differentiation of mesozoic basalts of the hartford basin connecticut the talcott oldest of the three basalts in the mesozoic hartford basin of connecticut contains abundant euhedral olivine and plagioclase phenocrysts and less common rounded augite plagioclase aggregates and orthopyroxene phenocrysts rimmed by augite and olivine the orthopyroxene which has a remarkably constant composition en 84 and is cr rich is believed to be a refractory residue from an upper mantle source region the holyoke basalt the middle unit is essentially aphyric with only minor plagioclase and olivine phenocrysts the hampden youngest of the three basalts contains abundant plagioclase and minor olivine and augite phenocrysts materials balance calculations using phenocryst compositions from the talcott basalt indicate that the holyoke can be derived from a talcott magma by addition of 7 8 orthopyroxene and removal of 7 9 olivine 15 clinopyroxene and 13 3 plagioclase the hampden basalt cannot be derived from a holyoke magma by any reasonable fractionation scheme but it can be derived from a talcott magma by removal of 4 4 olivine 12 0 clinopyroxene and 14 3 plagioclase one atmosphere melting experiments under controlled oxygen fugacities indicate successively lower liquidus temperatures for talcott holyoke and hampden basalts both the talcott and the holyoke have olivine and plagioclase on the liquidus simultaneously with augite and pigeonite appearing 15 c below the liquidus the hampden has plagioclase alone on the liquidus olivine and augite appear only 5 c below the liquidus orthopyroxene is not present in the low pressure experiments but is thought to have been stable on the liquidus at depths corresponding to pressures exceeding 8 kbar assimilation of orthopyroxene and crystallization of other phases necessary to produce the holyoke basalt from a talcott magma must have taken place at depth however because the low pressure phases obtained in the experiments are those required to produce the hampden from the talcott magma this fractionation likely occurred in a near surface magma chamber

synthesis and revision of groups within the newark supergroup eastern north america the newark supergroup currently includes nine stratigraphic groups each of which applies to part or all of the rock column of only one or a few basins because the group nomenclature within the newark supergroup is neither inclusive nor parallel in its concepts nearly half of the strata within the newark supergroup lacks any group placement a new system is proposed herein that 1 establishes unambiguous group boundaries 2 places all newark supergroup strata into groups 3 reduces the number of group names from nine to three 4 creates parallelism between groups and three major successive tectonic events that created the rift basins containing the newark supergroup and 5 coincidentally provides isochronous or nearly isochronous group boundaries these proposed groups are 1 the chatham group middle triassic to basal lower jurassic sedimentary rocks 2 the meriden group lower jurassic extrusive volcanic and sedimentary rocks and 3 the agawam group new name lower jurassic sedimentary rocks above all early mesozoic igneous intrusive and extrusive rocks this new rock classification system makes use of the fact that a discrete interval of synchronous or nearly synchronous volcanism and plutonism occurred throughout the early mesozoic rift system of eastern north america the presence or absence of volcanic rocks provides a powerful stratigraphic tool for establishing regional groups and group boundaries the presence of sedimentary rocks injected by diabase dikes and sills in the absence of extrusive volcanic rocks places newark supergroup rocks in the chatham group the presence of extrusive volcanic rocks interbedded with sedimentary rocks injected by diabase dikes and sills places newark supergroup rocks in the meriden group the presence of sedimentary rocks lacking both extrusive volcanic rocks and diabase dikes and sills places newark supergroup rocks in the agawam group application of this new regional group stratigraphy to the early mesozoic rift basins requires revision of the stratigraphy of several basins to make formation boundaries match group boundaries

emplacement of the 18 may 1980 lateral blast deposit ene of mount st helens washington facies variations east northeast of mount st helens preserve a record of depositional processes in the 18 may 1980 lateral blast cloud this paper reports new field grain size and component data from the ene sector of the timber blowdown zone and presents a model for blast flow and sedimentation the first erupted ejecta was rich in juvenile components and extends to the distal blowdown limit the last erupted ejecta was rich in accidental lithics and reached no further than a few kilometres from the mountain due to waning discharge the blast cloud was a turbulent stratified flow which transported and deposited sediment in the manner of a high density turbidity current the possibility that the blast was emplaced as a giant shearing fluidised bed is not favoured by compositional zoning patterns depositional conditions were strongly influenced by the rate of suspended load fallout from the blast within about 8 km from vent rapid sedimentation caused deposition under moderate to high concentration conditions and formation of a basal hindered settling zone able to detach gravitationally and drain into local depressions the resulting proximal facies resembles a low aspect ratio ignimbrite fines depletion in the proximal facies is attributed to a combination of residual turbulence and rapid gas escape during particle settling and compaction through the hindered settling zone component data suggest that the blast head played no significant role in the generation of fines depletion in the blast deposit as suggested by previous workers with increasing distance from vent the rate of particle fallout declined and sedimentation took place under increasingly dilute and tractional conditions building up antidune like bedforms wavelengths of these bedforms range from 20 to 1 m and decrease away from vent there is a systematic relationship between antidune migration direction and depositional slope the transition from proximal ignimbrite like to distal surge like facies suggests a possible gradation in transport and deposition processes between conventional pyroclastic surges and high velocity pyroclastic flows

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

dynamics of giant volcanic ash clouds from supervolcanic eruptions 1 the largest explosive volcanic eruptions that have occurred on earth generated giant ash clouds from rising plumes that spread in the stratosphere around a height of neutral buoyancy with estimated supply rates that are in the range 1011 to 1013 m3 s these giant ash clouds are controlled by a balance between gravity and coriolis forces forming spinning bodies of nearly fixed proportions after a few hours and are initially insensitive to stratospheric winds in contrast volcanic plumes from eruptions with small to intermediate magnitude spread as inertial intrusions under the influence of stratospheric winds with the earth s rotation being unimportant in the largest eruptions the giant spinning ash clouds typically develop diameters greater than 600 km and up to 6000 km in the most powerful super eruptions thus explaining why areas of continental size can be covered with volcanic ash the radial expansion and spinning velocities are calculated at tens of metres per second and increase with eruption intensity higher spreading velocities carry larger ash grain sizes to a given radius so that grain size at a given distance from the source increases with eruption intensity consistent with geological observations

mass partition during collapsing and transitional columns by using numerical simulations pyroclast dispersal and mass partition between convective and collapsing transport systems represent a major issue in the understanding of the dynamics of quasi steady explosive eruptions and the interpretation of their deposits the spatial and temporal dispersal of pyroclasts during the initial 15 min of collapsing and transitional columns was investigated by using a transient two dimensional and three phase one gas phase and two solid phases representative of pyroclasts of varying size and density flow model the different behaviors of the column were simulated by using different water contents of the eruptive mixture and assuming both pressure balanced and overpressured conditions at the vent for each simulation results allowed the quantification of the mass of pyroclasts of different size forming the pyroclastic density current the co ignimbrite column and the convective plumes rising from the proximal area and above the fountain for collapsing columns the total mass transported in the convective system composed of the plume above the fountain and the co ignimbrite column ranges from about 10 to 30 wt of the total erupted mass according to the specific water content of the mixture at the vent fine particles are dominant in this convective system with the increase of the water content the character of the column shows a collapsing buoyant transitional behavior such a regime is characterized by greater collapse height generation of more dilute density currents shorter flow runout less steady behavior of the column and intermittent feeding of the flows for these columns the total mass forming the convective portions reaches values of up to 50 wt of the erupted pyroclasts with a significant amount of coarse particles entrained in the convective plume above the fountain at higher water contents the column becomes fully buoyant with the whole mass feeding the convective column simulations assuming overpressured conditions at the vent are characterized by more unsteady dynamics of the dispersal process with significant variations in the collapse height of the column mass flow rate of the flow and amount of mass elutriated in the convective system simulation results suggest that plinian columns that undergo a transition from convective to collapsing regimes as a consequence in our case of a water content decrease in the magma but not necessarily limited to this case would be characterized by a gradual decrease of the carrying capacity of the convective column above the fountain and by the emplacement of pyroclastic density currents which evolve from dilute to dense gradually increasing their runout

pyroclastic flows from the 1991 eruption of unzen volcano japan pyroclastic flows from unzen were generated by gravitational collapse of the growing lava dome as soon as the parental lobe failed at the edge of the dome spontaneous shattering of lava occurred and induced a gravity flow of blocks and finer debris the flows had a overhanging tongue like head and cone or rollershaped vortices expanding outward and upward most of the flows traveled from 1 to 3 km but some flows reached more than 4 km burning houses and killing people in the evacuated zone of kita kamikoba on the eastern foot of the volcano the velocities of the flows ranged from 15 to 25 m s on the gentle middle flank observations of the flows and their deposits suggest that they consisted of a dense basal avalanche and an overlying turbulent ash cloud the basal avalanche swept down a topographic low and formed to tongue like lobe having well defined levees it is presumed to have moved as a non newtonian fluid the measured velocities and runout distances of the flows can be matched to a bingham model for the basal avalanche by the addition of turbulent resistance the rheologic model parameters for the 29 may flow are as follows the density is 1300 kg m3 the yield strength is 850 pa the viscosity is 90 pa s and the thickness of the avalanche is 2 m the ash cloud is interpreted as a turbulent mixing layer above the basal avalanche the buoyant portions of the cloud produced ash fall deposits whereas the dense portions moved as a surge separated from the parental avalanche the ash cloud surges formed a wide devastated zone covered by very thin debris the initial velocities of the 3 june surges when they detached from avalanches are determined by the runout distance and the angle of the energy line slope a comparison between the estimated velocities of the 3 june avalanches and the surges indicates that the surges that extended steep slopes along the avalanche path detached directly from the turbulent heads of the avalanches the over running surge that reached kita kamikoba had an estimated velocity higher than that of the avalanche this farther travelled surge is presumed to have been generated by collapse of a rising ash cloud plume

rheological changes induced by clast fragmentation in debris flows on the basis of rotating drum analogue experiments we describe a fragmentation process acting within debris flows during transport and its influence on rheologic behavior our hypothesis is based on a detailed textural analysis including granulometry clast morphology and rheologic properties of the fluid matrix results of the experiments point out that breakage of certain granulometric classes produces fine particles like fine sand and silt the population growth of fine clasts with time leads to an increase in yield strength and viscosity that progressively modifies the rheologic behavior from a textural point of view this is reflected in a bimodal granulometric distribution up to now this characteristic has been explained as the effect of bulking and or sedimentation processes during transport our experimental results show that the type of fragmentation depends on particle size and is the consequence of strong clast clast interaction and clast fluid interactions coarse particles develop small fractures which cause the loss of sharp edges and asperities medium sized particles develop through going fractures that cause them to break apart the latter process explains why intermediate granulometric classes progressively diminish with time in debris flows analogue experiments enable us to study the efficacy of clast fragmentation in modifying the textural character and flow behavior of debris flows without the influence of external factors such as erosion and sedimentation the obtained results constitute the base of a new approach for modeling debris flow dynamics

a geochemical investigation of fragmentation and physical fractionation in pyroclastic flows from the soufriere hills volcano montserrat abstract geochemical analysis is used to investigate fragmentation and physical fractionation in pyroclastic flows bulk analyses of the matrices

multi proxy dating the millennium eruption of changbaishan to late 946 ce ranking among the largest volcanic eruptions of the common era ce the millennium eruption of changbaishan produced a widely dispersed tephra layer known as the b tm ash which represents an important tie point for palaeoenvironmental studies in east asia hitherto there has been no consensus on its age with estimates spanning at least the tenth century ce here we identify the cosmogenic radiocarbon signal of 775 ce in a subfossil larch engulfed and killed by pyroclastic currents emplaced during the initial rhyolitic phase of the explosive eruption combined with glaciochemical evidence from greenland this enables us to date the eruption to late 946 ce this secure date rules out the possibility that the millennium eruption contributed to the collapse of the bohai kingdom manchuria korea in 926 ce as has previously been hypothesised further despite the magnitude of the eruption we do not see a consequent cooling signal in tree ring based reconstructions of northern hemisphere summer temperatures a tightly constrained date for the millennium eruption improves the prospect for further investigations of historical sources that may shed light on the eruption s impacts and enhances the value of the b tm ash as a chronostratigraphic marker

injection of gases into the stratosphere by explosive volcanic eruptions 1 explosive eruptions can inject large amounts of volcanic gases into the stratosphere these gases may be scavenged by hydrometeors within the eruption column and high uncertainties remain regarding the proportion of volcanic gases which eventually reach the stratosphere these are caused by the difficulties of directly sampling explosive volcanic eruption columns and by the lack of laboratory studies in the extreme parameter regime characterizing them using the nonhydrostatic nonsteady state plume model active tracer high resolution atmospheric model atham we simulated an explosive volcanic eruption we examined the scavenging efficiency for the climatically relevant gases within the eruption column the low concentration of water in the plume results in the formation of relatively dry aggregates more than 99 of these are frozen because of their fast ascent to low temperature regions consideration of the salinity effect increases the amount of liquid water by one order of magnitude but the ice phase is still highly dominant consequently the scavenging efficiency for hcl is very low and only 1 is dissolved in liquid water however scavenging by ice particles via direct gas incorporation during diffusional growth is a significant process the salinity effect increases the total scavenging efficiency for hcl from about 50 to about 90 the sulfur containing gases so2 and h2s are only slightly soluble in liquid water however these gases are incorporated into ice particles with an efficiency of 10 to 30 despite scavenging more than 25 of the hcl and 80 of the sulfur gases reach the stratosphere because most of the particles containing these species are lifted there sedimentation of the particles would remove the volcanic gases from the stratosphere hence the final quantity of volcanic gases injected in a particular eruption depends on the fate of the particles containing them which is in turn dependent on the volcanic and environmental conditions

hydrothermal alteration and diagenesis of terrestrial lacustrine pillow basalts coordination of hyperspectral imaging with laboratory measurements abstract we investigate an outcrop of 187 ma lacustrine pillow basalts of the talcott formation exposed in meriden connecticut usa focusing on coordinated analyses of one pillow lava to characterize the aqueous history of these basalts in the hartford basin this work uses a suite of multidisciplinary measurements including hyperspectral imaging other spectroscopic techniques and chemical and mineralogical analyses from the microscopic scale up to the scale of an outcrop the phases identified in the sample are albite large iron oxides and titanite throughout calcite in vesicles calcic clinopyroxene aegirine and fe mg bearing clay in the rind and fine grained hematite and pyroxenes in the interior using imaging spectroscopy the chemistry and mineralogy results extend to the hand sample and larger outcrop from all of the analyses we suggest that the pillow basalts were altered initially after emplacement either by heated lake water or magmatic fluids at temperatures of at least 400 600 c and the calcic clinopyroxenes and aegirine identified in the rind are a preserved record of that alteration as the hydrothermal system cooled to slightly lower temperatures clays formed in the rind and during this alteration the sample oxidized to form hematite in the matrix of the interior and fe 3 in the pyroxenes in the rind during the waning stages of the hydrothermal system calcite precipitated in vesicles within the rind later diagenetic processes albitized the sample with albite replacing plagioclase lining vesicles and accreting onto the exterior of the sample this albitization or na metasomatism occurred when the lake within the hartford basin evaporated during a drier past climatic era resulting in na rich brines as ca rich plagioclase altered to albite ca was released into solution eventually precipitating as calcite in previously unfilled vesicles dominantly in the interior of the pillow coordinated analyses of this sample permit identification of the alteration phases and help synthesize the aqueous history of pillow lavas of the talcott formation these results are also relevant to mars where volcanically resurfaced open basin lakes have been found and this hartford basin outcrop may be a valuable analog for any potential volcano lacustrine interactions the results can also help to inform the utility and optimization of potentially complementary synergistic and uniquely suited techniques for characterization of hydrothermally altered terrains

boundary layer fractionation constrained by differential information from the kutsugata lava flow rishiri volcano japan detailed investigation of an erupted magma with limited compositional diversity provides instantaneous information on incremental magma differentiation processes in a magma chamber kutsugata lava a suitable target of such study is a quaternary alkali basalt 51 3 53 2 wt in sio2 from rishiri volcano northern japan despite the narrow range in the whole rock compositional variation chemical and modal compositions of mineral phases crystallized in the magma chamber vary systematically with the whole rock composition in the north lava 51 3 51 9 wt in sio2 the less differentiated portion of the kutsugata lava most crystals which include low ni olivine and plagioclase were derived from the mushy boundary layer the main part of the magma body was principally aphyric 30 vol by such mechanisms as compaction and compositional convection this fractionated melt was mixed with the overlying main magma causing differentiation of the kutsugata magma the average temperature of the extracted melt is 1010 c significantly lower than 1100 c estimated for the main magma a quantitative model of magmatic differentiation which includes thermal and compositional evolution of a mushy boundary layer can successfully reproduce the observed compositional trends of the north lava

volcanic sulfate deposition to greenland and antarctica a modeling sensitivity study reconstructions of the atmospheric sulfate aerosol burdens resulting from past volcanic eruptions are based on ice core derived estimates of volcanic sulfate deposition and the assumption that the two quantities are directly proportional we test this assumption within simulations of tropical volcanic stratospheric sulfur injections with the maecham5 ham aerosol climate model an ensemble of 70 simulations is analyzed with so2 injections ranging from 8 5 to 700 tg with eruptions in january and july modeled sulfate deposition flux to antarctica shows excellent spatial correlation with ice core derived estimates for pinatubo and tambora although the comparison suggests the modeled flux to the ice sheets is 4 5 times too large we find that greenland and antarctic deposition efficiencies the ratio of sulfate flux to each ice sheet to the maximum hemispheric stratospheric sulfate aerosol burden vary as a function of the magnitude and season of stratospheric sulfur injection changes in simulated sulfate deposition for large so2 injections are connected to increases in aerosol particle size which impact aerosol sedimentation velocity and radiative properties the latter leading to strong dynamical changes including strengthening of the winter polar vortices which inhibits the transport of stratospheric aerosols to high latitudes the resulting relationship between antarctic and greenland volcanic sulfate deposition is nonlinear for very large eruptions with significantly less sulfate deposition to antarctica than to greenland these model results suggest that variability of deposition efficiency may be an important consideration in the interpretation of ice core sulfate signals for eruptions of tambora magnitude and larger

differential so2 column measurements of the mt pinatubo volcanic plume differential so2 column measurements of the mt pinatubo volcanic plume were made from a nasa electra aircraft flying in the caribbean in july 1991 the mean column content of the volcanic plume in the caribbean was 25 atm m 2 5 dobson units with periods of over 100 atm m observed the data indicate that an aerosol absorption or scattering effect occurs for long slant paths low sun elevation angles and 41 atm m an average obtained for 1 2 airmasses may be more representative of a true column average dispersion of the initial cloud from mt pinatubo and a one month so2 to sulfate conversion time constant are in good agreement with the column contents found here

the vol calpuff model for atmospheric ash dispersal 2 application to the weak mount etna plume of july 2001 1 here the application of the vol calpuff model by barsotti et al to a weak plume erupted from mount etna in july 2001 is presented and discussed the reconstruction of the explosive event was obtained by using high resolution weather forecasts produced by a mesoscale nonhydrostatic model and volcanic source data coming from observations and analytical studies the plume rise and atmospheric dispersal models were investigated over 5 d of eruption mostly in terms of column height aerial ash concentration and ground deposition modeling results are shown as a function of various source conditions and compared to independent observations derived from satellite images and deposit mapping the application of vol calpuff clearly highlights the crucial role played by meteorological conditions in determining dispersal dynamics some of the most important effects described by the model are 1 the large wind field influence on the plume height determination and tilting 2 the contrasting dispersal patterns of ash particles of different sizes 3 the complex and somehow nonintuitive distribution of ash on the ground resulting in preferential directions of dispersal and quite irregular deposit patterns and 4 the impossibility to reproduce both the column height and the deposit accumulation pattern by adopting a steady state vent mass flow rate over the investigated 4 d period due to observed temporal changes in eruption dynamics modeling results also suggest the need for further integration of simulation outcomes with remote sensing and field reconstructions on ash dispersal processes in future

particle sedimentation and diffusive convection in volcanic ash clouds 1 understanding the longevity of volcanic ash clouds generated by powerful explosive eruptions is a long standing problem for assessing volcanic hazards and the nature and time scale of volcanic forcings on climate change it is well known that the lateral spreading and longevity of these clouds is influenced by stratospheric winds particle settling and turbulent diffusion observations of the recent 2010 eyjafjallajokull and 2011 grimsvotn umbrella clouds as well as the structure of atmospheric aerosol clouds from the 1991 mt pinatubo event suggest that an additional key process governing the cloud dynamics is the production of internal layering here we use analog experiments on turbulent particle laden umbrella clouds to show that this layering occurs where natural convection driven by particle sedimentation and the differential diffusion of primarily heat and fine particles give rise to a large scale instability where umbrella clouds are particularly enriched in fine ash this particle diffusive convection strongly influences the cloud longevity more generally cloud residence time will depend on fluxes due to both individual settling and diffusive convection we develop a new sedimentation model that includes both sedimentation processes and which is found to capture real time measurements of the rate of change of particle concentration in the 1982 el chichon 1991 mt pinatubo and 1992 mt spurr ash clouds a key result is that these combined sedimentation processes enhance the fallout of fine particles relative to expectations from individual settling suggesting that particle aggregation is not the only mechanism required to explain volcanic umbrella longevity

stratigraphic record of the early mesozoic breakup of pangea in the laurasia gondwana rift system rift basins of the central atlantic margins cam of north america and morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early mesozoic the best known is the newark basin of new jersey new york and pennsylvania where an astronomically calibrated magnetic polarity time scale is developed lacustrine cycles of milankovitch origin are commonly present in cam basins with the period changing from 10 ky paleoequator with coals to 20 ky 4 10n to perhaps 40 ky northward with evaporites cycles of100 ky 413 ky and2 my are also important four mostly unconformity bounded tectonostratigraphic sequences are present the anisian ts i is fluvial and eolian ts ii ts iv late triassic to early jurassic consist of tripartite lacustrine sequences caused by extension pulses the newark basin accumulation rate history allows comparison with quantitative rift basin models the north american plate s slow northward drift resulted in a relative shift of climate although the rapid humidification during the latest triassic and early jurassic is associated with a sea level rise the triassic jurassic mass extinction is of independent origin plausibly impact related

experimental study of turbulence sedimentation and coignimbrite mass partitioning in dilute pyroclastic density currents abstract laboratory density currents comprising warm talc powder turbulently suspended in air simulate many aspects of dilute pyroclastic density currents pdcs and demonstrate links between bulk current behavior sedimentation and turbulent structures the densimetric and thermal richardson froude stokes and settling numbers match those of natural pdcs as does the ratio of thermal to kinetic energy density the experimental currents have lower bulk reynolds numbers than natural pdcs but the experiments are fully turbulent consequently the experiments are dynamically similar to the dilute portions of some natural currents in general currents traverse the floor of the experimental tank sedimenting particles and turbulently entraining heating and thermally expanding air until all particle sediments or the currents become buoyant and lift off to form coignimbrite plumes when plumes form currents often undergo local flow reversals current runout distance and liftoff position decrease with increasing densimetric richardson number and thermal energy density as those parameters increase total sedimentation decreases such that 50 of initial current mass commonly fractionates into the plumes in agreement with some observations of recent volcanic eruptions sedimentation profiles are best described by an entraining sedimentation model rather than the exponential fit resulting from non entraining box models time series analysis shows that sedimentation is not a constant rate process in the experiments but rather occurs as series of sedimentation erosion couplets that propagate across the tank floor tracking current motion and behavior during buoyant liftoff sedimentation beneath the rising plumes often becomes less organized auto correlation analysis of time series of particle concentration is used to characterize the turbulent structures of the currents and indicates that currents quickly partition into a slow moving upper portion and faster more concentrated lower portion air entrainment occurs within the upper region turbulent structures within the lower region track sedimentation erosion waves and indicate that eddies control deposition importantly both eddies and sedimentation waves track reversals in flow direction that occur following buoyant liftoff further these results suggest that individual laminations within pdc deposits may record passage of single eddies thus the duration of individual pdcs may be estimated as the product of the number of laminations and the current s turbulent timescale

a laboratory study of explosive volcanic eruptions this paper describes a series of laboratory experiments in which buoyant mixtures of methanol and ethylene glycol meg are injected as a downward propagating jet into a tank of fresh water as the meg mixes with water it becomes denser than the water if the meg mixes with sufficient water before its initial momentum is exhausted the jet fluid may become dense and continue downward into the tank as a convecting plume if the jet does not have sufficient initial momentum then a collapsing fountain develops and the material in the jet rises back toward the top of the tank and spreads laterally as a gravity current subsequent mixing can cause some of the material in the gravity current to become dense separate from the current and sink into the tank although the direction of gravity is reversed these experiments simulate many of the important dynamical features of eruption columns which can develop during explosive volcanic eruptions in the volcanic situation a hot dense and dusty mixture of gas ash and clasts is erupted from a vent at high speed if sufficient ambient air is entrained into the jet then the mixture may become buoyant through heating and expansion of the air it therefore continues rising high into the atmosphere otherwise the material collapses back to the ground these experiments allow one to investigate systematically the different styles of behavior of the erupted material as the eruption conditions change four different styles of behavior have been identified with transitions from one style to the next as the initial momentum flux of the jet is decreased 1 plinian style convecting columns 2 the periodic release of discrete convecting clouds originating close to the vent from a collapsed fountain 3 coignimbrite eruption columns centered some distance from the vent which are generated when a fraction of a pyroclastic flow becomes buoyant and 4 pyroclastic flows in which the majority of the material remains relatively dense and therefore spreads laterally from the vent using a simple theoretical model of the laboratory experiments an analytical expression describing the conditions necessary for collapse of the analogue laboratory columns has been derived this is successfully compared with the laboratory experiments the simple analysis predicts that column collapse may be induced by 1 increasing the density of the erupted material 2 decreasing the maximum buoyancy the mixture can attain on mixing with ambient 3 increasing the erupted mass flux for a given momentum flux or 4 decreasing the initial momentum flux for a given mass flux as may occur if the vent is eroded these results are consistent with earlier studies wilson et al 1980 wilson and walker 1987 bursik and woods 1991 although the analogue experimental system is somewhat simplified the observations of the periodic release of convecting thermals just after column collapse suggest a mechanism for the complex grading which is commonly found just below the collapse horizons in fall deposits for example the fogo a deposit walker and croasdale 1970 and the vesuvius a d 79 deposit carey and sigurdsson 1987 in conjunction with partial column collapse this periodicity also suggests a means by which flow deposits may become interspersed with fall deposits this feature has been observed in a number of cases including the taupo deposit wilson and walker 1985

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

applying the three dimensional model atham to volcanic plumes dynamic of large co ignimbrite eruptions and associated injection heights for volcanic gases 1 many of the past large volcanic eruptions like tambora in 1815 krakatau in 1835 and pinatubo in 1991 were secondary so called co ignimbrite eruptions that were forced over a large area instead of a point source as in the plinian case previous modeling studies were based on one dimensional plume models we used the fully three dimensional plume model atham active tracer high resolution atmospheric model to investigate the dynamics and the resulting plume heights of co ignimbrite eruptions in an idealized setup ash particles as well as a sulfur dioxide so2 tracer are included in the model in the analysis we focus on the behavior of so2 since the neutral buoyancy height is an ill defined parameter for gravitationally settling particles in contrast to plinian plumes the co ignimbrite plumes develop from multiple updrafts resulting in significantly reduced neutral buoyancy heights at least a two dimensional modeling framework is necessary to capture the relevant dynamical features

a review of tephra transport and dispersal models evolution current status and future perspectives abstract tephra transport models try to predict atmospheric dispersion and sedimentation of tephra depending on meteorology particle properties and eruption characteristics defined by eruption column height mass eruption rate and vertical distribution of mass models are used for different purposes from operational forecast of volcanic ash clouds to hazard assessment of tephra dispersion and fallout the size of the erupted particles a key parameter controlling the dynamics of particle sedimentation in the atmosphere varies within a wide range largest centimetric to millimetric particles fallout at proximal to medial distances from the volcano and sediment by gravitational settling on the other extreme smallest micrometric to sub micrometric particles can be transported at continental or even at global scales and are affected by other deposition and aggregation mechanisms different scientific communities had traditionally modeled the dispersion of these two end members volcanologists developed families of models suitable for lapilli and coarse ash and aimed at computing fallout deposits and for hazard assessment in contrast meteorologists and atmospheric scientists have traditionally used other atmospheric transport models dealing with finer particles for tracking motion of volcanic ash clouds and eventually for computing airborne ash concentrations during the last decade the increasing demand for model accuracy and forecast reliability has pushed on two fronts first the original gap between these different families of models has been filled with the emergence of multi scale and multi purpose models second new modeling strategies including for example ensemble and probabilistic forecast or model data assimilation are being investigated for future implementation in models and or modeling strategies this paper reviews the evolution of tephra transport and dispersal models during the last two decades presents the status and limitations of the current modeling strategies and discusses some emergent perspectives expected to be implemented at operational level during the next few years improvements in both real time forecasting and long term hazard assessment are necessary to loss prevention programs on a local regional national and international level

multiphase flow numerical modeling of the 18 may 1980 lateral blast at mount st helens usa volcanic lateral blasts are among the most spectacular and devastating of natural phenomena but their dynamics are still poorly understood here we investigate the best documented and most controversial blast at mount st helens washington state united states on 18 may 1980 by means of three dimensional multiphase numerical simulations we demonstrate that the blast front propagation final runout and damage can be explained by the emplacement of an unsteady stratified pyroclastic density current controlled by gravity and terrain morphology such an interpretation is quantitatively supported by large scale observations at mount st helens and will influence the definition and predictive mapping of hazards on blast dangerous volcanoes worldwide

uncertainty quantification and sensitivity analysis of volcanic columns models results from the integral model plume mom the behavior of plumes associated with explosive volcanic eruptions is complex and dependent on eruptive source parameters e g exit velocity gas fraction temperature and grain size distribution it is also well known that the atmospheric environment interacts with volcanic plumes produced by explosive eruptions in a number of ways the wind field can bend the plume but also affect atmospheric air entrainment into the column enhancing its buoyancy and in some cases preventing column collapse in recent years several numerical simulation tools and observational systems have investigated the action of eruption parameters and wind field on volcanic column height and column trajectory revealing an important influence of these variables on plume behavior in this study we assess these dependencies using the integral model plume mom whereby the continuous polydispersity of pyroclastic particles is described using a quadrature based moment method an innovative approach in volcanology well suited for the description of the multiphase nature of magmatic mixtures application of formalized uncertainty quantification and sensitivity analysis techniques enables statistical exploration of the model providing information on the extent to which uncertainty in the input or model parameters propagates to model output uncertainty in particular in the framework of the iavcei commission on tephra hazard modeling inter comparison study plume mom is used to investigate the parameters exerting a major control on plume height applying it to a weak plume scenario based on 26 january 2011 shinmoe dake eruptive conditions and a strong plume scenario based on the climatic phase of the 15 june 1991 pinatubo eruption

millimeter scale modal layering and the nature of the upper solidification zone in thick flood basalt flows and other sheets of magma abstract water flooding the surface of the holyoke flood basalt flow of connecticut and massachusetts was probably responsible for its entablature developing quench textures to depths of 80 m beneath the flow s surface despite the rapid cooling from above the entablature colonnade boundary is displaced above the center of the flow which can only mean that crystal mush sank from the roof zone to the floor of the flow during solidification the entablature of the holyoke flow exhibits a subtle quasi horizontal millimeter scale modal layering with sheets of ophitic pyroxene plagioclase clusters alternating with discontinuous sheets of residual liquid the layering is believed to have formed by repeated nucleation of pyroxene plagioclase clusters in a rapidly advancing thermal boundary layer the alternating layers of crystals and residual liquid produced a mush with planes of weakness along which the dense crystal mush could separate from the roof the layering parallels the cuspate entablature colonnade boundary which must therefore be a primary magmatic feature rather than simply where downward and upward propagating fractures met the modal layering has been found in other flood basalt flows but also in the roof zone of the palisades sill this texture may therefore be common in the roof zones of many sheet like bodies of magma

hydraulics of the august 7 1980 pyroclastic flow at mount st helens washington open channel hydraulic theory for flow of an inviscid fluid down a channel of changing slope and width yields a longitudinal velocity profile that matches measured velocities of the august 7 1980 pyroclastic flow at mount st helens the model is useful for prediction of zones of erosion deposition and hazards it requires only topographic data estimates of volumetric flow rate and a manning coefficient appropriate for the channel

computer simulation of transport and deposition of the campanian y 5 ash analyses of grain size and modal composition of the campanian tuff ash layer y 5 from 11 deep sea cores have been carried out this layer represents ash fall that has been correlated with the 38 000 y b p campanian ignimbrite thunell et al 1979 a deposit formed by the largest eruption documented in the mediterranean region during the late pleistocene barberi et al 1978 the bulk deposit is bimodal in grain size and dominated by glass shards the calculated mean grain size of the coarse mode of the individual size distributions decreases with distance from the source and progressively approaches a near constant fine mode of approximately 13 microns distal samples are unimodal in grain size these data combined with a set of vertical profiles of wind 10 year average have been used as input to a computer model that simulates fallout of tephra modelling indicates that the downwind variation of grain size of the coarse mode can be accurately reproduced with transport of ash between 5 and 35 km the observed fine mode of the deposit cannot however be generated by transport of ash as individual particles at these elevations such transport would result in deposition of virtually all of the fine ash beyond the studied area deposition of fine ash within the studied distance of 1600 km from source can only occur by fallout as particle aggregates from a high eruption plume or as individual particles from co ignimbrite ash clouds with a maximum elevation of 3 km the large volume of ash in the fine mode 70 wt and the irregularity in azimuth of low level winds argue against major low level transport of co ignimbrite ash rather the ash may have been derived from both a plinian eruption column and high altitude clouds of co ignimbrite ash with settling of fine ash as particle aggregates

crystal mush compaction and the origin of pegmatitic segregation sheets in a thick flood basalt flow in the mesozoic hartford basin connecticut

stratified flow in pyroclastic surges stratified flow theory is applied to pyroclatic surges in an effort to gain insight into transport dynamics during explosive eruptions particle transport is assumed to be by turbulent suspension and calculations contained herein show that this is likely for many cases including the 18 may 1980 blast at mount st helens the discussion centers on the rouse number pn which represents a ratio of particle settling velocity to scale of turbulence the brunt vaisala frequency n which is the maximum possible frequency of internal waves the froude number fr representing the ratio of inertial forces to gravitational forces and the richardson number ri a ratio of buoyant restoring forces to turbulent mixing forces the velocity or flow power dependence of bed form wavelength in surge deposits is related to a velocity dependence of wavelength of internal waves in the turbulent surge this produces a decrease in dune wavelength with increasing distance from vent migration direction of bed forms is related tofr as it is defined for a continuously stratified flow proximal to distal facies variations in surge deposits reflect increasingpn andri as the flows move away from their sources this produces the progression from sandwave to massive to planar facies with increasing distance from vent where the long axis of topography is at low angles to the flow direction massive facies in topographic lows may from concurrently with sandwave facies on highs due to the higher particle concentration in the lows where long axis of topography is at high angles to flow direction denser lower parts of the surge may be dammed or blocked blocked material tends to form massive flows that may move down slope independent of the overriding surge a model incorporating turbulent transport stratified flow and time evolution of pyroclastic surges is proposed for deposits which have been attributed to both pyroclastic flow and pyroclastic surge transport by various workers during the initial high energy waxing phase of the eruptive event pn is sufficiently low that only coarse but poorly sorted material is deposited to form relatively coarse bottom layers as the event wanes remaining finer material is deposited through a thin bed load to produce overlying bedded and cross bedded veneer deposits throughout most of the event blocking occurs to produce relatively thick and massive deposits in valley bottoms

paleomagnetism and k ar isochron dates of early jurassic basaltic flows and dikes of atlantic canada k ar isochron dates of 193 2 189 3 and 191 2 ma are reported for the shelburne dike of nova scotia the avalon dike of newfoundland and the caraquet dike of new brunswick respectively these major tholeiitic dikes agree in radiometric date with the north mountain basalt of nova scotia and with other tholeiitic flows of the newark supergroup that have been paleontologically assigned to the hettangian however further work is needed to resolve the discrepancy between the triassic jurassic boundary date of 193 6 ma suggested by the newark supergroup flows and the boundary dates of 204 213 ma adopted in recent time scales the north mountain basalt flows at nine sites on the north shore of the bay of fundy are shown to have likely magnetized during initial cooling yielding an hettangian virtual paleopole at 66 n 72 e dp 9 dm 14 new paleomagnetic results are also reported for the caraquet and avalon dikes the virtual paleopoles from hettangian flows and dikes of atlantic canada lie on a

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

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

insights into the formation and dynamics of coignimbrite plumes from one dimensional models coignimbrite plumes provide a common and effective mechanism by which large volumes of fine grained ash are injected into the atmosphere nevertheless controls on formation of these plumes as a function of eruptive conditions are still poorly constrained herein two 1 d axysymmetric steady state models were coupled the first describing the parent pyroclastic density current and the second describing plume rise global sensitivity analysis is applied to investigate controls on coignimbrite plume formation and describe coignimbrite source and the maximum plume height attained for a range of initial mass flow rates between 108 and 1010 kg s modeled liftoff distance the distance at which neutral buoyancy is attained assuming radial supercritical flow is controlled by the initial flow radius gas mass fraction flow thickness and temperature the predicted decrease in median grain size between flow initiation and plume liftoff is negligible calculated initial plume vertical velocities assuming uniform liftoff velocity over the pyroclastic density current invasion area are much greater several tens of m s than those previously used in modeling coignimbrite plumes 1 m s such velocities are inconsistent with the fine grain size of particles lofted into coignimbrite plumes highlighting an unavailability of large clasts possibly due to particle segregation within the flow prior to plume formation source radius and initial vertical velocity have the largest effect on maximum plume height closely followed by initial temperature modeled plume heights are between 25 and 47 km comparable with plinian eruption columns highlighting the potential of such events for distributing fine grained ash over significant areas

mt st helens evidence of increased magmatic gas component abstract this paper presents measurements of so 2 flux and ash leachate chemistry from mt st helens volcano during the period may 18 to july 22 which are in contrast to similar data from before may 18 comparison of post 18 may so 2 data with similar data from other volcanoes leads to the conclusion that between 15 and 25 may the so 2 flux reached typical magmatic levels ash leachate chemistry from the eruption of 18 may 22 june and 22 july also indicate a large magmatic gas component concentrations of cl and so 2 4 on may 18 ash increase with distance from the volcano and decrease with time leachate chemistry is used to estimate that a minimum of 2 4 10 5 tons of s were released on may 18 low f concentrations on the ash though increasing present to health hazards

a laboratory simulation of pyroclastic flows down slopes abstract laboratory experiments are described which explore the dynamical consequences of buoyant convective upflow observed above hot pyroclastic flows in nature the convection is produced by the hot ash particles exchanging heat with air mixed into the front and top of the pyroclastic flow this effect on the buoyancy due to the mixing of air and ash has been modelled in the laboratory using mixtures of methanol and ethylene glycol meg which have a nonlinear density behaviour when mixed with water intermediate mixtures of these fluids can be denser than either initial component and so the laboratory experiments were inverted models of the natural situation we studied meg flowing up under a sloping roof in a tank filled with water the experiments were performed both in a narrow channel and on a laterally unconfined slope the flow patterns were also compared with those of conventional gravity currents formed using fresh and salt water the presence of the region of reversed buoyancy outside the layer flowing along the slope had two significant effects first it periodically protected the flow from direct mixing with the environment resulting in pulses of relatively undiluted fluid moving out intermittently ahead of the main flow second it produced a lateral inflow towards the axis of the current which kept the current confined to a narrow tongue even on a wide slope in pyroclastic flows the basal avalanche portion has a much larger density contrast with its surroundings than the laboratory flows calculations show that mixing of air into the dense part of a pyroclastic flow cannot generate a mixture that is buoyant in the atmosphere however the overlying dilute ash cloud can behave as a gravity current comparable in density contrast to the laboratory flows and can become buoyant depending on the temperature and ash content in the august 7th pyroclastic flow of mount st helens hoblitt 1986 describes pulsations in the flow front which are reminiscent of those observed in the experiments as proposed by hoblitt the pulsations are caused by the ash cloud accelerating away from the front of the dense avalanche as a density current the ash cloud then mixes with more air becomes buoyant and lifts off the ground allowing the avalanche to catch up with and move ahead of the cloud the pulsing behaviour at the fronts of pyroclastic flows could account for the occurrence of cross bedded layer 1 deposits which occur beneath layer 2 deposits in many sequences

modern coccolithophore and carbonate sedimentation along a productivity gradient in the canary islands region seasonal export production and surface accumulation rates abstract coccolithophores one of the main primary and carbonate producers in the surface waters of the canary islands region were investigated to quantify coccolith and coccolith carbonate export fluxes and to determine possible trends in species composition related to different productivity conditions present day fluxes were compared to the long term records of coccolith and carbonate accumulation in holocene sediments underneath the mooring locations coccolithophore flux variations in sediment traps at three stations along an e w transect at approximately 29 n from the upwelling influenced north west african shelf region to the open ocean were recorded from january to september 1997 total coccolith fluxes along the studied transect were highly seasonal with pronounced sedimentation events occurring in february upper traps and march deep traps related to the winter phytoplankton bloom in surface waters while total coccolith flux rates and fluxes of different species at the two oceanic sites lp and estoc were comparable mean 6 4 and 5 4 10 8 coccoliths m 2 d 1 fluxes increased significantly towards the shallower site ebc mean 13 7 10 8 coccoliths m 2 d 1 this gradient points to increased productivity in surface waters at the near shore station probably associated with nutrient rich upwelling filaments detaching from the coast and or the easternmost islands additionally a strong influence of laterally advected coccolith rich material was demonstrated for the deeper sediment traps at the two offshore sites resulting in an increase of mean daily coccolith fluxes by a factor 3 lp and by a factor 2 estoc respectively estimated coccolith carbonate fluxes along the transect were 2 8 g m 2 ebc and 1 2 1 3 g m 2 estoc lp in the upper traps representing 31 33 of the total annual carbonate flux the coccolith carbonate supply was higher in the deeper traps with 63 at lp and 44 at estoc respectively average holocene coccolith and coccolith carbonate accumulation rates derived from surface samples at the mooring locations generally confirm the sediment trap results discrepancies mainly result from near bottom and down slope particle transfer processes which especially influence the site closer to the shelf dissolution processes are likely to affect primarily the deep sediments at the oligotrophic site lp the diverse subtropical coccolithophore assemblages were quite similar in all sediment trap samples from the three mooring sites with three species emiliania huxleyi florisphaera profunda gephyrocapsa ericsonii contributing significantly to the assemblage despite the good correspondence between the assemblage compositions along the transect some trends towards the upwelling influenced site ebc could be observed whereas all gephyrocapsa species mainly g ericsonii respond positively to higher productivity conditions at the near shore station calcidiscus leptoporus and the deep photic zone species f profunda increased in mean relative abundances towards the two offshore sites pointing to a preference for the more stable oligotrophic conditions of the subtropical gyre

pyflow_2 0 a computer program for calculating flow properties and impact parameters of past dilute pyroclastic density currents based on field data this paper presents pyflow 2 0 a hazard tool for the calculation of the impact parameters of dilute pyroclastic density currents dpdcs dpdcs represent the dilute turbulent type of gravity flows that occur during explosive volcanic eruptions their hazard is the result of their mobility and the capability to laterally impact buildings and infrastructures and to transport variable amounts of volcanic ash along the path starting from data coming from the analysis of deposits formed by dpdcs pyflow 2 0 calculates the flow properties e g velocity bulk density thickness and impact parameters dynamic pressure deposition time at the location of the sampled outcrop given the inherent uncertainties related to sampling laboratory analyses and modeling assumptions the program provides ranges of variations and probability density functions of the impact parameters rather than single specific values from these functions the user can interrogate the program to obtain the value of the computed impact parameter at any specified exceedance probability in this paper the sedimentological models implemented in pyflow 2 0 are presented program functionalities are briefly introduced and two application examples are discussed so as to show the capabilities of the software in quantifying the impact of the analyzed dpdcs in terms of dynamic pressure volcanic ash concentration and residence time in the atmosphere the software and user s manual are made available as a downloadable electronic supplement

plagioclase chain networks in slowly cooled basaltic magma plagioclase crystals in the slowly cooled interior of the thick holyoke flood basalt flow of connecticut linked to form monomineralic chains at an early crystallization stage partial melting experiments reveal that when the quartz tholeiite was only 25 crystallized the chains had already linked to form a continuous 3 d network at such an early stage of crystallization the network was weak highly permeable and easily deformed consequently the mush of plagioclase chains and interstitial pyroxene crystals underwent compaction in the lower third of the flow with the expelled liquid rising to the center of the flow where it crystallized to form coarse grained sheets of fractionated basalt plagioclase chains are most easily seen in the basalt after it has been partly melted and the late crystallizing minerals converted to glass the chains are several crystals wide the crystals which are approximately 0 5 mm long are attached together randomly normal zoning patterns indicate crystals had a brief period of growth before linking together the chains branch every few millimeters to form the 3 d network which was mapped using serial polished sections and x ray ct scans the chain frequency measured along vertical and horizontal traverses decreases toward the center of the flow in the compaction zone the frequency in the vertical direction is greater than in the horizontal making the reasonable assumption that these frequencies were initially the same the difference is used to calculate the degree of compaction the resulting pattern through the flow matches almost exactly the pattern indicated by variations in the incompatible elements plagioclase chains are also found in some coarser grained plutonic rocks if they are common their fabric may provide a new direct means of measuring the degree of compaction in crystal mushes

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

use of motion estimation algorithms for improved flux measurements using so 2 cameras abstract article history received 3 april 2014accepted 18 august 2014available online xxxxkeywords so 2 uxso 2 cameraplume speedplume modellingoptical owmotion estimation so 2 cameras are rapidly gaining popularity as a tool for monitoring so 2 emissions from volcanoes severaldifferent so 2 camera systems have been developed with varying patterns of image acquisition in space timeand wavelength despite this diversity there are two steps common to the work owsofmostofthesesystems aligning images of different wavelengths to calculate apparent absorbance and estimating plume transportspeeds both of which can be achieved using motion estimation algorithms here we present two suchalgorithms adualtreecomplexwavelettransform basedalgorithmandthefarnebackopticalflowalgorithm weassesstheiraccuracyusingasyntheticdatasetcreatedusingthenumericcloud resolvingmodelatham andthen apply them to real world data from villarrica volcano both algorithms are found to perform well and theatham simulations offer useful datasets for benchmarking and validating future algorithms 2014 the authors published by elsevier b v this is an open access article under the cc by license http creativecommons org licenses by 3 0

volcan reventador s unusual umbrella 1 photographs of a volcanic column in a recent eruption of reventador show a prominently scalloped umbrella that is unlike any umbrella previously documented on a volcanic column we propose that the scallops in this umbrella are the result of a turbulent rayleigh taylor rt instability a type of fluid instability with no precedents in volcanology negative buoyancy drives this instability and we ascribe the unusual negative buoyancy of the reventador umbrella to the fact that the reventador column fed on a cool co ignimbrite cloud from the wavelength of the scallops we estimate a value for the eddy viscosity of the umbrella d 4 000 m2 s the first such value to be inferred directly from an observation in the field collapse of the umbrella back to the ground could result in a previously unrecognized hazardous flow we hope this work will elicit new reports on scalloped umbrellas and further study of the characteristics and evolution of such umbrellas

explosive energy during volcanic eruptions from fractal analysis of pyroclasts abstract despite recent advances by means of experiments and high resolution surveys and the growing understanding of the physical processes before and during volcanic eruptions duration and type of eruptive activity still remain highly unpredictable this uncertainty hinders appropriate hazard and associated risk assessment tremendously in an effort to counter this problem experimentally generated pyroclasts have been studied by fractal statistics with the aim of evaluating possible relationships between eruption energy and fragmentation efficiency rapid decompression experiments have been performed on three differently porous sample sets of the 1990 1995 eruption of unzen volcano japan at 850 c and at initial pressure values above the respective fragmentation threshold u kueppers b scheu o spieler d b dingwell fragmentation efficiency of explosive volcanic eruptions a study of experimentally generated pyroclasts j volcanol geotherm res 153 2006 125 135 o spieler b kennedy u kueppers d b dingwell b scheu j taddeucci the fragmentation threshold of pyroclastic rocks epsl 226 2004 139 148 the size distribution of generated pyroclasts has been studied by fractal fragmentation theory and the fractal dimension of fragmentation df a value quantifying the intensity of fragmentation has been measured for each sample results show that size distribution of pyroclastic fragments follows a fractal law i e power law in the investigated range of fragment sizes indicating that fragmentation of experimental samples reflects a scale invariant mechanism in addition df is correlated positively with the potential energy for fragmentation pef while showing a strong influence of the open porosity of the samples results obtained in this work indicate that fractal fragmentation theory may allow for quantifying fragmentation processes during explosive volcanic eruptions by calculating the fractal dimension of the size distribution of pyroclasts it emerges from this study that fractal dimension may be utilised as a proxy for estimating the explosivity of volcanic eruptions by analysing their natural pyroclastic deposits

textural and chemical variation in plagioclase phenocrysts from the 1980 eruptions of mount st helens usa this study presents major and trace element chemistry of plagioclase phenocrysts from the 1980 eruptions of mount st helens volcano despite the considerable variation in textures and composition of plagioclase phenocrysts distinct segments have been cross correlated between crystals the variation of sr and ba concentration in the melt as calculated from the concentration in the phenocrysts using partition coefficients suggests the cores and rims crystallised from compositionally different melts offset by the plagioclase crystallisation vector in both of these melts sr and ba are correlated despite the abundance of plagioclase in the 1980 dacites we propose that rapid crystallisation of plagioclase upon magma ascent caused a shift in melt composition towards lower sr and higher ba as documented in the rims of the phenocrysts although the cores of the phenocrysts crystallised at relatively shallow depths they preserve the sr and ba of the deep seated melts as they ascended from a deeper region further magma ascent resulted in microlite nucleation which is responsible for a similar shift to even lower sr concentration as observed in the groundmass of post 18 may 1980 samples

ascent dynamics of large phreatomagmatic eruption clouds the role of microphysics 1 we examine the impact of abundant surface water interaction on the development of volcanic clouds from large scale 108 kg s 1 magma phreatomagmatic eruptions presenting the first 2 d large eddy simulations of wet volcanic plumes that incorporate the effects of microphysics the active tracer high resolution atmospheric model was forced with field derived inputs from an exceptionally large phreatomagmatic eruption the 27 ka oruanui supereruption taupo volcano new zealand surface water contents were varied from 0 to 40 wt for eruptions with equivalent magma eruption rates of 1 3 108 and 1 1 109 kg s 1 our findings confirm that increased surface water has a pronounced impact on column stability leading to transitional column behavior and hybrid clouds resulting from simultaneous ascent of material from stable columns and pyroclastic density currents pdcs contrary to the suggestion of previous workers however abundant surface water does not systematically lower the spreading level or maximum height of volcanic clouds owing to vigorous microphysics assisted lofting of pdcs the simulated behavior and ash cloud dimensions provide a close match to field evidence from the oruanui case study cloud heights from the collapsing eruption columns also show a notable sensitivity to changes in the altitude of the tropopause while ambient humidity primarily impacts the abundance of airborne hydrometeors particularly ice associated with the volcanic clouds general relationships between eruption style meteorological conditions and the resulting vertical profiles of volcanic emissions outlined here could also be adapted for use in operational volcanic ash forecasting and deposit reconstruction techniques already in existence

new early jurassic tetrapod assemblages constrain triassic jurassic tetrapod extinction event the discovery of the first definitively correlated earliest jurassic 200 million years before present tetrapod assemblage fundy basin newark supergroup nova scotia allows reevaluation of the duration of the triassic jurassic tetrapod extinction event present are tritheledont and mammal like reptiles prosauropod theropod and ornithischian dinosaurs protosuchian and sphenosuchian crocodylomorphs sphenodontids and hybodont semionotid and palaeonisciform fishes all of the families are known from late triassic and jurassic strata from elsewhere however pollen and spore radiometric and geochemical correlation indicate an early hettangian age for these assemblages because all typical triassic forms are absent from these assemblages most triassic jurassic tetrapod extinctions occurred before this time and without the introduction of new families as was previously suggested by studies of marine invertebrates this pattern is consistent with a global extinction event at the triassic jurassic boundary the manicouagan impact structure of quebec provides dates broadly compatible with the triassic jurassic boundary and following the impact theory of mass extinctions may be implicated in the cause

compositional heterogeneity of tephras from the 1980 eruptions of mount st helens samples collected at hourly intervals on may 18 19 1980 at three sites 200 km downwind from mount st helens have made possible a detailed reconstruction of the conditions that contribute to the compositional heterogeneity of mineral and glass components observed in distal tephra layers the air fall tephra deposited at the sites during the first 7 hours of the may 18 eruption is mostly coarse grained microlite rich nonjuvenile glass and feldspar grain size maxima in this initial tephra can be related to the cataclysmic blast at 0832 and a subsequent pulse of the eruption at 1200 juvenile microlite free glass increases in relative abundance at the sampling sites beginning at about 1900 such a change between nonjuvenile and juvenile tephra can be related to a 5 km increase in column height associated with the last major pulse of the eruption which occurred at 1700 at the volcano electron microprobe study of both microlite rich and microlite free pumice in the time series samples reveals significant compositional differences interstitial glass in nonjuvenile pumice deposited during the first few hours at the sampling sites is enriched in sio2 and k2o and depleted in tio2 feo and mgo relative to juvenile glass by comparison major element composition of the least evolved juvenile glass sampled during the last several hours of the eruption displays a slight trend toward less evolved composition least squares calculations suggest that the more evolved character of the nonjuvenile glass can be explained by greater fractional crystallization brought about by enhanced cooling in a cryptodome prior to eruption whereas the temporal changes observed in juvenile glass composition during the last several hours of the eruption suggest the presence of a small slightly zoned magma chamber at depth electron microprobe study of glass coated ilmenites magnetites and plagioclases provides the following estimates of the physical conditions in this reservoir 865 50 c ph2o 2 2 kbar and log o2 11 7 analyses of bulk pumice glass and selected mineral phases from may 25 june 12 july 22 and october 16 18 pumices erupted from mount st helens indicate that the bulk pumice magma compositions have become slightly more andesitic with time while mineral and co existing glass compositions have changed significantly in post may 18 eruptions with both being more highly evolved than those associated with the may 18 eruption an application of the magnetite ilmenite geothermometer to june 12 and july 22 samples indicates temperatures of 919 30 c and 930 50 c respectively least squares calculations suggest that such evolved post may 18 glass and mineral phases can be derived by fractional crystallization of a magma composition like bulk may 18 pumice into approximately 50 crystals and 50 residual liquid such partitioning between crystals and residual liquid appears to have occurred on the scale of centimeters and is interpreted as a consequence of accelerated crystallization under reduced water pressure

dynamics of co ignimbrite plumes generated from pyroclastic flows of mount st helens 7 august 1980 four co ignimbrite plumes were generated along the flow path of the pyroclastic flow of 7 august 1980 at mount st helens three of the plumes were generated in discrete pulses which can be linked to changes in slope along the channel one plume was generated at the mouth of the channel where the flow decelerated markedly as it moved onto the lower slopes of the pumice plain plume generation here may be triggered by enhanced mixing due to a hydraulic jump associated with an abrupt slope change measurements of plume ascent velocity and width show that the co ignimbrite plumes increased in velocity with height the plumes have initial velocities of 1 2 m s two of the plumes reached a velocity maximum 4 6 and 8 8 m s respectively at heights of 270 and 315 m above the flow and thereafter decelerated the other plumes reached velocities of 6 2 and 13 m s the four plumes become systematically less energetic downstream as measured by their ascent rates which can be interpreted as a consequence of decreasing interaction of the pyroclastic flow front with the atmosphere theoretical models of both co ignimbrite plumes and discrete co ignimbrite clouds assume that there is no initial momentum and both are able to predict the observed acceleration stage the rising plumes mix with and heat air and sediment out particles causing their buoyancy to increase theoretical models agree well with observations and suggest that the initial motion of the ascending material is best described as a discrete thermal cloud which expands as it entrains air whereas the subsequent motion of the head may become influenced by material supplied from the following plume the models agree well with observations for an initial temperature of the ash and air mixture in the range of 500 600 k which is in turn consistent with the measured initial ash temperature of around 920 k ash masses of 3 4 105 to 1 8 106 kg are estimated

large eddy simulation of gas particle kinematic decoupling and turbulent entrainment in volcanic plumes abstract in the framework of the iavcei international association of volcanology and chemistry of the earth interior intercomparison study on volcanic plume models we present three dimensional 3d numerical simulations carried out with the ashee ash equilibrium eulerian model the ashee model solves the compressible balance equations of mass momentum and enthalpy of a gas particle mixture and is able to describe the kinematic decoupling for particles characterized by stokes number i e the ratio between the particle equilibrium time and the flow characteristic time lower than 0 2 or particles smaller than about 1 mm the computational fluid dynamic model is designed to accurately simulate a turbulent flow field using a large eddy simulation approach and is thus suited to analyze the role of particle non equilibrium in the dynamics of turbulent volcanic plumes the two reference scenarios analyzed correspond to a weak mass eruption rate 1 5 10 6 kg s and a strong volcanic plume mass eruption rate 1 5 10 9 kg s in absence of wind for each scenario we compare the 3d results averaged in space and time with theoretical results obtained from integral plume models such an approach enables quantitative evaluation of the effects of grid resolution and the subgrid scale turbulence model and the influence of gas particle non equilibrium processes on the large scale plume dynamics we thus demonstrate that the uncertainty on the numerical solution associated with such effects can be significant of the order of 20 but still lower than that typically associated with input data and integral model approximations in the weak plume case 3d results are consistent with the predictions of integral models in the jet and plume regions with an entrainment coefficient around 0 10 in the plume region in the strong plume case the self similarity assumption is less appropriate and the entrainment coefficient in the plume region is more unstable with an average value of 0 24 for both cases integral model predictions diverge from the 3d plume behavior in the umbrella region the presented analysis of 3d numerical simulations thus enables identification of the critical hypotheses that underlie integral models used in operational studies in addition high resolution 3d runs allow reproduction of observable quantities such as infrasound signals which can be useful for constraining eruption dynamics during real events

determination of the mass eruption rate for the 2014 mount kelud eruption using three dimensional numerical simulations of volcanic plumes abstract using a three dimensional fluid dynamic model for eruption cloud dynamics we present numerical simulations of the development of a volcanic eruption column and umbrella cloud formed during the 13 february 2014 eruptions of mount kelud indonesia the model used in this study quantitatively reproduces the observed data and in particular the plume height and the horizontal expansion level and rate of the umbrella cloud the simulation results suggest that on the basis of the plume height and structures and the horizontal expansion level of the umbrella cloud the mass eruption rate mer for the 2014 kelud eruptions was 3 107 to 4 107 kg s 1 on the basis of the horizontal expansion rate of the umbrella cloud on the other hand the estimated mer was 1 108 kg s 1 the difference between these two estimates implies the strong diffusion in the umbrella cloud or the efficient entrainment of ambient air by eruption column

sediment laden gravity currents with reversing buoyancy there are many natural occurrences of sediment laden gravity currents in which the density of the interstitial fluid is less than that of the ambient fluid although the bulk density of the current is greater such currents are driven by the excess density of suspended particles however after sufficient particles have sedimented the current will become buoyant cease its lateral motion and ascend to form a plume examples of such currents include brackish underflows in deltas turbidity currents and pyroclastic flows experimental studies are described which show that due to sedimentation sediment laden gravity currents decelerate more rapidly than saline currents of the same density there is little difference in the experiments between a sediment laden current with neutrally buoyant interstitial fluid and one with buoyant interstial fluid until sufficient sediment has been lost to cause the latter kind of current to lift off a marked deceleration is then observed and a plume is generated with lift off occurring along the length of the current the resulting buoyant plume then generates a gravity current below the upper surface of the fluid in the tank the deposit from a current with buoyant fluid shows a fairly abrupt decrease in thickness beyond the lift off distance and has a flatter profile than that from a simple sediment current a theoretical model is presented which is based on the two layer shallow water equations and incorporates a model of the sedimentation in which particles are assumed to be uniformly suspended by the turbulence of the current the model shows good agreement with the observed lengths of the experimental currents as a function of time and predicts the lift off distance reasonably well these processes have implications for the behaviour of turbidity currents the interpretation of turbidites mixing processes in the oceans and the lift off of pyroclastic flows

a new view of the dynamics stability and longevity of volcanic clouds abstract powerful explosive volcanic eruptions inject ash high into the atmosphere which spreads to form umbrella clouds identifying key physical processes governing the dynamics stability and longevity of umbrella clouds is central to assessing volcanic hazards as well as the nature of volcanic forcings on climate here we present a series of laboratory experiments producing turbulent particle laden jets and subsequent axisymmetric intrusive gravity currents into a stratified environment our experiments reproduce many of the main dynamical regimes observed during the formation of an explosive volcanic column and highlight new dynamics for the umbrella cloud theoretical predictions of column collapse from a simple model of a turbulent jet are in good agreement with experimental observations as well as previous studies depending on the flow intensity the strength of the initial environmental density stratification and the particle concentration at the source resulting umbrella clouds can however evolve through a series of new regimes as a result of the dynamics of particle sedimentation within these flows as well as from their bases using scaling theory we show that during cloud spreading internal sedimentation drives the growth and intermittent overturn of thin gravitationally unstable particle boundary layers pbls as particle rich plumes this pbl driven convection can have remarkable effects ranging from progressive dilution of clouds to their catastrophic overturn and collapse in natural eruptions whether the dynamics of pbls play a major role in particle sedimentation depends on the grain size distribution inside the cloud and on eruption column height in general particles larger than 60 m 1 mm are expected to settle individually whereas finer particles will accumulate pbls resulting in the formation of armless mammatus clouds or dangerous gravity currents at much larger distances from the volcanic vent than ever considered before such dynamics is apparent in observations of numerous modern eruptions and is inferred from the deposits of historic and prehistoric eruptions for where there exist appropriate data consideration of the consequences of these phenomena for problems such as volcanic hazards to humans and climate change may thus be very important in the assessment of future eruptions

climate response to the toba super eruption regional changes climatic consequences of the young toba tuff ytt eruption about 73 ka are a crucial argument in the current discussion about the fate of modern humans especially in africa and asia earth system model esm simulations of the ytt eruption are used to investigate its regional climate impacts in particular focusing on areas relevant to human evolutionary issues during that time uncertainties concerning the stratospheric sulphur emission for the ytt eruption are addressed by comparing esm simulations of a 100 times pinatubo like eruption as an upper and a 3 times pinatubo like tambora eruption as a lower estimate information about transient changes in vegetation types after the ytt eruption are obtained by forcing an offline dynamical global vegetation model with the climate anomalies simulated by the esm under both glacial and interglacial background climate conditions the simulated temperature changes in those areas that were inhabited by humans suggest thermal discomfort but not a real challenge for survival precipitation is reduced in all regions during the first two years but recovers quickly thereafter some catchments in these regions ganges brahmaputra nile experience an over compensation in precipitation during the third to fifth post eruption years which is also reflected in anomalously strong river runoffs change in vegetation composition may have created the biggest pressure on humans who had to adapt to more open space with fewer trees and more grasses for some decades especially in the african regions the strongest environmental impacts of the ytt eruption are simulated under interglacial background conditions suggesting that the climate effects of the ytt eruption did not impact humans on a major scale and for a period long enough to have dramatic consequences for their survival

a new perspective of the alboran upwelling system reconstruction during the marine isotope stage 11 a high resolution coccolithophore record abstract a high resolution study of the mis 12 mis 11 transition and the mis 11 430 376 kyr coccolithophore assemblages at ocean drilling program site 977 was conducted to reconstruct the palaeoceanographic and climatic changes in the alboran sea from the variability in surface water conditions the nannofossil record was integrated with the planktonic oxygen and carbon stable isotopes as well as the uk 37 sea surface temperature sst at the studied site during the investigated interval the coccolithophore primary productivity reconstructed from the ppp primary productivity proxy absolute values of gephyrocapsa caribbeanica small gephyrocapsa group revealed pronounced fluctuations that were strongly associated with variations in the intensity of the regional alboran upwelling system the comparison of the nannoplankton record with opal phytolith content for the studied site and the already available pollen record at the nearby integrated ocean drilling program site u1385 suggests an association of the upwelling dynamics with the variability of the north atlantic oscillation like nao like phase high ppp during positive nao like phases is the result of intensified upwelling owing to the complete development of the surface hydrological structures at the alboran sea this scenario was identified during the mis 12 mis 11 transition 428 422 kyr the late mis 11c 405 397 kyr and mis11 b to mis 11a 397 376 kyr two short term minima in the ppp and sst were observed during mis 11 b and were coeval with the north atlantic heinrich type ht events ht3 390 kyr and ht2 384 kyr increased abundance of the subpolar coccolithus pelagicus subsp pelagicus and gephyrocapsa muellerae was consistent with the inflow of cold surface waters into the mediterranean sea during the ht events lowered ppp during negative nao like phases is the result of moderate upwelling by the incomplete development of surface hydrological structures at the alboran sea this scenario is expressed during the early mis 11c 422 405 kyr overall the results of our study provide evidence of the important role of atmospheric circulation patterns in the north atlantic region for controlling phytoplankton primary production and oceanographic circulation dynamics in the western mediterranean during mis 11

chronology and pyroclastic stratigraphy of the may 18 1980 eruption of mount st helens washington many timed observations make it possible to subdivide the 9 hour plinian eruption of mount st helens on may 18 1980 into six phases defined by eruption style the phases are correlated with stratigraphic subunits of ashfall tephra and pyroclastic flow deposits the suite of pyroclastic deposits indicates that the eruption became more pumice rich and compositionally diverse with time perhaps owing to concurrent eruption of less evolved gas poor parts of the magma body with the more evolved gas rich parts the paroxysmal phase i 0832 0900 consisted of landslides lithic pyroclastic flows of a lateral blast and other explosions and a weak pre plinian column phase i pyroclastic deposits include lithic ash flow deposits intercalated with and overlying the voluminous debris avalanche deposit and basal pumice lapilli tephra that underlies a pisolitic ash layer the early plinian phase ii 0900 1215 consisted of vertical ejection of tephra with an early pulse of small pyroclastic flows on the upper flanks 1010 1035 a brief period of lithic ash ejection 1035 1100 and a pumice rich pulse that accompanied growth in height of the eruption column 1100 1215 deposits include minor pyroclastic flows on the crater rim and a reversely graded sequence of proximal tephra that include the lower pumice lapilli layer the lower lithic ash layer and the middle pumice lapilli layer all of which consist of evolved white dacitic pumice 63 64 sio2 during the early ash flow phase iii 1215 1500 the height of the eruption column decreased vertical ejection of tephra ceased and pyroclastic flows were fed from intermittent fountains phase iii deposits consist of a poorly exposed sequence 12 m of ash flow tuff that consist of many thin flow units 2 m each containing pumiceous white dacite 63 64 sio2 and denser gray silicic andesite 61 62 sio2 and fine grained ash cloud deposits interbedded with a nongraded middle pumice ash layer the climactic phase iv 1500 1715 developed in two stages fountain fed pyroclastic flows followed by a short pulse 1625 1715 of vigorous vertical ejection of tephra these stages were accompanied by the peak seismic energy release and peak eruption column height respectively climactic deposits consist of a thick 35 m sequence of thick lapilli rich ash flow sheets 4 12 m each with white and gray pumice and streaky scoria bands 60 sio2 in pumice breccia clasts and the reversely graded upper pumice lapilli layer that is interbedded with fine grained ash cloud deposits during the late ash flow phase v 1715 1815 eruption intensity waned but included a brief episode of small pyroclastic flows 1745 1815 phase v deposits consist of small distributary lobes of ash flow tuff containing white and gray pumice and minor fine ash deposits phase vi activity 1815 to may 19 1980 consisted of a low energy ash plume with transient increases in intensity while seismicity continued at depth sustained vertical discharge of phase ii prodeced evolved dacitewith high s cl ratios ash flow activity of phase iii is attributed to decreases in gas content indicated by reduced s cl ratios and increased clast density of the less evolved gray pumice climactic events are attributed to vent clearing and exhaustion of the evolved dacite

nature of a flood basalt magma reservoir based on the compositional variation in a single flood basalt flow and its feeder dike in the mesozoic hartford basin connecticut the erosional remains of the mesozoic holyoke basalt in the hartford pomperaug and deerfield basins of connecticut and massachusetts indicate an original flow volume of 1200 km3 its feeder dike which is about 50 m wide and 160 km long can be traced down through 2 km of mesozoic sediments and as a result of faulting associated with basin formation through an additional 6 km of paleozoic metamorphic rocks chemical profiles through the distal and proximal parts of the flow and through the dike at depths of 2 4 and 8 km provide sequential samples of the magma that rose during this one eruptive event the flow and dike have restricted compositions that indicate saturation with olivine augite and plagioclase at depth the flow consisted largely of a liquid at the pigeonite reaction point dike compositions can be modeled as mixtures of this liquid with up to 24 crystals of plagioclase augite and olivine the dike compositions indicate equilibration with these minerals at 3 8 kbar this pressure corresponds to a depth of 12 2 km which is believed to have been the depth of the brittle ductile transition in the crust at the time this transition appears to be the only reasonable barrier that could have caused ponding of the magma at the mid crustal level the holyoke liquid is interpreted to have segregated from a compacting crystal mush following 30 crystallization of the magma in this mid crustal reservoir eruption of the basalt exhausted the supply of segregated liquid and when the remaining crystal mush began to rise in the dike the average density of the magma column increased until it matched the average density of the intruded crust and the eruption ended by analogy with the differentiation that took place in the solidifying holyoke flow on the surface the mid crustal magma reservoir is estimated to have had a volume of at least 12 000 km3 the magma in this chamber must have come from a still deeper chamber because it was too fractionated to have come directly from a mantle source

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

detailed multidisciplinary monitoring reveals pre and co eruptive signals at nyamulagira volcano north kivu democratic republic of congo this paper presents a thorough description of nyamulagira s january 2010 volcanic eruption north kivu democratic republic of congo based on a combination of field observation and ground based and space borne data it is the first eruption in the virunga volcanic province that has been described by a combination of several modern monitoring techniques the 2010 eruption lasted 26 days and emitted 45 5 106 m3 of lava field observations divided the event into four eruptive stages delimited by major changes in effusive activity these stages are consistent with those described by pouclet 1976 for historical eruptions of nyamulagira co eruptive signals from ground deformation seismicity so2 emission and thermal flux correlate with the eruptive stages unambiguous pre eruptive ground deformation was observed 3 weeks before the lava outburst coinciding with a small but clear increase in the short period seismicity and so2 emission the 3 weeks of precursors contrasts with the only precursory signal previously recognized in the virunga volcanic province the short term increase of tremor and long period seismicity which for example were only detected less than 2 h prior to the 2010 eruption the present paper is the most detailed picture of a typical flank eruption of this volcano it provides valuable tools for re examining former mostly qualitative descriptions of historical nyamulagira eruptions that occurred during the colonial period

co ignimbrite ash fall deposits of the 1991 eruptions of fugen dake unzen volcano japan abstract fugen dake the main peak of unzen volcano began a new eruption sequence on november 17 1990 on may 20 1991 a new lava dome appeared near the eastern edge of the fugen dake summit small scale 10 4 10 6 m 3 in volume merapi type block and ash flows were frequently generated from the growing lava dome during may june 1991 these pyroclastic flows were accompanied by co ignimbrite ash plumes that deposited ash fall deposits downwind of the volcano three examples of co ignimbrite ash fall deposits from unzen pyroclastic flows are described the volume of fall deposits was estimated to be about 30 by volume of the collapsed portions of the dome that formed pyroclastic flows this proportion is smaller than that described for other larger co ignimbrite ash fall deposits from other volcanoes grain size distributions of the unzen co ignimbrite ash fall deposits are bi modal or tri modal most ashes are finer than 4 phi and two modes were observed at around 4 7 phi and 9 phi they are composed mainly of groundmass fragments fractions of another mode at around 2 phi are rich in crystals derived from dome lava some of the fine ash component fell as accretionary lapilli from the co ignimbrite ash cloud indicating either moisture or electrostatic aggregation we believe that the co ignimbrite ash of unzen block and ash flows were formed by the mechanical fracturing of the cooling lava blocks as they collapsed and moved down the slope these ashes were entrained into the convective plumes generated off the tops of the moving flows

pyroclastic flows generated by gravitational instability of the 1996 97 lava dome of soufriere hills volcano montserrat numerous pyroclastic flows were produced during 1996 97 by collapse of the growing andesitic lava dome at soufriere hills volcano montserrat measured deposit volumes from these flows range from 0 2 to 9 106 m flows range from discrete single pulse events to sustained large scale dome collapse events flows entered the sea on the eastern and southern coasts depositing large fans of material at the coast small runout distance 1 km flows had average flow front velocities in the order of 3 10 m s while flow fronts of the larger runout distance flows up to 6 5 km advanced in the order of 15 30 m s many flows were locally highly erosive field relations show that development of the fine grained ash cloud surge component was enhanced during the larger sustained events periods of elevated pyroclastic flow productivity and sustained dome collapse events are linked to pulses of high magma extrusion rates

a comparison of eastern north america and coastal new england magma suites implications for subcontinental mantle evolution and the broad terrane hypothesis new england and maritime canada host two major suites of mesozoic diabase dykes the oldest is the coastal new england dykes that were emplaced between 225 and 230 ma these rocks are dominantly alkaline with trace element and isotopic compositions indicative of a high 238u 204pb mantle himu source the oldest of the 200 ma mesozoic rift magmas is represented by the talcott basalt of the hartford basin and its feeder dykes external to the basin is the compositionally equivalent higganum dyke the extension of the higganum the onway dyke in new hampshire is identical in major and trace element and isotopic compositions indicating that the dyke system represented a feeder to flows of flood basalt proportions the talcott system rocks have some trace element similarities with arc basalts and have been interpreted as representing melts of a subduction zone modified mantle beneath the laurentian gondwanan suture incompatible trace element ratios and ba th and u values are however unlike arc basalts

dimensions and dynamics of co ignimbrite eruption columns very powerful volcanic eruptions cannot always form classical plinian eruption columns1 4 instead collapsing fountains may develop above the vent and shed pyroclastic flows which spread laterally along the ground5 the upper part of these hot dense pyroclastic flows may become buoyant through the entrainment heating and expansion of ambient air coupled with the sedimentation of larger clasts suspended in the flow the buoyant material may rise in a co ignimbrite eruption column carrying massive quantities of fine dust and volatiles into the stratosphere6 7 here we present a model of this process and show that the co ignimbrite columns associated with the eruptions of toba8 9 75 000 years ago and tambora10 in 1815 may have ascended only about 32 and 23 km the latter is comparable with the less powerful 1982 plinian eruption column of el chichon11 this corroborates arguments that the mass of sulphuric acid aerosols injected into the stratosphere and not the eruptive power determines the climatic impact of an eruption12 13

the entrainment rate of non boussinesq hazardous geophysical gas particle flows an experimental model with application to pyroclastic density currents the entrainment rate of pyroclastic density currents is investigated by large scale experiments the ground flows are initiated by the impact on the terrain of a dense gas particle fountain issuing from a cylindrical conduit similarly to natural volcanic events on impact the excess density with respect to the surrounding atmosphere was up to 11 6 kg m3 making the currents non boussinesq a power law model of the entrainment rate is developed which is similar to that proposed for snow avalanches by ancey 2004 https doi org 10 1029 2003jf000052 and is verified for the richardson s number range between 0 25 and 5 95 rapid changes of the entrainment are caused by i strong accelerations at the fountain impact on the ground ii break in slope and iii topographic obstacles such changes together with the sedimentation rate influence flow mobility the use of the power law is suggested for modeling the motion of unsteady hazardous geophysical mass flows such as pyroclastic density currents and snow avalanches

inter comparison of three dimensional models of volcanic plumes abstract we performed an inter comparison study of three dimensional models of volcanic plumes a set of common volcanological input parameters and meteorological conditions were provided for two kinds of eruptions representing a weak and a strong eruption column from the different models we compared the maximum plume height neutral buoyancy level where plume density equals that of the atmosphere and level of maximum radial spreading of the umbrella cloud we also compared the vertical profiles of eruption column properties integrated across cross sections of the plume integral variables although the models use different numerical procedures and treatments of subgrid turbulence and particle dynamics the inter comparison shows qualitatively consistent results in the weak plume case mass eruption rate 1 5 106 kg s 1 the vertical profiles of plume properties e g vertical velocity temperature are similar among models especially in the buoyant plume region variability among the simulated maximum heights is 20 whereas neutral buoyancy level and level of maximum radial spreading vary by 10 time averaging of the three dimensional 3d flow fields indicates an effective entrainment coefficient around 0 1 in the buoyant plume region with much lower values in the jet region which is consistent with findings of small scale laboratory experiments on the other hand the strong plume case mass eruption rate 1 5 109 kg s 1 shows greater variability in the vertical plume profiles predicted by the different models our analysis suggests that the unstable flow dynamics in the strong plume enhances differences in the formulation and numerical solution of the models this is especially evident in the overshooting top of the plume which extends a significant portion 1 8 of the maximum plume height nonetheless overall variability in the spreading level and neutral buoyancy level is 20 whereas that of maximum height is 10 this inter comparison study has highlighted the different capabilities of 3d volcanic plume models and identified key features of weak and strong plumes including the roles of jet stability entrainment efficiency and particle non equilibrium which deserve future investigation in field laboratory and numerical studies

volcanic particle aggregation in explosive eruption columns part i parameterization of the microphysics of hydrometeors and ash abstract the aggregation of volcanic ash particles within the eruption column of explosive eruptions has been observed at many volcanoes it influences the residence time of ash in the atmosphere and the radiative properties of the umbrella cloud however the information on the processes leading to aggregate formation are still either lacking or very incomplete we examine the fate of ash particles through numerical experiments with the plume model atham active tracer high resolution atmospheric model in order to determine the conditions that promote ash particle aggregation in this paper we describe the microphysics and parameterization of ash and hydrometeors in a companion paper this issue we use this information in a series of numerical experiments the parameterization includes the condensation of water vapor in the rising eruption column the formation of liquid and solid hydrometeors and the effect of latent heat release on the eruption column dynamics are considered the interactions of hydrometeors and volcanic ash within the eruption column that lead to aggregate formation are simulated for the first time within a rising eruption column the microphysical parameterization follows a modal approach the hydrometeors are described by two size classes each of which is divided into a liquid and a frozen category by analogy with the hydrometeor classification we specify four categories of volcanic ash particles we imply that volcanic particles are active as condensation nuclei for water and ice formation ash can be contained in all categories of hydrometeors thus forming mixed particles of any composition reaching from mud rain to accretionary lapilli collisions are caused by gravitational capture of particles with different fall velocity coalescence of hydrometeor ash aggregates is assumed to be a function of the hydrometeor mass fraction within the mixed particles the parameterization also includes simplified descriptions of electrostatics and salinity effects

effects of topography on pyroclastic density current runout and formation of coignimbrites laboratory experiments of dilute mixtures of warm talc powder in air simulate dilute pyroclastic density currents pdcs and show the effects of topography on current runout buoyancy reversal and liftoff into buoyant plumes the densimetric and thermal richardson froude stokes and settling numbers for our experiments match those of natural pdcs the laboratory currents are fully turbulent although the experiments have lower reynolds numbers than pdcs in sum our experiments are dynamically similar to natural currents comparisons of currents traversing flat topography or encountering barriers show that runout distance is not significantly reduced for currents that traverse barriers with height

deposits associated with the 1990 1995 eruption of unzen volcano japan abstract the 1990 1995 eruption of unzen volcano in japan was characterized by lava dome growth and block and ash flows triggered by dome collapse the repeated dome collapse events produced block and ash flow ash cloud surge and fine grained ash fall deposits block and ash flow deposits which are confined to valleys are massive to reversely graded very poorly sorted and contain non vesiculated to poorly vesiculated blocks up to 10 m across the deposits often display finer grained basal parts coarse clast depleted flow units which have intermediate grain size distribution between main flow and surge deposits occur as marginal part of block and ash flow deposits ash cloud surge deposits which spread more widely are finer grained and better sorted than block and ash flow deposits ash fall deposits which were derived from ash clouds of block and ash flows and were dispersed around the volcano are very fine grained and are as well sorted as the surge deposits lahars resulting from remobilization of pyroclastic debris devastated the base of the volcano and their deposits are moderately fines depleted and occasionally display two different lahar facies debris flow and hyperconcentrated flow units

relating the physical properties of volcanic rocks to the characteristics of ash generated by experimental abrasion interactions between clasts in pyroclastic density currents pdcs generate volcanic ash that can be dispersed to the atmosphere in co pdc plumes and due to its small size is far travelled we designed a series of experiments to determine the effects of pyroclast vesicularity and crystal content on the efficiency and type of ash generated by abrasion two different pyroclastic materials were used 1 basaltic andesite pyroclasts from fuego volcano guatemala with 26 46 vesicularity and high groundmass crystallinity and 2 tephri phonolite avellino pumice vesuvius italy with 55 75 vesicularity and low groundmass crystallinity when milled both clast types produced bimodal grain size distributions with fine ash modes between 4 and 5 32 63 m although the vesicular avellino pumice typically generated more ash than the denser fuego pyroclasts the ash generating potential of a single pyroclast was independent of density and instead governed by heterogeneous crystal and vesicle textures one consequence of these heterogeneities was to cause the vesicular avellino clasts to split in addition to abrading which further enhanced abrasion efficiency the matrix characteristics also affected ash shape and componentry which will influence the elutriation and transport properties of ash in the atmosphere the experimental abrasion successfully replicated some of the characteristics of natural co pdc ash samples as shown by similarities in the adherence factor which measures the proportion of attached matrix on phenocrysts of both the experimentally generated ash and natural co pdc ash samples our results support previous studies which have shown that abrasion is an effective mechanism for generating fine ash that is similar in size 5 30 m to that found in co pdc deposits we further show that both the abundance and nature shape density components size distribution of those ash particles are strongly controlled by the matrix properties of the abraded pyroclasts

volcanic diapirs in the orange mountain flood basalt new jersey usa abstract diapir shaped structures 4 30 m high consisting of vesicular basalt have intruded into the interior of a 50 70 m thick subaerial orange mountain basalt flow exposed at several rock quarries in northern new jersey the basalt flowed onto a travertine encrusted mudflat saturated with alkali salts we propose that pressurized alkali vapors trapped under the lava created a vesicular and viscous flow bottom layer about 10 m thick vesicle coalescence within this layer increased its buoyancy where it locally accumulated into diapirs and displaced overlying lava large bubbles within the diapirs expanded upon intrusion into hot flow interiors where they explosively escaped leaving lenses of breccia some early diapirs reached the base of the upper lava crust these diapirs document vapor driven convection of large blobs of contaminated lava into the lava core of the orange mountain flow

experimental studies of particle laden plumes experiments are described in which buoyant plumes of fresh water and solid particles are generated in a tank of salt water dependence of the behavior of the plumes on particle concentration and grain size was studied at low concentrations behavior was similar to single component plumes and the principal effect of the particles was to reduce the buoyancy flux measurements of particle concentration across the plumes demonstrated that there were substantial amounts of particle reentrainment from an outer sedimenting veil reentrainment caused the plume margins to become denser than the ambient fluid total particle flux in the plumes increased with height and can be several times greater than the flux at the plume source plumes with high particle concentration exhibit several kinds of convective instability which generated gravity currents and rapid sedimentation gravity currents were generated at the margins of concentrated plumes these flows are attributed to reentrainment causing the flow margins to have excess density when the plume density was close to but less than the density of the ambient fluid a fountain forms high in the plumes which collapsed asymmetrically to generate a gravity current on one side of the plume when the density of the particle laden flow was greater than the ambient fluid a symmetrical fountain formed and gravity currents moved across the tank floor depositing sediment at a well defined distance from the source buoyant fluid ascended from the flow fronts to form a ring of plumes around the central fountain these plumes coalesced to form a broad buoyant cloud the plumes are generated by the sedimentation from the gravity currents which resulted in the fresh water and some entrained particles being released all the experimental plumes ascended to the top of the tank and spread out as gravity currents beneath the upper surface particles often fall from this layer in discrete parcels of particle rich fluid with shapes similar to thermals the fall velocities were much greater than the terminal velocities of individual particles and the sedimenting region is inhomogeneous these observations indicate that sedimentation is enhanced by convective instabilities when particle rich fluid is emplaced above particle free fluid the experiments indicate that there may be several different mechanisms of generating pyroclastic flows and surges from the collapse of volcanic eruptions columns the experiments also demonstrate that the sedimentation of particles from a plume has an important influence on dynamical behavior

a prognostic turbulence scheme for the nonhydrostatic plume model atham the presented turbulence scheme was developed for the active tracer high resolution atmospheric model atham to parameterize the effect of subgrid scale turbulence in contrast to the commonly used assumption of local isotropy in high resolution atmospheric modeling this scheme differentiates between horizontal and vertical turbulent exchange to represent the strong influence of buoyancy forces and vertical transports its computational efficiency is similar to classical turbulent kinetic energy approaches while preserving one of the main feature of higher order schemes the present extensions to include anisotropic effects in a turbulent kinetic energy approach do not need any ad hoc assumptions and are equivalent to the classical formulation in the isotropic limit the presence of high tracer concentrations in a particle laden plume is taken into account as well as supersonic effects at low mach numbers the turbulent exchange coefficients used in the equations of motion are derived from a set of three coupled differential equations for the horizontal and vertical turbulent energy and the turbulent length scale no turbulent equilibrium is assumed all turbulent quantities are treated prognostically numerical simulations of convective plumes of a typical plinian volcanic eruption with the nonhydrostatic plume model atham reveal that a complex treatment of turbulent quantities is necessary in order to capture the bulk characteristics of the plume such as the plume height the horizontal extent and plume development in time anisotropic effects of turbulence have a significant impact on the stability and internal structure of the plume for the first time results from a fully three dimensional simulation of a volcanic plume are presented because of its general formulation the presented turbulence scheme is suitable for a wide range of atmospheric applications

results of the eruptive column model inter comparison study this study compares and evaluates one dimensional 1d and three dimensional 3d numerical models of volcanic eruption columns in a set of different inter comparison exercises the exercises were designed as a blind test in which a set of common input parameters was given for two reference eruptions representing a strong and a weak eruption column under different meteorological conditions comparing the results of the different models allows us to evaluate their capabilities and target areas for future improvement despite their different formulations the 1d and 3d models provide reasonably consistent predictions of some of the key global descriptors of the volcanic plumes variability in plume height estimated from the standard deviation of model predictions is within 20 for the weak plume and 10 for the strong plume predictions of neutral buoyancy level are also in reasonably good agreement among the different models with a standard deviation ranging from 9 to 19 the latter for the weak plume in a windy atmosphere overall these discrepancies are in the range of observational uncertainty of column height however there are important differences amongst models in terms of local properties along the plume axis particularly for the strong plume our analysis suggests that the simplified treatment of entrainment in 1d models is adequate to resolve the general behaviour of the weak plume however it is inadequate to capture complex features of the strong plume such as large vortices partial column collapse or gravitational fountaining that strongly enhance entrainment in the lower atmosphere we conclude that there is a need to more accurately quantify entrainment rates improve the representation of plume radius and incorporate the effects of column instability in future versions of 1d volcanic plume models