the 1815 tambora ash fall implications for transport and deposition of distal ash on land and in the deep sea tambora volcano lies on the sanggar peninsula of sumbawa island in the indonesian archipelago during the great 1815 explosive eruption the majority of the erupted pyroclastic material was dispersed and subsequently deposited into the indian ocean and java sea this study focuses on the grain size distribution of distal 1815 tambora ash deposited in the deep sea compared to ash fallen on land grain size distribution is an important factor in assessing potential risks to aviation and human health and provides additional information about the ash transport mechanisms within volcanic umbrella clouds grain size analysis was performed using high precision laser diffraction for a particle range of 0 2 m 2 mm diameter the results indicate that the deep sea samples provide a smooth transition to the land samples in terms of grain size distributions despite the different depositional environments even the very fine ash fraction 10 m is deposited in the deep sea suggesting vertical density currents as a fast and effective means of transport to the seafloor the measured grain size distribution is consistent with an improved atmospheric gravity current sedimentation model that takes into account the finite duration of an eruption in this model the eruption time and particle fall velocity are the critical parameters for assessing the ash component depositing while the cloud advances versus the ash component depositing once the eruption terminates with the historical data on eruption duration maximum 24 h and volumetric flow rate of the umbrella cloud 1 5 2 5 1011 m3 s as input to the improved model and assuming a combination of 3 h plinian phase and 21 h co ignimbrite phase it reduces the mean deviation of the predicted versus observed grain size distribution by more than half 9 4 to 3 7 if both ash components are considered

patterns of deposition from experimental turbidity currents with reversing buoyancy turbidity currents are turbulent sediment laden gravity currents which can be generated in relatively shallow shelf settings and travel downslope before spreading out across deep water abyssal plains because of the natural stratification of the oceans and or fresh water river inputs to the source area the interstitial fluid within which the particles are suspended will often be less dense than the deep water ambient fluid consequently a turbidity current may initially be denser than the ambient sea water and propagate as a ground hugging flow but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient sea water when this occurs all or part of the turbidity current lofts to form a buoyant sediment laden cloud from which further deposition occurs deposition from such lofting turbidity currents containing a mixture of fine and coarse sediment suspended in light interstitial fluid is explored through analogue laboratory experiments complemented by theoretical analysis using a box and cloud model particular attention is paid to the overall deposit geometry and to the distributions of fine and coarse material within the deposit a range of beds can be deposited by bimodal lofting turbidity currents lofting may encourage the formation of tabular beds with a rapid pinch out rather than the gradually tapering beds more typical of waning turbidity currents lofting may also decouple the fates of the finer and coarser sediment depending on the initial flow composition the coarse fraction can be deposited prior to or during buoyancy reversal while the fine fraction can be swept upwards and away by the lofting cloud an important feature of the results is the non uniqueness of the deposit architecture different initial current compositions can generate deposits with very similar bed profiles and grading characteristics highlighting the difficulty of reconstructing the nature of the parent flow from field data it is proposed that deposit emplacement by lofting turbidity currents is common in the geological record and may explain a range of features observed in deep water massive sands thinly bedded turbidite sequences and linked debrites depending on the parent flow and its subsequent development for example a lofting flow may lead to a well sorted largely ungraded or weakly graded bed if the fines are transported away by the cloud however a poorly sorted largely ungraded region may form if during buoyancy reversal high local concentrations and associated hindered settling effects develop at the base of the cloud

hydrometeor enhanced tephra sedimentation constraints from the 18 may 1980 eruption of mount st helens 1 uncertainty remains on the origin of distal mass deposition maxima observed in many recent tephra fall deposits in this study the link between ash aggregation and the formation of distal mass deposition maxima is investigated through reanalysis of tephra fallout from the mount st helens 18 may 1980 msh80 eruption in addition we collate all the data needed to model distal ash sedimentation from the msh80 eruption cloud four particle size subpopulations were present in distal fallout with modes at 2 2 4 2 5 9 and 8 3 settling rates of the coarsest subpopulation closely matched predicted single particle terminal fall velocities sedimentation of particles 100 m was greatly enhanced predominantly through aggregation of a particle subpopulation with modal diameter 5 9 0 2 19 3 m mammatus on the msh80 cloud provided a mechanism to transport very fine ash particles with predicted atmospheric lifetimes of days to weeks from the upper troposphere to the surface in a matter of hours in this mechanism ash particles initiate ice hydrometeor formation high in the troposphere subsequently the volcanic cloud rapidly subsides as mammatus develop from increased particle loading and cloud base sublimation rapid fallout occurs as the cloud passes through the melting level in a process analogous to snowflake aggregation aggregates sediment en masse and form the distal mass deposition maxima observed in many recent volcanic ash fall deposits this work provides a data resource that will facilitate tephra sedimentation modeling and allow model intercomparisons

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

volcanic ash clusters tephra rafts and scavengers abstract much of the volcanic ash deposited in the vicinity of pullman washington from the may 18th eruption of mt st helens in 1980 fell in the form of composite ash clusters 0 25 to 0 5 mm in diameter particles in the clusters ranged from sub micron to more than 40 microns in size the porous clusters rafted large ash particles great distances and scavenged particles of all sizes as the wind blew them eastward the result is poorly sorted ash deposits as far as 644 km east missoula within individual clusters textural relationships suggest that both mechanical interlocking and electrostatic attraction played a role in cluster formation the clusters are very fragile and may never be preserved in the stratigraphic record but it is suggested that this kind of ash transport may well have occurred in the geologic past documentation of this ash cluster fall will promote a better understanding of the physical aspects of the downwind distribution of fine grained volcanic ash the poor size sorting in some ancient ash deposits may thus be explained

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

modeling ash fall distribution from a yellowstone supereruption we used the volcanic ash transport and dispersion model ash3d to estimate the distribution of ashfall that would result from a modern day plinian supereruption at yellowstone volcano the simulations required modifying ash3d to consider growth of a continent scale umbrella cloud and its interaction with ambient wind fields we simulated eruptions lasting 3 days 1 week and 1 month each producing 330 km3 of volcanic ash dense rock equivalent dre results demonstrate that radial expansion of the umbrella cloud is capable of driving ash upwind westward and crosswind n s in excess of 1500 km producing more or less radially symmetric isopachs that are only secondarily modified by ambient wind deposit thicknesses are decimeters to meters in the northern rocky mountains centimeters to decimeters in the northern midwest and millimeters to centimeters on the east west and gulf coasts umbrella cloud growth may explain the extremely widespread dispersal of the 640 ka and 2 1 ma yellowstone tephra deposits in the eastern pacific northeastern california southern california and south texas

origin of the mount pinatubo climactic eruption cloud implications for volcanic hazards and atmospheric impacts volcanic ash clouds can be fed by an upward directed eruption column plinian column or by elutriation from extensive pyroclastic flows coignimbrite cloud there is considerable uncertainty about which mechanism is dominant in large scale eruptions here we analyze in a novel way a comprehensive grain size database for pyroclastic deposits we demonstrate that the mount pinatubo climactic eruption deposits were substantially derived from coignimbrite clouds and not only by a plinian cloud as generally thought coignimbrite ash fall deposits are much richer in breathable 10 mm ash 5 25 wt than pure plinian ash at most distances from the source volcano we also show that coignimbrite ash clouds as at pinatubo are expected to be more water rich than plinian clouds leading to removal of more hcl prior to stratospheric injection thereby reducing their atmospheric impact

settling driven convection a mechanism of sedimentation from stratified fluids convection driven by sediment particles may play an important role in sedimentation from the base of buoyant hypopycnal plumes for example fluvial plumes in stratified estuaries and lakes black smokers on the ocean floor volcanic clouds and coastal currents in addition to the well known double diffusive convection mechanism another mode of convective instability development is by settling across the density interface we performed laboratory experiments to investigate this fingering convective instability mechanism and its effect on particle distribution in the water column and deposition at the bed a simple theoretical model of finger formation at a fluid density interface is developed based on an analogy with thermal plume formation at a flat heated plate this model which involves a thickening interface layer that becomes gravitationally unstable relative to the ambient fluid is in good agreement with measurements of finger size and instability wavelength from visualization experiments since fingering at the density interface drives larger scale convection in the fluid below a mass balance model of the lower layer assuming strong mixing i e uniform sediment concentration is successfully applied to predict sediment concentration in the water column and deposition at the bed strong mixing can be assumed since convective velocities are usually much greater than the particle fall velocities as convection proceeds the sediment concentrations in the two layers approach each other and convection will die out using the model equations we develop analytical expressions for the time when convection ceases and the portion of sediment remaining in the water column

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

the impact of the 1991 mount pinatubo tephra fallout on the geochemical environment of the deep sea sediments in the south china sea abstract seven years after the 1991 mount pinatubo eruption the current geochemical environment of ash covered deep sea sediments in the south china sea was investigated the depth distributions of o2 no3 mn2 corg and porosity at six representative sites covered with varying thicknesses of tephra are reported the shapes of the depth profiles reveal that o2 is totally exhausted within ash layers thicker than 3 cm while thinner layers are penetrated by oxygen followed by linear downcore profiles with depletion between 8 and 12 cm hence the zone between ash layer and total depletion of oxygen represents a zone of negligible oxygen consumption various multi layer models were developed to explain the observed oxygen concentration profiles these mathematical simulations also serve to assess both the development since the surface sediments were sealed by the ash fallout as well as the future evolution whereas thick tephra layers provoke a nearly stationary situation i e are capable of preventing oxygen from penetrating into the underlying sediments oxygenation of sediments below thin layers increases rapidly in these sediments the effect of oxygen diffusion velocity is drastically reduced by the reaction with dissolved manganese and therefore explains the linear profiles besides this study is suitable as a case study to assess the effects of human interventions in the deep sea ecosystem such as mining and waste dumping

fallout of volcanic ash to the deep south china sea induced by the 1991 eruption of mount pinatubo philippines an ongoing sediment trap experiment in the central south china sea provided the opportunity to investigate directly the mode and rates of a medial fallout of volcanic ash following the june 15 1991 eruption of mount pinatubo philippines within less than three days after the release of the major eruption plume ash accumulation 9 kg m 2 was simultaneously recorded by traps positioned in 1190 and 3730 m water depth at a distance of 586 km to the west of the volcano a numerical simulation of the fallout reveals that the vertical trajectories of the pyroclasts in both the atmosphere and ocean were controlled by particle aggregation the aggregation process caused a premature subaerial fallout of fine grained ash after crossing the air sea interface vertical settling of the ash clusters was enhanced by absorption of water leading to settling rates of more than 1670 m d aggregates were observed at all depths and their rapid settling is reflected in identical pyroclast spectra in intermediate and deep water this implies that particle sorting must have been complete in the upper water column and that the fallout was not perturbed by oceanic currents the tephra blankets an area of 37 10 4 km 2 in a fan shaped westward distribution which reflects the prevailing direction of the upper level winds our data show that atmospheric tephra dispersal patterns are recorded almost instantaneously on the deep sea floor and corroborate the key role of deep sea ash layers as highly reliable chronostratigraphic markers and as a geological tool to infer ancient wind fields

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

from gullies to mountain belts a review of sediment budgets at various scales this paper reviews the state of the art in the concept as well as in the application of sediment budgets in sedimentary research sediments are a product of mass dispersal at the earth surface and take part in global cycles sediment budgets aim at quantifying this mass transfer based on the principle of mass conservation and are the key to determine ancient fluxes of solid matter at the earth surface this involves fundamental questions about the interplay of uplift climate and denudation in mountain belts and transfer of sediments from the continents to the oceans as well as applied issues such as soil and gully erosion reservoir siltation and coastal protection first after introducing basic concepts relevant scales and methodologies the different components of quaternary routing systems from erosion in headwaters river systems glacial and paraglacial systems lakes deltas estuaries coasts shelves epicontinental seas and deep sea fans are discussed in terms of their sediment budget most suitable are sedimentologically closed or semi closed depositional environments e g alluvial fans lakes deltas and deep sea fans in a second step the dynamics of passive active and collisional tectonic settings and sediment budgets in related sedimentary basins are explored and new concepts of sediment portioning at large geodynamic scales are introduced ancient routing systems are more or less incomplete and may be intensively fragmented or destroyed in active tectonic settings in terms of sedimentary basin types rifts intracontinental and epicontinental settings are preferred objects of sediment budgets because of their persistence and relatively simple overall sedimentary architecture however closing basins such as foreland forearc retroarc piggy back and wedge top basins may provide excellent snapshots of orogenic sediment fluxes in a third step the large long lived routing systems of the amazon the ganges brahmaputra and the rhine are reviewed for each system estimates of either sediment volumes mass or sediment fluxes of continental and marine subsystems have been compiled in order to receive a complete routing in terms of mass conservation for specific time periods since the late glacial maximum as well as the cenozoic following lessons can be taken from these case studies i depositional centers and fluxes show strong shifts in space and time and call for caution when simply looking at subsystems ii the response times of these large systems are within the milankovich time interval thus lower than predicted from diffusion models iii cyclic routing of sediments in continental basins is much more dominated by climate human control than by eustacy and iv at long time scales ultimate sinks win over intermittent storage it is concluded from this review that the quantitative understanding of global sediment cycling over historic and geologic time and its response to allogenic forcing is still in its infancy and further research is needed towards a holistic view of sediment routing systems at various temporal and spatial scales and their coupling with global biogeochemical cycles this includes i to better determine response times of large routing systems by linking quaternary with cenozoic sediment budgets and continental with marine sub systems ii to combine advanced provenance techniques with sediment budgets in order to reconstruct ancient systems iii to study sediment partitioning at the basin scale iv to reconcile continental supply dominated sequence stratigraphy with the eustatic dominated marine concept and iv to account for non actualism of ancient systems with respect to their erosion and transport mode in particular during glaciations and pronounced arid intervals glacial and eolian sediment routing may cross over hydrologic boundaries of drainage basins thus challenging the principle of mass conservation

geochemistry of the late permian no 30 coal seam zhijin coalfield of southwest china influence of a siliceous low temperature hydrothermal fluid this paper describes the influence of siliceous low temperature hydrothermal fluid on the elemental concentrations and mineralogical characteristics of the late permian anthracitic ro max 3 58 coal seam no 30 from the zhijin coalfield in western guizhou province sw china coal samples were examined using instrumental neutron activation analysis inductively coupled plasma mass spectroscopy inductively coupled plasma atomic emission spectrometry x ray fluorescence powder x ray diffraction scanning electron microscopy equipped with energy dispersive x ray and isotope analysis the modes of occurrence of elements were determined using a sequential chemical extraction procedure the studies indicate that the no 30 coal seam has a very high content of veined quartz vol 9 4 whose isotope values of 30si and 18o are 0 6 and 15 4 respectively indicating that the quartz originated from siliceous low temperature hydrothermal fluid formation temperature 160 220 c rather than detrital material of terrigenous origin or magmatic hydrothermal inputs results of scanning electron microscopy equipped with energy dispersive x ray and sequential chemical extraction procedure show that the veined quartz is the dominant source of fe cu u pd pt and ir which are as high as 2 31 356 8 2 1 2 43 and 0 006 g g in this coal seam respectively the studies have also found that elements such as fe and cu are mainly in the veined quartz and they do not occur as sulfides in this coal seam in sharp contrast to many other coal seams in china the geochemical and mineralogical anomalies of the coal are attributed to the siliceous low temperature hydrothermal fluid

the plinian eruptions of 1912 at novarupta katmai national park alaska the three day eruption at novarupta in 1912 consisted of three discrete episodes episode i began with plinian dispersal of rhyolitic fallout layer a and contemporaneous emplacement of rhyolitic ignimbrites and associated proximal veneers the plinian column was sustained throughout most of the interval of ash flow generation in spite of progressive increases in the proportions of dacitic and andesitic ejecta at the expense of rhyolite accordingly plinian layer b which fell in unbroken continuity with purely rhyolitic layer a is zoned from 99 to 15 rhyolite and accumulated synchronously with emplacement of the correspondingly zoned ash flow sequence in mageik creek and the valley of ten thousand smokes vtts only the andesiterichest flow units that cap the flow sequence lack a widespread fallout equivalent indicating that ignimbrite emplacement barely outlasted the plinian phase on near vent ridges the passing ash flows left proximal ignimbrite veneers that share the compositional zonation of their valley filling equivalents but exhibit evidence for turbulent deposition and recurrent scour episode ii began after a break of a few hours and was dominated by plinian dispersal of dacitic layers c and d punctuated by minor proximal intraplinian flows and surges after another break dacitic layers f and g resulted from a third plinian episode iii intercalated with these proximally are thin intraplinian ignimbrites and several andesite rich fall flow layers both cd and fg were ejected from an inner vent 400 m wide nested within that of episode i into which the rhyolitic lava dome novarupta was still later extruded two finer grained ash layers settled from composite regional dust clouds layer e which accumulated during the d f hiatus includes a contribution from small contemporaneous ash flows and layer h settled after the main eruption was over both are distinct layers in and near the vtts but distally they merge with cd and fg respectively they are largely dacitic but include rhyolitic shards that erupted during episode i and were kept aloft by atmospheric turbulence published models yield column heights of 23 26 km for a 22 25 km for cd and 17 23 km for fg and peak mass eruption rates of 0 7 1x108 0 6 2x108 and 0 2 0 4x108 kg s 1 respectively fallout volumes adjusted to reflect calculated redistribution of rhyolitic glass shards are 8 8 km3 4 8 km3 and 3 4 km3 for episodes i ii and iii microprobe analyses of glass show that as much as 0 4 km3 of rhyolitic glass shards from eruptive episode i fell with cde and 1 1 km3 with fgh most of the rhyolitic ash in the dacitic fallout layers fell far downwind se of the vent near the rhyolite dominated ignimbrite however nearly all of layers e and h are dacitic showing that the downwind rhyolitic ash is of co plinian rather than co ignimbrite origin

sedimentological analysis of the tephra from the 12 15 august 1991 eruption of hudson volcano the tephra fallout from the 12 15 august 1991 explosive eruption of hudson volcano cordillera de los andes 45 54 s 72 58 w chile was dispersed on a narrow elongated ese sector of patagonia covering an area on land of more than 100 000 km2 the elongated shape of the deposit together with the relatively coarse mean and median values of the particles at a considerable distance from the vent were the result of strong winds blowing to the southeast during the eruption the thickness of the fall deposit decreases up to 250 km ese from hudson volcano where it begins to thicken again secondary maxima are well developed at approximately 500 km from the vent secondary maxima together with grainsize bimodality in individual layers and in the bulk deposit suggest that particle aggregation played an important role in tephra sedimentation the fallout deposit is well stratified with alternating fine grained and coarsegrained layers which is probably a result of strong eruptive pulses followed by relatively calm periods and or changes in the eruptive style from plinian to phreatoplinian the tephra is mostly composed of juvenile material the coarse mode mostly pumice shifts to finer sizes with distance from the volcano the fine mode mostly glass shards is always about 5 6 phi glass shards and pumice are mostly light gray to colorless however considerable amounts of dark poorly vesiculated blocky shards suggest a hydromagmatic component in the eruption a land based tephra volume of 4 35 km3 was estimated and a total volume of 7 6 km3 arose from an extrapolation which took into account the probable volume sedimented in the sea bulk density ranges from 0 9 to 1 10 gr cm3 beyond 110 km from the vent rather uniform density values measured in crushed samples 2 45 2 50 gr cm3 at all distances from the vent reveal a relatively homogeneous composition mean and median sizes decrease rapidly up to 270 km from the vent beyond that point they are more or less constant whereas the maximum size 1 phi shows a steady decrease up to 550 km a concomitant improvement in sorting is observed this is attributed to sorting due to wind transport combined with particle aggregation at different times and distances from the vent the hudson tephra fallout shares some strikingly similar features with the mount st helens 18 may 1980 and quizapu 1932 eruptions

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

volcanic ash fall events identified using principal component analysis of a high resolution speleothem trace element dataset large multivariate trace element datasets produced by la icp ms speleothem analysis can pose difficulties for analysis and interpretation processes acting on various timescales and magnitudes affect trace element concentrations and deconvolving the most important controls is often complex here principal component analysis pca is applied to identify the modes and timings of variation which best explain the overall variability in an exceptionally high resolution 10 m vertical resolution multivariate trace element record produced by la icp ms from a modern 1979 2001 belizean stalagmite with excellent age control principal component 1 pc1 in this dataset is defined by a weak correlation between multiple elements and may reflect non carbonate material incorporated within the speleothem elevated pc1 scores in atm 7 occur following regional volcanic eruptions with ash clouds extending over the cave site as demonstrated using nasa remote sensing data from the total ozone mapping spectrometer and hysplit trajectory modelling spikes in pc1 occur at the beginning of the wet season and this may reflect a seasonal flushing event that transports volcanogenic material through the karst and incorporates it within the speleothem our results suggest that pca can simplify exploration of large laser ablation datasets and that pca is a valuable tool for identifying the dominant controls on stalagmite trace element chemistry future studies should evaluate how transferable this technique is to other sites with different environmental conditions where volcanic ashfall has occurred this research potentially adds tephrochronology to the stalagmite dating toolkit or conversely opens the door to using stalagmites to identify previously unknown or uncertainly dated eruptions

bioturbational structures record environmental changes in the upwelling area off vietnam south china sea for the last 150 000 years the sediments in the upwelling area off central vietnam are totally bioturbated and display a low diverse assemblage of bioturbational structures during interglacial times marine isotope stage mis 1 5a 5c 5e summer monsoon leads to pronounced upwelling and seasonally pulsed arrival of organic matter on the seafloor these deposits are characterized by a 4 tier bioturbated zone with zoophycos zoophycos producers used this seasonal food source and show a cache behavioral strategy during glacial periods upwelling was weak and oxygenation of bottom water decreased as evidenced by bioturbational structures that show a decrease in size penetration depth and diversity enlarged freshwater influx during glacial times fuelled primary production and led to estuarine circulation the resultant oxygen minimum layer favored an increased deposition of organic matter that in turn affected sediment properties during mis 2 and 5b oxygenation was probably a little lower than today during mis 3 and 5d chondrites like burrows point to a stronger oxygen deficiency during mis 4 bottom water oxygenation was even lower and only biodeformational structures occur in soft sediment rich in benthic food based on these findings an ichnofabric model for food rich fairly soft deposits experiencing oxygen deficiency is suggested having biodeformational structures as low oxygen end member

a reappraisal of mount st helens ash clusters depositional model from experimental observation abstract ash clusters depositing the distal ash of the may 18 1980 eruption of mount st helens are supposed to be generated due to electrostatic forces within the eruption cloud therefore an experimental attempt was made to test electrostatic ash clustering which produced fallout with artificial ash clusters in the laboratory its grain size characteristics were similar to the mount st helens ash proximal fallout was coarse grained but showed a fine tail on the distribution curve medial ash was bimodal with the distribution minimum at 45 63 m distal ash was fine grained 63 m and cluster modifying ash 63 m clustering and subsequent deposition of two different typs of ash aggregates explain the grain size characteristics of the mount st helens and the experimental fallout ash proximal fallout was deposited as single grain clusters composed of a large particle 63 m with adhering fines settling at the grain specific rates of the largest particle distal fallout settled as fine ash clusters made up of ash 90 wt of which were

simulating the dispersal of tephra from the 1991 pinatubo eruption implications for the formation of widespread ash layers abstract puff and hazmap two tephra dispersal models developed for volcanic hazard mitigation are used to simulate the climatic 1991 eruption of mt pinatubo puff simulations indicate that the majority of ash was advected away from the source at the level of the tropopause 17 km several eruptive pulses injected ash and so2 gas to higher altitudes 25 km but these pulses represent only a small fraction 1 of the total erupted material released during the simulation comparison with toms images of the so2 cloud after 71 and 93 h indicate that the so2 gas originated at an altitude of 25 km near the source and descended to an altitude of 22 km as the cloud moved across the indian ocean hazmap simulations indicate that the pinatubo tephra fall deposit in the south china sea was formed by an eruption cloud with the majority of the ash concentrated at a height of 16 18 km results of this study demonstrate that the largest concentration of distal ash was transported at a level significantly below the maximum eruption column height 40 km and at a level below the calculated height of neutral buoyancy 25 km simulations showed that distal ash transport was dominated by atmospheric circulation patterns near the regional tropopause in contrast the movement of the so2 cloud occurred at higher levels along slightly different trajectories and may have resulted from gas particle segregations that took place during intrusion of the pinatubo umbrella cloud as it moved away from source

the impact of the 1991 mt pinatubo eruption on deep sea foraminiferal communities a model for the cretaceous tertiary k t boundary the ash layer from the 1991 mt pinatubo eruption provided a natural laboratory to assess mass mortality and the rates of recovery of deep marine ecosystems after a catastrophic event and to draw a parallel with the environmental impact of the k t boundary event on deep sea foraminiferal communities the first recolonization assemblages of benthic foraminifers after the mt pinatubo ash fall exhibit surprising similarities with benthic foraminiferal communities established following the k t boundary event i e comparatively low abundance and diversity absence of suspension feeders dominance of mobile infaunal taxa and a high proportion of agglutinated foraminifers the first foraminifers to recolonize the deep sea after both catastrophic events were opportunistic forms with high capability for rapid dispersal however major differences are evident in the timing and duration of the faunal transitions post eruption assemblages with high proportions of epibenthic suspension feeders became established after a short initial recolonization phase of approx 6 7 years on the mt pinatubo ash layer in the k t sections comparatively stable new benthic foraminiferal assemblages including suspension feeders only became established several thousand years after the event delayed recovery of the pelagic ecosystem and poor deep water ventilation probably slowed down the recovery of the benthic community structure after the k t boundary c 2005 elsevier b v all rights reserved

effects of the crater on eruption column dynamics 1 during explosive eruptions a mixture of pyroclasts and volcanic gas forms a buoyant eruption column or a pyroclastic flow we systematically investigate how the condition that separates these two eruption styles column collapse condition depends on crater shape and magma chamber conditions by integrating the theoretical models for conduit flow flow inside a crater and eruption column dynamics the results show that previous model predictions of column collapse condition based on the relationship between magma discharge rate and water content nf strongly depend on crater shape depth d and opening angle when a crater is present the decompression and or compression of gas pyroclast mixture inside and just above the crater result in two distinct types of column collapse collapse with increasing hm side collapse and that with decreasing lm side collapse hm side collapse is caused by an increase in conduit radius during the waxing stage of an eruption lm side collapse is associated with a decrease in magma chamber pressure during the waning stage the value of for hm side collapse varies by two orders of magnitude depending on crater shape for fixed nf this estimate also depends on assumed models for decompression into the atmosphere the value of for lm side collapse is 108 kg s 1 when d tan 102 m these results are consistent with the field observations from the st helens 1980 and pinatubo 1991 eruptions

influence of convective sedimentation on the formation of widespread tephra fall layers in the deep sea the formation of widespread volcanic ash fall layers in deep sea sediments was investigated experimentally to examine the settling behavior of tephra 20 180 m diameter as it travels from the atmosphere into water using a fallout mass flux rate that was constrained by measurements of distal fallout from the 1980 eruption of mount st helens 0 2 g cm 2 hr the experiments show that particle settling in the water column is dramatically accelerated by the formation of diffuse vertical gravity currents the currents form as a result of convective instabilities that develop in a surface boundary layer when the local particle concentration becomes large at the air water interface the settling velocity of particles drops abruptly and the concentration of particles increases because of the differential in mass flux above and below the fluid surface the implication of the experiments is that deposition of distal tephra fall layers in deep sea sediments may be dominantly controlled by diffuse vertical gravity currents as opposed to passive settling of individual particles through the water column this process greatly reduces the residence time of fine ash in the ocean and diminishes the role of ocean currents in influencing the distribution patterns of individual tephra layers support for this mechanism comes from observations of greatly accelerated tephra settling rates in the south china sea following the 1991 eruption of mount pinatubo in the philippines

fallout of pyroclastic debris from submarine volcanic eruptions volcanic fallout deposits on land being widespread and accessible for study have received much attention and have revealed a great deal about subaerial eruption mechanisms in contrast virtually nothing is known about equivalent deposits produced by submarine volcanoes despite the probable abundance of such material in today s oceans and in accreted volcanic arc terrains many submarine deposits may form by the fallout of debris to the sea floor downcurrent from the umbrella region of submarine eruption columns experiments on water saturated pumice and pieces of rock lithics show that particles settling to the sea floor at terminal velocities of 10 to 50 centimeters per second will display conspicuous bimodality of particle diameters pieces of pumice may be five to ten times as large as codeposited lithic fragments similar material erupted into the air and deposited on land displays less well developed bimodality pumice diameters are generally two to three times as large as associated lithics submarine fallout deposits are therefore distinctive and may be used to indicate a subaqueous origin for some of the great thicknesses of nonfossiliferous volcanic debris contained in ancient volcanic terrains worldwide whose environment of deposition has been uncertain

concentrations and origins of platinum group elements in late paleozoic coals of china the platinum group elements pges in 63 samples collected from the late paleozoic coal bearing strata in western guizhou province and north china were determined using high resolution inductively coupled plasma mass spectrometry hr icp ms the study shows that pges in coal have five different sources magmatic hydrothermal inputs low temperature hydrothermal fluids synsedimentary volcanic ash detrital minerals of terrigenous origin and seawater this study indicates that the first three sources can lead to enrichment of pges in these chinese coals the typical low contents of pges in most of the studied coals defined as background contents in this work mainly originate from detrital minerals the background content of pd 150 ng g is higher than that of pt 30 ng g and much higher than that of ru 5 ng g rh 14 ng g and ir 1 ng g the pd content is nearly 15 fold higher than the crustal abundance in contrast pt content is lower than its crustal abundance the relatively good correlation between pd pt and ash contents suggests that the pges are associated with minerals

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

fall vs flow activity during the 1991 climactic eruption of pinatubo volcano philippines six years after the 1991 mt pinatubo eruption deep erosion incisions into the pyroclastic deposits accumulated around the volcano enabled us to investigate the stratigraphy of the climactic deposits both in valley bottoms and on contiguous ridges stratigraphic relationships between fall flow and surge deposits in the marella drainage system indicate that during the climactic eruption a progressive shift occurred from an early convective regime to a transitional regime feeding both the plinian convective column and mostly dilute density currents to a fully collapsing regime producing mostly dense pyroclastic flows syn plinian dilute density currents surges propagated up to 10 km from the crater both along valley bottoms and on contiguous ridges of the marella valley whereas post plinian pyroclastic flows had greater runout 13 km were confined to valleys and were not associated with significant surges stratigraphic study and grain size analyses allow the identification of three types of intra plinian deposits a lower and often coarse grained surge deposits emplaced during the accumulation of the coarsest portion of the fallout bed at time intervals of 16 24 min b upper fine grained surge deposits interstratified with the fine grained portion of the fall bed and emplaced at shorter time intervals of 3 13 min and c small volume channel confined massive pumiceous flow deposits interbedded with the upper surges in the upper fine grained fall bed maximum clast size isopleths of 1 6 and 0 8 cm for lithics ml and 2 0 and 4 0 cm for pumices mp show almost symmetrical distribution around the vent indicating that the passing of the typhoon yunya during the climactic eruption had little effect on trajectories of high reynold number clasts significant distortion was however observed for the 3 2 cm ml and 6 0 cm mp proximal isopleths whose patterns were probably influenced by the interaction of the clasts falling from column margins with the uprising co ignimbrite ash plumes application of the carey and sparks 1986 model to the undisturbed isopleths generated by the umbrella cloud yields a maximum column height of 42 km in good agreement with satellite measurements systematic stratigraphic and vertical grain size studies of the plinian fall deposit in the marella valley combined with satellite data and eyewitness accounts reveal that the carrying capacity of the convective column and related fallout activity peaked in the early phase of the eruption beginning slightly before 13 41 and gradually declined until its cessation 3 h later most of the pumiceous pyroclastic flow deposits were emplaced after the end of the fallout activity at 16 30 but before the summit caldera collapse at approximately 19 11 only a small volume of pumiceous flow deposits accumulated after the final caldera collapse in contrast to the previous reconstruction of holasek et al 1996 which interpreted the progressive lowering of the column documented by satellite data as due to a decreasing mass eruption rate we suggest that a progressive shift from a plinian column to a large co ignimbrite column could also account for such a variation

influence of particle aggregation on deposition of distal tephra from the may 18 1980 eruption of mount st helens volcano the may 18 1980 eruption of mount st helens msh produced an extensive ashfall deposit in washington idaho and montana with a minumum volume of 0 55 km3 tephra an unusual feature of the deposit is the occurrence of a second thickness maximum 325 km ene of msh near ritzville washington grain size and component abundance analysis of samples along the main dispersal axis indicates that ash in this region is very fine grained mean size 22 m poorly sorted polymodal and rich in glass shards and pumice fragments a computer simulation of ash fallout from an atmospherically dispersed eruption plume was developed to evaluate various hypotheses for the origin of the distal ash characteristics particularly the thickness versus distance relationship the model was constrained by observations of the eruption column height elevation of major ash transport lateral spreading of the eruption plume and atmospheric wind structure in the vicinity of msh results of different simulations indicate that the second thickness maximum cannot be attributed to either decreased wind velocities over central washington or injection of fine ash above the horizontal wind velocity maximum near the tropopause for the model to fit the observed characteristics of the deposit significant particle aggregation of ash finer than 63 m must be invoked the best fit occurs when ash less than 63 m is aggregated into particles several hundred microns in diameter with a settling velocity of 0 35 m s support for this process comes from the observation and collection of fragile ash clusters of similar size which fell at pullman washington during the may 18 eruption sorem 1982 the premature fallout of fine ash as particle aggregates is a fundamental process in the origin of the grain size characteristics variations in component abundances and thickness versus distance relationship of the may 18 msh ash fall deposit

bimodal grain size distribution and secondary thickening in air fall ash layers investigation of the ashfall deposit from the 1980 mount st helens eruption reveals that the deposit is bimodal the finer population maintaining a uniform grain size distribution away from source and that the deposit exhibits secondary thickening beyond the 1 cm isopach grain size distribution shows that at least 64 of the deposit is finer than 63 m far more than is generally supposed for plinian eruptions an investigation of other ashfall deposits reveals similar grain size bimodality features which are interpreted as evidence of aggregation of fine particles in the eruption cloud our data suggest that aggregation may be a common process during ash fallout from explosive eruptions and that secondary thickening may often occur providing that other conditions are met

mineralogy and geochemistry of a late permian coal in the dafang coalfield guizhou china influence from siliceous and iron rich calcic hydrothermal fluids abstract this paper describes the influence of siliceous and iron rich calcic low temperature hydrothermal fluids lthf on the mineralogy and geochemistry of the late permian no 11 coal anthracitic r r 2 85 in the dafang coalfield in northwestern guizhou province china the no 11 coal has high contents of vein ankerite 10 2 vol and vein quartz 11 4 vol with formation temperatures of 85 and 180 c respectively indicating that vein ankerite and vein quartz were derived from low temperature calcic and siliceous hydrothermal fluids in two epigenetic episodes the vein quartz appears to have formed earlier than vein ankerite did and at least three distinct stages of ankerite formation with different ca sr and fe mn ratios were observed the two types of mineral veins are sources of different suites of major and trace metals scanning electron microscope and sequential extraction studies show that in addition to fe mg and ca vein ankerite is the dominant source of mn cu ni pb and zn in the coal and the contents of these five elements are as high as 0 09 and 74 0 33 6 185 and 289 g g respectively in contrast vein quartz is the main carrier mineral for platinum group elements pges pd pt and ir in the coal and the contents of pd pt and ir are 1 57 0 15 and 0 007 g g respectively sequential extraction showed a high pge content in the silicate fraction up to 10 4 g g pd 1 23 g g pt and 0 05 g g ir respectively it is concluded that the formation of ankerite and quartz and the anomalous enrichment of trace elements in the no 11 coal in the dafang coalfield guizhou result from the influx of calcic and siliceous low temperature hydrothermal fluids

distal enhanced sedimentation from volcanic plumes insights from the secondary mass maxima in the 1992 mount spurr fallout deposits some tephra fallout deposits show an increase of mass and thickness at distances from the source 100 km areas of secondary mass maximum asmm which demonstrates distal enhanced sedimentation from volcanic plumes we explore development of the asmms during the 1992 august and september mount spurr eruptions usa by combining eld data on the spatial distribution of mass and grain size with 1 simulations of individual particle settling through a homogeneous and horizontally strati ed atmosphere and 2 mesoscale models of the three dimensional wind eld that include the effect of the underlying topography the crosswind and downwind variations of deposit characteristics indicate that the increase of sedimentation at the asmms is not formed solely because of preferential settling of small ash particles 125 m as commonly assumed in aggregation models instead asmm grain sizes correspond to the ne modes of the bimodal total grain size distributions there also appears to be a link between the asmm and the topography the mass local minima occur across the windward ank of 2 km high mountain ranges while the asmms spread on the leeward ank mesoscale models of the three dimensional wind eld show vertical oscillations in the wind over mountainous regions which may enhance mechanisms of en masse sedimentation aggregation hydrometeor formation and particle boundary layers as well as strong spatial variations of the horizontal wind eld in the lower troposphere our study demonstrates the importance of using grain size as well as mass data to constrain the complex processes responsible for particle sedimentation from volcanic plumes

tephra layers of large explosive eruptions of baitoushan changbaishan volcano in the japan sea sediments this paper is based on the results of a comprehensive investigations of sediments from seven cores sampled during the international russian chinese cruise 53 of the r v akademik lavrentyev 2010 in the frames of the russian chinese collaboration between the pacific oceanological institute of the far eastern branch of the russian academy of sciences poi feb ras vladivostok russia and the first institute of oceanography fio qingdao china baitoushan chanbaishan volcano had several powerful explosive eruptions during the middle pleistocene holocene which produced widespread tephra layers the paper reports chemical composition of volcanic glasses and minerals from six tephra layers labeled as b og b sado b j b un1 b v and b tm which belong to baitoushan volcano and were identified in sediments of the northwestern part of the sea of japan the tephras were dated using geochronological data for the host sediments the estimated ages for the middle pleistocene tephra is 488 ka the late pleistocene tephras are 71 1 71 9 cal k b sado 50 8 cal ka b j 38 3 cal ka b un1 and 29 0 29 4 cal ka b v the ash layers consist of alkali rich glass of trachydacitic to alkaline rhyolitic composition and specific assemblage of minerals including fe rich augite hedenbergite aegirine augite aegirine arfvedsonite and fayalite the mineral assemblage is typical for alkalic volcanic rocks from continental rift setting aenigmatite a rare mineral from the group of inosilicates was firstly identified in distal tephra of baitoushan volcano supplied into marine sediments the composition of glasses and minerals from all layers are similar it testifies about steady state conditions of the magma accumulation under baitoushan volcano and about the bimodal character of magmatic chambers during the late pleistocene and holocene since 100 ka

an example of enhanced tephra deposition driven by topographically induced atmospheric turbulence spatial variations in the thickness and grain size characteristics of tephra fall deposits imply that tephra depositional processes cannot be fully captured by models of single particle sedimentation from the base of the eruption plume here we document a secondary thickness maximum in a 9 75 ka tephra fall deposit from chaiten volcano chile cha1 eruption this secondary thickness maximum is notably coarser grained than documented historical examples being dominated by medium grained ash and an origin via particle aggregation is therefore unlikely in the region of secondary thickening we propose that high levels of atmospheric turbulence accelerated particles held within the mid to lower troposphere 0 to 6 km towards the ground surface we suggest that this enhancement in vertical atmospheric mixing was driven by the breaking of lee waves generated by winds passing over elevated topography beneath the eruption plume lower atmospheric circulation patterns may exert a significant control on the dispersal and deposition of tephra from eruption plumes across all spatial scales particularly in areas of complex topography

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

measurements of diffusivity near the sediment water interface with a fine scale resistivity probe fine scale profiles of the sedimentary formation factor f were obtained from measurements of resistivity at millimetre intervals in marine sediments these profiles demonstrated that rapid decreases in diffusivity occurred in the upper few centimeters of both compact intertidal sands and fine silty muds in the compact sands a 70 decrease in the formation factor was observed within 2 cm of the interface close correlations were found between the formation factor and sediment porosity for both sediment types profiles of 1f predicted from these correlations and porosity profiles were very similar to those obtained from measurements of resistivity these correlations also suggested that 3 is a better approximation of the formation factor in fine muds than the archie relation 2 in both sediments the interfacial value of the diffusion coefficient was estimated to be between 74 and 87 of its value in free solution a value much higher than is normally assumed

a dual layer chicxulub ejecta sequence with shocked carbonates from the cretaceous paleogene k pg boundary demerara rise western atlantic abstract an up to 2 cm thick chicxulub ejecta deposit marking the cretaceous paleogene k pg boundary the k t boundary was recovered in six holes drilled during odp leg 207 demerara rise tropical western atlantic stunning features of this deposit are its uniformity over an area of 30 km2 and the total absence of bioturbation allowing documentation of the original sedimentary sequence high resolution mineralogical petrological elemental isotopic sr nd and rock magnetic data reveal a distinct microstratigraphy and a range of ejecta components the deposit is normally graded and composed predominantly of rounded 0 1 to max 1 mm sized spherules spherules are altered to dioctahedral aluminous smectite though occasionally relict si al rich hydrated glass is also present suggesting acidic precursor lithologies spherule textures vary from hollow to vesicle rich to massive some show in situ collapse others include distinct fe mg ca ti rich melt globules and lath shaped al rich quench crystals both altered glass spherules and the clay matrix site 1259b display strongly negative e nd t 65 ma values 17 indicating uptake of nd from contemporaneous ocean water during alteration finally fe mg rich spherules shocked quartz and feldspar grains few lithic clasts as well as abundant accretionary and porous carbonate clasts are concentrated in the uppermost 0 5 0 7 mm of the deposit the carbonate clasts display in part very unusual textures which are interpreted to be of shock metamorphic origin the preservation of delicate spherule textures normal grading with lack of evidence for traction transport and sub millimeter scale compositional trends provide evidence for this spherule deposit representing a primary air fall deposit not affected by significant reworking the odp leg 207 spherule deposit is the first known dual layer k pg boundary in marine settings it incorporates compositional and stratigraphic aspects of both proximal and distal marine sites its stratigraphy strongly resembles the dual layer k pg boundary deposits in the terrestrial western interior of north america although there carbonate phases are not preserved the occurrence of a dual ejecta layer in these quite different sedimentary environments separated by several thousands of kilometers provides additional evidence for an original sedimentary sequence therefore the layered nature of the deposit may document compositional differences between ballistic chicxulub ejecta forming the majority of the spherule deposit and material falling out from the vapor ejecta plume which is concentrated in the uppermost part

transport and sedimentation dynamics of transitional explosive eruption columns the example of the 800 bp quilotoa plinian eruption ecuador abstract impact of large scale explosive eruptions largely depends on the dynamics of transport dispersal and deposition of ash by the convective system in fully convective eruptive columns ejected gases and particles emitted at the vent are vertically injected into the atmosphere by a narrow buoyant column and then dispersed by atmosphere dynamics on a regional scale in fully collapsing explosive eruptions ash partly generated by secondary fragmentation is carried and dispersed by broad co ignimbrite columns ascending above pyroclastic currents in this paper we investigate the transport and dispersion dynamics of ash and lapillis during a transitional plinian eruption in which both plinian and co ignimbrite columns coexisted and interacted the 800 bp eruptive cycle of quilotoa volcano ecuador produced a well exposed tephra sequence our study shows that the sequence was accumulated by a variety of eruptive dynamics ranging from early small phreatic explosions to sustained magmatic plinian eruptions to late phreatomagmatic explosive pulses the eruptive style of the main 800 bp plinian eruption u1 progressively evolved from an early fully convective column plinian fall bed to a late fully collapsing fountain dense density currents passing through an intermediate transitional eruptive phase fall syn plinian dilute density currents in the transitional u1 regime height of the convective plinian column and volume and runout of the contemporaneous pyroclastic density currents generated by partial collapses were inversely correlated the convective system originated from merging of co plinian and co surge contributions this hybrid column dispersed a bimodal lapilli and ash fall bed whose grain size markedly differs from that of classic fall deposits accumulated by fully convective plinian columns sedimentological analysis suggests that ash dispersion during transitional eruptions is affected by early aggregation of dry particle clusters

linkages between sea ice coverage pelagic benthic coupling and the distribution of spectacled eiders observations in march 2008 2009 and 2010 northern bering sea icebreaker based sampling in the northern bering sea south of st lawrence island in march of 2008 2009 and 2010 has provided new data on overall ecosystem function early in the annual productive cycle while water column chlorophyll concentrations 5 m these data together with other physical biological and nutrient data are presented here in conjunction with observed sea ice dynamics and the distribution of an apex predator the spectacled eider somateria fischeri sea ice dynamics in addition to benthic food availability as determined by sedimentation processes play a role in the distribution of spectacled eiders which cannot always access the greatest biomass of their preferred bivalve prey overall the data and observations indicate that the northern bering sea is biologically active in late winter but with strong atmospheric and hydrographic controls these controls pre determine nutrient and chlorophyll distributions water column mixing as well as pelagic benthic coupling

rhenium osmium isotope and platinum group element systematics of marine vs non marine organic rich sediments and coals from egypt abstract sediments rich in organic matter are important archives of paleo environmental conditions these archives are often assumed to reflect fully marine conditions however the land proximal environments where many of these archives were deposited require an understanding of the sources of matter here we investigate organic rich sediments from egypt deposited in fully marine land proximal and coastal plain environments we focus on platinum group element inventories and re os isotope systematics and combine them with organic carbon and nitrogen analyses as well as organic petrography to distinguish between terrestrial and marine sources of organic matter we show that fully marine organic rich sediments have more strongly fractionated platinum group element patterns than average continental crust that mimic that of seawater with low ir and high os pt pd and re concentrations as well as high 187 re 188 os values rhenium and os concentrations correlate well with organic carbon and nitrogen in marine organic rich sediments in contrast platinum group element concentrations in terrestrial organic rich sediments coal and land proximal shales are similar to the upper continental crust such deposits generally do not show correlations of re and os with organic carbon and nitrogen concentrations complementing re os isotope analyses with pge analyses analogous to coupled nd isotope and ree analyses aids in the interpretation of re os isochron ages and os isotope initial ratios this is particularly helpful in interpreting geochemical data from sediments deposited in environments that may have been even temporarily isolated from the open ocean and thus record local rather than global geochemical signatures

particles in the great pinatubo volcanic cloud of june 1991 the role of ice 1 pinatubo s 15 june 1991 eruption was earth s largest of the last 25 years and it formed a substantial volcanic cloud we present results of analysis of satellite based infrared remote sensing using advanced very high resolution radiometer avhrr and tiros operational vertical sounder high resolution infrared radiation sounder 2 tovs hirs 2 sensors during the first few days of atmospheric residence of the pinatubo volcanic cloud as it drifted from the philippines toward africa an so2 rich upper 25 km portion drifted westward slightly faster than an ash rich lower 22 km part though uncertainty exists due to difficulty in precisely locating the ash cloud the pinatubo clouds contained particles of ice ash and sulfate which could be sensed with infrared satellite data multispectral ir data from hirs 2 were most useful for sensing the pinatubo clouds because substantial amounts of both ice and ash were present ice and ash particles had peak masses of about 80 and 50 mt respectively within the first day of atmospheric residence and declined very rapidly to values that were 10 mt within 3 days ice and ash declined at a similar rate and it seems likely that ice and ash formed mixed aggregates which enhanced fallout sulfate particles were detected in the volcanic cloud by ir satellites very soon after eruption and their masses increased systematically at a rate consistent with their formation from so2 which was slowly decreasing in mass during the same period the initially detected sulfate mass was 4 mt equivalent to 3 mt so2 and after 5 days was 12 16 mt equivalent to 9 12 mt so2

atmospheric distribution and removal of volcanic ash after the eruption of kasatochi volcano a regional model study 1 in august 2008 kasatochi volcano on the aleutian islands erupted without much advance warning volcanic ash released during this eruption quickly settled out of the atmosphere mainly into the ne pacific ocean the amount of volcanic ash as well as the ash fall area and volume into the ne pacific ocean remains speculative as only a limited number of measurements is available we used a three dimensional atmosphere chemistry aerosol model to determine the atmospheric distribution of so2 and volcanic ash and its fallout after the eruption of kasatochi volcano in a first step modeled atmospheric so2 distributions are compared with satellite data thereby evaluating the model capabilities to reasonably reproduce atmospheric transport patterns for modeled volcanic ash mass a considerable reduction of the atmospheric content already occurred by 10 august the second day after the eruption in accordance with satellite observations gravitational settling is the most efficient removal process for volcanic ash mass exceeding dry and wet deposition by far assuming an ash volume of 0 3 km3 released during the eruption of kasatochi volcano and a median ash particle diameter of 4 m the mass of volcanic ash removed at ground within the 0 1 mm isopach covers an area of 7 6 105 km2 over the ne pacific ocean and makes up 49 of the removed material out of the atmosphere the amount of ash and that of iron attached to it is sufficient to explain measured seawater co2 decrease at the ocean station papa in august 2008 induced by iron fertilization and subsequent phytoplankton production

the 1902 plinian eruption of santa maria volcano guatemala a new assessment of magnitude and impact using historical sources abstract large magnitude volcanic eruptions are rare for this reason those that have occurred in recent history provide important case studies of syn and post eruptive impacts one under studied example is the 1902 plinian eruption of santa maria volcano guatemala sources from the time tell us that volcanic ash from the eruption travelled thousands of kilometres and that associated hazards may have caused several thousand fatalities published estimates of erupted volume range from 4 3 27 km3 the maximum estimates would make the fall deposit the largest of the 20th century to improve constraints on the deposit extent and thickness as well as on the immediate impacts of the eruption on local populations we add to published accounts by compiling contemporary records reported in newspaper articles and telegrams quoted therein we use these records to extend existing isopach maps and to calculate a fall deposit volume of at least 11 4 km3 this is larger than fall deposits from pinatubo philippines 1991 and quizapu chile 1932 but smaller than the fall deposit produced by the 1912 eruption of katmai alaska usa we also provide evidence that supports both high fatality estimates and intentional government suppression of the true impact of the eruption

the run out distance of large scale pyroclastic density currents a two layer depth averaged model abstract we have developed a new two layer pyroclastic density current pdc model that considers the effects of the entrainment and thermal expansion of ambient air in the upper dilute layer in order to investigate the dominant factors controlling the run out distance of large scale pdcs numerical simulations show a dilute current spreading radially from the collapsing eruption column edge and forming a thin dense basal current through particle settling i e a two layer pdc forms forward propagation of the two layer pdc stops owing to lift off of the dilute current and or deposition of the dense current and eventually the two layer pdc converges to a steady state our parametric study classifies the flow patterns of steady state two layer pdcs into one of two flow regimes according to the relative magnitude of the run out distances of the dilute and dense currents this relative magnitude critically depends on the ratio of the deposition speed at the base of the dense current d to the speed of particles settling from the dilute current to the dense current ws the run out distance of the whole two layer pdc is determined by that of the dilute current when d ws is large 4 10 3 otherwise when d ws is small 4 10 3 the run out distance of the dense basal current exceeds that of the dilute current the former increases as d ws decreases the run out distance of the dilute current is too short to explain some of the long run out distances of pdcs observed in the field e g the 1991 pinatubo and 2014 kelud eruptions it is suggested that the dense current traveling beyond the lift off point of the parent dilute current plays a significant role in the emplacement of pdcs with such long run out distances

biotic response to explosive volcanism ostracod recovery after ordovician ash falls abstract the impact of two ordovician ash falls of different intensities was studied in order to determine the recovery patterns of benthic ostracods the studied sections are of sandbian age in nw estonia at poosaspea the kinnekulle k bentonite 40 cm derived from a major volcanic event and at ristna the grimstorp bentonite 6 cm in poosaspea important faunal changes are observed the three pre crisis dominant species i e tetrada memorabilis steusloffina sp nov and olbianella braderupensis were not recovered above the bentonite and at least two of them became extinct the post crisis ecosystem shows strong perturbations of diversity and abundance for a long period of time in ristna the impact of the ash fall is less dramatic all of the dominant pre crisis species survived although some changes in abundance and diversity are observed these results show that significant ash falls lead to marked rearrangement of assemblages and extinction of some taxa while less prominent volcanic episodes only result in temporary changes in the assemblage structure in both cases recovery follows several steps post event ecosystem with survival faunas very low abundance low diversity one two species opportunistic taxa e g sigmoopsis rostrata circulinella nuda dominate the assemblage early stages of recolonization with recovery faunas increasing abundance and diversity recolonization by pre event and immigrant species after a short disturbance period return to climax assemblages with specialized taxa high abundance high diversity although assemblages recovered rapidly after the crises the recovery periods still seem much longer than observed in recent foraminiferal assemblages causal links between the volcanic events and subsequent diversifications could not be demonstrated

the october 1902 plinian eruption of santa maria volcano guatemala abstract the october 1902 eruption of santa maria volcano guatemala was one of the largest this century it was preceded by a great earthquake on april 19 centered at the volcano as well as numerous other major earthquakes the 18 20 hour long plinian eruption on october 25 produced a column at least 28 km high reaching well into the stratosphere the airfall pumice deposit covered more than 1 2 million km2 with a trace of ash and was only two meters thick at the vent white dacitic pumice dark gray scoriaceous basalt with physically and chemically mixed intermediate pumice and loose crystals of plagioclase hornblende hypersthene biotite and magnetite make up the juvenile components of the deposit lithic fragments are of volcanic plutonic and metamorphic origin the plinian deposit is a fine grained crystal rich single pumice fall unit and shows inverse grading mapping of the deposit gives a volume of 8 3 km3 within the one mm isopach crystal concentration studies show that the true volume erupted was at least 20 km3 equivalent to 8 5 km3 of dense dacite and that 90 of the ejecta was less than 2 mm in diameter the plinian volume eruption rate averaged 1 2 105 m3s 1 and the average gas muzzle velocity of the column exceeded 270 ms 1 a total of 8 3 1018 j of energy were released by the eruption a knowledge of both theoretically derived eruption parameters and contemporary information allows a detailed analysis of eruption mechanisms this eruption was the major stratospheric aerosol injection in the 1902 1903 period however mid to low latitude northern hemisphere temperature deviation data for the years following the eruption show no significant temperature decrease this may be explained by the sulfur poor nature of dacite magmas suggesting that volatile composition rather than mass of volatiles is the controlling parameter in climatic response to explosive eruptions