validating earth and ocean tide models using tidal gravity measurements summary o1 and m2 observations from well calibrated spring gravimeters and superconducting gravimeters from the global geodynamics project ggp are used to test models of the earth s body tide and 10 ocean tide models it is shown that some of the ocean tide models give anomalous results in various parts of the world for example the schwiderski ocean tide model gives discrepancies in several areas and the fes series of ocean tide models have problems in the western pacific china japan and australia the majority of the high quality tidal gravity measurements in europe are in close agreement with the dehant defraigne and wahr ddw elastic and inelastic body tide models the gravimetric factors for the ddw elastic and inelastic models only differ by 0 12 per cent and the present calibration accuracy does not allow us to distinguish between these models but does reduce the previous upper bound on inelastic gravimetric factors the european observations give a phase lag of a few hundredths of a degree for the o1 body gravity tide which is consistent with the mathews inelastic body tide model at some european and worldwide stations the gravimetric factors differ by up to 0 3 per cent from the ddw model and it is suggested that further checks on the gravimeter calibrations are required accurate determinations of instrumental phase lags are now easier to achieve and the imaginary out of phase component of tidal gravity can be used for accurate tests of this component of ocean tide models

new transfer functions for nutations of a nonrigid earth there are differences between the observed values of nutation and the computed ones based on the international astronomical union iau 1980 adopted nutation series these differences can be expressed in the frequency domain where they may reach several milliarc seconds a level that is too large for practical use this paper aims to resolve part of these differences by computing a new theoretical model accounting for additional geophysical effects a new transfer function is computed based on an earth initially in a nonhydrostatic equilibrium corresponding to the steady state associated with the present mantle convection the mantle mass anomalies are deduced from seismic tomography data and the flow induced boundary deformations are computed from internal loading for an earth made up of a viscous inner core a liquid outer core a viscous mantle and a solid lithosphere in this way a new core mantle boundary cmb flattening is obtained which gives the observed free core nutation fcn period furthermore the global earth dynamical flattening induced by the mass anomalies in the mantle associated with tomography and by the mass anomalies due to the computed boundary deformations is in agreement with the j2 form factor or the observed precession constant in addition to this nonhydrostatic initial state the rheology of the mantle is considered as inelastic the transfer function for nutation is then obtained by numerical integration of motion equations from the earth s center up to the surface to provide a model which is completely self consistent in order to validate our model the transfer function is convolved with new rigid earth nutations ocean corrections are applied and the final results are then compared with the observed nutations or with the international earth rotation service iers nutation series the residuals between our model and the observation are about 3 times smaller than those between the iau 1980 adopted model and the observation however our model still presents residuals above the observational error this is particularly true for the out of phase part of the residuals while the in phase part gives very small residuals improvement of about 1 order of magnitude a further step in this study is a refinement of the modeling of geophysical fluids core ocean and atmosphere

crustal accretion model for iceland predicts cold crust we present a self consistent crustal accretion model of iceland that includes heat and mass transfer between an upwelling melting mantle and an accreting cooling crust this models predicts sub solidus crustal temperatures that are consistent with seismic estimates of the maximum depth of earthquake hypocenters and mid crustal shear wave quality factors and with geothermal estimates of surface heatflow

segmented lateral dyke growth in a rifting event at barðarbunga volcanic system iceland crust at many divergent plate boundaries forms primarily by the injection of vertical sheet like dykes some tens of kilometres long1 previous models of rifting events indicate either lateral dyke growth away from a feeding source with propagation rates decreasing as the dyke lengthens2 3 4 or magma flowing vertically into dykes from an underlying source5 6 with the role of topography on the evolution of lateral dykes not clear here we show how a recent segmented dyke intrusion in the bar arbunga volcanic system grew laterally for more than 45 kilometres at a variable rate with topography influencing the direction of propagation barriers at the ends of each segment were overcome by the build up of pressure in the dyke end then a new segment formed and dyke lengthening temporarily peaked the dyke evolution which occurred primarily over 14 days was revealed by propagating seismicity ground deformation mapped by global positioning system gps interferometric analysis of satellite radar images insar and graben formation the strike of the dyke segments varies from an initially radial direction away from the bar arbunga caldera towards alignment with that expected from regional stress at the distal end a model minimizing the combined strain and gravitational potential energy explains the propagation path dyke opening and seismicity focused at the most distal segment at any given time and were simultaneous with magma source deflation and slow collapse at the bar arbunga caldera accompanied by a series of magnitude m 5 earthquakes dyke growth was slowed down by an effusive fissure eruption near the end of the dyke lateral dyke growth with segment barrier breaking by pressure build up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries

on estimating crystal shape for crystal size distribution analysis abstract the accurate determination of three dimensional crystal habit long intermediate short axis is a requirement to enable correct stereological conversion of 2d crystal size measurements to true 3d crystal size distributions csds in this contribution we introduce a database and spreadsheet program which provides an objective estimate of true crystal habit from raw 2d measurements the database compares the sample s 2d measurements with 2d shape curves for random sections through 703 different habits the output gives the five best match curves and corresponding crystal habits based on a least squares fit between sample and database the minimum sample size required to give good shape estimates from 2d data is tested using random runs of sections through known shapes with different population densities at minimum 75 crystal sections are required to robustly determine crystal habit for csd measurements if crystals are tabular in shape with more acicular shapes requiring a minimum of 250 sections suggesting a sample size of 250 sections to be used for shape determination in natural examples where the true 3d shape is unknown the crystal habit of the best match shape can then be used to provide a more robust csd analysis which in turn can be used to investigate magmatic processes with more certainty

the spatial distribution of grains and crystals in rocks characterisation and analysis of the spatial distribution pattern sdp of grains or crystals in rocks is potentially a powerful technique which can be used to constrain the processes which operate in the formation of rocks a method to quantify the sdp of grains in thin section is presented the distance betwen the centre of a grain and the centre of its nearest neighbour is calculated for all the grains in the sample area to produce a distribution of distances that characterises the spatial pattern of grains in the rock this distribution is then normalised to a random distribution of points with the same population density to give a descriptive value r values of r for rock samples are plotted against porosity modal abundance of other phases in igneous and metamorphic rocks to characterise the sdp the sdp of randomly packed distributions of equal size spheres varies systematically with porosity producing a line on a porosity versus r plot termed the random sphere distribution line rsdl rocks which plot above the rsdl have an ordered sdp and those that plot below a clustered sdp the effects of variation in grain packing order grain sorting compaction and random crystallisation overgrowth on determined r values were investigated using a combination of 3 d sphere models and 2 d texture models the maximum possible value of r is 2 148 corresponding to a perfect section through hexagonal cubic close packing of grains the minimum value of r is dependent on the proportion of grains in the sample volume and may be as low as 1 2 for a sample volume with 30 grains which are clustered variations in size sorting can cause r to vary by approximately 0 25 mechanical compaction of a loose framework of grains results in a higher packing order and an increase in r continued compaction creates a fabric in the texture and r decreases as cluster patterns are developed perpendicular to the principal stress the overgrowth of grains in a touching framework alters the location of the geometric grain centre as the crystal shape changes leading to an increase in r as porosity decreases results reveal that grain sorting compaction and grain overgrowth produce different r versus porosity relationships which can be identified in and therefore used to constrain the relative importance of these processes in rock samples

waves of bubbles in basaltic magmas and lavas initially homogeneous suspensions of bubbles in basaltic magmas and lava flows may become unstable and form rising waves or layers of bubbles we derive a set of model equations for the two phase bubble liquid system and present the results of a linear stability analysis and numerical simulations periodic vesicle layers are preserved in columbia liver flows with a spacing of 1 m the prediction of the stability analysis combined with a simple model for solidification of the lava suggests that vesicle layers may represent waves of bubbles formed within the flow the spacing of layers is determined by a balance between the growth of bubbles and hydrodynamic self diffusion vesicular layers preserved in columbia liver flows may thus form by hydrodynamic processes and do not require the repeated injection of fresh volatile rich magma or a periodic nucleation of bubbles waves of bubbles may also develop in magma chambers and conduits and could play a role in eruption dynamics

formation and mechanics of magma reservoirs in iceland summary provided magma flow in a partially molten layer follows darcy s law of flow in porous media it can be demonstrated that magma in the proposed magma layer beneath iceland flows towards regions of reduced crustal thickness in these regions magma accumulates to form partially molten magma reservoirs which are thus located in the magma layer these reservoirs either give rise to surface eruptions or feed totally molten shallow magma chambers located in the crust that may erupt it is argued that the melt fraction varies throughout a reservoir being highest near the top where the reservoir may be totally molten but that the average is 0 25 it is concluded that for individual eruptions the reservoirs behave on the whole as a poroelastic material it is suggested that formation of crustal magma chambers is facilitated by the occurrence of stress barriers that lead to the formation of thick sills while liquid such sills absorb the magma of all dykes that enter them and may evolve into magma chambers ideal sites for stress barriers and thus for magma chambers are formations where individual layers have different elastic properties i e where the crust behaves as a multilayer denoting the bulk volume of the reservoirs by vb the volume of the crustal chambers by v and the volume of lava and dyke material in individual eruptions by ve it is found that vb 5365ve and v 1850ve using the estimated volumes of exposed plutons as a basis it is found that provided the feeder reservoir does not participate in the eruption the volume of individual eruptions from elastic crustal magma chambers in iceland is less than 0 25 km3 usually less than 0 1 km3 and that typical central volcano eruptions should be about 0 02 km3 for eruptions of the order of 1 km3 or larger the reservoirs must supply magma during the eruption it is concluded that from the point of view of volume historical eruptions of typical size could have come from elastic crustal magma chambers

the roza member columbia river basalt group a gigantic pahoehoe lava flow field formed by endogenous processes we present studies on the physical volcanology of the 15 ma roza member of the wanapum formation in the columbia river basalt group the roza member represents a compound pahoehoe flood basalt lava flow field with an area of 40 300 km 2 and a volume of 1300 km 3 it consists of 4 major lava flows each composed of numerous decimeter to kilometer long pahoehoe lobes roza lavas feature a wide range of pahoehoe surface structures such as lava rise plateaus tumuli and surface breakouts and we illustrate that the lava morphology is inconsistent with previous proposals of rapid emplacement for these lavas an integral component of the roza flow field is the sheet lobe with internal structures identical to those of inflated pahoehoe sheet lobes from hawaii and iceland both at the same scale and at much larger scales we identify a three part division of the sheet lobes into basal crust lava core and lava crust which are interpreted as the equivalent to the bottom crust the liquid lava core and the surface crust of an active inflating pahoehoe lobe the upper lava crust grows continuously during lava emplacement and its growth rate can be approximated by conductive cooling this relationship is used to calculate the emplacement time for individual roza sheet lobes and to derive a first order estimate on the duration of the roza eruption the results indicate that the emplacement of individual roza lobes lasted for months to years and that the lava flow field was constructed over a period of at least 14 years we propose that the roza flows achieved great areal dimensions and thicknesses by inflation and endogenous growth as the lava flowed from vent to flow front it traveled under an insulating crust which maintained cooling rates of 0 1 c km and allowed for efficient transport of lava over distances up to 300 km

pahoehoe transport as a correlated random walk 1 transport and emplacement of pahoehoe lava is often dominated by random influences such as budding small scale variations in topography degree of inflation and variations in how the skin cools stretches and cracks a random walk model is used to describe the transport of small pahoehoe lobes when random effects are a significant influence on emplacement we derive the stochastic formalism for random movements on a two dimensional grid our formulation features correlation and bias that determine the degree of randomness in the random walk of each parcel of lava qualitative and quantitative predictions of the random walk are compared with observations and data for pahoehoe lobes in hawaii the correlated random walk quantitatively describes lobe thickness transects whereas the uncorrelated random walk only reproduces the meandering of small filaments of a few toes correlation expresses momentum effects and a chain of memory from the flow front to the source of lava supply the correlated random walk features a channel forming regime that decays with distance from the source of lava supply the theory can also be interpreted in the context of a time dependent planar flow when many parcels of lava participate the overall shape of a one dimensional lobe has the appearance of a continuum wave the types of processes contained in this basic random walk model explain the multitude of concurrent or overriding features found in broad fields of toes the formalism can thus be extended to simulate large fields of emplaced pahoehoe in either terrestrial or planetary settings

body tides on a 3 d elastic earth toward a tidal tomography abstract the deformational and gravitational response of the earth to the tide generating potential has generally involved 1 d i e depth varying earth models progressive improvement in observational constraints on body tides generated from both ground and space based surveys suggests that an examination of the potential impact of lateral variations in earth structure is warranted we present a suite of predictions of the body tide response within the semi diurnal diurnal and long period tidal bands computed using a finite volume numerical code the calculations adopt 3 d density and elastic structure taken from seismic inferences and in a subset of the calculations dynamic topography on the surface and internal interfaces we find that perturbations in the radial displacement and surface gravity within the semi diurnal band reach 1 mm and 0 15 gal respectively the perturbations in the diurnal band are comparable to these values and within the long period band they are a factor of 3 5 smaller we also demonstrate that lateral variations in the elastic moduli which have been ignored in recent work contribute greater than 50 of the total perturbation the level of perturbation associated with 3 d structure exceeds the current observational uncertainty obtainable using space geodetic methods and this suggests the possibility of performing tidal tomographic inversions of such data

tectonics and magma dynamics coupling in a dyke swarm of iceland abstract to study the dynamics of dyke and fissure swarms in iceland we analyse the distribution of the dykes across the tertiary alftafjordur dyke swarm and that of open fissures and faults across the active krafla fissure swarm within these narrow 5 to 10 km wide and long length width ratio 10 swarms deformation is accommodated both by tectonics and magmatism the dyke swarm built during the westward regional tilting of the host rock lava pile the populations of dykes suggest that a characteristic thickness at about 3 m is involved during dyking dykes show a quasi periodic distribution across the swarm and form clusters spaced by about 2 5 km the analysis of the fissure distribution in the krafla volcanic system reveals a cluster spacing of about half of that of the dyke clusters we discuss the potential origins of these features as a result of magma dynamics host rock properties and tectonics clustering possibly reflects the intrinsic mechanical response to stretching of the upper levels of the brittle crust we propose a three dimensional model of dyke swarms in which magma likely migrates laterally within the upper crust from igneous centres where high magmatic supply rates locally perturb the regional stress field

pahoehoe and aa in hawaii volumetric flow rate controls the lava structure the historical records of kilauea and mauna loa volcanoes reveal that the rough surfaced variety of basalt lava called aa forms when lava flows at a high volumetric rate 5 10 m3 s and the smooth surfaced variety called pahoehoe forms at a low volumetric rate 5 10 m3 s this relationship is well illustrated by the 1983 1990 and 1969 1974 eruptions of kilauea and the recent eruptions of mauna loa it is also illustrated by the eruptions that produced the remarkable paired flows of mauna loa in which aa formed during an initial short period of high discharge rate associated with high fountaining and was followed by the eruption of pahoehoe over a sustained period at a low discharge rate with little or no fountaining the finest examples of paired lava flows are those of 1859 and 1880 1881 we attribute aa formation to rapid and concentrated flow in open channels there rapid heat loss causes an increase in viscosity to a threshold value that varies depending on the actual flow velocity at which when surface crust is torn by differential flow the underlying lava is unable to move sufficiently fast to heal the tear we attribute pahoehoe formation to the flowage of lava at a low volumetric rate commonly in tubes that minimize heat loss flow units of pahoehoe are small usually 1 m thick move slowly develop a chilled skin and become virtually static before the viscosity has risen to the threshold value we infer that the high discharge rate eruptions that generate aa flows result from the rapid emptying of major or subsidiary magma chambers rapid near surface vesiculation of gas rich magma leads to eruptions with high discharge rates high lava fountains and fast moving channelized flows we also infer that long periods of sustained flow at a low discharge rate which favor pahoehoe result from the development of a free and unimpeded pathway from the deep plumbing system of the volcano and the separation of gases from the magma before eruption achievement of this condition requires one or more episodes of rapid magma excursion through the rift zone to establish a stable magma pathway

formation of oskjuvatn caldera at askja north iceland mechanism of caldera collapse and implications for the lateral flow hypothesis the oskjuvatn caldera at askja volcano north iceland was formed as a result of an explosive eruption at askja on 28th 29th march 1875 oskjuvatn is one of the youngest collapse calderas on earth and its initiation and growth were observed and documented by explorers and geologists working in the askja region between 1875 and 1932 it is an example of caldera formation where the volume of the caldera collapse far exceeds the volume of associated erupted products the discrepancy between the collapse volume and associated erupted products has been used by previous workers as a justification for the hypothesis that the injection of lateral dykes from askja fed the february to october 1875 n jahraun fissure eruptions at the sveinagja graben some 60 km north of askja however historical accounts documenting the caldera formation in sufficient detail show clearly that oskjuvatn formed by piecemeal collapse taking over 40 years to reach its current form we use these accounts to undertake a detailed examination of the stages of caldera collapse and to compare them with the known magmatic output of askja in the years following the 1875 eruption arcgis software was used to calculate the volume of oskjuvatn during the various stages of collapse and the volume of material erupted after 1875 while a dyke extending between askja and sveinagja may be implied to account for the missing volume our results demonstrate that the volume of oskjuvatn in july 1875 closely corresponds to the volume of rhyolitic material erupted on 28th 29th march 1875 in addition geochemical evidence indicates that the n jahraun magmas were sourced from a deeper reservoir rather than by lateral injection from askja s shallow crustal magma chamber we therefore suggest that the injection of sills and dykes in a coherent intrusion complex beneath askja central volcano combined with background deflation of the magma storage zone beneath oskjuvatn caldera over 30 to 40 years following 1875 satisfactorily accommodates the volume required to form oskjuvatn caldera

pre eruption history of phyric basalts from dsdp legs 45 and 46 evidence from morphology and zoning patterns in plagioclase phyric basalts recovered from dsdp legs 45 and 46 contain abundant plagioclase phenocrysts which occur as either discrete single grains megacrysts or aggregates glomerocrysts and which are too abundant and too anorthitic to have crystallized from a liquid with the observed bulk rock composition almost all the plagioclase crystals are complexly zoned in most cases two abrupt and relatively large compositional changes associated with continuous internal morphologic boundaries divide the plagioclase crystals into three parts core mantle and rim the cores exhibit two major types of morphology tabular with a euhedral to slightly rounded outline or a skeletal inner core wrapped by a slightly rounded homogeneous outer core the mantle region is characterized by a zoning pattern composed of one to several spikes plateaus superimposed on a gently zoned base line with one large plateau always at the outside of the mantle and by in most cases a rounded internal morphology the inner rim is typically oscillatory zoned the width of the outer rim can be correlated with the position of the individual crystal in the basalt pillow the presence of a skeletal inner core and the concentration of glass inclusions in low an zones in the mantle region suggest that the liquid in which these parts of the crystals were growing was undercooled some amount the resorption features at the outer margins of low an zones indicate superheating of the liquid with respect to the crystal

architecture and emplacement of flood basalt flow fields case studies from the columbia river basalt group nw usa the physical features and morphologies of collections of lava bodies emplaced during single eruptions known as flow fields can be used to understand flood basalt emplacement mechanisms characteristics and internal features of lava lobes and whole flow field morphologies result from the forward propagation radial spread and cooling of individual lobes and are used as a tool to understand the architecture of extensive flood basalt lavas the features of three flood basalt flow fields from the columbia river basalt group are presented including the palouse falls flow field a small 8 890 km2 190 km3 unit by common flood basalt proportions and visualized in three dimensions the architecture of the palouse falls flow field is compared to the complex ginkgo and more extensive sand hollow flow fields to investigate the degree to which simple emplacement models represent the style as well as the spatial and temporal developments of flow fields evidence from each flow field supports emplacement by inflation as the predominant mechanism producing thick lobes inflation enables existing lobes to transmit lava to form new lobes thus extending the advance and spread of lava flow fields minimum emplacement timescales calculated for each flow field are 19 3 years for palouse falls 8 3 years for ginkgo and 16 9 years for sand hollow simple flow fields can be traced from vent to distal areas and an emplacement sequence visualized but those with multiple layered lobes present a degree of complexity that make lava pathways and emplacement sequences more difficult to identify

field characteristics of laterally emplaced dikes anatomy of an exhumed miocene dike swarm in reydarfjordur eastern iceland abstract many dikes of the tertiary breiddalur dike swarm in reydarfjordur have a great lateral extent but are vertically upward and or downward discontinuous field relationships indicate that they are not the feeders of the lava pile they intrude their characteristics can be best interpreted as them constituting the fossil expression of lateral magma emplacement analogous to that occurring in the actively spreading krafla volcanic center of the neovolcanic zone average dike thickness increases clearly with depth and the thickness versus depth relationship is different from that described for other tertiary dike swarms in eastern iceland it is suggested that dikes represent the extent of finite spreading which at higher levels in the crust is expressed by fissures and other extensional structures

numerical simulation of plagioclase rim growth during magma ascent at bezymianny volcano kamchatka abstract slow caal nasi interdiffusion in plagioclase crystals preserves chemical zoning of plagioclase in detail which along with strong dependence of anorthite content in plagioclase on melt composition pressure and temperature make this mineral an important source of information on magma processes a numerical model of zoned crystal growth is developed in the paper the model is based on equations of multicomponent diffusion with diagonal cross component diffusion terms and accounts for mass conservation on the melt crystal interface and growth rate controlled by undercooling the model is applied to the data of plagioclase rim zoning from several recent bezymianny volcano kamchatka eruptions we show that an equilibrium growth model cannot explain crystallization of naturally observed plagioclase during magma ascent the developed non equilibrium model reproduced natural plagioclase zoning and allowed magma ascent rates to be constrained matching of natural and simulated zoning suggests ascent from 100 to 50 mpa during 15 20 days magma ascent rate from 50 mpa to the surface varies from eruption to eruption plagioclase zoning from the december 2006 eruption suggests ascent to the surface in less than 1 day whereas plagioclase zoning from march 2000 and may 2007 eruptions are better explained by magma ascent over periods of more than 30 days based on comparison of diffusion coefficients for individual elements a mechanism of atomic diffusion during plagioclase crystallization is proposed

tides for a convective earth in this paper we give values of the tidal gravimetric factor as well as of the love numbers for the tidal surface displacement and for the tidal mass redistribution potential that are consistent with the presently adopted definitions we present analytical expressions for these quantities and compute numerical values for two rotating nonspherical earth models in the first model the earth is everywhere in hydrostatic equilibrium and the inner core and mantle are both elastic in the second model the earth is ellipsoidal with an inelastic mantle and with a nonhydrostatic initial state for which the effects of mantle convection and its associated boundary deformations are considered this latter model is constrained to reproduce the observed free core nutation period and global earth dynamical flattening

large cretaceous sphenodontian from patagonia provides insight into lepidosaur evolution in gondwana sphenodontian reptiles successfully radiated during triassic and jurassic times but were driven almost to extinction during the cretaceous period1 the sparse early cretaceous record of sphenodontians has been interpreted as reflecting the decline of the group in favour of lizards their suspected ecological successors2 however recent discoveries in late cretaceous beds in patagonia partially modify this interpretation numerous skeletons of a new sphenodontian priosphenodon avelasi gen et sp nov were collected from a single locality in the cenomanian turonian candeleros formation where it is more abundant than any other tetrapod group recorded in the quarry for example crocodyliformes serpentes dinosauria and mammalia 3 4 adult specimens of priosphenodon reached one metre in length larger than any previously known terrestrial sphenodontian here we propose using available evidence that sphenodontians were not a minor component of the cretaceous terrestrial ecosystems of south america and that their ecological replacement by squamates was delayed until the early tertiary the new discovery helps to bridge the considerable gap in the fossil record around 120 million years that separates the early cretaceous sphenodontians5 6 7 from their living relatives sphenodon

the effects of shape on crystal settling and on the rheology of magmas the effects of the shape of phenocrysts on their settling velocity and on the rheology of magmas are discussed spherical crystals fall at a velocity given by stokes law and need to be present in large concentrations before they have a marked effect on the viscosity of a suspension elongate crystals fall at a much smaller velocity which may be determined from the formulas and graphs given herein such elongate crystals can have a dramatic effect on the viscosity of a suspension even at low volume fractions suspended crystals and bubbles will not impart a yield stress to the magma unless they form a touching network across the entire suspension it is suggested therefore that most previous inferences of a yield stress in subliquidus magmas are erroneous measurements of the subliquidus rheology of magmas need to be accompanied by careful characterization of the microstructure and distribution of the solid phase on which such rheologies critically depend

the mode of emplacement of neogene flood basalts in eastern iceland the plagioclase ultraphyric basalts in the graenavatn group abstract plagioclase ultraphyric basalt lava with high fraction of solids have a mode of emplacement that is poorly understood in this study we conduct detailed mapping of a pub group in eastern iceland namely the graenavatn group and assess the group architecture flow morphology and internal structure with additional constraints from petrography petrology and crystal size distribution to derive information on emplacement dynamics of plagioclase ultraphyric basalts we also derive information on the plumbing system of the group with reference to the source of the macrocysts the group is exposed in steep glacially carved fjords and can be traced for more than 70 km along strike the flows have mixed architecture of simple and compound flows individual flow lobes have thicknesses in the range of 1 24 m and many reach widths and lengths exceeding 1000 m the flows vary from rubbly to slabby pahoehoe but are predominantly of pahoehoe type the aspect ratio of the group and the nature of the flows indicate fissure fed eruptions the plagioclase macrocrysts 5 30 mm are an rich exhibit bimodal size distribution and the modal proportions within the group varies from 15 40 clinopyroxene macrocrysts are also present ranging from 1 6 the lowermost flow is thickest and carries the greatest crystal cargo load the morphology of the lava flows suggests low viscous behavior at odds with the high crystal content the very calcic plagioclase macrocrysts an80 85 are in disequilibrium with the groundmass and plagioclase microlaths therein an50 70 meaning that the crystal laden magmas quickly ascended from deeper crustal levels to the surface the flows with highest crystal content may have maintained high temperatures by heat exchange with the primitive macrocrysts in the flows and developed non newtonian behavior such as shear thinning such conditions would have enabled the flows to advance rapidly during episodes with high effusion rates forming the simple flows and subsequently maintained by insulated lobe by lobe emplacement occasionally surges disrupted the crust to form rubbly and slabby pahoehoe a herschel bulkley model is applied to the flows yielding effusion rates in the order of 103 104 m 3 s for the largest eruptions variation in crystal proportions within the group and individual flows is considered to be the result of magmas penetrating a crystal mush followed by disaggregation and mobilization sorting by flotation mixing of magma batches and transportation of heterogeneous crystal laden magmas to the surface with opportunities for staging en route

validation of ocean tide models around antarctica using onshore gps and gravity data 1 ocean tide models around antarctica are presently only sparsely tested against independent data ocean tide modeling errors along with subsequent ocean tide loading otl displacement modeling errors alias into altimetry and time variable gravity e g gravity recovery and climate experiment grace time series for example to validate various ocean tide models around antarctica gps data from 15 sites have been used to derive three dimensional displacement estimates at eight diurnal and semidiurnal tidal frequencies using hundreds of days of gps data harmonic parameters were estimated on a daily basis then combined these were then compared with otl displacement estimates derived from global and regional ocean tide models in east antarctica where the tides are well defined submillimeter differences are demonstrated in each coordinate component with the lunar n2 and q1 constituents in closest agreement as found in other studies k1 and especially k2 agree less well the spatial variation in the misfits for these two constituents indicates a site dependency with the k2 errors also suggesting an interaction with satellite dependent effects in west antarctica where sites are nearer the largest ice shelves agreement with the older models csr3 and tpxo 2 and nao 99b is poor for all constituents modeled tidal gravity variations were also compared with gravity measurements at the south pole overall the gps and gravity data agree best with newer tide models namely tpxo 6 cada00 10 fes99 and cats02 01 however validation data are lacking at the southern extents of the large ice shelves and hence some uncertainty still exists in all ocean tide models in these regions

using quantitative textural analysis to understand the emplacement of shallow level rhyolitic laccoliths a case study from the halle volcanic complex germany received february 1 2002 accepted november 8 2002in qualitatively homogeneous magmatic bodies quantitativetextural analysis such as crystal size distribution modalabundance and spatial distribution pattern analyses allowstheir internal heterogeneity to be measured and interpreted inthis study these methods are applied to samples from a 300mdrill core through one of the porphyritic rhyolitic laccoliths petersberg unit of the 300ma halle volcanic complex germany qualitatively thegeochemicallyhomogeneouspetersbergunit does not show much textural variation quantitatively however the crystal size distributions of the three most commonphenocryst phases orthoclase plagioclase and quartz suggestcontinuouscrystalgrowthduringmagmaascentandemplacement but different growth histories of the phenocryst phases throughoutthe genesis of the laccolith in situ cooling did not affect thephenocryst population size distributions of the phenocrysts varyon a centimetre to decimetre scale but are similar on the scale ofthe laccolith the modal abundance of the phenocryst phases isvery similar throughout the drill core quantification of thespatial distribution of phenocrysts however reveals a trend forclusteringtowardstheinteriororupperpartofthelaccolith whichis attributed to flow and shear processes during emplacement anddiscontinuities in the interior relating to the intrusion of differentmagmapulses circularstatisticsoftheorientationoflongaxesofcrystals reveala weakalignment oftheorthoclaseand plagioclasephenocrystsonthesamplescaleasaresultofflowinthemagmainspite of little acicularity in general laccoliths can be fedby several pulses of magma without major cooling betweenbatches

effusion rate trends at etna and krafla and their implications for eruptive mechanisms abstract using effusion rates obtained from ground and satellite based data we build a data set of 381 effusion rate measurements during effusive activity at etna and krafla between 1980 and 1999 this allows us to construct detailed effusion rate curves for six fissure fed eruptions at etna and krafla and four summit fed eruptions at etna these define two trends type i and ii type i trends have effusion rates that rise rapidly to an initial peak before declining more slowly resulting in an exponential decrease in eruption rate and declining growth in cumulative volume type ii trends are characterised by steady effusion and eruption rates and hence a linear increase in cumulative volume the former is typical of fissure eruptions and can be explained by tapping of an enclosed pressurised system the latter are typical of persistent etnean summit eruptions plus one persistent effusive eruption at stromboli 1985 1986 examined here and can be explained by overflow of the time averaged magma supply we use our effusion rate data to assess the magma balance at etna 1980 1995 and krafla 1975 1984 between 1980 and 1995 etna was supplied at a time averaged rate of 6 8 2 3 m 3 s 1 of which 13 was erupted at krafla 817 30 10 6 m 3 was erupted and intruded during 1975 1984 and the ratio of erupted to intruded volume was 0 3 at etna there is evidence for intrusion of the unerupted magma within and beneath the edifice as well as storage in the central magma column at krafla unerupted magma was intruded into a rift zone but an increasing proportion of the supply was erupted from 1980 onwards a result of the rift zone capacity being reached magma intruded prior to an eruptive event may also be entrained and or pushed out during eruption to contribute to the initial high effusion rate phases of type i events the detail in our effusion rate curves was only possible using a thermal approach which estimates effusion rates using satellite data we look forward to analysing satellite derived effusion rate trends in real time using data from current and soon to be launched sensors

magnetostratigrahy of the exposed lava section east of the irdp drill hole in reydarfjordur eastern iceland magnetic polarity directions vgp of 154 exposed miocene basalt lavas from reydarfjordur eastern iceland can be used successfully for correlation with the irdp drill core three partly synchronous lava sections east of the drill site are predominantly normally magnetized and are stratigraphically of the same age as lavas dated k ar at about 9 to 10 5 m y mcdougall et al 1976 the age range and magnetic properties of these lavas the landward equivalents to marine magnetic anomaly 5 epoch 9 suggest that several reversely magnetized lavas in one of the investigated sections were remagnetized by a 10 m thick dyke the data presented suggest that in fresh lavas with low curie temperatures relatively thick dykes about 10 m may cause thermal overprinting of the host rocks to a distance from the dyke equal to its thickness these results are in contrast with the generally accepted thesis that dykes affect host rocks only up to about 1 5 of their thickness no systematic decrease in magnetic intensity with depth was observed for a 0 9 km thick vertical lava section in holmatindur about 13 5 km east of the drill site it is suggested that the heterogeneity of the lava pile in terms of magnetic intensity reflects primarily the distinct geochemistry and or grain size of magnetic phases of individual lavas

rheological properties of basaltic lavas at sub liquidus temperatures laboratory and field measurements on lavas from mount etna models of many magmatic processes require accurate data on the rheological properties of lava at sub liquidus temperatures laboratory measurements of the rheological properties of basalts erupted on mount etna in 1983 were made at various crystal concentrations in a specially designed furnace using a haake rotovisco viscometer attached to a spindle designed to eliminate slippage at the melt spindle interface measurements were made at strain rates between 0 3 and 5 s 1 over the range of eruption temperatures on mount etna 1084 1125 c at temperatures above 1120 c the 1983 lava behaves as a newtonian fluid at lower temperatures the lava is a thixotropic pseudoplastic fluid with a maximum yield strength of 78 pa at a temperature of 1087 c in view of its low yield strength over this temperature range the theological behaviour of the lava approximates to that of a power law fluid apparent viscosities at unit shear strain rates increase from 150 pa s at 1125 c to 3000 pa s at 1084 c unit strain rate apparent viscosities measured in the field using a rotating vane viscometer range from 1385 pa s to 1630 pa s these values are in close agreement with those measured at the same temperature in the laboratory and with those calculated theoretically from the physico chemical properties of the lava

a model for the rheology of particle bearing suspensions and partially molten rocks an edited version of this paper was published by agu copyright 2009 american geophysical union

stratigraphy and correlation of the region surrounding the irdp drill hole 1978 reydarfjordur eastern iceland the 1 9 km thick sequence intersected by the irdp 1978 drill hole at reydarfjordur eastern iceland is correlated with the westward dipping exposed volcanic pile on the basis of extensive field mapping and paleomagnetic studies the base of the landward extension of sea floor magnetic anomaly 5 epoch 9 can be located at the top of the grjota olivine tholeiite formation intersected at about 1 5 km in the core and exposed at sea level about 9 km east of the drill site other exposed marker formations can also be identified in the core the drill site is located within a relatively dense dyke swarm 10 crustal dilation previously interpreted as the feeder of the overlying volcanic formations field observations including vertically discontinuous dykes and the lack of lava feeder relationships suggest that the dykes were intruded by lateral injection from the south and are considerably younger than and thus could not have fed the exposed lava pile in the vicinity of the drill site it is proposed that about 10 3 m y ago roughly coinciding with the lower boundary of anomaly 5 the reydarfjordur volcanic center ceased to be active and volcanic activity shifted about 20 km to the west where the breiddalur and thingmuli volcanic centers later developed the exposed stratigraphic succession between thingmuli and reydarfjordur volcanic centers is composed of lavas deposited in flank areas relatively removed from a paleovolcanic zone which now probably lies buried to the west of the irdp drill site the lowest 450 m of the core may represent lavas related to activity in the reydarfjordur volcanic center 13 5 km to the east

nloadf a program for computing ocean tide loading the loading of the earth by the ocean tides produces several kinds of signals which can be measured by geodetic technique in order to compute these most accurately a combination of global and local models of the ocean tides may be needed the program nloadf convolves the green functions for loading with ocean tide models using a station centered grid with fixed dimensions making it easy to combine different ocean models without overlap in the convolution the program computes all the quantities of interest gravity displacement tilt and strain and includes the case where measurements are made beneath the surface of the ocean

precise comparisons of bottom pressure and altimetric ocean tides 1 a new set of pelagic tide determinations is constructed from seafloor pressure measurements obtained at 151 sites in the deep ocean to maximize precision of estimated tides only stations with long time series are used median time series length is 567 days geographical coverage is considerably improved by use of the international tsunami network but coverage in the indian ocean and south pacific is still weak as a tool for assessing global ocean tide models the data set is considerably more reliable than older data sets the root mean square difference with a recent altimetric tide model is approximately 5 mm for the m2 constituent precision is sufficiently high to allow secondary effects in altimetric and bottom pressure tide differences to be studied the atmospheric tide in bottom pressure is clearly detected at the s1 s2 and t2 frequencies the altimetric tide model is improved if satellite altimetry is corrected for crustal loading by the atmospheric tide models of the solid body tide can also be constrained the free core nutation effect in the k1 love number is easily detected but the overall estimates are not as accurate as a recent determination with very long baseline interferometry

analysis of tidal signals in surface displacement measured by a dense continuous gps array abstract we analyze the tidal displacement signals for the eight major diurnal and semidiurnal tides from global positioning system gps measurements made at the western united states over the past 16 years with 1075 independent stations by careful examinations among inland versus coastal gps data we are able to demonstrate that estimated precisions down to the level of 0 1 mm horizontal and 0 3 mm vertical have been reached for the tidal signals and that at such precisions coherent spatial patterns are revealed in the residual tidal amplitudes and phases after the removal of a priori modeled effects of body tides and ocean tidal loading otl we demonstrate the facility of modern precise gps data in not only constraining the ocean tide models but more significantly in providing source data in terms of regional complex love numbers for geophysical inference of the heterogeneities of elastic and inelastic structures in the solid earth s deep interior on tidal timescales

the rheology of crystal bearing basaltic magmas from stromboli and etna abstract our ability to forecast volcanic hazards at active volcanoes stems from our knowledge of parameters affecting eruption dynamics persistent activity displayed by basaltic volcanic systems such as etna and stromboli is governed mainly by the textural evolution and rheological properties of eruptive products here we investigate the high temperature 1131 c

troposphere mapping functions for gps and very long baseline interferometry from european centre for medium range weather forecasts operational analysis data 1 in the analyses of geodetic very long baseline interferometry vlbi and gps data the analytic form used for mapping of the atmosphere delay from zenith to the line of site is most often a three parameter continued fraction in 1 sin elevation using the 40 years reanalysis era 40 data of the european centre for medium range weather forecasts for the year 2001 the b and c coefficients of the continued fraction form for the hydrostatic mapping functions have been redetermined unlike previous mapping functions based on data from numerical weather models isobaric mapping functions niell 2000 and vienna mapping functions vmf boehm and schuh 2004 the new c coefficients are dependent on the day of the year and unlike the niell mapping functions niell 1996 they are no longer symmetric with respect to the equator apart from the opposite phase for the two hemispheres compared to vmf this causes an effect on the vlbi or gps station heights that is constant and as large as 2 mm at the equator and that varies seasonally between 4 mm and 0 mm at the poles the updated vmf based on these new coefficients and called vmf1 hereinafter yields slightly better baseline length repeatabilities for vlbi data the hydrostatic and wet mapping functions are applied in various combinations with different kinds of a priori zenith delays in the analyses of all vlbi international vlbi service for geodesy and astrometry ivs r1 and ivs r4 24 hour sessions of 2002 and 2003 the investigations concentrate on baseline length repeatabilities as well as on absolute changes of station heights

ocean tide loading displacements in western europe 2 gps observed anelastic dispersion in the asthenosphere gps observed vertical ocean tide loading displacements show in cornwall southwest england and in brittany northwest france discrepancies of 2 3 mm with predicted values based on the isotropic preliminary reference earth model for the main tidal harmonic m2 yet in central europe the agreement is better than 0 5 mm by comparison of ocean tide models and validation with tide gauge observations we demonstrate that the uncertainties in the former are too small to cause this disagreement furthermore we find that different local models of the crust and different global elastic reference models derived from seismological observations can only reduce the observed discrepancies to 1 2 mm which still exceeds the gps observational uncertainty of 0 2 0 4 mm it is customary to use the elastic properties of the earth as given by seismic models previously there has been insufficient evidence to determine how to modify these properties during the transformation from seismic to tidal frequencies to account for possible anelastic dispersion in the asthenosphere and so this effect has been ignored if we include this effect then our discrepancies reduce further to 0 2 0 4 mm this value is of the same order as the sum of the remaining errors due to uncertainties in the ocean tide models and in the gps observations themselves this research provides evidence in western europe of a reduction of around 8 10 of the seismic shear modulus in the asthenosphere at tidal frequencies in addition we find that the asthenosphere absorption band frequencies can be represented by a constant quality factor q

emplacement of dikes sills and crustal magma chambers at divergent plate boundaries abstract a model of dike emplacement at divergent plate boundaries is developed which predicts that below the uppermost 1 3 km of the oceanic crust the number and lengths of dikes in any particular swarm should increase but that the thickness should decrease with depth in the crust these predictions are supported by field observations it is proposed that rapid injections of dikes at divergent plate boundaries may temporarily alter the normal stress field in such a way that at a certain level in the crust subsequent dikes change into sills such sills may develop into crustal magma chambers either when many nearby sills combine into a large one or when an initial sill absorbs the magma of many dikes that enter it in a rapid succession while the sill is liquid for the fastest spreading ridges the initial thickness of a sill that is to develop into a crustal chamber need only attain 20 m whereas at the slowest spreading ridges the initial thickness must exceed 170 m because thin sills are much more likely to form than thick sills the probability of sills developing into crustal chambers increases with dike intrusion frequency hence with spreading rate furthermore the model predicts first that with increasing spreading rate the length of the chamber along the ridge axis should increase and second that the most likely site for magma chambers is at depths of 2 4 km both these predictions are supported by available data

ocean tide loading displacements in western europe 1 validation of kinematic gps estimates gps has been extensively used to estimate tidal ground displacements but the accuracy of this has not been systematically verified using more than 20 sites distributed across western europe we show that postprocessed kinematic precise point positioning gps with appropriately tuned process noise constraints is capable of recovering synthetic tidal displacements inserted into real data with a typical accuracy of 0 2 mm depending on the time series noise the kinematic method does not result in erroneous propagation of signals from one coordinate component to another or to the simultaneously estimated tropospheric delay parameters it is robust to the likely effects of day to day equipment and reference frame changes and to outages in the data a minimum data span of 4 years with at least 70 availability is recommended finally we show that the method of reducing apparent coordinate time series noise by constraining the tropospheric delay to values previously estimated in static batch gps analysis in fact results in the suppression of true tidal signals using our kinematic gps analysis approach periodic displacements can be reliably observed at the 0 2 mm level which is suitable for the testing and refinement of ocean tide and solid earth response models

eocene volcanism in offshore southern baffin bay new data are presented on the offshore part of the west greenland volcanic succession part of the north atlantic igneous province located in southern baffin bay the data were obtained from the delta 1 hydrocarbon exploration well drilled by cairn energy in 2011 wireline log data were collected over the drilled section providing information on the physical volcanology of the volcanic succession and 23 sidewall cores were analysed for their geochemical composition the well encountered 65 lava flows with a well developed core and crust signature typical for sub aerial eruptions major and trace element data showed a good correlation with parts of the succession onshore west greenland the xrf major and trace element data allowed careful picking of samples for 40ar 39ar dating and the main part of the sequence was found to be early eocene in age this coincides with the second main phase of volcanism in onshore west greenland and is likely to be linked to the change in the tectonic regime in baffin bay at this time this finding substantially expands the area of west greenland affected by volcanism during the eocene

high resolution chronostratigraphy of the cerro barcino formation patagonia paleobiologic implications for the mid cretaceous dinosaur rich fauna of south america abstract the cretaceous cerro barcino formation chubut group of central patagonia argentina has yielded a remarkable fossil vertebrate fauna which form important components of the south american mid cretaceous fauna including titanosauriform sauropod dinosaurs theropod dinosaurs crocodyliforms turtles and lepidosauromorphs however a lack of robust chronostratigraphic framework for its fossil occurrences has so far hampered a full realization of their paleobiologic significance this contribution presents new stratigraphic sedimentologic and u pb isotopic age data from 11 localities throughout the patagonian somuncura canadon asfalto basin and analyzes the evolutionary characteristics of the cerro barcino fauna within the biostratigraphic context of the cretaceous of gondwana four new high precision 206pb 238u zircon dates by the ca id tims method range from 118 497 0 063 ma to 98 466 0 048 ma 2 internal errors and limits the puesto la paloma cerro castano and las plumas members of the cerro barcino formation largely to the aptian albian and cenomanian stages of the cretaceous respectively accordingly the majority of the cerro barcino vertebrates fall within a 118 110 ma time interval in the latest early cretaceous which makes them the oldest documented component of the mid cretaceous faunal assemblage of gondwana paleobiologic analyses of the latter assemblage suggests a 10 m y period of faunistic stability characterized by only minor evolutionary novelties or faunal turnovers

relationship between plagioclase crystallization and cooling rate in basaltic melts rock textures commonly preserve a record of the near surface crystallization history of volcanic rocks under conditions of simple cooling without convection or mixing textures will reflect sample cooling rate the temperature at which crystallization was initiated and the distribution of mineral phase precipitation across the crystallization interval compilation of plagioclase size and number density data on natural dike sill and lava lake and experimental samples suggests that 1 growth and nucleation rates of plagioclase in natural basaltic samples are a predictable function of cooling rate and 2 the observed crystallization rate dependence on cooling rate is similar to that observed in experiments initiated at subliquidus temperatures comparison of natural and experimental samples thus suggests that most basalts crystallize under conditions of heterogeneous nucleation with the number density of preexisting nucleii partially controlling textural responses to cooling rate changes time scales of crystallization and cooling in magmatic systems are intimately linked through a balance between heat removal from the system and heat evolved through crystallization evaluation of textural data in the context of recent numerical models of crystallization in simple one and two component systems provides new insight into regularities in the crystallization behavior of basaltic magmas for example the rate of change in crystal size and number density as dictated by mass balance has been used as a measure of the relative importance of time scales of crystallization and cooling in numerical models of crystallizing systems in natural samples plagioclase size scales with the length scale of cooling such that a logarithmic plot of grain size as a function of normalized distance across the dike has a slope that appears approximately independent of dike width solidification time comparison with available textural data for other phenocryst phases suggests that the same may be true for pyroxene and magnetite crystallization with each phase having a characteristic slope probably controlled by the thermodynamic properties of the crystallizing phase measured crystal size distributions are unimodal and show maximum frequencies in the smaller size classes distributions broaden and the grain size at peak frequency increases with increasing crystallization times decreasing cooling rates in contrast partially crystallized makaopuhi lava lake samples have crystal size distributions that decrease exponentially with increasing crystal size measured size distributions in dikes can be explained by late stage modification of makaopuhi type distributions through loss of small crystals possibly the consequence of growth without nucleation finally this compilation of the textural response of basaltic magmas to changes in cooling rate suggests that empirical calibrations of crystallization rate dependence on cooling rate from natural samples provide a reasonable model for plagioclase crystallization in near surface basaltic systems predicted growth rates will be slow and relatively constant 10 10 10 11 cm s for crystallization times expected in most shallow volcanic systems 1000 years

low pressure phase equilibria of anhydrous anorthite bearing mafic magmas 1 one of the most persistent questions regarding the phase equilibria of mid ocean ridge basalts morb pertains to the petrogenesis of the anorthitic plagioclase phenocrysts an90 that are characteristic of the more primitive members of such suites anorthitic phenocrysts are present in many if not most morb suites in spite of the fact that no naturally occurring morb glasses have ever been discovered to be in equilibrium with plagioclase more calcic than an85 we have addressed this paradox by attempting to saturate natural basalts with anorthite in a series of 1 atm experiments using three different natural basaltic starting compositions an n morb an e morb and a continental high alumina basalt to ensure duplication of the olivine and anorthite saturation observed in natural anorthite bearing basalt the experiments were run in an93 6 capsules with fo92 olivine added to the starting glass the compositions of experimental liquids are generally colinear with the trends observed in the lava suites used as the source material for the starting glasses significantly aluminous spinel al2o3 contents of 61 68 wt was produced at 1290 c in all compositions and chromites al2o3 contents of 33 42 wt at lower temperatures in n morb derived liquids despite no spinel having been added to the starting mixture in addition the experiments produced basaltic liquid in equilibrium with both fo89 olivine and an85 feldspar at temperatures of 1230 and 1210 these liquids have compositions with mg at mg mg fet 100 that range from 63 to 85 the tio2 mgo correlation indicates large 16 23 amounts of crystallization for each percent decrease in mgo these results suggest the possibility that dry anorthite bearing basaltic magmas are the product of the interaction between primary melt and al spinel bearing upper mantle in addition the results indicate that morb magmas can undergo a large amount 50 of crystallization prior to reaching 8 mgo further although anorthite bearing magmas have characteristics consistent with their being a significant volumetric component of morb parent magmas the reaction mechanism suggested for their petrogenesis indicates that they are not necessarily primary magmas

formation of dykes feeder dykes and the intrusion of dykes from magma chambers the paper discussed the formation of dykes and applies the results to iceland it is postulated that dykes follow the pathway of least work and of least tensile strength and thereby intrude the subvertical joints in lava flows it is suggested that dykes form in magma pulses where each dyke is split in two by the next magma pulse and so on in iceland the estimated time between successive magma pulses is of the order of several hundred days statistical considerations indicate that in iceland the probability of seeing dykes end upwards is only 1 2 which agrees with observations it is concluded that many and probably the majority of dykes are non feeders this together with the low probability of finding the connection between feeder and lava flow explains the scarcity of observed feeder dykes it is concluded that overpressure in shallow magma chambers needed to drive magma through crustal fractures in iceland is usually smaller than the tensile strength of the host rock several mpa which thereby is the critical factor in dyke intrusion

an integrated field numerical approach to assess slope stability hazards at volcanoes the example of pacaya guatemala pacaya is an active stratovolcano located 30 km south of guatemala city guatemala a large 0 65 km3 sector collapse of the volcano occurred 0 6 1 6 ka b p producing a debris avalanche that traveled 25 km sw of the edifice the current cone has since rebuilt within the scarp of this ancestral collapse the structural setting of the volcano along with two recent smaller volume collapses in 1962 and 2010 suggests gravitational instability of this volcano to assess pacaya s stability and potential for another large lateral collapse of the active cone standard engineering methodologies for studying non volcanic slopes were used to examine the sw flank of the edifice a geomechanical model was developed based on the physical mechanical material properties of pacaya s intact rocks and rock mass characteristics found through field observations and laboratory tests slope stability was analyzed in several scenarios with the limit equilibrium method lem and finite element method fem including static conditions i e under gravity forces only and considering the application of magma pressure and seismic force as triggering mechanisms for slope failure results show that the edifice remains stable under gravity alone however a large scale collapse could be triggered by reasonable ranges of magma pressure 7 7 mpa if constant along a dyke or peak ground acceleration 460 cm s2 results also suggest that a layer of pyroclastics beneath the edifice could have controlled the ancestral sector collapse structural analysis shows that a transtensional stress regime is causing a nw se orientation of aligned features at the surface and may be a controlling mechanism for the direction of a future collapse fem results are concordant with those from lem and reveal that maximum shear strain patterns within the edifice may account for long lava flows erupted from lower vent elevations

the mode of emplacement of neogene flood basalts in eastern iceland facies architecture and structure of the holmar and grjota olivine basalt groups abstract holmar and grjota are two stratigraphically distinct transitional alkaline olivine basalt lava groups within the westward dipping neogene flood basalts of eastern iceland the holmar olivine basalt group separated from the overlying grjota olivine basalt group by only a few tholeiite flows can be traced over 80 km north south with thicknesses varying from 250 m where thickest to 30 m where thinnest the grjota group can be traced over 50 km also north south reaching thicknesses of 250 m and thinning down dip to 10 m in contrast to other groups in eastern iceland that thicken down dip the studied olivine basalt groups thicken up dip the groups filled topographic confinements and formed aprons around central volcanoes we have estimated the minimum volumes to be 119 km 3 for holmar and 86 km 3 for grjota scoria cones are found in the holmar group and two thick olivine dolerite sills cross cut the holmar group and probably belong to the plumbing system that fed the grjota group the architecture of the lava groups are near identical the architecture is compound with lobes stacked horizontally and vertically varying from 1 15 m thick and 2 200 m long but do also encompass a number of thicker 15 20 m and more extensive 1 km long lava lobe in the stacks filled lava tubes are commonly observed within the lava flows the constituent lobes of the flows are often directly emplaced or welded together suggesting rapid buildup but are also found interbedded with redbeds and thicker tuff deposits and occasionally preserve tree molds the internal structure follows the characteristics for lava lobe morphology in general with an upper vesicular crust forming half to one third of the total thickness a massive core with abundant vesicle cylinders and a thin basal vesicular crust flow tops are of the pahoehoe type seldom found with scoria or clinker inflation structures such as tumuli and inflation clefts were identified in the flows the eruptions were dominantly fissure fed with a few vents evolving to short lived point source volcanism the pre existing topography exerted control on the advancement of the flows and influenced the final architecture of the groups at each location it is evident that the large and dense spatial distribution of these groups including numerous thick lava units suggests large volcanic episodes together the groups imply a period with higher production of olivine basalts in iceland and form well defined stratigraphic markers the transitional alkaline olivine basalt groups are interpreted to delineate a fossil southward propagating rift flank volcanic zone located east of a now extinct and buried mature rift zone

the tidal displacement field at earth s surface determined using global gps observations 1 we investigate the 3 d tidal displacement field on earth s surface recorded globally by 456 continuous global positioning system gps stations of igs spanning 1996 2011 for eight principal diurnal and semidiurnal tidal constituents in phase and quadrature amplitudes of the residual tidal displacements after removal of an a priori body tide model are estimated using the precise point positioning ppp technique on the daily gps data the resultant daily estimates are combined to derive final estimates for each tide at each station the results are compared with the predictions of eight recent global ocean tide models separately for coastal 307 and inland 149 stations we show that gps can provide tidal displacement estimates accurate to the level of 0 12 mm horizontal and 0 24 mm vertical for the lunar only constituents m2 n2 o1 and q1 and less favorably for solar related tidal constituents s2 k2 k1 and p1 although improved by ambiguity resolution most recent ocean tide models fit the gps estimates equally well on the global scale but do not agree well between them in certain coastal areas especially for the vertical displacements suggesting the existence of model uncertainties near shallow seas the tidal residuals for the inland stations after removing both body tides and ocean tidal loading otl furthermore show clear continental scale spatial coherence implying deficiencies of the a priori body tide modeling in catching lateral heterogeneity in elastic as well as inelastic properties in the earth s deep interior we assert that the gps tidal displacement estimates now achieve sufficient accuracy to potentially provide constraints on the earth s structure

reevaluation of vesicle distributions in basaltic lava flows a fundamental dichotomy in the study of basaltic lava flows is that observations of active flows are restricted to flow surfaces yet older flows are often exposed only in vertical cross section cross sectional exposures of an inflated basaltic sheet flow emplaced in kalapana hawaii from 1990 to 1991 provide an unusual opportunity to merge these two viewpoints permitting the development of the internal structure of the flow to be viewed in the context of its known emplacement history we demonstrate that fundamental features of the flow structure a thick upper vesicular crust that diminishes downward in overall vesicularity a dense flow interior and a thin lower vesicular zone are generated through syn emplacement cooling of upper and lower flow crusts both the inverse correlation of overall vesicularity and vesicle size and the constant relative thickness of the upper vesicular zone are unique to inflated flows and permit a reinterpretation of flows previously interpreted to be ponded rapidly emplaced identification of inflation in turn implies near horizontal paleoslopes and permits estimates of flow duration based on upper flow crust thickness

crystal size distributions csd in three dimensions insights from the 3d reconstruction of a highly porphyritic rhyolite growth histories and residence times of crystals in magmatic systems can be revealed by studying crystal sizes size distributions and shapes in this contribution serial sectioning has been employed on a sample of porphyritic rhyolite from a permo carboniferous laccolith from the halle volcanic complex germany to reconstruct the distribution of felsic phenocrysts in three dimensions in order to determine their true shapes sizes and three dimensional size distributions a model of all three phenocryst phases quartz plagioclase k feldspar with 217 crystals and a larger model containing 1599 k feldspar crystals was reconstructed in three dimensions the first model revealed a non touching framework of crystals in three dimensions suggesting that individual crystals grew freely in the melt prior to quenching of the texture however crystal shapes are complex and show large variation on a zingg diagram intermediate over long axis plotted against short over intermediate axis they often do not resemble the crystallographic shapes expected for phenocrysts growing unhindered from a melt indicating complex growth histories in contrast the three dimensional size distribution is a simple straight line with a negative slope stereologically corrected size distributions from individual sections compare well with stereologically corrected size distributions obtained previously from the same sample however crystal size distribution csd data from individual sections scatter considerably it is shown that csds can be robustly reproduced with a sampling size of greater than 200 crystals the kind of shape assumed in stereological correction of csds however has a large influence on the calculation and estimation of crystal residence times

emplacement and inflation of pahoehoe sheet flows observations and measurements of active lava flows on kilauea volcano hawaii inflated pahoehoe sheet flows have a distinctive horizontal upper surface which can be several hundred meters across and are bounded by steep monoclinal uplifts the inflated sheet flows we studied ranged from 1 to 5 m in thickness but initially propagated as thin sheets of fluid pahoehoe lava generally 20 30 cm thick individual lobes originated at outbreaks from the inflated front of a prior sheet flow lobe and initially moved rapidly away from their source velocities slowed greatly within hours due to radial spreading and to depletion of lava stored within the source flow as the outward flow velocity decreases cooling promotes rapid crustal growth at first the crust behaves plastically as pahoehoe toes form after the crust attains a thickness of 2 5 cm it behaves more rigidly and develops enough strength to retain incoming lava thus increasing the hydrostatic head at the flow front the increased hydrostatic pressure is distributed evenly through the liquid lava core of the flow resulting in uniform uplift of the entire sheet flow lobe initial uplift rates are rapid flows thicken to 1 m in 1 2 hours but rates decline sharply as crustal thickness increases and as outbreaks occur from the margins of the inflating lobe one flow reached a final thickness of nearly 4 m after 350 hr inflation data define power law curves whereas crustal cooling follows square root of time relationships the combination of data can be used to construct simple models of inflated sheet flows as the flow advances preferred pathways develop in the older portions of the liquid cored flow these pathways can evolve into lavatube systems within a few weeks formation of lava tubes results in highly efficient delivery of lava at velocities of several kilometers per hour to a flow front that may be moving 1 2 orders of magnitude slower if advance of the sheet flow is terminated the tube remains filled with lava that crystallizes in situ rather than draining to form the cave like lava tubes commonly associated with pahoehoe flows inflated sheet flows from kilauea and mauna loa are morphologically similar to some thick icelandic and submarine sheet flows suggesting a similar mechanism of emplacement the planar sheet like geometry of flood basalt flows may also result from inflation of sequentially emplaced flow lobes rather than nearly instantaneous emplacement as literal floods of lava

magma dynamics beneath kameni volcano thera greece as revealed by crystal size and shape measurements size distributions of plagioclase crystals in series of recent porphyritic dacite lavas from kameni volcano greece can be modelled by mixing two populations of crystals each with overlapping linear crystal size distributions csd termed microlites and megacrysts the magmas bearing the microlites and megacrysts started to crystallise 6 13 and 24 96 years respectively before each eruption the dates of initiation of crystallisation of the megacrysts indicate that they are left overs of earlier injections of new magma into a shallow chamber some magma remains after each eruption and continues to crystallise new magma with few or no crystals is then introduced and the microlites crystallise from the mixed magma eruption followed 6 13 years after mixing such a model would suggest that some porphyritic magmas are products of a shallow magma chamber that is never completely emptied just topped up from time to time

structure and origin by injection of lava under surface crust of tumuli lava rises lava rise pits and lava inflation clefts in hawaii tumuli are positive topographic features that are common on hawaiian pahoehoe lava flow fields particularly on shallow slopes and 75 measured examples are presented here to document the size range tumuli form by up tilting of crustal plates without any crustal shortening and are thus distinguished from pressure ridges which are up buckled by laterally directed pressure the axial or star like systems of deep clefts that characterize tumuli are defined here as lava inflation clefts their tips advanced into red hot lava and they widened as uplift proceeded and while the lava crust was thickening flat surfaced uplifts formed like tumuli by injection of lava under a surface crust were previously called pressure plateaus but lava rise is proposed instead the pits that abound among lava rises previously attributed to collapse or subsidence are generally formed because the lava around them rose and the name lava rise pit is proposed unique examples of tumuli and lava rises from which lava drained out under a surface crust 1 5 to 2 5 m thick are described from kilauea caldera these examples show that in tumuli and lava rises the crust floats on considerable bodies of fluid lava and is able to do so because of its higher vesicle content the fluid lava loses many of its gas bubbles during residence beneath the crust the bulk densities of samples from tumuli show a general downward increase the form of the density profile is consistent with the relationship that for any given crustal thickness the density of fluid lava closely matched the average density of that crust suggesting that the lava was stably density stratified it is inferred that stable stratification was regulated by out flows of the more vesicular lava fractions loss of bubbles through the lava inflation clefts and entry of injected lava at its level of neutral buoyancy below the uppermost meter the downward decrease in vesicularity closely conforms with that expected by compression of a uniform mass of gas per unit mass of lava

probing asthenospheric density temperature and elastic moduli below the western united states periodic ocean tides continually provide a cyclic load on earth s surface the response to which can be exploited to provide new insights into earth s interior structure we used geodetic observations of surface displacements induced by ocean tidal loads to constrain a depth dependent model for the crust and uppermost mantle that provides independent estimates of density and elastic moduli below the western united states and nearby offshore regions our observations require strong gradients in both density and elastic shear moduli at the top and bottom of the asthenosphere but no discrete structural discontinuity at a depth of 220 kilometers the model indicates that the asthenosphere has a low density anomaly of 50 kilograms per cubic meter a temperature anomaly of 300 c can simultaneously explain this density anomaly and inferred colocated minima in elastic moduli

the sensitivity of surface mass loading displacement response to perturbations in the elastic structure of the crust and mantle surface mass loads generate a rich spectrum of deformation responses in the solid earth that might be exploited to probe the material properties of the crust and mantle here we present a detailed examination of load induced surface displacements and their sensitivities to systematic perturbations in elastic earth structure we compute love numbers and displacement load green s functions lgfs by integrating the equations of motion for spheroidal deformation of a radially heterogeneous and self gravitating earth sensitivity kernels are derived for individual love numbers numerically using finite differences and quasi analytically using calculus of variations we then generate sensitivity kernels for displacement lgfs by systematically perturbing the preliminary reference earth model we find that displacement lgfs are most sensitive to elastic structural perturbations within 500 km depth from the surface and for short source receiver distances for separate perturbations to the shear modulus bulk modulus and density within the crust and mantle the sensitivity kernels exhibit unique patterns consistent with the possibility to constrain the parameters independently given a spatially distributed set of sufficiently accurate loading response observations the sensitivity to density structure however is generally weak in comparison to elastic structure we also examine the sensitivity of surface displacements caused by m 2 ocean tidal loading otl to systematic perturbations in the elastic moduli and density since otl induced surface displacements are load and site dependent we focus on high resolution profiles across iceland as a case study the sensitivity kernels constitute a key element in the formulation of the inverse problem with application to geodetic tomography

cretaceous tetrapod fossil record sampling and faunal turnover implications for biogeography and the rise of modern clades we use newly compiled data on global occurrences of cretaceous lepidosaurs mammals and crocodylomorphs and existing data on dinosaurs to investigate faunal turnover and fossil record heterogeneity statistically significant relationships between many clade specific fossil record sampling proxies within major continental areas e g european mammal bearing formations suggest that temporal patterns of fossil record sampling intensity of the most abundant tetrapod clades are similar to each other with a few exceptions that might reflect clade specific facies preferences or differences in worker effort especially in poorly sampled regions such as gondwana however the absence of strong statistical relationships between tetrapod sampling proxies from different continental areas suggests that there is no unified global sampling signal for terrestrial tetrapods the cretaceous witnessed substantial faunal turnover and the rise of many advanced clades that today dominate terrestrial faunas despite strong spatiotemporal heterogeneity in sampling of the cretaceous tetrapod record it is clear that this transition occurred in a spatiotemporally staggered fashion thus it cannot be attributed to a temporally localised early late cretaceous cenomanian turonian extinction event many advanced clades including eutherian mammals iguanian and gekkotan squamates and the main cryptodiran turtle crown clades first appeared or first attained high fossil diversities in asia however relatively poor sampling and dating of middle cretaceous terrestrial deposits means that hypotheses of asian rather than laurasian diversifications remain tentative differences between gondwanan and laurasian faunas became progressively greater during the cretaceous and although many gondwanan clades survived the end cretaceous extinction event these only survive to the present as relictual populations with narrow geographic ranges e g monotremes and rhynchocephalians

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

non newtonian rheological law for highly crystalline dome lavas volcanic eruption models are hampered by the lack of multiphase magmatic flow laws most rheological models estimate the viscosity of multiphase lavas via the einstein roscoe equation but this simplification cannot be used for high crystallinity and it does not consider the non newtonian strain rate dependence of viscosity we carried out parallel plate experiments on natural samples to simulate multiphase lava deformation under various stresses and strain rates multiphase lavas exhibit an important component of shear thinning and appear to invalidate the adequacy of einstein roscoe based formulations for highly crystalline lava rheology the remarkable singular dependence of viscosity on strain rate yields a novel universal rheology law at eruptive temperatures t i e log 0 993 8974 t 0 543 log our work reveals the importance of considering microcracking and viscous dissipation at very high strain rate 10 3 s 1 explaining the occurrence of seismic swarms along the conduit margins and consequently supporting plug like magma ascent models

origin of vesicle layering and double imbrication by endogenous growth in the birkett basalt flow columbia river plateau abstract the 40 m thick birkett basalt pahoehoe flow at sentinel gap in the columbia river plateau has an unusually thick 15 m upper vesicular zone this zone includes a striking layering in which the layers have contrasted vesicle abundances and sizes most layers show a reverse grading of vesicle size and abundance the layering is interpreted to have grown endogenously by the cyclic injection of vesicular lava layers under the growing top crust accommodated by uplift of that crust grading of the layers resulted from vesicle growth and ascent each injection occurred at or near the boundary between vesicular and non vesicular lava of the preceding layer and split that layer into an upper vesicular part and a lower non vesicular part critical to this interpretation are 1 a pervasive foliation and lineation defined by the parallelism of strongly flattened and elongate vesicles transects the vesicle layers obliquely and 2 the magnetic fabric the anisotropy of magnetic susceptibility is oriented similarly to the vesicle foliation and also defines a cryptic foliation in the non vesicular zone having a dip opposed to that in the layered zone these foliations are interpreted to be opposed imbrications and indicate the flow azimuth of the lava they strongly support the concept of lava growth by successive thin sill like insertions of fresh vesicular lava between hot but static and effectively solid floor and roof

development of the 1990 kalapana flow field kilauea volcano hawaii the 1990 kalapana flow field is a complex patchwork of tube fed pahoehoe flows erupted from the kupaianaha vent at a low effusion rate approximately 3 5 m3 s these flows accumulated over an 11 month period on the coastal plain of kilauea volcano where the pre eruption slope angle was less than 2 the composite field thickened by the addition of new flows to its surface as well as by inflation of these flows and flows emplaced earlier two major flow types were identified during the development of the flow field large primary flows and smaller breakouts that extruded from inflated primary flows primary flows advanced more quickly and covered new land at a much higher rate than breakouts the cumulative area covered by breakouts exceeded that of primary flows although breakouts frequently covered areas already buried by recent flows lava tubes established within primary flows were longer lived than those formed within breakouts and were often reoccupied by lava after a brief hiatus in supply tubes within breakouts were never reoccupied once the supply was interrupted during intervals of steady supply from the vent the daily areal coverage by lava in kalapana was constant whereas the forward advance of the flows was sporadic this implies that planimetric area rather than flow length provides the best indicator of effusion rate for pahoehoe flow fields that form on lowangle slopes

timing and duration of volcanism in the north atlantic igneous province implications for geodynamics and links to the iceland hotspot abstract we combine new and published 40 ar 39 ar age determinations from incremental heating experiments on whole rocks and mineral separates to assess the timing duration and distribution of volcanic activity during construction of the north atlantic igneous province we use these ages together with volume estimates of erupted magmas and their cumulates to calculate melt production rates for the early tertiary flood basalts of east greenland and the faeroes islands the lavas lie at opposite ends of the greenland iceland faeroes ridge the postulated iceland hotspot track and record volcanic activity leading up to during and following continental breakup between greenland and europe dominantly basaltic but also alkalic and picritic magmas were erupted from beneath thick continental lithosphere simultaneously at 61 ma from baffin island to the western and eastern margins of greenland to the faeroe islands and the western british isles a roughly circular area 2000 km in diameter volcanic activity was increasingly intermittent by 57 56 ma but at 56 1 0 5 ma the average melt production rate increased by more than an order of magnitude over previous levels from 3000 km 3 km of rift my coinciding with continental rifting and shallow decompressional melting of the mantle that fed subaerial volcanic activity along most of the eastern margin of greenland and its complement on the northwestern european margin offshore abnormally thick oceanic crust was produced along the line of plate separation the upper part of this crust comprises seismically imaged seaward dipping subaerially erupted lavas by 50 ma eruption rates had diminished drastically and volcanic activity had narrowed to a much restricted portion of the east greenland margin at the western end of the greenland iceland ridge that subsequently connected in an age progressive trend to present hotspot activity in southeastern iceland the startup mantle plume head and tail model with moderate excess temperature t 100 c and active upwelling best explains the time space and compositional aspects of volcanism in this province

the mode of emplacement of neogene flood basalts in eastern iceland facies architecture and structure of simple aphyric basalt groups simple flows tabular in the neogene flood basalt sections of iceland are described and their mode of emplacement assessed the flows belong to three aphyric basalt groups the kumlafell group the holmatindur group and the hjalmadalur group the groups can be traced over 50 km and originate in the brei dalur thingmuli volcanic zone the groups have flow fields that display mixed volcanic facies architecture and can be classified after dominating type morphology the kumlafell and the holmatindur groups have predominantly simple flows of p hoehoe and rubbly p hoehoe morphologies with minor compound or lobate p hoehoe flows the hjalmadalur group has simple flows of rubbly p hoehoe but also includes minor compound or lobate flows of rubble and a simple flows are most common in the distal and medial areas from the vents while more lobate flows in proximal areas the simple flows are formed by extensive sheet lobes that are several kilometers long with plane parallel contacts some reaching thicknesses of 40 m aspect ratios 0 01 they have overlapping contacts and are free of tubes and inflation structures their internal structure consists generally of a simple upper vesicular crust a dense core and a thin basal vesicular zone the brecciated flow top is formed by clinker and crustal rubble the clinker often welded or agglutinated the simple flows erupted from seemingly short lived fissures and have the characteristics of cooling limited flows we estimate the effusion rates to be 105 m3 s for the simple flows of the kumlafell and holmatindur groups and 104 m3 s for the hjalmadalur group the longest flows advanced 15 20 km from the fissures with lava streams of fast propagating flows inducing tearing and brecciation of the chilled crust compound or lobate areas appear to reflect areas of low effusion rates or the interaction of the lava with topographic barriers or wetlands resulting in chaotic flowage slowing lobes with brecciated flow tops developed into a flows the groups interdigitated with lava groups from the rey arfjor ur volcanic zone to the east and the exhumed brei dalur thingmuli volcanic zone which appear to have formed as a flank lineament parallel the main rift zone flood basalt volcanism in flank areas may support a mantle anomaly more pronounced and or perhaps more widespread in the neogene of iceland than today eruptions of simple flows have not been observed in modern times and are significant for models of crustal accretion in iceland and other large igneous provinces

splendid and seldom isolated the paleobiogeography of patagonia the idea that south america was an island continent over most of the cenozoic during which its unusual mammalian faunas evolved in isolation is outstandingly influential in biogeography although large numbers of recent fossil discoveries and related advances require that the original isolation concept be significantly modified it is still repeated in much current literature the persistence of the idea inspired us to present here an integrated paleobiogeographic account of mammals reptiles and plants from the jurassic to the paleogene of patagonia which has by far the richest fossil record on the continent all three groups show distribution patterns that are broadly consistent with south america s long separation history first from laurasia by the late jurassic then from africa and india madagascar during the late early cretaceous and finally from antarctica and australia during the early middle eocene after which isolation finally commenced we highlight areas of promising future research a

stacking global gps verticals and horizontals to solve for the fortnightly and monthly body tides implications for mantle anelasticity the availability of long term position measurements from permanent gps stations distributed around the earth makes it feasible to extract small globally coherent long period geophysical signals from the data using 11 years of daily vertical and horizontal positions from over 600 permanent gps stations worldwide we solve for the amplitude and phase of the fortnightly and monthly body tides by stacking the surface displacements against spherical harmonics and isolating the fortnightly and monthly signals in the stacks we use our solutions to help constrain the earth s anelastic properties which are not well understood within the tidal frequency band our error estimates include the effects of the following 1 random noise across the fortnightly and monthly tidal bands 2 fortnightly and monthly ocean tide model errors 3 errors in the diurnal and semidiurnal ocean tide models that alias into the fortnightly and monthly frequency bands 4 errors in the solid earth green s functions used to compute ocean tidal loading corrections and 5 leakage from gps draconitic signals at periods close to the fortnightly and monthly frequencies the mantle anelasticity coefficients we infer from our solutions are consistent with a frequency dependence of mantle q with in the range 0 1 0 3

strainmeters and tiltmeters despite steady effort over the last century continuously recording tiltmeters and strainmeters have not yet been successful except for earth tide measurements this article reviews the techniques and instrument designs that have been developed in this field the continuous measurement of true tectonic motions which have rates of 10 14 s 1 requires extremely high instrument stability but more rapid motions tides and seismic waves apart are even smaller and not much more easily detectable much past effort has been spent improving the transducers used in these instruments which usually measure small displacements the commonest choices are optical the most accurate capacitive the most sensitive and inductive the most rugged nowadays building a transducer is the easiest part a much harder task equally important to a good design is attaching the instrument to the ground so that it can detect the signal wanted this part of the design includes choosing a location a large underground opening is thermally stable but distorting a surface installation is easy to build but noisy because of soil weathering and a borehole is inaccessible to weather but also to the operator all such installations and indeed the whole field of strain and tilt measurement of course rely on the assumption that the deformations of interest can be measured over baselengths of a few hundred meters or less this is true for tides and seismic waves but unproven for tectonic motions appropriate attachment techniques differ for each location and many mundane details such as cementing techniques for borehole instruments remain to be worked out the goal of measuring tectonic and tidal tilt has created many tiltmeter designs most are relatively small instruments that use some form of pendulum or bubble level a few use a liquid surface to measure tilts over a long baseline repeated experience has shown the latter type when well built to be superior to the former proving end monument motions to be a dominant source of noise the same appears to hold true for strainmeters the best results coming from long base laser instruments though strainmeters using rigid or flexible material length standards are useful for special purposes and borehole instruments show promise because achieving a good design has been so difficult it is important to select the goals an instrument must meet and be prepared to compromise on others the difficulty of validating results from this type of instrument makes comparison tests essential such tests as have been made so far show that good results cannot be gotten at low cost or without careful attention to details

plagioclase ultraphyric basalts of the galapagos archipelago abstract basalts containing as much as 50 plagioclase phenocrysts that attain lengths of several centimeters are common on the northern islands of the galapagos archipelago mineralogic and geochemical evidence requires that the large anorthitic phenocrysts nucleated and grew from a less evolved magma than that in which they were erupted we suggest that plagioclase ultraphyric basalts pubs form when a buoyant phenocryst laden magma enters a chamber containing a denser more evolved magma as the new magma mixes with the old anorthitic plagioclase phenocrysts may accumulate near the roof in a hybrid liquid thinner crust under the northern islands increases the probability that viscous plagioclase rich magmas can ascend to shallow magma chambers and may account for the fact that pubs are more common on the northern islands than in the rest of the archipelago

monomineralic glomerocrysts textural evidence for mineral resorption during crystallization of igneous rocks monomineralic aggregates or glomerocrysts are a distinctive feature of many igneous rocks those with crystals joined along prominent euhedral crystal faces form by synneusis while the mineral is crystallizing other glomerocrysts comprised of crystals joined along irregular embayed margins arguably formed while the crystals were being resorbed a model for glomerocryst formation during mineral resorption is described during resorption a boundary layer melt which envelops the dissolving crystals is produced when two or more dissolving crystals come into close proximity the intervening portion their respective boundary layer melts becomes isolated from chemical communication with the surrounding granitic liquid contributions from both dissolving crystals to this isolated portion of the boundary layer melt creates a melt composition that eventually becomes supersaturated with respect to the dissolving crystals this results in crystallization of new material from the intervening melt that bonds th

a time varying 3 d displacement model of the 5 9 year westward motion and its applications for the global navigation satellite system positions and velocities

multimission empirical ocean tide modeling for shallow waters and polar seas 1 a new global ocean tide model named dtu10 developed at technical university of denmark representing all major diurnal and semidiurnal tidal constituents is proposed based on an empirical correction to the global tide model fes2004 finite element solutions with residual tides determined using the response method the improvements are achieved by introducing 4 years of topex jason 1 interleaved mission into existing 18 years 1993 2010 of primary joint topex jason 1 and jason 2 mission time series hereby the spatial distribution of observations are doubled and satellite altimetry should be able to recover twice the spatial variations of the tidal signal which is particularly important in shallow waters where the spatial scale of the tidal signal is scaled down outside the 66 parallel combined envisat geosat follow on and ers 2 data sets have been included to solve for the tides up to the 82 parallel a new approach to removing the annual sea level variations prior to estimating the residual tides significantly improved tidal determination of diurnal constituents from the sun synchronous satellites e g ers 2 and envisat in the polar seas extensive evaluations with six tide gauge sets show that the new tide model fits the tide gauge measurements favorably to other state of the art global ocean tide models in both the deep and shallow waters especially in the arctic ocean and the southern ocean one example is a comparison with 207 tide gauge data in the east asian marginal seas where the root mean square agreement improved by 35 12 22 61 27 07 and 22 65 m2 s2 k1 and o1 for the dtu10 tide model compared with the fes2004 tide model a similar comparison in the arctic ocean with 151 gauge data improved by 9 93 0 34 7 46 and 9 52 for the m2 s2 k1 and o1 constituents respectively

pyroclastic edifices record vigorous lava fountains during the emplacement of a flood basalt flow field roza member columbia river basalt province usa the 1300 km 3 tholeiitic lava flow field of the 14 98 ma roza member of the columbia river basalt province has the best preserved vent system of any known continental flood basalt detailed geological mapping and logging of the exposed pyroclastic rocks along the 180 km long vent system enable the reconstruction of pyroclastic edifices partial cones built around vents the pyroclastic cones differ from those constructed during typical basaltic effusive eruptions and are characterized by low to moderate slope angles 1 km fountains enhanced by fallout from the lower parts of convective plumes that rose above the fountains