partitioning of pyroclasts between ballistic transport and a convective plume kīlauea volcano 19 march 2008 we describe the discrete ballistic and wind advected products of a small but exceptionally well characterized explosive eruption of wall rock derived pyroclasts from k lauea volcano on 19 march 2008 and for the first time integrate the size distribution of the two subpopulations to reconstruct the true size distribution of a population of pyroclasts as it exited from the vent based on thinning and fining relationships the wind advected fraction had a mass of 6 1 105 kg and a thickness half distance of 110 m placing it at the bottom end of the magnitude and intensity spectra of pyroclastic falls the ballistic population was mapped in the field and using structure from motion techniques to a diameter 10 20 cm over an area of 0 1 km2 with an estimated mass of 1 105 kg initial ejection velocities of 50 80 m s were estimated from inversion of isopleths the total grainsize distribution was estimated using a mass partitioning of 98 of wind advected material and 2 of ballistics resulting in median and sorting values of 1 7 and 3 1 it is markedly broader than those calculated for the products of magmatic explosive eruptions because the grainsize of 19 march 2008 clast population is unrelated to a volcanic fragmentation event and instead was inherited from a population of talus clasts that temporary blocked the vent prior to the eruption despite a conspicuous near field presence the ballistic subpopulation has only a minor influence on the grainsize distribution because of its rapid thinning and fining away from source

agronomic impact of tephra fallout from the 1995 and 1996 ruapehu volcano eruptions new zealand eruptions from ruapehu volcano on 11 and 14 october 1995 and 17 june 1996 distributed at least 36 106 m3 of sulphur s rich tephra over the central and eastern north island of new zealand the tephras added between 30 1500 kg ha 1 s to at least 25 000 km2 of land in primary production smaller but beneficial amounts of selenium se and in some areas potassium and magnesium were also supplied addition of s to the soils in the form of sulphate and elemental s resulted in a drop in soil ph and an increase in pasture s contents within seven weeks of the eruptions the soils affected by the tephra are naturally low in s and se but following the eruptions s was not required in fertilizer applications in many areas the strongest and longest lasting effects of s and se deposition were in high anion retention soils particularly hapludands moist moderately weathered soils derived from volcanic ash soluble fluorine concentrations within the tephras were low compared to historic icelandic and chilean examples however pastoral livestock deaths were apparently caused by fluorosis in addition to starvation when tephra covered feed the ruapehu tephra contained very low concentrations of other soluble toxic elements

conduit enlargement during the precursory plinian eruption of aira caldera japan increase in magma flux as the result of conduit enlargement is one of the key processes that triggered caldera collapse and eruption of the ito ignimbrite from aira caldera at 29 ka we examine the total volume of the pumice fall deposit vertical variations in grain size of pumice and the lithic content in the osumi pumice deposit to investigate the trigger for caldera collapse wider distribution of the later stage unit and the upward coarsening of grain size throughout the osumi pumice fall deposit indicate an increase in magma discharge toward the onset of collapse the total volume of lithic fragments in the osumi pumice fall deposit is estimated as 1 6 km3 based on the lithic content in several representative outcrops and the total volume of the osumi pumice fall deposit the lithic fragments in the osumi pumice fall deposit indicate intense mechanical erosion of the conduit during the plinian eruption prior to caldera collapse caldera collapse requires decompression of the magma chamber by withdrawal of magma effective enlargement of the conduit diameter during precursory eruptive phases is one of the important processes that subsequently allow the rapid discharge of a large volume of magma which in turn facilitates decompression of the reservoir and induces caldera collapse

monitoring ash emission episodes at mt etna the 16 november 2006 case study abstract mt etna in sicily italy is one of the best monitored basaltic volcanoes in the world due to the frequent eruptions from its summit and flanks routine monitoring carried out by istituto nazionale di geofisica e vulcanologia sezione di catania for surveillance purposes permits following the evolution of volcanic events in this paper a description of the ash monitoring system as occurred during the august december 2006 summit eruption at the southeast crater sec is shown this eruption was characterized by lava flow effusions and vigorous strombolian activity eighteen paroxysmal episodes occurred up to the end of november forming weak ash plumes accompanied by moderate tephra fallout over etna s slopes during these events we applied a multidisciplinary approach to promptly monitor the paroxysmal activity and the associated tephra fallout through analysis from seismic tremor and observation from live cameras sampling operations mapping and analysis of the deposit during the most significant episodes we carried out textural and grain size analysis on tephra samples and evaluated the total grain size deposit and the erupted volume while numerical simulations of tephra dispersal allowed better understanding eruptive dynamics an example of this methodology is applied to the 16 november episode during which seismic tremor furnished important constraints on the chronology this paroxysmal eruption produced light fallout on the north east sector of the volcano for about ten hours and a number of debris avalanches over the slopes of the sec cone the erupted deposit was composed for the most part of lithic components and characterized by a total size distribution centered on 2 2 while its total mass was evaluated 7 10 6 kg on the whole such integrated studies help to obtain information on magma fragmentation and eruptive mechanisms to characterize the explosive styles shown by etna and finally to better approach the monitoring of imminent eruptions

monitoring subglacial volcanic eruption using ground based c band radar imagery the main phase of the moderately sized november 2004 eruption of the grimsvotn volcano located in the center of the 8100 km2 vatnajokull glacier was monitored by the icelandic meteorological office c band weather radar in keflavik 260 km west of the volcano the eruption plume reached a height of 6 10 km relative to the vent the distribution of the most distal tephra was measured in the autumn of 2004 while the deposition on the glacier was mapped in the summers of 2005 and 2006 the tephra formed a well defined layer on the glacier in the region north and northeast of the craters the total mass of the tephra layer is quantitatively compared with the retrieved values obtained from an improved version of the volcanic ash radar retrieval varr algorithm varr was statistically calibrated with ground based ash size distribution samples taken at vatnajokull and by taking into account both antenna beam occlusion and wind driven plume advection the latter was implemented by using a space time image phase based cross correlation technique accuracy of the weather radar records was also reviewed noting that a large variability in the plume height estimation may be obtained using different approaches the comparisons suggest that at least for this subglacial eruption the surface tephra mass estimated by using the varr inversion approach is in a fairly good agreement with in situ measurements in terms of spatial extension distribution and amount

memovolc report on classification and dynamics of volcanic explosive eruptions classifications of volcanic eruptions were first introduced in the early twentieth century mostly based on qualitative observations of eruptive activity and over time they have gradually been developed to incorporate more quantitative descriptions of the eruptive products from both deposits and observations of active volcanoes progress in physical volcanology and increased capability in monitoring measuring and modelling of explosive eruptions has highlighted shortcomings in the way we classify eruptions and triggered a debate around the need for eruption classification and the advantages and disadvantages of existing classification schemes here we i review and assess existing classification schemes focussing on subaerial eruptions ii summarize the fundamental processes that drive and parameters that characterize explosive volcanism iii identify and prioritize the main research that will improve the understanding characterization and classification of volcanic eruptions and iv provide a roadmap for producing a rational and comprehensive classification scheme in particular classification schemes need to be objective driven and simple enough to permit scientific exchange and promote transfer of knowledge beyond the scientific community schemes should be comprehensive and encompass a variety of products eruptive styles and processes including for example lava flows pyroclastic density currents gas emissions and cinder cone or caldera formation open questions processes and parameters that need to be addressed and better characterized in order to develop more comprehensive classification schemes and to advance our understanding of volcanic eruptions include conduit processes and dynamics abrupt transitions in eruption regime unsteadiness eruption energy and energy balance

estimating volcanic plume heights from depositional clast size 1 tephra deposits retain a considerable amount of information about the nature of volcanic eruptions with plume height commonly inferred from maximum clast size measurements however current methods for inferring plume height from maximum clast size lose some of the accuracy in measurements made in the field and have limited application when trying to constrain the uncertainty in these parameters here a predictive numerical model is used to determine plume height from maximum clast size found in a deposit plume height is an essential parameter for inferring eruption magnitude as it is explicitly related to mass eruption rate we investigate the effects of different atmospheric and wind profiles allowing the input conditions to be location specific for each eruption the use of a predictive model reduces the uncertainty in determining plume height as it retains the detail of measurements made in the field and incorporates the uncertainty in these measurements in the results in the form of a probability distribution we have applied this approach to fall deposits from the 1991 eruption of pinatubo one of the few plinian eruptions in which the true height of the plume is well known the predicted plume heights are in good agreement with those found from satellite measurements this new approach provides a method for determining plume height from poorly preserved fall deposits from which a limited amount of data can be sampled leading to large uncertainties in the field measurements

initiation of dilute and concentrated pyroclastic currents from collapsing mixtures and origin of their proximal deposits numerical solution of the time dependent conservation equations for mass momentum specific internal energy and granular temperature in flows involving gas particle mixtures is used to explore the initiation of pyroclastic currents from collapsing mixtures such as during fountaining eruptions one objective is to determine when a depth averaged granular flow model or a box model for dilute currents is most applicable for hazards modeling of pyroclastic currents produced by column collapse a second objective is to gain insight into the formation of proximal breccia facies of ignimbrites collapsing gas particle mixtures impacting a flat surface are modeled with mixtures of coarse particles that are poorly coupled with the gas phase and well coupled fine particles resulting lateral flows are sensitive to the impact speed overall particle concentration and proportions of fine and coarse particles for total particle concentrations of around 1 vol an impacting mixture consisting of at least 50 coarse particles relative to fines will tend to form a concentrated lateral underflow which can be approximated by a depth averaged granular flow model for hazard assessment purposes starting from the impact zone low total particle concentrations e g total concentrations of 0 1 vol tend to produce dilute lateral flows that could be simplified to box model approaches for dilute pyroclastic currents larger total particle concentrations in impacting mixtures 10 vol produce granular underflows if they have any coarse particles but these can be complicated by mach number effects for intermediate concentrations of the impacting mixture a rough threshold for development of a concentrated underflow versus a dilute only current is based upon the flux per unit area of coarse particles to the impact and their stokes numbers in general some knowledge of the eruption column fountain conditions is required in order to make an informed decision as to which hazards modeling approach is most applicable for a given scenario modeling indicates that proximal breccias are related to influxes of coarse wall rock material into an eruptive mixture which increase both the total particle concentration and the proportion of coarse dense clasts in the mixture that subsequently collapses and impacts the ground the breccias record concentration of dominantly coarse clasts immediately upon impact and formation of concentrated flows that propagate laterally while expelled fines and gas flow rapidly overhead as dilute currents lateral and vertical heterogeneity in proximal deposits likely record rapid time and space variations in avalanches of material into eruptive vents and the occurrence of breccia hummocks might record the temporary positions of impact zones

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

structure degradation and changes in the mechanical behaviour of a stiff clay due to weathering the paper discusses the results of research into the causes of weathering of stiff pleistocene clays located in the montemesola basin ta italy and on the effects of weathering on the clay s mechanical behaviour the weathered clays are yellow brown and overlie the original grey clays in the whole basin the liquidity indexes of both the yellow and the grey clays their fabric as observed by means of scanning electron microscopy as well as the yellow clay oxidation features suggest that drying has been the main weathering process in the basin this is confirmed by the results of drying wetting cycle tests carried out in the laboratory on undisturbed clay samples which show the drying wetting cycles to produce changes in the grey clay similar to those present in situ due to weathering results of oedometer stress path and triaxial tests show that weathering has caused a degradation of the clay bonding and an associated reduction in the size of the clay state boundary surface both one dimensional an

eruptive dynamics of the citlaltepetl pumice at citlaltepetl volcano eastern mexico abstract citlaltepetl pico de orizaba is mexico s highest 5675 m a s l potentially active volcano which is presently in a dormant state between 9 0 and 8 5 ky b p a sequence of volcanic eruptions occurred at citlaltepetl volcano as part of the most explosive holocene episode this sequence is associated with the deposition of an intercalation of pumice fallout and scoria and pumice rich pyroclastic flow deposits named here as citlaltepetl pumice c p detailed stratigraphic and petrographic correlation of over 100 measured sections in conjunction with the analysis of the physical characteristics of the juvenile and lithic portions of each main layer of the sequence provided the basis to reconstruct the eruptive episodes and to assert the eruptive dynamics of the whole sequence which was divided into eight main eruptions separated by three brief periods of quiescence the eruption sequence started with a phreatic phase that soon developed into a bread crusted bomb bearing phase this was followed by a sequence of vigorous plinian explosive eruptions separated by brief periods of repose and a short dome collapse activity it was followed by another cycle of alternated scoria pyroclastic flows forming and plinian activity this eruptive sequence shows the complexity of single eruptive events with alternated contrasting styles suggested by the compositional differences between the pyroclastic flow and fallout products

total grain size distribution of four subplinian plinian tephras from hekla volcano iceland implications for sedimentation dynamics and eruption source parameters abstract the size distribution of the population of particles injected into the atmosphere during a volcanic explosive eruption i e the total grain size distribution tgsd can provide important insights into fragmentation efficiency and is a fundamental source parameter for models of tephra dispersal and sedimentation recent volcanic crisis e g eyjafjallajokull 2010 iceland and cordon caulle 2011 chile and the ensuing economic losses highlighted the need for a better constraint of eruption source parameters to be used in real time forecasting of ash dispersal e g mass eruption rate plume height particle features with a special focus on the scarcity of published tgsd in the scientific literature here we present tgsd data associated with hekla volcano which has been very active in the last few thousands of years and is located on critical aviation routes in particular we have reconstructed the tgsd of the initial subplinian plinian phases of four historical eruptions covering a range of magma composition andesite to rhyolite eruption intensity vei 4 to 5 and erupted volume 0 2 to 1 km3 all four eruptions have bimodal tgsds with mass fraction of fine ash

the orange tuff a late pleistocene tephra fall deposit emplaced by a vei 5 silicic plinian eruption in west java indonesia a vei 5 dacite eruption emplaced the orange tuff about between 34 3 cal kbp and 17 2 cal kbp gunung salak is the unit s source and the orange tuff represents the most recent such eruption from any of the volcanoes southwest of bogor indonesia the orange tuff is the region s first such documented tephra fall deposit whose characteristics and phenocryst geochemistry make it readily identifiable over at least 1250 km2 magnetite compositions and temperature and fo2 estimates inferred from fe ti oxide compositions are particularly useful for identifying the unit deposit characteristics suggest that the eruption lasted 1 11 h with mass eruption rates of 1 0 8 3 108 kg s and a column height of 31 40 km the eruption s column height and the deposit s 2 5 11 km3 volume suggest that the unit was dispersed over a much wider area than mapped the unit is a marker bed throughout its mapped distribution and has potential to be applied over a much broader area as a regional marker bed the large population and infrastructure proximal to salak suggest that the unit should be considered in hazards assessments despite its age and the lack of subsequent similar eruptions

characteristics of two phreatoplinian ashes and their water flushed origin abstract the whole deposit grain size populations have been determined for two phreatoplinian ashes of the rhyolitic taupo volcano new zealand one is much finer than plinian pumice deposits studied from the same volcano and the other differs in having a lower content of coarse pumice the poor sorting of the two ashes is attributed mainly to water scavenging of the ash cloud the very limited fractionation with distance from source combined with the very regular exponential thickness decrease indicates that the scavenging water was an integral part of the ash cloud and was derived from lake taupo at times when the proportion of erupted water to magma became particularly high erosion of the underlying deposits took place and to this is attributed the striking gullying of the surface which separates the two ashes

a sequence of a plinian eruption preceded by dome destruction at kelud volcano indonesia on february 13 2014 revealed from tephra fallout and pyroclastic density current deposits abstract a plinian style eruption with a radially spreading umbrella cloud occurred on february 13 2014 at kelud volcano indonesia we present the sequence of this plinian event based on a geological survey of the eruption products and analysis of satellite images the eruptive deposits were divided into four major depositional units units a b c and d and used to determine the sequence of events the plinian phase was preceded by partial destruction of the existing lava dome and generation of high energy pyroclastic density currents pdcs mainly toward the ne that produced a series of depositional subunits units a 0 2 and blown down trees stage 1 in the main phase of the plinian eruption tephra fallout unit b was widely distributed over east java stage 2 the winds above the volcano significantly affected the tephra dispersal process in stage 3 the plinian column collapsed generating dense pdcs that flowed down the volcano valleys producing pumiceous lobate deposits unit c the declining phase of the eruption produced fine rich fallout tephra layers unit d 1 2 from low level eruption plumes and or ash lofted from pdcs the eruption sequence constructed from field observations is supported by geophysical observations the deposit features and componentry suggest that newly ascended magma triggered the destruction of the lava dome and the generation of high energy pdcs and during the subsequent climactic phase the dome was completely destroyed we estimate a total erupted volume of 0 25 0 50 km 3 bulk deposit volume 0 14 0 28 km 3 in dense rock equivalent and a mass eruption rate of 6 5 2 8 10 7 kg s with a volcanic explosivity index of 4 the eruption sequence and physical parameters of the 2014 eruption will help assess future volcanic activity and hazards at kelud volcano

the 1732 surtseyan eruption of eggoya jan mayen north atlantic deposits distribution chemistry and chronology the island of jan mayen in the north atlantic ocean is home to the world s northernmost active subaerial volcano beerenberg of the five known historical eruptions on the island the locations of two eruptions 1732 and 1818 have not been accurately located it is known that the 1732 and 1818 eruptions occurred on the south flank of beerenberg and several eruption sites have been proposed for these events here we show that the tuff cone of eggoya on the sw flank of beerenberg was the site of the 1732 eruption based on interpretation of the deposits field relations and historical sources we further describe the deposits from the eruption and show that eggoya is the largest explosive eruption described from jan mayen emplacing at least at least 0 3 0 4 km3 vei 4 of basanitic tephra up to distances of at least 111 km from jan mayen and covering a minimum area of around 500 km2 within the 2 cm isopach we also present our eruption scenario and show that this was an emergent surtseyan eruption with activity shifting between tephra jetting continuous uprush and more magmatic phases

the evolution of bubble size distributions in volcanic eruptions we review observations of bubble size distributions bsds generated during explosive volcanic eruptions and laboratory explosions as inferred from vesicle size distributions found in the end products unimodal polymodal exponential and power law bsds are common even in the absence of coalescence and both power law and exponential distributions have been generated in the same eruption to date theoretical models have proposed incompatible mechanisms for producing the various distributions we here present a unifying mechanism data from our laboratory analogue experiments suggest that power law distributions are associated with highly non equilibrium degassing a numerical model is developed in which bubbles nucleate repeatedly and grow in the spaces between those of previous generations where in a non equilibrium degassing scenario the volatile concentration remains high this process causes the bsd to evolve from unimodal through exponential into a power law the exponent of the power law is a measure of the number of nucleation events or the duration of the nucleation period compared with the timescale of bubble growth the mathematical inevitability of the evolution from unimodal poissonian to power law is discussed the findings may resolve the apparent contradiction between the equilibrium degassing conduit flow models and the non equilibrium degassing conditions derived from bubble growth models of explosive volcanic eruptions the process of ongoing nucleation is the mechanism whereby the volcanic system maintains near equilibrium in the case of rapid depressurisation and slow volatile diffusion

three dimensional volcanic aerosol dispersal a comparison between multiangle imaging spectroradiometer misr data and numerical simulations 1 the three dimensional reconstruction of volcanic plumes is a central goal to enhance our understanding on dispersal processes in this paper we use data from the multiangle imaging spectroradiometer misr on board nasa s terra spacecraft combined with a stereo matching retrieval procedure we show the potential of misr in capturing important features of volcanic plumes like column height optical depth type and shape of the finest particles of two highly explosive eruptions occurring on mount etna in 2001 and 2002 this work tests how tephra dispersal models reconstruct the 3 d shape of volcanic clouds we compare misr data with fall3d an eulerian model for the transport and deposition of volcanic ash and aerosols coupled with the weather research and forecasting mesoscale meteorological model agreement between simulations and misr data is good regarding both events although it could be improved by increasing the accuracy of the meteorological data a better constraint on volcanological input parameters like the height of the eruptive column and improving our understanding of processes such as aggregation phenomena and volcanic cloud microphysics

a study of clast size distribution ash deposition and fragmentation in a hawaiian style volcanic eruption ash deposits from hawaiian style eruptions are generally of small volume but are important in understanding the mechanisms of these eruptions an analysis of the ash deposit from the 1959 kilauea iki eruption of kilauea volcano is presented and the whole deposit grain size distribution for the eruption is calculated the grain size distribution is found to be heavily skewed towards the coarsest clast sizes and to differ considerably from size distributions for plinian deposits

poisson processes of carbonate accumulation on paleozoic and holocene platforms abstract cambro ordovician carbonate lithofacies units in the elbrook and conococheague formations exposed at wytheville virginia as well as those in many other phanerozoic peritidal sequences exhibit exponential thickness frequency distributions that is occurrence frequency decreases exponentially with linear increase in unit thickness such distributions are characteristic of waiting times between independent poisson events this relative frequency of spaces of different size between horizons of lithologic change is what one would expect if the horizons were distributed randomly throughout carbonate successions abundances of different lithologies both as net stratigraphic thickness and as number of occurrences also decreases exponentially among successively rare sediment types with each lithology being about 60 as plentiful as the next more abundant rock type relations between net thickness and number of occurrences for each facies define a linear trend coincident with a mean thickness for all wytheville units of 0 48 m a relation indicating that thickness distribution is independent of facies type similar relations are apparent for the horizontal extent of carbonate sediment bodies from the holocene florida bahama platform areal extents of individual facies units lithotopes are described by a frequency distribution in agreement with that anticipated for a population of equidimensional facies elements whose diameter distribution follows an exponential frequency distribution although regional gradients in sediment texture and composition are also apparent along most transects from platform margin to interior such frequency distributions indicate that lateral extents of individual sediment reflect a largely stochastic distribution of facies boundaries across this holocene surface lithotope abundances also yield trends of exponentially decreasing dominance among successively subordinate facies with each being about 70 as extensive the next more abundant sediment type relations between areas and abundances for all lithotopes define a covariant trend corresponding to a mean area of 2 2 103 km2 for all florida bahamas lithotopes we consider several numerical models of stochastic carbonate accumulation although not demonstrably unique scenarios incorporating the sequential superposition of randomly placed coniform lithotopes result in thickness and area frequency distributions that are the same as those observed in ancient and modern platform deposits such simulations of poisson processes of sediment accumulation are in general agreement with stochastic models of lithologic heterogeneity that have been more widely applied to petroleum reservoirs and groundwater aquifers to the as yet unknown degree that peritidal lithofacies area and thickness are correlated data from paleozoic and holocene platforms suggest that carbonate units should exhibit length height ratios of approximately 105 given the decimeter scale over which facies are designated in most paleozoic peritidal successions these relations predict mean lateral extents on the order of several tens of kilometers a value in general agreement with the few data that exist on spatial continuities of peritidal lithotopes in paleozoic carbonate sequences

retrieval of microphysical and morphological properties of volcanic ash plumes from satellite data application to mt ruapehu new zealand a quantitative analysis of the properties of several mt ruapehu new zealand ash plumes has been performed using multispectral satellite data from the avhrr 2 and atsr 2 instruments the analysis includes identification of the plume from background clouds using the reverse absorption effect in the thermal channels modelling and retrieval of particle sizes determination of the plume height from cloud shadows stereoscopy and meteorological data and estimates of the mass of fine particles radii less than 10 m a new spectral technique for identifying opaque silica rich ash clouds is demonstrated by utilizing the near infrared 1 6 m and visible 0 67 m channels of the atsr 2 and the optical properties of a simple volcanic cloud are presented for use in radiative transfer studies it is found that the ruapehu eruption cloud contained silica rich ash particles with radii generally less than a few micrometres the distribution of fine particles is monomodal with a dominant mode peak of about 3 m radius mass loadings of fine particles are found to be in the range 1 to 7 mg m 3 and are consistent with estimates of mass loadings of volcanic clouds from eruptions of other volcanoes the height of the plume top derived from radiosonde data and plume top temperatures in the opaque regions was found to be between 7 5 and 8 5 km while the plume thickness was estimated to be between 1 5 and 3 km cloud height derived from atsr 2 stereoscopy on a different plume gave heights in the range 5 to 8 km the results of this study provide important information on the optical properties of nascent volcanic eruption plumes this information may prove useful in determining the potential effects of volcanic clouds on local climate and in assessing any hazard to aviation

modeling tephra dispersal in absence of wind insights from the climactic phase of the 2450 bp plinian eruption of pululagua volcano ecuador the determination of eruptive parameters is crucial in volcanology not only to document past eruptions but also for tephra fallout hazard assessments in most tephra fallout studies eruptive parameters have been determined either by empirical techniques or analytical models but the uncertainty of such parameters is usually not well described we have applied both empirical and analytical models to characterize the climactic phase of the 2450 bp plinian eruption of pululagua bf2 layer and explore the variations in the total erupted mass column height and total grain size distribution both approaches yield comparable results in the total mass of tephra erupted 4 5 1 5 1011 kg while they show some discrepancies for the determination of the column height 36 20 km from empirical techniques and 30 20 km from analytical techniques the total grain size distribution of the bf2 layers varies with the different techniques used for the calculation and significantly affects the outputs of analytical models furthermore the determination of the total grain size distribution depends strongly on the number and spatial distribution of the sample location inverting tephra fallout deposits on the total accumulation or thickness gives a good constraint on the total mass erupted but not on the column height however inverting on individual grain size classes better constrains the possible range of column heights but cannot resolve particle release height results from the inversion on individual grain size classes show that large diffusion coefficients are necessary to model the bf2 layer and might be required to model proximal tephra deposits in order not to overestimate the total erupted mass additionally we used a statistical method smoothed bootstrap approach to quantify the uncertainty in eruptive parameters such as column height and total erupted mass our uncertainty analysis yields a mean total erupted mass of 4 5 0 3 1011 kg and a mean column height of 30 3 km results from the uncertainty analysis compare well with results from other approaches finally although the climactic phase of the 2450 bp plinian eruption of pululagua occurred in relatively calm atmospheric conditions our results show that the dispersion of the bf2 layer was influenced by slight northeasterly wind conditions

new estimates of the 1815 tambora eruption volume abstract volume estimates of the 1815 tambora eruption were re analysed using new ash thickness data and new methods giving a range of possible volumes for the different eruption phases volume calculations include ash fall extrapolation and caldera size approximations as well as volume estimates from mass eruption rates and eruption duration to find the most likely range of volumes consistent with the different methods and possible eruption dynamics the results give a total volume of about 41 4 km3 dre made of 23 3 km3 dre ash fall and 18 6 km3 dre pyroclastic flows the ash fall volume can be further divided into 11 2 km3 dre plinian ash fall and 12 4 km3 dre co ignimbrite making the plinian ash fall larger than previously assumed and more intense due to a higher mass eruption rate of 2 109 kg s

mechanism and effect of chemical weathering of sedimentary rocks the mineralogy geochemistry and physical and mechanical properties of rocks from four weathering profiles of miocene to pleistocene mudstones and sandstones in japan showed that chemical weathering of sedimentary rocks is characterized by sequential reaction between percolating groundwater and rock forming minerals pyrite a common mineral contained in sedimentary rocks is especially important in these sequential reactions pyrite is oxidized by oxygen coming from the ground surface and sulfuric acid is generated at the base of the oxidized zone the sulfuric acid in turn dissolves rock forming materials to make a dissolved zone if the fluxes of oxygen and water are in the same direction sulfuric acid generated at the oxidation front migrates farther and forms a dissolved zone if these fluxes are in opposite directions the oxidized and dissolved zones are not differentiated rocks in the dissolved zone are caused to deteriorate by the acid leaching and are acidic if buffering minerals such as calcite and zeolite are absent in the oxidized zone sandstone is strengthened because of cementation by iron oxide or hydroxide while mudstone is weakened because it has greater clay fractions and larger specific surface areas than sandstone

eruption dynamics of the 22 23 april 2015 calbuco volcano southern chile analyses of tephra fall deposits abstract after 54 years since its last major eruption in 1961 calbuco volcano ensenada southern chile reawakened with few hours of warning on 22 april 2015 at 18 05 local time the main explosive eruption consisted of two eruption pulses lasting 1 5 and 6 h each one on 22 and 23 april producing stratospheric 15 km height eruption columns the erupted materials correspond to porphyritic basaltic andesite 55 wt of sio2 the tephra fall affected mainly the area northeast of the volcano and the finest ash was deposited over southern chile and patagonia argentina we studied the tephra fall deposits of both pulses in terms of stratigraphy distribution volume emplacement dynamics and eruption source parameters here we show field observations that have been made 5 470 km downwind and distinguish five layers layers a b b1 c and d representing different stages of the eruption evolution eruption onset layer a pulse 1 followed by the first paroxysmal event layer b pulse 1 in some places interbedded by layer b1 tentatively representing the sedimentation of a secondary plume during the end of pulse 1 we recognized a second paroxysm layer c pulse 2 followed by the waning of the eruption layer d pulse 2 the total calculated bulk tephra fall deposit volume is 0 27 0 007 km3 0 11 0 13 km3 dense rock equivalent 38 of which was erupted during the first phase and 62 during the second pulse this eruption was a magnitude 4 45 event vei 4 eruption of subplinian type

probing deep weathering in the shale hills critical zone observatory pennsylvania usa the hypothesis of nested chemical reaction fronts in the subsurface weathering is both an acid base and a redox reaction in which rocks are titrated by meteoric carbon dioxide co2 and oxygen o2 in general the depths of these weathering reactions are unknown to determine such depths cuttings of rose hill shale were investigated from one borehole from the ridge and four boreholes from the valley at the susquehanna shale hills observatory ssho pyrite concentrations are insignificant to depths of 23 m under the ridge and 8 9 m under the valley likewise carbonate concentrations are insignificant to 22 and 2 m respectively in addition a 5 6 m thick fractured layer directly beneath the land surface shows evidence for loss of illite chlorite and feldspar under the valley secondary carbonates may have precipited the limited number of boreholes and the tight folding make it impossible to prove that depth variations result from weathering instead of chemical heterogeneity within the parent shale however carbonate depletion coincides with the winter water table observed at 20 m ridge and 2 m depth valley it would be fortuitous if carbonate containing strata are found under ridge and valley only beneath the water table furthermore pyrite and carbonate react quickly and many deep reaction fronts for these minerals are described in the literature we propose that deep transport of o2 initiates weathering at ssho and many other localities because pyrite commonly oxidizes autocatalytically to acidify porewaters and open porosity according to this hypothesis the mineral distributions at ssho are nested reaction fronts that overprint protolith stratigraphy the fronts are hypothesized to lie subparallel to the land surface because o2 diffuses to the water table and causes oxidative dissolution of pyrite pyrite derived sulfuric acid h2so4 plus co2 also dissolve carbonates above the water table to understand how reaction fronts record long term coupling between erosion and weathering will require intensive mapping of the subsurface copyright 2013 john wiley sons ltd

fine ash content of explosive eruptions abstract in explosive eruptions the mass proportion of ash that is aerodynamically fine enough to cause problems with jet aircraft or human lungs 50

contrasting mechanisms of magma fragmentation during coeval magmatic and hydromagmatic activity the hverfjall fires fissure eruption iceland growing evidence for significant magmatic vesiculation prior to magma water interaction mwi has brought into question the use of diagnostic features such as low vesicularities and blocky morphologies to identify hydromagmatic pyroclasts we address this question by quantifying co variations in particle size shape and texture in both magmatic and hydromagmatic deposits from the hverfjall fires fissure eruption iceland overlapping vesicularity and bubble number density distributions measured in rapidly quenched magmatic and hydromagmatic pyroclasts indicate a shared initial history of bubble nucleation and growth with substantial vesiculation prior to mwi hydromagmatic fragmentation occurred principally by brittle mechanisms where the length scale and geometry of fracturing was controlled by the bubble population this suggests that the elevated fragmentation efficiency of hydromagmatic deposits is driven at least in part by brittle disintegration of vesicular pyroclasts due to high thermal stress generated during rapid cooling in this way the shape and size distributions of hydromagmatic pyroclasts both critical input parameters for ash dispersion models are strongly influenced by the dynamics of vesiculation prior to mwi this result underlines the need to analyse multiple grain size fractions to characterise the balance between magmatic and hydromagmatic processes during the hverfjall fires eruption the external water supply was sufficient to maintain mwi throughout the eruption with no evidence for progressive exhaustion of a water reservoir we suggest that both the longevity and the spatial distribution of mwi were determined by the pre existing regional hydrology and represent continuous interaction between a propagating dike and a strong groundwater flow system hosted within permeable basalt lavas

the spatial and temporal distribution of pipe formation offshore namibia a group of nearly 400 pipe structures from the continental slope of northern namibia are analysed for their spatial and temporal distribution the pipes most likely formed as a result of highly focused fluid venting and understanding the factors controlling their distribution in space and time is key to their genesis we analysed their spatio temporal distribution using an arbitrary chronostratigraphic timescale from which it is concluded that the pipes did not form at the same time pipe formation is shown to be intermittent and persistent with 2 29 pipes forming in each of the 20 arbitrary time intervals that are considered to span the neogene period the spatial distribution of these pipes is clustered to dispersed spatial statistics conducted on the distribution of pipe formation timings have shown that two statistically significant groups of pipes exist within the population 1 in the north and west and 2 in the south with the former occurring prior to the latter locally pipe formation is sporadic with clusters and outliers occurring during the same time period a conceptual model is proposed whereby pipe formation in specific locations is the result of localised breaching of the seals for isolated pressure cells which are locally independent yet broadly controlled an inferred basinal fluid source is thought to determine the broader patterns of pipe formation and the focus of this fluid source shifts from north to south with time at a local scale multiple local factors interact producing a sporadic pipe formation distribution through a prolonged period of highly focused fluid migration once formed the pipes continued to focus fluids intermittently leading in some cases to later pockmark formation

volcano stratigraphy and physical characterization of the san mateo pomez unit cerritos member temascalcingo volcano central mexico abstract the temascalcingo volcano is a dacitic stratovolcano located at the eastern part of the acambay graben a tectonic basin in the central sector of the trans mexican volcanic belt tmvb which is an active mostly calc alkaline volcanic arc that crosses mexico from the pacific ocean to the gulf of mexico this study characterises the explosive activity of the san mateo pumice eruption that is the most recent and largest paroxysmal episode of this volcano and the last unit of the cerritos member indeed this eruption is associated with an undated debris avalanche event consisting of a major sector collapse developed on the western flank of the volcano stratigraphic data suggest a highly explosive eruption that generated a relatively thick up to 10 m and widespread pumice fallout deposit trending to the ne and an aerial distribution of at least 100 km2 this subplinian type eruption of vei 4 lasted about 9 h and produced a plume height up to 12 km above the vent i e 14 km above sea level this type of explosive eruption is relatively common in the tmvb so a comprehensive geological study with the corresponding numerical simulations like the one that was carried out contributes to the understanding of the explosive volcanism of modest size stratovolcanoes that are common in the tmvb

discussion of eocene to mid pliocene landscape evolution in scandinavia inferred from offshore sediment volumes and pre glacial topography using inverse modelling pederen et al 2018 geomorphology 303 467 485 abstract pedersen et al 2018 use offshore sediment volumes to carry out inverse modelling of the scandinavian landscape during the cenozoic close inspection of the source area s for the sediment volume used in the study reveals that multiple source areas were responsible for the sediments fringing scandinavia in addition to a much more complex origin of the sediments than just scandinavia no consideration about the caliber of the sediments transport media maturation of the sediments and climate is included in the modelling by pedersen et al 2018 the study exposes a large gap between geological observations and modelling

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

implications of weathering on the engineering properties of the fuller s earth formation the fuller s earth formation is an overcon solidated jointed randomly assured calcareous mudstone with some thin to medium jointed argillaceous limestone bands south of bath the formation contains the commercial montmorillonite rich fuller s earth bed this paper reviews the effect of the proportion of calcite present on the moisture content atterberg limits particle size and residual shear strength attention is drawn to the importance of appreciating that the calcite percentage and the clay mineralogy are both likely to change with time as a result of weathering processes this will affect the stability of natural slopes and man made cuttings excavations etc la formation de terre a foulon est un limon compact calcaire surconsolide jointe et fissure au hasard qui contient des bandes de chaux argillacee jointees d epaisseur faible ou moderee au sud de bath la formation comprend la couche de terre a foulon commerciale qui est riche en montmorillonite l article examine l influence de la prop

characterization of the recent ash emissions at popocatepetl volcano mexico abstract nine representative ash emissions from 1994 1997 were studied to characterize the recent activity and the eruptive process at popocatepetl a series of tephra eruptions began on december 21 1994 and intermittent activity continues to present the first eruptions were phreatomagmatic but in mid march 1996 they turned magmatic cumulative volumes 529 1810 10 3 m 3 were determined for the first eruptions however when eruptions grew larger more widely spaced and magmatic the volumes were then calculated individually 22 1107 10 3 m 3 both using the simpson rule and based on 244 sampling sites this numerical integration method is more precise than other methods especially since sub mm isopachs are neglected in most cases dominant winds carried ash mainly to the east january through april 1995 and april 1996 except for the summer months when ash fell on mexico city to the northwest october 28 1996 and june 30 1997 in march 1996 changing wind direction produced ash fall to the southwest as well during the first year volume calculations indicated that emission rate was higher at the beginning of the eruptions and then declined and stopped activity resumed the following year with a similar pattern until larger amounts of magma ascended detailed studies of the ashfall provided constraints on the dynamics of the volcanic plumbing system tephra emission was related with clearing december 1994 to march 1995 and clogging of the vent may 1995 to february 1996 until a larger new ascending batch was able to clear its way to the surface march 1996 after april 1996 dome formation and explosive destruction were related to individual small ascending magma batches tephra from december 1994 to early march 1996 was made up mostly of andesitic lithic clasts and plagioclase and pyroxene crystals with minor amounts of accidental and accessory minerals in march 1996 prior to dome formation glass was also detected afterwards ash components were mostly dome lithics and scoria with minor amounts of plagioclase pyroxene and olivine crystals from the incoming magma batches

characteristics of tephra fall from eruptions at sakurajima volcano revealed by optical disdrometer measurements we investigated the main characteristics of tephra fall from the eruptions at sakurajima volcano in southern kyushu japan by using an optical disdrometer for simultaneous measurement of particle size and fall velocity measurements were carried out for 2 years at one station located 2 5 km south of the active crater this made it possible to detect 76 tephra fall events with the detection rate of the tephra events from these south directed eruption clouds being about 25 from the relationship between particle diameter and fall velocity we were able to estimate morphological parameters of volcanic particles measurements of temporal change in the tephra fall for each minute revealed that both the tephra diameter and fall velocity gradually decrease with time during each event where the ranges of the diameter and velocity for the events with south directed eruption clouds were 0 336 2 04 mm and 1 40 6 24 m s 1 respectively by using temporal changes in the diameter and velocity we estimated travel time and distance for the tephra falling from a release point in the eruption cloud to the station and found a positive correlation between the travel distance and column height for the south directed clouds with a determination coefficient of 0 498 for linear fitting the comparison between tephra data and seismic data revealed that episodic increases in the tephra diameter and fall velocity were correlated with a drastic increase in amplitude of explosion earthquake or tremor these results indicate that disdrometer measurements can provide valuable information about the quantitative features of the tephra fall and are useful for detecting changes in the magnitude of eruption if a number of suitably placed instruments are deployed

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

complex variations during a caldera forming plinian eruption including precursor deposits thick pumice fallout co ignimbrite breccias and climactic lag breccias the 184 ka lower pumice 1 eruption sequence santorini greece the 184 ka lower pumice 1 eruption sequence records a complex history of eruption behaviours denoted by two significant eruptive phases 1 a minor precursor lp1 pc and 2 a major plinian phase lp1 a b c the precursor phase produced 13 small volume pyroclastic fallout surge and flow deposits which record the transition from a dominantly magmatic to a phreatomagmatic eruptive style and exhibit a normal dacite to andesitic dacite to reverse andesitic dacite to dacite compositional zonation of juvenile pyroclasts in the stratigraphy incipient bioturbation and variability in unit thickness and lithology reflect multiple time breaks and highlight the episodic nature of volcanism prior to the main plinian eruption phase the plinian magmatic eruption phase is defined by three major stratigraphic divisions including a basal pumice fallout deposit lp1 a an overlying valley confined ignimbrite lp1 b and a compositionally zoned rhyodacite to basaltic andesite lithic rich lag breccia lp1 c which caps the sequence this sequence records the initial development of a buoyant convective eruption column and the transition to eruption column and catastrophic late stage caldera collapse events similarities in pyroclast properties i e chemistry density between the plinian fallout lp1 a and pyroclastic flow lp1 b deposits indicate that changes in magma properties exerted no influence on the dynamics and temporal evolution of the lp1 eruption conversely lithic breccias at the base of the lp1 b ignimbrite suggest that the transition from a buoyant convective column to column collapse was facilitated by mechanical erosion of the conduit system and or the initiation of caldera collapse leading to vent widening an increase in magma discharge rate and the increased incorporation of lithics into the eruption column causing mass overload lithic rich lag breccia deposits lp1 c which cap the eruption sequence record incremental high energy caldera collapse events whereby downfaulting occurred in discrete jumps resulting in variable magma discharge rates and the development of a fissure vent system

correlation of mineralogy and index properties with residual strength of iraklion marls abstract the marly formations of the city of iraklion in crete greece are described and classified according to their mineralogy and physical properties the residual angle of friction of these marls was determined using ring shear apparatus and the results were correlated with mineral composition and index properties such as atterberg limits and grain size distribution furthermore for better understanding of the determined interrelationships between the physical characteristics and the residual strength of these marls a number of marl bentonite mixtures were also tested thus the influence of the variation in clay mineral content on the residual strength was studied and correlations with clay sized fraction and plasticity index were attempted

a 7000 yr perspective on volcanic ash clouds affecting northern europe the ash cloud resulting from the a d 2010 eruption of eyjafjallajokull in iceland caused severe disruption to air travel across europe but as a geological event it is not unprecedented analysis of peats and lake sediments from northern europe has revealed the presence of microscopic layers of icelandic volcanic ash tephra these sedimentary records together with historical records of holocene ash falls demonstrate that icelandic volcanoes have generated substantial ash clouds that reached northern europe many times here we present the first comprehensive compilation of sedimentary and historical records of ash fall events in northern europe spanning the past 7000 yr ash fall events appear to have been more frequent in the past 1500 yr it is unclear whether this reflects a true increase in eruption frequency or dispersal or is an artifact of the records or the way in which they have been generated in the past 1000 yr volcanic ash clouds reached northern europe with a mean return interval of 56 9 yr the range of return intervals is between 6 and 115 yr probabilistic modeling using the ash records for the last millennium indicates that for any 10 yr period there is a 16 probability of a tephra fallout event in northern europe these values must be considered as conservative estimates due to the nature of tephra capture and preservation in the sedimentary record

grain size distribution of volcaniclastic rocks 1 a new technique based on functional stereology the power of explosive volcanic eruptions is reflected in the grain size distribution and dispersal of their pyroclastic deposits grain size also forms part of lithofacies characteristics that are necessary to determine transport and depositional mechanisms responsible for producing pyroclastic deposits however the common process of welding and rock lithification prevents quantification of grain size by traditional sieving methods for deposits in the rock record here we show that functional stereology can be used to obtain actual 3d volume fractions of clast populations from 2d cross sectional images tests made on artificially consolidated rocks demonstrate successful correlations with traditional sieving method we show that the true grain size distribution is finer grained than its representation on a random 2d section our method allows the original size of vesicular pumice clasts to be estimated from their compacted shapes we anticipate that the original grain size distribution of welded ignimbrites can also be characterized by this method our method using functional stereology can be universally applied to any type of consolidated weakly to non deformed clastic material regardless of grain size or age and therefore has a wide application in geology

weathering of valle ricca stiff and jointed clay abstract the study proposes a weathering model of pliocene pleistocene stiff and jointed blue grey clay transforming into yellow clay physical mineralogical chemical and textural changes as well as the weathering profile were investigated in a quarry of central italy based on geological records and inferences these changes are likely to have occurred within a time span of about 50 000 years bp upon overburden stress unloading and in a stress regime that is locally controlled by suction weathering propagated into the clay at a rate of about 0 3 mm year and was enhanced by the enlargement of the pre existing tectonic discontinuities and by the formation of new joints a mass loss of about 22 25 wt was calculated considering fe and p as immobile elements the individual oxides contribute to mass loss in the following order sio2 cao co2 al2o3 mgo k2o s na2o tio2 mno the fe2o3 fe2o3 feo ratio varies from 9 29 in the blue grey clay to 75 82 in the yellow one oxidation and or dissolution of 7 a fe2 bearing clay minerals mica like minerals and calcite and parallel increase of smectite and fe hydroxides play a critical role in the chemical changes and explain the higher plasticity of the yellow clay with respect to the blue grey one the role of water during the weathering process was inferred to occur in cyclical steps 1 seepage of meteoric water 2 dissemination of highly oxidizing meteoric water 3 triggering of oxidation and dissolution of minerals 4 water evaporation 5 partial migration of the elements contained in the aqueous solution and consequent deposition of minerals in the joints

potential impacts of tephra fallout from a large scale explosive eruption at sakurajima volcano japan we present an exposure analysis of infrastructure and lifeline to tephra fallout for a future large scale explosive eruption of sakurajima volcano an eruption scenario is identified based on the field characterization of the last subplinian eruption at sakurajima and a review of reports of the eruptions that occurred in the past six centuries a scenario based probabilistic hazard assessment is performed using the tephra2 model considering various eruption durations to reflect complex eruptive sequences of all considered reference eruptions a quantitative exposure analysis of infrastructures and lifelines is presented primarily using open access data the post event impact assessment of magill et al earth planets space 65 677 698 2013 after the 2011 vei 2 eruption of shinmoedake is used to discuss the vulnerability and the resilience of infrastructures during a future large eruption of sakurajima results indicate a main eastward dispersal with longer eruption durations increasing the probability of tephra accumulation in proximal areas and reducing it in distal areas the exposure analysis reveals that 2300 km of road network 18 km2 of urban area and 306 km2 of agricultural land have a 50 probability of being affected by an accumulation of tephra of 1 kg m2 a simple qualitative exposure analysis suggests that the municipalities of kagoshima kanoya and tarumizu are the most likely to suffer impacts finally the 2011 vei 2 eruption of shinmoedake demonstrated that the already implemented mitigation strategies have increased resilience and improved recovery of affected infrastructures nevertheless the extent to which these mitigation actions will perform during the vei 4 eruption presented here is unclear and our hazard assessment points to possible damages on the sakurajima peninsula and the neighboring municipality of tarumizu

the 5 660 ybp boqueron explosive eruption teide pico viejo complex tenerife quantitative hazard assessments of active volcanoes require an accurate knowledge of the past eruptive activity in terms of eruption dynamics and the stratified products of eruption teide pico viejo tpv is one of the largest volcanic complexes in europe but the associated eruptive history has only been constrained based on very general stratigraphic and geochronological data in particular recent studies have shown that explosive activity has been significantly more frequently common than previously thought our study contributes to characterization of explosive activity of tpv by describing for the first time the subplinian eruption of el boqueron 5 660 ybp a satellite dome located on the northern slope of the pico viejo stratovolcano stratigraphic data suggest complex shifting from effusive phases with lava flows to highly explosive phase that generated a relatively thick and widespread pumice fallout deposit this explosive phase is classified as a subplinian eruption of vei 3 that lasted for about 9 15 h and produced a plume with a height of up to 9 km above sea level i e 7 km above the vent mer of 6 9 8 2 105 kg s the tephra deposit minimum bulk volume of 4 6 107 m3 was dispersed to the ne by up to 10 m s winds a similar eruption today would significantly impact the economy of tenerife e g tourism and aviation with major consequences mainly for the communities around the icod valley and to a minor extent the orotava valley this vulnerability shows that a better knowledge of the past explosive history of tpv and an accurate estimate of future potentials to generate violent eruptions is required in order to quantify and mitigate the associated volcanic risk

estimating the volume of tephra deposits a new simple strategy volume determination of tephra deposits is necessary for the assessment of the dynamics and hazards of explosive volcanoes several methods have been proposed during the past 40 years that include the analysis of crystal concentration of large pumices integrations of various thinning relationships and the inversion of field observations using analytical and computational models regardless of their strong dependence on tephra deposit exposure and distribution of isomass isopach contours empirical integrations of deposit thinning trends still represent the most widely adopted strategy due to their practical and fast application the most recent methods involve the best fitting of thinning data using various exponential segments or a power law curve on semilog plots of thickness or mass area versus square root of isopach area the exponential method is mainly sensitive to the number and the choice of straight segments whereas the power law method can better reproduce the natural thinning of tephra deposits but is strongly sensitive to the proximal or distal extreme of integration we analyze a large data set of tephra deposits and propose a new empirical method for the determination of tephra deposit volumes that is based on the integration of the weibull function the new method shows a better agreement with observed data reconciling the debate on the use of the exponential versus power law method in fact the weibull best fitting only depends on three free parameters can well reproduce the gradual thinning of tephra deposits and does not depend on the choice of arbitrary segments or of arbitrary extremes of integration

chemical weathering mechanisms and their effects on engineering properties of soft sandstone and conglomerate cemented by zeolite in a mountainous area abstract sandstone and conglomerate cemented by zeolite crystals in a humid mountainous area in japan are weathered and also weakened or strengthened by chemical interaction with percolating water that was originally in equilibrium with the atmosphere near the ground surface carbonic acid generated by the dissolution of carbon dioxide from the atmosphere and biological activity in the soil dissolves zeolite and thereby weakens the rocks at the oxidation front the base of the oxidized zone oxygen from the atmosphere reacts with pyrite in the rock to form sulfuric acid and iron oxide and or hydroxide the iron oxide and or hydroxide precipitates on zeolite surfaces and strengthens the rocks by cementing the grains to each other beneath the oxidation front and extending to the dissolution front sulfuric acid migrates downward dissolves zeolite and thus weakens the rocks this weathering mechanism and the resulting changes in mechanical properties of rocks generally are to be expected in marine sandstone and conglomerate with small amounts of clay in the matrix because the most common cementing mineral is carbonate which is also easily dissolved by acid and further because pyrite is a common rock forming mineral in marine sedimentary rocks the effects of chemical weathering on the mechanical properties of sandstone and conglomerate are different from those of mudstone because the latter contains much larger amounts of clay minerals the cementation of constituent grains by iron oxide and or hydroxide is inhibited by clay minerals because clay minerals have high specific surface areas and also because large amounts of iron can be incorporated in the minerals

the immediate environmental effects of tephra emission the earth s history is punctuated by large explosive eruptions that eject large quantities of magma and silicate rock fragments into the atmosphere these tephra particles can sometimes be dispersed across millions of square kilometres or even entire continents the interaction of tephra with or in receiving environments may induce an array of physical chemical and biological effects the consequences for affected systems and any dependent communities may be chronic and localised in the event of frequent small eruptions while larger and rarer events may have acute regional scale impacts it is therefore necessary to document the range of possible impacts that tephra may induce in receiving environments and any resulting effects in interconnected systems we collate results from many studies to offer a detailed multidisciplinary and interdisciplinary review of the immediate post eruptive effects of tephra emission into the atmosphere onto vegetation soil or ice snow surfaces and in aquatic systems we further consider the repercussions that may be induced in the weeks to years afterwards in the atmosphere tephra can influence cloud properties and air chemistry by acting as ice nuclei in or by offering sites for heterogeneous reactions respectively tephra on vegetation causes physical damage and sustained coverage may elicit longer term physiological responses tephra deposits on soils may alter their capacity to exchange gas water and heat with the atmosphere or may have a specific chemical effect such as nutrient input or acidification on sensitive soils tephra deposition onto snow or ice may affect ablation rates rivers and lakes may experience turbidity increases and changes in their morphology as a result of fallout and prolonged months or years erosion from the tephra covered catchment in the first weeks after deposition tephra leaching may affect river chemistry the abundance and speciation of phytoplankton populations in lakes may be altered by tephra induced changes in water chemistry or sediment water nutrient cycling in the oceans tephra deposition may fertilise fe limited waters with potential impacts on the global carbon cycle embracing the full complexity of environmental effects caused by tephra fall demands a renewed investigative effort drawing on interdisciplinary field and laboratory studies combined with consideration of the interconnectivity of induced impacts within and between different receiving environments

total grain size distribution and volume of tephra fall deposits on 17 june 1996 ruapehu volcano new zealand produced a sustained andesitic sub plinian eruption which generated a narrow tephra fall deposit extending more than 200 km from the volcano the extremely detailed data set from this eruption allowed methods for the determination of total grain size distribution and volume of tephra fall deposits to be critically investigated calculated total grain size distributions of tephra fall deposits depend strongly on the method used and on the availability of data across the entire dispersal area the voronoi tessellation method was tested for the ruapehu deposit and gave the best results when applied to a data set extending out to isomass values of 1 g m 2 the total grain size distribution of a deposit is also strongly influenced by the very proximal samples and this can be shown by artificially constructing subsets from the ruapehu database unless the available data set is large all existing techniques for calculations of total grain size distribution give only apparent distributions the tephra fall deposit from ruapehu does not show a simple exponential thinning but can be approximated well by at least three straight line segments or by a power law fit on semi log plots of thickness vs area 1 2 integrations of both fits give similar volumes of about 4 106 m3 integration of at least three exponential segments and of a power law fit with at least ten isopach contours available can be considered as a good estimate of the actual volume of tephra fall integrations of smaller data sets are more problematic

tephra stratigraphy and eruptive volume of the may 2008 chaiten eruption chile on may 1st 2008 mount chaiten southern chile interrupted a long period of quiescence generating a sequence of explosive eruptions and causing the evacuation of chaiten town located a few kilometers south of the volcano the activity was characterized by several explosive events each associated with plumes which reached up to about 19 km above sea level the products were dispersed across a wide area with the finest ash reaching the atlantic coast of argentina our field observations in the proximal medial area 3 25 km from the vent indicate that the may 2008 tephra deposit consists of numerous layers most of which can be correlated with individual eruptive events these layers vary from extremely fine grained ash to layers of lapilli and blocks composed of both juvenile and lithic material here we describe the stratigraphy and physical characteristics of the may 2008 deposits and propose a reconstruction of the timing of the may 2008 events the deposits are mainly associated with the three main explosive phases which occurred on 1st 2nd may 3rd 5th may and 6th may with an estimated bulk tephra volume of 0 5 1 0 km3 integration of both exponential and power law fitting for the 6th may event represented by a layer composed mainly of lithic lapilli and blocks 2 mm an isopleth map was compiled from which a 19 km plume height was determined which is in good agreement with satellite observations

experimental constraints on the textures and origin of obsidian pyroclasts obsidian pyroclasts are commonly preserved in the fall deposits of explosive silicic eruptions recent work has suggested that they form by sintering of ash particles on the conduit walls above the fragmentation depth and are subsequently torn out and transported in the gas particle dispersion although the sintering hypothesis is consistent with the general vesicle textures and dissolved volatiles in obsidian pyroclasts previous sintering experiments do not capture all of the textural complexities observed in the natural pyroclasts here we design experiments in which unimodal and bimodal distributions of rhyolitic ash are sintered at temperatures and h2o pressures relevant to shallow volcanic conduits and under variable cooling rates the experiments produce dense welded obsidian that have a range of textures similar to those observed in natural pyroclasts we find that using a unimodal distribution of particles produces obsidian with evenly distributed trapped vesicles while a bimodal initial particle distribution produces obsidian with domains of poorly vesicular glass among domains of more vesicle rich glass we also find that slow cooling leads to resorption of trapped vesicles producing fully dense obsidian these broad features match those found in obsidian pyroclasts from the north mono california usa rhyolite eruption providing strong support to the hypothesis that obsidian can be produced by ash sintering above the fragmentation depth during explosive eruptions

modeling thickness variability in tephra deposition the attenuation of tephra fall thickness is most commonly estimated after contouring isolated and often irregular field measurements into smooth isopachs with varying degrees of subjectivity introduced in the process here we present an explicit description of the variability introduced into a semiempirical tephra attenuation relation this opens the way to fitting models to actual tephra observations through maximum likelihood estimation rather than using weighted least squares estimation on the isopachs the method is illustrated for small scale basaltic explosive eruptions using a simple but typical data set of the actual tephra thickness data published from the 1973 heimaey eruption of the distributions considered to describe variability in these measurements the lognormal performed poorly due to its tendency to predict a small number of greatly over thickened deposits the weibull and gamma distributions fitted the data to a very similar degree and produced very similar estimates for the effective volume mean wind direction and mass thickness attenuation rate the latter can be inverted to obtain an estimate of the mean column height the estimated wind direction and the column height derived from the estimated thickness attenuation parameter agreed very well with the direct observations made during the eruption augmented by a mixture framework allowing for the incorporation of multiple lobes and or vents the model was able to identify the source and direction of tephra deposition for the 1977 ukinrek maars eruptions from only the tephra thickness data

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

eruption source parameters for forecasting ash dispersion and deposition from vulcanian eruptions at tungurahua volcano insights from field data from the july 2013 eruption tungurahua volcano located in the central area of the ecuadorian sierra is erupting intermittently since 1999 alternating between periods of quiescence and explosive activity volcanic ash has been the most frequent and widespread hazard provoking air contamination episodes and impacts on human health animals and crops in the surrounding area after two months of quiescence tungurahua erupted violently on 14th july 2013 generating short lived eruptive columns rising up to 9 km above the vent characterized as a vulcanian eruption the resulting fallout deposits were sampled daily during and after the eruptions to determine grain size distributions and perform morphological and componentry analyses dispersion and sedimentation of ash were simulated numerically coupling the meteorological weather research forecasting wrf with the volcanic ash dispersion fall3d models the combination of field and numerical studies allowed constraining the eruption source parameters esp for this event which could be used to forecast ash dispersion and deposition from future vulcanian eruptions at tungurahua this set of pre defined esp was further validated using two different eruptions as blind test occurring on 16th december 2012 and 1st february 2014

reconstructing the largest explosive eruptions of mt ruapehu new zealand lithostratigraphic tools to understand subplinian plinian eruptions at andesitic volcanoes we analysed the tephra record of mt ruapehu for the period 27 097 957 to 10 000 cal years bp to determine the largest scale explosive eruptions expected from the most active new zealand andesitic volcano from the lithostratigraphic analysis a systematic change in the explosive behaviour is identified from older deposits suggesting dry magmatic eruptions and steady eruptive columns characterised by frothy to expanded pumice fabrics to younger deposits that are products of unsteady conditions and collapsing columns characterised by microvesicular fibrous and colour banded pumice fabrics the end members were separated by eruptions with steady columns linked to water magma interaction and highly unstable conduit walls dry magmatic eruptions producing steady plinian columns were most common between 27 097 957 and shortly after 13 635 165 cal years bp following this time activity continued with eruptions that produced dominantly oscillating unsteady columns which engendered pyroclastic density currents until 10 ka when there was an abrupt transition at mt ruapehu since which eruptions have been an order of magnitude lower in intensity and volume these data demonstrate long period transitions in eruption behaviour at an andesitic stratovolcano which is critical to understand if realistic time variable hazard forecasts are to be developed

microstructure and cementation of two carbonatic fine grained soils this paper presents an investigation of the microstructure and cementation of two carbonatic fine grained soils obtained from a deposit of lacustrine origin formed during the wisconsin glaciation

review of methods of estimating rhyolitic tephra volumes applications to the taupo volcanic zone new zealand there have been at least 35 rhyolitic plinian eruptions in the last 50 kyr from 2 volcanic centres in taupo volcanic zone tvz new zealand to determine the total volume of erupted material calculation techniques are reviewed and further developed all involve extrapolation from isopach maps three methods assume an exponential decay of thickness with distance from source and a further two are based on the area enclosed by each isopach comparison of methods shows those based on area to be more accurate except the log log plot of area and thickness which requires excessive extrapolation a log volume vs thickness plot is considered superior because minimal extrapolation is needed for most tephras volumes calculated by the different methods are in reasonable agreement volumes previously calculated by the crystal concentration method are 2 3 times greater than those from the six methods used here total pumice fragmentation is probably not required for the liberation of crystals and this would decrease calculated volumes during the last 50 kyr magma has been erupted at a constant mean rate in the taupo volcanic zone a simple step function shows a strong relationship between deviations from the mean rate and either the next erupted volume or the time to the next eruption extrapolation of these step functions suggests future eruptions in less than 400 years for okataina and about 8000 years for taupo the volume of rhyolitic material erupted from tvz within the last 50 kyr is estimated at 360 km3 of tephra 350 km3 of ignimbrite and 55 km3 of extrusive equivalent to about 350 km3 of magma at an average rate of eruption of 7 km3 year at least 4200 km3 of rhyolitic magma has been erupted since the inception of tvz about 0 6 m y ago if back are spreading of tvz at 7 mm yr is compensated for by dyke intrusion into the upper 10 km of crust 8400 km3 of magma is required the total volume of magma generated by partial melting is estimated at 12 600 km3 removal of this melt would cause subsidence of 2 1 km the present depth to subvolcanic basement in tvz

deposition and generation of multiple widespread fall units from the c ad 1314 kaharoa rhyolitic eruption tarawera new zealand the c ad 1314 kaharoa eruption from tarawera volcano north island new zealand was a complex long duration multi episode rhyolitic event up to 13 discrete sub plinian to plinian style phases occurred in two stages from at least two different vents along an 8 km long fissure the early explosive stage produced seven pumice lapilli fall units dispersed solely to the southeast of the volcano while a later stage produced six fall units dispersed almost entirely to the north and northwest the duration of fallout for these 13 lapilli units is estimated to have totaled about 1 5 days the presence of massive textured ash layers between many of the lapilli fall units suggests that longer duration pyroclastic density current producing phases and more quiescent fallout intervals occurred between the intense explosive phases of the eruption total duration of ash fallout 7 5 days the ash deposition extended the minimum duration of the explosive episodes to at least 9 days based on settling rates of the ash possibly the explosive phase of eruptive activity lasted for 2 weeks including some brief hiatuses and pyroclastic density current deposition and was followed by 4 years of mainly lava dome forming activity at least 15 km3 7 3 km3 dense rock equivalent dre of tephra was erupted during the main explosive episodes and at least 9 1 km3 dre during the whole eruption more than doubling the previous estimate this may be an underestimate by up to 50 of the fallout volume eruption column heights for the two most widely dispersed fall units are estimated to have ranged from 25 28 km above the vents and durations of individual lapilli fall unit forming phases ranged from 1 5 to 4 h but the ash producing phases lasted much longer individually up to 30 h and represent a longer lived shut down to each eruptive episode time averaged mass discharge rates are estimated to have varied by more than one order of magnitude during the main plinian style phases from 107 to 108 kg s however the explosive phases were unsteady as indicated by fluctuating grain size with stratigraphic height in the lapilli fall units and common capping ash beds the north northwesterly dispersal of the later stage fall units and the possible duration of 4 days for these episodes indicate an unusual period of southerly to southeasterly winds therefore the main explosive part of the kaharoa eruption is most likely to have occurred during the austral winter to spring months the kaharoa eruption style is also shared by the three previous rhyolite dominated eruptions that have built tarawera volcano over the past 22 000 years knowledge of the widespread pumice and ash fallout from the kaharoa eruption is important in quantifying the hazard from this type of extended duration explosive activity and has implications for future similar rhyolitic activity in new zealand

mantle lower crust petrology from inclusions in basaltic rocks in eastern australia an outline abstract xenoliths megacrysts and xenocrysts of high pressure origin are abundant in post carboniferous alkali volcanics in eastern australia five xenolithic groups are recognized corresponding to episodes of metamorphism and partial melting metamorphic textured peridotites olivine fo 86 92 include ubiquitous spinel peridotites and rare garnet peridotites pyrope 72 75 of upper mantle origin metamorphic textured pyroxenites scattered in association with the metamorphic textured peridotites have patchy distribution and include intrusive and cumulate types hornblendites and diorites very localized include unique amphibole apatite rocks granulites and gabbros are widespread and include garnet scapolite granulites eclogites and charnockites and rarely associated corundum anorthoclasite and sanidinite this last group represents predominantly lower crustal material megacrysts and xenocrysts commonly accompany these xenoliths and include olivine orthopyroxene clinopyroxene spinels garnet amphibole ilmenite magnetites rutile apatite micas anorthoclase plagioclases sanidine corundum zircon and diamond the xenoliths demonstrate a complex series of exsolution recrystallization and mixing events in an inhomogeneous upper mantle which contains records of periodic activity over at least the last 2000 m y evidence from australian xenolith suites provides further insight into the structure rock relationships and events that have affected the upper mantle

the size distribution of pyroclasts and the fragmentation sequence in explosive volcanic eruptions in an explosive eruption the atmospheric column dynamics depend strongly on the mass fraction of gas in the erupting mixture which is fixed by fragmentation in the volcanic conduit at fragmentation gas present in vesicular magmatic liquid gets partitioned between a continuous phase separating magma clasts and a dispersed phase in individual bubbles within the clasts as regards flow behavior it is the former continuous gas phase which matters and we show that its amount is determined by the fragment size analysis of 25 fall deposits and 37 flow deposits demonstrates that ash and pumice populations follow a power law size distribution such that n the number of fragments with radii larger than r is given by n r d d values range from 2 9 to 3 9 and are always larger than 3 0 in fall deposits d values for pyroclastic flow deposits are systematically smaller than those of fall deposits we show that at fragmentation the amount of continuous gas phase is an increasing function of the d value large d values cannot be attributed to a single fragmentation event and are due to secondary fragmentation processes laboratory experiments on bubbly magma and on solid pumice samples demonstrate that primary breakup leads to d values of 2 5 0 1 and that repeated fragment collisions act to increase the d value a model for size dependent refragmentation accounts for the observations we propose that in a volcanic conduit fragmentation proceeds as a sequence of events primary breakup releases a small amount of gas and is followed by fragment collisions due to refragmentation and decompression both the mass and volume fractions of continuous gas increase the final d value and hence the mass fraction of continuous gas at the vent depends on the time spent between primary fragmentation and eruption out of the vent

the effect of total grain size distribution on the dynamics of turbulent volcanic plumes abstract the impact of explosive volcanic plumes on climate and on air traffic strongly depends on the concentration and grain size distribution gsd of pyroclastic fragments injected into the atmosphere accurate and robust modelling of the evolution of gsd during pyroclast transport from the vent to the ash cloud is therefore crucial for the assessment of major volcanic hazards analysis of field deposits from various recent plinian eruptions shows that their total gsd is well described by a power law as expected from the physics of magma fragmentation with an exponent d ranging from 3 0 to 3 9 by incorporating these measured gsd into the initial conditions of a steady state 1d model of explosive eruption columns we show that they have a first order impact on the dynamical behaviour of explosive eruption columns starting from an initial value of d the model tracks the evolution of gsd in the column and calculates the dynamical consequences of particle sedimentation the maximum height reached by the column one of the first order results relevant to aircraft safety changes by 30 for mass fluxes of 10 7 kg s 1 or larger and by 45 85 for mass fluxes between 105 and 10 7 kg s 1 depending on exponent d we compare our predictions to a specially assembled set of geologic field data and remote sensing observations from 10 plinian eruptions for which maximum column height and mass flux are known independently the incorporation of realistic power law gsd in the model greatly improves the predictions which opens new perspectives for estimation of ash load and gsd in volcanic clouds from near real time measurements available from satellite payloads our results also contribute to the improvement of volcanic source term characterization that is required input for meteorological dispersion models

constraining particle size dependent plume sedimentation from the 17 june 1996 eruption of ruapehu volcano new zealand using geophysical inversions weak subplinian plinian plumes pose frequent hazards to populations and aviation yet many key parameters of these particle laden plumes are to date poorly constrained this study recovers the particle size dependent mass distribution along the trajectory of a well constrained weak plume by inverting the dispersion process of tephra fallout we use the example of the 17 june 1996 ruapehu eruption in new zealand and base our computations on mass per unit area tephra measurements and grain size distributions at 118 sample locations comparisons of particle fall times and time of sampling collection as well as observations during the eruption reveal that particles smaller than 250 m likely settled as aggregates for simplicity we assume that all of these fine particles fell as aggregates of constant size and density whereas we assume that large particles fell as individual particles at their terminal velocity mass fallout along the plume trajectory follows distinct trends between larger particles d 250 m and the fine population d 250 m that are likely due to the two different settling behaviors aggregate settling versus single particle settling in addition we computed the resulting particle size distribution within the weak plume along its axis and find that the particle mode shifts from an initial 1 mode to a 2 5 mode 10 km from the vent and is dominated by a 2 5 to 3 mode 10 180 km from vent where the plume reaches the coastline and we do not have further field constraints the computed particle distributions inside the plume provide new constraints on the mass transport processes within weak plumes and improve previous models the distinct decay trends between single particle settling and aggregate settling may serve as a new tool to identify particle sizes that fell as aggregates for other eruptions

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

a mechanism of chemical weathering of mudstone in a mountainous area abstract the chemical weathering of marine mudstone in humid mountainous areas of japan is dominated by the oxidation of pyrite a common mineral in marine sedimentary rocks this process occurs at the oxidation front that is the base of the oxidized zone and sulfuric acid is formed chlorite is transformed into smectite due to the oxidizing and acidic conditions as sulfuric acid migrates downward from the oxidation front minerals are dissolved and components are leached out from the underlying dissolved zone whose lower boundary is the dissolution front the oxidation and dissolution fronts migrate downward as weathering progresses in mountainous areas

tarawera 1886 new zealand a basaltic plinian fissure eruption abstract new zealand s biggest and most destructive volcanic eruption of historical times was that of tarawera in 1886 the resulting scoria fall has a dispersal very similar in extent to that of the vesuvius a d 79 pumice fall and is one of the few known examples of a basaltic deposit of plinian type a new estimate of the volume 2 km 3 is significantly greater than previous estimates the basalt came mainly from a 7 km length of fissure and emission and exit velocity were fairly uniform along at least 4 km of it this is one of the few documented examples of a plinian eruption from a fissure vent primary welding of the scoria fall resulted where the accumulation rate exceeded about 250 mm min 1 a model of the eruption dynamics is proposed which leads to an estimate of 28 km for the height of the eruption cloud and implies a magma volatile fraction of 1 5 3 violent phreatic explosions occurred in the southwestern extension of the fissure across the rotomahana geothermal field and it is thought that some of the water responsible for the power of the plinian eruption came from this source though its amount was not sufficient to turn the eruption into a phreatoplinian one

revised estimates for the volume of the late bronze age minoan eruption santorini greece the late bronze age minoan eruption of santorini greece occurred from within an existing caldera low temperature pyroclastic flow emplacement on shallow slopes outside the caldera can only be consistent with the caldera being filled with eruption products that are not preserved field observations and seismic reflection surveys suggest that this missing material has been downfaulted the volume of the caldera infill is estimated as 18 26 km 3 dense rock equivalent dre increasing the total of the minoan eruption deposits to 78 86 km 3 dre and making it the largest known holocene eruption this study highlights a general mechanism whereby caldera eruption volumes could be significantly underestimated

a significant middle pleistocene tephra deposit preserved in the caves of mulu borneo article i nfo article history received 23 may 2011 available online xxxx a distinctive white sediment in the caves of mulu sarawak borneo is a well preserved tephra representing a fluvially transported surface air fall deposit re deposited inside the caves we show that the tephra is not the younger toba tephra formerly considered as most likely the shards are rod shaped with elongate tubular vesicles the largest grains 170 m in length of rhyolitic composition and 87 sr 86 sr ratio of 0 70426 0 00001 u th dating of associated calcites suggest that the tephra was deposited before 125 4 ka and probably before 156 2 ka grain size and distance from closest potential source suggests an eruption of vei 7 prevailing winds grain size thickness of deposit location of potential sources and sr isotopic ratio limit the source to the philippines comparisons with the literature give the best match geochemically with layer 1822 from ku et al 2009a dated by ocean core stratigraphy to 189 ka this tephra represents a rare terrestrial repository indicating a very substantial plinian ultra plinian eruption that covered the mulu region of borneo with ash a region that rarely receives tephra from even the largest known eruptions in the vicinity it likely will be a valuable chronostratigraphic marker for sedimentary palaeontological and archaeological studies

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

effect of weathering on the compressibility and shear strength of a natural clay in situ seasonal changes expose soils to frequent wetting drying freezing thawing cycles such processes can favour and trigger shallow instabilities controlled by the weathering process this paper presents an experimental study carried out to investigate the effects of the weathering process caused by the wetting drying freezing thawing cycles on the compressibility and shear strength of a natural clay several specimens were trimmed from block samples of overconsolidated clays taken from a slope in south calabria italy specimens were subjected to wetting drying freezing thawing cycles of different durations and then tested with standard equipment oedometer and direct shear test results show that the wetting drying freezing thawing cycles caused a change in the initial microstructure that produced a decrease in the compression index and an increase in the swelling index moreover the direct shear test results show a decrease in the peak shear strength and demonstrate that a larger reduction occ

dynamics of the major plinian eruption of samalas in 1257 a d lombok indonesia the 1257 a d caldera forming eruption of samalas lombok indonesia was recently associated with the largest sulphate spike of the last 2 ky recorded in polar ice cores it is suspected to have impacted climate both locally and at a global scale extensive fieldwork coupled with sedimentological geochemical and physical analyses of eruptive products enabled us to provide new constraints on the stratigraphy and eruptive dynamics this four phase continuous eruption produced a total of 33 40 km3 dense rock equivalent dre of deposits consisting of i 7 9 km3 dre of pumiceous plinian fall products ii 16 km3 dre of pyroclastic density current deposits pdc and iii 8 9 km3 dre of co pdc ash that settled over the surrounding islands and was identified as far as 660 km from the source on the flanks of merapi volcano central java widespread accretionary lapilli rich deposits provide evidence of the occurrence of a violent phreatomagmatic phase during the eruption with a peak mass eruption rate of 4 6 108 kg s a maximum plume height of 43 km and a dispersal index of 110 500 km2 the 1257 a d eruption stands as the most powerful eruption of the last millennium eruption dynamics are consistent with an efficient dispersal of sulphur rich aerosols across the globe remarkable reproducibility of trace element analysis on a few milligrammes of pumiceous tephra provides unequivocal evidence for the geochemical correlation of 1257 a d proximal reference products with distal tephra identified on surrounding islands hence we identify and characterise a new prominent inter regional chronostratigraphic tephra marker

sedimentation from strong volcanic plumes 1 we develop descriptions of the key processes influencing tephra dispersal from strong volcanic plumes these are characterized by the development of a subvertical eruption column in the atmosphere that forms a spreading current at a level of neutral buoyancy we describe the propagation of the spreading current due to both gravity and wind advection using scaling arguments and a simplified geometry to model particle sedimentation in a windy as well as a wind free environment new parameterizations are used to describe the wind field below the spreading current particle aggregation and particle density variations we conducted a broad study to investigate the effects of these processes and made comparisons with field observations the greatest variations resulted from wind advection below the spreading current which shifts the plume corner mass accumulation and the position of transitions in fallout regimes downwind particle aggregation strongly depends on the initial grain size distribution and significantly affects deposit thinning depending on the aggregate size and density and on the relative amount of aggregating particles small aggregates can reproduce secondary maxima of mass accumulation when sedimenting in a wind field variation of particle density also affects the resulting thinning trend the model provides acceptable reproduction of observations of the propagation of the spreading current tested with the plinian phase of the 18 may 1980 eruption of mount st helens and of observed thinning of tephra fallout deposits tested with deposits from mount st helens 1980 askja d 1875 quizapu 1932 minoan eruption 3 6 ka b p novarupta a 1912 and hudson 1991

the 4 5 september 2007 lava fountain at south east crater of mt etna italy abstract continuous monitoring of paroxysmal eruptions at mt etna italy is performed from the istituto nazionale di geofisica e vulcanologia sezione di catania in recent years this activity has allowed us to study fallout deposits and track the evolution of eruptive phases this communication reports on the paroxysm that occurred in the afternoon of 4 september 2007 when a powerful lava fountain started from south east crater at the summit of etna the fountaining formed a plume up to 2 km high for almost 12 h causing abundant tephra fallout in the eastern sector of the volcano and emplacement of a thick about 4 km long clastogenic lava flow extensive area collection of tephra samples from the fallout deposit was performed within a few hours after the end of the paroxysm we calculated a total erupted volume of 3 92 4 9 10 5 m 3 and a total grain size fitted by a gaussian distribution with the mode of 0 and equal to 1 3 the total volume of the clastogenic lava flow deposit that resulted was 2 4 10 6 m 3 the systematic study of paroxysms at etna helps to better investigate etnean type lava fountains and to improve the classification of explosive activity on basaltic volcanoes

disruption of tephra fall deposits caused by lava flows during basaltic eruptions observations in the usa iceland and tenerife canary islands reveal how processes occurring during basaltic eruptions can result in complex physical and stratigraphic relationships between lava and proximal tephra fall deposits around vents observations illustrate how basaltic lavas can disrupt dissect spatially and temporally and alter sheet form fall deposits complexity arises through synchronous and alternating effusive and explosive activity that results in intercalated lavas and tephra deposits tephra deposits can become disrupted into mounds and ridges by lateral and vertical displacement caused by movement including inflation of underlying p hoehoe lavas and clastogenic lavas mounds of tephra can be rafted away over distances of 100 s to 1 000 s m from proximal pyroclastic constructs on top of lava flows draping of irregular topography by fall deposits and subsequent partial burial of topographic depressions by later lavas can result in apparent complexity of tephra layers these processes deduced from field relationships have resulted in considerable stratigraphic complexity in the studied proximal regions where fallout was synchronous or alternated with inflation of subjacent lava sheets these mechanisms may lead to diachronous contact relationships between fall deposits and lava flows such complexities may remain cryptic due to textural and geochemical quasi homogeneity within sequences of interbedded basaltic fall deposits and lavas the net effect of these processes may be to reduce the usefulness of data collected from proximal fall deposits for reconstructing basaltic eruption dynamics

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