kamchatka russia abstract observations made during january and april 2013 show that interactions between lava flows and snowpack during the 2012 13 tolbachik fissure eruption in kamchatka russia were controlled by different styles of emplacement and flow velocities a a lava flows and sheet lava flows generally moved on top of the snowpack with few immediate signs of interaction besides localized steaming however lavas melted through underlying snowpack 1 4 m thick within 12 to 24 h and melt water flowed episodically from the beneath flows pahoehoe lava lobes had lower velocities and locally moved beneath within the snowpack even there the snow melting was limited snowpack responses were physical including compressional buckling and doming and thermal including partial and complete melting maximum lava temperatures were up to 1355 k 1082 c type k thermal probes and maximum measured meltwater temperatures were 335 k 62 7 c theoretical estimates for rates of rapid e g radiative and slower conductive snowmelt are consistent with field observations showing that lava advance was fast enough for a a and sheet flows to move on top of the snowpack at least two styles of physical interactions between lava flows and snowpack observed at tolbachik have not been previously reported migration of lava flows beneath the snowpack and localized phreatomagmatic explosions caused by snowpack failure beneath lava the distinctive morphologies of sub snowpack lava flows have a high preservation potential and can be used to document snowpack emplacement during eruptions

morphological structural and textural variations in the 1988 1990 andesite lava of lonquimay volcano chile the 1988 1990 eruption of lonquimay volcano chile 38 s formed a 10 2 km long andesite lava with a volume of 0 23 km 3 over a period of 13 months the lava extrusion rate decreased with time as chamber pressure and vent dimensions decreased the velocity of the flow front decreased exponentially with distance from vent as a consequence of cooling and the increase of apparent viscosity at the flow front the lava developed a central channel which decreased in width and depth with time three prominent lava levees were formed on each margin and resulted from abandonment as the channel decreased in width as a result of a rapid decrease of flow rate over the first 100 days of activity a fourth major levee developed in february during a brief period of flow rate increase down the main channel but its walls were gradually exposed as the lava depth again decreased due to declining flow rate the structure of lava levees depended on their age and longevity of the flow in the adjacent channel initial levees were formed in the first few days as the lava spread laterally and then retreated leaving levees of massive lava more mature rubble levees were formed during the next month by the lava pushing and then shearing aa and blocky breccia which formed on the cooling flow margin fragmentation and abrasion formed a characteristic zonation in the levees a basal zone consists of very poorly sorted matrix rich breccia with very rounded vesicular clasts and bimodal grain size distribution the basal breccia zone strongly resembles block and ash flow deposits this zone passes up into a zone of clast supported clinker breccia which becomes increasingly matrix poor and coarser with clasts becoming more angular upwards the crest of the levee is composed of large 10 100 cm angular to subangular blocks with no matrix the zoned levees form after the active lava channel suddenly narrows lava depth initially increases and breccias are deposited on the channel margins and acquire the zoned structure by progressive shearing and accretion of clinkery aa breccia the lava level then drops exposing the steep inner scarp of a levee the most mature levee type formed in a long lived channel over several months the outer wall of the levee consists of zoned breccia but the inner wall consists of a massive curving wall of strongly foliated lava with well developed horizontal striations and ductile reidel shears the massive foliated facies is a consequence of prolonged flow which coats strongly sheared lava onto the inner levee wall scanning electron microscopy shows that the aa clinker clasts and foliated lava from the levee walls form at low melt fractions 15 in the last three months of the eruption the flow front ceased to advance but thickened as lava drained from proximal regions and intruded into the interior of the distal lava the last stages of lava movement were characterized by updoming in the central channel a lava surface feature named here armadillo structure was formed by deformation of the cooler but still ductile lava crust the deformation caused by underflow produced reidel shears dipping upstream and doming of the lava due to rotation of the shear planes the study demonstrates that lava morphology structure and texture are strongly influenced by variations of effusion rate local flow rate channel topography and thermal maturity of the lava which is reflected in downstream changes in viscosity

the influence of cross sectional channel geometry on rheology and flux estimates for active lava flows lava rheology and effusion rate are critical factors in determining the evolution of lava flows however direct and accurate field measurements are difficult to carry out and estimates are usually based on measurements of the flow s surface velocity and assumptions of sub surface geometry using numerical flow models we show that the potential for error due to geometry uncertainty is minimized if a semi elliptical cross sectional channel shape is assumed flow is simulated for isothermal newtonian temperature dependent newtonian and isothermal power law rheology lavas for isothermal newtonian lava we find that the error in channel shape alone can make apparent viscosity estimates 3 5 times too large e g for inappropriate use of the jeffreys equation on a narrow semi elliptical channel for a temperature dependent rheology using an analytical approximation for newtonian flow in a semi elliptical geometry yields apparent viscosity and flux values that are more accurate than estimates which assume a rectangular geometry for all channel shapes considered including rectangular channels viscosity calculations for real channels on mauna loa and mount etna show that for a newtonian rheology a semi elliptical analytical solution gives an approximation three times closer to the actual viscosity than a rectangle with the same depth while if the lava is shear thinning power law exponent m 0 6 a rectangular approximation is 15 more accurate our results can be used to bracket possible viscosity and flux estimates when channel topography is poorly constrained

monitoring of the volcanic rock compositions during the 2012 2013 fissure eruption at tolbachik volcano kamchatka abstract here we present the results from monitoring of the composition of rocks produced during the 2012 2013 fissure eruption at tolbachik volcano fte major and trace element concentrations in 75 samples are reported products of this eruption are represented by high alumina basaltic trachyandesites with higher alkalis and titanium contents than in all previously studied rocks of the tolbachik monogenetic volcanic field rocks erupted during the first three days 27 30 november from the northern also called menyailov group of vents are the most silica and alkali rich sio2 concentrations up to 55 35 wt and k2o up to 2 67 wt from december onwards when the eruptive activity switched from the menyailov vents to the southern naboko group of vents silica content dropped by 2 wt concentrations of mgo feo tio2 and mg increased and k2o and na2o concentrations and k2o mgo ratio decreased for the rest of the eruption the compositions of rocks remained constant and homogeneous no systematic compositional differences between lava bombs and scoria samples are evident trace element distributions in the rocks of the menyailov and naboko vent lavas are relatively uniform menyailov lavas have slightly higher th nb hf y and hree concentrations than the naboko vent lavas at more or less constant element ratios we explain the initial change in geochemistry by tapping of a slightly cooler and fractionated 3 mt and 8 cpx upper part of the magma storage zone before the main storage area began to feed the eruption thermodynamic constraints show that apparent liquidus temperatures varied from 1142 c to 1151 c and thermodynamic modeling shows that variations in compositions are consistent with a high degree of low pressure 100 300 mpa nominally anhydrous fractionation of a parent melt compositionally similar to the 1975 northern breakthrough high mg basalt geochemistry petrological observations and modeling are in agreement with the newly erupted material being derived from remnant high al magma from the 1975 76 southern breakthrough eruption with only slight amounts of cooling less than 1 c per year during the intervening 36 years

image based measurement of flux variation in distal regions of active lava flows 1 understanding the processes involved with the advance of lava flows is critical for improving hazard assessments at many volcanoes here we describe the application of computer vision and oblique photogrammetric techniques to visible and thermal images of active a flows in order to investigate distal flow processes at mount etna sicily photogrammetric surveys were carried out to produce repeated topographic data sets for calculation of volumetric lava flux at the flow fronts velocity profiles from a distal channel were obtained by rectification of a thermal image sequence and are used to investigate the rheological properties of the lava significant variations of the magma flux were observed and pulses of increased flux arrived within the flow front region on timescales of several hours the pulses are believed to be the distal result of more frequent flux changes observed in the vent region hence they reflect the importance of flow processes which are believed to cause the coalescence of flux pulses along the channel system as well as short period variations in effusion rate in considering advance processes for the individual flow fronts it must be assumed that they were fed by a highly unsteady flux which was volumetrically at least an order of magnitude lower than that observed near the vent

the emplacement of pahoehoe toes field observations and comparison to laboratory simulations we observed active pahoehoe lobes erupted on kilauea during may june 1996 and found a range of emplacement styles associated with variations in local effusion rate flow velocity and strain rate these emplacement styles were documented and quantified for comparison with earlier laboratory experiments at the lowest effusion rates velocities and strain rates smooth surfaced lobes were emplaced via swelling where new crust formed along an incandescent lip at the front of the lobe and the rest of the lobe was covered with a dark crust at higher effusion rates strain rates and velocities lobes were emplaced through tearing or cracking tearing was characterized by ripping of the ductile crust near the initial breakout point and most of the lobe surface was incandescent during its emplacement this mechanism was observed to generate both smooth surfaced lobes and when the lava encountered an obstacle folded lobes cracking lobes were similar to those emplaced via tearing but involved breaking of a thicker brittle crust at the initial breakout of the lobe and therefore required somewhat higher flow rates than did tearing cracking lobes typically formed ropy folds in the center of the lobe and smooth margins at the highest effusion rates strain rates and flow velocities the lava formed open channels with distinct levees the final lobe morphologies were compared to results from laboratory simulations which were designed to infer effusion rate from final flow morphology to quantitatively test the laboratory results on the scale of individual natural pahoehoe lobes there is general agreement between results from laboratory simulations and natural lavas on the scale of individual pahoehoe lobes but there are disparities between laboratory flows and lava flows on the scale of an entire pahoehoe lava flow field