variations in column height and magma discharge during the may 18 1980 eruption of mount st helens abstract peak eruption column heights for the b1 b2 b3 and b4 units of the may 18 1980 fall deposit from mount st helens have been determined from pumice and lithic clast sizes and models of tephra dispersal column heights determined from the fall deposit agree well with those determined by radar measurements b1 and b2 units were derived from plinian activity between 0900 and about 1215 hrs b3 was formed by fallout of tephra from plumes that rose off pyroclastic flows from about 1215 to 1630 hrs a brief return to plinian activity between 1630 and 1715 hrs was marked by a maximum in column height 19 km during deposition of b4 variations in magma discharge during the eruption have been reconstructed from modelling of column height during plinian discharge and mass balance calculations based on the volume of pyroclastic flows and coignimbrite ash peak magma discharge occurred during the period 1215 1630 hrs when pyroclastic flows were generated by collapse of low fountains through the crater breach pyroclastic flow deposits and the widely dispersed co ignimbrite ash account for 77 of the total erupted mass with only 23 derived from plinian discharge a shift in eruptive style at noon on may 18 may have been associated with increase in magma discharge and the eruption of silicic andesite mingled with the dominant mafic dacite increasing abundance of the silicic andesite during the period of highest magma discharge is consistent with the draw up and tapping of deeper levels in the magma reservoir as predicted by theoretical models of magma withdrawal return to plinian activity late in the afternoon when magma discharge decreased is consistent with theoretical predictions of eruption column behavior the dominant generation of pyroclastic flows during the may 18 eruption can be attributed to the low bulk volatile content of the magma and the increasing magma discharge that resulted in the transition from a stable convective eruption column to a collapsing one

origin of the giant eruption cloud of pinatubo june 15 1991 the series of eruptions of june 15 1991 at mt pinatubo philippines were observed hourly by satellite a giant discshaped cloud covering an area of 60 000 km2 appeared in the satellite images at 14 40 philippine time the cloud expanded radially against wind of 20 m s and spread to an area of more than 120 000 km2 within an hour according to eyewitness accounts there was heavy fine ash fall after 14 00 intermittent lapilli fall started at about 14 20 and heavy and continuous lapilli fall widely started at about 15 00 the occurrence of the giant cloud roughly corresponded to the initiation of the intermittent lapilli fall the air fall deposits of the major eruption are widely distributed including upwind from the vent they are composed of 3 units a silt size fine ash layer layer b a lapilli layer commonly including pumice grains of 1 cm in diameter layer c a lapilli bearing volcanic sand layer layer d judging from its wide distribution and depletion of coarse grains most of the fine ash of layer b is not distal deposits of a small eruption but is originated from a large co ignimbrite cloud it is suggested that the major eruption started with the generation of a pyroclastic flow which was subsequently followed by a plinian eruption resulting in the formation of the giant cloud and the lapilli fall the results of calculations on the dynamics of eruption cloud indicate that the dimension and dynamics of the giant eruption cloud is accounted for by a plinian eruption with a magma discharge rate of the order of 109 kg s

axisymmetric intrusive gravity currents in linearly stratified fluids two detailed field experiments were performed to investigate the spreading dynamics of axisymmetric inertia buoyancy controlled intrusive gravity currents in linearly stratified environments the appropriate intrusions were successfully generated using deep set point source bubble plume devices installed within different thermally stratified reservoirs the intrusive flows were found to progress at a rate predicted from a simple inertia buoyancy force balance with the intrusion thickness decreasing with distance from the source the results imply that shear waves of all modes were generated at the intrusion nose and able to propagate away to modify the flow field turbulent activity internal to the intrusions was found not to influence the spreading characteristics scaling arguments and the experimental findings were also used to derive a parameter describing the initial intrusion dynamics by combining the current findings with previously published results for intrusions progressing in the viscous buoyancy regime a relation describing the distance at which viscous forces become dominant was derived

impact of the lateral blast on the spatial pattern and grain size characteristics of the 18 may 1980 mount st helens fallout deposit the 18 may 1980 eruption of mount st helens started with a lateral blast that fed a pyroclastic surge which then uplifted to form a co blast plume thirty minutes later plinian activity started at the vent and fluctuated in intensity for 9 h the resulting fallout deposit documented to 600 km from vent presents some striking features 1 displacement of the overall deposit to the north of the vent 2 a secondary thickness and mass maximum at 300 km from vent 3 a total grain size distribution dominated by fine ash 62 wt of the deposit 63 m and 4 individual grain size distributions that vary dramatically in the crosswind direction from strongly bimodal in the south to skewed unimodal in the north results from a new deconvolution of the individual grain size distributions show that they are a combination of a coarse subpopulation that decreases in size with distance from vent and a constant fine subpopulation with a mean of 15 m relative proportions of each subpopulation vary asymmetrically in the crosswind directions with the fine subpopulation preponderant toward the north and the coarse one dominating the south of the deposit both reach their absolute maxima in mass on the deposit axis componentry analyses of selected samples show that blast derived material is greatly enriched toward the north of the deposit these results indicate that the co blast plume dispersed fine grained material over great distances and dominated the fine subpopulation comparison with reanalysis data of atmospheric wind fields and satellite images of the spreading ash cloud suggests contrasting ash transport and depositional processes for the early co blast plume and the later vent derived plinian plumes the co blast plume is displaced to the north it had a high overshoot height and eastward dispersion via strong winds low in the stratosphere 10 15 km the plinian plumes were lower and dispersed most of the material to the southeast as the direction of high velocity winds shifted just before the late climactic plinian eruptive phase fine ash fine subpopulation was deposited continuously throughout the deposit with an increase of sedimentation rate 300 km from the vent where there is a secondary maximum in the deposit mass and thickness fine ash probably settled by a combination of enhanced sedimentation mechanisms including not only aggregation but also gravitational convective instabilities of cloud base hydrometeor formation and destruction and entrainment of small particles by larger ones finally we show that half of the deposit by mass in the medial area was deposited by the co blast plume and that a significant proportion of the mount st helens fallout deposit is nonjuvenile which has implications for the magmatic budget of this eruption

a multidisciplinary effort to assign realistic source parameters to models of volcanic ash cloud transport and dispersion during eruptions during volcanic eruptions volcanic ash transport and dispersion models vatds are used to forecast the location and movement of ash clouds over hours to days in order to define hazards to aircraft and to communities downwind those models use input parameters called eruption source parameters such as plume height h mass eruption rate duration d and the mass fraction m63 of erupted debris finer than about 4 or 63 m which can remain in the cloud for many hours or days observational constraints on the value of such parameters are frequently unavailable in the first minutes or hours after an eruption is detected moreover observed plume height may change during an eruption requiring rapid assignment of new parameters this paper reports on a group effort to improve the accuracy of source parameters used by vatds in the early hours of an eruption we do so by first compiling a list of eruptions for which these parameters are well constrained and then using these data to review and update previously studied parameter relationships we find that the existing scatter in plots of h versus yields an uncertainty within the 50 confidence interval of plus or minus a factor of four in eruption rate for a given plume height this scatter is not clearly attributable to biases in measurement techniques or to well recognized processes such as elutriation from pyroclastic flows sparse data on total grain size distribution suggest that the mass fraction of fine debris m63 could vary by nearly two orders of magnitude between small basaltic eruptions 0 01 and large silicic ones 0 5 we classify eleven eruption types four types each for different sizes of silicic and mafic eruptions submarine eruptions brief or vulcanian eruptions and eruptions that generate co ignimbrite or co pyroclastic flow plumes for each eruption type we assign source parameters we then assign a characteristic eruption type to each of the world s 1500 holocene volcanoes these eruption types and associated parameters can be used for ash cloud modeling in the event of an eruption when no observational constraints on these parameters are available

satellite remote sensing of thermal activity at bezymianny and kliuchevskoi from 1993 to 1998 time series trends in thermal advanced very high resolution radiometer avhrr data from 1993 to 1998 provide insight into the active volcanic processes at bezymianny and kliuchevskoi two of the most dangerous volcanoes on the kamchatka peninsula the avhrr time series show differences in these volcanoes pre and postexplosive trends bezymianny exhibited a thermal precursory signal in all recorded explosions between 1993 and 1998 as well as continued postexplosive activity and kliuchevskoi showed only short lived thermal activity and exhibited precursors before the 1994 paroxysmal explosion these contrasting characteristics reflect different magma types and eruption styles at bezymianny a persistent thermal signal and precursory thermal increases are due to the slow ascent of andesitic magma whereas the more rapid rise effusion and cooling of basaltic magmas at kliuchevskoi give rise to a discontinuous thermal pattern documentation analysis and understanding of these characteristics contribute to the understanding of thermal signals and aid the development of monitoring algorithms and early warning techniques

estimation and propagation of volcanic source parameter uncertainty in an ash transport and dispersal model application to the eyjafjallajokull plume of 14 16 april 2010 data on source conditions for the 14 april 2010 paroxysmal phase of the eyjafjallajokull eruption iceland have been used as inputs to a trajectory based eruption column model bent this model has in turn been adapted to generate output suitable as input to the volcanic ash transport and dispersal model puff which was used to propagate the paroxysmal ash cloud toward and over europe over the following days some of the source param eters specifically vent radius vent source velocity mean grain size of ejecta and standard deviation of ejecta grain size have been assigned probability distributions based on our lack of knowledge of exact conditions at the source these probability distributions for the input variables have been sampled in a monte carlo fashion using a technique that yields what we herein call the polynomial chaos quad rature weighted estimate pcqwe of output parameters from the ash transport and dispersal model the advantage of pcqwe over monte carlo is that since it intelligently samples the input parameter space fewer model runs are needed to yield estimates of moments and probabilities for the output variables at each of these sample points for the input variables a model run is performed output moments and probabilities are then computed by properly summing the weighted values of the output parameters of interest use

the dynamics and thermodynamics of volcanic clouds theory and observations from the april 15 and april 21 1990 eruptions of redoubt volcano alaska on april 15 1990 and april 21 1990 two relatively small explosive eruptions occurred at redoubt volcano alaska lasting about 4 and 8 minutes respectively on both occasions the erupted material travelled as a pyroclastic flow down an ice canyon on the north flank of the volcano using slow scan television recordings of the eruption and the seismic record in both the near and far field we deduce that after a few minutes the upper parts of these pyroclastic flows became buoyant and a large and hot ash cloud ascended off the flow these thermals rose to a height of about 12 km at which point they began to spread laterally as umbrella clouds using a simple thermodynamic model we estimate that the clouds had a temperature in the approximate range 600 700 k as they rose buoyantly from the flow after entraining and heating air and melting and vaporizing ice we also estimate that in each eruption approximately 109 kg of fine ash was injected into the atmosphere during the april 15 eruption a slow scan television camera recorded the ascent of the cloud these observations are described analysed and compared with the predictions of a new model for the dynamics governing the ascent of such clouds in accord with the observations our model predicts that the cloud initially ascended rather sluggishly since it is only just buoyant on rising from the pyroclastic flow as it ascends it entrains and heats up more air and hence generates more buoyancy therefore it accelerates upwards only much higher in the cloud does the velocity decrease again as the thermal energy of the cloud becomes exhausted the model also predicts that the height of rise of such coignimbrite thermals is a function of the initial mass and temperature of the cloud but is almost independent of the initial velocity during the april 21 eruption a sequence of photographs recorded the lateral spreading of the umbrella cloud during an interval of about 10 minutes after the eruption these photographs are analysed and successfully compared with a simple model for the spreading of the umbrella cloud as a gravity current in a stratified environment using an avhrr satellite image of the air fall deposit from the april 15 eruption combined with a simple model we suggest that the primary mechanism of ash dispersal was transport by the ambient wind

anisotropy repeating earthquakes and seismicity associated with the 2008 eruption of okmok volcano alaska 1 we use shear wave splitting sws analysis and double difference relocation to examine temporal variations in seismic properties prior to and accompanying magmatic activity associated with the 2008 eruption of okmok volcano alaska using bispectrum cross correlation a multiplet of 25 earthquakes is identified spanning five years leading up to the eruption each event having first motions compatible with a normal fault striking ne sw cross correlation differential times are used to relocate earthquakes occurring between january 2003 and february 2009 the bulk of the seismicity prior to the onset of the eruption on 12 july 2008 occurred southwest of the caldera beneath a geothermal field earthquakes associated with the onset of the eruption occurred beneath the northern portion of the caldera and started as deep as 13 km subsequent earthquakes occurred predominantly at 3 km depth coinciding with the depth at which the magma body has been modeled using geodetic data automated sws analysis of the okmok catalog reveals radial polarization outside the caldera and a northwest southeast polarization within we interpret these polarizations in terms of a magma reservoir near the center of the caldera which we model with a mogi point source sws analysis using the same input processing parameters for each event in the multiplet reveals no temporal changes in anisotropy over the duration of the multiplet suggesting either a short term or small increase in stress just before the eruption that was not detected by gps or eruption triggering by a mechanism other than a change of stress in the system

uncertainty analysis of a model of wind blown volcanic plumes mathematical models of natural processes can be used as inversion tools to predict unobserved properties from measured quantities uncertainty in observations and model formulation impact on the efficacy of inverse modelling we present a general methodology history matching that can be used to investigate the effect of observational and model uncertainty on inverse modelling studies we demonstrate history matching on an integral model of volcanic plumes that is used to estimate source conditions from observations of the rise height of plumes during the eruptions of eyjafjallajokull iceland in 2010 and grimsvotn iceland in 2011 sources of uncertainty are identified and quantified and propagated through the integral plume model a preliminary sensitivity analysis is performed to identify the uncertain model parameters that strongly influence model predictions model predictions are assessed against observations through an implausibility measure that rules out model inputs that are considered implausible given the quantified uncertainty we demonstrate that the source mass flux at the volcano can be estimated from plume height observations but the magmatic temperature exit velocity and exsolved gas mass fraction cannot be accurately determined uncertainty in plume height observations and entrainment coefficients results in a large range of plausible values of the source mass flux our analysis shows that better constraints on entrainment coefficients for volcanic plumes and more precise observations of plume height are required to obtain tightly constrained estimates of the source mass flux

weather radar observations of the hekla 2000 eruption cloud iceland the hekla eruption cloud on 26 27 february 2000 was the first volcanic cloud to be continuously and completely monitored advecting above iceland using the c band weather radar near the keflavik international airport real time radar observations of the onset advection and waning of the eruption cloud were studied using time series of ppi plan position indicator radar images including vmi normal echotop and cappi level 2 displays the reflectivity of the entire volcanic cloud ranges from 0 to 60 dbz the eruption column above the vent is essentially characterised by vmi normal and cappi level 2 values 30 dbz due to the dominant influence of lapilli and ash tephra on the overall reflected signal the cloud generated by the column was advected downwind to the north northeast it is characterised by values between 0 and 30 dbz and the persistence of these reflections likely result from continuing water condensation and freezing on ash particles echotop radar images of the eruption onset document a rapid ascent of the plume head with a mean velocity of 30 to 50 m s 1 before it reached an altitude of 11 12 km the evolution of the reflected cloud was studied from the area change in pixels of its highly reflected portions 30 dbz and tied to recorded volcanic tremor amplitudes the synchronous initial variation of both radar and seismic signals documents the abrupt increase in tephra emission and magma discharge rate from 18 20 to 19 00 utc on 26 february from 19 00 the 45 dbz and 30 45 dbz portions of the reflected cloud decrease and disappear at about 7 and 10 5 h respectively after the eruption began indicating the end of the decaying explosive phase the advection and extent of the reflected eruption cloud were compared with eyewitness accounts of tephra fall onset and the measured mass of tephra deposited on the ground during the first 12 h differences in the deposit map and volcanic cloud radar map are due to the fact that the greater part of the deposit originates by fallout off the column margins and from the base of the cloud followed by advection of falling particle in lower level winds

total grain size distribution of an intense hawaiian fountaining event case study of the 1959 kīlauea iki eruption the 1959 eruption of k lauea iki on the island of hawai i is a principal example of powerful hawaiian fountaining over 36 days including repose periods 16 fountaining episodes created a small cone a downwind tephra blanket of approximately 0 003 km3 and a lava lake of about 0 04 km3 volume during the explosive activity the maximum fountain heights reached 600 m based on a dataset of more than 450 tephra grain size samples we present both a total grain size distribution tgsd of the entire downwind tephra deposit and also tgsds for two eruptive subunits the opening and the closing stages the opening stage was characterized by persistent fountaining over a period of 8 days with fountain heights averaging 100 m in contrast the closing stage was characterized by two short hours long but powerful fountaining episodes up to 600 m the significantly different fountaining intensities are reflected in the characteristics of the tgsds for the closing stages we link bimodality of tgsds to periods of simultaneous deposition of ballistics and fallout from the convective cloud both of which are a function of the maximum fountain height the 1959 k lauea iki case study presents a well constrained set of tgsd data linked with hawaiian style fountaining of two contrasting intensities and can be used as a valuable reference point for eruption source parameters in future modeling of pyroclast dispersal during hawaiian fountaining eruptions

a gravity current model for the may 18 1980 mount st helens plume observations of the stratospheric plume from the may 18 1980 mount st helens eruption suggest that it spread in the crosswind direction as an intrusive gravity current as it was transported downwind grain size analyses of the plinian tephra are consistent with this model suggesting that to distances of many hundreds of kilometers turbulent atmospheric diffusion played a secondary role in plume spreading and tephra dispersal

goes weather satellite observations and measurements of the may 18 1980 mount st helens eruption we demonstrate the use of geostationary operational environmental satellite goes images of the may 18 1980 mount st helens volcanic plume in providing details of the dynamics and changing character of this major explosive eruption visible and thermal infrared ir data from a sequence of images at 30 min intervals from 0850 to 1720 local time lt give information on dispersal and plume top temperature initial visible and ir images at 0850 show the top of a spreading co ignimbrite like umbrella plume and an overshooting column emerging from it both rising off the ground hugging pyroclastic gravity flow generated by the opening directed blast the overshooting column had a minimum temperature significantly colder than local ambient atmosphere indicating substantial undercooling and a maximum altitude of 31 2 km at 0920 this large plume system then formed a high velocity radially spreading gravitationally driven current before becoming advected in the wind field at an average downwind velocity of 29 m s within 30 to 60 min the undercooled plume adjusted to ambient temperatures after this initial event the eruption column fluctuated over the next 8 hours between stable plinian column rise and unstable conditions favoring column collapse leading to pyroclastic flows and further development of co ignimbrite ash columns over this period of observation profiles of plume top temperatures derived from ir data versus distance along the downwind axis have distinctive patterns with steep slopes associated with co ignimbrite plumes and shallower slopes associated with plinian plumes moreover reflectance values from visible goes data change from lower to higher during periods of transition from darker toned plinian to lighter toned coignimbrite plumes indicating that in this case satellite data resolved changes in eruptive style from plumes with a coarser to a finer dominant particle size

a new strategy for the estimation of plume height from clast dispersal in various atmospheric and eruptive conditions abstract plume height is an important parameter routinely used to characterize and classify explosive eruptions though the strategies to estimate key eruption source parameters such as erupted volume and mass flow rate have evolved over the past few decades the determination of plume height of past eruptions is still mostly based on empirical approaches that do not account for the new developments in plume modelling based on the interaction of plume and wind here we present a revised strategy for the retrieval of plume height from field data that accounts for key aspects of plume dynamics and particle sedimentation which include i the effect of wind advection on the buoyant plume ii a new parameterization of the gravitational spreading of the umbrella cloud for distances smaller than the radius of the plume iii the effect of particle shape on particle sedimentation iv the effect of different atmospheric profiles in different climate zones v three dimensional wind temperature and pressure data and vi topography in particular as wind can affect the dynamics and height of the plume new computed sedimentation patterns are more complex and result in non linear relationships between downwind and crosswind deposition our method is tested against observations of the 2011 eruption of shinmoedake japan the 1980 eruption of mount st helens usa and the 1991 eruption of pinatubo philippines these are well constrained examples of small intermediate and high intensity eruptions respectively intensity scenarios are introduced to account for the non unique relation between plume height and particle sedimentation resulting from wind advection of volcanic plumes we further demonstrate that needle like and disk like particle shapes can have downwind distances 36 to 70 larger than the equivalent spheres in addition we find that the effect of latitude on the determination of plume height is more significant for low and intermediate intensity scenarios with a discrepancy between 7 and 20

grain size areal thickness distribution and controls on sedimentation of the 1991 mount pinatubo tephra layer in the south china sea the june 15 1991 climactic eruption of mt pinatubo produced an extensive largely co ignimbrite derived airfall ash layer on luzon island and across the central south china sea the layer covers an area of 4 105 km2 with a volume of 5 5 km3 near the coast of luzon the deposit consists of two units a normally graded basal ash bed unimodal in grain size and a finer grained internally structureless upper ash bed showing grain size bimodality with increasing distance from the source the coarse particle populations of the two units merge and migrate towards a near constant fine population 11 m the distal region is covered by a fine mode dominated virtually ungraded single ash layer the reversal of the winds from easterly directions at upper tropospheric and stratospheric levels to westerly directions in the middle and lower troposphere indicates that both the coarse and fine mode components fell out from high altitude eruption clouds the high velocity upper level winds however would have transported fine grained ash particles far beyond the south china sea which suggests that their settling was accelerated by aggregation the boundary between the units thus marks a change from fallout of predominantly discrete pyroclasts to simultaneous fallout of aggregated fines and freely falling coarse grained particles the particle populations composing the upper ash bed were almost completely removed from the proximal areas by the upper level winds at lower elevations the counterclockwise circulation of a typhoon over the coastal area advected the ash south and eastward producing a thickness maximum in the medial region at about 160 km from source the strong displacement of fines possibly aided by wind turbulence led to a break in bulk tephra thinning rates close to the coastline in the distal region outside the influence of the typhoon southwest monsoonal winds caused a distinct lobe axis inflection and thickness asymmetry within this region at about 420 km from source fallout of particle aggregates created a second thickness maximum comparison of the field data with previous experimental observations and tephra flux records in the deep sea wiesner et al 1995 carey 1997 mccool 2002 implies that the transport of ash in the water column was largely determined by vertical density currents differences in the reaction of coarse and fine particles to turbulence in the descending plumes probably suppressed the segregation of fines but allowed the coarser pyroclasts to maintain their initial order of arrival at the sea surface considering typical fall rates of convective plumes modifications of the initial fallout position of the particles by the south china sea current system are on the order of only a few kilometers the results suggest that convective sedimentation processes ensure the preservation of atmospheric particle transport directions distances and fallout modes in the deep sea

interaction between volcanic plumes and wind during the 2010 eyjafjallajokull eruption iceland 1 estimates of volcanic source mass flux currently deduced from observations of plume height are crucial for ash dispersion models for aviation and population hazard this study addresses the role of the atmospheric wind in determining the height at which volcanic plumes spread in the atmosphere and the relationship between source mass flux and plume height in a wind field we present a predictive model of volcanic plumes that describes the bending over of the plume trajectory in a crosswind and show that model predictions are in accord with a dataset of historic eruptions if the profile of atmospheric wind shear is described the wind restricts the rise height of volcanic plumes such that obtaining equivalent rise heights for a plume in a windy environment would require an order of magnitude increase in the source mass flux over a plume in a quiescent environment our model calculations are used to calibrate a semi empirical relationship between the plume height and the source mass flux that explicitly includes the atmospheric wind speed we demonstrate that the model can account for the variations in plume height observed during the first explosive phase of the 2010 eyjafjallajokull eruption using independently measured wind speeds and show that changes in the observed plume height are better explained by changing meteorology than abrupt changes in the source mass flux this study shows that unless the wind is properly accounted for estimates of the source mass flux during an explosive eruption are likely to be very significant underpredictions of the volcanic source conditions

block rotation and termination of the hosgri strike slip fault california from three dimensional map restoration the hosgri fault is located immediately offshore of south central california and is part of the transform boundary between the pacific and north american plates this fault terminates to the southeast into east trending folds and reverse separation faults of the western transverse ranges our new structure contour maps of deformed horizons show a spatial relationship between faulting and folding consistent with right lateral slip restoration of these digital maps quantifies post miocene right lateral slip across the southern hosgri fault to be 3 5 km this slip is absorbed by folding thrust overlap and clockwise vertical axis rotation of elongate blocks between strands of the fault the restored part of a block located to the east has rotated 8 clockwise extrapolating this restored rotation to the 50 km block length produces an estimate of 7 km of dextral shear for a total including the 3 5 km fault slip of 10 5 km of post miocene displacement our three dimensional approach precludes interpretations for reverse slip on the hosgri fault and is not consistent with models for more than 80 km of late cenozoic right lateral fault slip

effect of wind on the rise height of volcanic plumes a theoretical model of a volcanic plume based on applying the equations of motion in a plume centered coordinate system suggests that the interaction between a volcanic plume and wind causes enhanced entrainment of air and horizontal momentum plume bending and a decrease in plume rise height at constant eruption rate because of rapid dilution in the high windspeeds of the polar jet plumes that vary over more than one order of magnitude in mass eruption rate 106 to 107 108 kg s if injected into the polar jet may all attain rise heights only slightly different from that of the core of the jet 10 km as opposed to 17 33 km in a still atmosphere

the initial giant umbrella cloud of the may 18th 1980 explosive eruption of mount st helens abstract the initial eruption column of may 18th 1980 reached nearly 30 km altitude and released 10 17 joules of thermal energy into the atmosphere in only a few minutes ascent of the cloud resulted in forced intrusion of a giant umbrella shaped cloud between altitudes of 10 and 20 km at radial horizontal velocities initially in excess of 50 m s the mushroom cloud expanded 15 km upwind forming a stagnation point where the radial expansion velocity and wind velocity were equal the cloud was initiated when the pyroclastic blast flow became buoyant the flow reduced its density as it moved away from the volcano by decompression by sedimentation and by mixing with and heating the surrounding air observations indicate that much of the flow covering an area of 600 km 2 became buoyant within 1 5 minutes and abruptly ascended to form the giant cloud calculations are presented for the amount of air that must have been entrained into the flow to make it buoyant assuming an initial temperature of 450 c and a magmatic origin for the explosion these calculations indicate that the flow became buoyant when its temperature was approximately 150 c and the flow consisted of a mixture of 3 25 10 11 kg of pyroclasts and 5 0 10 11 kg of air if sedimentation is considered these figures reduce to 1 1 10 11 kg of pyroclasts and 1 0 10 11 kg of air

infrasound observations of the 2008 explosive eruptions of okmok and kasatochi volcanoes alaska 1 the recent explosive eruptions of okmok and kasatochi volcanoes provide an opportunity to use seismic local infrasound distant infrasound array and remote sensing data in concert to better monitor volcanoes in the aleutian arc and to better understand the source processes the eruption of okmok volcano began on 12 july 2008 and included a seismically active phase that lasted continuously for about 10 h in contrast the eruption of kasatochi which began on 7 august 2008 consisted of five explosive events that lasted from 26 to 68 min each and had a cumulative duration of 3 4 h given the event times by local seismic stations the corresponding infrasound signals were found in the data recorded by local infrasound sensors and by distant infrasound arrays signals from the okmok eruption were detected by three international monitoring system ims arrays as far away as 4400 km signals from the kasatochi eruption were detected at greater distances up to 5200 km away by seven infrasound arrays including the ones that detected the event at okmok volcano back azimuth propagation and a simple acoustic wave propagation model in unison with known event times were used to confirm that the planar acoustic signals recorded at the arrays had originated from the eruptions the infrasound array data reflected the differences in eruption styles between okmok and kasatochi as the signals from kasatochi were of shorter duration of greater amplitude and detected over greater distances the infrasound array data were also able to distinguish between two types of tremor episodes that occurred at kasatochi volcano based on atmospheric disturbance

improving on mass flow rate estimates of volcanic eruptions 1 we introduce a novel analytical expression that allows for fast assessment of mass flow rate of both vertically rising and bent over volcanic plumes as a function of their height while first order physical insight is maintained this relationship is compared with a one dimensional plume model to demonstrate its flexibility and then validated with observations of the 1980 mount st helens and of the 2010 eyjafjallajokull eruptions the influence of wind on the dynamics of volcanic plumes is quantified by a new dimensionless parameter and it is shown how even vertically rising plumes such as the one associated with the mount st helens 1980 eruption can be significantly affected by strong wind comparison between a one dimensional model and the analytical equation gives anr2 value of 0 88 while existing expressions give negativer2 values due to their inability to adapt to different source and atmospheric conditions therefore this new expression has important implications both for current strategies of real time forecasting of ash transport in the atmosphere and for the characterization of explosive eruptions based on the study of tephra deposits in addition this work provides a framework for the application of more complete three dimensional numerical models as it greatly reduces the parameter space that needs to be explored

a laboratory study of the velocity structure in an intrusive gravity current laboratory experiments were performed in which an intrusive gravity current was observed using shadowgraph and particle tracking methods the intrusion was generated in a two layer fluid with a sharp interface by mixing the fluid behind a vertical lock gate and then suddenly withdrawing the gate from the tank the purpose of the experiments was to determine the structure of the velocity field inside the intrusion and the stability characteristics of the interface soon after the removal of the lock gate the front of the intrusive gravity current travelled at a constant speed close to the value predicted by theory for an energy conserving gravity current the observed structure of the flow inside the intrusion can be divided into three regions at the front of the intrusion there is an energy conserving head region in which the fluid velocity is nearly uniform with speed equal to the front speed this is followed by a dissipative wake region in which large billows are present with their associated mixing and in which the fluid velocity is observed to be non uniform and have a maximum speed approximately 50 greater than the front speed behind the wake region is a tail region in which there is very little mixing and the velocity field is nearly uniform with a speed slightly faster than the front speed

late quaternary history of atmospheric and oceanic circulation in the eastern equatorial pacific abstract four radiolarian assemblages have been defined in recent seafloor sediments of the equatorial pacific ocean the distribution of these assemblages corresponds to the modern pattern of oceanic circulation and water mass structure in this region the eastern pacific shallow permanent thermocline and the equatorial undercurrent peru current upwelling and the oxygen minimum the subtropical water mass warm western tropical water and the north equatorial countercurrent in twelve cores chosen to transect the region both longitudinally and latitudinally the distribution of these four assemblages has been reconstructed for six time intervals during the last 127 000 years 18 000 b p glacial stage 2 36 000 b p and 52 000 b p interstadial stage 3 65 000 b p glacial stage 4 82 000 b p and 120 000 b p interglacial stage 5 atmospheric and oceanic circulation changes through time have been inferred from the reconstructed microfossil assemblage distributions changes in assemblage distributions indicate that variations in intensity direction and mean position of the tradewinds caused marked changes in the oceanic circulation patterns through the last glacial cycle near the end of interglacial stage 5 the disappearance of the north equatorial countercurrent from the eastern pacific suggests that the mean position of the tradewinds was shifted to the south approximately 5 of latitude relative to the modern position so that the northeast trades prevented the flow of the north equatorial countercurrent into the eastern pacific near the end of interstadial stage 3 a change in wind direction occurred from predominantly zonal winds which enhance equatorial divergence and surfacing of the equatorial undercurrent to more meridional winds which enhance coastal upwelling associated with the peru current in the tropical pacific ocean late quaternary changes in atmospheric and oceanic circulation are linked with times of continental ice sheet growth in the northern hemisphere i e the interglacial to glacial transitions across oxygen isotope stage boundaries 5 4 and 3 2 the major changes in circulation seem to occur a few thousand years in advance of the glacial episodes at or near periods of ice sheet growth this relationship indicates that changes in atmospheric circulation in the tropics led and influenced the development of conditions suitable for polar and continental ice sheet growth in the northern hemisphere

interpretation of umbrella cloud growth and morphology implications for flow regimes of short lived and long lived eruptions new numerical and analytical modeling shows that the growth of a volcanic umbrella cloud expressed as the increase of radius with time proceeds through regimes dominated by different force balances four regimes are identified regime ia is the long time behavior of continuously supplied intrusions in the buoyancy inertial regime regime iia is the long time behavior of continuously supplied turbulent drag dominated intrusions regime ib is the long time behavior of buoyancy inertial intrusions of constant volume and regime iib that of turbulent drag dominated intrusions of constant volume power law exponents for spreading time in each regime are 3 4 ia 5 9 iia 1 3 ib and 2 9 iib both numerical modeling and observations indicate that transition periods between the regimes can be long lasting and during these transitions the spreading rate does not follow a simple power law predictions of the new model are consistent with satellite data from seven eruptions and together with observations of umbrella cloud structure and morphological evolution support the existence of multiple spreading regimes

the millennium eruption of hekla in february 2000 the 18th historic eruption of hekla started on 26 february 2000 it was a short lived but intense event emitting basaltic andesitic 55 5 wt sio2 pyroclastic fragments and lava during the course of the eruption monitoring was done by both instruments and direct observations together providing unique insight into the current activity of hekla during the 12 day eruption a total of 0 189 km3 dre of magma was emitted the eruptive fissure split into five segments the segments at the highest altitude were active during the first hours while the segments at lower altitude continued throughout the eruption the eruption started in a highly explosive manner giving rise to a subplinian eruptive column and consequent basaltic pyroclastic flows fed by column collapses after the explosive phase reached its maximum the eruption went through three more phases namely fire fountaining strombolian bursts and lava effusion in this paper we describe the course of events of the eruption of hekla and the origin of its magma and then show that the discharge rate can be linked to different style of eruptive activity which are controlled by fissure geometry we also show that the eruption phases observed at hekla can be linked with inferred magma chamber overpressure prior to the eruption

satellite observations and interpretation of the 1991 mount pinatubo eruption plumes we demonstrate the use of hourly geostationary meteorological satellite gms and noaa polar orbiting advanced very high resolution radiometer avhrr satellite images of the june 1991 mount pinatubo volcanic eruption plumes in providing details of the timing changing eruptive style and umbrella plume movement and dynamics a chronology of explosive events which culminated in a 9 hour long climactic phase on june 15 has been determined from satellite data and favorably compared to ground based and other ancillary information maximum eruption column altitudes of 40 km and column top undercooling in excess of 55 c below the ambient atmosphere occurred during the climactic phase phases dominated by plinian versus coignimbrite eruptive plumes can be distinguished on the images analysis of the spreading umbrella plume during the climactic phase suggests that over the first 4 5 hours the plume spread laterally as a gravitational intrusion before becoming advected in the ambient winds we compare the rate of plume growth to a model of a radially symmetric continuously fed intrusion to describe the motion the rate of plume growth shows good agreement with this simple model for the first 4 5 hours from column top heights we determine eruption rates and obtain an independent estimate of the total volume of magma erupted from june 12 16 of 5 5 km3 dense rock equivalent dre in good agreement with an independent estimate of the total eruptive volume made from deposits on land and submarine ash fall of up to 5 3 km3 dre we also show that secondary explosions in the pinatubo ignimbrite deposits produced ash plumes reaching altitudes as high as 19 km in september 1991 this study indicates that realistic interpretation and monitoring of major eruption plumes can be accomplished by analysis of high temporal resolution satellite data

a user friendly one dimensional model for wet volcanic plumes 1 this paper presents a user friendly graphically based numerical model of one dimensional steady state homogeneous volcanic plumes that calculates and plots profiles of upward velocity plume density radius temperature and other parameters as a function of height the model considers effects of water condensation and ice formation on plume dynamics as well as the effect of water added to the plume at the vent atmospheric conditions may be specified through input parameters of constant lapse rates and relative humidity or by loading profiles of actual atmospheric soundings to illustrate the utility of the model we compare calculations with field based estimates of plume height 9 km and eruption rate 4 105 kg s during a brief tephra eruption at mount st helens on 8 march 2005 results show that the atmospheric conditions on that day boosted plume height by 1 3 km over that in a standard dry atmosphere although the eruption temperature was unknown model calculations most closely match the observations for a temperature that is below magmatic but above 100 c

globally detected volcanic lightning and umbrella dynamics during the 2014 eruption of kelud indonesia abstract volcanic lightning shows considerable promise as a monitoring and research tool to characterize explosive eruptions its key strengths are rapid and remote detection because the radio signals produced by lightning can propagate thousands of km at the speed of light despite these tantalizing properties the scientific work on volcanic lightning has only recently started gaining momentum much more is needed to understand what lightning reveals about the evolution of an eruption in near real time here we examine the timing and energy release of lightning generated by the eruption of kelud volcano in indonesia on 13 february 2014 as detected by the world wide lightning location network wwlln the eruption column reached at least 26 km above sea level representing the highest plume since the advent of global lightning networks in the last decade therefore it provides valuable constraints on the electrification of end member sustained plinian columns we investigate the lightning in context with satellite images photographs and other published studies results show that the earliest satellite detected activity was a thermal anomaly at 15 46 utc corresponding to a directed blast at the onset of eruption and only a few lightning strokes following a brief pause the eruption produced a sustained column and umbrella cloud that spread outward into the tropical stratosphere rates of umbrella expansion provide an average mass eruption rate mer in the range of 8 107 1 108 kg s 1 a more nuanced picture emerges from the time varying mers determined between each satellite pass which show rapid intensification during the first hour of eruption followed by constant mer for about an hour and waning toward the end after 17 50 utc at this stage decreasing flux into the umbrella cloud coincides with column instability and formation of pyroclastic density currents as recorded by photos from the ground 17 45 utc we infer that some of the erupted mass partitioned into ground hugging currents leading to a lower apparent mer interestingly there is not a 1 1 correlation between lightning intensity and mer over the course of eruption stroke rates increase sharply within the first 30 40 min during rapid intensification of the plume and then drop below 2 strokes per min once the mer remains constant this suggests that electrification was controlled by the rate of increase in mer in other words the acceleration of particles out of the vent we also show that lightning stroke rates and energies are greatest within 50 km of the vent even when the ash cloud extends 200 km downwind indicating that lightning was focused in the regions of highest particle concentration and turbulence overall we conclude that abrupt changes in lightning rates are clearly linked to changes in eruption behavior and that rapid detection could aid monitoring efforts to characterize eruption rates or styles

estimation of eruption source parameters from umbrella cloud or downwind plume growth rate abstract we introduce a new method to estimate mass eruption rate mer and mass loading from the growth of a volcanic umbrella cloud or downwind plume using satellite images or photographs where ground based observations are available this new method is compared with pre existing models and documented mass eruption rate given in the research literature we applied the method to five well studied eruptions mount st helens 1980 redoubt 1990 pinatubo 1991 hekla 2000 and eyjafjallajokull 2010 and to five less well documented eruptions kliuchevsko i 1994 okmok 2008 kasatochi 2008 sarychev peak 2009 and bezymianny 2012 the mass eruption rate is obtained by estimation of the radius of the umbrella cloud with time or by estimation of the width of the downwind plume with distance from the volcano the results given by the new method show a more fully characterized mer as a function of time than do the results given by pre existing methods and allow a faster remote assessment of the mass eruption rate even for volcanoes that are difficult to study the method thus may provide an additional important path to the estimation of source parameters and the forecasting of ash cloud propagation in addition in cases where numerous methods are available use of the method yields new independent measures of mass eruption rate hence an ability to estimate uncertainty in mass eruption rate which could be used in probabilistic estimations of ash cloud propagation

characterization of the 2008 kasatochi and okmok eruptions using remote infrasound arrays 1 the 2008 plinian eruptions of kasatochi and okmok volcanoes were recorded by six remote international monitoring system infrasound arrays high amplitude infrasound at these stations combined with remote sensing permits insight into important volcanic source parameters such as origin times durations and source characteristics infrasound from the 7 8 august kasatochi eruption consists of three well defined eruption pulses with the first two steam rich and the last ash rich pulse 2 is the most energetic and impulsive okmok produced over 9 h of continuous infrasound on 12 13 july acoustic propagation modeling for the okmok eruption and first kasatochi pulse predict thermospheric ducting and origin times consistent with seismic and satellite observations however theoretical acoustic origin times of pulses 2 3 are predicted to occur 15 min earlier than the seismic stratospheric ducting for these later pulses provides more consistent origin times although both volcanoes ejected ash into the stratosphere 15 km kasatochi produced higher amplitude infrasound than okmok previous studies have shown sustained infrasound with frequencies 2000 km and does not seem to be appreciably affected by changes in ash content between the eruption pulses

sedimentation of tephra by volcanic plumes i theory and its comparison with a study of the fogo a plinian deposit sao miguel azores sedimentation of ejecta from volcanic plumes has been studied as a function of distance from the source in the fogo a plinian deposit sao miguel azores the fogo a trachytic pumice deposit is reversely graded and can be divided into two parts on the basis of pumice colour abundance of syenite accessory lithic clasts and distribution the lower syenite poor part was dispersed to the south and was clearly influenced by wind the upper syenite rich part is coarsegrained and has a nearly symmetrical distribution around the vent elongation of isopachs to the east indicate a weak wind influence the grain size variations of lithic and crystal components in the upper coarse part were studied total accumulation and accumulation per unit area expressed in kg m2 show good fits to a gaussian function at distances greater than 7 km for grain diameters less than 2 cm these results agree with a theoretical model for a radially spreading turbulent current moving over a quiescent fluid the gaussian coefficient is shown to be a function of grain size and the flow rate of material into the umbrella region of the eruption column the coefficient is therefore also a function of column height the column height deduced from these data is 21 km which is in broad agrrement with the column height of 27 km deduced from maximum clast dispersal using the method of carey and sparks 1986 the accumulation of clasts larger than 2 cm agrees with a theory for the fallout of clasts from the margins of the ascending eruption column which treats the plume as a succession of large eddies that decrease their mass of particles as an exponential function of time calculations are also presented for the influence of the radial inflow of surrounding air into the column on the deposition of clasts these calculations constrain the wind speed during the later part of the fogo a eruption to be at most a few metres per second the study has allowed four different dynamic categories of clast behaviour to be recognised in eruption columns

the 7 8 august 2008 eruption of kasatochi volcano central aleutian islands alaska 1 kasatochi volcano in the central aleutian islands erupted unexpectedly on 7 8 august 2008 kasatochi has received little study by volcanologists and has had no confirmed historical eruptions the island is an important nesting area for seabirds and a long term biological study site of the u s fish and wildlife service after a notably energetic preeruptive earthquake swarm the volcano erupted violently in a series of explosive events beginning in the early afternoon of 7 august each event produced ash gas plumes that reached 14 18 km above sea level the volcanic plume contained large amounts of so2 and was tracked around the globe by satellite observations the cumulative volcanic cloud interfered with air travel across the north pacific causing many flight cancelations that affected thousands of travelers visits to the volcano in 2008 2009 indicated that the eruption generated pyroclastic flows and surges that swept all flanks of the island accumulated several tens of meters of pyroclastic debris and increased the diameter of the island by about 800 m pyroclastic flow deposits contain abundant accidental lithic debris derived from the inner walls of the kasatochi crater juvenile material is crystal rich silicic andesite that ranges from slightly pumiceous to frothy pumice fine grained pyroclastic surge and fall deposits with accretionary lapilli cover the lithic rich pyroclastic flow deposits and mark a change in eruptive style from episodic explosive activity to more continuous ash emission with smaller intermittent explosions pyroclastic deposits completely cover the island but wave erosion and gully development on the flanks have begun to modify the surface mantle of volcanic deposits

tephra sedimentation during the 2010 eyjafjallajokull eruption iceland from deposit radar and satellite observations the april may 2010 eruption of eyjafjallajokull volcano iceland was characterized by a nearly continuous injection of tephra in the atmosphere that affected various economic sectors in iceland and caused a global wide interruption of air traffic eruptive activity during 4 8 may 2010 was characterized based on short duration physical parameters in order to capture transient eruptive behavior of a long lasting eruption i e total grainsize distribution erupted mass and mass eruption rate averaged over 30 minute activity resulting 30 minute total grainsize distribution based on both ground and msg seviri satellite measurements is characterized by mdphi of about 2 phi and a fine ash content of about 30wt accumulation rate varied by two orders of magnitude with an exponential decay away from the vent whereas mdphi shows a linear increase until about 18 km from vent reaching a plateau of about 4 5 phi between 20 56 km associated mass eruption rate is in between 0 6 1 2 x 10 5 kg s 1 in situ sampling showed how fine ash mainly fell as aggregates of various typologies about 5 to 9 wt of the erupted mass remained in the cloud up to 1000 km from the vent suggesting that nearly half of the ash 7 phi settled as aggregates within the first 60 km particle sphericity and shape factor varied between 0 4 and 1 with no clear correlation with size and distance from vent our experiments also demonstrate how satellite retrievals and doppler radar grainsize detection can provide real time description of the source term but for a limited particle size range

volcanic plumes and wind jetstream interaction examples and implications for air traffic abstract volcanic plumes interact with the wind at all scales on smaller scales wind affects local eddy structure on larger scales wind shapes the entire plume trajectory the polar jets or jetstreams are regions of high generally eastbound winds that span the globe from 30 to 60 in latitude centered at an altitude of about 10 km they can be hundreds of kilometers wide but as little as 1 km in thickness core windspeeds are up to 130 m s modern transcontinental and transoceanic air routes are configured to take advantage of the jetstream eastbound commercial jets can save both time and fuel by flying within it westbound aircraft generally seek to avoid it using both an integral model of plume motion that is formulated within a plume centered coordinate system bent as well as the active tracer high resolution atmospheric model atham we have calculated plume trajectories and rise heights under different wind conditions model plume trajectories compare well with the observed plume trajectory of the sept 30 oct 1 1994 eruption of kliuchevskoi volcano kamchatka russia for which measured maximum windspeed was 30 40 m s at about 12 km tephra fall patterns for some prehistoric eruptions of avachinsky volcano kamchatka and inyo craters ca usa are anomalously elongated and inconsistent with simple models of tephra dispersal in a constant windfield the avachinsky deposit is modeled well by bent using a windspeed that varies with height two potentially useful conclusions can be made about air routes and volcanic eruption plumes under jetstream conditions the first is that by taking advantage of the jetstream aircraft are flying within an airspace that is also preferentially occupied by volcanic eruption clouds and particles the second is that because eruptions with highly variable mass eruption rate pump volcanic particles into the jetstream under these conditions it is difficult to constrain the tephra grain size distribution and mass loading present within a downwind volcanic plume or cloud that has interacted with the jetstream furthermore anomalously large particles and high mass loadings could be present within the cloud if it was in fact formed by an eruption with a high mass eruption rate in terms of interpretation of tephra dispersal patterns the results suggest that extremely elongated isopach or isopleth patterns may often be the result of eruption into the jetstream and that estimation of the mass eruption rate from these elongated patterns should be considered cautiously

satellite and ground observations of the june 2009 eruption of sarychev peak volcano matua island central kuriles after 33 years of repose one of the most active volcanoes of the kurile island arc sarychev peak on matua island in the central kuriles erupted violently on june 11 2009 the eruption lasted 9 days and stands among the largest of recent historical eruptions in the kurile island chain satellite monitoring of the eruption using moderate resolution imaging spectroradiometer meteorological agency multifunctional transport satellite and advanced very high resolution radiometer data indicated at least 23 separate explosions between 11 and 16 june 2009 eruptive clouds reached altitudes of generally 8 16 km above sea level asl and in some cases up to 21 km asl clouds of volcanic ash and gas stretched to the north and northwest up to 1 500 km and to the southeast for more than 3 000 km for the first time in recorded history ash fall occurred on sakhalin island and in the northeast sector of the khabarovsky region russia based on satellite image analysis and reconnaissance field studies in the summer of 2009 the eruption produced explosive tephra deposits with an estimated bulk volume of 0 4 km3 the eruption is considered to have a volcanic explosivity index of 4 because the volcano is remote there was minimal risk to people or infrastructure on the ground aviation transport however was significantly disrupted because of the proximity of air routes to the volcano