eudaemonema webbi sp nov mammalia mixodectidae from the late paleocene of western canada the youngest known mixodectid mixodectidae mammalia archonta are an unusual poorly known family of dermopteran like mammals that have been discovered at several north american localities of primarily early paleocene age among the three or four recognized mixodectid genera eudaemonema simpson is perhaps one of the least understood being known from only a few localities of late torrejonian and earliest tiffanian age this paper reports on a new species of eudaemonema from the late paleocene of alberta canada that significantly extends the geographic and stratigraphic ranges of the genus eudaemonema webbi sp nov is known from middle and late tiffanian localities in central and south central alberta and it represents the youngest and northernmost species of eudaemonema so far discovered e webbi differs from the genotypic species e cuspidata in being larger and in having a suite of dental characters e g molariform posterior premolars enlarged molar protocone and hypocone development of a second grinding platform on the

in situ observation of the percolation threshold in multiphase magma analogues magmas vesiculate during ascent producing complex interconnected pore networks which can act as outgassing pathways and then deflate or compact to volcanic plugs similarly in conduit fragmentation events during dome forming eruptions create open systems transiently before welding causes pore sealing the percolation threshold is the first order transition between closed and open system degassing dynamics here we use time resolved synchrotron source x ray tomography to image synthetic magmas that go through cycles of opening and closing to constrain the percolation threshold c at a range of melt crystallinity viscosity and overpressure pertinent to shallow magma ascent during vesiculation we observed different percolative regimes for the same initial bulk crystallinity depending on melt viscosity and gas overpressure at high viscosity 106 pa s and high overpressure 1 4 mpa we found that a brittle viscous regime dominates in which brittle rupture allows system spanning coalescence at a low percolation threshold c 0 17 via the formation of fracture like bubble chains percolation was followed by outgassing and bubble collapse causing densification and isolation of the bubble network resulting in a hysteresis in the evolution of connectivity with porosity at low melt viscosity and overpressure we observed a viscous regime with much higher percolation threshold c 0 37 due to spherical bubble growth and lower degree of crystal connection finally our results also show that sintering of crystal free and crystal bearing magma analogues is characterised by low percolation thresholds c 0 04 0 10 we conclude that the presence of crystals lowers the percolation threshold during vesiculation and may promote outgassing in shallow crystal rich magma at initial stages of vulcanian and strombolian eruptions

thermal vesiculation during volcanic eruptions a textural examination of volcanic ash erupted from santiaguito volcano in guatemala coupled with an analysis of the geophysical signals indicates that rapid heating during fault friction can cause melting and vesiculation development of bubbles of hydrated silicic magma thus strongly affecting magma strength and eruptive behaviour

gas transport and bubble collapse in rhyolitic magma an experimental approach a series of experiments was conducted to test concepts of porous flow degassing of rhyolitic magma during ascent and of the subsequent collapse of vesicles in degassed magma to form obsidian dense synthetically hydrated natural glasses were pressurized under water saturated conditions and then decompressed to achieve a range of porosities in the presence of a tracer vapor d2o rapid isotopic exchange indicative of vapor transport rather than of simple diffusion occurred at a porosity 60 vol in accord with earlier gas permeability measurements on cold natural samples in another series of experiments natural and synthetic pumices vesiculated by degassing to atmospheric pressure rapidly collapsed to dense glass on repressurization to the modest pressures prevailing in lava flows no relict bubble textures remained these results support the hypothesis that effusive eruptions result from the syneruptive escape of gas from permeable magmatic foam and that a process analogous to welding yields dense lavas when such foams are extruded

diatoms as quantitative paleodepth indicators in coastal areas of the southeastern beaufort sea arctic ocean abstract surface sediment diatom assemblages in depth profiles along the southeastern beaufort sea coasts canada were analysed to describe the relationship between species distribution and water depth of deposition the 74 coastal stations sampled were distributed in several sedimentary environments from salt marshes to the inner shelf the relationship between diatom species distribution and water depth was examined using canonical correspondence analysis cca and partial cca the water depth accounted for 9 7 of the variance in the data set the diatom water depth relationship is believed to be controlled by the shoreface circulation which results in a shift in the relative abundance of the epipsammon epipelon and plankton along the water depth gradient upper shoreface assemblages are dominated mainly by epipelic species and a few number of epipsammic taxa whereas deeper environments are dominated by planktonic species a transfer function was derived using weighted averaging regression and calibration to reconstruct the water depth of deposition over the coastal interval from mean sea level to a maximum of 14 m depth on the coastal shelf of the southeastern beaufort sea the transfer function allows relative sea level to be predicted from fossil diatom assemblages with a root mean square error of 1 43 m this model is likely to produce reliable water depth inferences along the southeastern beaufort sea coasts and in other shallow sandy microtidal environments dominated by low energy waves and influenced by freshwater discharge the transfer function was used to provide quantitative paleodepth inferences for late holocene sediments from the atkinson point area based on fossil diatom assemblages

controls on the formation and stability of gas hydrate related bottom simulating reflectors bsrs a case study from the west svalbard continental slope 1 the growth and stability of the free gas zone fgz beneath gas hydrate related bottom simulating seismic reflectors bsrs is investigated using analytical and numerical analyses to understand the factors controlling the formation and depletion of free gas for a model based on the continental slope west of svalbard a continental margin of north atlantic type we find that the fgz is inherently unstable under a wide range of conditions because upward flow of under saturated liquid depletes free gas faster than it is produced by hydrate recycling in these scenarios the 150 m thick fgz that presently exists there would deplete within 105 106 years we suggest the fgz is in a stable state however that is formed by a diffusion dominated mechanism that produces low concentrations of gas in a fgz of steady state thickness gas forms across a thick zone because the upward fluid flux is relatively low and because the gas water solubility decreases to a minimum several hundred meters below the seabed this newly understood solubility curvature effect is complementary to hydrate recycling but becomes the most important factor controlling the presence and properties of the bsr in environments where the rate of upward fluid flow and the rate of hydrate recycling are both relatively low i e rifted continental margins if the present day fgz is in steady state we estimate that the upward fluid flux in the west svalbard site must be less than 0 15 mm a 1

fracture and compaction of andesite in a volcanic edifice the failure mode of lava dilatant or compactant depends on the physical attributes of the lava primarily the porosity and pore size and the conditions under which it deforms the failure mode for edifice host rock has attendant implications for the structural stability of the edifice and the efficiency of the sidewall outgassing of the volcanic conduit in this contribution we present a systematic experimental study on the failure mode of edifice forming andesitic rocks porosity from 7 to 25 from volcan de colima mexico the experiments show that at shallow depths 1 km while low porosity 10 lava remains dilatant the failure of high porosity lava is compactant and driven by cataclastic pore collapse although inelastic compaction is typically characterised by the absence of strain localisation we observe compactive localisation features in our porous andesite lavas manifest as subplanar surfaces of collapsed pores in terms of volcano stability faulting in the upper edifice could destabilise the volcano leading to an increased risk of flank or large scale dome collapse while compactant deformation deeper in the edifice may emerge as a viable mechanism driving volcano subsidence spreading and destabilisation the failure mode influences the evolution of rock physical properties permeability measurements demonstrate that a throughgoing tensile fracture increases sample permeability i e equivalent permeability by about a factor of two and that inelastic compaction to an axial strain of 4 5 reduces sample permeability by an order of magnitude the implication of these data is that sidewall outgassing may therefore be efficient in the shallow edifice where rock can fracture but may be impeded deeper in the edifice due to compaction the explosive potential of a volcano may therefore be subject to increase over time if the progressive compaction and permeability reduction in the lower edifice cannot be offset by the formation of permeable fracture pathways in the upper edifice the mode of failure of the edifice host rock is therefore likely to be an important factor controlling lateral outgassing and thus eruption style effusive versus explosive at stratovolcanoes

a revision of the late cretaceous paleocene eutherian mammal cimolestes marsh 1889 cimolestes marsh is a north american eutherian mammal primarily known from latest cretaceous deposits in alberta wyoming saskatchewan and montana at present five species of cimolestes are considered valid all lancian in age they include one of the largest north american late cretaceous therian mammals as well as one of the smallest a size range far exceeding that within other genera of tribosphenic therians contemporary with cimolestes such as the leptictoid eutherian gypsonictops simpson or genera of alphadontid or pediomyid marsupials moreover the species of cimolestes display a disparity of dental morphology in addition to size well in excess of interspecific differences within these genera given these considerations cimolestes is clearly a grade taxon uniting species sharing an adaptively subzalambdodont dentition but showing divergent specializations within this pattern that are inconsistent with monophyly of its presently included species to correct these imbalances this paper limit

in situ degassing study on crystal bearing stromboli basaltic magmas implications for stromboli explosions 1 three dimensional crystal and bubble sizes and distributions in experimentally produced vesicular crystal bearing stromboli basalts and natural scoria were studied with x ray microtomography ct at high 1 85 m and low 5 46 9 0 m resolution the permeabilities from lattice boltzmann lb simulations and experimental measurements are about 1 2 orders of magnitude higher than in aphyric stromboli basalts at porosity 31 6 55 3 we propose that the higher permeability in crystal bearing samples results in highly efficient degassing in shallow highly porphyritc hp magma as opposed to the deeper aphyric lp magma in paroxysmal explosions the lp magma flows up in a cylindrical conduit due to the density and viscosity difference between the two magmas this type of convection can cause the lp magma with exsolved gas to be efficiently transferred through the overlying hp magma potentially resulting in the more violent paroxysmal explosions

aceroryctes dulcis a new palaeoryctid mammalia eutheria from the early eocene of the wasatch formation of southwestern wyoming usa the palaeoryctidae are a group of small bodied likely insectivorous mammals known principally from the paleocene and early eocene from approximately 65 to 53 ma of north america here we report on a new palaeoryctid from the early eocene early wasatchian wa3 north american land mammal age main body of the wasatch formation washakie basin near bitter creek station in southwestern wyoming usa acerorcytes dulcis gen et sp nov is unique among palaeoryctids in having a double rooted p2 with a small anterior cusp p3 with pronounced para and metastylar cusps and a reduced but conspicuous metacone p4 with a weakly developed metacone and an anteroposteriorly compressed protocone and m1 2 with deep ectoflexus and a sharp metastylar blade a phylogenetic analysis based on 32 dental characters of the nine known north american palaeoryctid species including aceroryctes dulcis recovered eight equally parsimonious cladograms similar to prior studies the analysis suggests that the genus palaeoryctes

oscillatory rheology measurements of particle and bubble bearing fluids solid like behavior of a crystal rich basaltic magma the rheology of crystal and bubble bearing magmas governs the propagation of seismic waves as well as eruption dynamics here rheology includes viscous and elastic components and their ratio known as attenuation we perform an oscillatory rheology measurements which provide storage elastic component and loss viscous component moduli and attenuation with frequency dependence using particle and bubble bearing fluids whose liquid viscosity is in the range of that of a basaltic melt we find that both the storage and loss moduli dramatically increase with the particle fraction but weakly depend on the bubble fraction solid like behavior equivalent to attenuation 40 vol the shallow conduit of stromboli volcano filled by a crystal rich and low viscosity basaltic magma may be an example where shear waves propagate and brittle fractures occur to cause explosive eruptions because of its high crystallinity

kinematic interpretation of the 3d shapes of metamorphic core complexes 1 metamorphic core complexes form dome shaped structures in which the ductile crust is exhumed beneath a detachment fault the 3d dome geometry inferred by mapping the schistosity in the exhumed crust can be either elongated normal to the stretching direction or along it in the first case the domes are interpreted as having formed during extension however in the second case they are interpreted either as strike slip transpressive or constrictive extensional structures depending on the geodynamic context numerical models of metamorphic core complexes published to date are all two dimensional and therefore theoretically only apply to domes which are elongated normal to the stretching direction here we explore by means of 3d thermomechanical modeling the impact of 3d kinematic extensional boundary conditions on the shape of metamorphic core complexes we examine the impact of a transtensional step over and of horsetail splay fault kinematics on the dynamics of exhumation finite strain and p t paths and compare them to cylindrical 3d models we show for the first time that domes formed in transtensional step over or at the tip of propagating strike slip faults display a finite strain field which can be interpreted as characteristic of a transpressive domes although no shortening was applied in the far field applying our models to the cyclades we propose that the coeval formation of domes elongated normal and parallel to the stretching during the miocene can be the result of horsetail splay fault kinematics which could correspond to the formation of a tear in the aegean slab

diversity and climate change in the middle late wasatchian early eocene willwood formation central bighorn basin wyoming abstract densely distributed mammal samples from the willwood formation in the central part of wyoming s bighorn basin span episodes of major climate change previous work has focused on dramatic short term 0 5 myr during a 1 myr period of relatively static cool temperatures and a subsequent 1 myr period of warming that begins with the biohorizon b event and ends with the early eocene climatic optimum eeco in which the earth reached the hottest temperatures of the cenozoic geographic information systems is used to create spatially constrained subsamples to limit and explore the effects of the species area relationship on multiple aspects of diversity including the alpha average locality and beta locality differentiation components of species richness and the evenness and relative dominance of species abundance distributions results demonstrate previously unrecognized spatial bias in the upper levels of the section that complicate the interpretation of faunal response to the eeco evenness is strongly related to alpha richness whereas beta richness and dominance vary independently evenness increases significantly and richness becomes significantly more variable during warming richness also increases but the rise in alpha richness is not significant and the rise in beta richness is equivocal the dominance of the fauna by two abundant lineages escalates consistently regardless of changes in temperature diversity is not obviously affected across the biohorizon b event indicating that further study is necessary

vesiculation and quenching during surtseyan eruptions at hunga tonga hunga ha apai volcano tonga surtseyan eruptions are shallow to emergent subaqueous explosive eruptions that owe much of their characteristic behavior to the interaction of magma with water the difference in thermal properties between water and air affects the cooling and postfragmentation vesiculation processes in magma erupted into the water column here we study the vesiculation and cooling processes during the 2009 and 2014 2015 surtseyan eruptions of hunga tonga hunga ha apai volcano by combining 2 d and 3 d vesicle scale analyses of lapilli and bombs and numerical thermal modeling most of the lapilli and bombs show gradual textural variations from rim to core the vesicle connectivity in the lapilli and bombs increases with vesicularity from fully isolated to completely connected and also increases from rim to core in transitional clasts we interpret the gradual textural variations and the connectivity vesicularity relationships as the result of postfragmentation bubble growth and coalescence interrupted at different stages by quenching in water the measured vesicle size distributions are bimodal with a population of small and large vesicles we interpret this bimodality as the result of two nucleation events one prefragmentation with the nucleation and growth of large bubbles and one postfragmentation with nucleation of small vesicles we link the thermal model with the textural variations in the clasts showing a dependence on particle size leidenfrost effect and initial melt temperature in particular the cooling profiles in the bombs are consistent with the gradual textural variations from rim to core in the clasts likely caused by variations in time available for vesiculation before quenching

in situ confirmation of permeability development in shearing bubble bearing melts and implications for volcanic outgassing the ferocity of volcanic eruptions their penchant for either effusive or explosive behaviour is to a large extent a matter of the ease with which volatiles are able to escape the volcanic system of particular importance are the mechanisms by which permeable networks within magma are fabricated and how they permit gas escape thereby diffusing possibly calamitous explosions here we present a series of experiments that confirms sample scale fracture propagation and permeability development during shearing viscous flow of initially impermeable bubble bearing 2 10 4 s 1 at moderate shear strain rates 2 10 4 s 1 3 via en echelon mode i fractures produced by repeated fracture events at high shear strain rates 4 5 10 4 s 1 permeability develops shortly after the onset of inelastic deformation and is again established through a series of en echelon mode i fractures critically strain is not immediately localized on mode i fractures making them long lived and efficient outgassing channels that are ideally oriented for directing volatiles from the central conduit upward and outward toward the conduit rim indeed mode i fracture arrays may prove necessary for dissipating gas overpressures in the central regions of the magma column which are considered difficult to outgas these experiments highlight mechanisms that are likely active along conduit margins and constrain previously postulated processes under truly applicable conditions

fault textures in volcanic conduits evidence for seismic trigger mechanisms during silicic eruptions it is proposed that fault textures in two dissected rhyolitic conduits in iceland preserve evidence for shallow seismogenic faulting within rising magma during the emplacement of highly viscous lava flows detailed field and petrographic analysis of such textures may shed light on the origin of long period and hybrid volcanic earthquakes at active volcanoes there is evidence at each conduit investigated for multiple seismogenic cycles each of which involved four distinct evolutionary phases in phase 1 shear fracture of unrelaxed magma was triggered by shear stress accumulation during viscous flow forming the angular fracture networks that initiated faulting cycles transient pressure gradients were generated as the fractures opened which led to fluidisation and clastic deposition of fine grained particles that were derived from the fracture walls by abrasion fracture networks then progressively coalesced and rotated during subsequent slip phase 2 developing into cataclasite zones with evidence for multiple localised slip events fluidisation and grain size reduction phase 2 textures closely resemble those formed on seismogenic tectonic faults characterised by friction controlled stick slip behaviour increasing cohesion of cataclasites then led to aseismic distributed ductile deformation phase 3 and generated deformed cataclasite zones which are enriched in metallic oxide microlites and resemble glassy pseudotachylite continued annealing and deformation eventually erased all structures in the cataclasite and formed microlite rich flow bands in obsidian phase 4 overall the mixed brittle ductile textures formed in the magma appear similar to those formed in lower crustal rocks close to the brittle ductile transition with the rheological response mediated by strain rate variations and frictional heating fault processes in highly viscous magma are compared with those elsewhere in the crust and this comparison is used to appraise existing models of volcano seismic activity based on the textures observed it is suggested that patterns of long period and hybrid earthquakes at silicic lava domes reflect friction controlled stick slip movement and eventual healing of fault zones in magma which are an accelerated and smaller scale analogue of tectonic faults

gas driven filter pressing in magmas insights into in situ melt segregation from crystal mushes gas driven filter pressing is the process of melt expulsion from a volatile saturated crystal mush induced by the buildup and subsequent release of gas pressure filter pressing is inferred to play a major role in magma fractionation at shallow depths 10 km by moving melt and gas relative to the solid crystalline framework however the magmatic conditions at which this process operates remain poorly constrained we present novel experimental data that illustrate how the crystal content of the mush affects the ability of gas driven filter pressing to segregate melt hydrous haplogranite 2 1 wt water in the melt and dacite 4 2 wt water in the melt crystal mushes with a wide range of crystallinities 34 80 vol crystals were investigated using in situ high temperature 500 800 c synchrotron x ray tomographic microscopy with high spatial 3 m pixel and temporal resolution 8 s per three dimensional data set our experimental results show that gas driven filter pressing operates only below the maximum packing of bubbles and crystals 74 vol above this threshold the mush tends to fracture and gas escapes via fractures therefore the efficiency of gas driven filter pressing is promoted close to the percolation threshold and in situations where a mush inflates slowly relative to build up of pressure and expulsion of melt such observations offer a likely explanation for the production of eruptible crystal poor magmas within earth s crust

quantification of the dry history of the martian soil inferred from in situ microscopy 1 the particle size distribution psd of a martian soil sample a useful indicator of the underlying soil formation processes has been determined using optical and atomic force microscopy data acquired by the phoenix mars lander in particular the presence and fraction of clay sized particles in the psd reflects the extent of aqueous interaction with the soil two size populations have been identified for the martian sample larger mostly rounded grains and small reddish fines notably with a very low mass proportion in the clay size range below 2 m these fines reflect the smallest scale formation processes and indicate a single method of production for the particles up to 11 m a much larger value than that expected for the aqueous interaction of clay formation this suggests the fines are predominantly the product of global aeolian weathering under very dry conditions the proportion of clay sized soils can be used to estimate that there has been much less than 5 000 years exposure to liquid water over the history of the soil from the perspective of the psd lunar regolith rather than terrestrial soil is the best analog to martian soil a globally homogenous soil with such a psd would be an unlikely habitat for the propagation of life on mars

the porosity of pyroclasts as an indicator of volcanic explosivity abstract the porosity of pyroclasts is a valuable indicator of the character of a volcanic eruption here we analyse the porosity distribution of deposits of 17 different volcanic eruptions covering a broad range of inferred magma properties and observed eruption styles histograms of porosity versus pyroclast frequency show distinctive features in terms of the mean variance modality and skewness we present characteristic porosity distributions for five different eruption style categories dome forming explosive basaltic cryptodome forming subplinian plinian ultraplinian and phreatomagmatic we find that the mean porosity values of the deposits correlate positively with the volcanic explosivity index vei of newhall and self 1982 regardless of the degree of complexity of the individual distributions we then propose causes of the deviations from a general trend in terms of magma viscosity degassing efficiency and cap rock confinement finally a generalised correlation between clast porosity and explosivity of an eruption is developed that should help together with conventional field techniques facilitate the interpretation of pyroclastic sequences even in cases where no direct observation of the eruption exists

evaluation of hydrogeochemical processes and groundwater quality in the jhansi district of bundelkhand region india a base line study involving analysis of groundwater samples from the jhansi district were carried out to determine the major and trace element chemistry and to assess the hydrogeochemical processes and water quality for domestic and irrigation uses study results show that groundwater is mildly acidic to alkaline in nature and hco3 cl ca2 na and mg2 are the major contributing ions for the dissolved loads the data plotted on the gibbs and piper diagrams reveal that the groundwater chemistry is mainly controlled by rock weathering with secondary contribution from anthropogenic sources in a majority of the groundwater samples alkaline earth metals exceed alkalies and weak acid dominate over strong acids ca mg hco3 is the dominant hydrogeochemical facies in the majority of the groundwater samples the computed saturation indices demonstrate that groundwater is oversaturated with respect to dolomite and calcite kaolinite is the possible mineral that is in equilibrium with the water implying that the groundwater chemistry favors kaolinite formation a comparison of groundwater quality parameters in relation to specified limits for drinking water shows that the concentrations of tds f no3 total hardness and fe are exceeding the desirable limits in many water samples quality assessment for irrigation uses reveal that the groundwater is of good to suitable category higher salinity and residual sodium carbonate values at some sites restrict the suitability of groundwater and need an adequate drainage and water management plan for the area

the effect of particle shape on suspension viscosity and implications for magmatic flows 1 the rheology of crystal bearing magma and lava depends on both the shape and volume fraction of the suspended crystals we present the results of analogue rheometric experiments on monodisperse suspensions of solid particles in a newtonian liquid in which particle volume fraction and aspect ratio rp are varied systematically we find that the effect of on viscosity is well captured by the maron pierce model and that this model is valid across the range of particle aspect ratios investigated 0 04 rp 22 i e strongly oblate to strongly prolate when the maximum packing fraction m is treated as a fitting parameter the value of m derived from fitting to our experimental data depends strongly and systematically on particle aspect ratio hence m represents an effective proxy for the influence of particle shape on suspension rheology we present a simple relationship for m rp which allows the viscosity of a suspension to be calculated as a function of and rp only we investigate the impact of accounting for crystal shape when modelling volcanic flows by simulating the eruption of magma carrying crystals of different aspect ratio and conclude that the effect of crystal shape should not be neglected

introducing the volcanic unrest index vui a tool to quantify and communicate the intensity of volcanic unrest accurately observing and interpreting volcanic unrest phenomena contributes towards better forecasting of volcanic eruptions thus potentially saving lives volcanic unrest is recorded by volcano observatories and may include seismic geodetic degassing and or geothermal phenomena the multivariate datasets are often complex and can contain a large amount of data in a variety of formats low levels of unrest are frequently recorded causing the distinction between background activity and unrest to be blurred despite the widespread usage of these terms in unrest literature including probabilistic eruption forecasting models and in volcanic alert level val systems frequencies and intensities of unrest episodes are not easily comparable over time or between volcanoes complex unrest information is difficult to communicate simply to civil defence personnel and other non scientists the volcanic unrest index vui is presented here to address these issues the purpose of the vui is to provide a semi quantitative rating of unrest intensity relative to each volcano s past level of unrest and to that of analogous volcanoes the vui is calculated using a worksheet of observed phenomena ranges for each phenomenon within the worksheet can be customised for individual volcanoes as demonstrated in the companion paper for taupo volcanic centre new zealand potter et al 2015 the vui can be determined retrospectively for historical episodes of unrest based on qualitative observations as well as for recent episodes with state of the art monitoring this enables a long time series of unrest occurrence and intensity to be constructed and easily communicated to end users the vui can also assist with val decision making we present and discuss two approaches to the concept of unrest

coupled effect of magma degassing and rheology on silicic volcanism abstract explosive volcanism such as the 1991 mt pinatubo philippines and the 2008 mt chaiten chile eruptions is caused by violent vesiculation of hydrous magma however gas may efficiently separate from magma owing to the enhancement of gas permeability by shear deformation of magma flowing in a volcanic conduit this makes it difficult to maintain the driving force of explosive volcanism although explosive volcanism is actually common here we propose that shear localization in a volcanic conduit controls the eruption style and explosivity based on deformation experiments of vesicular magma linked with synchrotron radiation x ray radiography and computed tomography we observed for the first time in situ that the shear localization caused magma fracturing and formed a slip plane and thus inhibited deformation and outgassing elsewhere we also observed the compaction of vesicular magma into a dense lava as a result of outgassing when shear localization did not occur in a natural setting shear localizes along the edges of a volcanic conduit where the strain rate is high causing a highly permeable fracturing layer to form at the conduit s edge and leaving less sheared and less outgassed magma at its center the less outgassed magma in the center may ascend rapidly and cause explosive volcanism non explosive lava effusion may occur only when shear localization does not occur effectively this new view explains the rapid ascent of viscous magma and the formation of pyroclasts with contrasting vesicularity pyroclastic obsidian and highly vesiculated pumice

geochronology and mammalian biostratigraphy of middle and upper paleocene continental strata bighorn basin wyoming the bighorn basin of northwestern wyoming preserves one of the most complete records of middle paleocene to lower eocene continental biota the geochronology of this important interval depends partly on numerical calibration of the geomagnetic polarity time scale gpts but the middle and late paleocene parts of the gpts have been poorly constrained radioisotopically a new volcanic ash from the northern bighorn basin provides the first radioisotopic age for upper middle paleocene strata upper selandian and is an important calibration point for the base of polarity chron c26n and the selandian thanetian stage boundary in the gpts sanidine from the ash has a weighted mean age of 59 00 0 30 2 ma based on twenty three 40 ar 39 ar bulk laser fusion analyses the ash corroborates the revised age estimate for the base of chron c26n in the most recent geomagnetic polarity time scale gpts 04 and confirms that c26n is older than depicted in the 1995 gpts we place paleocene mammalian biozones in the bighorn basin into a refined geochronologic framework these biozones are the primary basis for biostratigraphic correlation of middle and upper paleocene continental deposits in north america new paleomagnetic data provide synchronous tie points for correlation among three stratigraphic sections in the northern bighorn basin and to the gpts paleomagnetic correlation study of new fossil material review of known faunas and refined stratigra phy enable us to reevaluate several biozones we define three new zones based on first occurrences of taxa the phenacolemur ti 4b probathyopsis ti 5a revised and copecion cf 3 revised zones the phenacolemur zone includes some faunas previously placed in the plesiadapis churchilli and plesiadapis fodinatus zones ti 4 and ti 5a respectively the probathyopsis zone replaces the p fodinatus zone and the copecion zone replaces the phenacodus ectocion acme zone cf 3 seven of the biozones considered here are subdivisions of the tiffanian land mammalage thetiffanianwasoriginallytypifiedbythemasonpocketfaunainsouthwest ern colorado but it is now much better known from faunas in the northern bighorn basin biostratigraphic evidence and new paleomagnetic data from the bighorn basin indicate that mason pocket is considerably older than was previously recognized and occurs in chron c26r rather than c25r the geochronologic framework presented here helps to constrain the temporal ranges of species that occur in the middle and late tiffanian and it allows the bighorn basin record to be better compared to other faunal floral and paleoclimate records both regionally and globally

a physical model for metal extraction and transport in shallow magmatic systems 1 the highest concentrations of metals e g cu au ag mo in the earth s crust are found in porphyry type deposits the metals are ultimately sourced from magmas and appear to be concentrated hundred to thousand fold from typical magmatic contents ppm ppb in the exsolved volatile phase to better quantify the purging and transport of metals we develop a physical model of volatile evolution in an incrementally built upper crustal magma reservoirs that considers 1 partitioning of metals from the melt to an exsolved volatile phase and 2 advection of the buoyant volatile phase using a single dimensionless parameter the peclet number pe ratio of advection rate over diffusion rate we propose that metal extraction and segregation from magmas can occur in 3 stages with different pe 1 during exsolution of the magmatic volatile phase in shallow crystal poor magma bodies slow volatile advection pe 1 2 during the growth of volatile channels that develop in the reservoir as crystallinity increases pe 1 and 3 during advection in connected channels rapid volatile advection high pe 1 for each stage a metal enrichment factor can be calculated allowing insight into the optimal conditions to maximize metal mass flux into the overlying hydrothermal system the model predicts that the most efficient purging of metals occurs for magmas with intermediate volatile contents and is enhanced during late stage magmatic activity as the reservoirs reach high crystallinity and are not disturbed by volcanic venting in agreement with natural observations suggesting that ore formation post dates volcanic activity

types and mechanisms of strombolian explosions characterization of a gas dominated explosion at stromboli textural and chemical analyses of bombs quenched directly from a normal explosion at stromboli volcano italy were integrated with coincident seismic acoustic and thermal data the data set defines a new gas dominated type of strombolian eruption named type 0 these events are characterized by high velocity emission 150 250 m s 1 of a few relatively small juvenile particles with entrained non juvenile clasts that previously fell back into the vent to be re erupted for the studied event the explosion depth was more than 250 m deep and the particles showed little residence time in the shallow system slug ascent velocities over the final 20 35 m of magma filled conduit and the low viscosity of the resident magma are all consistent with simple bubble burst in a clean conduit this conduit type and eruption style likely fit popular slug ascent and burst models used to explain strombolian eruptions in contrast the ballistic dominated type of explosions type 1 are associated with larger proportions of stagnant material in the shallow system magma mix we argue that the additional volume of this stagnant material pushes the free surface upward because of the larger volume of material available for entrainment into a type 1 slug burst which has to fragment through a thick cap of degassed material type 1 events tend to be rich in particles in contrast the less spectacular gas rich type 0 events have little material to entrain thus being poor in lapilli and bombs

textural and geophysical characterization of explosive basaltic activity at villarrica volcano 1 villarrica volcano chile is one of the most active volcanoes in south america its activity is currently characterized by continuous degassing from a summit lava lake vent punctuated by explosive events during november 2004 a multidisciplinary experiment was deployed for a 10 d period to define the style of emission and infer shallow conduit dynamics at this basaltic center this involved collection of thermal seismic and infrasonic data to describe the background activity confined inside the crater and use of samples to texturally and chemically characterize the ejecta from more energetic explosions able to attain the crater rim the background activity was characterized by gas bursting with a frequency of 9 events per minute this involved emission of gas puffs fed by bubble bursting with larger bursts emplacing sheets of magma onto the lower crater walls the ejecta population from the more energetic events was characterized by the coexistence of both scoriae and golden pumice these two types of clasts have different textures but identical glass compositions suggesting that they underwent different conduit histories the golden pumice is interpreted as the expanding inner part of a short lived jet fed by a rapidly ascending magma batch the scoria forms the outer portion of the jet and comprises degassed material entrained during passage of the fresh batch through material residing in the upper most portion of the conduit we thus have a largely degassed upper column that feeds persistent bubble bursting through which fresh batches occasionally rise to feed events of relatively higher energy

on the slow decompressive response of volatile and crystal bearing magmas an analogue experimental investigation abstract the degassing kinetics of ascending magma strongly affect eruption dynamics the kinetics are in turn influenced by magma properties the investigation of the relationship between magma properties and eruption dynamics is a key element in revealing the processes characterizing magmatic flows within the shallow conduit to explore the effects of physical properties on degassing in basaltic eruptive systems we have designed and carried out experiments on the slow decompressive response of analogue magmas composed of silicone oil based suspensions using a shock tube apparatus four series of experiments were performed 1 particle free silicone oils with viscosity ranging from 1 to 1000 pa s were used to constrain the liquid response 2 silicone oils with variable proportion of suspended micrometric spherical particles were employed to assess the effect of different crystal fractions 3 suspensions of elongated particles in silicone oils were used to investigate the role of crystal shape 4 the effects of saturation time and pressure were examined the rheology of both spherical and elongated particle bearing suspensions were characterized by concentric cylinder rotational rheometry the flow dynamics of the bubbly fluid from the process of bubble nucleation up to the development of a permeable bubble network were constrained using image analysis different fluid regimes were distinguished i nucleation ii foam build up and iii foam oscillation by comparing results obtained from the different series of experiments we were able to assess the primary role played by the presence of particles on the evolution of the gas volume fraction within the samples particle fraction has a dominant role at high concentration affecting the motion of the fluid finally particle shape influences the long term degassing efficiency of the fluid using scaling considerations such observations are applied to mafic to intermediate systems the results of our experimental investigation contribute to constraining vesiculation processes in magmas of various crystallinities at shallow depths

in situ x ray tomographic microscopy observations of vesiculation of bubble free and bubble bearing magmas magma degassing is thought to play a major role in magma fractionation transport storage and volcanic eruption dynamics however the conditions that determine when and how magma degassing operates prior to and during an eruption remain poorly constrained we performed experiments to explore if the initial presence of gas bubbles in magma influences the capability of gas to escape from the magma vesiculation of natural h2o poor 1 wt silicic obsidian glasses was investigated by in situ high temperature above the glass transition experiments using synchrotron based x ray tomographic microscopy with high spatial 3 m pixel and temporal resolution 1 second per 3d dataset as a validation a second set of experiments was performed on identical starting materials using a karl fisher titration setup to quantify the amount of extracted gas that escapes via volatile diffusion and or bubble coalescence during vesiculation in both sets of experiments vesiculation was triggered by heating the samples at room pressure our results suggest that the presence of pre existing gas bubbles during a nucleation event significantly decreases the tendency of bubbles to coalesce and inhibits magma outgassing in contrast in initially bubble free samples the nucleation and growth of bubbles is accompanied by significant coalescence and outgassing we infer that volatile undersaturated i e bubble free magmas in the reservoirs are more likely to erupt effusively while the presence of excess gas already at depth i e bubble bearing systems increases the likelihood of explosive eruptions

permeability reduction of fractured rhyolite in volcanic conduits and its control on eruption cyclicity repetitive explosions of silicic volcanoes are thought to be triggered by volcanic gases in the shallow parts of the conduit to trap the volcanic gases in the conduit the lava dome or plug must be impermeable however silicic magma undergoes brittle fracturing during ascent because its viscosity increases via dehydration and groundmass crystallization since fractured magma has high permeability the reduction of permeability is a key process that allows gases to accumulate leading to an explosion we performed uniaxial compression experiments on rhyolite fragments at temperatures of 700 900 c to investigate the permeability reduction of fractured rhyolite experimental results show that permeability is controlled by porosity and permeability reduction can be caused by compaction of fractured magma based on the observed relationship between permeability and porosity we calculate the time scale of permeability reduction i e the transition from permeable to impermeable magma the calculated time scale 100 1000 s is much shorter than the eruption repose 1 10 h observed at sakurajima volcano japan this result implies that an impermeable lava dome and plug formed during the eruption repose in contrast the repose time 20 40 min of santiaguito volcano guatemala is shorter than the time scale of permeability reduction 10 h this indicates that gases could not have accumulated before volcanic explosions and that other mechanisms could control eruption cyclicity

nonisothermal viscous sintering of volcanic ash volcanic ash is often deposited in a hot state volcanic ash containing glass deposited above the glass transition interval has the potential to sinter viscously both to itself particle particle and to exposed surfaces here we constrain the kinetics of this process experimentally under nonisothermal conditions using standard glasses in the absence of external load this process is dominantly driven by surface relaxation in such cases the sintering process is rate limited by the melt viscosity the size of the particles and the melt vapor interfacial tension we propose a polydisperse continuum model that describes the transition from a packing of particles to a dense pore free melt and evaluate its efficacy in describing the kinetics of volcanic viscous sintering we apply our model to viscous sintering scenarios for cooling crystal poor rhyolitic ash using the 2008 eruption of chaiten volcano as a case example we predict that moderate linear cooling rates of 0 1 c min 1 can result in the common observation of incomplete sintering and the preservation of pore networks

fragmentation and plinian eruption of crystallizing basaltic magma abstract basalt is the most ubiquitous magma on earth erupting typically at intensities ranging from quiescently effusive to mildly explosive the discovery of highly explosive plinian eruptions of basaltic magma has therefore spurred debate about their cause silicic eruptions of similar style are a consequence of brittle fragmentation as magma deformation becomes progressively more viscoelastic magma eventually crosses the glass transition and fragments due to a positive feedback between water exsolution viscosity and decompression rate in contrast to silicic eruptions the viscosity of basaltic magmas is thought to be too low to reach conditions for brittle fragmentation pyroclasts from several basaltic plinian eruptions however contain abundant micron size crystals that can increase magma viscosity substantially we therefore hypothesize that magma crystallization led to brittle fragmentation during these eruptions using combined oscillatory and extensional rheometry of concentrated particle liquid suspensions that are dynamically similar to microcrystalline basaltic magma we show that high volume fractions of particles and extension rates of about 1 s 1 or greater result in viscoelastic deformation and brittle fracture we further show that for experimentally observed crystallization rate basaltic magma can reach the empirical failure conditions when erupting at high discharge rates

stability of foams in silicate melts bubble coalescence and the spontaneous disruption of high porosity foams in silicate melts are the result of physical expulsion of interpore melt syneresis leading to bubble coalescence and diffusive gas exchange between bubbles melt expulsion can be achieved either along films between pairs of bubbles or along plateau borders which represent the contacts between 3 or more bubbles theoretical evaluation of these mechanisms is confirmed by experimental results enabling us to quantify the relevant parameters and determine stable bubble size and critical film thickness in a foam as a function of melt viscosity surface tension and time foam stability is controlled primarily by melt viscosity and time melt transport leading to coalescence of bubbles proceeds along inter bubble films for smaller bubbles and along plateau borders for larger bubbles thus the average bubble size accelerates with time in silicate melts the diffusive gas expulsion out of a region of foam is effective only for water and even then only at small length scales as the diffusion of co2 is negligible the results of our analyses are applicable to studies of vesicularity of lavas melt degassing and eruption mechanisms

factors controlling permeability porosity relationships in magma a model has been developed to investigate the sensitivity of magma permeability k to various parameters power law relationships between k and porosity are revealed in agreement with previous experimental and theoretical studies these relationships take the form mathtype mtef 2 1 feaaeaart1ev0aaatcvaufkttlearuavtnhis1mbaexatlxbi9gbae rbd9wdylwzybwexlmbbxgbcf2cpn2qvrwzqf2zlnharyavp1wzzbit ldhis9wbh5garqqtubsr4rnchbgeagqivci8ffyjh8sipiydhavhbb f9v8qqaqfr0xc9pk0xbba9q8wqffeay bilkvclq jhqpepeea0 as 0fb9pgeayrxxe9vr0 vr0 vqpwqaaeaabigaciaacaqabeaadaabau aaaoqaaiqbdugarzaajagaeyypa0jaem4aasmaei4la8iaemocai3a awbaasqabeaacqaiyagmaagccqgh9aqpcqwghbqycqggoaakcqahgp gzcqghsislcqahgpgzdawgaawcbagaem4yammaemocaihabeaakiab cmcapmaacaaaleqabagaemoyaigaaaaa 4ce4 hat k k r 2 a phi phi cr b where r is the mean bubble radius cr is the percolation threshold below which permeability is zero and a and b are constants it is discovered that mathtype mtef 2 1 feaaeaart1ev0aaatcvaufkttlearuavtnhis1mbaexatlxbi9gbae rbd9wdylwzybwexlmbbxgbcf2cpn2qvrwzqf2zlnharyavp1wzzbit ldhis9wbh5garqqtubsr4rnchbgeagqivci8ffyjh8sipiydhavhbb f9v8qqaqfr0xc9pk0xbba9q8wqffeay bilkvclq jhqpepeea0 as 0fb9pgeayrxxe9vr0 vr0 vqpwqaaeaabigaciaacaqabeaadaabau aaaoqaaiqbdugarzaajagaeyoei0iaeqoxdygaaa 3cdb hat k phi relationships are independent of bubble size the percolation threshold was found to lie at around 30 porosity polydisperse bubble size distributions bsds give permeabilities around an order of magnitude greater than monodisperse distributions at the same porosity if bubbles are elongated in a preferred direction then permeability in this direction is increased but perpendicular to this direction permeability is unaffected in crystal free melts the greatest control on permeability is the ease of bubble coalescence in viscous magmas or when the cooling time scale is short bubble coalescence is impeded and permeability is much reduced this last effect can cause variations in permeability of several orders of magnitude

experimental constraints on permeable gas transport in crystalline silicic magmas the gas and fluid transport in magmas via permeable flow through interconnected bubble networks controls the rate of outgassing from magmas ascending in volcanic conduits and the fluid transport in the mushy boundary layer of magma reservoirs hence clarifying its mechanism and rate is crucial to understanding the explosivity of volcanic eruptions and the evolution and dynamics of a magma reservoir recent experimental studies have determined the gas permeabilities in crystal free rhyolite and basalt however no experimental study has investigated the effect of the crystal contents on the permeable gas transport in magmas in this study we performed decompression experiments for hydrous rhyolitic melts having crystallinities of 30 and 50 vol to examine the effect of crystals on the bubble microstructure and gas permeability during magma vesiculation size controlled 100 meshed corundum crystals were used as an analog of the phenocrysts in silicic magmas microstructural analyses using x ray ct showed that bubbles coalesce and their connectivity increases with a decrease in the final pressure after the decompression that is an increase in the vesicularity as long as the vesicularities of melt part in the crystal free basis melt vesicularity were similar no clear effect of the crystallinity on the degree of bubble coalescence and connectivity was observed at melt vesicularities 68 vol this result indicates that the permeable fluid transport through a deep volcanic conduit which has been proposed on the basis of the observations of volcanic gases and natural products is so slow that other processes like shear deformation or magma convection may be needed to explain the observations