combining local and remote infrasound recordings from the 2009 redoubt volcano eruption abstract the explosive phase of the 2009 redoubt volcano eruption produced predominantly short duration high amplitude infrasound signals recorded up to 4500 km away all 19 numbered explosive events were recorded at a local microphone dfr 12 km as well as at an infrasound array in fairbanks alaska i53us 547 km most with high signal to noise ratios the local microphone provides an estimate of the source parameters and comparison between the two datasets allows the unique opportunity to evaluate acoustic source term estimation at a remote array high waveform similarity between dfr and i53us occurs during much of the explosive phase due to strong stratospheric ducting permitting accurate source constraints inferred from i53us data cross correlation analysis after applying a hilbert transform to the i53us data shows how the acoustic energy has passed through a single caustic as predicted by ray theory similar to previous studies significant low frequency infrasound from redoubt recorded at i53us is coincident with high altitude ash emissions the largest events also produced considerable energy at greater than 50 s periods likely related to the initial oscillations of the volcanic plume or jet many of the explosive events have emergent onsets somewhat unusual for explosive short duration eruptions comparison of the satellite derived so2 emissions with the relative amount of acoustic energy at i53us shows a very high statistically significant correlation this study reiterates the utility of using remote infrasound arrays for detection of hazardous emissions and characterization of large volcanic eruptions and demonstrates how under typical meteorological conditions remote infrasound arrays can provide an accurate representation of the acoustic source

the dynamics of southern ocean storm tracks abstractthe mechanisms that initiate and maintain oceanic storm tracks regions of anomalously high eddy kinetic energy are studied in a wind driven isopycnal primitive equation model with idealized bottom topography storm tracks are found downstream of the topography in regions strongly influenced by a large scale stationary meander that is generated by the interaction between the background mean flow and the topography in oceanic storm tracks the length scale of the stationary meander differs from that of the transient eddies a point of distinction from the atmospheric storm tracks when the zonal length and height of the topography are varied the storm track intensity is largely unchanged and the downstream storm track length varies only weakly the dynamics of the storm track in this idealized configuration are investigated using a wave activity flux related to the eliassen palm flux and eddy energy budgets it is found that vertical fluxes of wave activity which correspond to eddy growth

residual mean solutions for the antarctic circumpolar current and its associated overturning circulation abstract residual mean theory is applied to the streamwise averaged antarctic circumpolar current to arrive at a concise description of the processes that set up its stratification and meridional overturning circulation on an f plane simple solutions are found in which transfer by geostrophic eddies colludes with applied winds and buoyancy fluxes to determine the depth and stratification of the thermocline and the pattern of associated residual meridional overturning circulation

geodetic observations during the 2009 eruption of redoubt volcano alaska abstract in march 2009 redoubt volcano about 160 km to the sw of anchorage alaska began its most recent explosive eruption deformation induced by this event was recorded by a gps campaign network consisting of 14 benchmarks which had been established in 1991 after the previous eruption the network was partially reoccupied in 2001 and 2008 and no volcanic deformation was detected during that period in response to precursory unrest starting in january 2009 the alaska volcano observatory temporarily deployed continuously recording gps instruments at four of the campaign benchmarks only days before the onset of explosive activity in march 2009 the only gps instrument recording continuously during the months prior to the eruption was the plate boundary observatory pbo station ac17 about 28 km northeast of the volcano s summit data from this station reveals subtle motion radially outward from the volcano beginning as early as may 2008 which reversed with the onset of explosive activity using simple analytical models we link the precursory activity to a point source intrusion of 0 0194 0 03400 0092 km3 in volume at 13 50 17 3310 17 km below sea level bsl superscripts and subscripts refer to upper and lower ends of confidence intervals at the 95 level during the explosive phase about 0 05 0 10 028 km3 of magma was evacuated from a prolate spheroid with its centroid at 9 17 15 176 92 km bsl a semimajor axis of 4 50 10 001 25 km length and a semi minor axis of 0 475 4 00 3 km the effusive activity is inferred to come from the same source decreasing in volume by 0 0167 0 02280 0106 km3 including observations from seismology and petrology we hypothesize a mid crustal two reservoir system with material sourced from 20 km flowing in at about 13 5 km depth and reheating residual material in the proposed spheroid the mixture migrated to shallower depth 2 4 5 km bsl and reheated material there as this residual magma erupted it was replaced by the material from the spheroidal reservoir at 7 11 5 km depth which renders the shallow source undetectable for geodetic instruments in addition to long term displacements we investigate sub daily kinematic positioning solutions and find that large short term positioning offsets correlate with large explosive events spikes in phase residuals plotted along the sky tracks of individual satellites can be related to individual plumes given favorable satellite station geometry which may be of use in volcano monitoring

geochemistry of the 1989 1990 eruption of redoubt volcano part ii evidence from mineral and glass chemistry abstract early stages december 1989 of the 1989 1990 eruption of redoubt volcano produced two distinct lavas both lavas are high silica andesites with a narrow range of bulk composition 58 64 wt and similar mineralogies phenocrysts of plagioclase hornblende augite hypersthene and fe ti oxides in a groundmass of the same phases plus glass the two lavas are distinguished by groundmass glass compositions one is dacitic and the other rhyolitic sharp boundaries between the two glasses in compositionally banded pumices lack of extensive coronas on hornblende phenocrysts and seismic data suggest that a magma mixing event immediately preceeded the eruption in december 1989 textural disequilibrium in the phenocrysts suggests both magmas dacitic and rhyolitic glasses had a mixing history prior to their interaction and eruption in 1989 sievey plagioclase and overgrowths of magnetite on ilmenite are textures that are at least consistent with magma mixing the presence of two hornblende compositions one a high al pargasitic hornblende and one a low al magnesiohornblende in both the dacitic and rhyolitic groundmasses indicates a mixing event to yield these two amphibole populations prior to the magma mixing in december 1989 the pargasitic hornblende and the presence of ca rich overgrowths in the sievey zones of the plagioclase together indicate at least one component of this earlier mixing event was a mafic magma either a basalt or a basaltic andesite eruptions in 1990 produced only andesite with a rhyolitic groundmass glass glass compositions in the 1990 andesite are identical to the rhyolitic glass in the 1989 andesite cognate xenoliths from the magma chamber or conduit are also found in the 1990 lavas magma mixing probably triggered the eruption in 1989 the eruption ended when this rather viscous rhyolitic groundmass glass magma capable of entraining sidewall xenoliths magma stabalized within the conduit

parameterizing ocean eddy transports from surface to bottom 1 we consider new parameterization schemes for the extra transport velocity by eddies in a stratified fluid with particular emphasis on baroclinic instability these come in the form of elliptic equations previously unmentioned which we derive for the eddy induced overturning stream function they guarantee decrease of the mean field potential energy our principal example gives a relationship between the vertical shear of the overturning velocity and the buoyancy torque of the main geostrophic current the parameterized velocity is nonsingular at the bottom and the sea surface contrasting with previous constant coefficient theories based on depth diffusion idealized two dimensional numerical experiments successfully reproduce meridional overturning circulation even when the background density gradient is uniform everywhere the eady problem or when the bottom is steeply sloped we further demonstrate that adding an eddy form drag wave stress term in the trm momentum equations yields overturning of the velocity field

source characterization for an explosion during the 2009 eruption of redoubt volcano from very long period seismic waves abstract the 2009 eruption of redoubt produced several very long period vlp signals associated with explosions we invert for the source location and mechanism of an explosion at redoubt volcano using waveform methods applied to broadband recordings such characterization of the source carries information on the geometry of the conduit and the physics of the explosion process inversions are carried out assuming the volcanic source can be modeled as a point source with mechanisms described by a a set of 3 orthogonal forces b a moment tensor consisting of force couples and c both forces and moment tensor components we find that the source of the vlp seismic waves during the explosion is well described by either a combined moment force source located northeast of the crater and at an elevation of 1 6 km asl or a moment source at an elevation of 800 m to the southwest of the crater the moment tensors for the solutions with moment and force and moment only share similar characteristics the source time functions for both moment tensors begin with inflation pressurization and execute two cycles of deflation reinflation depressurization repressurization although the moment force source provides a better fit to the data we find that owing to the limited coverage of the broadband stations at redoubt the moment only source is the more robust and reliable solution based on the moment only solution we estimate a volume change of 19 000 m3 and a pressure change of 7 mpa in a dominant sill and an out of phase volume change of 5000 m3 and pressure change of 1 8 mpa in a subdominant dike at the source location these results shed new light on the magmatic plumbing system beneath redoubt and complement previous studies on vulcanian explosions at other volcanoes

eddy advective and diffusive transports of heat and salt in the southern ocean there are two distinct mechanisms by which eddies provide systematic transport of tracer on isopycnals the advective transport associated with the slumping of isopycnals and the diffusive transport associated with down gradient diffusion depending on the large scale tracer distribution eddy advective transport has either the same direction as or opposite direction to eddy diffusive transport as a consequence eddy advection and eddy diffusion can reinforce each other for some tracers but oppose each other for other tracers using scaling analysis it is argued that the relative directions of eddy advective and diffusive transports can be determined simply from the relative slopes of tracers and isopycnals an eddy resolving 1 12 global ocean model is used to illustrate the two eddy transport mechanisms for temperature and salinity in the southern ocean applications to other tracers such as oxygen are discussed the diagnosed eddy diffusivity for temperature and salinity is found to be considerably different from the eddy diffusivity for eddy advective transport velocity

real time seismic amplitude measurement rsam a volcano monitoring and prediction tool seismicity is one of the most commonly monitored phenomena used to determine the state of a volcano and for the prediction of volcanic eruptions although several real time earthquake detection and data acquisition systems exist few continuously measure seismic amplitude in circumstances where individual events are difficult to recognize or where volcanic tremor is prevalent analog seismic records provide a quick visual overview of activity however continuous rapid quantitative analysis to define the intensity of seismic activity for the purpose of predicing volcanic eruptions is not always possible because of clipping that results from the limited dynamic range of analog recorders at the cascades volcano observatory an inexpensive 8 bit analog to digital system controlled by a laptop computer is used to provide 1 min average amplitude information from eight telemetered seismic stations the absolute voltage level for each station is digitized averaged and appended in near real time to a data file on a multiuser computer system raw realtime seismic amplitude measurement rsam data or transformed rsam data are then plotted on a common time base with other available volcano monitoring information such as tilt changes in earthquake activity associated with dome building episodes weather and instrumental difficulties are recognized as distinct patterns in the rsam data set rsam data for domebuilding episodes gradually develop into exponential increases that terminate just before the time of magma extrusion mount st helens crater earthquakes show up as isolated spikes on amplitude plots for crater seismic stations but seldom for more distant stations weather related noise shows up as low level long term disturbances on all seismic stations regardless of distance from the volcano implemented in mid 1985 the rsam system has proved valuable in providing up to date information on seismic activity for three mount st helens eruptive episodes from 1985 to 1986 may 1985 may 1986 and october 1986 tiltmeter data the only other telemetered geophysical information that was available for the three dome building episodes is compared to rsam data to show that the increase in rsam data was related to the transport of magma to the surface thus if tiltmeter data is not available rsam data can be used to predict future magmatic eruptions at mount st helens we also recognize the limitations of rsam data two examples of rsam data associated with phreatic or shallow phreatomagmatic explosions were not preceded by the same increases in rsam data or changes in tilt associated with the three dome building eruptions

a model of the zonally averaged stratification and overturning in the southern ocean the ocean area south of the antarctic circumpolar current acc frontal system is a region of major watermass modification influx of north atlantic deep water nadw small scale mixing eddy transport and diffusion as well as the fluxes of momentum and buoyancy at the sea surface combine in a complex array of processes to generate the unique stratification of the southern ocean with its southward uprising isopycnals and northward flux of antarctic intermediate water aaiw and antarctic bottom water comprehensive analytical models of this scenario are rare the authors develop and apply a model based on zonally and temporally averaged theory to explain the conversion of nadw into aaiw with all of the aforementioned processes contained in an extremely simplified way eddies appear via a transformed eulerian mean tem approach with a conventional downgradient parameterization of the meridional density flux the structure of the eddy coefficient is estimated from hydrographic and wind stress data by a simple inverse approach mixing is limited to a near surface layer and is treated in a most simple entrainment form the model determines the zonal mean density stratification in the southern ocean and the baroclinic transport of the acc from the applied wind stress and the surface density flux and unravels the role and importance of the different processes responsible for shaping the stratification ekman and eddy induced advection and pumping mixing surface buoyancy flux and eddy induced diffusion all of these processes must be present to yield an agreement between the simulated stratification and the observed one but details of their parameterization might not be too critical the acc transport is shown to have a contribution forced by the local wind stress as well as another contribution relating to the nonlocal forcing by wind stress and density flux over the entire antarctic zone

an analysis of tropical instability waves in a numerical model of the pacific ocean 2 generation and energetics of the waves this work was supported by the department of com merce noaa under grant na56gp0026 one of the au thors sm was partially supported by a nasa global change fellowship ngt 30288 another author ab was supported by a ucar postdoctoral fellowship

character mass distribution and origin of tephra fall deposits from the 2009 eruption of redoubt volcano alaska highlighting the significance of particle aggregation abstract the 2009 eruption of redoubt volcano included 20 tephra producing explosions between march 15 2009 and april 4 2009 utc next generation radar nexrad data show that plumes reached heights between 4 6 km and 19 km asl and were distributed downwind along nearly all azimuths of the volcano explosions lasted between 0 8 mm thick including communities along the kenai peninsula 80 100 km and the city of anchorage 170 km trace ash on march 15 a small 4 6 km asl phreatic explosion containing minor non juvenile ash erupted through the summit ice cap the first five magmatic explosions events 1 5 occurred within a 6 hour period on march 23 plumes rose to heights between 5 5 km and 14 9 km asl during 2 to 20 minute duration explosions and were dispersed mainly along a nne trajectory trace ash fall was reported as far as fairbanks owing to a shift in wind direction and heavy snowfall during these events field discrimination among many of these layers was possible all deposits comprise a volumetrically significant amount of particle aggregates yet only event 5 deposits contain coarse clasts including glacier ice the most voluminous tephra fall was deposited on march 24 event 6 from a 15 minute explosion that sent a plume to 18 3 km asl and dispersed tephra to the wnw within 10 km of the vent this deposit contains 1 11 cm pumice clasts in a matrix of 1 2 mm aggregate lapilli a small dome was presumably emplaced between march 23 and march 26 and was subsequently destroyed during 1 14 minute magmatic explosions of events 7 8 march 26 that sent plumes between 8 2 km and 19 km asl ash fell along a broad swath to the ese covering communities along the kenai peninsula with up to 1 mm of ash proximal deposits are largely composed of aggregate lapilli of 1 2 mm with very little coarse juvenile material events 9 18 march 27 sent plumes between 5 2 km and 15 5 km asl during particle size data showing a preponderance of fine ash even in the most proximal locations along with the abundance of aggregate lapilli documented in most samples confirms that particle aggregation played a significant role in the 2009 eruption and induced premature fallout of fine ash

statistical forecasting of repetitious dome failures during the waning eruption of redoubt volcano alaska february april 1990 abstract the waning phase of the 1989 1990 eruption of redoubt volcano in the cook inlet region of south central alaska comprised a quasi regular pattern of repetitious dome growth and destruction that lasted from february 15 to late april 1990 the dome failures produced ash plumes hazardous to airline traffic in response to this hazard the alaska volcano observatory sought to forecast these ash producing events using two approaches one approach built on early successes in issuing warnings before major eruptions on december 14 1989 and january 2 1990 these warnings were based largely on changes in seismic activity related to the occurrence of precursory swarms of long period seismic events the search for precursory swarms of long period seismicity was continued through the waning phase of the eruption and led to warnings before tephra eruptions on march 23 and april 6 the observed regularity of dome failures after february 15 suggested that a statistical forecasting method based on a constant rate failure model might also be successful the first statistical forecast was issued on march 16 after seven events had occurred at an average interval of 4 5 days at this time the interval between dome failures abruptly lengthened accordingly the forecast was unsuccessful and further forecasting was suspended until the regularity of subsequent failures could be confirmed statistical forecasting resumed on april 12 after four dome failure episodes separated by an average of 7 8 days one dome failure april 15 was successfully forecast using a 70 confidence window and a second event april 21 was narrowly missed before the end of the activity the cessation of dome failures after april 21 resulted in a concluding false alarm although forecasting success during the eruption was limited retrospective analysis shows that early and consistent application of the statistical method using a constant rate failure model and a 90 confidence window could have yielded five successful forecasts and two false alarms no events would have been missed on closer examination the intervals between successive dome failures are not uniform but tend to increase with time this increase attests to the continuous slowly decreasing supply of magma to the surface vent during the waning phase of the eruption the domes formed in a precarious position in a breach in the summit crater rim where they were susceptible to gravitational collapse the instability of the february 15 april 21 domes relative to the earlier domes is attributed to reaming the lip of the vent by a laterally directed explosion during the major dome destroying eruption of february 15 a process which would leave a less secure foundation for subsequent domes

on the pressure gradient force over steep topography in sigma coordinate ocean models abstract the error in computing the pressure gradient force near steep topography using terms following coordinates is investigated in an ocean model using the family of vertical differencing schemes proposed by arakawa and suarez the truncation error is estimated by substituting known buoyancy profiles into the finite difference hydrostatic and pressure gradient terms the error due to hydrostatic inconsistency which is not simply a space truncation error is also documented the results show that the pressure gradient error is spread throughout the water column and it is sensitive to the vertical resolution and to the placement of the grid points relative to the vertical structure of the buoyancy field being modeled removing a reference state as suggested for the atmosphere by gary reduces the truncation error associated with the two lowest vertical modes by a factor of 2 to 3 as an example the error in computing the pressure gradient using a standard 10 level primitive equation model appl

an overview of the 2009 eruption of redoubt volcano alaska abstract in march 2009 redoubt volcano alaska erupted for the first time since 1990 explosions ejected plumes that disrupted international and domestic airspace sent lahars more than 35 km down the drift river to the coast and resulted in tephra fall on communities over 100 km away geodetic data suggest that magma began to ascend slowly from deep in the crust and reached mid to shallow crustal levels as early as may 2008 heat flux at the volcano during the precursory phase melted 4 of the drift glacier atop redoubt s summit petrologic data indicate the deeply sourced magma low silica andesite temporarily arrested at 9 11 km and or at 4 6 km depth where it encountered and mixed with segregated stored high silica andesite bodies the two magma compositions mixed to form intermediate silica andesite and all three magma types erupted during the earliest 2009 events only intermediate and high silica andesites were produced throughout the explosive and effusive phases of the eruption the explosive phase began with a phreatic explosion followed by a seismic swarm which signaled the start of lava effusion on march 22 shortly prior to the first magmatic explosion early on march 23 2009 utc more than 19 explosions or events were produced over 13 days from a single vent immediately south of the 1989 90 lava domes during that period multiple small pyroclastic density currents flowed primarily to the north and into glacial ravines three major lahars flooded the drift river terminal over 35 km down river on the coast tephra fall deposited on all aspects of the edifice and on several communities north and east of the volcano and at least two and possibly three lava domes were emplaced lightning accompanied almost all the explosions a shift in the eruptive character took place following event 9 on march 27 in terms of infrasound signal onsets the character of repeating earthquakes and the nature of tephra ejecta more than nine additional explosions occurred in the next two days followed by a hiatus in explosive activity between march 29 and april 4 during this hiatus effusion of a lava dome occurred whose growth slowed on or around april 2 the final explosion pulverized the very poorly vesicular dome on april 4 and was immediately followed by the extrusion of the final dome that ceased growing by july 1 2009 and reached 72 m m 3 in bulk volume the dome remains as of this writing effusion of the final dome in the first month produced blocky intermediate to high silica andesite lava which then expanded by means of lava injection beneath a fracturing and annealing cooling surface crust in the first week of may a seismic swarm accompanied extrusion of an intermediate to high silica andesite from the apex of the dome that was highly vesicular and characterized by lower p 2 o 5 content the dome remained stable throughout its growth period likely due to combined factors that include an emptied conduit system steady degassing through coalesced vesicles in the effusing lava and a large crater pit created by the previous explosions we estimate the total volume of erupted material from the 2009 eruption to be between 80 m and 120 m m 3 dense rock equivalent dre the aim of this report is to synthesize the results from various datasets gathered both during the eruption and retrospectively and which are represented by the papers in this publication we therefore provide an overall view of the 2009 eruption and an introduction to this special issue publication

low frequency variability of southern ocean jets both observations and high resolution numerical models show that the southern ocean circumpolar flow is concentrated in a large number approximately 8 to 12 of narrow filamentary jets it is shown here that coherent jets exhibit a range of low frequency variability on timescales of months to years that can lead to displacement and to intermittent formation and dissipation of jets using output from an eddy resolving ocean general circulation model in local regions near topographic features the impact of energy exchange between eddy and mean flow components on jet persistence and variability is examined a novel approach that uses a time dependent definition of the mean flow provides a clearer picture of eddy mean flow interactions in regions with spatially and temporally varying flow structure the dynamics are largely consistent with those in idealized quasi geostrophic models including topographically organized and surface enhanced reynolds stress forcing of the mean flow jets form during periods of enhanced eddy activity but may persist long after the eddy activity has decayed similarly jets may evolve in a downstream sense with jet formation localized near topography and undergoing modification in response to changing bathymetry the evolution of both temperature and potential vorticity is used to show that the low frequency variability of the jets impacts water mass structure and tracer transport this study highlights various examples of southern ocean dynamics that will prove difficult to capture through parameterizations in coarser climate models

syneruptive mixing degassing and crystallization at redoubt volcano eruption of december 1989 to may 1990 abstract the 1989 1990 eruption of redoubt volcano included initial energetic vertical venting of pumiceous tephra followed by shedding of dense pyroclastic flows from successive unstable domes the suite of quenched magmatic materials thus produced coupled with detailed seismic observations provides a record of establishment and subsequent evolution of an active magma column in the upper crust the initial eruptive event involved a dacite magma with rhyolite melt and an andesite magma with dacite melt the dacite magma contains reaction rim free hornblende high cl concentrations 0 12 0 02 wt of melt and is microlite free all evidence for rapid ascent from depth in contrast the andesite component is microlite rich though this characteristic may have arisen by mixing between the two magmas rather than by slow ascent abundant dense juvenile lava like clasts with low h2o 0 1 0 3 wt were ejected in the initial eruption event implying that the magma column had reached the near surface and its upper portion had undergone degassing and bubble collapse prior to explosive disruption later eruptive events contain evidence of progressive blending of the two magmatic components as well as mixing between fresh reservoir derived and old conduit resident magma magma apparently ascended to the surface from the 6 10 km deep source chamber in a series of pulses rather than by steady flow or gradual emptying of a shallowly intruded body increased shallow long period seismicity which may indicate subsurface degassing from the flowing magma column occurred 5 days before each major eruptive event petrologic evidence indicates that each eruption contained some magma that ascended quickly from the chamber with time the proportion of new magma in eruptive batches may have decreased however even the final dome contains magma that left the chamber no more than a few days before extrusion together the pulses apparently record passage of an andesite plume through redoubt s dacite magma reservoir

photogrammetric monitoring of lava dome growth during the 2009 eruption of redoubt volcano abstract the 2009 eruption of redoubt volcano alaska began with a phreatic explosion on 15 march followed by a series of at least 19 explosive events and growth and destruction of at least two and likely three lava domes between 22 march and 4 april on 4 april explosive activity gave way to continuous lava effusion within the summit crater we present an analysis of post 4 april lava dome growth using an oblique photogrammetry approach that provides a safe rapid and accurate means of measuring dome growth photogrammetric analyses of oblique digital images acquired during helicopter observation flights and fixed wing volcanic gas surveys produced a series of digital elevation models dems of the lava dome from 16 april to 23 september the dems were used to calculate estimates of volume and time averaged extrusion rates and to quantify morphological changes during dome growth effusion rates ranged from a maximum of 35 m 3 s 1 during the initial two weeks to a low of 2 2 m 3 s 1 in early summer 2009 the average effusion rate from april to july was 9 5 m 3 s 1 early rapid dome growth was characterized by extrusion of blocky lava that spread laterally within the summit crater in mid to late april the volume of the dome had reached 36 10 6 m 3 roughly half of the total volume and dome growth within the summit crater began to be limited by confining crater walls to the south east and west once the dome reached the steep north sloping gorge that breaches the crater growth decreased to the south but the dome continued to inflate and extend northward down the gorge effusion slowed during 16 april 1 may but in early may the rate increased again this rate increase was accompanied by a transition to exogenous dome growth from mid may to july the effusion rate consistently declined the decrease is consistent with observations of reduced seismicity gas emission and thermal anomalies as well as declining rates of geodetic deflation or inflation these trends suggest dome growth ceased by july 2009 the volume of the dome at the end of the 2009 eruption was about 72 10 6 m 3 more than twice the estimated volume of the largest dome extruded during the 1989 1990 eruption in total the 2009 dome extends over 400 m down the glacial gorge on the north end of the crater with a total length of 1 km width of 500 m and an average thickness of 200 m

microseismic activity within a serac zone in an alpine glacier glacier d argentiere mont blanc france a passive seismic study was carried out underneath glacier d argenti ere mont blanc france where an array of seismometers was installed in a subglacial access tunnel the data show a very high emissivity from the glacier fracturing can be discriminated from serac falls using the signal characteristics we apply seismic array methods to locate the sources of these signals using a two step grid search in the parameter space four clusters of activity are found close to the network showing that this fracturing does not take place uniformly over the glacier but rather in isolated small zones we compute a local magnitude using regional earthquakes for calibration the magnitudes follow a classical gutenberg richter law in the range ml 3 to 0 15 showing that no characteristic size events dominate the process we suggest that those spatial clusters of icequakes could reveal the heterogeneous nature of the friction at the base of the glacier with patches of high frictional stresses locally generating intense fracturing within the ice mass

deep crustal melt plumbing of barðarbunga volcano iceland understanding magmatic plumbing within the earth s crust is important for understanding volcanic systems and improving eruption forecasting we discuss magma plumbing under bar arbunga volcano iceland over a 4 year period encompassing the largest icelandic eruption in 230 years microseismicity extends through the usually ductile region of the earth s crust from 7 to 22 km depth in a subvertical column moment tensor solutions for an example earthquake exhibits opening tensile crack behavior this is consistent with the deep 7 km seismicity being caused by the movement of melt in the normally aseismic crust the seismically inferred melt path from the mantle source is offset laterally from the center of the bar arbunga caldera by 12 km rather than lying directly beneath it it is likely that an aseismic melt feed also exists directly beneath the caldera and is aseismic due to elevated temperatures and pervasive partial melt under the caldera

the wind driven ocean circulation with an isopycnal thickness mixing parameterization abstract numerical solutions are examined for the nearly adiabatic large scale ocean circulation in a midlatitude rectangular domain with steady wind driving the model used is the balance equations and its various subsets hence dynamical effects at finite rossby number are included the solutions are steady ones and the necessary transports by the missing mesoscale eddies are parameterized in part using the authors previous proposal for isopycnally oriented mixing of tracers and isopycnal thickness or static stability this yields qualitatively credible quasi adiabatic solutions for realistic magnitudes for the subgrid scale transport coefficients among these solutions are ones with nearly homogeneous fields of potential vorticity on upper thermocline isopycnal surfaces even though the parameterized eddy mixing does not act directly to this end

a monochromatic earthquake suggesting deep seated magmatic activity beneath the izu ooshima volcano japan after a quiescence of 12 years the izu ooshima volcano located about 30 km east of the izu peninsula in central japan erupted on november 15 1986 on august 27 1985 about 1 year before the eruption a peculiar earthquake of magnitude 2 7 took place near the moho boundary just beneath the izu ooshima volcano where seismic activity is otherwise absent analysis of digital data obtained by the telemetered seismic network of the national research center for disaster prevention reveals the following distinctive features of the seismic waves 1 the main part of the wave train is composed of s waves and a small p phase precedes it 2 the spectral density has a sharp peak at 1 0 hz which is independent of the epicentral distance azimuth and time indicating a monochromatic spectrum at the source 3 ground motion for the initial part of the s wave is polarized in the n s direction at almost all the stations the amplitude ratios of s to p waves and the polarization pattern of s waves suggest that a traction force caused by magma flow is a more probable source than a double couple mechanism free oscillation of the magma reservoir or opening of a tensile crack we propose a traction force model for this earthquake in which magma flow through a conduit produces unidirectional viscous force on the conduit walls the observations imply a n s force direction and a maximum force of about 2 8 1010 n the pressure difference between the ends of the conduit is estimated as 6 1 107 pa 610 bar under the assumption of conduit dimensions of 2 km 1 km the monochromatic nature of the source spectrum is difficult to account for by the free oscillation of a magma reservoir we tentatively suggest the intermittent opening of a barrier in the conduit as a plausible mechanism of the periodic oscillation

do tropical cells ventilate the indo pacific equatorial thermocline source waters of the indo pacific equatorial thermocline are studied with a high resolution ocean model in the annual mean fields tropical and subtropical overturning cells are found that upwell at the equator and downwell at 5 degrees and 20 degrees poleward of the equator respectively tropical cells are common in ocean models but their role in ventilating the equatorial thermocline is obscure because the downwelled water is too warm to match the subsurface equatorial waters the tropical cells are much weaker when the overturning is considered in density coordinates when high frequency mass fluxes are included tropical cells are compensated by an eddy induced overturning seasonal variations and tropical instability waves are responsible for the compensation it follows that only subtropical cells transfer surface water to the equatorial thermocline strong tropical cells are shown to be an artefact

three dimensional p and s wave velocity structure of redoubt volcano alaska the three dimensional p and s wave structure of redoubt volcano alaska and the underlying crust to depths of 7 8 km is determined from 6219 p wave and 4008 s wave first arrival times recorded by a 30 station seismograph network deployed on and around the volcano first arrival times are calculated using a finite difference technique which allows for flexible parameterization of the slowness model and easy inclusion of topography and source receiver geometry the three dimensional p wave velocity structure and hypocenters are determined simultaneously while the three dimensional s wave velocity model is determined using the relocated seismicity and an initial s wave velocity model derived from the p wave velocity model assuming an average vp vs ratio of 1 78 convergence is steady with approximately 73 and 52 reduction in p and s wave arrival time rms respectively after 10 iterations the most prominent feature observed in the three dimensional velocity models derived for both p and s waves is a relative low velocity near vertical pipelike structure approximately 1 km in diameter that extends from 1 to 6 km beneath sea level this feature aligns axially with the bulk of seismicity and is interpreted as a highly fractured and altered zone encompassing a magma conduit the velocity structure beneath the north flank of the volcano between depths of 1 and 6 km is characterized by large lateral velocity variations high velocities within this region are interpreted as remnant dikes and sills and low velocities as regions along which magma migrates no large low velocity body suggestive of a magma chamber is resolved in the upper 7 8 km of the crust

evidence for northward thrusting south west of the rhodes basin models of convergence between the major african and european plates involve a stretching aegean plate whose present motion relative to africa is south west1 3 this motion has resulted in subduction of eastern mediterranean sea floor as shown by seismicity volcanism and morphology the southern boundary of the aegean plate is formed by the hellenic trench intensive study culminating in the use of submersibles and multibeam echo sounding as part of the hellenic arc and trench program4 has outlined the complexity of this boundary detailed reflection profiling which we carried out in autumn 1980 of the eastern portion of the hellenic trench system shows arcward verging thrusting south west of the rhodes basin we conclude that collision of the african continental margin with the hellenic arc is now in progress causing overriding by the mediterranean ridge along the southeastern branch of the hellenic trench system

the dynamics of the antarctic circumpolar current abstract the dynamics of the antarctic circumpolar current acc in a near eddy resolving model of the southern ocean fram are investigated a streamwise coordinate system is used rather than a more conventional approach of considering zonally averaged quantities the motivation for this approach is the large deviation from a purely zonal flow made by the current comparisons are made with a zonal mean analysis of the same model it is found that the topographic form drag is the main sink of the momentum that is input by the wind however in contrast to a zonal mean analysis other terms namely horizontal mixing bottom friction and advection of momentum are no longer negligible the total effect of transient eddies is to produce a drag on the mean flow again in contrast to the zonally averaged case the vertical penetration of stress is considered a generalized formula is derived for the interfacial form stress averaged along a convoluted path and that includes nonquasigeostrophic effects the i

a numerical study on the successive formation of meddy like lenses 1 we present a process study on the sustaining mechanism of lens formation using a series of numerical experiments of a density current over a sloping bottom with a cape along the coastline water parcels in the bottom density current are shed into the offshore region leading to periodic formation of anticyclonic lenses as part of baroclinic dipolar vortices the cyclonic partner is more prominent at the surface and the coupled vortices are carried by the mean current established in the offshore region parameter dependence of dipole generation is examined which suggests that the background current is necessary for the detached eddies to be coherent in the downstream direction and for shedding events to repeat nof and pichevin 1996 it is also shown that the density mixing of the bottom current provides criteria for cyclogenesis at the sea surface a detailed analysis is given by a five layer model forced by a water mass source sink which reproduces the baroclinic dipolar vortices similar to those observed in the preceding z coordinate model we find that the dipole generation is due to the finite amplitude divergence convergence of the baroclinic current passing the cape stern and chassignet 2000 the overall analyses suggest three necessary conditions for successive eddy formation 1 a localized variation in the coastline causing the finite amplitude disturbance 2 mixing of mediterranean water with the surrounding fluids leading to anticyclonic rotation of meddies as well as cyclogenesis at the surface and 3 background currents that advect the detached vortices out of the source region index terms 4255 oceanography general numerical modeling 4219 oceanography general continental shelf processes 4520 oceanography physical eddies and mesoscale processes 4528 oceanography physical fronts and jets keywords eddy shedding dense water plume numerical simulation

eddy dynamics in a primitive equation model sensitivity to horizontal resolution and friction a primitive equation model of an idealized ocean basin driven by simple study wind and buoyancy forcing at the surface is used to study the dynamics of mesoscale eddies model statistics of a six year integration using a fine grid 1 6 0 2 with reduced coefficients of horizontal friction are compared to those using a coarser grid 1 3 0 4 but otherwise identical configuration eddy generation in both model cases is primarily due to the release of mean potential energy by baroclinic instability horizontal reynolds stresses become significant near the midlatitude jet of the fine grid case with a tendency for preferred energy transfers from the eddies to the mean flow using the finer resolution eddy kinetic energy nearly doubles at the surface of the subtropical gyre and increases by factors of 3 4 over the jet region and in higher latitudes the spatial characteristics of the mesoscale fluctuations are examined by calculating zonal wavenumber spectra and velocity autocorrelation functions with the higher resolution the dominant eddy scale remains approximately the same in the subtropical gyre but decreases by a factor of 2 in the subpolar areas the wavenumber spectra indicate a strong influence of the model friction in the coarse grid case especially in higher latitudes using the coarse grid there is almost no separation between the energetic eddy scale and the scale where friction begins to dominate leading to steep spectra beyond the cutoff wavenumber using the finer resolution an inertial subrange with a k 3 power law begins to emerge in all model regions outside the equatorial belt despite the large increase of eddy intensity in the fine grid model effects on the mean northward transport of heat are negligible strong eddy fluxes of heat across the midlatitude jet are almost exactly compensated by changes of the heat transport due to the mean flow

the 1989 earthquake swarm beneath mammoth mountain california an initial look at the 4 may through 30 september activity abstract mammoth mountain is a 50 000 to 200 000 year old cumulovolcano standing on the southwestern rim of long valley in eastern california on 4 may 1989 two m 1 earthquakes beneath the south flank of the mountain marked the onset of a swarm that has continued for more than 6 months in addition to its longevity noteworthy aspects of this persistent swarm include 1 an exponential like increase in the rate of activity through the first month 2 a vertically oriented planar distribution of hypocenters at depths between 6 and 9 km with a north northeast strike roughly perpendicular to the average t axis orientation for the swarm earthquakes 3 recurring spasmodic bursts rapid fire sequences of similar sized earthquakes with overlapping coda and occasional earthquakes with enhanced low frequency energy 4 a uniform temporal distribution of the four largest m 3 events over the first 4 months of the swarm with a cumulative seismic moment for the entire sequence through 30 september corresponding to a single m 4 earthquake 5 a b value of 1 2 and 6 submicrostrain perturbations on the nearby borehole dilatometer the first of which led the onset of swarm activity by more than 2 weeks these aspects of the swarm together with its location along the southern extension of the youthful mono inyo volcanic chain which last erupted 500 to 600 years ago point to a magmatic source for the modest but persistent influx of strain energy into the crust beneath mammoth mountain

evolution of the december 14 1989 precursory long period event swarm at redoubt volcano alaska abstract the intermittency pattern and evolution in waveforms of long period lp seismic events during the intense 23 h swarm that preceded the december 14 1989 eruption of redoubt volcano are investigated utilizing cross correlation to exploit the high degree of similarity among waveforms a substantially more complete event catalog is generated than was available from near realtime detection based on short term long term amplitude ratios which was saturated by the high rate of activity the temporal magnitude distribution of the predominant lp events is found to have an unusual banded structure in which the average magnitude of each band slowly increases and then decreases through time a bifurcation that appears in the uppermost band shortly after the peak in magnitudes is characterized by a quasi periodicity in intermittency and magnitude that is reminiscent of one of the classic routes to chaotic behavior in some non linear systems the waveforms of the predominant events evolve slowly but unsteadily through time these gradual changes appear to result from variations in the relative amplitudes of spectral peaks that remain stable in frequency which suggests that they are due to differential excitation of a single resonant source two other previously unrecognized repetitive waveforms are also identified but the signals from these secondary events are not clearly recorded at distances beyond the closest station similarities among the spectra of the predominant and secondary events suggest that the signals from these events also could represent different modes of exciting the same source significant changes in the rates and the sizes of the largest of these secondary events appear to coincide with the peak in the size distribution of the predominant lps at least some of the non repetitive lp waveforms in the swarm appear to be the result of the superposition of signals from the rapid repetition of predominant lp source thus placing a constraint on the repeat time of the triggering mechanism for this source a lone hybrid event which has a waveform character intermediate between the predominant lp events and high frequency volcano tectonic events was also identified in the swarm the occurrence of this event provides important evidence that the low frequency character of the lp events is a source rather than a path or site effect

the influence of magma ascent path on the texture mineralogy and formation of hornblende reaction rims abstract although hornblende reaction rims are widely used as a tool for evaluating magma ascent during volcanic eruptions very few studies constrain the manner in which they form this study investigates the influence of magma ascent path on the formation of hornblende reaction rims to do this we conducted isothermal 840 c decompression experiments using dacite pumice samples erupted in december 1989 from redoubt volcano alaska experiments were first held within the hornblende stability field determined through phase equilibria experiments for 3 to 5 days before being decompressed to different pressures ranging from 100 to 2 mpa for 1 to 30 days before being quenched decompression was performed in either multiple equal steps constant rate or in one single step results from multi step experiments show that reaction rims form preferentially at pressures from 10 to 40 mpa and that this favorable pressure range narrows and decreases with increased decompression duration hornblendes in multi step experiments are tightly enclosed by fine grained reaction rims composed of plagioclase and orthopyroxene crystals with high aspect ratios ranging from 1 to 12 for single step experiments reaction rims also form preferentially within a narrow pressure range 60 70 mpa where they consist of medium grained plagioclase titanomagnetite and orthopyroxene crystals with aspect ratios ranging from 1 to 6 that broadly surround subrounded hornblendes hornblendes from single step experiments dropped to lower pressures

roles of mesoscale eddies in the kuroshio paths a high resolution ocean general circulation model is developed to simulate connections between the kuroshio path variations and mesoscale eddy activities as realistically as possible the climatological mean of the modeled kuroshio takes a nearshore nonlarge meander path it is found that the model is capable of simulating two types of nonlarge meander state and a possible version of the large meander state the offshore nonlarge meander is generated through interaction between the kuroshio and an anticyclonic eddy the large meander occurs just after significant intensification of the anticyclonic kuroshio recirculation successive intrusion of anticyclonic eddies from the upstream region is responsible for this process those anticyclonic eddies are advected by the kuroshio from the region northeast of luzon island and increase the upstream kuroshio volume transport on an interannual time scale the cyclonic eddies propagating from the kuroshio extension region on the other hand weaken the kuroshio meander after the merger the kuroshio path variations south of japan thus seem to be closely related to eddy activities in the subtropical gyre system

swarms of similar long period earthquakes in the mantle beneath mauna loa volcano abstract we present analyses of two swarms of long period lp earthquakes at 30 km depth that accompanied the geodetically observed 2002 2005 mauna loa intrusion the first lp earthquake swarm in 2002 consisted of 31 events that were precursory and preceded the start of mauna loa inflation the second lp swarm of two thousand events occurred from 2004 2005 the rate of lp earthquakes slowed significantly coincident with the occurrence of the december 26 2004 m w 9 3 sumatra earthquake suggesting that the seismic waves from this great earthquake may have had a dynamic triggering effect on the behavior of mauna loa s deep magma system using waveform cross correlation and double difference relocation we find that a large number of earthquakes in each swarm are weakly similar and can be classified into two families the relocated hypocenters for each family collapse to compact point source regions almost directly beneath the mauna loa intrusion we suggest that the observed waveform characteristics are compatible with each family being associated with the resonance of a single fluid filled vertical crack of fixed geometry with differences in waveforms between events being produced by slight variations in the trigger mechanism if these lp earthquakes are part of the primary magma system that fed the 2002 2005 intrusion as indicated by the spatial and temporal associations between mantle seismicity and surface deformation then our results raise the possibility that this magma system may be quite focused at these depths as opposed to being a diffuse network it is likely that only a few locations of mauna loa s deep magma system met the geometric and fluid dynamic conditions for generating lp earthquakes that were large enough to be recorded at the surface and that much of the deep magma transfer associated with the 2002 2005 intrusion occurred aseismically

a numerical investigation of choked flow dynamics and its application to the triggering mechanism of long period events at redoubt volcano alaska we use numerical simulations of transonic flow through a crack to study the dynamics of the formation of shock waves downstream from a nozzle like constriction inside the crack the model solves the full set of navier stokes equations in two dimensions via an explicit multifield finite difference representation the crack walls are assumed to be perfectly rigid and elastic coupling to the solid is not considered the simulations demonstrate how the behavior of unsteady shock waves near the walls can produce recurring step like pressure transients in the flow which in turn induce resonance of the fluid filled crack the motion of the shock waves is governed primarily by smooth low amplitude pressure fluctuations at the outlet of the crack the force induced on the walls scales with the amplitude of the shock which is a function of the magnitude of the inlet pressure aperture of the constriction and thickness of the boundary layer the applied force also scales in proportion to the spatial extent of the shock excursion which depends on the fluctuation rate of outlet pressure using the source parameters of long period lp events at redoubt volcano alaska as a guide for our simulations we infer that coupling of the shock to the walls occurs for crack inlet to outlet pressure ratios pi po 2 31 and that the position of the shock front becomes most sensitive to outlet pressure fluctuations for flow regimes with pi po 2 48 for such regimes fluctuations of outlet pressure of up to 0 5 mpa at rates up to 3 mpa s are sufficient to induce pressure transients with magnitudes up to 12 5 mpa over 0 1 2 5 m of the walls within 0 5 s these flow parameters may be adequate for triggering the lp events in the precursory swarm to the december 14 1989 eruption of redoubt according to the flow model the recurrence rate and amplitudes of l p events are inferred to be a manifestation of the response of a shallow hydrothermal reservoir to the sustained injection of superheated steam from a magma column roofing below this reservoir

westward motion of mesoscale eddies abstract since the pioneering work of nof the determination of the westward drift of mesoscale eddies under the planetary beta effect has been a recurrent theme in mesoscale oceanography and several different formulae have been proposed in the literature here recpatiulation is sought and within the confines of a single layer model a generalized formula is derived although it is similar to nof s the present formula is established from a modified definition and with fewer assumptions it also recaptiulates all other formulae for the one layer model and applies to a wide variety of situations including cases when the vortex develops a wake of rossby waves or undergoes axismmetrization following the derivation of the formula a physical interpretation clarifies the migration mechanism which can be divided between a self induced propulsion and a reaction from the displaced ambient fluid numerical simulations with primitive and geostrophic equations validate the formula for a variety of length sc

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

precursory swarms of long period events at redoubt volcano 1989 1990 alaska their origin and use as a forecasting tool abstract during the eruption of redoubt volcano from december 1989 through april 1990 the alaska volcano observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long period lp seismic events dominant period of about 0 5 s the initial eruption on december 14 occurred after 23 years of quiescence and was heralded by a 23 hour swarm of lp events that ended abruptly with the eruption after a series of vent clearing explosions over the next few days dome growth began on december 21 another swarm with lp events similar to those of the first began on the 26th and ended in a major tephra eruption on january 2 eruptions continued over the next two weeks and then ceased until february 15 when a large eruption initiated a long phase of repetitive dome building and dome destroying episodes that continued into april warnings were issued before the major events on december 14 and january 2 but as the eruptive sequence continued after january 2 the energy of the swarms decreased and forecasting became more difficult a significant but less intense swarm preceded the february 15 eruption which was not forecast this eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until march 4 when the first of three new stations was installed within 3 km of the active vent from march 4 to the end of the sequence on april 21 there were eight eruptions six of which were preceded by detectable swarms of lp events although weak these swarms provided the basis for warnings issued before the eruptions on march 23 and april 6 the initial swarm on december 13 had the following features 1 short duration 23 hours 2 a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm followed by a decline of activity during the 5 hours preceding the eruption 3 a magnitude range from 0 4 to 1 6 4 nearly identical lp signatures with a dominant period near 0 5 s 5 dilatational first motions everywhere and 6 a stationary source location at a depth of 1 4 km beneath the crater this occurrence of long period events suggests a model involving the interaction of magma with groundwater in which magmatic gases steam and water drive a fixed conduit at a stationary point throughout the swarm the initiation of that sequence of events is analogous to the failure of a pressure relief valve connecting a lower supercharged magma dominated reservoir to a shallow hydrothermal system a three dimensional model of a vibrating fluid filled crack recently developed by chouet is found to be compatible with the seismic data and yields the following parameters for the lp source crack length 280 380 m crack width 140 190 m crack thickness 0 05 0 20 m crack stiffness 100 200 sound speed of fluid 0 8 1 3 km s compressional wave speed of rock 5 1 km s density ratio of fluid to rock 0 4 and ratio of bulk modulus of fluid to rigidity of rock 0 03 0 07 the fluid filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0 4 to 40 bar such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack

seismic structure changes beneath redoubt volcano during the 2009 eruption inferred from local earthquake tomography we present seismic velocity models of the area beneath redoubt volcano alaska corresponding to two time periods before and after the strong eruption that occurred in march 2009 the calculations were based on tomographic inversion of p and s arrival time data recorded by 19 stations using the local earthquake tomography code lotos we performed thorough analysis of the results based on synthetic tests in each of the time periods that allow real time variations in structure to be distinguished from artifacts caused by changes in the observation system configurations in the resulting images corresponding to the period before the eruption the summit area is characterized by higher values of both p and s velocities and moderate values of the vp vs ratio this may correspond to the rigid igneous rocks composing the body of the volcano that lack significant liquid content in the second episode corresponding to the time of the eruption the p velocity remained high whereas the s velocity became very low the anticorrelation of p and s anomalies in the summit area produced a vp vs ratio as high as 2 2 which is seen down to 2 3 km depth this indicates presence of mobile phase at shallow depth beneath the volcano which can be either in the form of partial melt or fluid saturated rocks

long period seismicity at shishaldin volcano alaska in 2003 2004 indications of an upward migration of the source before a minor eruption abstract we have analyzed the long period lp seismic activity at shishaldin volcano aleutians islands alaska in the period october 2003 july 2004 during which a minor eruption took place in may 2004 with ash and steam emissions thermal anomalies volcanic tremor and small explosions we have focused the attention on the time evolution of lp rate size spectra and polarization dip angle along the dataset we find an evolution toward more shallow dip angles in the polarization of the waveforms during the sequence the dip angle is a manifestation of the source location because the lp seismic sources are presumed to reflect the aggregation of gas slug or pockets within the melt we use the polarization dip at the lp onset as a proxy for the nucleation depth of the seismic events within the conduit we refer to this parameter as the nucleation dip and the position along the conduit of the gas aggregation as nucleation depth the nucleation dip changes throughout the dataset it shows a sharp decrease between the end of december 2003 and the end of january 2004 followed by a gradual increase until the onset of the eruption at the same time a general increase of the lp rate occurs we have associated the dip evolution with a sinking and a subsequent decrease of the nucleation depth which would quickly migrate up to about 8 km below the crater rim followed by a slow depth decrease which culminates in the eruption the change in the nucleation depth reflects either a pressure variation within the plumbing system which would affect the confining pressure experienced by the gas aggregations we have imputed such a pressure change to the intrusion of batches of magma from a deeper magma chamber 5 km for a cylindric conduit with rigid walls this leads to a volume of the injected new magma of 10 5 10 7 m 3 compatible with estimates in other areas suggesting that the lp process can be considered a good proxy of the thermodynamical conditions of the shallow plumbing system

characterization of seismic events during the 2009 eruption of redoubt volcano alaska abstract seismic events were automatically detected and characterized throughout the 2009 eruption of redoubt volcano alaska on a single short period station located 3 km from the volcanic crater a total of 126 789 individual events were identified from continuous recording of seismic data from january 1 to june 30 average 29 events per hour using a short term average long term average detection algorithm nine metrics were computed for this suite of events including event duration inter event time event rate peak amplitude peak to peak amplitude root mean square rms amplitude peak frequency center frequency and frequency index eight swarms were identified with event rates exceeding 100 events per hour the first two occurred in late january and are attributed to high amplitude spasmodic tremor five additional swarms were manually repicked including swarms on february 26 27 march 20 23 march 27 march 29 and april 2 4 three of these swarms immediately preceded major explosions including march 20 23 march 27 and april 2 4 a final swarm on may 2 9 was re picked using a correlation detection scheme we identified 146 event families that occurred within this suite of selected events using a cross correlation technique seven explosions were each immediately preceded by one or more event families events from the dominant family during each of these periods was additionally re picked using correlation detection the procession of event metrics and occurrence of event families formed a complex distribution throughout the eruption a single station approach was used to gain a fine scale view of variations in seismic behavior at redoubt with a focus on potential indicators of impending explosions these techniques may serve an important role in future real time eruption monitoring efforts

seismological aspects of the 1989 1990 eruptions at redoubt volcano alaska the ssam perspective abstract ssam is a simple and inexpensive tool for continuous monitoring of average seismic amplitudes within selected frequency bands in near real time on a pc based data acquisition system during the 1989 1990 eruption sequence at redoubt volcano the potential of ssam to aid in rapid identification of precursory long period lp event swarms was realized and since this time ssam has been incorporated in routine monitoring efforts of the alaska volcano observatory in particular an eruption that occurred on april 6 was successfully forecast primarily on the basis of recognizing the precursory lp activity on ssam of twenty two significant eruptions that occurred between december 14 and april 21 eleven had precursory swarms longer than one hour in duration that could be detected on ssam for individual swarms the patterns of relative spectral amplitudes are distinct at each station and remain largely stationary through time thus indicating that one source may have been preferentially and repeatedly activated throughout the swarm typically a single spectral band dominates the signal at each seismic station for the vigorous one day swarm that preceded the first eruption on december 14 signals were sharply peaked in the 1 9 2 7 hz band at the closest station located 4 km from the vent but were dominated by 1 3 1 9 hz energy at three more distant stations located 7 5 22 km from the vent the tendency for the signals from different swarms recorded at the same station to be peaked in the same frequency band suggests that all of the sources are characterized by a predominant length scale signals from the precursory lp swarms became weaker as the eruption sequence progressed and swarms that occurred in march and april could only be detected at seismographs on the volcanic edifice onset times of precursory lp swarms prior to eruptions ranged from a few hours to about one week but after the initial vent clearing phase that ended december 19 these intervals tended to become progressively shorter for successive swarms these trends in the relative onset times and intensities of successive precursory lp swarms are consistent with an overall depressurization of the magmatic system through time in general each of the swarms had an emergent onset but the intensities did not always increase steadily until the eruptions instead as the time of an eruption approached the intensity usually increased more rapidly before peaking and then declining prior to the eruption for three of the swarms two distinct peaks in intensity were apparent the time intervals between final peaks in swarm intensity and ensuing eruptions ranged from about 2 hours to almost 2 days but the peaks always occurred closer to the eruptions than to the swarm onsets both the onset of lp swarm activity and a decline in intensity prior to an eruption may represent critical points in the process of pressurization that drives the flow of fluids and gas in a sealed magmatic system a notable exception to this pattern is the eruption of march 9 which lacked a detectable precursory lp swarm but was followed by an unusually long period of strong lp seismicity that may have been stimulated by a depressurization of the magmatic system resulting from dome failure on both december 14 and january 2 the spectra of early syn eruptive signals have peaked signatures much like those of the spectra of precursory lp activity from shortly before the eruptions these similarities may indicate that the source of precursory seismicity continued to be active during at least the early part of each eruption in syn eruptive signals from march and april recorded at stations on the volcanic edifice the dominant spectral energy progressively shifts with time during the eruption to lower frequencies at least part of the energy in these signals may have been generated by the debris flows associated with dome failures

energetics of eddy mean flow interactions in the gulf stream region a detailed energetics analysis of the gulf stream gs and associated eddies is performed using a highresolution multidecadal regional ocean model simulation the energy equations for the time mean and timevaryingflowsarederivedasatheoreticalframeworkfortheanalysis theeddy meanflowenergycomponents and their conversions show complex spatial distributions in the along coast region the cross stream and cross bump variations are seen in the eddy mean flow energy conversions whereas in the off coast region a mixed positive negative conversion pattern is observed the local variations of the eddy mean flow interaction are influenced by the varying bottom topography when considering the domain averaged energetics theeddy meanflowinteractionshowssignificantalong streamvariability upstreamofcapehatteras the energy is mainly transferred from the mean flow to the eddy field through barotropic and baroclinic instabilities upon separating from the coast the gs becomes highly unstable and both energy conversions intensify when the gs flows into the off coast region an inverse conversion from the eddy field to the mean flow dominates the power transfer for the entire gs region the mean current is intrinsically unstable and transfers 28 26gw of kinetic energy and 26 80gw of available potential energy to the eddy field the mesoscaleeddykineticenergyisgeneratedbymixedbarotropicandbaroclinicinstabilities contributing28 26 and 9 15gw respectively beyond directly supplying the barotropic pathway mean kinetic energy also provides 11 55gw of power to mean available potential energy and subsequently facilitates the baroclinic instability pathway

temporal changes of medium properties during explosive volcanic eruption volcanic evolutions typically accompany significant changes in medium properties monitoring the seismic properties may be useful in identifying the state of volcanic evolution temporal variation of shallow crustal vp vs ratios before and during the 2009 eruption of redoubt volcano alaska is investigated using the p and s traveltimes of local earthquakes high vp vs ratios of 1 9 are observed over a wide region in the precursory phase suggesting the presence of partial melts in the medium at least several months before explosive eruptions the high v p v s ratios decrease until the early effusive phase with rates of 0 179 year 1 in the precursory phase 65 days and 2 147 year 1 in the explosive phase 40 days which is equivalent to a decrease in the bulk modulus of fluids by 1 1 and 7 9 gpa respectively the decreasing v p v s ratios in the precursory phase may be due to increasing amounts of overpressurized gas and water vapor in the medium the rapid decrease in vp vs ratios during the explosive phase may be caused by melt eruption and gas emission the vp vs ratios were observed to be nearly stationary since the early effusive phase suggesting rare presence of melts and low levels of pore pressures with degassing these observations suggest that monitoring vp vs ratios may be useful to identify the eruption state

seismic evolution of the 1989 1990 eruption sequence of redoubt volcano alaska abstract redoubt volcano in south central alaska erupted between december 1989 and june 1990 in a sequence of events characterized by large tephra eruptions pyroclastic flows lahars and debris flows and episodes of dome growth the eruption was monitored by a network of five to nine seismic stations located 1 to 22 km from the summit crater notable features of the eruption seismicity include 1 small long period events beginning in september 1989 which increased slowly in number during november and early december 2 an intense swarm of long period events which preceded the initial eruptions on december 14 by 23 hours 3 shallow swarms 0 to 3 km of volcano tectonic events following each eruption on december 15 4 a persistent cluster of deep 6 to 10 km volcano tectonic earthquakes initiated by the eruptions on december 15 which continued throughout and beyond the eruption 5 an intense swarm of long period events which preceded the eruptions on january 2 and 6 nine additional intervals of increased long period seismicity each of which preceded a tephra eruption hypocenters of volcano tectonic earthquakes suggest the presence of a magma source region at 6 10 km depth earthquakes at these depths were initiated by the tephra eruptions on december 15 and likely represent the readjustment of stresses in the country rock associated with the removal of magma from these depths the locations and time history of these earthquakes coupled with the eruptive behavior of the volcano suggest this region was the source of most of the erupted material during the 1989 1990 eruption this source region appears to be connected to the surface by a narrow pipe like conduit as inferred from the hypocenters of volcano tectonic earthquakes concentrations of shallow volcano tectonic earthquakes followed each of the tephra eruptions on december 15 these shocks may represent stress readjustment in the wall rock related to the removal of magma and volatiles at these depths this shallow zone was the source area of the majority of long period seismicity through the remainder of the eruption the long period seismicity likely reflects the pressurization of the shallow portions of the magmatic system

progressive reactivation of the volcanic plumbing system beneath tolbachik volcano kamchatka russia revealed by long period seismicity abstract after lying dormant for 36 yr the tolbachik volcano of the klyuchevskoy group started to erupt on 27 november 2012 we investigate the preparatory phase of this eruption via a statistical analysis of the temporal behavior of long period lp earthquakes that occurred beneath this volcanic system the lp seismicity occurs close to the surface beneath the main volcanic edifices and at 30 km depth in the vicinity of a deep magmatic reservoir the deep lp earthquakes and those beneath the klyuchevskoy volcano occur quasi periodically while the lp earthquakes beneath tolbachik are clustered in time as the seismicity rate increased beneath tolbachik days before the eruption the level of the time clustering decreased we interpret this as a manifestation of the evolution of the volcano plumbing system we suggest that when a plumbing system awakes after quiescence multiple cracks and channels are reactivated simultaneously and their interaction results in the strong time clustering of lp earthquakes with time this network of channels and cracks evolves into a more stable state with an overall increased permeability where fluids flow uninhibited throughout the plumbing system except for a few remaining impediments that continue to generate seismic radiation the inter seismic source interaction and the level of earthquake time clustering in this latter state is weak this scenario suggests that the observed evolution of the statistical behavior of the shallow lp seismicity beneath tolbachik is an indicator of the reactivation and consolidation of the near surface plumbing system prior to the tolbachik eruption the parts of the plumbing system above the deep magmatic reservoir and beneath the klyuchevskoy volcano remain in nearly permanent activity as demonstrated by the continuous occurrence of the deep lp earthquakes and very frequent klyuchevskoy eruptions this implies that these parts of the plumbing system remain in a stable permeable state and contain a few weakly interacting seismogenic sources our results provide new constraints on future mechanical models of the magmatic plumbing systems and demonstrate that the level of time clustering of lp earthquakes can be a useful parameter to infer information about the state of the plumbing system

energetics of the global ocean the role of layer thickness form drag abstract understanding the role of mesoscale eddies in the global ocean is fundamental to gaining insight into the factors that control the strength of the circulation this paper presents results of an analysis of a high resolution numerical simulation in particular the authors perform an analysis of energetics in density space such an approach clearly demonstrates the role of layer thickness form drag residual effects of hydrostatic pressure perturbations which is hidden in the classical analysis of the energetics of flows for the first time in oceanic studies the global distribution of layer thickness form drag is determined this study provides direct evidence to verify some basic characteristics of layer thickness form drag that have often been assumed or speculated about in previous theoretical studies the results justify most of the previous assumptions and speculations including those associated with i the presence of an oceanic energy cycle explaining the relationship between layer th

the surface branch of the zonally averaged mass transport circulation in the troposphere the near surface branch of the overturning mass transport circulation in the troposphere containing the equatorward flow is examined in isentropic and geometric coordinates a discussion of the zonal momentum balance within isentropic layers shows that the equatorward flow at a given latitude is confined to isentropic layers that typically intersect the surface at that latitude as a consequence of mass transport within the surface mixed layer much of the equatorward flow occurs in layers with potential temperatures below the mean surface potential temperature in the conventional transformed eulerian mean formulation for geometric coordinates the surface branch of the overturning circulation is represented in an unrealistic manner streamlines of the residual circulation do not close above the surface a modified residual circulation is introduced that is free from this defect and has the additional advantage that its computation unlike that of the conventional residual circulation does not require division by the static stability which may approach zero in the planetary boundary layer it is then argued that cold air advection by the residual circulation is responsible for the formation of surface inversions at all latitudes in idealized gcms with weak thermal damping also included is a discussion of how a general circulation theory for the troposphere must be built upon a theory for the near surface meridional mass fluxes

long period seismicity at redoubt volcano alaska 1989 1990 related to magma degassing abstract the mass of exsolved magmatic h 2 o is estimated and compared to the mass of superheated steam 25 50 mtons released through the resonating crack producing the december 13 14 1989 swarm of long period seismic events at redoubt volcano results indicate degassing of a h 2 o co 2 so 2 saturated magma upon ascending from at least 12 km to 3 4 km beneath the crater as the source of the superheated steam the mass of exsolved h 2 o 3 2 250 mtons is estimated from solubility diagrams of h 2 o co 2 saturated silicate melts for the ascent history of the redoubt magmas crystal size distribution seismological petrological and geochemical data are used to constrain the ascent history of the two andesitic magmas prior to the eruption two stages of crystallization are inferred from crystal size distributions of plagioclase crystals in andesites erupted in december 1989 the first stage occurred 30 150 years before the eruption in both magmas and the second stage occurred at least 8 years and 15 years before the eruption in the dacitic andesite and rhyolitic andesite respectively the depths of crystallization are constrained from the spatial and temporal variations of volcano tectonic earthquakes locations lahr et al 1994 and from the p wave and s wave velocity structures benz et al 1996 these data suggest that the rhyolitic andesite magma ascended to a depth of 7 8 km within at least 15 years of the eruption within at least 8 years of the eruption the dacitic andesite magma migrated to a depth just below the other magma body where it resided until hours to days of the eruption at this time the dacitic andesite magma mixed with the rhyolitic andesite magma and established the reservoir for the eruption near the top of the reservoir some of the mixed magma was displaced into fractures which extended 4 5 km toward the surface this displaced magma created the eruption conduit and released the fluids related to the resonating crack this scenario is consistent with the trends in major and trace element chemistry and the stability of hornblende in the pre eruption redoubt magmas it also provides a source for the so 2 and co 2 emissions measured during the eruption

geochemistry of the 1989 1990 eruption of redoubt volcano part i whole rock major and trace element chemistry the 1989 1990 eruption of redoubt volcano produced medium k calc alkaline andesite and dacite of limited compositional range 58 2 63 4 sio2 and entrained quenched andesitic inclusions 55 sio2 which bear chemical similarities to the rest of the ejecta the earliest december 15 magmas are pumiceous often compositionally banded and the majority is relatively mafic 59 sio2 the most silicic magmas of the eruption are the late december to early january domes up to 63 4 sio2 subsequent magmas formed domes and rare pumices which converge on 60 sio2 chemical variations among ejecta comprise tight linear two component arrays for all elements for which the analytical uncertainty is much less than the compositional range the two component arrays are interpreted as mixing arrays between unrelated magmas because several of the arrays are at steep angles to the normal liquid line of descent additionally the felsic endmember cannot be easily related to the mafic endmember by normal high temperature igneous processes e g the silicic endmember has higher zr yet lower hf than the mafic endmember also relative enrichments of highly incompatible elements are dramatically different across the arrays the mixing event must have preceded eruption by a significant yet unspecified amount of time because groundmass glass compositions are homogeneous for all post december samples swanson et al 1994 this volume in spite of the whole rock chemical diversity this implies time for additional crystallization after the mixing event swanson et al 1994 this volume discuss evidence for a potentially different mixing event recorded only in december 15 magmas cognate cumulate xenoliths composed of pl cpx opx hb mt melt were recovered from january and april deposits these blocks differ from local batholithic country rock in their low concentrations of incompatible elements e g rb 60 wt they have mg cr ni sc and v contents higher than the andesites but lower than redoubt basalts and basaltic andesites thus they may be crystallization products of andesites but do not represent the cumulate residue of basalt fractionation the xenoliths were probably derived from a shallow or intermediate crustal chamber

on the driving processes of the atlantic meridional overturning circulation because of its relevance for the global climate the atlantic meridional overturning circulation amoc has been a major research focus for many years yet the question of which physical mechanisms ultimately drive the amoc in the sense of providing its energy supply remains a matter of controversy here we review both observational data and model results concerning the two main candidates vertical mixing processes in the ocean s interior and wind induced ekman upwelling in the southern ocean in distinction to the energy source we also discuss the role of surface heat and freshwater fluxes which influence the volume transport of the meridional overturning circulation and shape its spatial circulation pattern without actually supplying energy to the overturning itself in steady state we conclude that both wind driven upwelling and vertical mixing are likely contributing to driving the observed circulation to quantify their respective contributions future research needs to address some open questions which we outline

high precision earthquake location and three dimensional p wave velocity determination at redoubt volcano alaska 1 redoubt volcano alaska poses significant volcanic hazard to the cook inlet region and overlying flight paths during and following the most recent eruption in 1989 1990 the alaska volcano observatory deployed up to 10 seismometers to improve real time monitoring capabilities at redoubt and continues to produce an annual earthquake catalog with associated arrival times for this volcano we compute a three dimensional p wave velocity model using double difference tomography combined with waveform cross correlation techniques to identify families of similar earthquakes and increase earthquake location precision at redoubt absolute and differential times for well constrained events are used to simultaneously invert for hypocenter location and p wave velocity structure shot and earthquake arrival times recorded by temporary stations deployed on redoubt in july 1991 supplement the catalog picks double difference tomography reduces uncertainties associated with absolute and relative earthquake locations and provides a clearer picture of three dimensional velocity heterogeneity all redoubt data available through november 2005 are relocated through the three dimensional model and we investigate seismicity associated with the 1989 1990 eruption and compare cross correlation coefficients to identify similar earthquakes within the catalog waveform similarity is high at redoubt especially during the eruptive phases and event families include long period shallow summit hybrid and both shallow summit and midcrust level volcano tectonic earthquakes we do not resolve a low velocity feature in the three dimensional p wave model that can be interpreted as a source magma chamber and prefer the idea of an interconnected body of dikes and sills as the source of magma erupted in 1989 1990

proximal pyroclastic deposits from the 1989 1990 eruption of redoubt volcano alaska stratigraphy distribution and physical characteristics abstract more than 20 eruptive events during the 1989 1990 eruption of redoubt volcano emplaced a complex sequence of lithic pyroclastic flow surge fall ice diamict and lahar deposits mainly on the north side of the volcano the deposits record the changing eruption dynamics from initial gas rich vent clearing explosions to episodic gas poor lava dome extrusions and failures the repeated dome failures produced lithic pyroclastic flows that mixed with snow and glacial ice to generate lahars that were channelled off drift glacier into the drift river valley some of the dome failures occurred without precursory seismic warning and appeared to result solely from gravitational instability material from the disrupted lava domes avalanched down a steep partly ice filled canyon incised on the north flank of the volcano and came to rest on the heavily crevassed surface of the piedmont lobe of drift glacier most dome collapse events resulted in single monolithologic massive to reversely graded medium to coarse grained sandy pyroclastic flow deposits containing abundant dense dome clasts these deposits vary in thickness grain size and texture depending on distance from the vent and local topography deposits are finer and better sorted down flow thinner and finer on hummocks and thicker and coarser where ponded in channels cut through the glacial ice the initial vent clearing explosions emplaced unusual deposits of glacial ice snow and rock in a frozen matrix on the north and south flanks of the volcano similar deposits were described at nevado del ruiz columbia and have probably been emplaced at other snow and ice clad volcanoes but poor preservation makes them difficult to recognize in the geologic record in a like fashion most deposits from the 1989 1990 eruption of redoubt volcano may be difficult to recognize and interpret in the future because they were emplaced in an environment where glacio fluvial processes dominate and quickly obscure the primary depositional record

observations of deep long period dlp seismic events beneath aleutian arc volcanoes 1989 2002 abstract between october 12 1989 and december 31 2002 the alaska volcano observatory avo located 162 deep long period dlp events beneath 11 volcanic centers in the aleutian arc these events generally occur at mid to lower crustal depths 10 45 km and are characterized by emergent phases extended codas and a strong spectral peak between 1 0 and 3 0 hz observed wave velocities and particle motions indicate that the dominant phases are p and s waves dlp epicenters often extend over broad areas 5 20 km surrounding the active volcanoes the average reduced displacement of aleutian dlps is 26 5 cm2 and the largest event has a reduced displacement of 589 cm2 or ml 2 5 aleutian dlp events occur both as solitary events and as sequences of events with several occurring over a period of 1 30 min within the sequences individual dlps are often separated by lower amplitude volcanic tremor with a similar spectral character occasionally volcano tectonic earthquakes that locate at similar depths are contained within the dlp sequences at most aleutian volcanoes dlps appear to loosely surround the main volcanic vent and occur as part of background seismicity a likely explanation is that they reflect a relatively steady state process of magma ascent over broad areas in the lower and middle portions of the crust at mount spurr dlp seismicity was initiated by the 1992 eruptions and then slowly declined until 1997 at shishaldin volcano a short lived increase in dlp seismicity occurred about 10 months prior to the april 19 1999 eruption these observations suggest a link between eruptive activity and magma flux in the mid to lower crust and uppermost mantle

isopycnal averaging at constant height part i the formulation and a case study simple eulerian averaging of velocities density and tracers at constant position is the most natural way of averaging however eulerian averaging gives incorrect watermass distributions and properties as well as spurious diabatic circulations such as the deacon cell instead of averaging at constant height averaging along isopycnals removes such fictitious mixing and diabatic circulations such isopycnal averaging is normally performed at constant latitude that is averaging along isopynals as they heave up and down as a result height information is lost and the sea surface becomes much warmer or lighter than with simple eulerian averaging in fact averaging can be performed along arbitrarily aligned surfaces this study considers a particular case in which isopycnal averaging is performed at constant height thus this new isopycnal averaging follows isopycnals as they meander horizontally at constant z height information is now retained at the cost of losing latitudinal information the advantage of this averaging is that it avoids the problem of giving a surface that is too warm associated with this new isopycnal averaging a vertical transport streamfunction in r z space can be defined in analogy to the conventional meridional overturning streamfunction in y r space here in part i this constant height isopycnal averaging is explained and illustrated in an idealized zonal channel model in part ii the relationship between the two different isopycnal averagings and the eulerian mean eddy flux divergence is explored

earthquake classification location and error analysis in a volcanic environment implications for the magmatic system of the 1989 1990 eruptions at redoubt volcano alaska abstract determination of the precise locations of seismic events associated with the 1989 1990 eruptions of redoubt volcano posed a number of problems including poorly known crustal velocities a sparse station distribution and an abundance of events with emergent phase onsets in addition the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm this algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations the velocity model was calibrated on the basis of a posteruptive seismic survey in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice the model consists of a stack of homogeneous horizontal layers setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice detailed analysis of hypocentral errors shows that the long period lp events constituting the vigorous 23 hour swarm that preceded the initial eruption on december 14 could have originated from a point 1 4 km below the crater floor a similar analysis of lp events in the swarm preceding the major eruption on january 2 shows they also could have originated from a point the location of which is shifted 0 8 km northwest and 0 7 km deeper than the source of the initial swarm we suggest this shift in lp activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of december volcano tectonic vt earthquakes did not occur until after the initial 23 hour long swarm they began slowly just below the lp source and their rate of occurrence increased after the eruption of 01 52 ast on december 15 when they shifted to depths of 6 to 10 km after january 2 the vt activity migrated gradually northward this migration suggests northward propagating withdrawal of magma from a plexus of dikes and or sills located in the 6 to 10 km depth range precise relocations of selected events prior to january 2 clearly resolve a narrow steeply dipping pencil shaped concentration of activity in the depth range of 1 7 km which illuminates the conduit along which magma was transported to the surface a third event type named hybrid which blends the characteristics of both vt and lp events originates just below the lp source and may reflect brittle failure along a zone intersecting a fluid filled crack the distribution of hybrid events is elongated 0 2 0 4 km in an east west direction this distribution may offer constraints on the orientation and size of the fluid filled crack inferred to be the source of the lp events

dome growth and destruction during the 1989 1990 eruption of redoubt volcano abstract much of the six month long 1989 1990 eruption of redoubt volcano consisted of a dome growth and destructive phase in which 14 short lived viscous silicic andesite domes were emplaced and 13 subsequently destroyed the life span of an individual dome ranged from 3 to 21 days and volumes are estimated at 1 10 6 to 30 10 6 m 3 magma supply rates to the vent area averaged about 5 10 5 m 3 day for most of the dome building phase and ranged from a high of 2 2 10 6 m 3 per day initially to a low of 1 8 10 5 m 3 per day at the waning stages of the eruption the total volume of all domes is estimated to be about 90 10 6 m 3 and may represent as much as 60 70 of the volume for the entire eruption the site of 1989 1990 dome emplacement like that in 1966 was on the margin of a north facing amphitheatre like summit crater the domes were confined on the east and west by steep cliffs of pre eruption cone building volcanic rocks and thus were constrained to grow vertically rapid upward growth in a precarious site caused each dome to spread preferentially to the north resulting in eventual gravitational collapse as long as the present conduit remains active at redoubt volcano any dome formed in a new eruption will be confined to a narrow steeply sloping gorge leading to rapid vertical growth and a tendency to collapse gravitationally repetitive cycles of dome formation and failure similar to those seen in 1989 1990 are probably the norm and must be considered in future hazard analyses of redoubt volcano

the seismicity of the 2009 redoubt eruption article redoubt volcano erupted in march 2009 following 6 months of precursory seismic activity the 4 5 month long eruptive sequence was accompanied by phreatic and magmatic explosions periods of steady dome growth lahars seismic swarms extended episodes of volcanic tremor and changes in the background seismicity rate this study presents a seismic chronology of the eruption and places it in context with the variety of other geological and geophysical data that were recorded during the eruptive period we highlight 6 notable seismic swarms 3 of which preceded large explosions the swarms varied from an hour to several days in duration and contained tens to over 7000 earthquakes many of the swarms were dominated by low frequency type earthquakes that contained families of repeating events seismic tremor varied considerably in frequency amplitude and duration during the eruption with distinct characteristics accompanying different types of volcanic activity the explosion signals during march 23 24 were the most energetic and the explosions on march 26 29 contained proportionally more low frequency energy 0 033 0 3 hz two seismic stations were particularly well suited to recording lahars that flowed down the drift river valley data from these stations showed that lahars were generated by the majority of the explosion events as well as during the continuous eruptive activity on march 29 when no large explosions occurred we also examine the seismicity which occurred outside of the explosion and swarm episodes and find several families of repeating vt earthquakes which begin shortly before the april 4 explosion and that continue

isopycnal momentum budget of the antarctic circumpolar current in the fine resolution antarctic model abstract the momentum budget of the antarctic circumpolar current acc is analyzed using data from the fine resolution antarctic model fram using density as a vertical coordinate since density is approximately conserved on streamlines this steady budget is balanced volume heat and salt budgets are also computed within density layers although these remain time dependent the leading order momentum balance is of approximate equality of the form drag on the top and bottom surfaces of each undulating density layer but because density layers outcrop at the surface this does not imply that the surface wind stress is simply transferred downward by form drag without change of amplitude restricting attention to the net form drag on a layer this is found to be balanced by coriolis force and if the layer outcrops the amount of wind stress put into the layer where it outcrops between 40 and 60 of the density layers at any latitude outcrop somewhere at the surface so that wind stress can be moved d

seismic observations of redoubt volcano alaska 1989 2010 and a conceptual model of the redoubt magmatic system abstract seismic activity at redoubt volcano alaska has been closely monitored since 1989 by a network of five to ten seismometers within 22 km of the volcano s summit major eruptions occurred in 1989 1990 and 2009 and were characterized by large volcanic explosions episodes of lava dome growth and failure pyroclastic flows and lahars seismic features of the 1989 1990 eruption were 1 weak precursory tremor and a short 23 hour long intense swarm of repetitive shallow long period lp events centered 1 4 km below the crater floor 2 shallow volcano tectonic vt and hybrid earthquakes that separated early episodes of dome growth 3 13 additional swarms of lp events at shallow depths precursory to many of the 25 explosions that occurred over the more than 128 day duration of eruptive activity and 4 a persistent cluster of vt earthquakes at 6 to 9 km depth in contrast the 2009 eruption was preceded by a pronounced increase in deep lp dlp events at lower crustal depths 25 to 38 km that began in mid december 2008 two months of discontinuous shallow volcanic tremor that started on january 23 2009 a strong phreatic explosion on march 15 and a 58 hour long swarm of repetitive shallow lp events the 2009 eruption consisted of at least 23 major explosions between march 23 and april 5 again accompanied by shallow vt earthquakes several episodes of shallow repetitive lp events and dome growth continuing until mid july increased vt earthquakes at 4 to 9 km depth began slowly in early april possibly defining a mid crustal magma source zone magmatic processes associated with the 2009 eruption seismically activated the same portions of the redoubt magmatic system as the 1989 1990 eruption although the time scales and intensity vary considerably among the two eruptions the occurrence of precursory dlp events suggests that the 2009 eruption may have involved the rise of magma from lower crustal depths based on the evolution of seismicity during the 1989 1990 and 2009 eruptions the redoubt magmatic system is envisioned to consist of a shallow system of cracks extending 1 to 2 km below the crater floor a magma storage or source region at roughly 3 to 9 km depth and a diffuse magma source region at 25 to 38 km depth close tracking of seismic activity allowed the alaska volcano observatory to successfully issue warnings prior to many of the hazardous explosive events that occurred in 2009