experimental constraints on the rheology eruption and emplacement dynamics of analog lavas comparable to mercury s northern volcanic plains we present new viscosity measurements of a synthetic silicate system considered an analogue for the lava erupted on the surface of mercury in particular we focus on the northern volcanic plains nvp which correspond to the largest lava flows on mercury and possibly in the solar system high temperature viscosity measurements were performed at both superliquidus up to 1736 k and subliquidus conditions 1569 1502 k to constrain the viscosity variations as a function of crystallinity from 0 to 28 and shear rate from 0 1 to 5 s 1 melt viscosity shows moderate variations 4 16 pa s in the temperature range 1736 1600 k experiments performed below the liquidus temperature show an increase in viscosity as shear rate increases from 0 1 to 5 s 1 resulting in a shear thinning behaviour with a decrease in viscosity of ca 1 log unit the low viscosity of the studied composition may explain the ability of nvp lavas to cover long distances on the order of hundreds of kilometres in a turbulent flow regime using our experimental data we estimate that lava flows with thickness of 1 5 and 10 m are likely to have velocities of 4 8 6 5 and 7 2 m s respectively on a 5 ground slope numerical modelling incorporating both the heat loss of the lavas and its possible crystallization during emplacement allows us to infer that high effusion rates 10000 m3 s are necessary to cover the large distances indicated by satellite data from the messenger spacecraft

magma dynamics feeding yasur s explosive activity observed using thermal infrared remote sensing 1 a thermal infrared thermometer was used to record the passage of hot gases and fragments across a measurement area located at the exit of one of yasur s active vents recording was completed over 2 h during september 2011 a total of 200 explosive events were recorded we define two types of event low energy events with typical thermal energies of 14 kj and high energy events with typical thermal energies of 97 kj around 180 low energy events were recorded which together released 457 kj of radiant energy in contrast only 20 high energy events were recorded but they released 2042 kj we suggest that low energy events originate from a relatively shallow degassed magma reservoir and are associated with bursting of bubbles formed by bubble coalescence during ascent instead high energy events originate from a relatively deep fresh magma reservoir and are associated with slugs formed by foam collapse

degassing behaviour at basaltic volcanoes new insights from experimental investigations of different conduit geometry and magma viscosity abstract understanding gas magma dynamics in volcanic conduits and linking them with the associated geophysical signals at the surface is of fundamental importance in monitoring active volcanoes in the past a significant number of studies have been devoted to this topic addressing the onset the key factors governing each degassing regime and the related markers at the surface particularly at basaltic volcanoes here we first review such a broad and increasing literature focusing on the main approaches used in the attempt of deciphering conduit dynamics by indirect observations 1 analogue laboratory experiments and 2 seismo acoustic measurements then we combine the two techniques into a novel set of experiments addressing a crucial yet unexplored issue the irregularity i e the departure from an ideal smooth cylindrical shape of the conduit surface we built a set of epoxy conduits with various fractal dimensions dc i e irregularity of the internal surface using silicone oil as a proxy for magma different degassing patterns bubbly slug and churn annular flow were reproduced by changing systematically 1 injected gas flux 5 to 180 10 3 l s 2 analogue magma viscosity 10 to 1000 pas 3 fractal dimension dc of the conduit surface i e dc 2 dc 2 18 and dc 2 99 the experiments were monitored by means of a video camera and a set of sensor aimed to detect the seismic and acoustic signals results show that viscosity strongly influences the transition among degassing patterns and the recurrence rate of slug bursts at the surface moreover we observed an increase of the exponent of the power law equation linking squared seismic amplitude to gas flow rate with conduit roughness the opposite trend was noticed with increasing liquid viscosity these results have important implications for linking seismic tremor to eruption source parameters such as the volume discharge rate at different volcanoes or for investigating its temporal evolution at a single vent

loki io a periodic volcano loki is the most powerful volcano in the solar system it has been observed to be in continuous though variable activity since 1979 synthesis of more than a decade of groundbased data suggests that loki eruptions are cyclic with a 540 day period application of a simple lava cooling model to temperatures in loki patera and eruption start and end times implies that brightenings are due to a resurfacing wave propagating across the patera the data are most consistent with lava lake overturn but resurfacing by lava flows cannot be ruled out a porosity gradient in the lake crust could cause lava lake overturn to occur periodically on the timescale observed

long period events the most characteristic seismicity accompanying the emplacement and extrusion of a lava dome in galeras volcano colombia in 1991 abstract since its reactivation in 1988 the principal eruptions of galeras volcano occurred on may 4 9 1989 july 16 1992 and january 14 march 23 april 3 april 14 and june 7 1993 the initial eruption was a phreatic event which clearly marked a new period of activity a lava dome was extruded within the main crater in october 1991 and subsequently destroyed in an explosive eruption on july 16 1992 the eruptions that followed were all vulcanian type explosions the seismicity accompanying the emplacement extrusion and destruction of the lava dome was dominated by a mix of long period lp events and tremor displaying a variety of waveforms repetitive lp events with dominant periods in the range 0 2 1 s were observed in october and november 1991 and visually correlated with short energetic pulses of gas venting through a crack bisecting the dome surface each lp event was characterized by a weak precursory signal with dominant periods in the range 0 05 0 1 s lasting roughly 7 s using the fluid driven crack model of chouet 1988 1992 we infer that two distinct cracks may have acted as sources for the lp and precursor signals spectral analyses of the data yield the following parameters for the lp source crack length 240 360 m crack width 130 150 m crack aperture 0 5 3 4 mm crack stiffness 100 500 sound speed of fluid 880 m s and excess pressure 0 01 0 19 mpa similar analyses yield the parameters of the precursor source crack length 20 30 m crack width 15 25 m crack aperture 2 3 8 7 mm crack stiffness 5 15 sound speed of fluid 140 m s and excess pressure 0 06 0 15 mpa combined with geologic and thermodynamic constraints obtained from field observations these seismic parameters suggest a gas release mechanism in which the episodic collapse of a foam layer trapped at the top of the magma column subjacent to the dome releases a slug of pressurized gas which escapes to the surface while dilating a preexisting system of cracks in the dome structure accordingly the fracture observed on the crystallized dome body is the surface extension of the lp source crack where lp activity is induced by the rapid emission and expansion of gas flowing through this conduit the width and aperture of the crack estimated in the model are in good agreement with the length and aperture of the fracture estimated from visual observations the source parameters of the precursor signal are suggestive of a nozzle like conduit connecting the lp source crack to the underlying magma reservoir excitation of this conduit segment is attributed to the rapid emission and acceleration of the frothy fluid resulting from the collapse of the foam layer at the top of the reservoir the calculated periodicity of foam collapse events is in agreement with the observed average rate of thirteen lp events per hour

externally triggered renewed bubble nucleation in basaltic magma the 12 october 2008 eruption at halema uma u overlook vent kīlauea hawai i usa 1 from october 2008 until present dozens of small impulsive explosive eruptions occurred from the overlook vent on the southeast side of halema uma u crater at k lauea volcano usa these eruptions were triggered by rockfalls from the walls of the volcanic vent and conduit onto the top of the lava column here we use microtextural observations and data from clasts erupted during the well characterized 12 october 2008 explosive eruption at halema uma u to extend existing models of eruption triggering we present a potential mechanism for this eruption by combining microtextural observations with existing geophysical and visual data sets we measure the size and number density of bubbles preserved in juvenile ejecta using 2d images and x ray microtomography our data suggest that accumulations of large bubbles with diameters of 50 m to at least millimeters existed at shallow levels within the conduit prior to the 12 october 2008 explosion furthermore a high number density of small bubbles 50 m is measured in the clasts implying very rapid nucleation of bubbles visual observations combined with preexisting geophysical data suggest that the impact of rockfalls onto the magma free surface induces pressure changes over short timescales that 1 nucleated new additional bubbles in the shallow conduit leading to high number densities of small bubbles and 2 expanded the preexisting bubbles driving upward acceleration the trigger of eruption and bubble nucleation is thus external to the degassing system

cyclic eruptions and sector collapses at monowai submarine volcano kermadec arc 1998 2007 1 repeated multibeam bathymetric surveys at monowai cone a shallow submarine basaltic volcano and part of the monowai volcanic center in the northern kermadec arc were conducted in 1998 2004 and 2007 these surveys document dramatic depth changes at the volcano including negative changes up to 176 m from two sector collapses and positive changes up to 138 m from volcanic reconstruction near the summit and debris avalanche deposits downslope of the slide scars one sector collapse occurred on the se slope between 1998 and 2004 with a volume of 0 09 km3 and another occurred on the sw slope between 2004 and 2007 with a volume of 0 04 km3 the volume of positive depth change due to addition of volcanic material by eruption is of the same order 0 05 km3 between 1998 and 2004 and 0 06 km3 between 2004 and 2007 during these time intervals monitoring by the polynesian seismic network detected frequent t wave swarms at monowai indicative of explosive eruptive activity every few months an unusual t wave swarm on 24 may 2002 was previously interpreted as the collapse event between the 1998 and 2004 surveys but no similarly anomalous t waves were detected between 2004 and 2007 probably because the polynesian seismic network stations were acoustically shadowed from the second slide event we interpret that the sector collapses on monowai are caused by the unstable loading of fragmental erupted material on the summit and steep upper slopes of the volcano 20 moreover there appears to be a cyclic pattern in which recurrent eruptions oversteepen the cone and periodically lead to collapse events that transport volcaniclastic material downslope to the lower apron of the volcano volumetric rate calculations suggest that these two processes may be more or less in equilibrium the repeated collapses at monowai are relatively modest in volume involving only 0 1 0 5 of the edifice volume have occurred much more frequently than is estimated for larger debris avalanches at subaerial volcanoes and may be characteristic of how persistently active shallow submarine arc volcanoes grow

modeling lava lake heat loss rheology and convection 1 measurements at erta ale s lava lake and theoretical equations for lake rheology density driven convection and thermally driven plume ascent allow the constraint of lake dynamics cooling and crystallization expected from surface heat losses imply a viscosity increase from 150 pa s to 300 1800 pa s for cooled surface layers convection is expected to proceed vigorously under low viscosity conditions driving rapid 0 1 0 4 m s 1 surface motions and sluggishly under moderate to high viscosity conditions to drive slower motions 0 08 m s 1 convection is likely driven by small 6 kg m 3 density differences where surface cooling can influence lake rheology and explain variable rates of surface convective motion

thermal observations of gas pistoning at kilauea volcano 1 data acquired by three continuously recording thermal infrared thermometers situated on the north rim of pu u o o crater at kilauea volcano during 2002 revealed episodes of periodic thermal pulses originating from a degassing vent on the crater floor these thermal pulses are interpreted as gas release jetting events associated with gas pistoning a mechanism observed previously at both mauna ulu and pu u o o during a 35 day long period spanning june and july 2002 gas pistoning was frequently the dominant mode of gas release with as many as several hundred pulses occurring in uninterrupted series on other days degassing alternated between periods of quasi continuous gas jetting and intervals of gas pistoning that contained a few to a few dozen pulses characteristic time intervals between pistoning events ranged from 2 up to 7 min we identify three types of pistoning type 1 involves emission of lava followed by gas jetting and drain back type 2 is the same but the elevated position of the vent does not allow postjet drain back and type 3 involves gas jetting only with no precursory lava flow to explain gas pistoning we apply a model whereby a stagnant cap of degassed magma develops in the conduit below the vent gas bubbles rise through the magma column and collect under the cap the collective buoyancy of these bubbles pushes the cap upward when the cap reaches the surface it erupts from the vent as a lava flow unloading of the conduit magma in this way results in an abrupt pressure drop i e the overburden felt by the bubbles is reduced causing explosive gas expansion in the form of gas jetting from the vent this terminates the event and lava drains back into the conduit to start the cycle anew in the case where there is no surface lava emission or drain back the cap instead pushes into and spreads out within a subsurface cavity again this unloads the conduit magma and terminates in explosive gas release once gas is expelled lava in the cavity is free to drain back we hypothesize that pistoning is a stable mode of degassing for low viscosity basaltic magmas with appropriate conduit geometries and volatile supply rates

shallowly driven fluctuations in lava lake outgassing gas pistoning kīlauea volcano abstract lava lakes provide ideal venues for directly observing and understanding the nature of outgassing in basaltic magmatic systems k lauea volcano s summit lava lake has persisted for several years during which seismic and infrasonic tremor amplitudes have exhibited episodic behavior associated with a rise and fall of the lava surface gas pistoning since 2010 the outgassing regime of the lake has been tied to the presence or absence of gas pistoning during normal behavior no gas pistoning the lake is in a spattering regime consisting of higher tremor amplitudes and gas emissions in comparison gas piston events are associated with an abrupt rise in lava level up to 20 m during which the lake enters a non spattering regime with greatly decreased tremor and gas emissions we study this episodic behavior using long term multidisciplinary monitoring of the lake including seismicity infrasound gas emission and geochemistry and time lapse camera observations the non spattering regime i e rise phase of a gas piston cycle reflects gas bubbles accumulating near the top of the lake perhaps as a shallow foam while spattering regimes represent more efficient decoupling of gas from the lake we speculate that the gas pistoning might be controlled by time varying porosity and or permeability in the upper portions of the lava lake which may modulate foam formation and collapse competing models for gas pistoning such as deeply sourced gas slugs or dynamic pressure balances are not consistent with our observations unlike other lava lakes which have cyclic behavior that is thought to be controlled by deeply sourced processes external to the lake itself we show an example of lava lake fluctuations driven by cycles of activity at shallow depth and close to the lake s surface these observations highlight the complex and unsteady nature of outgassing from basaltic magmatic systems

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

time scales of foam stability in shallow conduits insights from analogue experiments volcanic systems can exhibit periodical trends in degassing activity characterized by a wide range of time scales understanding the dynamics that control such periodic behavior can provide a picture of the processes occurring in the feeding system towards this end we analyzed the periodicity of outgassing in a series of decompression experiments performed on analogue material argon saturated silicone oil plus glass beads fibers scaled to serve as models of basaltic magma to define the effects of liquid viscosity and crystal content on the time scale of outgassing we investigated both 1 pure liquid systems at differing viscosities 100 and 1000 pa s 2 particle bearing suspensions diluted and semi diluted the results indicate that under dynamic conditions e g decompressive bubble growth fluid ascent within the conduit the periodicity of foam disruption may be up to several orders of magnitude less than estimates based on the analysis of static conditions this difference in foam disruption time scale is inferred to result from the contribution of bubble shear and bubble growth to inter bubble film thinning the presence of particles in the semi diluted regime is further linked to shorter bubble bursting times likely resulting from contributions of the presence of a solid network and coalescence processes to the relative increase in bubble break up rates finally it is argued that these experiments represent a good analogue of gas piston activity i e the periodical rise and fall of a basaltic lava lake surface implying a dominant role for shallow foam accumulation as a source process for these phenomena this article is protected by copyright all rights reserved

the contribution of experimental volcanology to the study of the physics of eruptive processes and related scaling issues a review abstract the experimental approach has become a major tool increasingly used by volcanologists in recent decades to investigate the physics of eruptive processes in complement to field and theoretical works researchers have developed various methodologies to study volcanic phenomena at reduced length scale the works involve natural or analogue materials and their types range from first order tests to identify fundamental processes and make qualitative comparison with field observations to more sophisticated experiments in which precise data obtained in a controlled environment can be used to validate outputs of theoretical models scaling is a central issue to ensure dynamic similarity between the small scale experiments and the large scale volcanic phenomena when natural conditions cannot be simulated due to inherent length scale difference and or technical limitations in this respect dimensionless numbers are used to map physical regimes and to define scaling laws which allow experimental results to be extrapolated to natural scale this review presents the variety of experimental studies conducted to investigate subterraneous and aerial volcanic phenomena involving in particular fluid particle mixtures we focus on the major scaling issues and the physical regimes investigated and we also highlight in a historical perspective some of the major advances achieved through experimental studies finally we conclude on some perspectives for future works

identification of variable convective regimes at erta ale lava lake abstract during february 17 19 2002 we collected a combined thermal and seismic data set for persistent lava lake activity at erta ale volcano ethiopia these data indicate that the lake cycled between periods characterized by low 0 01 0 08 m s 1 and high 0 1 0 4 m s 1 surface velocities typically lasting tens to hundreds of minutes these periods of high and low velocity motion define periods of vigorous and sluggish convection respectively spectral analysis revealed that vigorous convection periods were characterized by high frequencies and energies in the thermal data and an increased presence of high frequency energy in the seismic data the data show that vigorous periods were characterized by formation of hot short lived plastic crusts and sluggish periods by cooler longer lived brittle crusts here the higher transit velocity across the lake surface from upwelling zones of crust formation to downwelling zones of crust destruction during the vigorous periods decreases the crust lifetime this in turn decreases the total cooling and thickening experienced by a plate of crust moving across the lake surface two scenarios can be envisaged to explain such convection cycles the first relates variable convection rates to changes in the volume flux and rheology of magma entering the lake in the second cyclic convection is set up by the generation of convective instabilities within the lake in this case cooling of a surface layer generates a slow moving viscous increasingly dense convection layer at the lake surface which is consumed and replaced during overturn

time lapse camera observations of gas piston activity at pu u ō ō kīlauea volcano hawai i gas pistoning is a type of eruptive behavior described first at k lauea volcano and characterized by the commonly cyclic rise and fall of the lava surface within a volcanic vent or lava lake though recognized for decades its cause continues to be debated and determining why and when it occurs has important implications for understanding vesiculation and outgassing processes at basaltic volcanoes here we describe gas piston activity that occurred at the pu u cone in k lauea s east rift zone during june 2006 direct detailed measurements of lava level made from time lapse camera images captured at close range show that the gas pistons during the study period lasted from 2 to 60 min had volumes ranging from 14 to 104 m3 displayed a slowing rise rate of the lava surface and had an average gas release duration of 49 s our data are inconsistent with gas pistoning models that invoke gas slug rise or a dynamic pressure balance but are compatible with models which appeal to gas accumulation and loss near the top of the lava column possibly through the generation and collapse of a foam layer

fluctuations in surface height of active lava lakes during 1972 1974 mauna ulu eruption kilauea volcano hawaii an active lava lake is one that forms directly on top of a magma column as opposed to an inactive one formed by passive ponding of lava within a preexisting crater two active lava lakes operating within summit craters of newly constructed volcanic shields at mauna ulu and alae were the longest lived of any observed in a hawaiian rift zone to date small scale fluctuations a few to 20 m in the height of lake surfaces are typically associated with degassing gas piston activity larger fluctuations as great as 200 m reflect major changes in eruptive activity measurements of surface height fluctuations of mauna ulu lake show gross positive correlation with variation in summit tilt which in turn reflects the inflation deflation state of kilauea s summit magma reservoir a more tenuous conclusion is that a sympathetic variation possibly exists between surface heights of the mauna ulu and alae lakes collectively these observations 1 require the existence of a fully engorged connected open and hydraulically efficient magma conduit system linking the summit reservoir with the lava lakes 2 provide additional evidence for the postulated regime of quasi steady state magma transfer that characterized much of the eruption 3 imply that fluctuations in lake surface reflect variation in magma supply rate to the reservoir and or outflow rate from the mauna ulu alae vents and 4 suggest undetected episodes of magma intrusion or storage in kilauea s east rift zone during 1973

numerical study of k1 internal tides in the kuril straits 1 tide induced strong diapycnal mixing in the kuril straits is thought to be one of the essential processes controlling water mass formation in the north pacific in order to make a definite quantification of diapycnal diffusivity in the kuril straits we drive a three dimensional numerical model and examine the generation propagation and dissipation features of internal waves which play an essential role in transferring energy from the predominant k1 barotropic tide to diapycnal mixing processes it is shown that most of the internal wave energy subtracted from the k1 barotropic tide is dissipated within the kuril straits such that the local dissipation efficiency becomes 0 8 1 0 about three times the value previously employed this is because the k1 tidal frequency is subinertial in this area so that significant amount of k1 tidal energy is fed into coastal trapped waves ctws which stay around each island without propagating away from the straits ctws induce strong velocity shear near the ocean bottom causing bottom confined intense mixing with a vertical decay scale 200 m less than half the value previously employed although there remains some uncertainties resulting from the employed parameterizations of viscosity and diffusivity the average diapycnal diffusivity in the kuril straits becomes 25 10 4 m2 s 1 about three times the value previously estimated although it is still an order of magnitude less than assumed for the kuril straits in the existing ocean general circulation models

gas mobility in rheologically layered volcanic conduits the role of decompression rate and crystal content on the ascent dynamics of magmas abstract unravelling the rheological behaviour of magmas is fundamental for hazard assessment at shallow depth the combined effects of degassing vesiculation and crystallization are likely to produce dramatic changes in the rheology hence modulating flow dynamics and eruptive style the rheological evolution from a low viscosity crystal poor bubble free water rich melt to a highly viscous crystal rich vesicular magma containing a water poor melt often occurs in the conduit to clarify the viscous flow dynamics of rheologically layered volcanic conduits we performed decompression experiments using a magma analogue system characterized by a low viscous layer l 10 pa s at the bottom and a high viscous particle bearing layer h 1000 pa s at the top silicone oils and spherical glass beads are employed as magma and crystal analogues respectively three sets of experiments address the effects of 1 decompression rate ca 10 2 and 104 mpa s 2 crystal content in the high viscosity magma 0 10 30 and 70 vol and 3 volume ratio of the two rheological layers 0 6 or 0 3 our results indicate that decompression rate exerts the most dramatic role yielding changes in time scale of outgassing up to two orders of magnitude and affecting the style of decompression response permeable outgassing or fragmentation the solid fraction 1 strongly modulates gas mobility 2 influences the pervasiveness of fragmentation and 3 affects the extent of mingling in the experimental conduit these results demonstrate that the properties of a shallow partially crystallized portion of the magmatic column and its response to varying ascent rate are primary controls on eruptive style

application of lead isotopes to mineral exploration in glaciated terrains the 206pb 204pb ratios of fine grained fractions from glacial tills indicate the presence of known proterozoic volcanogenic massive sulfide deposits at chisel lake near snow lake manitoba canada data from 2 m and other size fractions define a linear array on a 207pb 204pb vs 206pb 204pb diagram with a slope that yields an age similar to the age of the deposits and the surrounding country rocks some of the least radiogenic till samples were found down ice from the deposits suggesting that the pb isotopic compositions from till may provide a new approach to mineral exploration for massive sulfide deposits in glaciated terrains

seismic source dynamics of gas piston activity at kilauea volcano hawai i since 2008 eruptive activity at the summit of kilauea volcano hawai i has been confined to the new overlook pit crater within the halema uma u crater among the broad range of magmatic processes observed in the new pit are recurring episodes of gas pistoning the gas piston activity is accompanied by seismic signals that are recorded by a broadband network deployed in the summit caldera we use raw data recorded with this network to model the source mechanism of representative gas piston events in a sequence that occurred on 20 25 august 2011 during a gentle inflation of the kilauea summit to determine the source centroid location and source mechanism we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous medium that takes topography into account we apply a new waveform inversion method that accounts for the contributions from both translation and tilt in horizontal seismograms through the use of green s functions representing the seismometer response to translation and tilt ground motions this method enables a robust description of the source mechanism over the period range 1 10 000 s most of the seismic wavefield produced by gas pistoning originates in a source region 1 km below the eastern perimeter of the halema uma u pit crater the observed waveforms are well explained by a simple volumetric source with geometry composed of two intersecting cracks featuring an east striking crack dike dipping 80 to the north intersecting a north striking crack another dike dipping 65 to the east each gas piston event is marked by a similar rapid inflation lasting a few minutes trailed by a slower deflation ramp extending up to 15 min attributed to the efficient coupling at the source centroid location of the pressure and momentum changes accompanying the growth and collapse of a layer of foam at the top of the lava column assuming a simple lumped parameter representation of the shallow magmatic system the observed pressure and volume variations can be modeled with the following attributes foam thickness 10 50 m foam cell diameter 0 04 0 10 m and gas injection velocity 0 01 0 06 m s 1 gas piston activity occurs in a narrow pipe with diameter of 6 m connecting the halema uma u pit crater to the subjacent dike system the height of the magma column is estimated at 104 m at the start of the sequence based on the period of very long period vlp oscillations accompanying the onset of the gas piston signal based on the change in the period of vlp oscillations and tilt evidence the height of the magma column is inferred to have risen by up to 23 m by the end of the 5 day long sequence a penny shaped crack model of the dike geometry yields effective diameters of 1 2 2 9 km for the east dike and 0 7 km for the north dike the shallower north dike segment is embedded in a relatively weak medium compatible with expected mechanical properties in the hydrothermal environment of this dike

an analogue experimental model of depth fluctuations in lava lakes lava lakes consisting of molten degassing lava in summit craters of active basaltic volcanoes sometimes exhibit complex cycles of filling and emptying on time scales of hours to weeks such as recorded at pu u o o in hawaii and oldoinyo lengai in tanzania here we report on a new series of analogue laboratory experiments of two phase flow in a reservoir conduit lava lake system which spontaneously generates oscillations in the depth of liquid within the lake during the recharge phase gas supplied from a subsurface reservoir of degassing magma drives liquid magma up the conduit causing the lake to fill as the magmastatic pressure in the lake increases the upward supply of magma driven by the gas bubbles falls eventually the upflow becomes unstable and liquid drains downwards from the lake driven by the magmastatic pressure of the overlying lake suppressing the ascent of any more bubbles from the chamber at a later stage once the lake has drained sufficiently the descent speed of liquid through the conduit decreases below the ascent speed of the bubbles and the recharge cycle resumes application of a quantitative model of the experiments to the natural system is broadly consistent with field data

cyclic spattering seismic tremor and surface fluctuation within a perched lava channel kīlauea volcano in late 2007 a perched lava channel built up to 45 m above the preexisting surface developed during the ongoing eruption near pu u cone on k lauea volcano s east rift zone the lava channel was segmented into four pools extending over a total of 1 4 km from late october to mid december a cyclic behavior consisting of steady lava level rise terminated by vigorous spattering and an abrupt drop in lava level was commonly observed in pool 1 we use geologic observations video time lapse camera images and seismicity to characterize and understand this cyclic behavior spattering episodes occurred at intervals of 40 100 min during peak activity and involved small 5 10 m high fountains limited to the margins of the pool most spattering episodes had fountains which migrated downchannel each spattering episode was associated with a rapid lava level drop of about 1 m which was concurrent with a conspicuous cigar shaped tremor burst with peak frequencies of 4 5 hz we interpret this cyclic behavior to be gas pistoning and this is the first documented instance of gas pistoning in lava well away from the deeper conduit our observations and data indicate that the gas pistoning was driven by gas accumulation beneath the visco elastic component of the surface crust contrary to other studies which attribute similar behavior to the periodic rise of gas slugs the gas piston events typically had a gas mass of about 2 500 kg similar to the explosions at stromboli with gas accumulation and release rates of about 1 1 and 5 7 kg s 1 respectively the time averaged gas output rate of the gas pistoning events accounted for about 1 2 of the total gas output rate of the east rift zone eruption

on the slow decompressive response of volatile and crystal bearing magmas an analogue experimental investigation abstract the degassing kinetics of ascending magma strongly affect eruption dynamics the kinetics are in turn influenced by magma properties the investigation of the relationship between magma properties and eruption dynamics is a key element in revealing the processes characterizing magmatic flows within the shallow conduit to explore the effects of physical properties on degassing in basaltic eruptive systems we have designed and carried out experiments on the slow decompressive response of analogue magmas composed of silicone oil based suspensions using a shock tube apparatus four series of experiments were performed 1 particle free silicone oils with viscosity ranging from 1 to 1000 pa s were used to constrain the liquid response 2 silicone oils with variable proportion of suspended micrometric spherical particles were employed to assess the effect of different crystal fractions 3 suspensions of elongated particles in silicone oils were used to investigate the role of crystal shape 4 the effects of saturation time and pressure were examined the rheology of both spherical and elongated particle bearing suspensions were characterized by concentric cylinder rotational rheometry the flow dynamics of the bubbly fluid from the process of bubble nucleation up to the development of a permeable bubble network were constrained using image analysis different fluid regimes were distinguished i nucleation ii foam build up and iii foam oscillation by comparing results obtained from the different series of experiments we were able to assess the primary role played by the presence of particles on the evolution of the gas volume fraction within the samples particle fraction has a dominant role at high concentration affecting the motion of the fluid finally particle shape influences the long term degassing efficiency of the fluid using scaling considerations such observations are applied to mafic to intermediate systems the results of our experimental investigation contribute to constraining vesiculation processes in magmas of various crystallinities at shallow depths

a comparison of long coastal trapped wave theory with observations off peru abstract the agreement between coastal trapped wave theory and observation is studied for the case of observations made off peru during the 1977 cuea joint ii experiment wave properties are calculated using a numerical model with realistic horizontally uniform stratification and realistic bottom topography these properties are then explored as a function of the ratio of the first internal rossby radius of deformation to the shelf slope width the agreement of observed and calculated first mode free wave phase speeds 230 cm s 1 is excellent while modal structures agree more poorly a forced wave calculation using observed winds and currents as input is used to hindcast alongshore currents and sea level in the frequency band where smith 1978 observed free coastal trapped waves during 1977 the model suggests that most of the observed sea level and alongshore velocity fluctuations in the 5 10 day period band are due to free waves originating equatorward of 5 deg s while winds between 5 deg s and

stability of foams in silicate melts bubble coalescence and the spontaneous disruption of high porosity foams in silicate melts are the result of physical expulsion of interpore melt syneresis leading to bubble coalescence and diffusive gas exchange between bubbles melt expulsion can be achieved either along films between pairs of bubbles or along plateau borders which represent the contacts between 3 or more bubbles theoretical evaluation of these mechanisms is confirmed by experimental results enabling us to quantify the relevant parameters and determine stable bubble size and critical film thickness in a foam as a function of melt viscosity surface tension and time foam stability is controlled primarily by melt viscosity and time melt transport leading to coalescence of bubbles proceeds along inter bubble films for smaller bubbles and along plateau borders for larger bubbles thus the average bubble size accelerates with time in silicate melts the diffusive gas expulsion out of a region of foam is effective only for water and even then only at small length scales as the diffusion of co2 is negligible the results of our analyses are applicable to studies of vesicularity of lavas melt degassing and eruption mechanisms

distribution and formation of okhotsk sea intermediate water an analysis of isopycnal climatological data 1 in order to clarify the distribution and formation of okhotsk sea intermediate water osiw an isopycnal climatological data set based on all of the available historical observations is developed and examined the isopycnal maps clearly show that there are two direct ventilation sources for osiw dense shelf water dsw with cold and fresh properties influenced by sea ice formation in the northwest shelf region and forerunner of soya warm current water fscw which has warm and saline properties originating in the japan sea the cold and fresh water extends southward from the northwest shelf to the shelf slope off sakhalin island it suggests that dsw is transported southward by the east sakhalin current the dsw enters the kuril basin and mixes with fscw and western subarctic water wsaw originating from the north pacific to form osiw the annual mean production rate of dsw estimated from the total volume of dsw over the shelf in spring and summer is 0 67 sv 1 sv 106 m3 s the annual mean volume transport of fscw is estimated to be 0 08 sv on the basis of its cross section area and the current speed assumption of isopycnal mixing yields a mixing ratio of 1 1 0 1 among dsw wsaw and fscw to form osiw we estimate the annual production rate of osiw to be 1 4 sv the corresponding osiw s renewal time is 7 years continued assumption of isopycnal mixing yields a mixing ratio of 0 6 0 4 between wsaw and osiw to form oyashio intermediate water oyiw

explosive volcanic activity at mt yasur a characterization of the acoustic events 9 12th july 2011 abstract volcanic processes occur in a wide range of temporal and spatial scales however a key step of magma ascent is recognizable in the dynamics of gas and magma in the shallow plumbing system where volatiles play a fundamental role in controlling the eruptive style with the aim of investigating shallow degassing processes an experimental setup was deployed at mt yasur an active volcano located in tanna island vanuatu arc from 9th to 12th july 2011 the setup comprised high speed and thermal cameras as well as a microphone capable of recording both in the infrasonic and audible range the analysis of acoustic signals validated by observing images from the high speed and thermal cameras has enabled characterizing the explosive activity during the investigated period two types of explosions distinct for spectral features and waveforms were observed i minor events corresponding to small overpressurized bursts occurring almost continuously ii major events characterizing the strombolian activity at mt yasur by investigating variation in the occurrence rate of the minor events we found that on a short timescale the dynamics responsible for the two types of explosions are decoupled these results together with previous literature data bring additional evidence of the existence of distinct sources of degassing finally major events can be distinguished as emergent events i e long lasting signals corresponding to ash rich explosions and impulsive events featuring shorter duration and larger amplitude

determining flow type shear rate and shear stress in magmas from bubble shapes and orientations we interpret the shear environments that produced bubble textures in obsidian samples using the results of theoretical numerical and experimental studies on the deformation of bubbles in shear flows in particular we use the shapes and orientations of bubbles vesicles in obsidian to estimate shear rates and shear stresses and assess flow type simple vs pure shear this technique can be used to determine shear rates in volcanic conduits the origin of pyroclastic obsidian and the emplacement history and dynamics of obsidian flows a spherical bubble in a viscous fluid subjected to a low reynolds number steady flow field deforms until it reaches a steady shape and orientation bubble deformation is governed by the competing stresses from shearing that deforms and surface tension that rerounds the ratio of these stresses is the capillary number ca because the relationships among ca bubble orientation and shape differ for pure and simple shear we can distinguish between these flow types using preserved bubble geometries furthermore because ca is a function of shear rate we can use relationships between ca and the magnitude of deformation to calculate shear rates when melt viscosity and surface tension are known to demonstrate the potential of the technique we examine three obsidian samples chosen for diversity of origin and texture two of the samples have low crystallinities and banding defined by layers of different vesicularity bubble geometries in a spatter fed obsidian flow sample record deformation by pure shear whereas a juvenile obsidian clast from a pyroclastic fall deposit records predominantly simple shear a third sample from an obsidian flow has banding marked by variable concentrations of microlites and shows bubble deformation most consistent with dominantly simple shear and some bubble relaxation the highest shear rate and shear stress are recorded by the pyroclastic obsidian shear rate 0 01 s 1 shear stress 60 kpa the spatter fed obsidian flow sample deformed by pure shear records the lowest shear stress 4 9 kpa the obsidian flow sample deformed by simple shear records the lowest shear rates 10 6 6 10 6 9 s 1 despite high shear stresses 22 36 kpa because of the high viscosity of the degassed rhyolite 0 13 wt water