turbulent heat flux in the upper ocean under sea ice turbulence data from three arctic drift station experiments demonstrate features of turbulent heat transfer in the oceanic boundary layer time series analysis of several w t records shows that heat and momentum flux occur at nearly the same scales typically by turbulent eddies of the order of 10 20 m in horizontal extent and a few meters in vertical extent probability distribution functions of w t have large skewness and kurtosis where the latter confirms that most of the flux occurs in intermittent events with positive and negative excursions an order of magnitude larger than the mean value an estimate of the eddy heat diffusivity in the outer ekman part of the boundary layer based on measured heat flux and temperature gradient during a diurnal tidal cycle over the yermak plateau slope north of fram strait agrees reasonably well with the eddy viscosity with values as high as 0 15 m2 s 1 an analysis of measurements made near the ice ocean interface at the three stations shows that heat flux increases with both temperature elevation above freezing and with friction velocity at the interface it also reveals a surprising uniformity in parameters describing the heat and mass transfer e g the thickness of the transition sublayer from a modified version of the yaglom kader theory is about 10 cm at all three sites despite nearly a fivefold difference in the under ice roughness z0 which ranges from approximately 2 to 9 cm a much simplified model for heat and mass transfer at the ice ocean interface suggested by the relative uniformity of the heat transfer coefficients at the three sites is outlined

seasonal variations in the west spitsbergen current estimated from bottom pressure measurements from 1982 to 1985 two pressure gauges were deployed across the continental shelf northwest of spitsbergen to determine the seasonal variations in the barotropic component of the west spitsbergen current the variation in current velocity was calculated after analysis and removal of the tidal signals and correction of the pressure difference across the 47 km section for bottom buoyancy effects the pressure derived velocity fluctuates about 10 cm s 1 peak to peak with the maximum northward flow occurring in the winter the maximum appears to the correlated with the seasonal cycle of wind stress curl in the northern greenland sea in fact the magnitude of the velocity variation corresponds to the sverdrup transport due to the fluctuation in wind stress curl at 79 n 7 5 e the idea that the observed variation might also be due to the spin up of the basin by wind stress curl is explored with two simple analytical models basin spin up does appear to be a possible cause however east greenland current velocity data from muench et al 1986 indicate that the fluctuation about the mean in the deep currents on the western side of the basin is northward in winter while basin spin up would produce a southward fluctuation this supports the idea that sverdrup transport dominates basin spin up at least at the margins of the basin the fluctuations in transport and heat flux though the pressure gauge section are estimated to be 2 sv and 30 to 60 tw peak to peak these values are major fractions of historical estimates of the mean transport and heat flux values in the west spitsbergen current and they are significant fractions of the total oceanic fluxes into the arctic ocean this suggests that long time series are required to make meaningful estimates of the heat budget of the arctic

very long period oscillations of mount erebus volcano as the signal decays vlp scalar moments up to 5 10 11 n m exceed sp moments by an order of magnitude or more suggesting distinct though genetically related sp and vlp source mechanisms we conclude that vlp signals arise from excitation of a quasi linear resonator that is intimately associated with the conduit system and is excited by gravity and inertial forces associated with gas slug ascent eruption and magma recharge vlp signal stability across hundreds of eruptions spanning 5 years the persistence of the lava lake and the rapid posteruptive lava lake recovery indicate a stable near summit magma reservoir and vlp source process index terms 4544 oceanography physical internal and inertial waves 7280 seismology volcano seismology 8419 8414 volcanology eruption mechanisms 8419 volcanology eruption monitoring 7280 keywords strombolian very long period volcano seismology

mixing in the west spitsbergen current abstract twenty eight profiles of temperature and salinity down to 1 km depth have been measured in the area north from the coast of svalbard to latitude 84 40 n between 0 and 32 e longitude they show atlantic waters of the west spitsbergen current entering the arctic ocean in a bifilimentary mode one filament following the coastline and the other 300 km farther north apparently following the continental shelf break the profiles show these filaments mixing into the ambient water in a series of intrusive layers which are remarkably uniform over distances of hundreds of kilometers a triple peak structure at the atlantic water maximum is the dominant oceanographic characteristic of the area with salt fingering occurring on the upper surface of the cold intrusions and indications of double diffusive exchanges through the lower surface a system or eddies or meanders is postulated as the mechanism for the production of multiple fronts allowing the intrusive layers to extend to distances much greater t

ground based thermal imaging of lava lakes at erebus volcano antarctica abstract mount erebus a large intraplate stratovolcano dominating ross island antarctica hosts the world s only active phonolite lava lakes the main manifestation of activity at erebus volcano in december 2004 was as the presence of two convecting lava lakes within an inner crater the long lived ray lake 1400 m2 in area was the site of up to 10 small strombolian eruptions per day a new but short lived 1000 1200 m2 lake formed at werner vent in december 2004 sourced by lava flowing from a crater formed in 1993 by a phreatic eruption we measured the radiative heat flux from the two lakes in december 2004 using a compact infrared ir imaging camera daily thermal ir surveys from the main crater rim provide images of the lava lake surface temperatures and identify sites of upwelling and downwelling the radiative heat outputs calculated for the ray and werner lakes are 30 35 mw and 20 mw respectively we estimate that the magma flux needed to sustain the combined heat loss is 250 710 kg s 1 that the minimum volume of the magma reservoir is 2 km3 and that the radius of the conduit feeding the ray lake is 2 m

sustaining persistent lava lakes observations from high resolution gas measurements at villarrica volcano chile active lava lakes as the exposed upper part of magmatic columns are prime locations to investigate the conduit flow processes operating at active degassing volcanoes persistent lava lakes require a constant influx of heat to sustain a molten state at the earth s surface several mechanisms have been proposed to explain how such heat transfer can operate efficiently these models make contrasting predictions with respect to the flow dynamics in volcanic conduits and should result in dissimilar volatile emissions at the surface here we look at high frequency so2 fluxes plume composition thermal emissions and aerial video footage from the villarrica lava lake in order to determine the mechanism sustaining its activity we found that while fluctuations are apparent in all datasets none shows a stable periodic behaviour these observations suggest a continuous influx of volatiles and magma to the villarrica lava lake we suggest that ascending volatile rich and descending degassed magmas are efficiently mixed within the volcanic conduit resulting in no clear periodic oscillations in the plume composition and flux we compare our findings to those of other lava lakes where equivalent gas emission time series have been acquired and suggest that gas flux magma viscosity and conduit geometry are key parameters determining which flow mechanism operates in a given volcanic conduit the range of conduit flow regimes inferred from the few studied lava lakes gives a glimpse of the potentially wide spectrum of conduit flow dynamics operating at active volcanoes

storm driven mixing and potential impact on the arctic ocean 1 observations of the ocean atmosphere and ice made by ice ocean environmental buoys indicate that mixing events reaching the depth of the halocline have occurred in various regions in the arctic ocean our analysis suggests that these mixing events were mechanically forced by intense storms moving across the buoy sites in this study we analyzed these mixing events in the context of storm developments that occurred in the beaufort sea and in the general area just north of fram strait two areas with quite different hydrographic structures the beaufort sea is strongly influenced by inflow of pacific water through bering strait while the area north of fram strait is directly affected by the inflow of warm and salty north atlantic water our analyses of the basin wide evolution of the surface pressure and geostrophic wind fields indicate that the characteristics of the storms could be very different the buoy observed mixing occurred only in the spring and winter seasons when the stratification was relatively weak this indicates the importance of stratification although the mixing itself was mechanically driven we also analyze the distribution of storms both the long term climatology and the patterns for each year in the past 2 decades the frequency of storms is also shown to be correlated but not strongly to arctic oscillation indices this study indicates that the formation of new ice that leads to brine rejection is unlikely the mechanism that results in the type of mixing that could overturn the halocline on the other hand synoptic scale storms can force mixing deep enough to the halocline and thermocline layer despite a very stable stratification associated with the arctic halocline the warm subsurface thermocline water is not always insulated from the mixed layer

analogue experiments on the rise of large bubbles through a solids rich suspension a weak plug model for strombolian eruptions abstract physical interactions between bubbles and crystals affect gas migration and may play a major role in eruption dynamics of crystal rich magmas strombolian eruptions represent an end member for bubble crystal interactions in which large bubbles significantly larger than the crystal size rise through a crystal rich near surface magma indeed volcanoes that produce strombolian eruptions often generate ejecta with 30 vol often 45 vol average crystallinity at stromboli volcano italy average crystallinity can reach 55 vol which is approaching the eruptibility limit for magmas at such high crystallinities the solids interact mechanically with each other and with bubbles this complex rheology complicates the two phase liquid gas slug flow model often applied to strombolian eruptions to examine the effect of crystals on bubble rise we performed analogue experiments in which large bubbles rise in a vertical tube filled with silicone oil and polypropylene particles the particles have a slightly lower density than the oil and therefore form a layer of oil particles at the upper surface we varied surface pressure particle volume fraction length of the particle bearing cap and bubble size to examine the ways in which these parameters influence strombolian type eruptions we show that in experiments suspended solids begin to affect bubble rise dynamics at particle volume fractions as low as 30 vol or when divided by the random close packing value a normalized particle fraction 0 64 bubbles in experiments with higher particle contents deform as they rise and burst through a small aperture generating surface fountains that begin abruptly and decay slowly and longer lasting acoustic signals of lower amplitude than in particle poor experiments particle fractions 38 vol 0 80 generated strong deformations on fast expanding bubbles that applied a high stress on the cap but they trapped bubbles that were less overpressured qualitatively the gas release behavior observed in particle rich experiments is consistent with observations of strombolian eruptions moreover we estimate that the observed crystallinity of pyroclasts at stromboli volcano represents 0 8 from this we suggest a weak plug model for strombolian eruptions that evolves towards a low viscosity equivalent of vulcanian style plug failure with a more crystalline stronger and less permeable plug importantly this model allows the rise of several bubbles in the conduit at the same time and suggests that longer lasting more pulsatory and complex eruptions may reveal an increase in near surface crystallinity shedding some light on changing conduit conditions that could help determine the different gas rise regimes involved in passive degassing puffing and different expressions of strombolian explosions

correlations between so2 flux seismicity and outgassing activity at the open vent of villarrica volcano chile 1 the characteristics of the open vent activity of villarrica volcano chile were studied in detail by integrating visual observations of the lava lake analysis of the seismic tremor and measurements of so2 flux the outgassing activity comprises a persistent gas plume emission from the bottom of the crater as well as frequent explosive events three main styles of bubble bursting were identified at the surface of the active lava lake seething magma small short lived lava fountains and strombolian explosions seething magma consists of continual burst of relatively small bubbles a few meters in diameter with varying strength over the entire surface of the lava lake small lava fountains seen as a vigorous extension of seething magma commonly have durations of 20 120 s and reach 10 40 m high above the lava lake correlations between seismicity and visual observations indicate that the seismic tremor is mostly caused by the explosive outgassing activity furthermore for different periods between 2000 and 2006 during which the activity remained comparable the real time seismic amplitude measurement system rsam and so2 emission rates show a very good correlation higher so2 emissions appeared to be related to higher levels of the lava lake stronger bubble bursting activity and changes in the morphology and texture of the crater floor background low levels of activity correspond to a lava lake located 80 m below the crater rim small and or blocky morphology of the roof seismic amplitude rsam lower than 25 units few volcano tectonic earthquakes and daily averages of so2 emissions lower than 600 mg d

resonant wave reflection by transverse bedforms and its relation to beaches and offshore bars abstract on an erodible sand bed there may be a coupling between the reflection of incident wave energy and the development of transverse bedforms the nature of this interaction is examined with particular reference to a laboratory experiment in which a veneer of sand was introduced into a pre existing fixed pattern of bars the observed motion of the mobile sand suggested potential development of this existing bar system in the up wave direction but not in the down wave direction it is argued here that this phenomenon may be significant in terms of the growth of shore parallel bars off beaches and for coastal protection in general

tide mediated warming of arctic halocline by atlantic heat fluxes over rough topography atlantic water brings heat to the subsurface arctic ocean pan arctic microstructure measurements of energy dissipation suggest that vertical mixing is substantial over the continental slopes tidally induced and insensitive to sea ice cover

a relationship between heat transfer to sea ice and temperature salinity properties of arctic ocean waters it is demonstrated that the characteristic temperature salinity relationship shown by thermocline waters of the arctic ocean can be reproduced using a simple model based on transfer of heat directly from these waters to sea ice from this we deduce that there is direct sensible heat flux from waters of atlantic origin to the ice cover such interaction could play a major role in determining the physical properties of arctic water masses

video and seismic observations of strombolian eruptions at erebus volcano antarctica abstract between 1986 and 1990 the eruptive activity of erebus volcano was monitored by a video camera with on screen time code and recorded on video tape corresponding seismic and acoustic signals were recorded from a network of 6 geophones and 2 infrasonic microphones two hundred strombolian explosions and three lava flows which were erupted from 7 vents were captured on video in december 1986 the strombolian eruptions ejected bombs and ash in november 1987 large bubble bursting strombolian eruptions were observed the bubbles burst when the bubble walls thinned to 20 cm explosions with bomb flight times up to 14 5 s were accompanied by seismic signals with our local size estimate unified magnitudes m u up to 2 3 explosions in pools of lava formed by flows in the inner crater were comparatively weak changes in eruptive activity occurred in 1987 when the lava lake was buried by a landslide from the crater wall two new vents formed and seismic activity peaked as the landslide was ingested lava flows from a vent on the eastern side of the crater formed small lakes and a vent on the north began to flow in 1990 by december 1990 the entire floor of the inner crater was buried by up to 20 000 m 3 of new lava different families of nearly identical eruption earthquakes occurred each year whose foci were contained within small shallow volumes immediately after several bubble bursting eruptions clear views of the empty vent were recorded the vent was seen to taper downwards to about half its diameter at the bottom our observations confirm models of strombolian eruptions suggesting they arise from gas slugs rising through a conduit into a flared vent

ice seawater turbulent boundary layer interaction with melting or freezing abstract a second moment turbulence closure model is applied to the problem of the dynamic and thermodynamic interaction of sea ice and the ocean surface mixed layer in the case of ice moving over a warm ocean surface layer melting is intrinsically a transient process that is melting is rapid when warm surface water initially contacts the ice then the process slows when surface water is insulated from deeper water due to the stabilizing effect of the melt water and the thermal energy stored in the surface layer is depleted effectively the same process prevails when ocean surface water flows under stationary ice in which case after an initial rapid increase the melting process decreases with downstream distance accompanying the stabilizing effect of the melt water is a reduction in the ice seawater interfacial shear stress this process and model simulators are used to explain field observations wherein ice near the marginal ice zone diverges from the main pack when the surface ice layer is m

winter ocean ice interactions under thin sea ice observed by iaoos platforms during n ice2015 salty surface mixed layer and active basal melt iaoos ice atmosphere arctic ocean observing system platforms measuring physical parameters at the atmosphere snow ice ocean interface deployed as part of the n ice2015 campaign provide new insights on winter conditions north of svalbard the three regions crossed during the drifts the nansen basin the sofia deep and the svalbard northern continental slope featured distinct hydrographic properties and ice ocean exchanges in the nansen basin the quiescent warm layer was capped by a stepped halocline 60 and 110 m and a deep thermocline 110 m ice was forming and the winter mixed layer salinity was larger by 0 1 g kg than previously observed over the svalbard continental slope the atlantic water aw was very shallow 20 m from the surface and extended offshore from the 500 m isobath by a distance of about 70 km sank along the slope 40 m from the surface and probably shed eddies into the sofia deep in the sofia deep relatively warm waters of atlantic origin extended from 90 m downward resulting from different pathways these waters had a wide range of hydrographic characteristics sea ice melt was widespread over the svalbard continental slope and ocean to ice heat fluxes reached values of 400 wm 2 mean of 150 wm 2 over the continental slope sea ice melt events were associated with near 12 hour fluctuations in the mixed layer temperature and salinity corresponding to the periodicity of tides and near inertial waves potentially generated by winter storms large barotropic tides over steep topography and or geostrophic adjustments this article is protected by copyright all rights reserved

explosive volcanic eruptions ix the transition between hawaiian style lava fountaining and strombolian explosive activity the commonest eruption styles of basaltic volcanoes involve hawaiian lava fountaining or intermittent strombolian explosions we investigate the ways in which magma rise speed at depth magma volatile content and magma viscosity control which of these eruption styles takes place we develop a model of the degree of coalescence between gas bubbles in the magma which allows us to simulate the transition between the two extreme styles of activity we find that magma rise speed is the most important factor causing the transition with gas content and viscosity also influencing the rise speed at which the transition occurs counter to intuitive expectations a decrease in gas content does not cause a transition from hawaiian to strombolian activity but instead causes a transition to passive effusion of vesicular lava rather a change from hawaiian to strombolian style requires a significant reduction in magma rise speed

seabed wave resonance and sand bar growth the interaction of surface water waves with undulating sea bed topography is of fundamental importance to coastal engineersand sedimentologists for example wave reflection from submerged bars on beaches may provide a mechanism for protecting the beach from further wave attack additionally the interaction of surface water waves with other tidally or wave generated bedforms such as sandwaves on offshore banks may modify wave climates on adjacent coastlines while there have been numerous studies of the interaction of sea waves with engineering structures such as breakwaters piers and jetties there have been comparatively few investigations of wave interactions with naturally occurring bedforms predictions have recently been made of the amount of wave energy reflected as a result of resonant interactions between surface water waves and undulating sea bed topography but with no supporting experimental proof i describe here preliminary results from what are believed to be the first published laboratory measurements of resonant interactions between surface water waves and submerged bars which show that significant and large amounts of wave energy may be reflected and that these reflections are brought about by resonant interactions between surface water waves and the bedforms in particular at resonance incident surface water wavelengths are approximately twice the bedform wavelengths these results have implications not only in terms of wave reflection from naturally occurring bedforms say bars on beaches but also for sediment transport processes in general

slug stability in flaring geometries and ramifications for lava lake degassing long lived persistently active lava lakes are rare but have been studied extensively because they may provide a natural laboratory for studying magmatic convection in basaltic and other low viscosity volcanoes however lava lakes differ from other volcanic systems in various ways particularly geometry the presence of the lava lake requires a sudden and significant flaring of the conduit the goal of this paper is to advance our understanding of the effect that a sudden increase in the conduit width has on the stability of large gas slugs and bubbles ascending from the plumbing system we investigate this question by linking analog laboratory experiments to direct numerical simulations in two dimensions we find that the rapid change in the geometry associated with the transition from the conduit to the lava lake causes large gas slugs to break up the nondimensional regime over which we observe the breakup depends sensitively on the flare angle of the lava lake and the importance of inertial effects in the flow implying that degassing related eruptive activity at open system volcanoes is sensitive to the upper conduit and lake geometries applying this idea to the likely geometries and viscosities of actual lava lakes our study suggests that all lava lakes except erebus fall well within the regime where large gas slugs are prone to breakup

mixing rates and vertical heat fluxes north of svalbard from arctic winter to spring mixing and heat flux rates collected in the eurasian basin north of svalbard during the n ice2015 drift expedition are presented the observations cover the deep nansen basin the svalbard continental slope and the shallow yermak plateau from winter to summer mean quiescent winter heat flux values in the nansen basin are 2 w m 2 at the ice ocean interface 3 w m 2 in the pycnocline and 1 w m 2 below the pycnocline large heat fluxes exceeding 300 w m 2 are observed in the late spring close to the surface over the yermak plateau the data consisting of 588 microstructure profiles and 50 days of high resolution under ice turbulence measurements are used to quantify the impact of several forcing factors on turbulent dissipation and heat flux rates wind forcing increases turbulent dissipation seven times in the upper 50 m and doubles heat fluxes at the ice ocean interface the presence of warm atlantic water close to the surface increases the temperature gradient in the water column leading to enhanced heat flux rates within the pycnocline steep topography consistently enhances dissipation rates by a factor of four and episodically increases heat flux at depth it is however the combination of storms and shallow atlantic water that leads to the highest heat flux rates observed ice ocean interface heat fluxes average 100 w m 2 during peak events and are associated with rapid basal sea ice melt reaching 25 cm d

reply to the comment by mike r james et al on it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity 1 the current paradigm for normal eruptions at stromboli volcano and strombolian type activity more generally posits that each eruption represents the burst of a large pocket of gas commonly referred to as slug at the free surface of themagma column this slug model has been investigated and refined primarily through analog fluid dynamical experiments at the laboratory scale there is no doubt that these studies have advanced our understanding of strombolian eruptions considerably however given the very fundamental status of the slug model for our current thinking about strombolian type eruptions it is paramount to carefully assess all underlying assumptions of the model one important uncertainty lies in the scaling behavior of the observed slug dynamics in the laboratory scale invariance requires all nondimensional numbers to be identical but it is generally not feasible to match all of the nondimensional numbers characterizing the volcanic conduit exactly in a laboratory experiment numerical computations offer a means of directly comparing slug dynamics at drastically different scales suckale et al 2010b we find that the very large slugs in volcanic conduits are more prone to dynamic instabilities and breakup than the comparatively small slugs in laboratory settings this finding in itself does of course not disprove the slug model it merely points to potentially important differences in slug stability at volcanic scales as opposed to laboratory scales 2 being careful and critical of the errors and interpretations of numerical simulations is important similarly the appropriateness of laboratory analogs must also be examined james et al 2011 raise a valid point asking whether our simulations are capable of reproducing stable slug rise in water figure 1 shows a computation performed for the experimental parameters provided by james et al 2011 in agreement with the analog experiments we do indeed find that this slug rises stably in water i e the slug ascends buoyantly within the conduit without experiencing catastrophic breakup as defined by suckale et al 2010b thus the experiments by james et al 2011 do not appear to contradict our computations we also reproduce computationally stable slug flow at finite reynolds number re shown in the experiment specified by jaupart and vergniolle 1989 suckale et al 2010b it is worth noting that in both cases the set of nondimensional numbers characterizing the experiment are not identical to those thought to be representative of the volcanic conduit and thus potential differences in the fluid dynamical behavior are not unexpected 3 that we observe stable slugs in water but not in magma supports an argument raised by james et al 2011 namely that re is an insufficient parameter for comparing slug dynamics at different spatial scales we welcome their discussion of the drawbacks of using a single re to describe slugs focusing on re to characterize our computations was a purely pragmatic decision first re is commonly used for the purpose of comparing fluid dynamical computations at different scales second we were able to use estimates for re characterizing strombolian slugs based on observational data measured at stromboli vergniolle and brandeis 1996 third we observed a correlation between re and breakup within the regime we investigated which is not unexpected since re is an indirect measure of the size of a gas bubble or slug that being said a more comprehensive set of nondimensional numbers is undoubtedly needed to evaluate scaling behavior of slugs for different fluid dynamical regimes including nondimensional criteria that capture the wavelength of potential interface instabilities in relation to the curvature of the interface and the time scale associated with instability growth to the time scale associated with advection of the instability along the interface our study is a first step toward gaining a better understanding of slug stability 4 from a theoretical point of view very large and dynamic gas volumes are not expected to be indefinitely stable the light gas slug moves underneath a column of very heavy magma and this unstable density stratification is prone to the formation of rayleigh taylor instabilities at the essentially flat upper surface of the slug grace et al 1978 developed a semiempirical rationalization of this process that affords rough estimates of maximum stable sizes as listed in table 1 of suckale et al 2010b the appeal of this model lies primarily in its simplicity but this very simplicity also department of earth atmospheric and planetary sciences massachusetts institute of technology cambridge massachusetts usa department of mathematics and statistics mcgill university montreal quebec canada

gas driven lava lake fluctuations at erta ale volcano ethiopia revealed by modis measurements the long lived lava lake of erta ale volcano ethiopia is remotely monitored by moderate resolution imaging spectroradiometers modis installed on satellites the normalised thermal index nti wright et al remote sens environ 82 135 155 2002 is shown to be proportional to the volume of the lava lake based on visual observations the lava lake s variable level can be plausibly related to a stable foam i e a mixture composed of densely packed non coalescing bubbles in suspension within a liquid this foam is trapped at the top of the magma reservoir and its thickness changes in response to the gas flux feeding the foam being successively turned on and off the temporal evolution of the foam thickness and the resulting variation of the volume of the lava lake is calculated numerically by assuming that the gas flux feeding the foam initially constant and homogeneous since december 9 2002 is suddenly stopped on december 13 2002 and not restarted before may 2003 the best fit between the theoretical foam thickness and the level of the lava lake deduced from the nti provides an estimate of both the reservoir radius 155 170 m and the gas flux feeding the foam 5 5 10 3 7 2 10 3 m 3 s 1 when existing this is in agreement with previous estimates from acoustic measurements bouche et al earth planet sci lett 295 37 48 2010 the very good agreement between the theoretical foam thickness and that deduced from modis data shows for the first time the existence of a regime based on the behaviour of a stable foam whose spreading towards the conduit wide conduit condition can explain the long lived activity our predictive model which links the gas flux at the vent to the foam spreading could potentially be used on any volcano with a long lived activity the underlying gas flux and the horizontal surface area of the magma reservoir can then be deduced by combining modelling to continuous measurements of gas flux the lava lake when high often shows regular rise and fall of its level we have recognised a minimum of 26 very well marked cycles between january 2001 and december 13 2002 corresponding to a typical return time of 10 8 2 3 days and a gas volume of 8 3 105 2 0 105 m 3 this corresponds to a gas volume fraction in the reservoir equal to 0 023 0 063 the yearly gas flux estimated between december 13 2002 and september 27 2004 varies between 2 3 10 6 and 5 9 10 6 m 3 s 1 at the depth of the reservoir the long time series provided by infra red sensors mounted on satellites could be used on any persistent volcano to detect potential periodic variations in the level of lava lakes or lava columns providing that the vent has a funnel shape as often and is sufficiently large

gas slug ascent through changes in conduit diameter laboratory insights into a volcano seismic source process in low viscosity magmas seismic signals generated during the flow and degassing of low viscosity magmas include long period lp and very long period vlp events whose sources are often attributed to dynamic fluid processes within the conduit we present the results of laboratory experiments designed to investigate whether the passage of a gas slug through regions of changing conduit diameter could act as a suitable source mechanism a vertical liquid filled glass tube featuring a concentric diameter change was used to provide canonical insights into potentially deep or shallow seismic sources as gas slugs ascend the tube we observe systematic pressure changes varying with slug size liquid depth tube diameter and liquid viscosity gas slugs undergoing an abrupt flow pattern change upon entering a section of significantly increased tube diameter induce a transient pressure decrease in and above the flare and an associated pressure increase below it which stimulates acoustic and inertial resonant oscillations when the liquid flow is not dominantly controlled by viscosity net vertical forces on the apparatus are also detected the net force is a function of the magnitude of the pressure transients generated and the tube geometry which dictates where and hence when the traveling pressure pulses can couple into the tube in contrast to interpretations of related volcano seismic data where a single downward force is assumed to result from an upward acceleration of the center of mass in the conduit our experiments suggest that significant downward forces can result from the rapid deceleration of relatively small volumes of downward moving liquid

comment on it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity by j suckale b h hager l t elkins tanton and j c nave

dynamics of degassing at kilauea volcano hawaii at kilauea volcano hawaii the recent long lived eruptions of mauna ulu and pu u o o have occurred in two major stages defining a characteristic eruptive pattern the first stage consists of cyclic changes of activity between episodes of fire fountaining and periods of quiescence or effusion of vesicular lava the second stage consists only of continuous effusion of lava we suggest that these features reflect the dynamics of magma degassing in a chamber which empties into a narrow conduit in the volcano chamber gas bubbles rise through magma and accumulate at the roof in a foam layer the foam flows toward the conduit and its shape is determined by a dynamic balance between the input of bubbles from below and the output into the conduit the foam thickness is proportional to lq e2 l g 1 4 where l and l are the viscosity and density of magma e is the gas volume fraction in the foam g is the acceleration of gravity and q is the gas flux the bubbles in the foam deform under the action of buoyancy and the maximum permissible foam thickness is hc 2 e lgr where is the coefficient of surface tension and r is the original bubble radius if this critical thickness is reached the foam collapses into a large gas pocket which erupts into the conduit foam accumulation then resumes and a new cycle begins the attainment of the foam collapse threshold requires a gas flux in excess of a critical value which depends on viscosity surface tension and bubble size hence two different eruption regimes are predicted 1 alternating regimes of foam buildup and collapse leading to the periodic eruption of large gas volumes and 2 steady foam flow at the roof leading to continuous bubbly flow in the conduit the essential result is that the continuous process of degassing can lead to discontinuous eruptive behavior data on eruption rates and repose times between fountaining phases from the 1969 mauna uiu and the 1983 1986 pu u o o eruptions yield constraints on three key variables the area of the chamber roof must be a few tens of square kilometers with a minimum value of about 8 km2 magma reservoirs of similar dimensions are imaged by seismic attenuation tomography below the east rift zone close to the roof the gas volume fraction is a few percent and the gas bubbles have diameters lying between 0 1 and 0 6 mm these estimates are close to the predictions of models for bubble nucleation and growth in basaltic melts as well as to the observations on deep submarine basalts the transition between cyclic and continuous activity occurs when the mass flux of gas becomes lower than a critical value of the order of 103 kg s in this model changes of eruptive regime reflect changes in the amount and size of bubbles which reach the chamber roof

the first second of volcanic eruptions from the erebus volcano lava lake antarctica energies pressures seismology and infrasound 1 we describe a multiparameter experiment at erebus volcano antarctica employing doppler radar video acoustic and seismic observations to estimate the detailed energy budget of large up to 40 m diameter bubble bursts from a persistent phonolite lava lake these explosions are readily studied from the crater rim at ranges of less than 500 m and present an ideal opportunity to constrain the dynamics and mechanism of magmatic bubble bursts that can drive strombolian and hawaiian eruptions we estimate the energy budget of the first second of a typical erebus explosion as a function of time and energy type we constrain gas pressures and forces using an analytic model for the expansion of a gas bubble above a conduit that incorporates conduit geometry and magma and gas parameters the model consistent with video and radar observations invokes a spherical bulging surface with a base diameter equal to that of the lava lake the model has no ad hoc free parameters and geometrical calculations predict zenith height velocity and acceleration during shell expansion during explosions the energy contained in hot overpressured gas bubbles is freed and partitioned into other energy types where by far the greatest nonthermal energy component is the kinetic and gravitational potential energy of the accelerated magma shell 10 9 j seismic source energy created by explosions is estimated from radar measurements and is consistent with source energy determined from seismic observations for the generation of the infrasonic signal a dual mechanism incorporating a terminally disrupted slug is proposed which clarifies previous models and provides good fits to observed infrasonic pressures a new and straightforward method is presented for determining gas volumes from slug explosions at volcanoes from remote infrasound recordings

the role of large bubbles detected from acoustic measurements on the dynamics of erta ale lava lake ethiopia the activity at the surface of the lava lake on erta ale volcano ethiopia shows that large bubbles are regularly breaking at a fixed position on the lava lake this is also where the small lava fountains are sometimes produced since this location is likely to be directly above the volcanic conduit feeding the lava lake we have done continuous measurements between march 22 and 26 2003 to understand the degassing of a volcano in permanent activity the bubble size has been first estimated from videos which once combined with the acoustic pressure can constrain the source of the sound the gas volume and overpressure stayed roughly constant between 36 700 m3 and 4 103 1 8 104 pa respectively simultaneous thermal measurements showed regular peaks which occurred when the crust was broken by a large bubble hence gave a direct indication on the typical return time between the bubbles 1 h these spherical cap bubbles had a high reynolds number 4600 20000 therefore a wake periodically unstable formed and detached from the bubble bottom the bubbly wake if the detachment occurs close to the surface can explain the duration of lava fountains measured on the videos the periodic arrival of bubbly wakes which mostly detach from the driving spherical cap within the lava lake could explain the absence of cooling at erta ale erebus antartica villarica chile and nyiragongo democratic republic of congo without invoking a convective downflow of magma in the conduit as previously done

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

sand transport by unbroken water waves under sheet flow conditions a model of wave induced onshore sand transport and resulting topographical changes seaward of the break point on a sloping beach is presented for the specific case in which the waves are random normally incident weakly nonlinear and relatively long the bottom boundary layer is fully turbulent and sand transport occurs as sheet flow the model consists of the following components 1 a new empirical expression for sand transport as sheet flow in which the instantaneous transport rate is directly proportional to the instantaneous bottom shear stress 2 an expresssion for the mean bottom shear stress based on a theoretical analysis of the bottom boundary layer 3 a simple representation of the shoaling wave field in which the local properties are described by linear long wave theory the probability density function of the surface displacement is gaussian and the waves conserve energy flux as they shoal and 4 the equation for conservation of sediment mass computations based on the model compare favorably with recently reported field measurements of the onshore motion of a long offshore bar

degassing dynamics of basaltic lava lake at a top ranking volatile emitter ambrym volcano vanuatu arc persistent lava lakes are rare on earth and provide volcanologists with a remarkable opportunity to directly investigate magma dynamics and degassing at the open air ambrym volcano in vanuatu is one of the very few basaltic arc volcanoes displaying such an activity and voluminous gas emission but whose study has long remained hampered by challenging accessibility here we report the first high temporal resolution every 5 s measurements of vigorous lava lake degassing inside its 300 m deep benbow crater using op ftir spectroscopy our results reveal a highly dynamic degassing pattern involving i recurrent 100 200 s short period oscillations of the volcanic gas composition and temperature correlating with pulsated gas emission and sourced in the upper part of the lava lake ii a continuous long period 8 min modulation probably due to the influx of fresh magma at the bottom of the lake and iii discrete co2 spike events occurring in coincidence with the sequential bursting of meter sized bubbles which indicates the separate ascent of large gas bubbles or slugs in a feeder conduit with estimated diameter of 6 1 m this complex degassing pattern measured with unprecedented detail and involving both coupled and decoupled magma gas ascent over short time scales markedly differs from that of quieter lava lakes at erebus and kilauea it can be accounted for by a modest size of benbow lava lake and its very high basalt supply rate 20 m3 s 1 favouring its rapid overturn and renewal we verify a typical basaltic arc signature for ambrym volcanic gas and based on contemporaneous so2 flux measurements we evaluate huge emission rates of 160 gg d 1 of h2o 10 gg d 1 of co2 and 8 gg d 1 of total acid gas so2 hcl and hf during medium activity of the volcano in 2008 such rates make ambrym one of the three most powerful volcanic gas emitters at global scale whose atmospheric impact at local and regional scale may be considerable

a coupled one dimensional sea ice ocean model a prognostic one dimensional mixed layer pycnocline model describing the vertical structure of the upper ocean is coupled to a thermodynamic sea ice model the coupled prognostic model is compared with the more usual sea ice model overlying a fixed mixed layer with constant oceanic heat flux and is then applied to investigate the effect of temporal and regional variations of the entrained oceanic heat flux on the sea ice cover in both polar regions in the southern ocean a standard simulation is compared with two perturbation experiments which both describe the occurrence of a polynya in the arctic ocean the effect of possible soviet river diversions is investigated finally the response of the coupled model to paleoclimatic forcing and boundary conditions is presented

halocline water formation in the barents sea hydrographic data from the first phase of the coordinated eastern arctic experiment cearex are analyzed the data consist of temperature and salinity measurements made by a ship based conductivity temperature depth ctd instrument and by a drifting salargos buoy these data were collected in the autumn and early winter of 1988 1989 in the northern barents sea mostly in ice covered conditions and then across the marginal ice zone miz the data show that relatively warm salty water of atlantic origin is modified by air cooling and ice melting to produce lighter water that has properties identical to lower halocline water found in the arctic ocean this occurs mostly at the miz and to a lesser degree within the ice pack itself at the miz the halocline water subducts underneath the lighter meltwater that resides directly under the ice pack geostrophic velocity calculations indicate that it then turns eastward and flows toward the kara sea in keeping with previous chemical tracer analyses a rough calculation reveals that the amount of halocline water formed in this way in the barents sea and fram strait is 30 50 of that formed by ice growth in eastern arctic polynyas

hydrography of the west spitsbergen current svalbard branch autumn 2001 1 the atlantic inflow is the primary source of water and heat to the arctic ocean a large portion enters through fram strait where it splits into the yermak and svalbard branches in october to november 2001 the uscgc healy occupied five oceanographic transects across the svalbard branch west and north of spitsbergen temperature and salinity sections show the warm salty atlantic water cooling and freshening as it flows along the continental slope for 553 km the temperature in the upper 500 m of the water column decreased by 0 25 c 100 km implying a heat flux across the sea surface of up to 520 w m2 if one assumes a nominal current of speed of 0 1 m s a temperature salinity t s analysis shows that the shape of the t s curves can be explained in terms of the ratio of the atmospheric to ice melt heat flux the observations imply that ice melt accounts for progressively more surface cooling as the flow moves toward the arctic ocean an autonomous underwater vehicle completed a vertical section in the region of maximum water mass gradient and revealed layer interleaving in fine detail data from this cruise extend a long time series of atlantic layer source temperature beginning in 1910 saloranta and haugan 2001 the extended observations show that after the temperature of the atlantic layer inflow reached a peak in 1992 it cooled to a minimum in 1998 and rose again through 2001

on the ice and heat balance in fram strait the sea ice margin northwest of spitsbergen is schematically represented by a stationary wedge maintained by opposing ice and warm atlantic water advection ice melt and cooling of the surface water generate a mixed layer with properties approximating those found elsewhere in the arctic basin the heat energy required to melt the advancing ice is roughly comparable to the rate of heat loss of the west spitsbergen current and suggests that direct heat exchange with the atmosphere is less important only a small fraction of the nearly fresh water from ice melt exits through eastern fram strait and most of it appears to return to the arctic basin whether or not it contributes to the formation and maintenance of the arctic mixed layer depends on the largely unknown circulation pattern north of fram strait an example of the large interannual variation of the mean wind stress field is shown to illustrate the likelihood of an equally large variance of the ice and surface water circulation

nearshore water motion and mean flows in a multiple parallel bar system abstract measurements of surface waves and nearshore water motion were made with wave staffs and electromagnetic currentmeters across the straight outer bars of a multiple parallel bar system at wasaga beach georgian bay ontario three sets of experiments were carried out between 1983 and 1985 and this paper examines the characteristics of spatial and temporal variations in incident waves and mean flows incident wave spectra during storms are typical of fetch limited conditions with a prominent peak in the wind wave frequency and a sharp cut off towards lower frequencies there is little evidence of significant energy at infragravity frequencies mean flows perpendicular to the shoreline during storms measured at 0 1 m above the bed are offshore with speeds of 0 04 0 10 m s 1 during moderate storms and 0 25 m s 1 during intense fall storms longshore currents are relatively weak and their direction closely follows changes in the incident wind angle about shore perpendicular there is no evidence of rip cell development and offshore return flow occurs as an undertow uniformly alongshore forming a simple two dimensional net circulation pattern the presence of the undertow very close to the bed is an important control on the direction of suspended sediment transport and thus in maintaining the equilibrium of the nearshore bars

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

spatial and temporal variations in spectra of storm waves across a barred nearshore abstract wave staffs and electromagnetic current meters were deployed on a profile across a two bar system at wendake beach southern georgian bay this paper examines spatial and temporal changes in the characteristics of wave form and the spectra of surface elevation and on offshore current motion during one storm non linear effects of wave shoaling and breaking across the bars result in the appearance of secondary waves and both the wave and on offshore current spectra have significant harmonic peaks during most of the storm significant low frequency energy occurs only during the peak of the storm while the peak frequency remains constant across the bar system the proportion of energy in the primary peak is greatest in the troughs and lowest over the bar crests and there are similar changes in the proportion of energy in the first harmonic however in both surface elevation spectra and on offshore current spectra the greatest proportion of energy is found in frequencies related to the incident wind waves

it takes three to tango 2 bubble dynamics in basaltic volcanoes and ramifications for modeling normal strombolian activity this is the second paper in a two part series examining numerical simula tions of buoyancy driven ow in the presence of large viscosity contrasts in the rst pa per we demonstrated that a combination of three numerical tools an extended ghost uid type method the level set approach and the extension velocity technique accurately simulate complex interface dynamics in the presence of large viscosity contrasts in this paper we use this three fold numerical method to investigate bubble dynamics in the conduits of basaltic volcanos with a focus on normal strombolian eruptions strombolian type activity named after the famously episodic eruptions at stromboli volcano is char acterized by temporally discrete fountains of incandescent clasts the mildly explosive nature of normal strombolian activity as compared to more eusive variants of basaltic volcanism is related to the presence of dissolved gas in the magma yielding a complex two phase ow problem we present a detailed scaling analysis allowing identication of the pertinent regime for a given ow problem the dynamic interactions between gas and magma can be clas sied into three non dimensional regimes based on bubble sizes and magma viscosity re solving the uid dynamics at the scale of individual bubbles is not equally important in all three regimes as long as bubbles remain small enough to be spherical their dy namic interactions are limited compared to the rich spectrum of coalescence and breakup processes observed for deformable bubbles in particular once inertia ceases to be neg ligible one key nding in our simulations is that both large gas bubbles and large conduit lling gas pockets slugs are prone to dynamic instabilities that lead to their rapid breakup during buoyancy driven ascent we provide upper bound estimates for the maximum sta ble bubble size in a given magmatic system and discuss the ramications of our results for two commonly used models of normal strombolian type activity the rise speed dependent rsd model and the collapsing foam cf model

heat flux at the ice ocean interface the role of the oceanic heat flux fw in the sea ice energy and mass balance is discussed and a method is described for determining fw from measurements of the temperature and thickness of sea ice results obtained using this method and data collected in the fall of 1988 during a drift in the eastern arctic northeast of fram strait are presented estimates of fw ranged from 0 to 37 w m 2 and varied in both time and space the gradual variation over the course of the drift reflects transformation of the west spitsbergen current into arctic water masses a significant intersite variability on horizontal scales of 10 to 100 m is ascribed to the interaction between under ice topographic features and turbulent energy and mass transfer in the boundary layer in addition there is a variability in the ice growth rate on horizontal scales of 0 1 to 1 m which is ascribed to the instability of the ice ocean phase boundary in the presence of turbulent flow these observations have implications for modeling and future experiments

hydrography and vertical fluxes of heat and salt northeast of svalbard in autumn temperature and salinity data collected by a salargos buoy during october 1988 northeast of svalbard norway as part of the coordinated eastern arctic research experiment are analyzed as the buoy drifted across the continental slope the data show a transition from central arctic conditions where the thermocline lies below the halocline to shelf conditions where the two coincide surface waters on the shelf were above the freezing point losing heat to sea ice advected southward by the wind the atlantic inflow current was also observed on the continental slope with a maximum temperature above 3 c a storm caused upwelling and entrainment of this current leading to strong ice ocean heat fluxes and ice melting the resulting flux of fresh water stabilized the surface layer and shut off further entrainment this episodic process can lead to bigger heat losses from the atlantic inflow current than previously considered for ice covered conditions

dynamics and thermodynamics of the ice upper ocean system in the marginal ice zone of the greenland sea measurements were made of the ice upper ocean system in the marginal ice zone of the greenland sea during a 4 day storm in which wind blew the ice south across a frontal region coinciding with the ice edge that had existed when the storm began in response to wind stress of about 0 2 pa a turbulent boundary layer developed under the ice that exhibited marked ekman rotation in both mean velocity average surface speed about 0 17 m s 1 deflection angle about 33 and turbulent stress profiles typical reynolds stress about 0 1 pa ablation of the ice undersurface increased rapidly after crossing the surface temperature front and the observed melt rate corresponded with direct heat flux measurements in the oceanic boundary layer with maximum upward heat flux of about 200 w m 2 we discuss overall momentum and energy balances interpret observed boundary layer measurements with a numerical model and show that molecular effects are important for heat and mass transport at the hydraulically rough ice ocean interface we also develop a simple model for predicting ice melt from interfacial stress and temperature and salinity of the mixed layer

using sea ice to measure vertical heat flux in the ocean results of an experiment performed at drifting ice station fram i in the arctic ocean northwest of spitzbergen during march may 1979 indicate that sensible heat flux from the ocean to the ice cover was less than 2 w m 2 the estimate is based on measurements of temperature gradient growth rate and salinity of young sea ice uncertainty in the magnitude of the heat flux results more from evidence of horizontal inhomogeneity in the growing ice sheet than from measurement errors

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

bar morphology of dissipative beaches an empirical model this study of 150 examples of nearshore bar morphology along the highly dissipative beaches 33 of the southeast mediterranean shoreline employs 32 years of aerial photography and wave data aided by detailed short term field studies three major bar types were delineated non rhythmic parallel meandering bars inner single crescentic bars and double crescentic bars each of these bar families includes variations the bars were related to daily ship and shore wave data including wave spectra from the day of observation back to 60 days prior to the observation the increase in total bar occurrence during summer is related to crossing of a major wave energy threshold in the spring when significant wave heights 1 m sharply increase to 70 85 in april may the bar morphology wave comparisons further indicate that as the significant wave heights decrease and remain below 1 m non rhythmic bars form within 7 10 days single crescentic bars require 15 days and double crescentic bars require 20 30 days this adjustment period of the bars to wave power causes a delayed response which accounts for lack of coincidence between wave energy and bar occurrence the formation of the initial double crescentic bar and its transformation to the mature double crescentic type requires a short pulse of wave energy 0 5 h13 1 5 m some bar families occur throughout the year the aseasonal occurrence is best shown by the mature double crescentic type which apparently is the final stage in the crescenticbar development sequence however other bar families show a tendency for a seasonal distribution which reflects their sensitivity to wave energy inner single crescentic and initial double crescentic bars are largely restricted to the calmest wave months of may april to october november there is an antiphase relationship between the frequencies of non rhythmic and crescentic bars

shallow degassing events as a trigger for very long period seismicity at kīlauea volcano hawai i the first eruptive activity at k lauea volcano s summit in 25 years began in march 2008 with the opening of a 35 m wide vent in halema uma u crater the new activity has produced prominent very long period vlp signals corresponding with two new behaviors episodic tremor bursts and small explosive events both of which represent degassing events from the top of the lava column previous work has shown that vlp seismicity has long been present at k lauea s summit and is sourced approximately 1 km below halema uma u by integrating video observations infrasound and seismic data we show that the onset of the large vlp signals occurs within several seconds of the onset of the degassing events this timing indicates that the vlp is caused by forces sourced at or very near the lava free surface due to degassing transmitted down the magma column and coupling to the surrounding rock at 1 km depth

textural and geophysical characterization of explosive basaltic activity at villarrica volcano 1 villarrica volcano chile is one of the most active volcanoes in south america its activity is currently characterized by continuous degassing from a summit lava lake vent punctuated by explosive events during november 2004 a multidisciplinary experiment was deployed for a 10 d period to define the style of emission and infer shallow conduit dynamics at this basaltic center this involved collection of thermal seismic and infrasonic data to describe the background activity confined inside the crater and use of samples to texturally and chemically characterize the ejecta from more energetic explosions able to attain the crater rim the background activity was characterized by gas bursting with a frequency of 9 events per minute this involved emission of gas puffs fed by bubble bursting with larger bursts emplacing sheets of magma onto the lower crater walls the ejecta population from the more energetic events was characterized by the coexistence of both scoriae and golden pumice these two types of clasts have different textures but identical glass compositions suggesting that they underwent different conduit histories the golden pumice is interpreted as the expanding inner part of a short lived jet fed by a rapidly ascending magma batch the scoria forms the outer portion of the jet and comprises degassed material entrained during passage of the fresh batch through material residing in the upper most portion of the conduit we thus have a largely degassed upper column that feeds persistent bubble bursting through which fresh batches occasionally rise to feed events of relatively higher energy

the west spitsbergen current disposition and water mass transformation recent work suggests that the west spitsbergen current which provides the principal contribution to the arctic ocean of salt and sensible heat as well as of a variety of anthropogenic tracers is a rather complex circulation feature north of 79 n where the isobaths diverge markedly the current contains two separate warm cores that follow different isobaths the western core carried by the offshore branch of the current follows the western flank of the yermak plateau and north of 80 n at least part of this flow detaches from the plateau probably to contribute to the recirculation in fram strait in contrast the inshore branch follows the shelf break into the arctic ocean it is this inshore branch that provides the primary focus in this paper during the transit of the inshore waters past northwestern spitsbergen the core properties change primarily through vertical heat flux which during ice free conditions in winter is estimated to be of the order of 200 w m 2 from the core layer alone together with some freshening within the arctic ocean this process is responsible for fully transforming the original atlantic water into arctic intermediate water within about 600 km of fram strait

oceanic thermohaline intrusions observations intrusions are commonly observed in the upper deep and coastal oceans and are closely linked to lateral fluxes of heat salt and momentum this is a review of observations of intrusions and the results of comparisons of properties such as scale slopes microstructure activity and fluxes with theoretical models a summary of estimates of lateral heat fluxes indicates a wide range of lateral diffusivities we conclude by noting that our present knowledge is insufficient to predict the structure length scales and lateral fluxes of thermohaline intrusions with confidence and list a number of unresolved questions suggestions are made for compilation of existing data into a database for exploratory analysis and testing of theoretical hypotheses an outline is given of a potential collaborative field experiment using ctd fluorescent dye and microstructure observations

sequential stage development of crescentic bars hahoterim beach southeastern mediterranean abstract sequential bar development involving in order multiple bars ridge and runnels transverse oblique bars and meandering or crescentic shore attached or detached bars of both outer and nested inner systems were delineated at hahoterim beach northern israel the concomitant wave data including wave directions energy spectrum significant wave height and length of the calm period showed strong correlation with the bar stages there is a notable lack of correlation between bar stages and incident wave periods which were quite variable even on a daily basis two bar developmental sequences were delineated one shore normal and the other initially oblique but gradually rotating to shore normal in the mature stage threshold conditions for the initial stage development of shore normal crescentic systems were defined as h1 3 1 0 m peak spectral density of 1 m2 hz and swell directions within 7 from the normal the outer crescentic systems formed within 1 to 2 weeks the nested inner crescentic bar system formed under different wave conditions development of inner micro cresentic bars required 3 to 7 weeks of calm waves h1 3 0 3 m except for a short initiating pulse of wave energy from waves of about i m in height the double crescentic pattern indicates the optimal evolutiona y stage of crescentic systems the residence time of bar types was determined by the frequency of crossing of these threshold conditions the outer bars and the mega rip channels composed the most stable inshore elements out of phase relationships between inner and outer bar systems resulted from the lag in response of the outer bars behind changes in wave direction among the inner crescentic bars and shore rhythms phase correlation was the was the rule regional aerial photography and wave data indicate that the bar wave relationships at hahoterim axe representative of the eastern flank of the nile including most of the israeli coast although the bar types described from other coasts are similar to those mapped at hahoterim and the threshold wave conditions for initiation of bar stage development appear to be similar the frequency of occurrence of specific bar types appears to be different at hahoterim

diffusive vertical heat flux in the canada basin of the arctic ocean inferred from moored instruments 1 observational studies have shown that an unprecedented warm anomaly has recently affected the temperature of the atlantic water aw layer lying at intermediate depth in the arctic ocean using observations from four profiling moorings deployed in the interior of the canada basin between 2003 and 2011 the upward diffusive vertical heat flux from this layer is quantified vertical diffusivity is first estimated from a fine scale parameterization method based on ctd and velocity profiles resulting diffusive vertical heat fluxes from the aw are in the range 0 1 0 2 w m 2 on average although large over the period considered the variations of the aw temperature maximum yields small variations for the temperature gradient and thus the vertical diffusive heat flux in most areas variations in upward diffusive vertical heat flux from the aw have only a limited effect on temperature variations of the overlying layer however the presence of eddies might be an effective mechanism to enhance vertical heat transfer although the small number of eddies sampled by the moorings suggest that this mechanism remains limited and intermittent in space and time finally our results suggest that computing diffusive vertical heat flux with a constant vertical diffusivity of 2 10 6 m2 s 1 provides a reasonable estimate of the upward diffusive heat transfer from the aw layer although this approximation breaks down in the presence of eddies

acoustic source characterization of impulsive strombolian eruptions from the mount erebus lava lake abstract we invert for acoustic source volume outflux and momentum imparted to the atmosphere using an infrasonic network distributed about the erupting lava lake at mount erebus ross island antarctica by modeling these relatively simple eruptions as monopole point sources we estimate explosively ejected gas volumes that range from 1 000 m 3 to 24 000 m 3 for 312 lava lake eruptions recorded between january 6 and april 13 2006 though these volumes are compatible with bubble volumes at rupture as estimated from explosion video records departures from isotropic radiation are evident in the recorded acoustic wavefield for many eruptions a point source acoustic dipole component with arbitrary axis orientation and strength provides precise fit to the recorded infrasound this dipole source axis corresponding to the axis of inferred short duration material jetting varies significantly between events physical interpretation of dipole orientation as being indicative of eruptive directivity is corroborated by directional emissions of ejecta observed in erebus eruption video footage although three azimuthally distributed stations are insufficient to fully characterize the eruptive acoustic source we speculate that a monopole with a minor amount of oriented dipole radiation may reasonably model the primary features of the recorded infrasound for these eruptions

bars bumps and holes models for the generation of complex beach topography in shallow water any two waves of the same frequency are shown to produce complex patterns of drift velocity above the sea bed if the longshore components hi h of the wave numbers of the two waves are different these steady flow patterns exhibit a longshore periodicity of wave number hi h irrespective of whether the waves propagate in the same direction say hi he positive or in opposite directions he negative the interaction of two edge wave modes is examined in detail the drift velocities are calculated and a simple sediment transport model is used to predict the beach topography that would be in equilibrium with these flow patterns as expected crescentic sand bars are produced by the special case of standing edge waves hi h intriguingly for all other cases a combination of complex transverse bars plus meandering or straight offshore bars result patterns that are surprisingly reminiscent of many published descriptions of complex rhythmic topography the extension of the model to three or more waves produces topography that appears to be very irregular although the pattern should repeat over sufficiently long distances along the beach even with only three waves these distances may be very large compared to the scale of the bars