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

quiescent explosive transitions during dome forming volcanic eruptions using seismicity to probe the volcanic processes leading to the 29 july 2008 vulcanian explosion of soufriere hills volcano montserrat

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

volcano ice interactions precursory to the 2009 eruption of redoubt volcano alaska abstract in late summer of 2008 after nearly 20 years of quiescence redoubt volcano began to show signs of abnormal heat flow in its summit crater in the months that followed the excess heat triggered melting and ablation of redoubt s glaciers beginning at the summit and propagating to lower elevations as the unrest accelerated a variety of morphological changes were observed including the creation of ice cauldrons areas of wide spread subsidence punctures in the ice carved out by steam and deposition from debris flows in this paper we use visual observations satellite data and a high resolution digital elevation model of the volcanic edifice to calculate ice loss at redoubt as a function of time our aim is to establish from this time series a proxy for heat flow that can be compared to other data sets collected along the same time interval our study area consists of the drift glacier which flows from the summit crater down the volcano s north slope and makes up about one quarter of redoubt s total ice volume of 4 km 3 the upper part of the drift glacier covers the area of recent volcanism making this part of ice mass most susceptible to the effect of volcanic heating moreover melt water and other flows are channeled down the drift glacier drainage by topography leaving the remainder of redoubt s ice mantle relatively unaffected the rate of ice loss averaged around 0 1 m 3 s over the last four months of 2008 accelerated to over twenty times this value by february 2009 and peaked at greater than 22 m 3 s just prior to the first major explosion on march 22 2009 we estimate a cumulative ice loss over this period of about 35 million cubic meters m m 3

tremor and its duration amplitude distribution at popocatepetl volcano mexico the duration amplitude distribution was calculated for the tremor observed at popocatepetl volcano during episodes of activity in 2000 2012 2013 and 2014 an exponential function was used to obtain a good fit for the duration amplitude distribution and the source of volcanic tremor is probably generated by the transportation of magmatic fluids and its coupling with the host rock within the volcanic conduit in particular harmonic tremor has shown large amplitudes durations and mean values of amplitude more than spasmodic or pulsalting tremor this is due to different generation mechanisms in the case of harmonic tremor it is produced during magma ascent and lava dome growth whilst spasmodic and pulsalting tremor are associated with fragmentation of the lava dome and gas emissions this paper presents the duration amplitude distribution as a method to estimate the intensity of the tremor at popocatepetl a volcano with the major risk in all mexico

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

an overview of lava dome evolution dome collapse and cyclicity at soufriere hills volcano montserrat 2005 2007 1 the third episode of lava dome growth at soufriere hills volcano montserrat was characterised by higher average magma discharge rates than either previous dome growth episode at this volcano and yet fewer collapses during sustained dome growth at moderate high average rates 6 m3 s we identified 2 6 week discharge pulses that each supplied c 20 mm3 magma from depth our observations are consistent with some existing models but we explain discrepancies by a combination of higher volatile contents and higher ascent rates cycles of c 11 16 days were evident in rockfall lp rockfall and shallow lp earthquake counts related to dome growth and degassing we speculate that degassing at the conduit margins together with stick slip conduit flow may drive these cycles only one major collapse 10 mm3 occurred during the third episode on may 20 2006 as a new magma pulse entered the dome and coincided with heavy rainfall

saturated and subcooled hydrothermal boiling in groundwater flow channels as a source of harmonic tremor the potential of hydrothermal boiling in groundwater flow channels for generating harmonic tremor a relatively monochromatic ground vibration associated with volcanic activity is examined we use simple organ pipe theory of normal mode fluid vibration and fundamental energy considerations to develop a first order analytical model of a hydrothermal boiling source of harmonic tremor we use this model to estimate order of magnitude groundwater flow channel lengths and boiling heat transfer rates required to produce harmonic tremor with dominant frequencies in the range 0 5 5 hz and surface wave reduced displacements of up to 100 cm2 depending on groundwater sound speed flow channel lengths of the order of 1 1000 m are required to produce fluid vibration eigenfrequencies in the range 0 5 5 hz the boiling heat transfer rate required to produce tremor with a given surface wave reduced displacement depends on the tremor frequency and on whether saturated boiling or subcooled boiling is the cause of the tremor saturated boiling produces groundwater vibration via steam bubble growth whereas subcooled boiling produces groundwater vibration via steam bubble collapse we find that subcooled hydrothermal boiling is from 102 to 104 times more efficient than saturated boiling in converting boiling thermal power to seismic power for example the boiling heat transfer rates required to produce 1 hz tremor with reduced displacements of up to 100 cm2 via subcooled boiling are generally less than a few thousand megawatts for saturated boiling the required boiling heat transfer rates are several orders of magnitude larger than this the highest values of heat flow reported in the literature for volcanic crater lakes and terrestrial and ocean floor geothermal areas are of the order of 1000 mw taking this value as a first order estimate of an upper limit on possible boiling heat transfer rates in volcanic hydrothermal systems our results suggest that saturated hydrothermal boiling is capable of generating only low amplitude harmonic tremor with surface wave reduced displacements no higher than a few square centimeters however subcooled hydrothermal boiling could potentially generate high amplitude harmonic tremor with reduced displacements as large as several hundred square centimeters as a specific application of our model we evaluate the potential of hydrothermal boiling for generating harmonic tremor at recently active mount st helens and nevado del ruiz volcanoes we conclude that subcooled boiling likely could have produced the tremor episodes considered at both volcanoes saturated boiling also could explain the nevado del ruiz tremor but probably not the more powerful mount st helens tremor

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

models of tremor and low frequency earthquake swarms on montserrat recent observations from soufriere hills volcano in montserrat reveal a wide variety of low frequency seismic signals we discuss similarities and differences between hybrid earthquakes and long period events and their role in explosions and rockfall events these events occur usually in swarms and occasionally merge into tremor an observation that can shed further light on the generation and composition of harmonic tremor we use a 2d finite difference method to model major features of low frequency seismic signatures and compare them with the observations a depth dependent velocity model for a fluid filled conduit is introduced which accounts for the varying gas content in the magma and the impact on the seismic signals is discussed we carefully analyse episodes of tremor that show shifting spectral lines and model those in terms of changes in the gas content of the magma as well as in terms of a time dependent triggering mechanism of low frequency resonances in this way we explain the simultaneous occurrence of low frequency events and tremor with a spectral content comprising integer harmonics

observations of volcanic lightning during the 2009 eruption of redoubt volcano abstract observations of volcanic lightning during the eruption of redoubt volcano in march and april 2009 were made with the lightning mapping array during the eruption twenty three distinct episodes of volcanic lightning were observed electrical activity occurred as either a volcanic lightning storm with up to thousands of lightning discharges or as a weak electrical event with only a handful of lightning discharges during the volcanic lightning storms we observed two phases of electrical activity the explosive phase and the plume phase the explosive phase consisted of very small discharges on the order of 10 100 m occurring directly above the vent while an explosive eruption was ongoing whereas the plume phase was comprised of discharges occurring throughout the plume subsequent to the explosive eruption the area of discharges during the explosive phase ranged from less than 1 km2 to 50 km2 or more the electrical activity at the beginning of the plume phase was dominated by small discharges over time the horizontal extent of the flashes increased with the largest flashes occurring at the end of the plume phase the distribution of the horizontal size of the discharges over the lifetime of the storm indicate that the charge structure of the plume evolved from a complex and clumpy structure to a more simple horizontally stratified structure plume height was shown to be a key factor in the quantity of lightning in a storm the volcanic lightning storms occurred in plumes with column heights greater than 10 km the tall plumes may contribute to the efficiency of charge generation through ice collisions by providing strong updrafts from the large thermal energy input from the eruption

local seismic and infrasound observations of the 2009 explosive eruptions of redoubt volcano alaska article i nfo local seismic and infrasound data are used to characterize the march april 2009 eruptions of redoubt volca no alaska data are from a network of ten seismic stations ranging from 2 6 to 21 km from the vent and a single infrasound sensor 12 2 km from the vent measurements were made for more than 30 explosive erup tions including the 19 numbered events that were identified during the eruption response more than 30 smaller explosions were also identified measured parameters include onset time duration reduced dis placement dr pressure seismic energy and acoustic energy results were compared with complementary gas and lightning data based on ratios of pressure to dr and acoustic to seismic energy we find that the initial group of explosive eruptions on 23 24 march was relatively stronger seismically and included the four highest dr values we infer that these represent vent enlargement or stronger coupling between the magma and wall rocks one event at 12 31 ut on 23 march had an extremely high pressure of 250 pa for the initial pulse and was likely weakly seismically coupled a second group of explosive eruptions on 27 29 march was relatively stronger acoustically deposits were finer grained and of different lithology with less scoria and more dense clasts these two groups may represent different modes of gas release cumulative acoustic energy as a function of time correlates well with comparable lightning and so2 data suggesting that all three provide insight regarding different factors of gas release for the eruption as a whole the number of events identified depends on criteria measured and depends on the goals of the investigations overall the eruptions were substantially stronger than recent eruptions in alaska with some durations exceeding 1 h and pressures an order of magnitude higher

dynamics of seismogenic volcanic extrusion at mount st helens in 2004 05 the 2004 05 eruption of mount st helens exhibited sustained near equilibrium behaviour characterized by relatively steady extrusion of a solid dacite plug and nearly periodic shallow earthquakes here we present a diverse data set to support our hypothesis that these earthquakes resulted from stick slip motion along the margins of the plug as it was forced incrementally upwards by ascending solidifying gas poor magma we formalize this hypothesis with a dynamical model that reveals a strong analogy between behaviour of the magma plug system and that of a variably damped oscillator modelled stick slip oscillations have properties that help constrain the balance of forces governing the earthquakes and eruption and they imply that magma pressure never deviated much from the steady equilibrium pressure we infer that the volcano was probably poised in a near eruptive equilibrium state long before the onset of the 2004 05 eruption

a phase coherence approach to identifying co located earthquakes and tremor we present and use a phase coherence approach to identify seismic signals that have similar path effects but different source time functions co located earthquakes and tremor the method used is a phase coherence based implementation of empirical matched field processing modified to suit tremor analysis it works by comparing the frequency domain phases of waveforms generated by two sources recorded at multiple stations we first cross correlate the records of the two sources at a single station if the sources are co located this cross correlation eliminates the phases of the green s function it leaves the relative phases of the source time functions which should be the same across all stations so long as the spatial extent of the sources are small compared with the seismic wavelength we therefore search for cross correlation phases that are consistent across stations as an indication of co located sources we also introduce a method to obtain relative locations between the two sources based on back projection of interstation phase coherence we apply this technique to analyse two tremor like signals that are thought to be composed of a number of earthquakes first we analyse a 20 s long seismic precursor to a m 3 9 earthquake in central alaska the analysis locates the precursor to within 2 km of the mainshock and it identifies several bursts of energy potentially foreshocks or groups of foreshocks within the precursor second we examine several minutes of volcanic tremor prior to an eruption at redoubt volcano we confirm that the tremor source is located close to repeating earthquakes identified earlier in the tremor sequence the amplitude of the tremor diminishes about 30 s before the eruption but the phase coherence results suggest that the tremor may persist at some level through this final interval

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

feasibility study of spectral pattern recognition reveals distinct classes of volcanic tremor abstract systematic investigations of the similarities and differences among volcanic tremor at a range of volcano types may hold crucial information about the plausibility of inferred source mechanisms which in turn may be important for eruption forecasting however such studies are rare in part because of an intrinsic difficulty with identifying tremor signals within very long time series of volcano seismic data accordingly we develop an efficient tremor detection algorithm and identify over 12 000h of volcanic tremor on 24 stations at k lauea okmok pavlof and redoubt volcanoes we estimate spectral content over 5 minute tremor windows and apply a novel combination of principal component analysis pca and hierarchical clustering to identify patterns in the tremor spectra analyzing several stations from a given volcano together reveals different styles of tremor within individual volcanic settings in addition to identifying tremor properties common to all stations in a given network we find localized tremor signals including those related to processes such as lahars or dike intrusions that are only observed on some of the stations within a network subsequent application of our analysis to a combination of stations from the different volcanoes reveals that at least three main tremor classes can be detected across all settings whereas a regime with a ridge of high power distributed over 1 2hz and a gradual decay of spectral power towards higher frequencies is observed dominantly at three volcanoes k lauea okmok redoubt with magma reservoirs centered at less than 5km below sea level b s l a spectrum with a steeper slope and a narrower peak at 1 2hz is observed only in association with open vents k lauea and pavlof a third regime with a peak at approximately 3hz is confined to two stratovolcanoes pavlof and redoubt these observations suggest generic relationships between the spectral character of the observed signals and volcano characteristics such as magma viscosity storage depths and the physical properties of volcanic edifices similarities among the spectral patterns detected at stations 4km and 8 10km distance from the centers of volcanic activity respectively indicate that path effects do not strongly influence spectral shapes at distances of a few kilometers from the inferred source of the signals our preliminary work shows that a global comparison of tremor is feasible our results suggest that further work on data from a larger sample and diverse range of volcano types will reveal additional classes of tremor signals and plausibly identify fingerprints of source processes that are specific to volcano type but independent of volcano location

using repeating volcano tectonic earthquakes to track post eruptive activity in the conduit system at redoubt volcano alaska in the year following the end of the 2009 eruption of redoubt volcano alaska four signifi cant swarms of low frequency lowmagnitude m l 0 1 earthquakes occurred at shallow depths beneath the summit because swarms of low frequency lf earthquakes preceded eruptions in 1989 and 2009 the posteruption swarms caused considerable concern and prompted the alaska volcano observatory to raise the monitoring levels on three occasions none of these swarms led to eruptions however and most observers including us initially concluded that the swarms had been caused by minor stress adjustments in the new lava dome or in the surrounding summit glaciers new observations reveal that the shallow lf swarms were accompanied by 2 families of repeating earthquakes at depths between 3 km and 6 km below sea level where the magma storage region is thought to be these mid crustal volcano tectonic vt type earthquakes were identical to earthquakes recorded during the 2009 redoubt eruption more than 6 months earlier focal mechanisms demonstrate that these earthquakes have thrust mechanisms inconsistent with the strike slip nature of regional faulting based on these observations we conclude that they are generated through processes occurring within the magma storage region the concurrence of the repeating vt earthquakes with the shallow lf swarms indicates that the shallow lf earthquakes were also magmatically driven our results emphasize that even brief episodes of low amplitude earthquake activity such as the lf swarms observed at redoubt following the 2009 eruption can be indicative of magmatic activity perhaps more signifi cant however is the demonstration that the conduit system at redoubt remained active intact and capable of transporting heat and fl uids to the surface months after the eruption was considered over

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

recent eruptions at bezymianny volcano a seismological comparison abstract for the past few decades bezymianny volcano has erupted once to twice per year here i examine eight eruptive events between 2006 and 2010 this is the first time period for which proximal or broadband seismic data have been recorded at bezymianny several recurring patterns are demonstrated in advance of eruptions eruptions are generally preceded by 12 36 h of tremor energy elevated by 2 to 3 orders of magnitude locatable earthquake activity is quite erratic in the days before eruptions for eruptions of juvenile magma however the cumulative moment magnitude increases with the repose time since the previous eruption though tenuous this relationship is statistically significant and could improve forecasts of bezymianny eruptions the most energetic eruptions demonstrate increasing multiplet activity in the run up followed by a rapid cessation at the time of eruption when present this behavior marks increasing pressure in the conduit system as degassing eclipses the capacity for venting very long period seismicity 20 s periods accompanies some eruptions these tend to be the same short lived high energy eruptions that exhibit multiplet precursors four eruptions are examined in detail to illustrate the variety in eruption mechanisms lava dome collapses sustained eruptions singular paroxysmal explosions and post explosion lava flows occur in different combinations demonstrating that more than one eruption trigger is regulating bezymianny compared to bezymianny s fifty year modern history recent eruptions have been shorter lived and separated by longer repose times some evidence suggests that these eruptions may be increasingly explosive a speculation that carries significant hazard implications if true however this threat is tempered by solid evidence that the most explosive eruptions are preceded by the clearest precursors suggesting an ability to improve the already excellent eruption forecasts available for bezymianny

the rise and fall of periodic drumbeat seismicity at tungurahua volcano ecuador abstract highly periodic drumbeat long period lp earthquakes have been described from several andesitic and dacitic volcanoes commonly accompanying incremental ascent and effusion of viscous magma however the processes controlling the occurrence and characteristics of drumbeat and lp earthquakes more generally remain contested here we use new quantitative tools to describe the emergence evolution and degradation of drumbeat lp seismicity at the andesitic tungurahua volcano ecuador in april 2015 the signals were recorded during an episode of minor explosive activity and ash emission without lava effusion and are the first to be reported at tungurahua during the ongoing 17 yrs of eruption following four days of high levels of continuous and pulsed tremor highly periodic lp earthquakes first appear on 10 april over the next four days inter event times and event amplitudes evolve through a series of step wise transitions between stable behaviors each involving a decrease in the degree of periodicity families of similar waveforms persist before during and after drumbeat activity but the activity levels of different families change coincidentally with transitions in event rate amplitude and periodicity a complex micro seismicity initiation sequence shows pulse like and stepwise changes in inter event times and amplitudes in the hours preceding the onset of drumbeat activity that indicate a partial de coupling between event size and rate the observations increase the phenomenology of drumbeat lp earthquakes and suggest that at tungurahua they result from gas flux and rapid depressurization controlled by shear failure of the margins of the ascending magma column

observations of volcanic tremor at mount st helens volcano digital recordings of ground motion during tremor episodes accompanying eruptions at mount st helens volcano in the state of washington on august 7 and october 16 18 1980 are studied the spectra of the vertical component waveforms contain at least two dominant peaks at 1 0 and 1 3 hz for all events recorded during both eruptions that were studied spectra of horizontal ground motion show peaks at 0 9 and 1 1 hz the relative amplitude of the two peaks changes between tremor episodes and during single tremor episodes and shows no consistent relation to amplitude of ground motion spectra of long period earthquakes are very similar to those of tremor events suggesting that tremor is composed of many long period earthquakes that occur over a period of time the unique waveform of tremor events observed at mount st helens must be due to a source effect since the relative amplitude of the two dominant peaks changes during tremor episodes the path effect on tremor waveforms is small since there are no peaks in the spectra of waveforms recorded during tectonic earthquakes occurring in the vicinity of mount st helens the consistency of the location of the spectral peaks for the wide range of tremor amplitudes means that there must be a physical length at the source that is constant independent of the amplitude of motion at the source variations in amplitude of motion generated during tremor events must be due to variations in the force driving the tremor amplitudes of ground motion varies between 0 11 and 4 7 m seismic moment rates during the two eruptions are calculated using the model of aki et al 1977 and found to vary between 6 1018 and 1 1020 dynes cm s 1 which are larger than values found by aki et al 1977 who studied amplitudes of shallow tremor events recorded during the october 1963 eruption of kilauea volcano in hawaii study of tremor amplitudes recorded at corvallis oregon leads to the conclusion that tremor accompanying the cataclysmic may 18 1980 eruption was at least one order of magnitude larger in amplitude than tremor during august and october

high resolution satellite and airborne thermal infrared imaging of precursory unrest and 2009 eruption at redoubt volcano alaska abstract a combination of satellite and airborne high resolution visible and thermal infrared tir image data detected and measured changes at redoubt volcano during the 2008 2009 unrest and eruption the tir sensors detected persistent elevated temperatures at summit ice melt holes as seismicity and gas emissions increased in late 2008 to march 2009 a phreatic explosion on 15 march was followed by more than 19 magmatic explosive events from 23 march to 4 april that produced high altitude ash clouds and large lahars two or three lava domes extruded and were destroyed between 23 march and 4 april after 4 april the eruption extruded a large lava dome that continued to grow until at least early july 2009

remagnetizations as a tool to analyze the tectonic history of inverted sedimentary basins a case study from the basque cantabrian basin north spain 1 in this work we use syntectonic remagnetization data to determine the synrift geometry of inverted basins this methodology analyzes remagnetization directions in order to obtain the tilting of beds at the moment of the acquisition of the overprint filtering the subsequent compressional deformation we collected samples from jurassic and lower cretaceous limestones and red beds cabuerniga and pas groups in the cabuerniga basin one of the most important mesozoic basins developed near the iberia europe mesozoic plate boundary in northern spain that later inverted during the uplift of the pyrenees these deposits represent the synrift sequence linked to a widespread extensional stage in the iberian basins during the mesozoic all sampled rocks show a normal polarity remagnetization fold and conglomerate tests indicate that remagnetization postdates the main extensional stage of basin formation late jurassic barremian and was acquired before the subsequent compressional deformation the analysis of these overprinted directions allows the basin geometry of the studied area to be restored at the moment of acquisition of the remagnetization this approach represents a powerful tool to study basinal evolution and uplift of sedimentary basins to be tested in other inverted basins with syn extensional related secondary overprints

fault movements and tectonics of eastern iran boundaries of the lut plate summary from 1977 march 21 to 1981 july 28 about 15 earthquakes with ms 6 0 and many earthquakes with ms 4 5 have occurred in iran the upsurge of seismic activity started following the khorqu earthquake of 1977 march 21 ms 7 0 south east of the fars folded series of zagros this shock had a thrust focal mechanism solution indicating the general northward movement of the arabian plate with respect to the iranian landmass it was followed by six major damaging earthquakes in eastern iran the earthquakes are associated with extensive faulting which surrounds the lut plate 1 the zarand earthquake of 1977 december ms 5 8 was associated with about 20 km of fault trace severe mass wasting and about 20 cm of right lateral movement 2 the tabas earthquake of 1978 september ms 7 7 with about 75 km of multiple thrust faulting and a maximum vertical displacement of 35 cm 3 the kurizan earthquake of 1979 november ms 6 0 with more than 17 km of strike slip fault trace and a maximum right lateral displacement of 90 cm and a vertical displacement of 60 cm 4 the koli earthquake of 1979 november ms 7 1 with at least 65 km of fault trace and a maximum left lateral displacement of 255 cm and a vertical displacement of 380 cm 5 golbaf earthquakes of 1981 june ms 6 0 with at least 16 km of observed fault trace and a maximum vertical displacement of 15 cm 6 the chaharfarsang sirch earthquake of 1981 july ms 7 1 with about 70 km of discontinuous fault trace and 20 cm of right lateral motion and 15 cm of vertical motion portable networks of seismographic stations were deployed following each event results of aftershock studies are compared with field observations the observed faults and aftershock zones appear to mark the broad deformational boundaries of the lut plate

seismic and acoustic signatures of surficial mass movements at volcanoes abstract surficial mass movements such as debris avalanches rock falls lahars pyroclastic flows and outburst floods are a dominant hazard at many volcanoes worldwide understanding these processes cataloging their spatio temporal occurrence and detecting tracking and characterizing these events would advance the science of volcano monitoring and help mitigate hazards seismic and acoustic methods show promise for achieving these objectives many surficial mass movements generate observable seismic and acoustic signals and many volcanoes are already monitored significant progress has been made toward understanding modeling and extracting quantitative information from seismic and infrasonic signals generated by surficial mass movements however much work remains in this paper we review the state of the art of the topic covering a range of scales and event types from individual rock falls to sector collapses we consider a full variety of volcanic settings from submarine to subaerial shield volcano to stratovolcano finally we discuss future directions toward operational seismo acoustic monitoring of surficial mass movements at volcanoes

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

voluminous ice rich and water rich lahars generated during the 2009 eruption of redoubt volcano alaska abstract redoubt volcano in south central alaska began erupting on march 15 2009 and by april 4 2009 had produced at least 20 explosive events that generated multiple plumes of ash and numerous lahars the 3108 m high snow and ice clad stratovolcano has an ice filled summit crater that is breached to the north the volcano supports about 4 km 3 of ice and snow and about 1 km 3 of this makes up the drift glacier on the north side of the volcano explosive eruptions between march 23 and april 4 which included the destruction of at least two lava domes triggered significant lahars in the drift river valley on march 23 and april 4 and several smaller lahars between march 24 and march 31 mud line high water marks character of deposits areas of inundation and estimates of flow velocity revealed that the lahars on march 23 and april 4 were the largest of the eruption in the 2 km wide upper drift river valley average flow depths were at least 2 5 m average peak flow velocities were likely between 10 and 15 ms 1 and peak discharges were on the order of 10 4 10 5 m 3 s 1 the area inundated by lahars on march 23 was at least 100 km 2 and on april 4 about 125 km 2 two substantial lahars emplaced on march 23 and one on april 4 had volumes on the order of 10 7 10 8 m 3 and were similar in size to the largest lahar of the 1989 90 eruption the two principal march 23 lahars were primarily flowing slurries of snow and ice derived from drift glacier and the drift river valley where seasonal snow and tabular blocks of river ice were entrained and incorporated into the lahars despite morphologic evidence of two lahars only a single deposit up to 5 m thick was found in most places and it contained about 80 95 of poorly sorted massive to imbricate assemblages of snow and ice clasts the deposit was frozen soon after it was emplaced and later eroded and buried by the april 4 lahar the lahar of april 4 in contrast was primarily a hyperconcentrated flow as interpreted from 1 to 6 m thick deposits of massive to horizontally stratified sand to fine gravel rock material in the april 4 lahar deposit is predominantly juvenile andesite whereas rock material in the march 23 deposit is rare and not obviously juvenile we infer that the lahars generated on march 23 were initiated by a rapid succession of vent clearing explosions that blasted through about 50 100 m of crater filling glacier ice and snow producing a voluminous release of meltwater from drift glacier the resulting surge of water entrained snow fragments of glacier and river ice and river water along its flow path small volume pyroclastic flows possibly associated with destruction of a small dome or minor eruption column collapses may have contributed additional meltwater to the march 23 lahars meltwater generated by subglacial hydrothermal activity and stored beneath drift glacier may have been ejected or released rapidly as well the april 4 lahar was initiated when hot dome collapse pyroclastic flows entrained and swiftly melted snow and ice on drift glacier the resulting meltwater incorporated pyroclastic debris and rock material from drift glacier to form the largest lahar of the 2009 eruption the peak discharge of the april 4 lahar was in the range of 60 000 160 000 m 3 s 1 for comparison the largest lahar of the 1989 90 eruption had a peak discharge of about 80 000 m 3 s 1 lahars generated by the 2009 eruption led to significant channel aggradation in the lower drift river valley and caused extensive inundation at an oil storage and transfer facility located there the april 4 2009 lahar was 6 30 times larger than the largest meteorological floods known or estimated in the drift river drainage

seismological evidence for long term and rapidly accelerating magma pressurization preceding the 2009 eruption of redoubt volcano alaska abstract successful eruption forecasts are heavily dependent on the recognition of well established patterns in volcano monitoring data therefore it is critical to develop in retrospect an understanding of the physical basis for cases of abnormal precursory behavior as the basis for a a complete understanding of the range of precursory signals that may be expected at a particular volcano and b development of new monitoring approaches to detect more subtle signals of the underlying processes responsible for common patterns of seismic unrest here using a hybrid analysis of shear wave splitting sws and double couple fault plane solutions fps we document the timing and nature of local stress field changes in the months to days preceding the 2009 eruption of redoubt volcano alaska which was characterized by an abnormally long period of precursory low frequency seismicity reflected in multiple escalations of alert levels prior to the eruption we find that an approximately 90 change in the polarization of fast s wavelets accompanied the earliest signs of seismic unrest in 2008 and continued through the eruption before diminishing in 2009 a similar change in the orientation of vt fps occurred 18 48 h prior to the eruption onset on march 23 2009 but almost two months after a strong increase in the rate of shallow vt earthquakes combined our sws and fps results show the earliest and latest known changes in seismic monitoring data respectively and are suggestive of a protracted period of slow magma ascent followed by a short period of rapidly increasing magma pressurization beneath the volcano these results demonstrate the power of a combined stress field analysis for clarifying the processes driving ambiguous seismic unrest at active volcanoes

doppler weather radar observations of the 2009 eruption of redoubt volcano alaska abstract the u s geological survey usgs deployed a transportable doppler c band radar during the precursory stage of the 2009 eruption of redoubt volcano alaska that provided valuable information during subsequent explosive events we describe the capabilities of this new monitoring tool and present data captured during the redoubt eruption the minimax 250 c mm 250c radar detected seventeen of the nineteen largest explosive events between march 23 and april 4 2009 sixteen of these events reached the stratosphere above 10 km within 2 5 min of explosion onset high column and proximal cloud reflectivity values 50 to 60 dbz were observed from many of these events and were likely due to the formation of mm sized accretionary tephra ice pellets reflectivity data suggest that these pellets formed within the first few minutes of explosion onset rapid sedimentation of the mm sized pellets was observed as a decrease in maximum detection cloud height the volcanic cloud from the april 4 explosive event showed lower reflectivity values due to finer particle sizes related to dome collapse and related pyroclastic flows and lack of significant pellet formation eruption durations determined by the radar were within a factor of two compared to seismic and pressure sensor derived estimates and were not well correlated ash dispersion observed by the radar was primarily in the upper troposphere below 10 km but satellite observations indicate the presence of volcanogenic clouds in the stratosphere this study suggests that radar is a valuable complement to traditional seismic and satellite monitoring of explosive eruptions

ground vibrations produced by rock motions and debris flows 1 in this study we compare ground vibrations generated by various rocks and debris flows at the same channel to explore the origin of ground vibrations caused by debris flows in field experiments we identified the ground vibrations caused by motions of individual rocks ground vibrations were detected by geophones and analyzed in the time frequency domains we found that ground vibrations caused by individual rocks were 10 150 hz and that larger stones generate ground vibrations with lower peak frequencies a sphere packing model of granular rocks was used to estimate the propagation speed of ground vibrations this was found to be underestimated when compared with our experimental data the signal decay rate was obtained under the assumption that ground vibrations propagate as exponentially attenuating cylindrical waves ground vibrations produced by a debris flow at ai yu zi creek nan tou taiwan on 2 july 2004 revealed that the debris flow forefront produced vibrations lower than 50 hz and ranged between 50 and 100 hz after the front had passed when the main front was closest to the sensor the frequency spectrum covered a wide range from 10 to 250 hz the mean velocity of the debris flow front was 13 3 m s frequencies of ground vibrations caused by individual rocks are within the frequency range of ground vibrations captured during the debris flow confirming that one of the main sources of ground vibration caused by debris flows is the interaction of rocks or boulders with the channel bed

seismic characterization of the fall 2007 eruptive sequence at bezymianny volcano russia we examine an eruptive sequence in late 2007 at bezymianny volcano to characterize the magmatic plumbing system and eruption related seismicity earthquake locations reveal seismicity below and offset to the north of the volcano along a tectonic fault based on historical seismicity the magma chamber is postulated to have a top at about 6 km depth minor dome explosions large sub plinian eruptions and dome collapses are analyzed using an automated event classification scheme low frequency tremor interpreted as gas escape and low frequency earthquakes are a dominant proportion of the energy released we also examine multiplet earthquakes whose behavior during the study period changed significantly and systematically before the largest eruption demonstrating the potential of tracking multiplets to assess changing conditions with the conduit

evaluation of redoubt volcano s sulfur dioxide emissions by the ozone monitoring instrument abstract the 2009 eruption of redoubt volcano alaska provided a rare opportunity to compare satellite measurements of sulfur dioxide so2 by the ozone monitoring instrument omi with airborne so2 measurements by the alaska volcano observatory avo herein we 1 compare omi and airborne so2 column density values for redoubt s tropospheric plume 2 calculate daily so2 masses from mount redoubt for the first three months of the eruption 3 develop simple methods to convert daily measured so2 masses into emission rates to allow satellite data to be directly integrated with the airborne so2 emissions dataset 4 calculate cumulative so2 emissions from the eruption and 5 evaluate omi as a monitoring tool for high latitude degassing volcanoes a linear correlation r2 0 75 is observed between omi and airborne so2 column densities omi daily so2 masses for the sample period ranged from 60 1 kt on 24 march to below detection limit with an average daily so2 mass of 6 7 kt the highest so2 emissions were observed during the initial part of the explosive phase and the emissions exhibited an overall decreasing trend with time omi so2 emission rates were derived using three methods and compared to airborne measurements this comparison yields a linear correlation r2 0 82 with omi derived emission rates consistently lower than airborne measurements the comparison results suggest that omi s detection limit for high latitude springtime conditions varies from 2000 to 4000 t d cumulative so2 masses calculated from daily omi data for the sample period are estimated to range from 542 to 615 kt with approximately half of this so2 produced during the explosive phase of the eruption these cumulative masses are similar in magnitude to those estimated for the 1989 90 redoubt eruption strong correlations between daily omi so2 mass and both tephra mass and acoustic energy during the explosive phase of the eruption suggest that omi data may be used to infer relative eruption size and explosivity further when used in conjunction with complementary datasets omi daily so2 masses may be used to help distinguish explosive from effusive activity and identify changes in lava extrusion rates the results of this study suggest that omi is a useful volcano monitoring tool to complement airborne measurements capture explosive so2 emissions and provide high temporal resolution so2 emissions data that can be used with interdisciplinary datasets to illuminate volcanic processes

rockfalls at augustine volcano alaska the influence of eruption precursors and seasonal factors on occurrence patterns 1997 2009 abstract rockfalls have been recorded in seismic data at augustine volcano from 1997 to the present typical events last about 30 s and have frequencies 4 hz on stations within 5 km of the summit many rockfalls are well recorded on summit seismic stations suggesting that they originate from the steep summit dome typical background years such as 2003 or 2004 had several dozen events in the summer and fall june to november that were strong enough to trigger an automatic event detection system for example 17 rockfalls were recorded in 2003 mostly in late summer when air temperatures were warm and rainfall rates were highest and 28 events were recorded in 2004 also in late summer in 2005 about eight months before the onset of the eruption of augustine in january 2006 there was a significant increase in the number of rockfalls detected this increase of surface rockfall activity occurred at nearly the same time as precursory earthquake activity increased beneath augustine overall there were more than 340 rockfalls in 2005 consisting of both short less than 30 s and long greater than 30 s duration events the high rate of rockfalls in 2005 constitutes a new class of precursory signal that needs to be incorporated into long term monitoring strategies at augustine and elsewhere during the eruption numerous rockfalls continued to occur and block and ash flows dominated the seismic records when the volcano began a phase of dome growth and collapse the high rates of rockfalls continued after the eruption ended due the new unstable lava dome and adjacent tephra at the summit as of 2009 the rockfall rates are still high but are declining steadily

injection transport and deposition of tephra during event 5 at redoubt volcano 23 march 2009 abstract among the events of the 2009 eruption at redoubt volcano alaska event 5 was the best documented by radar satellite imagery and deposit mapping we use the new eulerian tephra transport model ash3d to simulate transport and deposition of event 5 tephra at distances up to 350 km the eruption which started at about 1230 utc on 23 march 2009 sent a plume from the vent elevation estimated at 2 3 0 1 km above sea level or a s l to about 16 2 km above sea level in 5 min the plume was a few kilometers higher than would be expected for the estimated average mass eruption rate and atmospheric conditions possibly due to release of most of the eruptive mass in the first half of the 20 minute event the eruption injected tephra into a wind field of high shear with weak easterly winds below 3 km elevation strong southerly winds at 6 10 km and weak westerlies above 16 km model simulations in this wind field predicted development of a northward migrating inverted v shaped cloud with a southwest trending arm at a few kilometers elevation which was not visible in ir satellite images due to cloud cover and a southeast trending arm at 10 km elevation that was clearly visible simulations also predicted a deposit distribution that strongly depended on plume height a plume height below 15 km predicted ash deposits that were located west of those mapped whereas good agreement was reached with a modeled plume height of 15 18 km field sampling of the deposit found it to contain abundant tephra aggregates which accelerated the removal of tephra from the atmosphere we were able to reasonably approximate the effect of aggregation on the deposit mass distribution by two methods 1 adjusting the grain size distribution taking the erupted mass 2 isomass lines that was within a few tens of percent of mapped area however they under predicted deposit mass at very proximal 250 km locations modeled grain size distributions at sample locations are also generally coarser than observed the mismatch may result from a combination of limitations in field sampling approximations inherent in the model errors in the numerical wind field and aggregation of particles larger than 0 063 mm

seismic and hydroacoustic observations of the 2016 17 bogoslof eruption in mid december 2016 bogoslof volcano alaska began an 8 5 month long eruption that produced at least 70 explosions and three lava domes bogoslof is an emergent submarine volcano with only the very top forming a small island so the eruptive activity mostly occurred from a vent submerged beneath a bay or lagoon the bogoslof eruption was recorded on regional seismic and infrasound arrays as well as by a hydrophone that was deployed locally during the second half of the eruption since few emergent volcanic eruptions have seismo acoustic recordings these observations taken in context with satellite and other observations provide an opportunity to greatly improve our understanding of the seismo acoustic signals produced by these eruptions the instruments detected a range of activity including earthquakes tremor and mass flow events earthquakes occurred before during after and unassociated with explosions and also often occurred in swarms the 47 seismically detected swarms and 27 additional hydroacoustically detected swarms can be further broken into four types precursory post eruptive general and tremor dominated most seismic swarms were less than 10 h long had fewer than 50 earthquakes and had average earthquake rates below 20 h for the explosions we calculate a tremor magnitude frequency index and average frequency the tremor magnitudes determined from the hydrophone data show a roughly linear relation to explosion plume height though this relation was not clear in the more limited seismic data lastly we categorize the activity into five eruption phases based on seismo acoustic character precursory opening explosive i pause and explosive ii

temporal change of upper crustal vp vs ratios with volcanic evolution in redoubt volcano abstract volcanic activities accompany changes in the physical and chemical properties of the medium the ratio between p and s wave velocities v p v s is sensitive to the medium property changes we investigate temporal variations of the v p v s ratios in the upper crust around redoubt volcano in the 1989 2014 time period using the traveltimes of local earthquakes the v p v s ratios reached 2 0 immediately prior to the 1989 1990 and 2009 eruptions these high v p v s ratios may be associated with partial melts in the edifice the v p v s ratios rapidly decreased to 1 7 during the 1989 1990 and 2009 eruptions due to decreasing temperatures fluids and pore pressures and increasing effective stresses after melt eruptions and gas emission the change rates of the v p v s ratios showed evident spatial distributions the v p v s ratios increased at a rate of 0 025 0 003 yr 1 below the 2009 vent during the inter eruption period between the 1989 1990 and 2009 eruptions due to an increase in the temperature which may be associated with the recharge of the magma in the lower crust the increase rate of the v p v s ratios was as low as 0 005 0 001 yr 1 in the regions located away from the eruption site the v p v s ratios appear to have increased consistently at a rate of 0 017 0 004 yr 1 since the 2009 eruption

duration amplitude relationships of volcanic tremor and earthquake swarms preceding and during the 2009 eruption of redoubt volcano alaska abstract duration amplitude relationships were studied for tremor episodes and earthquake swarms occurring during the 2009 eruption of redoubt volcano alaska duration amplitude distribution plots were generated daily from january 1 to may 31 and fit with both an exponential law and power law comparing r2 values of the fit for both laws showed that the exponential law fit better for days in which volcanic tremor and earthquake swarms occurred while the power law fit better for other days fitting segments of seismic data with both an exponential and a power law leads to a metric that has potential for volcano monitoring r2exp r2pow the ratio of the r2 fits using the exponential law and the power law the ratio r2exp r2pow tended to be greater than 1 when volcanic activity or precursory seismic activity was occurring and less than 1 when no volcano seismic activity was occurring duration amplitude plots were generated for episodes of volcanic tremor that were identified by the r2exp r2pow 1 method and compared in an attempt to identify changes that may have occurred during the eruption stronger episodes of volcanic tremor showed higher characteristic amplitudes maximum heights of the plumes generated by the explosions showed a positive correlation with the characteristic amplitude of the concurrent tremor

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

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

volcanic tremor wave field during quiescent and eruptive activity at mt etna sicily abstract this paper reports the results of an analysis of volcanic tremor at etna in the years 1987 to 1992 the data utilized were obtained from the osservatorio vesuviano s serra la nave permanent station and several seismic surveys carried out by means of portable digital seismic stations equipped with three component geophones the spatial temporal patterns of main parameters such as intensity spectral content polarization and wave composition of volcanic tremor in different phases of etna s activity were studied eruptive activity appears to be significantly correlated with volcanic tremor in particular it is worth pointing out that the magma upwelling in the terminal part of the conduit is characterized by a marked increase in low frequency components 3 4 hz of the spectrum of volcanic tremor hence volcanic tremor at etna can be considered as a short period precursor of eruptions an analysis of polarization and propagation velocity of volcanic tremor shows the presence of love waves overlapping other seismic phases

emplacement of the final lava dome of the 2009 eruption of redoubt volcano alaska abstract after more than 8 months of precursory activity and over 20 explosions in 12 days redoubt volcano alaska began to extrude the fourth and final lava dome of the 2009 eruption on april 4 by july 1 the dome had filled the pre 2009 summit crater and ceased to grow by means of analysis and annotations of time lapse webcam imagery oblique image photogrammetry techniques and capture and analysis of forward looking infrared flir images we tracked the volume textural effusive style and temperature changes in near real time over the entire growth period of the dome the first month of growth april 4 may 4 produced blocky intermediate to high silica andesite lava 59 62 3 wt sio 2 that initially formed a round dome expanding by endogenous growth breaking the surface crust in radial fractures and annealing them with warmer fresh lava on or around may 1 more finely fragmented and scoriaceous andesite lava 59 8 62 2 wt sio 2 began to appear at the top of the dome coincident with increased seismicity and gas emissions the more scoriaceous lava spread radially over the dome surface while the dome continued to expand from endogenous growth and blocky lava was exposed on the margins and south side of the dome by mid june the upper scoriaceous lava had covered 36 of the dome surface area vesicularity of the upper scoriaceous lava range from 55 to 66 some of the highest vesicularity measurements recorded from a lava dome we suggest that the stability of the final lava dome primarily resulted from sufficient fracturing and clearing of the conduit by preceding explosions that allowed efficient degassing of the magma during effusion the dome was thus able to grow until it was large enough to exceed the magmastatic pressure in the chamber effectively shutting off the eruption

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

volcanic seismicity at montserrat a comparison between the 2005 dome growth episode and earlier dome growth in 2005 soufriere hills volcano on montserrat started its third major episode of dome growth since the current eruption started in 1995 the style of seismicity associated with dome growth has changed in particular the events known as hybrid earthquakes have reduced in numbers by an order of magnitude compared to previous dome growth episodes in the past hybrid earthquakes have been associated with magma ascent and so it is surprising to observe prolonged periods of rapid dome growth during which very few hybrid earthquakes are recorded in addition the frequency of the codas of hybrid earthquakes as well as of some of the so called long period events has changed the changes in recorded seismicity have had a marked effect on the techniques used to monitor the state of the volcano and those events that continue to be recorded in large numbers rockfall events have been used to assess the state of activity at the 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

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

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