deep sea eruptions boosted by induced fuel coolant explosions the majority of earth s volcanic eruptions occur beneath the sea but the limited number of direct observations and samples limits our understanding of these unseen events subaerial eruptions lend some insight but direct extrapolation from the subaerial to the deep sea is precluded by the great differences in pressure thermal conditions density and rheology and the interplay among them here we present laboratory fragmentation experiments that mimic deep sea explosive eruptions and compare our laboratory observations with those from the kilometre deep submarine eruption of havre volcano kermadec arc new zealand in 2012 we find that the havre eruption involved explosive fragmentation of magma by a pressure insensitive interaction between cool water and hot magma termed an induced fuel coolant interaction the laboratory experiments show that this water magma interaction is initiated by the formation of cracks in cooling magma into which the water coolant can infiltrate driving explosive fragmentation explosive submarine eruptions have previously been considered unlikely because stabilization of a vapour film at the magma water contact was thought to be a key requirement but is suppressed at depths exceeding 100 m however here we demonstrate that these induced fuel coolant interactions between magma and water can occur in a range of wet environments regardless of pressure from the subaerial to the deep sea and may operate on different planets as well as apply to materials other than magma and water

a new method for the determination of the specific kinetic energy ske released to pyroclastic particles at magmatic fragmentation theory and first experimental results brittle magmatic fragmentation plays a crucial role in explosive eruptions it represents the starting point of hazardous explosive events that can affect large areas surrounding erupting volcanoes knowing the initial energy released during this fragmentation process is fundamental for the understanding of the subsequent dynamics of the eruptive gas particle mixture and consequently for the forecasting of the erupting column s behavior the specific kinetic energy ske of the particles quantifies the initial velocity shortly after the fragmentation and is therefore a necessary variable to model the gas particle conduit flow and eruptive column regime in this paper we present a new method for its determination based on fragmentation experiments and identification of the timings of energy release the results obtained on compositions representative for basaltic and phonolitic melts show a direct dependence on magma material properties poorly vesiculated basaltic melts from stromboli show the highest ske values ranging from 7 3 to 11 8 kj kg while experiments with highly vesiculated samples from stromboli and vesuvius result in lower ske values 3 1 to 3 8 kj kg the described methodology presents a useful tool for quantitative estimation of the kinetic energy release of magmatic fragmentation processes which can contribute to the improvement of hazard assessment

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

shallow vent architecture during hybrid explosive effusive activity at cordon caulle chile 2011 12 evidence from direct observations and pyroclast textures in june 2011 an eruption of rhyolite magma began at the puyehue cordon caulle volcanic complex southern chile by january 2012 explosive activity had declined from sustained pyroclastic plinian to sub plinian fountaining to mixed gas and ash jetting punctuated by vulcanian blasts this explosive activity was accompanied by synchronous effusion of obsidian lava in a hybrid explosive effusive eruption fortuitous climatic conditions permitted ground based observation and video recording of transient vent dynamics as well as real time collection of proximal juvenile ash as it sedimented from the active plume the main eruptive vent complex and site of lava effusion was represented by two loci of vulcanian blasts within a single tephra cone containing a pancake shaped proto lava dome these blast loci each consisted of clusters of sub vents that expressed correlated shifts in eruption intensity indicating the presence of partially connected and or branching zones of high permeability within the upper conduit pyroclast textures were examined by x ray computed microtomography and their permeability was modeled by lattice boltzmann simulations the porosity 39 to 67 and darcian permeability 3 1x10 15 m2 perpendicular to fabric to 3 8x10 11 m2 parallel to fabric of fine ash emitted during ash jetting indicates that the permeable zones comprised highly sheared tube like bubbly magma and contrast with the low porosity 17 and nul permeability of bombs ejected to hundreds of metres from the vent in vulcanian blasts residual h2o content of ash 0 14 wt and two bombs 0 2 0 25 wt determined by karl fischer titration indicate degassing of this pyroclastic material to near atmospheric pressures ash textures and simple degassing vesiculation models indicate the onset of permeability by ductile processes of shear enhanced bubble coalescence in the upper 1 to 1 5 km of the conduit repeated ash jetting and vulcanian blasts indicate that such ductile processes were not sufficiently effective to accommodate all degassing requirements and additional brittle e g fragmentation events transiently assisted in maintaining an open system degassing regime that permitted long lived hybrid explosive effusive activity the eruption at cordon caulle has provided an excellent opportunity to closely observe key processes of silicic volcanism

using fractal analysis to quantitatively characterize the shapes of volcanic particles 1 the shapes of volcanic particles reflect numerous eruptive parameters e g magma viscosity volatile content and degree of interaction with water and are useful for understanding fragmentation and transport processes associated with volcanic eruptions however quantitative analysis of volcanic particle shapes has proven difficult because of their morphological complexity and variability here a newly developed procedure for shape analysis based on fractal geometry is described and tested although volcanic particle shapes are not truly fractal their complexity can be effectively characterized in terms of fractal values pseudofractal dimensions reflecting morphological invariance over discrete ranges of scale using fractal data produced by dilation of a particle s two dimensional boundary a spectrum of fractal dimensions is calculated for each particle by taking the first derivative of the dilation data compared with fractal methods that express shape in terms of only one or two fractal dimensions typically derived from the slope of data on a richardson plot this technique results in better discrimination between samples in addition use of multiple fractal values allows incorporation of multivariate statistical analysis further strengthening the differentiating power of the technique this fractal spectrum technique yields promising results for samples of sideromelane shards from iceland and is likely to be effective at characterizing other kinds of volcanic particle shapes

deep sea fragmentation style of havre revealed by dendrogrammatic analyses of particle morphometry in 2012 the eruption of deep sea volcano havre produced an abundance of fine ash at a depth of 1000 m below sea level in this study the 2d shapes of havre ash grains retrieved from the seafloor were compared quantitatively with those of particles generated in a suite of different fragmentation experiments which used remelted rhyolitic rock and pumice from the eruption site a new statistical data analysis technique denoted as dendrogrammatic analysis of particle morphology dapm is introduced it is designed to compare large numbers of morphometric data sets containing shape information for a set of ash particles to group them by morphological similarities and to visualize these clusters in a dendrogram further steps involve t tests and equivalence tests and reveal morphometric differences as well as matching features the dapm suggests that the majority of havre ash was thermohydraulically produced by induced fuel coolant interaction a subset of ash particles features an elongated tube morphology their morphometry matches that of particles that were experimentally produced by a combination of shearing and quenching and we infer that the natural particles were formed by synextrusive ash venting

the timing of martian valley network activity constraints from buffered crater counting abstract valley networks concentrations of dendritic channels that often suggest widespread pluvial and fluvial activity have been cited as indicators that the climate of mars differed significantly in the past from the present hyperarid cold desert conditions some researchers suggest that the change in climate was abrupt while others favor a much more gradual transition thus the precise timing of valley network formation is critical to understanding the climate history on mars we examine thirty valley network incised regions on mars including both cratered upland valley networks and those outside the uplands and apply a buffered crater counting technique to directly constrain when valley network formation occurred the crater populations that we derive using this approach allow assessment of the timing of the last activity in a valley network independent of the mapping of specific geological units from these measurements we find that valley networks cluster into two subdivisions in terms characteristics and age 1 valley network activity in the cratered highlands has an average cessation age at the noachian hesperian boundary and all valleys that we crater counted are early hesperian or older no evidence is found for valley networks in the cratered uplands of late hesperian or amazonian age the timing of the cessation of cratered upland valley network activity at the noachian hesperian boundary also corresponds to a decline in the intensity of large crater formation and degradation and to the apparent end of phyllosilicate type weathering 2 a few valley network incised regions formed outside of the cratered uplands on volcanic edifices in association with younger impact craters and on the rim of valles marineris we applied our buffered crater counting technique to four such valleys on the volcanoes ceraunius tholus hecates tholus and alba patera and on the rim of echus chasma and find that each has distinctive and different late hesperian or early amazonian ages indicating that valley networks formed from time to time in the post noachian period unlike the cratered upland valley networks these isolated occurrences are very local and have been interpreted to represent local conditions e g snowpack melted during periods of intrusive volcanic activity in contrast to a gradual cessation in the formation of valley networks proposed by some workers our new buffered crater counting results indicate a relatively abrupt cessation in the formation of the widespread cratered upland valley networks at approximately the end of the noachian followed only by episodic and very localized valley network formation in later mars history very likely due to specific conditions e g local magmatic heating these valley network ages and correlations are thus consistent with a major change in the near surface aqueous environment on mars at approximately the noachian hesperian boundary the noachian environment supported surface running water and fluvial erosion across mars in the cratered uplands enhanced crater degradation and a weathering environment favoring the formation of phyllosilicates the hesperian amazonian environment was more similar to the hyperarid cold desert of today with valley networks forming only extremely rarely and confined to localized special conditions sources of water for these latter occurrences are likely to be related to periodic mobilization and equatorward migration of polar volatiles due to variations in spin axis orbital parameters and to periodic catastrophic emergence of groundwater

thermohydraulic explosions in phreatomagmatic eruptions as evidenced by the comparison between pyroclasts and products from molten fuel coolant interaction experiments 1 thermohydraulic explosions were produced by molten fuel coolant interaction mfci experiments using remelted shoshonitic rocks from vulcano italy the fragmentation history and energy release were recorded the resulting products were recovered and analyzed with the scanning electron microscope fine particles from experiments show shape and surface features that result from melt fragmentation in brittle mode these clasts relate to the thermohydraulic phase of the mfci where most of the mechanical energy is released they are here called active particles the total surface area of such particles is proportional to the energy of the respective explosions other particles from experiments show shape and surface features that result from melt fragmentation in a ductile regime these fragments called passive particles form after the thermohydraulic phase during the expansion phase of the mfci in order to verify thermohydraulic explosions in volcanic eruptions we compared experimental products with samples from phreatomagmatic base surge deposits of vulcano ash particles from the experiments show features similar to those from the deposits suggesting that the experiments reproduced the same fragmentation dynamics to achieve discrimination between active and passive particles we calculated shape parameters from image analysis the mass of active particles in base surge deposits was calculated as the material properties for the natural samples are identical to the experimental ones the energy measurements and calculations of the experiments can be applied for a single phreatomagmatic eruption at vulcano a maximum mechanical energy release of 2 75 1013 j was calculated representing a tnt analogue of 6 5 kt

unusual fluidal behavior of a silicic magma during fragmentation in a deep subaqueous eruption havre volcano southwestern pacific ocean magma responds to applied stresses in either a viscous or elastic manner depending on the time scales over which strain is accommodated for silicic magmas high strain rates of explosive volcanism cause brittle fragmentation and produce abundant small particles ash the a d 2012 havre kermadec arc southwestern pacific ocean eruption at 900 m water depth deposited a unit of silicic ash with features indicative of syn and or post fragmentation viscous deformation viscously deformed ash makes up 3 35 of the two main ash subunits s1 and s2 with the remaining ash formed by brittle fragmentation viscous behavior of melt during production of fine ash is unexpected for the silicic havre magma and for the high strain rates typical of fine fragmentation the occurrence together of viscous and brittle ash grains suggests local and or short term variations in eruption conditions we infer an explosive eruption mechanism modified by magma water interaction during which multi source steam veiled fragmentation sites permitted rapid viscous deformation of ash prior to contact with water

generation of volcanic ash by basaltic volcanism 1 the recent eruptions of eyjafjallajokull and grimsvotn volcanoes in iceland demonstrate the importance of a better understanding of processes leading to the formation of volcanic ash specifically of fine volcanic ash that poses a threat to air traffic continuous deformation and brittle type experiments were carried out to better constrain these processes the studies on short time continuous deformation behavior of basaltic melt showed viscoelastic properties deviating from hydrodynamic newtonian models by more than 5 orders of magnitude high temperature deformation experiments on basaltic rock samples revealed an increase of elastic strengths as approaching the melting regime also pointing to a very complex behavior at the solid ductile boundary understanding magma fragmentation from the liquid side is a challenge but meanwhile we propose a pragmatic solution a thermodynamic model based on fracture mechanics this model is in agreement with experiments and observations that show that fine volcanic ash is produced by brittle type fragmentation of magma a critical material property was defined characterizing the conditions for brittle fragmentation the fracture surface energy density which represents the critical fragmentation energy short term fracture experiments using silicate glass have been performed to investigate the formation of ash sized particles by brittle failure and to extract this critical physical property which was found to range between 40 and 130 j m2 this value is in good agreement to fragmentation energies determined from experiments using remelted volcanic rocks now there is a tool to define critical conditions for the production of volcanic ash of a specific magma type

soil nitrogen isotopic composition of the xifeng loess paleosol sequence and its potential for use as a paleoenvironmental proxy abstract the isotopic composition of soil nitrogen soil 15 n values has been widely used to explore the soil biogeochemical cycle and study land vegetation conditions however the 15 n values in the loess paleosol sequence have not been thoroughly studied in this study we provide the first report of 15 n values from the xifeng loess paleosol profile which spans the last 130 ka the 15 n values show great variation 2 1 6 1 in the xifeng loess sequence according to these results the 15 n values have a similar pattern with changes in the magnetic susceptibility ms and exhibit significant differences within the glacial interglacial cycle over the last 130 ka we hypothesize that climate conditions and land vegetation conversion could be reflected by the changes in the 15 n values within the glacial interglacial cycle 1 the 15 n values are positively correlated with the reconstructed mean annual temperature mat and mean annual precipitation map on the glacial interglacial time scale moreover it appears that the mat may be more effective than the map for the 15 n changes in the xifeng loess paleosol sequence 2 vegetation changing from grasses to shrubs may cause 15 n depletion during the glacial period in addition increasing grass groups may cause 15 n enrichment of the soil during the interglacial stage in the xifeng loess paleosol sequence because nitrogen is one of the most significant nutrient elements for vegetation paleovegetation changes may be the main controlling factor for 15 n values in the loess paleosol section therefore 15 n values have the potential for use as a proxy in paleoenvironmental reconstructions of the chinese loess plateau

loess stratigraphy in central china abstract loess sequences in central china provide a detailed record of climate changes during the last 2 5 million years at least 44 major shifts from glacial to interglacial conditions occurred during this time in china prolonged loess deposition lasting more than 40 millennia occurred eleven times with only four of these intervals in brunhes chron the climate oscillations took place with increased frequency between 2 4 and 0 5 ma compared to the last half million years major shifts toward cooler and drier climates occurred at about 2 4 ma 1 2 ma and 0 5 ma while less pronounced shifts are dated to 1 65 ma 0 8 ma and 0 2 ma three of the last four reversals of the earth s magnetic field whose lithostratigraphic position has been detail are recorded in a glacial deposit the low field magnetic susceptibility of loess and soils which reflects the concentration of ultrafine magnetite is related to the degree of pedogenesis and serves as a proxy measure of climate the accumulation rate of the magnetite was fairly constant throughout the last 1 2 million years and can serve as a measure of time susceptibility records from localities near xifeng and luochuan located 160 km apart are compared and used to define informal lithostratigraphic units in the loess plateau of china

towards fast and routine analyses of volcanic ash morphometry for eruption surveillance applications the morphometry of volcanic ash produced by explosive eruptions yields ample information on fragmentation processes e g magmatic vs magma water interactions and on transport and sedimentation mechanisms most previous works on volcanic clast morphometry focused on the apparent 2d projected shape of ash grains here termed apash to infer processes and eruptive styles however textural analyses of ash grains has remained a long and tedious task that made such approaches inappropriate for eruption surveillance duties in this work we show that new technological advances on automated dispersion of granular materials imaged with a camera coupled microscope and enhanced computer capabilities enable fast and high resolution image acquisition of thousands of ash grains that resolve this limitation with a morpho grainsizer designed for such fast and routine measurements we perform a series of apash analyses on selected ash fractions of tephra deposits from known eruptive styles we record the size aspect ratio circularity and convexity of apash images and assess resolution reproducibility minimum population size and total analytical duration and offer recommendations for the reporting of apash data for inter laboratory comparisons to avoid fractal geometry concerns our analyses are carried out at constant size range 250 300 m and optical magnification 5 on 3000 grains per samples collected from homogenized samples results from the andesitic 1999 ongoing eruption of tungurahua volcano ecuador show that ash particles from the moderate 2001 phase are relatively equant and convex in shape while the stronger 2006 subplinian phase produced ash grains with more elongated less circular and less convex apash signatures ash grains from a basaltic scoria cone forming eruption show even more ragged apash characteristics overall our protocol allows obtaining accurate and reproducible morphometric measurements that reveal subtle variations of the morphological signature and the short duration 1 8 hours of the whole analytical process renders high resolution analyses of ash shape achievable for volcano surveillance applications this research ultimately aims to set up a morphometric database of apash results for well defined eruptive styles in order to interpret on a short term basis any apash data from active volcanoes for monitoring purposes

subaqueous eruption fed density currents and their deposits density currents fed directly from subaqueous eruptions can be divided conceptually into three groups based on modes of fragmentation and transport i explosive fragmentation with deposition from a gas supported current ii explosive fragmentation with deposition from a water supported current iii fragmentation of flowing lava with deposition from a water supported current fig 1 group i products include subaqueously emplaced welded ignimbrite and other high temperature emplaced subaqueous pyroclastic flow deposits group ii products are the most varied and include representatives of both high and low concentration turbidity currents grainflows and debris flows and are termed eruption fed aqueous density currents some clasts in such currents are transported and even deposited at high temperature but the transporting currents ranging from grain flows to dilute turbidity currents are water dominated even though steam may be developed along large clasts margins group iii products formed from lava flow fed density currents tend to be weakly dispersed down gradient along the seafloor and generally consist largely of fragments formed by dynamo thermal quenching and spalling bursting of bubbles formed by vapor expansion probably contributes to some group iii beds distinctive column margin fall deposits may form in water excluded zones that developed very locally around vents in association with group i and ii deposits and are distinguished by heat retention structures indicators of gas phase transport and absence of current formed depositional features 2000 elsevier science b v all rights reserved

winter spring precipitation as the principal control on predominance of c3 plants in central asia over the past 1 77 myr evidence from δ13c of loess organic matter in tajikistan abstract although changes in atmospheric co2 levels are thought to be the major factor driving long term c3 c4 vegetation evolution recent studies tend to emphasize the effect of regional climate conditions on c3 c4 variations the middle latitudes 30 45 in which c3 c4 plants are highly sensitive to environmental changes provide an optimal basis for the investigation of the relative impacts of climate and pco2 on shifts in c3 c4 cover in order to assess the factors controlling these shifts as well as the complex interactions between environmental factors the carbon isotopic composition of bulk organic matter from the chashmanigar loess section southern tajikistan was measured for the past 1 77 myr in general the 13c record shows mostly negative values throughout the sequence almost all 13c values falling between 23 and 26 indicating a predominance of c3 plants in central asia over this time period despite the presence of numerous glacial interglacial cycles from 0 85 myr to the present the 13c values become increasingly positive reflecting a growing c4 signal however this c4 component is not detectable prior to 0 25 myr after which minor peaks are evident at 228 171 and 18 kyr the 13c record from chashmanigar indicates that winter spring precipitation i e mediterranean climatic conditions have characterized central asia throughout the past 1 77 myr leading to the predominance of c3 vegetation in the context of glacial interglacial scale changes in atmospheric co2 therefore it is climate rather than pco2 that controls c3 c4 variations in asia s middle latitudes the gradual increase in the c4 component since 0 85 myr especially the notable peaks after 0 25 myr may have been caused by an increase in summer precipitation due to an enhanced southward shift of the climate zones

fe isotopic composition of the quaternary red clay in subtropical southeast china redoxic fe mobility and its paleoenvironmental implications abstract to probe fe isotopic signatures of the quaternary red clay qrc in subtropical southeastern china two qrc profiles located in southern anhui province southeast china were studied the whole profiles were generally in a narrow range in 56 fe of 0 040 0 061 0 117 0 048 the yellow brown earth ybe and uniform red clay urc of the upper profiles were similar in 56 fe to the xiashu loess along the yangtze river southeast china and the loess paleosols and tertiary red clay in the chinese loess plateaus northwest china as well as the baseline of terrestrial igneous rocks the slight variation of 56 fe from the ybe to the urc suggests that the chemical weathering and rubification on the aerobic surface did not fractionate fe isotopes significantly the reticulate red clay rrc underlying the ybe and urc fluctuated in 56 fe to some extent the white veins separated from the lower rrc were depleted of fe oxides and heavier in fe isotopes and the red veins on the contrary were isotopically lighter in fe 56 fe of the white veins 0 345 0 053 on average was significantly higher than the bulk samples 0 033 0 044 on average and the red veins 0 021 0 046 on average this suggests that the reticulate textures of the rrc were formed by the reductive removal re precipitation of fe due to the cyclical changes of redoxic conditions fe isotopic composition of the qrc was dominantly controlled by the redoxic mobility of fe rather than the degree of weathering 56 fe of the profiles was not correlated with the paleoclimatic events and thus cannot be used as a paleoclimatic proxy the fractionation of fe isotopes in the lower rrc however indicated the occurrence of over humid paleoclimate with alternations between drought and wetness in southern china during the pleistocene

characterization of shape and terminal velocity of tephra particles erupted during the 2002 eruption of etna volcano italy in this paper we present a complete morphological characterization of the ash particles erupted on 18 december 2002 from etna volcano italy the work is based on the acquisition and processing of bidimensional digital images carried out by scanning electron microscopy sem to obtain shape parameters by image analysis we measure aspect ratio ar form factor ff compactness cc and rectangularity rt of 2065 ash particles with size between 0 026 and 1 122 mm we evaluate the variation of these parameters as a function of the grain size ash particles with a diameter of 0 250 mm are subelongate we find that on average particles with a diameter of 0 50 mm are angular using this morphological analysis and an empirical relation between the drag coefficient cd and reynolds number re of wilson and huang earth planet sci lett 44 311 324 1979 we calculate the terminal settling velocities vwh the comparisons between these velocities and those calculated with the formula of kunii and levenspiel fluidization engineering wiley new york pp 97 1969 vkl which considers ash particles as spheres show that vkl are in average 1 28 greater than vwh hence we quantify the systematic error on the spatial distribution of the mass computed around the volcano carried out by tephra dispersal models when the particles are assumed to be spherical

negative δ18o δ13c relationship of pedogenic carbonate from northern china indicates a strong response of c3 c4 biomass to the seasonality of asian monsoon precipitation abstract evaluating how future climate changes may impact c3 c4 biomass in east asia depends largely on the understanding of the relationship between past c3 c4 variations and asian monsoon circulation the glacial interglacial variations in c3 c4 biomass have been readily ascribed to the summer monsoon however the internal processes governing the link of c3 c4 vegetation to the asian monsoon have not been clearly described here we present isotopic results of pedogenic carbonate from northern china for the holocene the last and penultimate interglacial periods comparison of the observed and predicted 18o values of modern soil carbonate from gravelly soils suggests that pedogenic carbonate forms mainly in warm rainy season carbonate nodules from the chinese loess demonstrate a distinct negative 18o 13c relationship and a wider scatter of isotopic values in the southern loess plateau than in the northern part by combining rainfall 18o of precipitation and the peak of c3 and c4 plant metabolism we develop a conceptual model to explain the isotopic signatures of the carbonate nodules our model shows that a narrowly focused season of monsoon precipitation at a specific site produces low 18o values of soil water and simultaneously favors c4 over c3 plants our model further suggests that the scattered isotopic values of soil carbonate reflect a strong summer monsoon while the focused values indicate a weak summer monsoon 13c values of soil carbonate indicate a striking pattern of northward increasing c4 vegetation for the last interglacial while a flat spatial pattern is seen for the penultimate interglacial and the holocene it is inferred that the summer monsoon was stronger during the last interglacial than during the penultimate interglacial and the holocene leading to a northward displacement of c3 forest ecosystems into the southern loess plateau in addition an in phase relationship between intra nodule 13c and 18o values suggests a strong and possibly rapid response of c3 c4 biomass to the seasonality of asian monsoon precipitation in this context if the last interglacial period mis 5 is taken as an analog for the projected near future then c3 plants may be favored in the south while c4 plants may be efficient in the north

tectonic history of the tharsis region mars the faults of the tharsis region of mars have been mapped and delineated on the basis of age the orientation of each group of faults was analyzed to determine if they were radial to a point the results indicate that there are at least four discrete centers of faulting within the tharsis area which are of significantly different age the four centers proposed are from oldest to youngest 1 in the thaumasia highlands 2 in northern syria planum and finally 3 and 4 near pavonis mons while episodes 3 and 4 occupy the same geographic position they are separated in time by the development of the tharsis lava plains and shields each episode of tectonism was separated from the next by a period of major basaltic volcanism the tectonic features of the tharsis area are thus viewed as being the cumulative result of the superposition of several discrete episodes of faulting rather than the result of one episode about a single point

direct video and hydrophone observations of submarine explosive eruptions at nw rota 1 volcano mariana arc 1 extraordinary video and hydrophone observations of a submarine explosive eruption were made with a remotely operated vehicle in april 2006 at a depth of 550 560 m on nw rota 1 volcano in the mariana arc the observed eruption evolved from effusive to explosive while the eruption rate increased from near zero to 10 100 m3 h during the peak in activity cyclic explosive bursts 2 6 min long were separated by shorter non eruptive pauses lasting 10 100 s the size of the ejecta increased with the vigor of the explosions a portable hydrophone deployed near the vent recorded sounds correlated with the explosive bursts the highest amplitudes were 50 db higher than ambient noise at frequencies between 10 and 50 hz the acoustic data allow us to quantify the durations amplitudes and evolution of the eruptive events over time the low eruption rate high gas lava ratio and rhythmic eruptive behavior at nw rota 1 are most consistent with a strombolian eruptive style we interpret that the eruption was primarily driven by the venting of magmatic gases which was also the primary source of the sound recorded during the explosive bursts the rhythmic nature of the bursts can be explained by partial gas segregation in the conduit and upward migration in a transitional regime between bubbly flow and fully developed slug flow the strongest explosive bursts were accompanied by flashes of red glow and oscillating eruption plumes in the vent apparently caused by magma seawater interaction and rapid steam formation and condensation this is the first time submarine explosive eruptions have been witnessed with simultaneous near field acoustic recordings

crater fault interactions a metric for dating fault zones on planetary surfaces abstract constructing a tectonic history of a planetary surface requires determining precise fault ages a task not always possible with current analytical methods here we introduce a new method to constrain the ages of faults improving upon earlier methods that used cross cutting relationships with crater dated host surfaces and apply it to faulted terrains by counting all craters and categorizing them into faulted unfaulted and unclear types to date deformation directly additionally we construct a simple probabilistic model to account for regions of low fault density this new technique is applied to the tectonically complex thaumasia plateau mars to assess the timing of regional faulting and demonstrate its usefulness and ease of application

the role of bubbles in generating fine ash during hydromagmatic eruptions the abundant fine ash produced in the 2011 subglacial eruption of grimsvotn iceland highlights the fragmentation efficiency of mafic hydromagmatic eruptions which is considerably higher than for comparable dry eruptions ash from the 2011 eruption can be divided into three morphological components vesicular particles shards and dense fragments distinguished by the size and abundance of constituent vesicles we use the vesicle characteristics to define a new shape factor the concavity index which provides an unbiased way to classify individual ash particles as either bubbly vesicular particles and shards or dense the relative proportion of bubbly and dense particles varies systematically with grain size with the proportion of bubbly grains decreasing as the particle size approaches the modal bubble diameter measured bubble volume distributions are similar to those of rapidly quenched pyroclasts from hawaiian fountains and suggest a comparable degassing history during magma ascent yet concordance between the size distributions of ash and of bubbles in the grimsvotn samples stands in contrast to the size distributions in hawaiian fountains where pyroclasts are orders of magnitude larger than individual bubbles we propose that the grimsvotn ash formed by brittle disintegration of vesicular pyroclasts and that fragmentation efficiency was amplified by residual thermal stresses in glass quenched by glacial water the strong control of resulting particle sizes and morphologies by the size and spatial distribution of bubbles demonstrates that the bubble population cannot be ignored when modeling hydromagmatic fragmentation

changes in vegetation type on the chinese loess plateau since 75 ka related to east asian summer monsoon variation abstract floral communities in terrestrial habitats such as steppes are highly sensitive to regional climate changes here we generated carbon and nitrogen isotope profiles for soil organic matter som in the weinan loess paleosol section in order to investigate changes in floral communities on the chinese loess plateau clp and their relationship to climate variation since 75 ka 13csom at weinan ranges from 23 6 to 18 0 and 15nsom ranges from 3 4 to 5 5 modeling based on the 13csom record suggests that the proportion of c4 plants c4 has varied from lower during cold intervals with minima of 24 32 at 73 1 ka 20 9 ka lgm and 0 6 ka to higher during warm intervals with maxima of 62 64 at 53 0 ka and 8 2 ka the 13csom and 15nsom profiles are strongly correlated r 0 82 p

c3 c4 vegetation evolution over the last 7 0 myr in the chinese loess plateau evidence from pedogenic carbonate δ13c the stable carbon and oxygen isotopic compositions of soil carbonate were measured on an eolian loess and red clay sequence at lingtai the chinese loess plateau this sequence is composed of 130 m of tertiary red clay deposits with a basal age of 7 05 ma overlain by 175 m of pleistocene loess in the field we identified ca 110 carbonate nodule horizons in the red clay and 27 nodule horizons in the loess these carbonate nodule horizons are formed by leaching and re precipitation of carbonate from the eolian material the d13c record of soil carbonate indicates a major expansion of c 4 plants at ca 4 0 myr in the loess plateau this event is comparable in timing with the expansion of c 4 plants in northern north america cerling et al 1997 nature 389 153 158 but is ca 3 million years later than the c 4 biomass expansion in pakistan quade et al 1989 nature 342 163 166 the pedogenic characteristics of the soils and the d18o record in the red clay suggest that the c 4 plant expansion in the loess plateau was not driven by local climatic changes which may support cerling et al s 1997 assertion that the decline of atmospheric co 2 levels in the neogene is responsible for this global vegetation change our record also implies that the tibetan plateau could have been uplifted to a critical height in the late miocene thus resulting in the formation of the atmospheric great east asia trough 2000 elsevier science b v all rights reserved

furthering the investigation of eruption styles through quantitative shape analyses of volcanic ash particles abstract volcanic ash morphology has been quantitatively investigated for various aims such as studying the settling velocity of ash for modelling purposes and understanding the fragmentation processes at the origin of explosive eruptions in an attempt to investigate the usefulness of ash morphometry for monitoring purposes we analyzed the shape of volcanic ash particles through a combination of 1 traditional shape descriptors such as solidity convexity axial ratio and form factor and 2 fractal analysis using the euclidean distance transform edt method we compare ash samples from the hydrothermal eruptions of iwodake japan in 2013 tangkuban perahu indonesia in 2013 and marapi sumatra indonesia in 2015 the dome explosions of merapi java indonesia in 2013 the vulcanian eruptions of merapi in 2010 and tavurvur rabaul papaua new guinea in 2014 and the plinian eruption of kelud indonesia in 2014 particle size and shape measurements were acquired from a particle size analyzer with a microscope camera attached to the instrument clear differences between dense blocky particles from hydrothermal or dome explosions and vesicular particles produced by the fragmentation of gas bearing molten magma are well highlighted by conventional shape descriptors and the fractal method in addition subtle differences between dense blocky particles produced by hydrothermal explosions dome explosions or quench granulation during phreatomagmatic eruptions can be evidenced with the fractal method the combination of shape descriptors and fractal analysis is therefore potentially able to distinguish between juvenile and non juvenile magma which is of importance for eruption monitoring

shifting styles of basaltic explosive activity during the 2002 03 eruption of mt etna italy abstract the 2002 03 flank eruption of etna was characterized by two months of explosive activity that produced copious ash fallout constituting a major source of hazard and damage over all eastern sicily most of the tephra were erupted from vents at 2750 and 2800 m elevation on the s flank of the volcano where different eruptive styles alternated the dominant style of explosive activity consisted of discrete to pulsing magma jets mounted by wide ash plumes which we refer to as ash rich jets and plumes similarly ash rich explosive activity was also briefly observed during the 2001 flank eruption of etna but is otherwise fairly uncommon in the recent history of etna here we describe the features of the 2002 03 explosive activity and compare it with the 2001 eruption in order to characterize ash rich jets and plumes and their transition with other eruptive styles including strombolian and ash explosions mainly through chemical componentry and morphology investigations of erupted ash past models explain the transition between different styles of basaltic explosive activity only in terms of flow conditions of gas and liquid our findings suggest that the abundant presence of a solid phase microlites may also control vent degassing and consequent magma fragmentation and eruptive style in fact in contrast with the strombolian or hawaiian microlite poor fluidal sideromelane clasts ash rich jets and plumes produce crystal rich tachylite clasts with evidence of brittle fragmentation suggesting that high groundmass crystallinity of the very top part of the magma column may reduce bubble movement while increasing fragmentation efficiency

the terminal velocity of volcanic particles with shape obtained from 3d x ray microtomography new experiments of falling volcanic particles were performed in order to define terminal velocity models applicable in a wide range of reynolds number re experiments were carried out with fluids of various viscosities and with particles that cover a wide range of size density and shape particle shape which strongly influences fluid drag was measured in 3d by high resolution x ray microtomography by which sphericity 3d and fractal dimension d3d were obtained they are easier to measure and less operator dependent than the 2d shape parameters used in previous papers drag laws that make use of the new 3d parameters were obtained by fitting particle data to the experiments and single equation terminal velocity models were derived they work well both at high and low re 3 10 2 re 104 while earlier formulations made use of different equations at different ranges of re the new drag laws are well suited for the modelling of particle transportation both in the eruptive column where coarse and fine particles are present and also in the distal part of the umbrella region where fine ash is involved in the large scale domains of atmospheric circulation a table of the typical values of 3d and d3d of particles from known plinian subplinian and ash plume eruptions is presented graphs of terminal velocity as a function of grain size are finally proposed as tools to help volcanologists and atmosphere scientists to model particle transportation of explosive eruptions

identifying magma water interaction from the surface features of ash particles the deposits from explosive volcanic eruptions those eruptions that release mechanical energy over a short time span1 are characterized by an abundance of volcanic ash2 3 this ash is produced by fragmentation of the magma driving the eruption and by fragmenting and ejecting parts of the pre existing crust host rocks interactions between rising magma and the hydrosphere oceans lakes and ground water play an important role in explosive volcanism4 5 because of the unique thermodynamic properties of water that allow it to very effectively convert thermal into mechanical energy although the relative proportion of magma to host rock fragments is well preserved in the pyroclastic rocks deposited by such eruptions it has remained difficult to quantitatively assess the interaction of magma with liquid water from the analysis of pyroclastic deposits2 3 4 5 here we report the results of a study of natural pyroclastic sequences combined with scaled laboratory experiments we find that surface features of ash grains can be used to identify the dynamic contact of magma with liquid water the abundance of such ash grains can then be related to the water magma mass ratios during their interaction

quantitative discrimination of magma fragmentation and pyroclastic transport processes using the fractal spectrum technique abstract the morphology of volcanic particles can yield insight into magma fragmentation transport processes and style of eruption however the complexity and variability of volcanic particle shapes make quantitative characterization difficult the technique applied in this study is based on fractal geometry which has been successfully used to characterize a wide variety of particles and shapes here fractal data is produced by dilation of the 2 d particle boundary to produce a full spectrum of fractal dimensions over a range of scales for each particle multiple fractal dimensions which can be described as a fractal spectrum curve are calculated by taking the first derivative of data points on a standard richardson plot use of multiple fractal dimensions results in more effective discrimination than expressions of shape based on one or two fractal dimensions quantitative comparisons are carried out using multivariate statistical techniques such as cluster and principal components analysis applications to samples from well documented eruptions e g mt st helens 1980 tambora 1815 surtsey 1963 64 indicate that the fractal spectrum technique provides a useful means of characterizing volcanic particles and can be helpful for identifying the products of specific fragmentation processes volatile exsolution phreatomagmatic quench granulation and modes of volcanic transport deposition tephra fall pyroclastic flow blast surge

leaf wax n alkane distributions in chinese loess since the last glacial maximum and implications for paleoclimate abstract leaf wax n alkanes have been recently introduced into loess deposits for paleovegetation and paleoclimate reconstruction however the paleoclimate significance of some n alkane parameters such as chain length ratios l h c 27 c 31 c 29 c 31 and c 27 c 29 c 31 c 33 remains to be clarified in order to evaluate the validity of those proxies in loess deposits leaf wax n alkanes were analyzed from a northwest southeast transect on the chinese loess plateau since the last glacial maximum lgm the n alkanes show a bimodal distribution between c 14 and c 33 with carbon number maxima c max at c 14 or c 16 and at c 31 or c 33 indicative of both terrestrial plant and microbial origin l h variations are in good agreement with climate changes both temporally and spatially i e the higher l h ratio the warmer and wetter climate and vice versa therefore the l h ratio in chinese loess can serve as an efficient proxy for paleoclimate by comparing long chain n alkane ratios with pollen records we suggest that the generally used woody plant proxies c 27 and c 29 and grass proxies c 31 and c 33 are not applicable to chinese loess as the chinese loess plateau was dominated by herbs in both the lgm and the holocene the long chain n alkane ratios may mainly reflect changes in the species composition of local vegetation for a better understanding of leaf wax n alkanes in chinese loess further studies are required to investigate the n alkane distributions in both the major plant species and their associated surface soils on the chinese loess plateau

phreatomagmatic explosions of rhyolitic magma experimental and field evidence 1 experimental studies on explosive molten fuel coolant interaction mfci using basaltic melt compositions and water as the coolant have provided insight into the physical processes of basaltic and andesitic phreatomagmatic volcanism abundant field evidence indicates that rhyolitic and dacitic phreatomagmatism occurs in nature but it has not been possible until now to generate laboratory mfci explosions from the interaction between high silica melts and water under laboratory conditions the high viscosity of these melts apparently prevents formation of an effective hydrodynamic premix of melt and water the documented precursor of experimental explosive mfci caused by mafic melts our new experiments utilized samples from a rhyolitic tuff ring volcano in mexico tepexitl an experimental approach was developed in which premixing conditions were generated by mechanical deformation of the melt leading to brittle type fragmentation at the melt water interface physical measurements recorded during laboratory explosion provide quantitative evidence for rhyolitic explosive mfci additionally a comparison of experimentally produced particles with natural ones from tepexitl deposits show nearly identical chemical mineralogical composition grain size and grain morphology detailed textural analysis confirmed the presence of phreatomagmatically produced particles in both experimental and natural analog particles the results from this series of experiments indicate that under natural conditions stress induced magma fracturing can lead to a critical magma water interface growths and trigger phreatomagmatic explosions of high silica magma the water source for these eruptions may include shallow aquifers surface water bodies strong precipitation and intrusion into ice or wet unconsolidated sediments

a 135 000 year vostok specmap common temporal framework the object of the present study is to introduce a means of comparing the vostok and marine chronologies our strategy has been to use the 18o of atmospheric o2 denoted 18oatm from the vostok ice core as a proxy for the 18o of seawater denoted 18osw our underlying premise in using 18oatm as a proxy for 18osw is that past variations in 18osw an indicator of continental ice volume have been transmitted to the atmospheric o2 reservoir by photosynthesizing organisms in the surface waters of the world s oceans we compare our record of 18oatm to the 18osw record which has been developed from studies of the isotopic composition of biogenic calcite 18oforam in deep sea cores we have tied our 18oatm record from vostok to the specmap timescale throughout the last 135 kyr by correlating 18oatm with a 18osw record from v19 30 results of the correlation indicate that 77 of the variance is shared between these two records we observed differences between the 18oatm and the 18osw records during the coldest periods which indicate that there have been subtle changes in the factors which regulate 18oatm other than 18osw our use of 18oatm as a proxy for 18osw must therefore be considered tentative especially during these periods by correlating 18oatm with 18osw we provide a common temporal framework for comparing phase relationships between atmospheric records from ice cores and oceanographic records constructed from deep sea cores our correlated age depth relation for the vostok core should not be considered an absolute vostok timescale we consider it to be the preferred timescale for comparing vostok climate records with marine climate records which have been placed on the specmap timescale we have examined the fidelity of this common temporal framework by comparing sea surface temperature sst records from sediment cores with an antarctic temperature record from the vostok ice core we have demonstrated that when the southern ocean sst and antarctic temperature records are compared on this common temporal framework they show a high degree of similarity we interpret this result as supporting our use of the common temporal framework for comparing other climate records from the vostok ice core with any climate record that has been correlated into the specmap chronology

magnetic susceptibility evidence of monsoon variation on the loess plateau of central china during the last 130 000 years the magnetic susceptibility of loess and paleosols in central china represents a proxy climate index closely related to past changes of precipitation and vegetation and thus to summer monsoon intensity time series of magnetic susceptibility constructed for three loess paleosol sequences in the southern part of the chinese loess plateau document the history of summer monsoon variation during the last 130 000 yr they correlate closely with the oxygen isotope record of stages 1 to 5 in deep sea sediments soils were forming during intervals of strong summer monsoon whereas loess units were deposited at times of reduced monsoon intensity the chinese loess paleosol sequence can thus be viewed as a proxy record of asian monsoon variability extending over the last 2 5 myr

the fracture behaviour of volcanic glass and relevance to quench fragmentation during formation of hyaloclastite and phreatomagmatism quench fragmentation is a non explosive process that occurs when molten magma is super cooled to glass upon contact with ambient water this occurs when coherent lavas are erupted subaqueously when they flow into water when magma intrudes into water saturated sediments and when magma and water interact explosively during phreatomagmatism quench fragmentation also occurs alongside explosive phreatomagmatic activity although products of quench fragmentation hyaloclastite sensu stricto have been discussed qualitatively in the volcanological literature compared to explosive fragmentation processes very little is known about the exact dynamics of quench fragmentation of magma and how this relates to the rheology and physical properties of volcanic glass based on literature from materials engineering we present a detailed review of the processes by which glass forms the properties of glass and the fracture mechanics that cause it to fragment non explosively we also consider how this can be applied to understanding the dynamics behind the volcanological processes of in situ glass fragmentation during quenching in wet environments and phreatomagmatism important parameters for the occurrence of quench fragmentation are the temperature difference between the magma and the ambient water and how much the ambient water is superheated above its leidenfrost temperature the geometry of the lava or magma intrusion the thermal conductivity and the thermal expansion are also of great importance the resistance of the magma against fragmentation can be increased with the presence of crystals provided the thermal expansion of the crystals does not greatly exceed that of the glass vesicles have the opposite effect unless the magma is highly vesicular this overview then provides a solid basis for further quantitative study of quench fragmentation and hyaloclastite formation

quantitative shape measurements of distal volcanic ash 1 large scale volcanic eruptions produce fine ash 200 m which has a long atmospheric residence time 1 hour or more and can be transported great distances from the volcanic source thus becoming a hazard to aircraft and public health ash particles have irregular shapes so data on particle shape size and terminal velocities are needed to understand how the irregular shaped particles affect transport processes and radiative transfer measurements in this study a methodology was developed to characterize particle shapes sizes and terminal velocities for three ash samples of different compositions the shape and size of 2500 particles from 1 distal fallout 100 km of the 14 october 1974 fuego eruption basaltic 2 the secondary maxima 250 km of the 18 august 1992 spurr eruption andesitic and 3 the miocene ash hollow member nebraska rhyolitic were measured using image analysis techniques samples were sorted into 10 to 19 terminal velocity groups 0 6 59 0 cm s using an air elutriation device grain size distributions for the samples were measured using laser diffraction aspect ratio feret diameter and perimeter measurements were found to be the most useful descriptors of how particle shape affects terminal velocity these measurement values show particle shape differs greatly from a sphere commonly used in models and algorithms the diameters of ash particles were 10 120 larger than ideal spheres at the same terminal velocity indicating that irregular particle shape greatly increases drag gas adsorption derived surface areas are 1 to 2 orders of magnitude higher than calculated surface areas based on measured dimensions and simple geometry indicating that particle shapes are highly irregular correction factors for surface area were derived from the ash sample measurements so that surface areas calculated by assuming spherical particle shapes can be corrected to reflect more realistic values

lower temperature as the main cause of c4 plant declines during the glacial periods on the chinese loess plateau abstract the distribution of c3 and c4 plants changed in regionally contrasting ways during the last glacial period c4 plant expansion in low latitude africa and america coincided with c4 plant decreases in mesoamerica and the us great plains this c4 plant expansion has been attributed to lower pco2 and increased aridity and the decline in c4 plants is believed to have been caused by increased winter precipitation and lower temperatures however it is still difficult to generalize whether pco2 temperature or aridity was mainly responsible for c3 vs c4 vegetation changes during glacial periods paleoclimate conditions on the chinese loess plateau clp offer opportunities to further evaluate the role of temperature in the c3 vs c4 competition detailed climate records have shown that the clp region was drier and colder during glacial periods with aridity favoring c4 expansion and lower temperatures favoring c3 expansion here we present two high resolution compound specific carbon isotope records of n alkanes from the clp as vegetation biomarkers to estimate the relative abundance of c4 plants during the last two glacial interglacial transitions more negative 13c values during the glacial periods from two clp sites clearly show that in contrast with low latitude sites c4 plants declined this decrease in c4 abundance was caused by lower temperature despite the lower pco2 and increased aridity on the clp during glacial time

humid glacials arid interglacials critical thoughts on pedogenesis and paleoclimate based on multi proxy analyses of the loess paleosol sequence crvenka northern serbia abstract loess paleosol sequences lps provide unique terrestrial archives for past environmental and climate changes the loess units are generally interpreted to reflect more arid conditions whereas paleosols are thought to document more humid conditions this paradigm may however deserve to be challenged in some regions because it does not take into account past changes in dust accumulation rates here we present a multi proxy sedimentological and geochemical characterization of the lps crvenka serbia spanning the last 140 ka commonly used analyses such as magnetic susceptibility organic carbon content grain size and weathering indices allow the quantification of the intensity of pedogenesis however loess accumulation rates were much higher during glacials than during interglacials so that it is not trivial to infer past rates of pedogenesis and related paleoclimate conditions novel proxies based for example on lipid biomarkers and their isotopic composition are not so directly affected by changes in loess accumulation rates and might provide interesting new insights long chain plant derived n alkanes in the lps crvenka suggest a minor but non negligible contribution of deciduous trees and shrubs c27 and c29 during mis 1 2 4 and 6 whereas grasses and herbs c31 and c33 dominate the alkane input during mis 3 and 5 this is in agreement with the notion that parts of southeast europe served as refugia for deciduous trees during glacials on the other hand edaphic conditions on the drought prone loess plateaus seem to have been more arid during mis 3 and 5 compound specific d analyses on the alkanes show only little changes on glacial interglacial timescale when compared with the isotopic enrichment of the mediterranean sea during the last glacial this likely indicates a complex combination of reduced temperatures increased rainfall reduced evapotranspiration and more advection of north atlantic moisture although disentangling these factors is difficult interpretation in terms of humid glacials and more arid interglacials seems to be supported also by other novel lipid biomarkers so called gdgts glycerol dialkyl glycerol tetraethers

quantitative estimates of palaeoprecipitation at xifeng in the loess plateau of china abstract using10be recent studies heller et al 1993 beer et al 1993 have tried to reconstruct palaeoclimatic records by separating the secondary pedogenic and primary aeolian detrital contributions to the magnetic susceptibility of chinese loess here we use a technique which monitors the temperature dependence of magnetic remanence to estimate the magnetisation and relative contribution of the superparamagnetic sp single domain sd and multidomain md ferrimagnetic components in the xifeng loess section on the assumption that the sp ferrimagnetic component is dominantly of pedogenic origin the magnetisation of this component has also been determined for samples taken from the topmost palaeosol s0 at six sites over the loess plateau and directly correlated with present day precipitation at these sites this correlation is then used to estimate quantitatively palaeoprecipitation for the topmost 16 m of the xifeng section which covers about the last 140 000 years the data indicate a considerably reduced precipitation during the glacial loess forming periods and a significantly higher level of precipitation than today during the last interglacial period

grain shape of basaltic ash populations implications for fragmentation here we introduce a new quantitative method to produce grain shape data of bulk samples of volcanic ash and we correlate the bulk average grain shape with magma fragmentation mechanisms the method is based on automatic shape analysis of 2d projection ash grains in the size range 125 63 m loose bulk samples from the deposits of six different basaltic eruptions were analyzed and 20 000 shape measurements for each were obtained within 45 min using the particle insight dynamic shape analyzer pidsa we used principal component analysis on a reference grain dataset to show that circularity rectangularity form factor and elongation best discriminate between the grain shapes when combined the grain population data show that the studied eruptive environments produce nearly the same range of grain shapes although to different extents our new shape index the regularity index ri places an eruption on a spectrum between phreatomagmatic and dry magmatic fragmentation almost vesicle free surtseyan ash has an ri of 0 207 0 002 2 whereas vesiculated hawaiian ash has an ri of 0 134 0 001 2 these two samples define the end member ri while two subglacial one lacustrine and another submarine ash sample show intermediate ris of 0 168 0 002 2 0 175 0 002 2 0 187 0 002 2 and 0 191 0 002 2 respectively the systematic change in ri between wet and dry eruptions suggests that the ri can be used to assess the relative roles of magmatic vs phreatomagmatic fragmentation we infer that both magmatic and phreatomagmatic fragmentation processes played a role in the subglacial eruptions

the late quaternary loess record of tokaj hungary reconstructing palaeoenvironment vegetation and climate using stable c and n isotopes and biomarkers abstract large areas of southeast europe are covered by pleistocene loess deposits with interbedded palaeosol layers reflecting interglacials or stadials these loess palaeosol sequences are valuable terrestrial archives for continuous palaeoclimatic and palaeoenvironmental information in recent years the traditional paradigm of treeless full glacial palaeoenvironments has increasingly been called into question as there is palynological anthracological and malacological evidence for the continuous presence of trees from loess palaeosol sequences in the carpathian basin this paper aims at contributing to this discussion by applying biogeochemical geophysical and sedimentological methods to a late quaternary loess palaeosol profile at tokaj ne hungary previous studies at the same location have focused on molluscs and charcoal while this study concentrated on stable c and n isotopes and lipid biomarkers long chain n alkanes c 23 c 33 which form major constituents of plant leaf waxes have successfully been used as biomarkers over the last years and allow for a reconstruction of palaeovegetation based on the differentiation of grassland vs shrubs and trees stable carbon isotopes were used to further differentiate between c 3 and c 4 palaeovegetation and stable n isotopes to reconstruct the n cycle and climatic variations magnetic susceptibility ms organic carbon and grain size distribution which may serve as proxies for e g the intensity of pedegenesis weathering and palaeowind strength were measured to complement the biogeochemical results and to establish a pedo and biostratigraphy although the results do not agree in every detail with previous studies there are surprising matches and similarities in the data alkane and stable n isotopic data indicate that pedogenesis occurred under productive fertile steppe grasslands probably in an intensified seasonal climate and during reduced sedimentation two short treeless steppe periods were found between 26 and 12 ka bp however periods characterised by a cooler climate in which trees and shrubs expanded were also found this interpretation is also supported by previous mollusc data that provide evidence for several periods of favourable conditions for tree growth

late holocene aridification recorded in the stable carbon and nitrogen isotope composition of soils from nainital lesser himalaya abstract this study incorporates micromorphology geochemistry and stable carbon and nitrogen isotope compositions of soil organic matter 13c and 15n in a radiocarbon dated holocene alfisol section from nainital northwest himalaya india to understand pedogenic and vegetation response to changing indian summer monsoon ism soil micromorphology suggests this soil to be an alfisol that formed in semiarid to humid conditions extensive illuviation with thick clay pedofeatures found in the bt horizon suggests wet conditions and intense monsoon during early to middle holocene 9 0 4 6 ka the 13c varies from 14 2 to 22 6 and reflects abrupt changes in the proportions of c3 and c4 plants in the ecosystem during late holocene an average 13c of 21 6 1 0 during early to middle holocene 9 0 4 6 ka indicates that the vegetation was dominated by c3 plants growth under hot humid and strong monsoonal conditions on the other hand 13c 16 7 2 1 during late holocene 4 1 ka suggests distinct vegetation shift towards increasing c4 plants abundance related to aridification weak ism at 4 ka the pattern of 15n variability in the soil is similar to that observed for the 13c variability in the profile the 15n varies from 4 4 to 8 3 with significantly more positive values during late holocene weaker monsoon compared to early to middle holocene stronger monsoon consistent with the relationship between 15n and mean annual precipitation observed on a global scale our study demonstrates a strong and rapid adjustment of vegetation in response to ism variability during holocene

thick shell tectonics on one plate planets applications to mars a theory for stress distributions in thick lithospheric shells on one plate planets is developed based on the zero frequency equations of a self gravitating elastic spherical shell overlying a strengthless fluid stress distributions in lithospheres are reviewed for both the compensated and flexural modes in the former case surface stresses only depend on surface topography while for the latter case it is shown for long wavelengths that stress trajectories are mainly dependent on the lithospheric lateral density distribution and not on elastic properties computational analyses are carried out for mars and it is found that isostatically compensated models correctly predict the graben structure in the immediate tharsis region and a flexural loading model is satisfactory in explaining the graben in the regions surrounding tharsis a three stage model is hypothesized for the evolution of tharsis isostasy with north south graben formation on tharsis followed by flexural loading and radial graben formation on the perimeter of tharsis followed by a last stage of loading with little or no regional deformation this model is consistent with the martian lithosphere monotonically thickening over geologic time

statistical analysis of textural data from complex pyroclastic sequences implications for fragmentation processes of the agnano monte spina tephra 4 1 ka phlegraean fields southern italy the agnano monte spina eruption 4 1 ka generated pyroclastic deposits with complex internal stratigraphy that reflects variations in eruptive style to obtain constraints on the fragmentation processes we analysed grain size and scanning electron microscopy sem data by means of multivariate statistical techniques of the cluster and factor analysis types the results allow the identification of end member deposits related to either pure magmatic activity or pure phreatomagmatic activity in addition some deposits show evidence of the contemporaneous operation of both end member fragmentation modes the presence of the two contrasting fragmentation processes during the various phases of explosive activity is tentatively interpreted to be a function in inhomogeneities in gas exsolution processes within the magma column that feeds the eruption

did an extensive forest ever develop on the chinese loess plateau during the past 130 ka a test using soil carbon isotopic signatures abstract pleistocene vegetation history on the chinese loess plateau has been traditionally investigated using palynological methods and questions remain regarding whether an extensive broadleaf deciduous forest ever developed on the loess table under favorable climatic conditions the authors have employed a c isotope approach to address this question by comparing 13 c values in soil organic matter from different loess ecological domains with known source vegetation to the c isotope values obtained from a paleosol section that can be dated back to 130 ka the c isotopic compositions of modern soils from the loess table and the loess desert transition gave 13 c values of 24 5 to 18 2 and 25 7 to 20 7 respectively these c isotopic ratios are consistent with the standing modern vegetation that is dominated by a mixture of c 3 and c 4 plants and can be distinguished from that in the patchy forest areas where exclusive c 3 trees yield a narrow 13 c value range from 26 9 to 25 average 26 1 obtained 13 c compositions from paleosols and loess sediments in the lantian and the luochuan profiles vary from 24 to 16 9 indicating a grass dominated steppe with shifting c 3 and c 4 contributions controlled mainly by paleoclimatic changes during the late pleistocene the present results suggest no extensive forest coverage on the loess table during the past 130 ka even under the most suitable conditions for forest development this conclusion supports the explanation of natural causes for the development of only patchy forests on the modern loess table and provides critical historical information toward the vegetation restoration project that is currently underway on the chinese loess plateau

the history and variability of the east asian paleomonsoon climate abstract changes in the east asian paleomonsoon reflect interactions between the global atmosphere ocean land and ice systems and are also an expression of their combined effect within the boundary conditions imposed by the east asian continent and solar radiation the history of the east asian monsoon is an alternation between dominance by the dry cold winter and warm humid summer monsoons high resolution eolian sequences preserved in the chinese loess plateau reveal that the east asian monsoon may have commenced at least 7 2 ma ago they also provide evidence indicating that the pulsed uplift of the tibetan plateau at about 3 4 and 7 2 ma may have played an important role in inducing climate change the palaeoclimatic records of the last glacial cycle show high frequency variability on time scales of 1000 year or even shorter and instability of the east asian paleomonsoon system the high frequency variability could be due to a non linear response to orbital forcing or a result of the coupling processes between different components of the global system cold air activity in northern high latitudes the trans equatorial air streams from the southern hemisphere and possibly enso may have played an important role in east asian monsoon variability the synchroneity of all the palaeoclimatic events along the polar equator polar pep transect is still an open question correlation of limited palaeoclimatic records for the last 30 kyr obtained from east asia and australia suggests that the trans equatorial air streams driven by the monsoon and trade winds may have had an influence on opposite hemispheres

the late pleistocene belotinac section southern serbia at the southern limit of the european loess belt environmental and climate reconstruction using grain size and stable c and n isotopes the belotinac loess section is one of the southernmost loess paleosol environmental archives for the late quaternary in serbia the climate at this site is intermediate between the continental and the mediterranean realms which makes this loess archive potentially highly sensitive to past climatic changes this paper presents new insights into the paleoenvironmental history during the last glacial period in southern serbia using grain size and isotope proxy data the grain size parameters from the belotinac section reveal variations in the paleowind dynamics and weathering intensity and suggest the nearby valley of the ju na morava river as an important source of aeolian sediments in this area based on a multiproxy dataset alternating phases of weak interstadials and phases of enhanced loess deposition at this site were identified nitrogen isotope data suggest that during marine isotope stage 3 ecosystems of high biomass productivity and rather open n cycles prevailed during marine isotope stage 2 productivity was reduced and the n cycle was more strongly closed probably due to a shorter growing season and more pronounced temperature decline carbon isotope data indicate a possible contribution of c4 plants to the holocene vegetation but not to the glacial and interstadial ecosystems of the late pleistocene changes in atmospheric co2 level are not reflected in the carbon isotope record these findings are discussed in the light of paleoclimate proxy datasets from the morava river valley and carpathian basin as well as through comparison of carbon isotope records from loess sections in se central europe and in the rhine valley two different loess provinces exist in terms of glacial interglacial humidity changes a province of glacial drying and a province of glacial humidification the first includes loess sites under more oceanic influence where loess 13c records indicate humid interglacials and interstadials and relatively drier glacial periods the second includes the loess sites of the carpathian basin and especially the southern serbian loess area of belotinac where loess 13c records indicate more intensive aridity during interglacials but a reduced soil moisture deficit and a more humid climate due to lower evapotranspiration in interstadials and even more in glacial periods

are the ashes from the latest eruptions 2010 2016 at turrialba volcano costa rica related to phreatic or phreatomagmatic events abstract the initial eruptive episodes of explosive eruptions are classified as phreatic if the amount of juvenile material scoria glass pumice is null and the amount of fresh accidental lithics and hydrothermally altered lithics is substantial phreatic eruptions have been in some cases recognized as precursory events preceding phreatomagmatic and magmatic eruptive phases usually the lithological features of tephra deposits are investigated and sampled in the field investigation of ash samples under binocular microscope or by back scattered electron bse microscope images of polished sections is usually considered sufficient to typify the fragmentation mechanism of the eruption the opening eruptive phases at turrialba volcano together with the formation of new intracraters i e 2010 2012 2014 and the enlargement of the western crater 29 october 2014 to present were classified in previous papers and internal reports as phreatic we studied a series of ash samples erupted from 2010 to 2016 with the aim of understanding the fragmentation processes characterizing the vent opening phases we used sem eds analyses in addition to field and microscopic investigation results showed a composition of accidental lithics of fresh to hydrothermally altered clasts and secondary minerals 82 98 besides juvenile andesite fragments 2 18 which leads us to revisit the classification of the initial eruptive phases of turrialba as phreatomagmatic our method allowed the detection of a juvenile component directly involved in an effective magma water interaction which was possible only by a scrutinous examination of the glass surface textures by sem in the range size between 3 and 3 5 phi we recommend such a type of investigation when the identification of fresh magma in a new eruption is crucial for the preparedness and hazard evaluation at active volcanoes

the long term paleomonsoon variation recorded by the loess paleosol sequence in central china abstract the loess paleosol sequence in central china during the last 2 5 ma is a good record of the asian monsoon variation which could be considered as the concrete realization of global paleoclimatic cycles the geological and biological evidence of the loess paleosol sequence indicates that the loess was mainly the dust deposits transported by the northerly wind of winter monsoons and also suffered to some extent from pedogenesis caused by weakened summer monsoons and that the paleosol accreted by the rather slow dust accumulation was closely related to strengthened summer monsoons an alternating occurrence of loess and paleosol in the luochuan section implies the variation history of warm humid climate with a summer monsoon dominance and cold dry climate with a winter monsoon dominance the magnetic susceptibility of loess and paleosol can be regarded as a proxy index of asian monsoon variation an analysis of the susceptibility curve and structure characters of luochuan section shows that the asian monsoon circulation was strengthened from early pleistocene to late pleistocene and the 500 ka bp point and 1200 ka bp point seem to be a threshold and a turning point respectively in terms of the long term paleomonsoon variation in asia

last glacial pollen record from lanzhou northwestern china and possible forcing mechanisms for the mis 3 climate change in middle to east asia abstract the vegetation on the northeastern margin of the tibetan plateau is highly sensitive to climatic changes and thus represents a potentially interesting environmental archive pollen samples from the fanjiaping loess section in lanzhou on the western chinese loess plateau clp were analyzed in conjunction with osl dating the results indicate that pollen zone b 60 6 46 0 ka correlative to the early mis 3 had the greatest abundances of cupressaceae tsuga gramineae and cyperaceae of the entire section suggesting a warm phase during the last glacial period these pollen taxa decreased significantly in abundance in the zones c 46 0 39 0 ka and d 39 0 27 0 ka reflecting a substantial climate cooling from the middle mis 3 to mis 2 these results correlate with climate records from the south china sea the clp baikal lake north america north atlantic ocean and other regions and probably correspond with the decline of northern high latitude insolation and the increase of global ice volume from 50 to 20 ka in particular arboreal pollen fern spore and algae abundances declined sharply since 40 ka while shrub and herb pollen reached the highest abundances conifer pollen picea and abies abundance also rose markedly and increased up the section this implies significant climate deterioration and likely corresponded with substantial growth of the polar ice sheets since 40 ka the decreasing temperature caused by an insolation decline during the last glacial period probably reinforced the cooling effect in a snow ice albedo feedback which would result in less climate sensitivity to radiative forcing meanwhile vegetation decline in the northern hemisphere during the last glacial period and tundra development at high latitudes possibly caused additional cooling enhancing the growth of polar ice sheets since 40 ka the development of polar ice sheets increased the polar to equator temperature and pressure gradients strengthening the westerlies and supplying plenty of moisture to northwest china during 40 30 ka lake sediments developed widely on the tibetan plateau during 40 30 ka probably related to an increase in the seasonality of middle to low latitude insolation which caused an enhancement of glacier melting on the plateau

temporal variation in volcanic ash texture during a vulcanian eruption at the sakurajima volcano japan abstract we discuss the process of vulcanian eruptions on the basis of temporal variation of the texture of andesitic volcanic ash ejected from the sakurajima volcano japan falling ash samples were collected every 2 50 min for petrological analysis these ash samples contained juvenile particles altered rock fragments and fragments of crystals here we subdivide the juvenile particles into blocky vesicular and fluidal particles because the crystallinities of the vesicular and fluidal particles are lower than those of the blocky particles we refer to the vesicular and fluidal particles as low crystallinity particles lcps and the blocky particles as high crystallinity particles hcps the temporal variation observed in ash texture reveals that the ratio of lcps to hcps lcp hcp was small at the initiation of the eruption and increased as the eruption progressed the higher microlite crystallinity in the hcps indicates crystallization under lower pressures for longer durations relative to the lcp magma the increase of the lcp hcp ratio during a single vulcanian eruption suggests that the emission of less viscous gas rich magma under a cap rock increases as the eruption progresses such temporal variation in ash texture reflects the transition from a sudden explosion to continuous ash emission during a vulcanian eruption

pyroclast characteristics of a subaqueous to emergent surtseyan eruption black point volcano california abstract we present the first ever quantitative analysis of pyroclast textures from subaqueous deposits of a surtseyan emergent volcano the volcano black point formed in mono lake s pleistocene precursor lake russell at 13 300 500 bp from an explosive basaltic eruption involving the interaction of shallow lake water 105 m with vesiculating magma the bulk of the edifice comprises unconsolidated tephra and represents submerged stages of eruption thin summit deposits formed during a final phase of emergent eruption and produced a group of low tuff rings lapillus clasts 16 mm to 32 mm and fine ash grains 4 0 0625 mm from the subaqueous deposits have textures that reveal a conduit history of bubble nucleation growth collapse intense microlite crystallisation and magma water interaction lapilli vesicularity ranges broadly to high values up to 89 while vesicle number densities 5 4 102 4 8 104 vesicles per mm3 are comparable to those published for strombolian and plinian basaltic eruptions 1 104 vesicles per mm3 vesicle size and volume distributions suggest continuous bubble nucleation but the suite of data as a whole indicates that a late stage nucleation event played a significant role in shaping the eruption ash grain morphology and surface features indicative of magma water interactions attest to water s role in fragmentation overall the pyroclast textures are consistent with water modification of a rather intense basaltic eruption which might have been of a violent strombolian or plinian style if the eruption had been dry and occurred subaerially

dynamics of an open basaltic magma system the 2008 activity of the halema uma u overlook vent kīlauea caldera on march 19 2008 a small explosive event accompanied the opening of a 35 m wide vent overlook vent on the southeast wall of halema uma u crater in k lauea caldera initiating an eruptive period that extends to the time of writing the peak of activity in 2008 consisted of alternating background open system outgassing and spattering punctuated by sudden short lived weak explosions triggered by collapses of the walls of the vent and conduit near daily sampling of the tephra from this open system along with exceptionally detailed observations allow us to study the dynamics of the activity during two eruptive sequences in late 2008 each sequence includes background activity preceding and following one or more explosions in september and october 2008 respectively componentry analyses were performed for daily samples to characterise the diversity of the ejecta nine categories of pyroclasts were identified in all the samples including wall rock fragments the six categories of juvenile clasts can be grouped in three classes based on vesicularity 1 poorly 2 uniformly highly to extremely and 3 heterogeneously highly vesicular the wall rock and juvenile clasts show dissimilar grainsize distributions reflecting different fragmentation mechanisms the wall rock particles formed by failure of the vent and conduit walls above the magma free surface and were then passively entrained in the eruptive plume the juvenile componentry reveals consistent contrasts in degassing and fragmentation processes before during and after the explosive events we infer a crude layering developed in the shallow melt in terms of both rheology and bubble and volatile contents beneath a convecting free surface during background activity a tens of centimetres thick viscoelastic surface layer was effectively outgassed and relatively cool while at depths of less than 100 m the melt remained slightly supersaturated in volatiles and actively vesiculating decoupled metre sized bubbles rising through the column burst through the free surface frequently ejecting fragments of the outgassed upper layer when the surface was abruptly perturbed by the rock falls existing mm sized bubbles expanded leading to the acceleration of adjacent melt upward and consecutive explosions while renewed nucleation created a minor population of 10 micron sized bubbles after each explosive event in september october 2008 this layering was re established but with decreasing vigour suggesting that the magma batch as a whole was becoming progressively depleted in dissolved volatiles

summer monsoon intensity controls c4 c3 plant abundance during the last 35 ka in the chinese loess plateau carbon isotope evidence from bulk organic matter and individual leaf waxes the natural abundance of c3 and c4 plants is affected by multiple environmental factors including temperature moisture balance and atmospheric pco2 the relative importance of these factors is a subject of considerable debate and may vary in different natural ecosystems previous studies generally focus on single loess sequences in the chinese loess plateau and conflicting conclusions on c4 c3 have been reached when studying carbon isotope ratios in carbonate and organic matter in this paper we report a comprehensive carbon isotopic characterization of total organic carbon toc and individual higher plant leaf waxes from five loess sequences spanning the last 35 ka from the chinese loess plateau clp the five coring sites encompass large gradients of annual mean temperature 9 2 13 9 c and precipitation 402 673 mm allowing us to assess the controlling mechanisms on c4 c3 plant ratios glacial interglacial sequences provide carbon isotope data for comparison with other climatic and environmental proxies such as lithology and magnetic susceptibility our results demonstrate that increased c4 c3 ratios are positively correlated with higher temperature and increased summer rainfall which characterize stronger summer monsoon in all five sites we conclude c4 abundance increases from the last glacial to the holocene in response to greater monsoon activity and that the c4 expression is suppressed in the cold and drier intervals

effect of obliteration on crater count chronologies for martian surfaces 1 the density of impact craters calibrated against lunar data is currently the only quantitative measure of surface age for terrestrial planetary surfaces unlike the moon however mars has been weathered and eroded obliterating some small 10 km diameter craters a phenomenon addressed in the mariner viking days of mars exploration but commonly overlooked in recent studies we present a quantitative model that extends this earlier work to assess the effect of erosion and infilling on surface ages inferred from crater frequency distributions our work affirms that small cratersizedistributionscanbeinterpretedquantitatively in terms of effects of erosion and crater infilling at rates comparable to those reported for mars a reanalysis of prior studies indicates that low to moderate long term rates of erosion and crater infilling can mask an ancient age and result in small crater populations similar to those offered as evidence for young and geologically significant surface activity citation smith m r a r gillespie and d r montgomery 2008 effect of obliteration on crater count chronologies for martian surfaces geophys res lett 35 l10202 doi 10 1029 2008gl033538

characteristics of rootless cone tephra emplaced by high energy lava water explosions the effects of external water during hydrovolcanic eruptions are difficult to quantify however research investigating the explosive interactions between surface lava flows and water has provided new insights into explosion dynamics previous work has focused on relatively low energy lava water explosions from a 100 m diameter cone in the rau holar cone group in iceland for comparison we study ejecta derived from higher energy explosions at the 400 m diameter pu u k holo rootless cone in hawai i one of the largest rootless cones on earth this comparative approach elucidates the effect of lava water mixing conditions and range of explosivity on ejecta characteristics utilizing grain size analysis we found that pu u k holo beds typically have median grain sizes at the cone rim that are smaller than 3 8 mm and are on average finer grained than those of the rau holar cone ash sized grains the most energetically significant ejecta size fraction typically make up 20 of bed ejecta with a maximum of 90 both greater proportions than found in beds of the rau holar cone utilizing grain morphology crystal texture and surface feature analysis we found that the abundance of ash sized grains associated with high heat transfer rates i e active particles increases at pu u k holo as explosivity increases which is an important consideration for energy modeling this dataset also includes ejecta from the finest grained beds and therefore highest energy lava water explosions studied to date

martian cratering 8 isochron refinement and the chronology of mars abstract this paper reviews and refines the technique of dating martian surfaces by using impact crater isochrons defined as size distributions of impact craters on undisturbed martian surfaces of specified ages in the 1970s this system identified not only abundant ancient martian volcanic surfaces but also extensive lava plains with ages of a few 108 y old this dating was initially controversial but confirmed in the 1980s and 90s by martian meteorites the present update utilizes updated estimates of the mars moon cratering ratio the most important calibration factor improves treatment of gravity and impact velocity scaling effects combines aspects of the crater size distribution data from earlier work by both neukum and hartmann and for the first time applies a correction for loss of small meteoroids in the martian atmosphere from popova et al 2003 meteorit planet sci 38 905 925 the updated isochrons are not radically different from the previous 2002 iteration but fit observed data better and give somewhat older model ages for features dated from small craters diameter d 100 m crater counts from young lava flows in various areas give good fits to the new isochrons over as much as 3 orders of magnitude in d confirming the general isochron shape and giving crater retention ages in the range of some 106 to some 108 y interpreted as lava flow ages more complex older units are also discussed uncertainties are greatest if only small craters d 100 m are used suggestions by other workers of gross uncertainties due to local secondary craters and deposition exhumation are discussed they do not refute our conclusions of significant volcanic fluvial and other geologic activity in the last few percent of martian geologic time or the importance of cratering as a tool for studying processes such as exhumation indeed crater count data suggest certain very recent episodes of deposition exhumation and ice flow possibly associated with obliquity cycles of 10 7 y timescale evidence from ancient surfaces suggests higher rates of volcanism fluvial activity glaciation and other processes in noachian hesperian time than in amazonian time

comparative analyses of glass fragments from brittle fracture experiments and volcanic ash particles explosive volcanic eruptions are characterized by the rapid fragmentation of a magmatic melt into ash particles in order to describe the energy dissipation during fragmentation it is important to understand the mechanism of material failure a quantitative description of fragmentation is only possible under controlled laboratory conditions industrial silicate glasses have a high structural affinity with magmatic melts and have the advantage of being transparent which allows the study of the evolution of fractures by optical methods on a time scale relevant for explosive volcanism with this aim a series of low speed edge on hammer impact experiments on silicate glass targets has been conducted leading to the generation of fragments in the grain size spectra of volcanic ash in order to verify the general transferability of the experimentally generated fragmentation dynamics to volcanic processes the resulting products were compared by means of statistical particle shape analyses to particles produced by standardized magma fragmentation experiments and to natural ash particles coming from deposits of basaltic and rhyolitic compositions from the 2004 grimsvotn and the quaternary tepexitl tuff ring eruptions respectively natural ash particles from both grimsvotn and tepexitl show significant similarities with experimental fragments of thermally pre stressed float glasses indicating a dominant influence of preexisting stresses on particle shape and suggesting analogous fragmentation processes within the studied materials

estimating rates of decompression from textures of erupted ash particles produced by 1999 2006 eruptions of tungurahua volcano ecuador persistent low to moderate level eruptive activity of andesitic volcanoes is difficult to monitor because small changes in magma supply rates may cause abrupt transitions in eruptive style as direct measurement of magma supply is not possible robust techniques for indirect measurements must be developed here we demonstrate that crystal textures of ash particles from 1999 to 2006 vulcanian and strombolian eruptions of tungurahua volcano ecuador provide quantitative information about the dynamics of magma ascent and eruption that is difficult to obtain from other monitoring approaches we show that the crystallinity of erupted ash particles is controlled by the magma supply rate msr ash erupted during periods of high magma supply is substantially less crystalline than during periods of low magma supply this correlation is most easily explained by efficient degassing at very low pressures 50 mpa and degassing driven crystallization controlled by the time available prior to eruption our data also suggest that the observed transition from intermittent vulcanian explosions at low msr to more continuous periods of strombolian eruptions and lava fountains at high msr can be explained by the rise of bubbles through strombolian or trapping of bubbles beneath vulcanian vent capping variably viscous and crystalline magma

particle size density relationships in pyroclastic deposits inferences for emplacement processes in moving pyroclastic systems particles are sorted as a function of their sizes densities and shapes the analysis of the distribution of these characteristics in particle populations of pyroclastic deposits is a major tool in evaluating properties and regimes of parent transport systems this paper reports a study of size density relationships of component subpopulations from selected quaternary pyroclastic deposits of the latera volcanic complex vulsini italy by means of integrated field and laboratory investigations including grain size and component analyses density measurements and sem crystal morphoscopy three kinds of particle size density relationships characterize the studied deposits as follows 1 a significant correlation of decreasing sizes with increasing component densities exists for direct suspension sedimentation products including plinian fall and pyroclastic surge deposits 2 a wide data dispersion with poor correlation normally occurs for the main zones of deposits from high concentration pyroclastic flows and 3 component subpopulations occur in a narrow size range irrespective of density in granular systems dominated by grain collisions such as traction zones beneath low concentration pyroclastic surges and sheared basal layers of pyroclastic flows the regression coefficients of size density relationships appear as a comparative measure of particle concentration in the parent systems consistent with that inferred from the degree of sorting and abrasion of crystal subpopulations from sequential fragmentation transport analysis of grain size data and quantitative morphoscopy the crystal component becomes less sorted and more abraded as the fit to the size density relationship decreases from plinian fall to pyroclastic surge to pyroclastic flow consistent with increasing particle concentration in the transporting current

black point pyroclasts of a surtseyan eruption show no change during edifice growth to the surface from 100 m water depth abstract surtseyan eruptions have long been studied from their edifice deposits emplaced subaqueously or subaerially here we characterize a surtseyan eruption from both edifice and ash sheet deposits using a combination of techniques the volcano studied is black point which erupted into lake russell about 13 000 years ago from a water depth of 105 m producing a total of 0 8 km3 of tephra the techniques applied to samples acquired by targeted sampling based on geological observations in the field include geochemical characterization of the eruption products grain size analysis of the ash size fraction at proximal and medial sites three dimensional characterization of vesicles in lapilli and particle shape analysis for ash grains using the recently introduced freeware partisan the aim of this combined approach is to determine how the eruption evolved through its course from before magma fragmentation to the mechanisms of formation transport and deposition of the tephra field observations are consistent with the ash sheet deposits forming from eruption fed density currents and or fallout through the water column from a subaerial plume umbrella cloud geochemical correlation links the mound deposits as well as the tuff rings with a stratigraphic sequence at about 2 km west from the edifice both show non linear but broadly correlative geochemical variations in deposits from the subaqueous stage of the eruption through the subaerial one pyroclast vesicle textures indicate that volatile expansion played only a minor role in magma fragmentation and that there was a high level of bubble coalescence and hence outgassing during the eruption we infer that fragmentation was mostly phreatomagmatic resulting from explosive interactions between rising magma and water saturated sediments two dimensional particle shape analysis of ash grains shows a large variability in the shape parameters of convexity and solidity this tells us little about fragmentation style but serves as a proxy for magma vesicularity the most interesting aspect of this eruption is that none of the shape parameters or qualitative observations show any sort of systematic change during the course of the eruption despite the eruption having begun in 100 m of water and ended up subaerial

primary centers and secondary concentrations of tectonic activity through time in the western hemisphere of mars five main stages of radial and concentric structures formed around tharsis from the noachian through the amazonian as determined by geologic mapping of 24 452 structures within the stratigraphic framework of mars and by testing their radial and concentric orientations tectonic activity peaked in the noachian stage 1 around the largest center claritas an elongate center extending more than 20 in latitude and defined by about half of the total grabens which are concentrated in the syria planum thaumasia and tempe terra regions during the late noachian and early hesperian stage 2 extensional structures formed along the length of present day valles marineris and in thaumasia with a secondary concentration near warrego vallis radial to a region just to the south of the central margin of valles marineris early hesperian stage 3 radial grabens in pavonis syria ulysses and tempe terra and somewhat concentric wrinkle ridges in lunae and solis plana and in thaumasia sirenum memnonia and amazonis are centered northwest of syria with secondary centers at thaumasia tempe terra ulysses fossae and western valles marineris late hesperian early amazonian stage 4 structures around alba patera the northeast trending alignment of tharsis montes and olympus mons appears centered on alba patera stage 5 structures middle late amazonian represent the last pulse of tharsis related activity and are found around the large shield volcanoes and are centered near pavonis mons tectonic activity around tharsis began in the noachian and generally decreased through geologic time to the amazonian statistically significant radial distributions of structures formed during each stage centered at different locations within the higher elevations of tharsis secondary centers of radial structures during many of the stages appear related to previously identified local magmatic centers that formed at different times and locations throughout tharsis

tectonic history of the syria planum province of mars we attribute most of the development of extensive fractures in the tharsis region to discrete tectonic provinces within the region rather than to tharsis as a single entity one of these provinces is in syria planum faults and collapse structures in the syria planum tectonic province on mars are grouped into 13 sets based on relative age areal distribution and morphology according to superposition and fault crosscutting relations and crater counts we designate six distinct episodes of tectonic activity in the following chronologic order stage i is an early to late noachian deformation forming mostly east west structures fault set ia some large volcanoes also formed faults were produced possibly by flexural uplift also arcuate north trending grabens set ib indicate that faulting is transitional to the next stage stage ii is late noachian to early hesperian radial faulting centered in syria planum possibly due to isostatic uplift in late noachian set iia to early hesperian set iib time stage iii is early to late hesperian faulting tangential to syria planum that was related to local centers of uplift sets iii1 iii3 on the periphery of syria planum stage iv is a late hesperian graben formation that was circumferential to syria planum set iva caused either by collapse associated with eruption of magma or by flexure of the lithosphere due to volcanic loading in association with volcanism minor faulting occurred producing an oval pattern of faults in southwest syria planum set ivbl and a radial pattern south of the planum set ivb2 that apparently rejuvenated buried stage ii faults stage v is a late hesperian to early amazonian development of grabens and troughs of noctis labyrinthus and western valles marineris set v that was probably instigated by local uplift exposure of groundwater or ground ice zones may have produced further collapse and trough enlargement stage vi is early amazonian northwest trending faulting in noctis fossae set vil perhaps due to tharsis monies centered tectonism and north northwest normal faulting along the eastern side of the claritas rise set vi2 that was due to tectonic subsidence the duration of tectonic activity in the syria planum province was perhaps 2 3 b y photoclinometric topographic profiles across 132 grabens and fault scarps show that syria planum grabens have widths average of 2 5 km and most range from 1 to 6 km similar to lunar grabens but the martian grabens have slightly higher side walls average about 132 m and gentler wall slopes average of 9 and range of 2 25 than lunar grabens 93 m high and 18 slopes scarp degradation on mars has progressed through quakes impact shaking and dry slope processes the lower slopes may be due to mars higher gravity estimates of the amount of extension for individual grabens range from 20 to 350 m most estimates of the thickness of the faulted layer range from 0 5 to 4 5 km average is 1 5 km this thickness range corresponds closely to the 0 8 to 3 6 km range in depth for pits troughs and canyons in noctis labyrinthus and along the walls of valles marineris we propose that the predominant 1 to 1 5 km values obtained for both the thickness of the faulted layer and the depths of the pits troughs and theater heads of the canyons reflect the initial depth to the water table in this region as governed by the depth to the base of ground ice maximum depths for these features may indicate lowered groundwater table depths and the base of ejecta material

breaking news on the formation of volcanic ash fracture dynamics in silicate glass abstract in explosive volcanic eruptions magmatic melts behave like brittle solids under rapid loading volcanic ash particles predominantly are generated by brittle fragmentation induced within pre stressed magma in volcanic conduits here we present straightforward measurements of fracture area velocity i e surface generation rates in analog materials under volcanic time and deformation rates using a high resolution high speed camera at up to 2 5 million frames per second surface generation rates are directly linked to energy dissipation and can be related to pyroclast formation during explosive volcanism according to our findings pre existing stress fields play a crucial role for the evolution of cracks control the dynamics of fracture area growths during fragmentation and thus strongly modify the production of volcanic ash

processes controlling the shape of ash particles results of statistical ipa abstract ash particles have unique morphologies and shapes that are characteristic of certain fracture mechanisms and can be used to identify the type of fragmentation such as magmatic brittle or ductile fragmentation and phreatomagmatic molten fuel coolant interaction type fragmentation identifying these two different fragmentation processes is especially important in complex volcanic systems where both fragmentation processes can occur in this study image parameter analysis and statistical parameter analysis are used to compare ash particles from standardised magma fragmentation experiments with natural ash particles from the pleistocene lake purrumbete maar southeastern australia the pyroclastic lake purrumbete maar sequence containsvarious deposit types that show evidence for changing eruption conditions therefore it is of a main interest to determine the main fragmentation mechanism that formed these deposits a comparison with experimental ash particles revealed that lake purrumbete ash particles show significant differences from experimental samples of magmatic brittle type fragmentation whereas they show no significant differences from phreatomagmatic molten fuel coolant interaction type fragmentation samples indicating a predominance of phreatomagmatic fragmentation during the eruption of lake purrumbete the experiments further show that pre existing stresses also influence the particle shape and may be the reason for the absence of a significant similarity between most of the particle populations

color measurements of volcanic ash deposits from three different styles of summit activity at sakurajima volcano japan conduit processes recorded in color of volcanic ash abstract we measured quantitatively colors of volcanic ash deposits erupted from three different styles of summit activity strombolian activity vulcanian explosions and continuous ash venting activity at sakurajima volcano from 1974 to 1985 colors of strombolian ash samples have larger yellow components of their visible spectra b values than those of explosion and continuous venting ash samples colors of explosion ash samples show larger variation in both red and yellow components of their visible spectra a and b values respectively while colors of continuous venting ash samples are in the narrow ranges within colors of explosion ash samples colors of components with lower densities than 3 1 g cm 3 groundmass and phenocrystic plagioclase obtained by magnetic and heavy liquid separation methods are similar to the unseparated bulk ash samples this result suggests that the color variations of ash deposits are mainly originated from the particles composed of groundmass the particles can be classified into three different types of particles with different vesicularity and crystallinity vesicular particle vp dense particle with vesicles dpv and dense particle without vesicles dp analytical results of component proportions chemical compositions of groundmass glasses ferrous iron contents and surface ferric materials show that 1 vp has larger yellow components of the visible spectrum b values and high ferrous iron content and is less crystallized than the dp and dpv 2 dp has larger red and yellow components of its visible spectrum a and b values respectively and involves ferric materials on the surfaces produced by oxidation process and 3 dpv has smaller red and yellow components of its visible spectrum a and b values respectively and involves less ferric materials on the ash surfaces color differences of ash deposits from three different activity styles can be explained by the different mixing ratios of vp dpv and dp during the strombolian activity the vp is a main component in the ash which is formed from relatively less degassed and crystallized magma in the vulcanian explosion and continuous ash venting activity the proportions of dpv and dp in ash are larger than that in the strombolian activity the highly crystallized dp may correspond to a vent cap and dpv to a magma below the cap the color measurements of ash deposits provide information on the pre eruptive processes at the shallower levels of a conduit

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

compound specific d h ratios and molecular distributions of higher plant leaf waxes as novel paleoenvironmental indicators in the chinese loess plateau abstract we measured d h ratios of individual long chain leaf wax n alkanes isolated from a loess profile spanning the last 130 ka from xifeng china the d values show large variation 140 to 200 for the past 130 ka and are highly correlated with changes in magnetic susceptibility ms an accepted proxy for past monsoon circulation in the chinese loess plateau peaks in high d values 140 to 160 coincide with low ms values for loess sections formed under relatively dry conditions marine isotope stages miss 2 and 4 whereas peaks in low d values 190 to 200 coincide with high ms values for paleosol sections formed under relatively wet conditions miss 1 3 and 5 we attribute the isotopic variations to the combined effects of varying aridity which controls the soil and leaf water evaporation and temperature and monsoon intensity which alter the d h ratios of precipitation we also discovered a strong negative correlation between the molecular distributions ratios of c31 c29 and c31 c27 n alkanes and the d values of n alkanes based on studies of modern plants and the xifeng loess sequence the complex relationship between ms and monsoon circulation has been difficult to understand mechanistically however the climatic controls on the d h ratios of individual long chain n alkanes and c31 c29 n alkane ratios can be readily demonstrated and calibrated from modern plants and surface soils therefore these new molecular and isotopic proxies have potential as quantitative proxies for paleoenvironmental reconstruction in the chinese loess plateau

characterization of the luminance and shape of ash particles at sakurajima volcano japan using ccd camera images we develop a new method for characterizing the properties of volcanic ash at the sakurajima volcano japan based on automatic processing of ccd camera images volcanic ash is studied in terms of both luminance and particle shape a monochromatic ccd camera coupled with a stereomicroscope is used to acquire digital images through three filters that pass red green or blue light on single ash particles we measure the apparent luminance corresponding to 256 tones for each color red green and blue for each pixel occupied by ash particles in the image and the average and standard deviation of the luminance the outline of each ash particle is captured from a digital image taken under transmitted light through a polarizing plate also we define a new quasi fractal dimension d qf to quantify the complexity of the ash particle outlines we examine two ash samples each including about 1000 particles which were erupted from the showa crater of the sakurajima volcano japan on february 09 2009 and january 13 2010 the apparent luminance of each ash particle shows a lognormal distribution the average luminance of the ash particles erupted in 2009 is higher than that of those erupted in 2010 which is in good agreement with the results obtained from component analysis under a binocular microscope i e the number fraction of dark juvenile particles is lower for the 2009 sample the standard deviations of apparent luminance have two peaks in the histogram and the quasi fractal dimensions show different frequency distributions between the two samples these features are not recognized in the results of conventional qualitative classification criteria or the sphericity of the particle outlines our method can characterize and distinguish ash samples even for ash particles that have gradual property changes and is complementary to component analysis this method also enables the relatively fast and systematic analysis of ash samples that is required for petrologic monitoring of ongoing activity such as at the sakurajima volcano

a critical reevaluation of palaeoclimate proxy records from loess in the carpathian basin abstract in the carpathian basin loess is the most important archive of quaternary palaeoclimate evolution but only in the past two decades systematic and high resolution investigations were conducted those studies remarkably improved our knowledge of the regional past environmental change palaeoclimate inferences based on the magnetic susceptibility and grain size distribution as the most commonly used palaeoenvironmental proxies for the carpathian basin loess indicate colder and drier climatic conditions during glacials when compared to interglacials with an increasing number of studies using novel proxies in loess research such a traditional understanding of dry and cold glacials and humid and warm interglacials in the carpathian basin has been questioned as an illustrative example mollusc based climate reconstructions suggest generally warm and very dry summer conditions with mean july temperatures up to 21 c for the southern carpathian basin during the last glacial results based on stable carbon isotopes strongly oppose such high summer temperatures but studies based on n alkanes are in general agreement with the mollusc data when it comes to the vegetation reconstruction indicating mostly steppic conditions however n alkanes studies contradict warm and dry glacial conditions as indicated by mollusc based reconstructions pointing instead to cold and relatively humid glacials in addition there is an ongoing debate whether or not millennial scale climatic oscillations can be observed in the carpathian basin loess as well as whether this area was an important northern hemisphere dust source or rather a sink of far distance dust transport consequently the current state of the art of the palaeoclimate reconstructions from loess in the carpathian basin is rather inconsistent in order to make sense of the existing palaeoclimate data from the carpathian basin loess we have reevaluated and reinterpreted the available data we discuss and propose a coherent interpretation of rock magnetic grain size malacological stable carbon and nitrogen isotope n alkane and bacterial membrane lipid data for the last glacial cycle loess archives from the carpathian basin we show that glacial conditions in the carpathian basin led to a notable increasing north south gradient in temperature and an even stronger expressed decreasing trend in humidity and that most of the biomarker proxy data conducted in loess for the very dry southern part of the carpathian basin show a strong bias towards arid conditions in particular palaeotemperature reconstructions seem to be misleading glacial conditions were drier and colder than previously proposed summer temperatures likely under 15 c during glacials but notably warmer than in other parts of western central and eastern europe the vegetation consisted mostly of steppic environments during both glacials and interglacials we indicate that the carpathian basin has a potential to be a major dust source of the northern hemisphere during glacials although it was at the same time exposed to the deposition of fine far distance travelled dust moreover the main issues in the regional and continental correlation of loess are highlighted as well as the sensitivity of the carpathian basin loess to the millennial scale climate variability recorded in other northern hemisphere records finally we suggest that the onset of loess formation in the investigated area occurred during the middle pleistocene transition and it was probably related to intensive silt production related to glacier dynamics in the alpine ice cap

hazard of pyroclastic density currents at the campi flegrei caldera southern italy as deduced from the combined use of facies architecture physical modeling and statistics of the impact parameters abstract pyroclastic density currents of the recent eruptions at campi flegrei caldera cfc southern italy have been studied with the aim of assessing the potential impact of similar events in the future eruptions of different scales have been investigated by means of the combined use of facies architecture laboratory analysis and physical modeling both in the small averno 2 and intermediate astroni scales facies analysis indicates that deposits result from the emplacement of pyroclastic density currents like base surge formed by multiple closely timed impulses of phreatomagmatic origin in the large scale event agnano monte spina the facies architecture suggests that the currents started as concentrated flows near the vent as originating from the collapse of a dense eruptive column and evolved laterally into expanded flows by the propagation of the basal shear current laboratory analyses on samples from the main layers of deposits allowed obtaining the input data for the pyflow code which was used for reconstructing the flow dynamic characteristics of the currents the expected damage is discussed in terms of the probability density function of dynamic pressure and particle volumetric concentration in this way the range of potential impact that similar pyroclastic density currents could cause to buildings infrastructures and population is defined in the large scale event the dynamic pressure ranges from 9 38 to 1 00 kpa integrating the basal 10 m of the current at distances of 1 5 and 4 0 km from the vent respectively the values are highly influenced by the local topography in the intermediate scale event the dynamic pressure ranges from 2 43 to 0 26 kpa at distances of 1 1 and 1 4 km from the vent respectively in the small scale event the dynamic pressure ranges from 1 49 to 0 39 kpa at distances of 0 5 and 1 1 km from the vent respectively the particle volumetric concentration at a height of 2 m within the current is always lower than 0 01 but typically it is higher than 0 001 inside the caldera and could have severe effects on the unsheltered population also at locations topographic highs where velocity and dynamic pressures are low in distal reaches outside the caldera the widespread fine ash originated by buoyancy from the currents which was transported by lower atmosphere winds is to be considered as a fallout load slowly accumulating on the ground surface and building roofs during the waning stage of the current

distinguishing styles of explosive eruptions at erebus redoubt and taupo volcanoes using multivariate analysis of ash morphometrics abstract the style and dynamics of volcanic eruptions control the level and type of hazards posed for local populations and can have a temporary long range impact on climate if eruptions are extremely energetic the purpose of this study is to provide a statistical approach to ash morphometrics in order to provide a means by which to evaluate diverse eruption styles and mechanisms of fragmentation the methodology presented can be applied to tephra deposits worldwide and may aid volcanic hazard mitigation by better defining a volcano s history of explosive behavior ash sized grains were collected from tephra deposits on mount erebus antarctica discriminant analysis of all parameters was found to be the best at differentiating the tephra deposits and allowing for interpretation of eruptive styles in conjunction with field observations a linear array of data forming a positive slope in factor space which explains 99 of the total data variance is interpreted to represent a continuum between fragmentations involving water magma interaction wet to grains that were formed predominately by magmatic dry fragmentation mechanisms the taupo hatepe ash which was deposited from a phreatoplinian eruption column has the highest factor values in the array which signifies in part more rectangular blocky morphologies with smooth grain edges factor values for the 2009 redoubt eruption events 2 4 are nearly as high as hatepe ash and based on this we suggest that it was produced in part by phreatomagmatic fragmentation this is supported by field observations that document melting and eruption through glacial ice during the early phases of the 2009 activity redoubt ash grains from later stages of the same eruption events 9 18 show a significant shift to lower values in factor space more irregular vesiculated grains and are interpreted to be a consequence of dryer conditions coarse ash data from mount erebus are completely separated from taupo and redoubt grains in factor space due primarily to the difference in mean gray value which is a proxy for vesicle density and size the vesicle characteristics larger and deeper are consistent with documented strombolian style activity and the scatter in grain shape data support fragmentation by a mixture of wet and dry processes as has previously been proposed based on deposit characteristics and resemblance to tephra produced by current activity

molecular records of continental air temperature and monsoon precipitation variability in east asia spanning the past 130 000 years our current understanding of past changes in east asian summer monsoon easm precipitation intensity derives from several loess paleosol sequences and oxygen isotope 18o records of well dated stalagmites although temperature is generally presumed to have had minimal impact on easm records past air temperature dynamics over east asia are so far relatively poorly understood mainly due to the lack of tools to reconstruct continental paleotemperatures here we report a high resolution record of east asian air temperature over the past 130 000 years based on soil bacterial lipid signatures preserved in a loess paleosol sequence from the mangshan loess plateau in china we find that maximum local insolation is the main driver of air temperature although greenhouse gas concentrations and southern hemisphere climate may influence temperature at times when insolation is weak causing a decoupling with easm precipitation intensity direct comparison of our temperature record with precipitation induced changes in past soil ph derived from the same suite of lipids confirms this decoupling subsequent cross spectral analysis of the two molecular proxy records reveals that variations in monsoon precipitation consistently lag those in air temperature throughout the whole record at the dominant precession band the length of this lag is variable however and increases as glaciation develops this observation is consistent with an increasing influence of northern hemisphere ice sheets on the modulation of easm response to insolation forcing during ice ages

stress induced brittle fragmentation of magmatic melts theory and experiments 1 the release of kinetic energy during explosive volcanic eruptions is a key parameter for hazard assessment and civil defense the explosive production of volcanic ash by intensive fragmentation of magma and host rocks represents a substantial part of this energy for cases of explosive eruption where predominantly host rock was fragmented phreatomagmatic eruptions to form the major part of volcanic ash rock mechanical parameters could be measured and fragmentation energies assigned in cases where most of the produced ash is of juvenile origin magmatic eruptions a general method for the determination of fragmentation energy is still lacking in this article we introduce a thermodynamic approach that relates grain size data of the produced ash deposits to shear rates acting during the deformation of magma with the use of a standardized fragmentation experiment the physical parameters needed to determine the specific fragmentation energy and deformation history were measured the experiment was calibrated and tested with two case histories of the campi flegrei volcanic field southern italy both eruptions are classified as most probable worst case scenarios during the next period of activity to be expected within the next 10 100 years using the experimentally determined specific fragmentation energies the total mass of produced ash of each eruption and assuming an energy dissipation as observed in the experiments the total kinetic energy release of the worst case campi flegrei eruptive events to come were calculated with 25 and 40 kt tnt equivalent

correlation between climate events in the north atlantic and china during the last glaciation episodes of massive iceberg release heinrich events 1 3 into the north atlantic ocean during the last glaciation were associated with recurring episodes of unusually cold north atlantic surface water bond cycles 4 and cold air temperatures over greenland dansgaard oeschger events 5 6 four of the youngest of these cold events have also been reported in climate records from sites outside the north atlantic region7 but until now the entire suite has been identified only in north atlantic marine sediments greenland ice core records and tentatively in french lake sediments8 here we examine grain size data from chinese loess and intercalated accretionary palaeosols of last glacial age for evidence of similar climate signals remote from the north atlantic region we see grain size maxima with ages that match those of the last six heinrich events which we interpret as an indication of the changing strength of the east asian winter monsoon which largely controls the transport and deposition of central asian aeolian dust thus it seems that these heinrich events have left their signature in the chinese loess record this is consistent with simulations of the glacial climate9 which imply that the climates of the north atlantic and china were linked by the effect of westerly winds

image processing analysis in reconstructing fragmentation and transportation mechanisms of pyroclastic deposits the case of monte pilato rocche rosse eruptions lipari aeolian islands italy abstract a quantitative study of particle morphology of samples from monte pilato rocche rosse deposits lipari aeolian islands italy shows a significant variability in particle structure and texture the study consisted of image processing techniques and multivariate statistical methods in analysis of the quantitative particle morphology data with the goal of identifying the genetic processes responsible for the formation of the deposits from these investigations we numerically define the form of the clasts thus avoiding subjectivity in the classification of clast morphology starting from this clast definition we then construct diagrams in which clasts due to different genetic processes i e magmatic vs hydromagmatic fragmentation are discriminated based on simple nondimensional parameters the application of the methods used seems to be of general interest in discriminating the fragmentation and transportation dynamics responsible for the formation of pyroclastic deposits