formation of an a ā lava delta insights from time lapse multibeam bathymetry and direct observations during the stromboli 2007 eruption five consecutive multibeam bathymetries collected before during and after the 2007 stromboli eruption combined with visual inspections allowed us to document the morphological evolution of an a lava fed delta and to reconstruct the main processes acting during its submarine emplacement the 2007 stromboli delta extended down to 600 m water depth and covered an area of 420 103 m2 with a maximum thickness of 65 m and a total estimated volume of 7 106 m3 i e three times larger than its subaerial counterpart the lava delta grew mainly through the emplacement of discrete lobes about 50 150 m in size lobes were fed from point sources along the paleoshoreline and their subaqueous pathways seem to be mainly controlled by the submarine morphology with flows mostly filling in depressions left by previous lobes the main controlling factors on the lobe morphology and thickness are the effusion rates and the pre eruption morphology i e the geometry and gradients of the basal surface data also shows that sudden slope failure of portions of the submarine delta may occur simultaneously with accretion implying that a significant part of the delta material can be transported to greater depths by submarine gravity flows the present study is relevant for future monitoring and hazard assessment during the growth of active lava fed deltas as well as for a better interpretation of ancient volcaniclastic successions inland

palaeoenvironment reconstruction volcanic evolution and geochronology of the cerro blanco subcomplex nevados de chillan volcanic complex central chile nevados de chillan volcanic complex central chile has been active for at least 640 ka a period spanning a number of glacial and interglacial periods geologic mapping radiometric dating and geochemical analysis have identified six new volcanic units and produced four new 40ar 39ar ages for cerro blanco the northern subcomplex of nevados de chillan volcano compositions range from dacite to basaltic andesite and a new geologic map is presented examination of lava fracture structures on both newly mapped lavas and those mapped during previous studies has enabled interpretations of former eruptive environments palaeoenvironment reconstructions combined with 40ar 39ar ages and comparison with the marine oxygen isotope record show that at least three phases of volcanic activity have occurred during the evolution of cerro blanco 1 a constructive pre caldera collapse period 2 a period of caldera formation and collapse and 3 a constructive period of dome growth forming the modern day volcanic centre this style of volcanic evolution whereby large scale caldera collapse is followed by growth of a new stratocone is common at andean volcanoes

products of subglacial volcanic eruptions under different ice thicknesses two examples from antarctica late cenozoic subglacially erupted volcanic sequences are scattered throughout the antarctic peninsula two of the best preserved examples at mount pinafore alexander island c 5 5 6 ma and brown bluff graham land c 1 ma are complete enough to be regarded as sequence holotypes for this uncommonly preserved eruptive depositional setting despite a common glacial association the sedimentary lithofacies in the two outcrops suggest flowing and ponded water conditions respectively indicating significant differences in the depositional palaeoenvironments the original ice thicknesses exerted a major control on the lithofacies which resulted from each eruptive phase at mount pinafore the lithofacies were confined within a steep sided valley during successive eruptions beneath thin 100 150 m wet based ice the much thicker succession at brown bluff is a tindar tuya edifice which formed within a small basin probably 15 km across confined by ice 400 m thick

reconstructing atmospheric histories from measurements of air composition in firn 1 this paper investigates the use of a numerical model of firn diffusion and bubble trapping in the reconstruction of atmospheric records from firn measurements we describe the concept of mean age and effective age of tracers in firn air and how the growth rate of a tracer in the atmosphere can alter the effective age we discuss an iterative method to assign effective ages to firn measurements for tracers with fairly simple atmospheric histories taking into account atmospheric growth rate variations we then develop a bayesian synthesis inversion calculation for inverting firn concentration measurements this calculation gives estimates of the atmospheric concentration record with uncertainties the dating and inversion techniques are demonstrated here with carbon tetrachloride measurements from a long firn record from law dome antarctica the techniques are then applied to measurements of a range of halocarbons in a companion paper by sturrock et al 2002

melting of the glacier base during a small volume subglacial rhyolite eruption evidence from blahnukur iceland abstract although observations of recent volcanic eruptions beneath vatnajokull iceland have improved the understanding of ice deformation and meltwater drainage little is known about the processes that occur at the glacier base we present observations of the products of a small volume effusive subglacial rhyolite eruption at blahnukur torfajokull iceland lava bodies typically 7 m long have unusual conical morphologies and columnar joint orientations that suggest emplacement within cavities melted into the base of a glacier cavities appear to have been steep walled and randomly distributed these features can be explained by a simple model of conductive heat loss during the ascent of a lava body to the glacier base the released heat melts a cavity in the overlying ice the development of vapour escape pipes in the waterlogged permeable breccias surrounding the lava allows rapid heat transfer between lava and ice the formed meltwater percolates into the breccias recharging the cooling system and leaving a steam filled cavity the slow ascent rates of intrusive rhyolitic magma bodies provide ample time for a cavity to be melted in the ice above even during the final 10 m of ascent to the glacier base an equilibrium cavity size is calculated at which melting is balanced by creep closure this is dependent upon the heat input and the difference between glaciostatic and cavity pressure the cavity sizes inferred from blahnukur are consistent with a pressure differential of 2 4 mpa suggesting that the ice was at least 200 m thick this is consistent with the volcanic stratigraphy which indicates that the ice exceeded 350 m in thickness although this is the first time that a subglacial cavity system of this type has been reconstructed from an ancient volcanic sequence it shares many characteristics with the modern firn cave system formed by fumarolic melting within the summit crater of mount rainier washington at both localities it appears that localised heating at the glacier base has resulted in heterogeneous melting patterns despite the different rheological properties of ice and firn similar patterns of cavity roof deformation are inferred the development of low pressure subglacial cavities in regions of high heat flux may influence the trajectory of rising magma with manifold implications for eruptive mechanisms and resultant subglacial volcanic landforms

implications of ice core smoothing for inferring co2 flux variability 1 ice core records are commonly used to infer information about past variability of co2 fluxes because of processes involved in enclosing this air in ice ice core records are a smoothed representation of the actual past atmospheric variations as such there is a limit to how much information ice core measurements can contain about flux variability on short timescales with a numerical model of the firn processes we quantify this smoothing and describe how it can be reproduced with pulse response functions we generate and make available pulse response functions for co2 at the de08 site on law dome antarctica we discuss implications of the smoothing for inferring co2 flux variability from the law dome ice core record in particular we look at results from an intercomparison of terrestrial biosphere models over the twentieth century and show how much of the co2 variability would be reflected in the law dome ice core record we also smooth atmospheric 13co2 from a study that compared fixed and varying isotopic discrimination we find that the impact of changing discrimination shown previously to be large on interannual timescales is small on the decadal scales accessible from ice core records

palaeogene lacustrine record in mallorca nw mediterranean spain depositional palaeogeographic and palaeoclimatic implications for the ancient southeastern iberian margin abstract middle bartonian middl1e eocene and chattian upper oligocene lacustrine and alluvial lacustrine successions exist in mallorca northwestern mediterranean they yield a significant palaeobiological record comprising fossil land plants and vertebrates and constitute the best available depositional record for a preliminary palaeogeographic and palaeoclimatic analysis of the northeastern part of the palaeogene southern iberian margin western tethys both lacustrine systems developed under similar warm and humid climatic conditions increasingly affected by seasonal and or pluriannual rhythms marked by changing precipitation patterns these climatic conditions were mainly caused by the low palaeolatitude where the lacustrine systems evolved the still probable although decreasing influence of indo pacific warm surface currents and the occurrence of very extensive marine water masses adjacent to wide emerged continental zones the palaeogene lacustrine systems were shallow and characterised by low gradient depositional conditions they were perennial open freshwater oligosaline carbonate lakes where eutrophy thermal meromixis and anoxic bottom conditions could develop allowing the accumulation and preservation of macrophytic plant remains of the circum lacustrine marginal belt and neighbouring terrestrial mesophytic zones the higher plant algal bacterial organic contribution balance favoured the generation of mineable huminitic coal seams carbominerites and of gas prone kerogene type iii and iib source rocks the hydrogen bicarbonate rich waters led to high biogenic and inorganic bio induced carbonate sediment production biogenic muds cyanobacterial incrustations and travertine and tufa precipitation constituted the major carbonate products moreover the high ph conditions in the lacustrine water bodies and in the lacustrine sediment pore waters favoured bacterial sulphate reduction contributing to organic sulphur enrichment in coals these highly alkaline conditions also resulted in some cases in the exceptionally good preservation of chlorophyllinite a rare liptinite maceral recorded in the eocene coal deposits the middle eocene lacustrine system did not evolve in a very well defined tectonic setting characterised by the generation of low uplifts and gently subsiding basins terrigenous contributions from the source areas and clastic sedimentation were restricted to river mouths high autochthonous carbonate production and accumulation characterised most of the remaining lacustrine zones a significant spring recharge of the lacustrine zones is suggested by the well developed spring related travertine deposits by contrast the oligocene lacustrine zones developed both in fluvial related floodplains and in the distal zones of a major alluvial system which was fed from tectonically active source areas located to the nw of the island a more significant water runoff contribution is suggested for this system although underground recharge could also be substantial

structures and facies associated with the flow of subaerial basaltic lava into a deep freshwater lake the sulphur creek lava flow north cascades washington abstract the ca 8800 14c yrs bp sulphur creek lava flowed eastward 12 km from the schriebers meadow cinder cone into the baker river valley on the southeast flank of mount baker volcano the compositionally zoned basaltic to basaltic andesite lava entered crossed and partially filled the 2 km wide and 100 m deep early holocene remnant of glacial lake baker the valley is now submerged beneath a reservoir but seasonal drawdown permits study of the distal entrant lava as a lava volume that may have been as much as 180 106 m3 entered the lake the flow invaded the lacustrine sequence and extended to the opposite east side of the drowned baker river valley the volume and mobility of the lava can be attributed to a high flux rate a prolonged eruption or both basalt exposed below the former level of the remnant glacial lake is glassy or microcrystalline and sparsely vesicular with pervasive hackly or blocky fractures together with pseudopillow fractures these features reflect fracturing normal to penetrative thermal fronts and quenching by water a fine grained hyaloclastite facies was probably formed during quench fragmentation or isolated magma water explosions although the structures closely resemble those developed in lava ice contact environments establishing the depositional environment for lava exhibiting similar intense fracturing should be confirmed by geologic evidence rather than by internal structure alone the lava also invaded the lacustrine sequence forming varieties of peperite including sills that are conformable within the invaded strata and resemble volcaniclastic breccias the peperite is generally fragmental and clast or matrix supported fine grained and rounded fluidal margins occur locally the lava formed a thickened subaqueous plug that as the lake drained in the mid holocene was exposed to erosion the baker river then cut a 52 m deep gorge through the shattered highly erodible basalt

lillooet glacier basalts southwestern british columbia canada products of quaternary glaciovolcanism the retreat of lillooet glacier lg has exposed a succession of pillow basalt and subordinate amounts of breccia and hyaloclastite the lithofacies and physiographic setting suggest that the deposits have a glaciovolcanic origin and represent a partially dissected basaltic pillow dominated tindar chemically the lg volcanic rocks are basalt to basaltic andesite and as a group they represent the highest silica quaternary mafic products in the garibaldi volcanic belt gvb like other northern gvb alkaline basalts they lack the nb ta depletion signature typically associated with subduction related products geochemical and petrologic analysis indicates that the lg basalts are comagmatic and that chemical variations within the suite are consistent with sorting of the observed phenocryst assemblage olivine plagioclase thermodynamic modeling establishes shallow crustal pre eruptive storage conditions at 2 kbar 1 kbar 100 mpa or 7 5 km and an h2o content of 0 5 1 wt we estimate that the

palaeomagnetic refinement of the eruption ages of holocene lava flows and implications for the eruptive history of the tongariro volcanic centre new zealand

atmospheric co2 fluctuations during the last millennium reconstructed by stomatal frequency analysis of tsuga heterophylla needles a stomatal frequency record based on buried tsuga hetero phylla needles reveals significant centennial scale atmospheric co2 fluctuations during the last millennium the record includes four co2 minima of 260 275 ppmv ca a d 860 and a d 1150 and less prominently ca a d 1600 and 1800 alternating co2 max ima of 300 320 ppmv are present at a d 1000 a d 1300 and ca a d 1700 these co2 fluctuations parallel global terrestrial air temperature changes as well as oceanic surface temperature fluc tuations in the north atlantic the results obtained in this study corroborate the notion of a continuous coupling of the preindus trial atmospheric co2 regime and climate

dynamic controls on accretion and lithification of modern gypsum dominated thrombolites los roques venezuela meter sized thrombolites coated by well developed zonally differentiated microbial mats have been found growing in the shallow waters depth 1 m of a restricted hypersaline lagoon on the archipelago los roques in venezuela by contrast within the deeper parts of the studied lagoon sedimentation is characterized by several decimeters of organic rich material containing gypsum granules lacking carbonate cementation the lithification of the thrombolites is thought to have proceeded as follows first extracellular polymeric substances eps comprising the microbial mat concentrate ca2 and other metal cations by adsorption from the hypersaline waters second some of these bound metals then serve as nucleation sites for primary calcium carbonate caco3 precipitation third while carbonate phases are forming in some zones of the mat in others zones they are being re dissolved due to the acidity generated through the metabolism of sulfide oxidizing bacteria fourth as the dissolved sulfide is oxidized into sulfate the pore water become saturated with respect to gypsum caso4 2h2o fifth as primary gypsum precipitates within the structures endolithic sulfate reducing bacteria metabolize the sulfate moiety in the mineral phase while simultaneously oxidizing the eps trapped during accretion sixth as microbial eps degradation proceeds the anaerobic oxidation of specific protein fractions of the eps matrix leads to increased alkalinity the partial dissolution of gypsum supersaturation with respect to calcium carbonate and ultimately pseudomorphic aragonite replacement this differs from secondary calcite cements in being enriched in 12c and depleted in minor and trace metals initially associated with the eps the biogeochemical processes occurring in this thrombolite constructing lagoon represent a novel field site for studying the chemical and isotopic processes characterizing early diagenetic gypsum and the role microbes play in its precipitation dissolution and calcification in this regard insights gained from this modern field site will help to better understand mechanisms by which some precambrian microbialites were lithified

evoluton of polygonal fracture patterns in lava flows cooling induced fractures also known as columnar joints divide basaltic lava flows into prismatic columns with polygonal cross sections the regularity and symmetry of the fracture patterns have long fascinated naturalists in view of the recent selection of two candidate nuclear waste sites in areas where polygonally fractured volcanic rocks are located a better understanding of the fracture patterns is required field data indicate that the tetragonal networks at flow surfaces evolve systematically to hexagonal networks as the joints grow inward during solidification of lava this evolution occurs by the gradual change of most orthogonal intersections to nonorthogonal intersections of about 120 degrees the surface features and intersection geometries of columnar joints show that joint segments at any given level form sequentially yet harmoniously

ridge forming ice bounded lava flows at mount rainier washington large 0 3 4 km3 andesite and dacite lava flows at mount rainier washington sit atop or are perched along the sides of high ridges separating deep valleys early researchers proposed that these ridge forming lavas flowed into paleovalleys and displaced rivers to their margins entrenchment of the rivers then left the lavas atop ridges on the basis of exceptional flow thickness ice contact features and eruption age measurements we propose that the lavas flowed beside and between valley glaciers that filled the adjacent valleys in the pleistocene when the glaciers retreated the flows were left high on the adjacent ridges these lavas were never situated at valley floors and do not represent products of reversed topography instead ridge forming and perched lava flows at mount rainier and at many other high stratovolcanoes illustrate the ability of ice to dam deflect and confine flowing lava

disruption of drift glacier and origin of floods during the 1989 1990 eruptions of redoubt volcano alaska abstract melting of snow and glacier ice during the 1989 1990 eruption of redoubt volcano caused winter flooding of the drift river drift glacier was beheaded when 113 to 121 10 6 m 3 of perennial snow and ice were mechanically entrained in hot rock avalanches and pyroclastic flows initiated by the four largest eruptions between 14 december 1989 and 14 march 1990 the disruption of drift glacier was dominated by mechanical disaggregation and entrainment of snow and glacier ice hot rock avalanches debris flows and pyroclastic flows incised deep canyons in the glacier ice thereby maintaining a large ice surface area available for scour by subsequent flows downvalley flow rheologies were transformed by the melting of snow and ice entrained along the upper and middle reaches of the glacier and by seasonal snowpack incorporated from the surface of the lower glacier and from the river valley the seasonal snowpack in the drift river valley contributed to lahars and floods a cumulative volume equivalent to about 35 10 6 m 3 of water which amounts to nearly 30 of the cumulative flow volume 22 km downstream from the volcano the absence of high water marks in depressions and of ice collapse features in the glacier indicated that no large quantities of meltwater that could potentially generate lahars were stored on or under the glacier the water that generated the lahars that swept drift river valley was produced from the proximal eruption induced volcaniclastic flows by melting of snow and ice

late miocene valley confined subglacial volcanism in northern alexander island antarctic peninsula isolated late miocene volcanogenic sequences in northern alexander island antarctic peninsula form an unusual cogenetic association of volcaniclastic sandy gravelly lithofacies including tillites and volcanic lava hyalocalstite lithofacies using simple lithofacies analysis and theoretical considerations of hydrodynamic effects of subglacial eruptions valley confined volcanic activity beneth thin wet based ice is suggested the alexander island successions are complete enough to be regarded as model sequences for this uncommonly recorded type of eruptive depositional activity the sedimentary lithofacies represent resedimented tuffs and meltout or flow tills which were probably deposited in subglacial ice tunnels eroded or enlarged by volcanically heated meltwater the volcanic lithofacies formed by the interaction of hot magma with the ice tunnel walls generating abundant meltwater and water saturatedsediments resulting in the formation of heterogeneous masses of lava and hyaloclastite there is no obvious sequence organisation in the sedimentary sections this is probably due to a complex interplay of eruption related and environmental hydrodynamic factors affecting the relative proportions of water and entrained sediment

subglacial and ice contact volcanism at the oraefajokull stratovolcano iceland eruptions of oraefajokull have produced mafic and silicic magmas and have taken place in both glacial and interglacial periods the geology of the volcano records the differing response of magmas of contrasting composition to interaction with ice of variable thickness and gives insight into the development of a long lived ice covered stratovolcano vatnafjall a ridge on the southeast flank of oraefajokull is the first area of the volcano to have been mapped in detail and the geological map is presented here alongside descriptions of each erupted unit the oldest units comprise pillow lavas hyaloclastite and jointed lava flows that were formed during subglacial basaltic eruptions involving abundant meltwater the products of a subsequent explosive initially phreatomagmatic subglacial rhyolite eruption were confined by ice to form a tephra pile over 200 m thick that was intruded by dense rhyolite magma towards the end of the eruption confinement by ice caused a later trachydacite lava flow to form buttresses and a steep pillar whilst some of the meltwater produced infiltrated the lava to generate red and black glassy breccias and cause localised steam explosions it is likely that much of it drained down the steep topography the most recently erupted units are subaerial basaltic lava flows the oldest of which were erupted during an interglacial period and have subsequently been partially eroded and scoured by advancing ice ice has been important in shaping the edifice by confining eruptive products to form constructional features and by later eroding parts of them to form deep valleys reconstructions of volcano ice interaction allowed the local thickness of the glacier at the time of each eruption to be estimated and demonstrates that the upper surface of the ice has varied in elevation by over 700 m

swift snowmelt and floods lahars caused by great pyroclastic surge at mount st helens volcano washington 18 may 1980 the initial explosions at mount st helens washington on the moring of 18 may 1980 developed into a huge pyroclastic surge that generated catastrophic floods off the east and west flanks of the volcano near source surge deposits on the east and west were lithic sorted lacking in accretionary lapilli and vesiculated ash not plastered against upright obstacles and hot enough to char wood all attributes of dry pyroclastic surge material deposited at the surge base on steep slopes near the volcano transformed into high concentration lithic pyroclastic flows whose deposits contain charred wood and other features indicating that these flows were hot and dry stratigraphy shows that even the tail of the surge had passed the east and west volcano flanks before the geomorphically distinct floods lahars arrived this field evidence undermines hypotheses that the turbulent surge was itself wet and that its heavy components segregated out to transform directly into lahars nor is there evidence that meters thick snow slab avalanches intimately mixed with the surge to form the floods the floods must have instead originated by swift snowmelt at the base of a hot and relatively dry turbulent surge impacting hot pyroclasts probably transferred downslope momentum to the snow surface and churned snow grains into the surge base melting snow and accumulating hot surge debris may have moved initially as thousands of small thin slushflows as these flows removed the surface snow and pyroclasts newly uncovered snow was partly melted by the turbulent surge base this and accumulating hot surge debris in turn began flowing a self sustaining process feeding the initial flows the flows thus grew swiftly over tens of seconds and united downslope into great slushy ejecta laden sheetfloods gravity accelerated the floods to more than 100 km h as they swept down and off the volcano flanks while the snow component melted to form great debris rich floods lahars channeled into valleys

entablature fracture types and mechanisms entablature is the term used to describe zones or tiers of irregular jointing in basaltic lava flows it is thought to form when water from rivers dammed by the lava inundates the lava flow surface and during lava meltwater interaction in subglacial settings a number of different fracture types are described in entablature outcrops from the burfell lava and older lava flows in jorsardalur southwest iceland these are striae bearing column bounding fractures and pseudopillow fracture systems that themselves consist of two different fracture types master fractures with dimpled surface textures and subsidiary fractures with curved striae the interaction of pseudopillow fracture systems and columnar jointing in the entablature produces the chevron fracture patterns that are commonly observed in entablature cube jointing is a more densely fractured version of entablature which likely forms when more coolant enters the hot lava the entablature tiers display closely spaced striae and dendritic crystal shapes which indicate rapid cooling master fracture surfaces show a thin band with an evolved composition at the fracture surface mineral textures in this band also show evidence of quenching of this material this is interpreted as gas driven filter pressing of late stage residual melt that is drawn into an area of low pressure immediately preceding or during master fracture formation by ductile extensional fracture of hot partially crystallised lava this melt is then quenched by an influx of water and or steam when the master fracture fully opens our findings suggest that master fractures are the main conduit for coolant entering the lava flow during entablature formation

quantification of extraterrestrial lava flow effusion rates through laboratory simulations we have used carefully controlled laboratory simulations to develop a model which relates lava flow morphology to effusion rate and rheology through comparisons with measured and estimated eruption rates on earth this approach allows us to constrain eruptive styles and compositions of extraterrestrial lava flows by applying this model to lava flows on the moon mars and venus we have determined that all the common flow morphologies domes folds and levees on these planets could have been produced by basalt like or andesite like lavas through either continuous or episodic emplacement the presence of more evolved magma compositions on other planets is not required to explain any of the observed lava flow morphologies

contrasting tectonic and sedimentary history of the central and eastern parts of the polish carpathian foredeep basin results of seismic data interpretation polish carpathian foredeep basin pcfb is located at the junction between western and eastern european platforms such location caused different evolution of various parts of this basin in the central part of the pcfb growth fault propagation folds related to latest badenian stages of thrusting in this segment of the carpathians developed only minor normal faulting related to miocene reactivation of older basement faults was detected paleovalleys mapped within the mesozoic basement were interpreted as palaeogene tectonically controlled erosional features developed after inversion of the polish trough in the central pcfb post evaporitic sediments were supplied into the foredeep basin from south from the eroded carpathians in the eastern part of the pcfb a system of large normal faults related to miocene flexure induced reactivation of inherited mesozoic faults was identified within the hangingwall of this system reverse faults rotated blocks and basement pop up structures were described their formation was related to combined effect of compressional stresses transferred from the carpathian collision zone and reactivation of older large scale fault caused by both flexural extension and strike slip movements during deposition of the miocene foredeep sediments differential compaction also played an important role gentle onlap of the middle badenian evaporites by post evaporitic sediments towards the nw was interpreted as a result of tectonically driven relative sea level rise and re establishment of marine connections with eastern paratethys

cooling process recorded in subglacially erupted rhyolite glasses rapid quenching thermal buffering and the formation of meltwater the thermal histories of two subglacial rhyolite glasses from torfajokull complex of south central iceland have been determined from changes in the relaxation of enthalpy in the calorimetric glass transition interval heat capacity measurements of bulk glass samples from rau ufossafjoll sample number js 1 1 and blahnukur sample number js 2 1 by differential scanning calorimetry show marked differences in the temperature of the onset of glass transition tg on reheating the average tg is 750 k for js 1 1 whereas it is 850 k for js 2 1 these differences in the onset of tg are related to quench rate through considerations of the activation energy and timescales for structural relaxation modeled using the kohlrausch williams watt function multiple glass samples from the two torfajokull locations recover different average values and distributions of a fictive temperature t f which we interpret in terms of differences in the thermal histories of the glasses in both glass samples the range of fictive temperatures and by implication apparent cooling rates is lower than those estimated for a glass rapidly quenched by contact with cold glacial melt water and requires that the glass was annealed at temperatures in the glass transition interval associated with relaxation times of the order of 1000 10 000 s the complex cooling histories of the torfajokull samples show that the products of subglacial eruptions may be held at elevated temperatures for several hours and as a result may drive vigorous convection in the ice bound vaults above erupting rhyolite deposits

solidifying bingham extrusions a model for the growth of silicic lava domes in a previous study of the effects of cooling and solidification on flows issuing onto a horizontal plane and spreading under gravity we considered the case of a viscous fluid that solidifies to form a thin surface crust with a finite yield strength in that case the coupling of solidification and viscous stresses in the flow led to a sequence of flow regimes or styles of flow and crustal deformation here we study the spreading from a small source of a plastic material having a yield strength before cooling in this case the fluid again begins to freeze as it spreads radially under gravity and forms a dome having a surface crust which is stronger than the extruded fluid if cooling is sufficiently rapid compared to gravity driven spreading the flow is found to be controlled by solidification the flow again takes on one of a number of flow regimes depending on the pace of solidification relative to the rate of lateral flow or extrusion rate however these flow regimes are quite different from those for the viscous extrusions implying that the internal yield stress has a strong influence on the behaviour styles of flow ranged from inflation of an axisymmetric dome to irregular extrusion of lateral lobes and vertical spines these qualitatively different regimes have much in common with the eruption styles of volcanic lava domes produced by effusion of extremely viscous silicic magmas which may possess a yield strength and the model provides information about the factors influencing the morphology and hazards of such volcanic flows

volcanic mixed avalanches a distinct eruption triggered mass flow process at snow clad volcanoes a generally unrecognized type of pyroclastic deposit was produced by rapid avalanches of intimately mixed snow and hot pyroclastic debris during eruptions at mount st helens nevado del ruiz and redoubt volcano between 1982 and 1989 these mixed avalanches traveled as far as 14 km at velocities up to 27 m s involved as much as 10 7 m 3 of rock and ice and left unmelted deposits of single flow units as thick as 5 m during flow downslope heat transfer from hot rocks to snow produced meltwater that partially saturated the mixtures apparently giving these mixed avalanches mobilities equal to or greater than those of dry debris avalanches of similar volume the avalanches studied for this report began as snow avalanches triggered during explosive phases of the eruptions by ballistic bombardment of snow slopes by hot pyroclastic debris erosion by the avalanches incorporated additional snow fragments of glacier ice and other rock debris mixed avalanche deposits were massive very poorly sorted and ungraded to inversely graded prior to melting although rock debris composed as much as 70 wt of the frozen samples the bulk volumetric content of rock debris was only 9 to 36 snow and ice composed between 36 and 72 of the frozen samples with void space making up the remainder of the volume deformation and consolidation after melting of the ice content reduced the deposits to loose porous layers that were only a fraction of their original thickness and that later gave little hint of their origin after melting and desiccation the deposits are highly susceptible to erosion and unlikely to be well preserved in the stratigraphic record

thermo mechanical model for incremental fracturing in cooling lava flows abstract this study presents an idealized quantitative model of stress development and incremental fracturing in cooling lavas it appears that columnar jointing forms in lavas by a process of incremental fracturing driven by thermal stresses the fractures progress inward from the cooling surfaces as time increases the cooling of a horizontal layer of lava has been modeled analytically for three cooling regimes conductive cooling with liquid magma present conductive cooling after total solidification and hydrothermal cooling horizontal thermal stresses develop and cause vertical fractures at the upper and lower surfaces of the lava as the lava cools layer after layer becomes elastic thermal stresses develop in these thin layers between previously fractured lava where it is assumed stresses have been released and the hot interior lava where temperatures exceed the elastic temperature limit stresses are analyzed by treating each unfractured elastic layer as a slab restrained in bending unrestrained from contraction the stress level at which incremental fracturing occurs extending previous fractures and the effect of stress and temperature conditions on fracture penetration are discussed our analysis yields values for the length of incremental fracture as a function of time and material strength for both a thin lava flow cooling conductively incremental fracture lengths increase with time and for a thicker lava flow in which hydrothermal convection is important incremental fracture lengths are constant with time our results are compared to observed striae widths measured from the base of basaltic lava columns striae represent successive incremental fractures the comparison shows agreement in magnitude and trend after some amount of cooling i e striae and incremental fracture lengths increase with time at an accelerating rate

subglacial volcanics on the control of magma chemistry on pillow dimensions abstract axial dimensions glass thicknesses and plunges of 822 icelandic pillows of olivine tholeiitic to andesitic compositions are presented the pillows formed during subglacial volcanic eruptions at water depths of a few hundred meters their average diameters are olivine tholeiite 40 cm tholeiite and basaltic andesite 15 cm and andesite 30 cm the olivine tholeiite pillows have highly vesicular glass rims and vesicular interiors whereas the tholeiite and basaltic andesite pillows are characterized by very low vesicularity throughout the andesite pillows have nonvesicular glass margins but commonly highly vesicular interiors the glass rims thicken linearly with increasing diameter both for the olivine tholeiite and the andesite pillows although the increment is much faster for the latter the small average diameter pillows of tholeiite and basaltic andesite are characterized by highly abundant and evenly dispersed euhedral grains of magnetite during formation the olivine tholeiite pillows can apparently expand relatively freely prior to the crust attaining sufficient strength to prevent further growth the non vesicular and relatively thick crust of tholeiite basaltic andesite and andesite pillows apparently obtains strength quickly to prevent further growth

kalman filter analysis of ice core data 2 double deconvolution of co2 and δ13c measurements 1 a new method for deconvolving ice core co2 and 13co2 measurements to estimate net co2 uptake by the terrestrial biosphere and the oceans has been developed the method which uses the kalman filter incorporates statistical analysis into the calculation this allows a more rigorous analysis of co2 variability than the usual deconvolution method the kalman filter method estimates uncertainties on the deduced fluxes as part of the calculation the deconvolution method is applied to the law dome co2 and 13c ice core record the calculation suggests that natural variability in co2 fluxes may be as large as 1 gtc yr 1 gtc is gigatonnes carbon 1 gt 1015 g on the timescale of just less than a decade the law dome co2 measurements show a slight decrease in co2 around the 1940s analysis with the carbon cycle model and a numerical model of firn processes suggests that about 3 gtc yr 1 uptake mostly oceanic is required in the 1940s to match the ice core measurements the estimates of variation in the terrestrial biospheric flux between 1950 and 1980 from the double deconvolution calculation are in very good agreement with an independent estimate of the global terrestrial flux from a climate driven ecosystem model

morphological and sedimentological characteristics of the neogene submarine coherent lavas and hyaloclastites in southwest hokkaido japan abstract the neogene formations in southwest hokkaido japan are mostly composed of submarine volcanic products such as submarine coherent lavas and hyaloclastites associated with feeder dikes this paper presents criteria for recognition of submarine effusion products through description of the morphological and sedimentological characteristics of coherent lavas such as pillow lobes sheet flow lava lobes and pseudo pillow lavas and hyaloclastites and feeder dikes and a small amount of associate pyroclastic rocks

use of joint growth directions and rock textures to infer thermal regimes during solidification of basaltic lava flows abstract thermal contraction joints form in the upper and lower solidifying crusts of basaltic lava flows and grow toward the interior as the crusts thicken lava flows are thus divided by vertical joints that by changes in joint spacing and form define horizontal intraflow layers known as tiers entablatures are tiers with joint spacings less than about 40 cm whereas colonnades have larger joint spacings we use structural and petrographic methods to infer heat transfer processes and to constrain environmental conditions that produce these contrasting tiers joint surface morphology indicates overall joint growth direction and thus identifies the level in a flow where the upper and lower crusts met rock texture provides information on relative cooling rates in the tiers of a flow lava flows without entablature have textures that develop by relatively slow cooling and two joint sets that usually meet near their middles which indicate mostly conductive cooling entablature bearing flows have two main joint sets that meet well below their middles and textures that indicate fast cooling of entablatures and slow cooling of colonnades entablatures always occur in the upper joint sets and sometimes alternate several times with colonnades solidification times of entablature bearing flows constrained by lower joint set thicknesses are much less than those predicted by a purely conductive cooling model these results are best explained by a cooling model based on conductive heat transfer near a flow base and water steam convection in the upper part of an entablature bearing flow calculated solidification rates in the upper parts of such flows exceed that of the upper crust of kilauea iki lava lake where water steam convection is documented use of the solidification rates in an available model of water steam convection yields permeability values that agree with measured values for fractured crystalline rock we conclude therefore that an entablature forms when part of a flow cools very rapidly by water steam convection flooding of the flow top by surface drainage most likely induces the convection colonnades form under conditions of slower cooling by conductive heat transfer in the absence of water

post evaporitic restricted deposition in the middle miocene chokrakian karaganian of east crimea ukraine abstract in the middle miocene of east crimea gypsum evaporites formed in a shallow basin from mixed seawater nonmarine waters are overlain by marl siltstone and claystone which contain a few horizons of stromatolitic limestone the thickness and abundance of the stromatolitic horizons increase up the section in the siliciclastic portion of the section a very poor and taxonomically impoverished assemblage of benthic foraminifers jadammina nonion haynesina astrononion and eponides is recorded it is typical for a shallow water marsh or lagoon environment with a lowered salinity accordingly the brackish conditions prevailing during gypsum precipitation in east crimea continued afterwards although at the end of evaporite deposition the basin became desiccated and then it was rapidly reflooded by brackish water the impoverished biota and the occurrence of microbialites in the ptashkino section indicate extremely unfavourable conditions for most living organisms during the deposition of both the terrigenous and carbonate beds the water salinity thus was probably not only lowered but also anomalous in composition if compared to normal marine water the occurrence of carbonate stromatolitic horizons is probably related to the periodic shallowing of the basin caused by a drop of the lake water table driven by climatic factors the resulted changes allowed for a growth of the bizarre microbial serpulid communities that gave birth to most of the stromatolites in karaganian time the eastern paratethys was a huge lake isolated from the tethys this lake responded to any climatic fluctuation that in turn might lead to water level oscillations in humid climate periods the lake could be open with a surface outflow and when it was drier it could be a closed system without surface outflow gypsum evaporites and stromatolitic carbonates are clear evidence of strong evaporation in a dry climate that probably induced water level fall in the whole basin however all the time the environmental conditions were predominantly brackish even during gypsum precipitation as suggested by the chemical composition of fluid inclusions in gypsum similar conditions may be expected in other evaporite hosted predominantly brackish basins such as some messinian basins of the eastern mediterranean where some evaporites were deposited in the oligohaline to mesohaline conditions typical of the lago mare deposits

eruptive history and geochronology of mount mazama and the crater lake region oregon geologic mapping k ar and 40 ar 39 ar age determinations supplemented by paleomagnetic measurements and geochemical data are used to quantify the quaternary volcanic history of the crater lake region in order to define processes and conditions that led to voluminous explosive eruptions the cascade arc volcano known as mount mazama collapsed during its climactic eruption of 50 km 3 of mainly rhyodacitic magma 7700 yr ago to form crater lake caldera the mazama edifice was constructed on a pleistocene silicic lava field amidst monogenetic and shield volcanoes ranging from basalt to andesite similar to parental magmas for mount mazama between 420 ka and 35 ka mazama produced medium k andesite and dacite in 2 1 proportion the edifice was built in many episodes some of the more voluminous occurred approximately coeval with volcanic pulses in the surrounding region and some were possibly related to deglaciation following marine oxygen isotope stages mis 12 10 8 6 5 2 and 2 magmas as evolved as dacite erupted many times commonly associated with or following voluminous andesite effusion establishment of the climactic magma chamber was under way when the first preclimactic rhyodacites vented ca 27 ka the silicic melt volume then grew incrementally at an average rate of 2 5 km 3 k y 1 for nearly 20 k y the climactic eruption exhausted the rhyodacitic magma and brought up crystal rich andesitic magma mafic cumulate mush and wall rock granodiorite postcaldera volcanism produced 4 km 3 of andesite during the first 200 500 yr after collapse followed at ca 4800 yr b p by 0 07 km 3 of rhyodacite the average eruption rate for all mazama products was 0 4 km 3 k y 1 but major edifice construction episodes had rates of 0 8 km 3 k y 1 the long term eruption rate for regional monogenetic and shield volcanoes was d 0 07 km 3 k y 1 but only 0 02 km 3 k y 1 when the two major shields are excluded plutonic xenoliths and evidence for crystallization differentiation imply that the amount of magma intruded beneath mount mazama is several times that which has been erupted the eruptive and intrusive history reflects competition between 1 crystallization driven by degassing and hydrothermal cooling and 2 thermal input from a regional magma flux focused at mazama before ca 30 ka relatively small volumes of nonerupted derivative magma crystallized to form a composite pluton because the upper crust had not been heated sufficiently to sustain voluminous convecting crystal poor melt subsequently and perhaps not coincidentally during mis 2 a large volume of eruptible silicic magma accumulated in the climactic chamber probably because of heating associated with mantle input to the roots of the system as suggested by eruption of unusually primitive magnesian basaltic andesite and tholeiite west of mazama

experimental simulation of basalt columns abstract basalt columns can be simulated by the desiccation of mixtures of starch and water this note presents photos of starch columns from laboratory experiments and summarizes results of an extended study muller g 1998 starch columns analog model for basalt columns j geophys res 103 15239 15253 basalt cooling and starch desiccation are diffusion processes causing contraction and cracks column related crack patterns in basalt and starch are largely similar differences in their spatial and time scales are due to the difference in the diffusion constants which is about two orders of magnitude starch experiments give a few new insights into basalt column formation

natural and anthropogenic changes in atmospheric co2 over the last 1000 years from air in antarctic ice and firn a record of atmospheric co2 mixing ratios from 1006 a d to 1978 a d has been produced by analysing the air enclosed in three ice cores from law dome antarctica the enclosed air has unparalleled age resolution and extends into recent decades because of the high rate of snow accumulation at the ice core sites the co2 data overlap with the record from direct atmospheric measurements for up to 20 years the effects of diffusion in the firn on the co2 mixing ratio and age of the ice core air were determined by analyzing air sampled from the surface down to the bubble close off depth the uncertainty of the ice core co2 mixing ratios is 1 2 ppm 1 preindustrial co2 mixing ratios were in the range 275 284 ppm with the lower levels during 1550 1800 a d probably as a result of colder global climate natural co2 variations of this magnitude make it inappropriate to refer to a single preindustrial co2 level major co2 growth occurred over the industrial period except during 1935 1945 a d when co2 mixing ratios stabilized or decreased slightly probably as a result of natural variations of the carbon cycle on a decadal timescale

starch columns analog model for basalt columns desiccation of starch water mixtures produces tensile crack patterns which appear to be interesting but largely unknown study objects for fracture mechanics structural geology and volcanology this paper concentrates on columnar jointing and on columns in starch starch columns have polygonal cross sections and are very similar to basalt columns they are produced by lamp drying starch specimens with dimensions of several centimeters and have diameters in the millimeter range the columns develop behind a crack front which propagates from the surface into the interior the experiments supported by x ray tomograms show that polygonal regularity of the crack pattern is not present at the surface but develops during penetration this transition is steered by a minimum fracture energy principle the analogy between basalt cooling and starch desiccation is far reaching water concentration in starch is analogous to temperature in basalt both quantities obey diffusion equations water loss is equivalent to heat loss the resulting contraction stresses have similar dependences on depth and time and in both cases the material strength is exceeded the starch experiments show that column diameters are controlled by the depth gradient of water concentration at the crack front high low gradients are connected with thin thick columns by analogy a similar relation with the temperature gradient exists for basalt columns the normalized starch gradients are about 3 orders of magnitude larger than the normalized gradients in basalt this explains why starch columns are much thinner than basalt columns the gradients are so different because the crack front speeds differ by a factor of about 10 after 3 days the speed is about 10 mm d in starch but about 100 mm d in basalt peck 1978 the speed difference in turn results from the difference of the diffusion constants the hydraulic diffusivity of starch is 2 orders of magnitude lower than the thermal diffusivity of basalt

conductive cooling of lava columnar joint diameter and stria width as functions of cooling rate and thermal gradient abstract much evidence exists that column diameter and stria width of columnar joints in lava flows vary inversely with cooling rate t t and thermal gradient t x at the point of fracture as the flow cools some evidence suggests that lava flows cool conductively a conductive cooling model yields cooling rate and thermal gradient through space and time for cooling igneous bodies both for extrusive and intrusive settings thermal gradient and cooling rate are then linked to stria width and column diameter with faster cooling leading to narrower columns and steeper gradients to narrower striae this model shows large regions within a body where the ratio of thermal gradient to cooling rate is nearly constant and predicts that the ratio of stria width to column diameter is also nearly constant this prediction is consistent with field observations both in this and other works the model also suggests that if conductive cooling dominates then joint spacing i e column diameter should increase inward from the margins of the body as should stria width

fluid inclusion analysis of twinned selenite gypsum beds from the miocene of the madrid basin spain implication on dolomite bioformation this research work is centred on continental lacustrine gypsum deposits of miocene age cropping out in the easternmost part of the madrid basin these gypsum deposits accumulated in a continental saline lake are characterized by a spectacular distinctive christmas tree morphology and a peculiar dolomite replacement a combination of microscopic petrography and scanning electron microscopy and analytical techniques fluid inclusion microthermometry x ray energy dispersive spectroscopy and x ray diffractometry was used in order to study the crystallographic distribution and the composition of the fluid inclusions within the gypsum the objectives were to characterize the continental brine from which the mineral precipitated and to detect mineral and element traces that could indicate early diagenetic processes altering the gypsum deposits data from primary fluid inclusions indicated that gypsum precipitated from an aqueous fluid lake water of low to moderate total salinity between 20 and 90 g l nacl secondary fluid inclusions represent interstitial lake brine in contact with gypsum slightly enriched in total salt content as crystal formation proceeded textural ultrastructural and microanalytical analysis indicate that the presence of dolomite precipitates inside the gypsum layers is related to the microbial colonization of the gypsum deposits and the biomineralization of the cell walls and extracellular polymeric substances around the cells our investigation emphasizes necessity of a multidisciplinary approach to assess geobiological processes

the shutdown of an anoxic giant magnetostratigraphic dating of the end of the maikop sea abstract paratethys the lost sea of central eurasia was an anoxic giant during oligocene early miocene maikop series times with a size matching the modern day mediterranean sea and a history of anoxic conditions that lasted for over 20 myrs the eastern part of this realm black sea caspian sea domain holds key records for understanding the build up maintenance and collapse of anoxia in marginal seas here we show that the collapse of anoxic maikop conditions was caused by middle miocene paleogeographic changes in the paratethys gateway configuration when a mid langhian badenian tarkhanian transgression flooded and oxygenated the eastern paratethys we present an integrated magneto biostratigraphic framework for the early middle miocene tarkhanian chokrakian karaganian regional stages of the eastern paratethys and date the lithological transition from anoxic black shales of the maikop series to fossiliferous marine marls and limestones of the regional tarkhanian stage for this purpose we selected two long and time equivalent sedimentary successions exposed along the belaya and the pshekha rivers in the maikop type area in ciscaucasia southern russia we show that a significant but short marine incursion took place during the tarkhanian ending the long lasting maikop anoxia of the basin our magnetostratigraphic results reveal coherent polarity patterns which allow a straightforward correlation with the time interval 15 12 ma of the geomagnetic polarity time scale the tarkhanian flooding occurred during a relatively short normal polarity interval that correlates with c5bn resulting in an age of 14 85 ma the regional tarkhanian chokrakian stage boundary is located within c5adn at an age of 14 75 ma and the chokrakian karaganian boundary is tentatively correlated with c5acn and an age of 13 9 13 8 ma our new tarkhanian flooding age reveals a paleogeographic scenario that is different from many previous reconstructions instead of envisaging marine connections to the indian ocean we show that major changes in connectivity between the eastern and central paratethys seas have caused the influx of marine waters during the tarkhanian an increase in marine connectivity with the mediterranean during a short episode of rapid sea level rise triggered mixing and ended the widespread anoxia in the eastern paratethys the mixing episode was short lived 100 kyr as the sea level rise slowed down and connectivity degraded because of tectonic uplift in the gateway area

eruption mechanisms and short duration of large rhyolitic lava flows of yellowstone abstract large volume effusive rhyolite lava flows are a common but poorly understood occurrence from silicic volcanic centers we integrate characterization of lava flow topographic morphology and petrographic textures and zoning of crystals with physical models of viscous fluid flow in order to interpret the eruption durations and discharge rates for the most recent effusive volcanic eruptions from yellowstone these large volume 10 70 km3 crystal poor rhyolite lavas erupted within the yellowstone caldera as 100 200 m thick flows and have a cumulative erupted volume of 650 km3 that is similar to less frequent caldera forming events but occur as individual eruptions spread over 100 ka most of this work is focused on the axisymmetric 124 ka 50 km3 summit lake flow we examined crystallinity major and trace element concentrations oxygen and hydrogen isotopic values and quartz morphology and zoning in samples from the center to margin of this flow water contents down to 0 1 wt and d values of 110 are low and require closed system degassing until near surface lithostatic pressure while major elements are consistent with water undersaturated pre eruptive storage and crystallization at 4 8 km depth we found some evidence for subtle km scale zoning within the lavas but describe significant microscopic scale compositional diversity including sharp boundaries between high ti cores and 200 m thick rims on quartz phenocrysts embayed quartz external morphology and rim growth may be the result of undercooling during coalescence of magma bodies during shallow transport between dikes and sills modeling the emplacement of the lava flow as a simple viscous fluid suggests that emplacement of rhyolite lava at 800 c occurred over 2 to 5 yrs with high discharge rates 100 m3 s such high magma discharge rates are accommodated through 6 km long fissures that allow for slower magma ascent velocities of 10 yr flow durations and significant cooling of the flow front that should result in a more complex compound flow morphology than observed higher temperatures require unrealistically wide 50 m dike widths to accommodate large discharge rates petrographic and isotopic evidence from crystals suggests recharge and merger of individual magma batches occurs on a similar timescale to the eruption duration and may directly cause overpressure and emplacement of these rhyolite lava flows from a shallow ephemeral magma chamber large volume rhyolitic lavas are able to erupt effusively through elongate fissures that utilize preexisting zones of crustal weaknesses such as ring fractures less common explosive eruptions at yellowstone may result when ascending magmas are forced through narrower conduits or when recharge rates are especially high the results of this study provide a unique top down constraint on effusive eruption rates make new interpretations of common petrographic textures and presents a comprehensive model for eruption control

paleoenvironmental changes at the messinian pliocene boundary in the eastern mediterranean southern cyprus basins significance of the messinian lago mare abstract the study of the late messinian early pliocene sediments in south cyprus pissouri and polemi basins and the comparison with the offshore coeval deposits drilled in the odp leg 160 boreholes provide new data illustrating the environmental changes which occurred in the eastern mediterranean at the end of the salinity crisis the messinian pliocene transition is marked by a very rapid environmental change indicated by sharp variations in lithology sedimentology microfaunal assemblages and stable isotope composition the latest messinian interval is dominated by the lago mare oligo mesohaline environments the most striking feature in the pissouri basin is the intercalation between the uppermost gypsum bed and the base of the zanclean deposits of four main horizons of paleosols interbedded with carbonates and conglomerates paleosols indicate periods of subaerial exposure long enough to permit pedogenesis to develop conglomerates indicate intense erosion of the troodos massif and its sedimentary cover as a result of the water level drop tectonic activity and more humid climatic conditions thus several subaerial exposure phases occurred in the marginal areas like the pissouri basin whereas shallow oligohaline conditions persisted in the deeper parts of the basin as indicated at odp site 968 both in the pissouri basin and on the flank of the erathostenes seamount the late messinian paleosols are directly overlain by the lowermost pliocene sediments deposited in well oxygenated deep marine conditions this drastic change of water depth shows that the water level of the late messinian saline to brackish lakes dropped far below that of the world ocean at least more than several hundred meters both these base level fluctuations and the oligohaline conditions caused intensive erosion karstification of the upper gypsum beds as also reported from many other mediterranean regions moreover the study of the polemi sections shows that oligohaline conditions had already started during the deposition of the upper gypsum sub unit typical brackish and fresh water assemblages are present in the last two gypsum layers and intergypsum beds this indicates that freshwater dilution i e the lago mare conditions resulted from a progressive change of the hydrological budget which started during deposition of the upper evaporites and climaxed after the deposition of the uppermost gypsum layer classical lago mare facies during this time periods of increased evaporation over precipitation led to deposition of the uppermost gypsum layers this evolution is interpreted as being due both to the severance from the open ocean and to the increasing contribution of the runoff precipitation versus marine inputs in the hydrological budget of the mediterranean

cooling rates of hyaloclastites applications of relaxation geospeedometry to undersea volcanic deposits glass fragments from three different hyaloclastites have been used to evaluate the range of cooling rates experienced by undersea volcanic deposits we found that the glass fragments retain structures with a range of apparent quench rates from 25 to 0 15 k min 1 the most rapid cooling rates are interpreted to be those resulting from cooling of the lava near the water interface simple conductive cooling models produce a range of quench rates comparable to those of the more rapidly cooled samples the very slow apparent quench rates are unlikely to result from simple linear cooling through the glass transition because of the onset of crystallization instead they are indicators of a more complex thermal history that involves the annealing of glasses at temperatures within the glass transition interval for a dwell time sufficient to allow the relaxation of the glass to lower temperature structures the thermal history recorded in these samples illustrates the complexity of eruptive processes and demonstrates that quench rates for natural glasses retain information relevant to more complex cooling models

the temporal record of magmatism at cerro uturuncu bolivian altiplano twenty six new 40ar 39ar plateau ages for 23 lavas and domes from the uturuncu volcano in the altiplano of sw bolivia reveal a protracted eruptive history from 1050 5 to 250 5 ka eruptions have been exclusively effusive producing some 50 km3 of high k dacites and silicic andesites bimodal mineral compositions complex mineral textures the presence of andesitic magmatic enclaves within dacites and linear chemical trends on binary element plots all indicate that magma mixing is an important petrogenetic process at uturuncu post 458 ka distinct high and low mgo cr magmas are resolved these magmas erupt during similar times suggesting that eruptions are tapping different parts of the magma system albeit from the same vent system volcanic and petrological features are consistent with the existence of a vertically extensive magma mush column beneath uturuncu and calculated buoyancy forces are sufficient to drive effusive eruptions eruptive activity is episodic with six eruptive periods separated by hiatuses of 50 kyr cumulative volume curves demonstrate that the majority of the edifice formed between 595 and 505 ka the episodicity of eruptions is most likely to be related to fluctuations in the magma supply to the underlying altiplano puno magma body

the glaciovolcanic evolution of an andesitic edifice south crater tongariro volcano new zealand abstract unusual deposits mapped and logged in detail around the summit area of tongariro volcano tongariro volcanic centre new zealand indicate that the construction and evolution of a substantial portion of this andesitic stratovolcano was beneath a significant ice cap or summit glacier as the edifice was built under and through the overlying ice the style of volcanism evolved in a complex history of growth initially a 100 m thick widespread hyaloclastite deposit was emplaced within a subglacial eruption formed meltwater lake this was followed by several phases of effusive and explosive eruptions producing lava flows and primary volcaniclastic deposits emplaced along channels carved into the ice by heated meltwater the clastic deposits contain quenched bombs and structural features that indicate waterlain transport and emplacement and soft sediment deformation such accumulation of water on a steep sided edifice without evidence for a subaerial crater lake along with lava flow features indicating confinement suggest that a substantial summit glacier was responsible for the production and retention of water and the architecture of these deposits recent studies at nearby ruapehu volcano have provided good evidence for glaciovolcanic interactions during the last glacial period however until now little was known of the physical lava ice interactions in the centre during the last interglacial period and the earlier part of the last glacial period 110 64 ka these new data support a reinterpretation for the volcanic evolution of the older tongariro edifice and the emplacement mechanisms of primary volcaniclastic deposits they also help to constrain local ice thicknesses and extents at the times of eruption in addition this study contributes to a sparse global catalogue of glaciovolcanic deposits of andesitic composition particularly of primary volcaniclastics preserved at mid latitude stratovolcanoes the variety of deposit types indicates a volcano building and evolving with glaciation and is an outstanding example of the types of glaciovolcanic interaction that can occur at one volcano

tectonic control for evaporite formation in the eastern betics tortonian spain tectonic uplift and sea level lowering are two proposed mechanisms to explain the development of thresholds in front of the widespread evaporite basins of the circum mediterrranean region during the miocene here we apply a multi disciplinary approach to the continuously marine sequences of the murcia cartagena basin to investigate which mechanism is responsible for the tortonian evaporites of the eastern betics first we develop a high resolution chronology for the venta de la virgen section by integration of biostratigraphic magnetostratigraphic and isotopic dating results next we construct palaeobathymetry and geohistory curves for this section and the abad composite of the sorbas basin we show that the apparent differential vertical motions between the two sections cannot be explained by sea level change but only by local tectonics the murcia cartagena basin shows significant tectonic uplift during the late tortonian and early messinian while the neighboring fortuna basin was rapidly subsiding we conclude that tectonic activity on the alhama de murcia fault was responsible for the emergence of a threshold that finally led to evaporite formation in the fortuna basin

modelling the evolution of columnar joints abstract cooling cracks developing from the margins of solidifying lava flows or intrusive dykes or sills often propagate inward and divide the rock into prismatic columns it has been shown that 1 the initial crack pattern that forms at the surface of the body is not as regular as the pseudo hexagonal pattern which evolves later 2 columnar structures develop by repeated step wise crack advances forming cm to dm transverse bands on the column faces 3 even within well developed colonnades the polygonal outlines continue to shift slightly from one crack advance to the next we propose that each new crack should propagate parallel to the highest thermal gradient ahead of the current crack tip when adjacent columns are of unequal size the local asymmetry of the isotherms drives the new crack toward the biggest and hottest column we present a geometrical model and algorithm that follows this rule and mimics the successive crack advances as the cooling front migrates into the lava sheet or dyke the model polygonal pattern obtained consists of convex irregular polygons with a variable number of sides but in which pentagons and hexagons predominate the algorithm successfully reproduces the rapid evolution from an initial immature crack pattern to a pseudo hexagonal mature one in which the average number of sides approaches six it predicts also the predominance of y type crack junctions the rapid evolution toward columns of approximately equal sizes and the persistent changes in length and diverging orientation of growth steps observed along the sides of columns the model polygonal patterns exhibit geometrical properties which are very similar to those observed in well developed columnar jointed flows such as the giant s causeway

structures textures and cooling histories of columbia river basalt flows flood basalt flows of the columbia river basalt group commonly exhibit well developed colonnade and entablature structures formed during cooling of individual flows the colonnade refers to the well defined columnar structure of many flows which appears in the lowermost 10 to 30 and in places the uppermost 10 to 20 entablature refers to those parts of a flow that have smaller column diameters and more irregular pattern fractures than those of colonnade entablature commonly occupies the central 60 to 70 of a flow in some cases however the entablature is interrupted by colonnade in such cases the entablature and colonnade may be repeated once or twice within a single flow in other cases flows may lack an entablature entirely petrographic examination reveals a pronounced correlation between structural and textural features thin sections of colonnade basalt have relatively coarse cruciform or octahedral fe ti oxide crystals and 20 glassy mesostasis the central entablature basalt in contrast has much more mesostasis as much as 60 and has textural features such as feathery fe ti oxide crystals indicative of more rapid cooling these features are the reverse of what might be expected for normal conductive cooling because cooling rates at the flow margins should be greater than those in the flow interior we reconciled the observed basalt textures with thermal models by taking into account rainfall and deranged drainage during crystallization of the flow downward migration of water through cracks would cause convective cooling of underlying unsolidified lava this effect and its consequences have been modeled numerically in order to clarify the physical constraints on the mechanism by which the central part of the lava can be quenched we have found that a water infiltration front can explain the presence of a thick quenched flow interior provided that the infiltration front moves downward just behind the lava solidification front despite heavy rainfall on hawaii for example 250 cm yr at kilauea iki exposed prehistoric lava flows on that island exhibit only colonnades we deduce from this that heavy rainfall alone is inadequate to quench flow interiors extensive flooding by deranged drainage or perhaps extremely heavy rainfall 250 cm yr is apparently required to produce entablatures the model also can be used to explain the occurrence of repeated entablature and colonnade by considering the effects of intermittent inundation the imposition of boundary conditions that mimic the removal and reoccurrence of flooding yields cooling histories that are consistent with the development of multiple colonnades and entablatures

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

progressive cooling of the hyaloclastite ridge at gjalp iceland 1996 2005 abstract in the subglacial eruption at gjalp in october 1996 a 6 km long and 500 m high subglacial hyaloclastite ridge was formed while large volumes of ice were melted by extremely fast heat transfer from magma to ice repeated surveying of ice surface geometry measurement of inflow of ice and a full stokes 2 d ice flow model have been combined to estimate the heat output from gjalp for the period 1996 2005 the very high heat output of order 10 6 mw during the eruption was followed by rapid decline dropping to 2500 mw by mid 1997 it remained similar until mid 1999 but declined to 700 mw in 1999 2001 since 2001 heat output has been insignificant probably of order 10 mw the total heat carried with the 1 2 10 12 kg of basaltic andesite erupted 0 45 km 3 dre is estimated to have been 1 5 10 18 j about two thirds of the thermal energy released from the 0 7 km 3 edifice in gjalp occurred during the 13 day long eruption 20 was released from end of eruption until mid 1997 a further 10 in 1997 2001 and from mid 2001 to present only a small fraction remained the post eruption heat output history can be reconciled with the gradual release of 5 10 17 j thermal energy remaining in the gjalp ridge after the eruption assuming single phase liquid convection in the cooling edifice the average temperature of the edifice is found to have been approximately 240 c at the end of the eruption dropping to 110 c after 9 months and reaching 40 c in 2001 although an initial period of several months of very high permeability is possible the most probable value of the permeability from 1997 onwards is of order 10 12 m 2 this is consistent with consolidated palagonitized hyaloclastite but incompatible with unconsolidated tephra this may indicate that palagonitization had advanced sufficiently in the first 1 2 years to form a consolidated hyaloclastite ridge resistant to erosion no ice flow traversing the gjalp ridge has been observed suggesting that it has effectively been shielded from glacial erosion in its first 10 years of existence

the beginning development and termination of the middle miocene badenian salinity crisis in central paratethys abstract middle miocene badenian evaporites of the carpathian region are underlain and overlain by deep water deposits the onset of evaporite deposition was sudden but not synchronous in all facies zones and the deposition of evaporites was controlled by the evolution of carpathian orogen in the carpathian foredeep and most probably in other basins the badenian evaporites represent the lower part of the nn6 zone halite and associated deposits in the central part of the badenian evaporite basin show the same facies successions and marker beds can be traced across and between individual basins characteristic marker beds made it possible to correlate various facies zones of the marginal ca sulfate platform these marker beds seem to reflect events that may be related to sudden and widespread changes in water chemistry which in turn imply major changes in basin hydrology the onset of the evaporitic deposition in the carpathian foredeep was clearly diachronous and the evaporites deposited in the basin centre preceded the beginning of evaporite sedimentation in the marginal basin however depositional history in the marginal basin and the basin centre was the same a general transgressive sequence of evaporites found in the carpathian foredeep resulted from the migration of facies zones induced by the nappe movement isotopic studies of badenian foraminifers occurring below evaporites suggest that the interrupted communication of the paratethys with the ocean was a consequence of eustatic sea level fall possibly related to climatic cooling and it was coupled with a tectonic closure of connection with the tethys thus both tectonics and eustacy have contributed to the origin of salinity crisis sedimentological and geochemical data indicate recycling of evaporites throughout most of the evaporite deposition the recycling at the end of gypsum deposition in the marginal sulfate platform was accompanied by a change in the hydrology of the central paratethys that was tectonically driven and possibly related to the block tectonic phase manifested in the marginal part of the carpathian foredeep basin the change in hydrology implied the dilution of brines by inflowing marine water and this terminated the middle miocene badenian salinity crisis the onset of the badenian salinity crisis shows great similarities to the onset of the messinian salinity crisis and the terminations of both crises were different

the initial cooling of pahoehoe flow lobes in this paper we describe a new thermal model for the initial cooling of pahoehoe lava flows the accurate modeling of this initial cooling is important for understanding the formation of the distinctive surface textures on pahoehoe lava flows as well as being the first step in modeling such key pahoehoe emplacement processes as lava flow inflation and lava tube formation this model is constructed from the physical phenomena observed to control the initial cooling of pahoehoe flows and is not an empirical fit to field data we find that the only significant processes are a heat loss by thermal radiation b heat loss by atmospheric convection c heat transport within the flow by conduction with temperature and porosity dependent thermal properties and d the release of latent heat during crystallization the numerical model is better able to reproduce field measurements made in hawai i between 1989 and 1993 than other published thermal models by adjusting one parameter at a time the effect of each of the input parameters on the cooling rate was determined we show that a the surfaces of porous flows cool more quickly than the surfaces of dense flows b the surface cooling is very sensitive to the efficiency of atmospheric convective cooling and c changes in the glass forming tendency of the lava may have observable petrographic and thermal signatures these model results provide a quantitative explanation for the recently observed relationship between the surface cooling rate of pahoehoe lobes and the porosity of those lobes jones 1992 1993 the predicted sensitivity of cooling to atmospheric convection suggests a simple field experiment for verification and the model provides a tool to begin studies of the dynamic crystallization of real lavas future versions of the model can also be made applicable to extraterrestrial submarine silicic and pyroclastic flows

latest cenomanian earliest turonian low oxygen tolerant benthonic foraminifera a case study from the sergipe basin n e brazil and the western anglo paris basin southern england abstract distinctive sedimentological geochemical isotopic and micropalaeontological response characterise the nature of sediments deposited under hypoxic anoxic bottom conditions during the latest cenomanian to earliest turonian of most of the world s basins the composition of the biota is a direct response to overall environmental conditions the recognition of distribution patterns of low oxygen tolerant microfauna is therefore of primary importance in evaluating and reconstructing the regional palaeoceanographic settings where such events took place a case study is presented from two coeval stratigraphic sequences the sergipe basin northeastern brazil and the western anglo paris basin southern england the associated benthonic foraminiferal assemblages from oxygen depleted environments consist mostly of opportunistic r selected species basic patterns in community trophic structures appear to have primarily dictated the composition of the biota the assemblages from outer shelf to upper slope oxygen depleted environments are commonly characterised by 1 low diversity 2 limited intraspecific variation 3 predominance c 40 60 of the total foraminiferal assemblage of epifaunal deposit feeding plano concavo convex trochospiral calcareous hyaline morphotypes gavelinellids conorboidids rosalinids and bagginids 4 variable numbers c 10 30 of infaunal bacterial detrital scavengers tapered and elongate morphotypes turrilinids bolivinids buliminellids fursenkoinids polymorphinids and caucasinids 5 epifaunal shallow infaunal deposit feeding lenticular morphotypes coiled vaginulinids c 5 19 6 variable numbers c 10 30 of agglutinated specimens lituolids discamminids eggerellids textulariids trochamminids ammodiscids tritaxiids and valvulinids and 7 dominance about 60 80 of minute c 100 200 m in maximum diameter width or length calcareous hyaline taxa during widespread dysaerobic quasi anaerobic episodes highly oxygen depleted bottom conditions are marked by the absence of benthonic microfauna minor taxonomic differences between the two studied areas are mostly due to palaeobiogeographic provincialism

glaciovolcanic emplacement of an intermediate hydroclastic breccia lobe complex during the penultimate glacial period 190 130 ka ruapehu volcano new zealand

extended cooling and viscous flow of large hot rhyolite lavas implications of numerical modeling results abstract a common misconception about rhyolite lava flows is that they cannot advance far from their vents and are constrained to be small due to their high viscosities although a high viscosity lava will indeed flow quite slowly it may advance a great distance if the lava efficiently retains heat and thus mobility and if the available magma supply is large to evaluate this possibility a finite difference numerical model was used to determine the rate of heat loss from units interpreted to be large rhyolite lavas cooling of such 100 300 m thick units is very slow and is further retarded by a vesicular carapace and by evolution of latent heat thermal history alone suggests that large thick lava flows could remain active for several decades to constrain the duration of flow advance of these units their inferred apparent viscosities are compared with those of active lava flows mean flow velocity of some large rhyolites in southwestern idaho usa was estimated based on the observation that the units must still have been advancing by viscous flow at the start of spherulite crystallization indicating perhaps a 10 to 18 year flow duration based on studies of obsidian dome california mean flow velocities would have been roughly 0 59 to 2 5 km yr and calculated average apparent viscosities of the flows ranged from 1 8 to 3 6 orders of magnitude greater than the viscosity of the lava itself this relationship also holds for active andesite and basaltic andesite block lava flows which have apparent viscosities 2 7 to 4 orders of magnitude greater than lava viscosities this implies that large rhyolites may indeed have been emplaced in the same manner as less silicic block lavas and that long distance viscous flow is not unrealistic for rhyolite lavas a good example of a large volume lava is the 15 km 3 rhyolite of the badlands sw idaho where vent relations show that lava effused from a fissure and advanced up to 9 km more extensive rhyolites could also be emplaced solely by effusion extended flow of these lavas may lead to the remelting and removal of basal crumble breccias and to the formation of welded shard textures in their margins both processes tending to obscure the lava flow origin of the units the great dimensions of lava like rhyolitic units with volumes of 10 to at least 200 km 3 are not a sufficient reason to assume they erupted as ignimbrites

volcano ice interactions in the arsia mons tropical mountain glacier deposits fan shaped deposits fsd superposed on the sides of the tharsis montes volcanic edifices are widely interpreted to have been formed by cold based glaciation during the late amazonian a period when the tharsis montes were volcanically active we survey the similar to 166 000 km 2 arsia mons fsd using new high resolution image and topography data and describe numerous landforms indicative of volcano ice interactions these include 1 steep sided mounds morphologically similar to terrestrial tindar that form by subglacial eruptions under low confining pressure 2 steep sided leveed flow like landforms with depressed centers interpreted to be subglacial lava flows with chilled margins 3 digitate flows that we interpret as having resulted from lava flow interaction with glacial ice at the upslope margin of the glacier 4 a plateau with the steep sides and smooth capping flow of a basaltic tuya a class of feature formed when subglacial eruptions persist long enough to melt through the overlying ice and 5 low areally extensive mounds that we interpret as effusions of pillow lava formed by subglacial eruptions under high confining pressure together these eruptions involved hundreds of cubic kilometers of subglacially erupted lava thermodynamic relationships indicate that this amount of lava would have produced a similar volume of subglacial liquid meltwater some of which carved fluvial features in the fsd landforms in the fsd also suggest that glaciovolcanic heat transfer induced local wet based flow in some parts of the glacier glaciovolcanic environments are important microbial habitats on earth and the evidence for widespread liquid water in the amazonian aged arsia mons fsd makes it one of the most recent potentially habitable environments on mars such environments could have provided refugia for any life that developed on mars and survived on its surface until the amazonian

forest re growth on medieval farmland after the black death pandemic implications for atmospheric co2 levels well dated pollen assemblages from an organic rich infill of an oxbow lake of the river roer southeastern netherlands provide a high resolution reconstruction of regional vegetation development and land use for the period between ad 1000 and 1500 regional effects of the mid 14th century plague pandemic known as the black death are reflected by a period of significant agricultural regression between ad 1350 and 1440 concomitant re growth of forest indicates the existence of a terrestrial carbon sink following the black death pandemic a direct temporal correlation of the reconstructed changes in land cover with a proxy record of atmospheric co2 mixing ratios based on stomatal frequency analysis of quercus robur leaf remains suggests the coupling of long term co2 trends of the 13th 15th centuries and coeval trends in regional forest density during the period of maximum reforestation between ad 1400 and 1440 co2 levels seem to be relatively low but the onset of a co2 decline may predate the spread of the black death in europe 2005 elsevier b v all rights reserved

gypsum facies transitions in basin marginal evaporites middle miocene badenian of west ukraine in the middle miocene badenian gypsum basin of the carpathian foredeep west ukraine three main zones of gypsum development occur in the peripheral parts of the basin zone i consists entirely of stromatolitic gypsum formed in a nearshore zone zone ii is located more basinward and is characterized by stromatolitic gypsum in the lower part of the section overlain by a sabre gypsum unit zone iii occurs in still more basinward areas and is characterized by giant gypsum intergrowths or secondary nodular gypsum pseudomorphs of these in the lowermost part overlain by stromatolitic gypsum sabre gypsum and then by clastic gypsum units correlation between these facies and zones has been achieved using lithological marker beds and surfaces of particular importance for correlation is a characteristic marker bed usually 20 40 cm thick of cryptocrystalline massive gypsum occurring in zones ii and iii the marker was not distinguished in zone i possibly because this bed is older than the entire gypsum section of that zone these new results strongly suggest that the deposition of giant gypsum intergrowth facies and stromatolitic gypsum facies was coeval in some sections of zones i and ii limestone intercalations have been recorded within the upper part of the gypsum sections considerable scatter of the 18o and 13c values of these limestones indicates variable diagenetic overprints of marine carbonates but a marine provenance of the limestones is confirmed by microfacies analysis some of the limestones are coeval with an intercalation of gypsarenitic mostly laminated gypsum occurring in the sabre gypsum unit of zones ii and iii badenian gypsum formed in extremely shallow water to subaerial environments on broad very low relief areas of negligible brine depth which could be affected by rapid transgressions stable isotope 34s 18o studies of the gypsum demonstrate that the sulphate was of sea water origin or was derived from dissolution of miocene marine evaporites investigations of individual inclusions in the gypsum indicate decreased water salinity when compared with modern marine derived calcium sulphate saturated water groundwater influences are indicated by high calcium sulphate contents of the brines in the evaporite basin the chemical composition of badenian waters was thus a mixture of relic sea water depleted in nacl groundwater enriched in calcium sulphate and surface run off

lava and ice interaction at stratovolcanoes use of characteristic features to determine past glacial extents and future volcanic hazards structures resulting from lava and ice interaction are common at glaciated stratovolcanoes during summit eruptions at stratovolcanoes meltwater is produced and travels freely down steep slopes and thin permeable valley glaciers eroding the ice and enlarging preexisting glacial drainages as a result eruptions in this environment have produced few catastrophic floods lava flowing into the open channels and voids in the glaciers becomes confined and grows thicker filling the available space and producing steep sided bodies with smooth bulbous contact surfaces quenching of lava against ice or by water forms small scale features such as tensional fractures and glass as the amount of meltwater in contact with the lava increases the type and abundance of smaller scale features become similar to those produced during subglacial eruptions into meltwater lakes identification of large and small scale lava ice contact features in the field can be used to reconstruct paleoglacial extent and combined with geochronology of lavas to determine past paleoclimate an understanding of lava ice interaction allows us to better assess the hazards posed by future eruptions at glaciated volcanoes

pseudopillow fracture systems in lavas insights into cooling mechanisms and environments from lava flow fractures abstract detailed field observations of structures within the flow front of a holocene trachyandesite lava from snaefellsnes iceland are presented the lava provides exceptional three dimensional exposure of complex brittle and ductile deformation textures that record processes of lava fracture and quenching driven by external water the flow front interior is characterised by structures consisting of a large metre scale curviplanar master fracture with many smaller centimetre scale subsidiary fractures perpendicular to the master fracture such structures have previously been recognised in a range of lava compositions from basalt to dacite and called pseudopillows or pseudopillow fractures we propose the term pseudopillow fracture systems to emphasise the consistent package of different fracture types occurring together all documented occurrences of pseudopillow fracture systems are in lavas that have been inferred to interact with an aqueous coolant i e liquid water ice or snow we use fracture surface textures and their orientation in relation to flow banding to identify three distinct types of master fracture and two types of subsidiary fractures master fracture surface textures used to identify fracture mechanisms include chisel marks striae cavitation dimples river lines and rough smooth fracture surface textures these indicate both brittle and ductile fracture happening on different types of master fracture chisel marks on subsidiary fractures indicate comparative cooling rates cooling directions and isotherm orientations at the time of fracture we propose a model for pseudopillow fracture system formation taking into account all the various fracture types textures and fracture propagation mechanisms and discuss their implications for interaction mechanisms between lava flows and external coolants

surface morphology of columnar joints and its significance to mechanics and direction of joint growth columnar joints in basaltic lava flows display conspicuous bands oriented normal to column axes new observations show that each band contains a single plumose structure and thus represents an individual crack or joint segment formed during a discrete growth event analysis of plumose structure and intersections of cracks leads to a new kinematic model of columnar jointing and provides the first direct proof that columnar joints grow incrementally from exterior to interior regions of solidifying magma bodies columnar joints form by nucleation and growth of new cracks on the edges of older cracks each new crack begins at a point and propagates mostly normal to column axes and along the leading edge of a developing column face where thermal stress is concentrated inward propagation of cracks toward hotter regions is limited by a decrease of thermal stress and by the brittle ductile transition of lava outward and lateral propagation is limited by mechanical interaction with previous cracks and by low thermal stress in already fractured lava cracks often diverge slightly from the planes of previous cracks probably because of spatial and temporal changes in directions of local principal stresses mechanical interaction causes a diverging crack to overlap curve toward and usually intersect the previous crack behind its edge leaving a blind tip that points in the overall growth direction of the columnar joints this and other directional criteria are applied to determine joint growth patterns in several lava flows of the western united states in two tiered and multi tiered flows downward growing columnar joints usually meet upward growing joints well below the middle of the flows which indicates very rapid cooling of upper portions relative to lower portions this supports the idea that convection of water in columnar joints connected to the surface may be an important mechanism for cooling the upper portions of these flows whereas conduction is probably the dominant cooling mechanism at the bases

magmatic evolution of the puyehue cordon caulle volcanic complex 40 s southern andean volcanic zone from shield to unusual rhyolitic fissure volcanism abstract magmas erupted from quaternary volcanoes of southern andes between 37 and 46 s latitude are mainly basaltic to andesitic however pccvc 40 s shows a singular magmatic evolution due to the abnormal evacuation of rhyolites especially in the last 100 ka in addition pccvc is the result of juxtaposing products from the nw trending alignment of cordillera nevada caldera cordon caulle fissure volcano and the puyehue stratocone using 40 ar 39 ar and 14 c geochronology it can be established that they evolved since ca 500 ka as coeval but separated vents with a first stage of shield volcanism followed by repeated collapses that formed an internal nw elongated graben from ca 100 ka volcanic activity occurred in both a fissure system cordon caulle and a central volcano puyehue holocene explosive eruptions mainly in the puyehue crater accompanied the dome growing along a nw trending fissure system last historical eruptions were in 1921 and 1960 when nw fissures of cordon caulle fed rhyodacitic lava flows in 1960 the fissure eruption was triggered by a remote mw 9 5 thrust earthquake cordillera nevada caldera presents a reduced compositional range 52 63 sio 2 and geochemical features of low pressure magma mixing and assimilation instead cordon caulle and puyehue volcanoes have a wide silica range 48 71 sio 2 and an outstanding affinity which can be modelled with initial high pressure fractional crystallization moderate magma mixing and subsequent low pressure fractional crystallization from a common parental source the exceptional magmatic evolution and eruptive style of pccvc in southern andes could be related with the physics of the plumbing system which in turn can be controlled by external factors as the structure of the continental crust and the ongoing stress regime

morphological features of miocene submarine coherent lavas from the green tuff basins examples from basaltic and andesitic rocks from the shimokita peninsula northern japan basaltic and andesitic volcanic rocks of miocene age exposed in the shimokita peninsula northern japan illustrate morphological features of typical submarine coherent lavas of the green tuff basins in japan they are pillow lobes with surface structures such as ropey wrinkles corrugations spreading cracks and tensional cracks and lava lobes composed of a lithic core and glassy border zone or rim with an in situ breccia zone grading outward into surrounding hyaloclastite in addition they include massive lavas with columnar joints and jointed dykes the submarine coherent lavas and dykes are commonly associated with hyaloclastic breccias such as pillow fragment breccia and angular fragment breccia the descriptions of the miocene volcanic rocks in the shimokita peninsula provide good criteria for recognition of submarine coherent lavas of basalt and andesite

reconstructing recent atmospheric trace gas concentrations from polar firn and bubbly ice data by inverse methods we present a method to extract the atmospheric signal of trace gas mixing ratios from firn and bubbly ice measurements this method validated using data from antarctic sites vostok and de08 includes a numerical model that simulates air transport in the firn and inverse theory we focus here on atmospheric ch4 reconstruction but the method can be used to reconstruct recent changes in any trace gas elemental or isotopic composition measured in firn and ice that has no chemical interaction with solid h2o this study also provides useful information on the effective diffusity porosity relationship and quantifies the smoothing effect due to gas diffusion in firn and at pore closure showing the typical time periods of events that are filtered by the firn and therefore not observed in the gas record of ice cores

subglacial intermediate volcanism at kerlingarfjoll iceland magma water interactions beneath thick ice the products of andesite and dacite glaciovolcanism at kerlingarfjoll are unlike others previously described in the literature three sequences of lithofacies are described and interpreted here the andesitic deposits at campsite gully are divided into massive vitriclastic lapilli tuff with intrusions fluidal clast bearing vitriclastic lapilli tuff and stratified pumice rich vitriclastic lapilli tuff at tindur andesitic eruptions produced contorted pillow fragment breccia and the clast supported lithic breccia finally pillow lava with intrusions and crudely bedded vitriclastic lapilli tuff of dacitic composition are described at haraldur abundant vitriclasts the presence of pillow lavas hackly fracturing of lava bodies and lack of oxidation of clasts demonstrate that each of these lithofacies formed in the presence of abundant water this contrasts with all other descriptions of subglacially erupted intermediate magmas which are characterised by jointed and glassy lava flows and domes with a marked scarcity of fragmental material the kerlingarfjoll sequences therefore demonstrate that it is possible for intermediate magmas to generate and interact with significant volumes of water at the base of a glacier preliminary estimates of volatile contents in glassy clasts correspond to quenching pressures equivalent to 500 m water or 550 m ice this is consistent with eruption beneath an ice sheet that was thick enough to overwhelm the underlying topography and where meltwater drainage was controlled by the morphology of the glacier surface it is argued that the drainage of water due to steep topography and or thin and fractured ice as opposed to thermodynamic considerations is the most likely explanation for the absence of evidence for significant magma water interaction in previously described instances of intermediate glaciovolcanism the apparent low viscosity of the kerlingarfjoll magmas may relate to relatively high eruption temperatures and or the inhibition of degassing of the magma due to high ambient pressures and the consequent limitation of groundmass crystallisation

foraminiferal record of marine transgression during deposition of the middle miocene badenian evaporites in central paratethys borkow section polish carpathian foredeep benthic and planktonic foraminifera from a marly clay intercalation sandwiched between mid badenian middle miocene gypsum deposited in an environment of an evaporitic shoal 1 m deep at borkow southern poland indicate a major marine flooding event in the previously isolated carpathian foredeep basin central paratethys after this very short term environmental change benthic foraminifers started to colonize a new niche which was previously defaunated and the pattern of benthic foraminiferal colonization is similar to that related to the reflooding which terminated the badenian evaporite deposition the benthic foraminifer assemblages are composed of pioneer opportunistic r selected species dominated by elphidiids the connection of the carpathian foredeep basin with the marine reservoir was short lived the marly clay intercalations in evaporite sequences originating in bared basins can thus register major environmental changes

morphometric study of pillow size spectrum among pillow lavas measurements of h and v dimensions in the horizontal and vertical directions of pillows exposed in vertical cross section were made on 19 pillow lavas from the azores cyprus iceland new zealand tasmania the western usa and wales the median values of h and v plot on a straight line that defines a spectrum of pillow sizes having linear dimensions five times greater at one end than at the other basaltic toward the small size end and andesitic toward the large size end the pillow median size is interpreted to reflect a control exercised by lava viscosity pillows erupted on a steep flow foot slope in lava deltas can however have a significantly smaller size than pillows in tabular pillowed flows inferred to have been erupted on a small depositonal slope indicating that the slope angle also exercised a control pipe vesicles generally abundant in the tabular pillowed flows and absent from the flow foot pillows have potential as a paleoslope indicator pillows toward the small size end of the spectrum are smooth surfaced and grew mainly by stretching of their skin whereas disruption of the skin and spreading were important toward the large size end disruption involved increasing skin thicknesses with increasing pillow size and pillows toward the large size end are more analogous with toothpaste lava than with pahoehoe and are inferred from their thick multiple selvages to have taken hours to grow pseudo pillow structure is also locally developed an example of endogenous pillow lava growth that formed intrusive pillows between normal pillows is described from sicily isolated pillow like bodies in certain andesitic breccias described from iceland were previously interpreted to be pillows but have anomalously small sizes for their compositions it is now proposed that they may lack an essential attribute of pillows namely the development of bulbous forms by the inflation of a chilled skin and are hence not true pillows para pillow lava is a common lava type in the flow foot breccias it forms irregular flow sheets that are locally less than 5 cm thick and failed to be inflated to pillows perhaps because of an inadequate lava supply rate or too high a flow velocity

cooling rate variation in natural volcanic glasses from tenerife canary islands silicate melts form glasses in a variety of geological environments the relaxation equilibration of the frozen glass structure provides a means of investigating the quench rates of natural glasses and this cooling history provides an important constraint for models of melt dynamics phonolite glasses from the central volcanic edifice of tenerife canary islands indicate a range of five orders of magnitude cooling rate determined by modeling the relaxation of the structure dependent property enthalpy h across the glass transition the relaxation of enthalpy is determined by heat capacity c p h t measurement of natural glass samples by differential scanning calorimetry dsc upon heating the heat capacity curve in the vicinity of the glass transition has a geometry characteristic of the previous cooling rate a series of thermal treatments applied to each individual sample results in a set of sample specific parameters which are used to model the heat capacity curve of the naturally cooled glass the cooling rate is then derived the equivalence of shear and enthalpic relaxation enables the relaxation of enthalpy for these volcanic samples to be described by a general term for the evolution of fictive temperature quench rates for thirty one glasses are calculated to be within the range 10 c s 1 to 7 c per day the cooling rates quoted are linear approximations across the glass transition within different volcanic facies cooling rates depend on several factors the most rapidly cooled glasses occur where samples lose heat by radiation from the surface our analyses indicate that in certain environments a natural annealing process results in slow quench rates this is interpreted as either a slow initial cooling process or the reheating of a glass to an annealing temperature within the glass transition interval the latter results in relaxation to a lower temperature structure controls on these processes include the initial temperature and dissipation of thermal energy from the volcanic body our results are consistent with an influence of volatiles on quench rates in volcanic bombs where glass adjacent to vesicular layers is relatively rapidly quenched we interpret this as a rapid quench rate frozen into the glass resulting from a change in viscosity due to volatile degassing in lava flows the conduction of heat from the hot flow interior controls the cooling process and diminishes the effect of volatile exsolution relaxation geospeedometry can be applied to glass samples from a variety of geological environments where cooling rates cannot be measured directly such measurements provide a means of determining cooling rates for a variety of volcanic processes an independent calibration for existing temperature and time data and a means for testing cooling rate dependent models