nonexplosive and explosive magma wet sediment interaction during emplacement of eocene intrusions into cretaceous to eocene strata trans pecos igneous province west texas abstract eocene intrusion of alkaline basaltic to trachyandesitic magmas into unlithified upper cretaceous maastrichtian to eocene fluvial strata in part of the trans pecos igneous province in west texas produced an array of features recording both nonexplosive and explosive magma wet sediment interaction intrusive complexes with 40 ar 39 ar dates of 47 46 ma consist of coherent basalt peperite and disrupted sediment two of the complexes cutting cretaceous strata contain masses of conglomerate derived from eocene fluvial deposits that at the onset of intrusive activity would have been 400 500 m above the present level of exposure these intrusive complexes are inferred to be remnants of diatremes that fed maar volcanoes during an early stage of magmatism in this part of the trans pecos province disrupted cretaceous strata along diatreme margins record collapse of conduit walls during and after subsurface phreatomagmatic explosions eocene conglomerate slumped downward from higher levels during vent excavation coherent to pillowed basaltic intrusions emplaced at the close of explosive activity formed peperite within the conglomerate within disrupted cretaceous strata in the conduit walls and within inferred remnants of the phreatomagmatic slurry that filled the vents during explosive volcanism a younger series of intrusions with 40 ar 39 ar dates of 42 ma underwent nonexplosive interaction with upper cretaceous to paleocene mud and sand dikes and sills show fluidal billowed quenched margins against the host strata recording development of surface instabilities between magma and groundwater rich sediment accentuation of billowed margins resulted in propagation of intrusive pillows into the adjacent sediment more intense disruption and mingling of quenched magma with sediment locally produced fluidal and blocky peperite but sufficient volumes of pore fluid were not heated rapidly enough to generate phreatomagmatic explosions this work suggests that trans pecos texas may be an important locale for the study of subvolcanic phreatomagmatic processes and associated phenomena eocene intrusions in the study area underwent complex interactions with wet sediment at shallow levels beneath the surface in strata as old as maastrichtian which must have remained unlithified and rich in pore water for 20 25 ma

rhyolitic globular peperites from the aznalcollar mining district iberian pyrite belt spain physical and chemical controls abstract globular peperites are exposed along the aznalcollar mining district iberian pyrite belt ipb spain these rocks originated by mingling of a low viscosity rhyolitic sill with unlithified wet sediments highly amygdaloidal up to 80 vol millimeters to centimeters across rhyolite globules extend from the upper contact of the sill for several centimeters into fine grained volcaniclastic host rocks the sill is very similar to other rhyolites in the ipb in terms of petrography and chemistry it is aphyric to very sparsely quartz phyric with small quartz phenocrysts vesicularity has been measured in the sill as vesicle area fraction determined by point counting over a rectangular grid and number density per unit area determined by counting every vesicle within the grid area amygdale distribution measured within the sill indicates a process by which vesicles migrated vertically from the lower portions of the sill to the roof zone we suggest that this migration process caused local density changes large enough to allow the rhyolitic magma to become buoyant enough to move through the overlying sediments producing globular peperites globular structures are preserved when rhyolite globules entered the wet sediment

magma sediment mingling in an ordovician rift basin the plouezec plourivo half graben armorican massif france the plouezec plourivo basin ppb armorican massif is an ordovician half graben filled with red bed deposits lying on a cadomian metamorphic basement peperites crop out along its northeast coastal sector in connection with diverse magmatic and hydrothermal products combining field structural observations and geochemical analyses of magmatic rocks leads us to propose a model of emplacement of peperites in an extensional setting the ppb peperites result from mingling between magma and initially wet sediment the main corresponding facies consist of rounded magmatic bodies corrugated lava sediment contacts and a remarkable thin sheet of fluidized sediment extending over about 100 m parallel and c 10 cm above the base of a porphyritic lava flow a few ppb peperites formed under a dominant brittle regime are autoclastic breccias at the base of a lava flow and polymict breccias including both fluidal and blocky volcanic clasts sediment fluidization formation of vapor films magma sediment density contrasts and non explosive fragmentation are the main mechanisms invoked to generate the ppb peperites the c 100 m extended sediment derived sheet lying near the base of a lava flow likely formed by diapiric rise of fluidized sediment through molten lava we show that silicic contamination accompanied these peperitic processes

water magma interaction some theory and experiments on peperite formation experiments using molten thermite as a magma analog produce peperite when the melt interacts with wet sand these experiments also show explosive behavior developing strombolian and surtseyan like bursts the results demonstrate that the application of fuel coolant interaction fci theory is appropriate for interpretation of peperites the theory described includes discussion of the importance of mass interaction ratios of wet sediment and magma rs which determine thermal equilibrium temperature limits and contact interface dynamics the dynamics of the interface between magma and wet sediments involves heat transfer over a wide range of rates from passive quenching to explosive fragmentation a vapor film layer develops at the interface and acts both as an insulating barrier promoting passive quenching as well as a potential energy reservoir that can cause magma fragmentation mingling of the magma with wet sediments and explosive quenching when the vapor film becomes unstable an important parameter in determining the behavior of the vapor film is the value of rs which controls whether heat can be convectively removed from the layer as more is being added from its contact with magma if rs 1 for fully saturated sediments there is enough water in the sediments to make convective heat flow effective in quenching the magma but below that value there is the potential that the vapor film will be unstable producing highly dynamic phenomena including explosive fragmentation at values of rs 0 1 there is insufficient water to allow the escalation of explosive fragmentation

magma composition and viscosity as controls on peperite texture an example from passamaquoddy bay southeastern canada silurian mafic lava flows and rhyolite sills in the passamaquoddy bay area southeastern canada interacted with wet sediment to produce peperitic breccia the pahoehoe type mafic flows flowed over and bulldozed into wet unconsolidated silt and sand to produce both blocky and fluidal peperite at their lower contacts soft sediment deformation structures in the siltstone adjacent to the flows irregularly shaped vesicles in the siltstone and siltstone filled vesicles in the mafic lava all indicate the sediment was wet at the time of flow emplacement sills of rhyolite emplaced into the same sedimentary sequence also interacted with the wet sediment and produced peperite at both the upper and lower contacts evidence for the rhyolitic magma interacting with wet sediment includes sediment filled vesicles in rhyolite quartz filled vesicles in siltstone and angular non vesicular shards of rhyolite in clastic dykes peperite formed by this process is exclusively blocky the rhyolitic magma in the passamaquoddy bay sequence and other examples of high viscosity magma producing only blocky peperite suggest that in contrast to low viscosity magmas which produce a combination of blocky and fluidal peperite only blocky peperite will form associated with highly viscous rhyolite magma the sediment that interacted with both the mafic and rhyolitic lavas is of similar texture indicating that in this case sediment texture did not control peperite type the change from fluidal to blocky peperite texture may also be controlled in part by the magma temperature and or confining pressure and the generation and maintenance of a steam film at the magma wet sediment interface

warm ocean is eroding west antarctic ice sheet 1 satellite radar measurements show that ice shelves in pine island bay have thinned by up to 5 5 m yr 1 over the past decade the pattern of shelf thinning mirrors that of their grounded tributaries the pine island thwaites and smith glaciers and ocean currents on average 0 5 c warmer than freezing appear to be the source the synchronised imbalance of the inland glaciers is the result of reduced lateral and basal tractions at their termini and the drawdown of grounded ice shows that antarctica is more sensitive to changing climates than was previously considered

distribution of water masses and meltwater on the continental shelf near the totten and moscow university ice shelves warm waters flood the continental shelf of the amundsen and bellingshausen seas in west antarctica driving rapid basal melt of ice shelves in contrast waters on the continental shelf in east antarctica are cooler and ice shelves experience relatively low rates of basal melt an exception is provided by the totten and moscow university ice shelves on the sabrina coast where satellite derived basal melt rates are comparable to west antarctica recent oceanographic observations have revealed that relatively warm 0 4 c modified circumpolar deep water mcdw enters the cavity beneath the totten ice shelf through a 1100 m deep trough delivering sufficient heat to drive rapid basal melt here we use observations from a recent summer survey to show that mcdw is widespread on the continental shelf of the sabrina coast forming a warm up to 0 3 c and saline 34 5 34 6 bottom layer overlaid by cold freezing point and fresh salinity 34 3 winter water dense shelf water is not observed a 1000 deep m trough allows water at 1 3 c to reach the moscow university ice shelf cavity to drive basal melt freshening by addition of glacial meltwater is widespread on the southern shelf at depths above 300 400 m with maximum meltwater concentrations up to 4 5 ml l 1 observed in outflows from the ice shelf cavities our observations indicate that the ocean properties on the sabrina coast more resemble those found on the continental shelf of the amundsen and bellingshausen seas than those typical of east antarctica

circumpolar mapping of antarctic coastal polynyas and landfast sea ice relationship and variability abstractsinking of dense water from antarctic coastal polynyas produces antarctic bottom water aabw which is the densest water in the global overturning circulation and is a key player in climate change as a significant sink for heat and carbon dioxide very recent studies have suggested that landfast sea ice fast ice plays an important role in the formation and variability of the polynyas and possibly aabw however they have been limited to regional and case investigations only this study provides the first coincident circumpolar mapping of antarctic coastal polynyas and fast ice the map reveals that most of the polynyas are formed on the western side of fast ice indicating an important role of fast ice in the polynya formation winds diverging from a boundary comprising both coastline and fast ice are the primary determinant of polynya formation the blocking effect of fast ice on westward sea ice advection by the coastal current would be another key factor these effects on the variability in

antarctic bottom water production from the vincennes bay polynya east antarctica one year moorings at depths greater than 3000m on the continental slope off vincennes bay east antarctica reveal the cold 0 5 degrees c and fresh 34 64 signals of newly formed antarc

antarctic bottom water from the adelie and george v land coast east antarctica 140 149 e 1 we report on observations of dense shelf water overflows and antarctic bottom water aabw formation along the continental margin of the adelie and george v land coast between 140 e and 149 e vertical sections and bottom layer water mass properties sampled during two rvib nathaniel b palmer hydrographic surveys nbp00 08 december 2000 january 2001 and nbp04 08 october 2004 describe the spreading of cold dense shelf water on the continental slope and rise from two independent source regions the primary source region is the adelie depression exporting high salinity dense shelf water through the adelie sill at 143 e an additional eastern source region of lower salinity dense shelf water from the mertz depression is identified for the first time from bottom layer properties northwest of the mertz sill and mertz bank 146 e 148 e that extend as far as the buffon channel 144 75 e in summer regional analysis of satellite derived ice production estimates over the entire region from 1992 to 2005 suggests that up to 40 of the total ice production for the region occurs over the mertz depression and therefore this area is likely to make a significant contribution to the total dense shelf water export concurrent time series from bottom mounted microcats and adcp instruments from the mertz polynya experiment april 1998 to may 1999 near the adelie sill and on the upper continental slope 1150 m and lower continental rise 3250 m to the north describe the seasonal variability in downslope events and their interaction with the ambient water masses the critical density for shelf water to produce aabw is examined and found to be 27 85 kg m 3 from the adelie depression and as low as 27 80 kg m 3 from the mertz depression this study suggests previous dense shelf water export estimates based on the flow through the adelie sill alone are conservative and that other regions around east antarctica with similar ice production to the mertz depression could be contributing to the total aabw in the australian antarctic basin

aeromagnetic mapping of the structure of pine canyon caldera and chisos mountains intrusion big bend national park texas analysis of aeromagnetic and gravity data reveals new details of the structure igneous geology and temporal evolution of the prominent enigmatic ca 32 ma pine canyon caldera and the chisos mountains big bend national park texas the main caldera fi lling pine canyon rhyolite the oldest member of the south rim formation is reversely magnetized allowing it to be used as a key marker bed for determining caldera fi ll thickness modeling of gravity and magnetic anomalies indicates that the pine canyon rhyolite is probably thicker in the northeastern part of the caldera lineaments in the magnetic data suggest the presence of buried faults beneath the caldera that may have led to increased downdrop in the northeast versus the southwest allowing a thicker section of caldera fi ll to accumulate there the pine canyon caldera has been interpreted as a downsag caldera because it lacks surfi cial faulting so these inferred faults are the fi rst mapped features there that could be responsible for caldera collapse the caldera boundary correlates well with the margins of a gravity low general features of the caldera match well with basic models of downsag calderas meaning that the pine canyon caldera may be a classic example of downsagging of which few well described examples exist in terms of a geophysical signature the source of a long wavelength magnetic high over the chisos mountains is interpreted as a previously unknown broad intrusion the long axis of which trends parallel to a major crustal boundary related to the ouachita orogeny or an even earlier precambrian margin this feature represents the largest intrusion 28 34 km diameter 1 4 km thick 700 3000 km 3 in volume in an area where relatively small laccoliths are ubiquitous the intrusion most likely represents a long lived 1 m y reservoir replenished by small batches of magma of varying composition as refl ected in the variation of eruptive products from the pine canyon and sierra quemada calderas the intrusion may represent the easternmost occurrence of voluminous tertiary magmatism in the southwestern united states

antarctic bottom water warming and freshening contributions to sea level rise ocean freshwater budgets and global heat gain abstractfreshening and warming of antarctic bottom water aabw between the 1980s and 2000s are quantified assessing the relative contributions of water mass changes and isotherm heave the analysis uses highly accurate full depth ship based conductivity temperature depth measurements taken along repeated oceanographic sections around the southern ocean fresher varieties of aabw are present within the south pacific and south indian oceans in the 2000s compared to the 1990s with the strongest freshening in the newest waters adjacent to the antarctic continental slope and rise indicating a recent shift in the salinity of aabw produced in this region bottom waters in the weddell sea exhibit significantly less water mass freshening than those in the other two southern basins however a decrease in the volume of the coldest deepest waters is observed throughout the entire southern ocean this isotherm heave causes a salinification and warming on isobaths from the bottom up to the shallow potential tem

large multidecadal salinity trends near the pacific antarctic continental margin abstract ocean temperature and salinity measurements on and near the antarctic continental shelf in the southwest pacific sector are evaluated for evidence of temporal change shelf water in the southwest ross sea has declined in salinity by 0 03 decade 1 from 1958 to 2008 while its temperatures have increased in proportion to the influence of salinity on the sea surface freezing point modified deep water intrusions that reach the central ross ice shelf have freshened at a similar rate and cooled by 0 5 c since the late 1970s salinity has decreased by 0 08 decade 1 in the westward coastal and slope front currents consistent with increased melting of continental ice upstream in the amundsen sea overturning of those near surface waters during winter sea ice formation and mixing across the slope front is sufficient to account for the 5 decade shelf water salinity change a strong correlation between the freshening and change in the southern annular mode index suggests a link with the large scale atmosp

variation in peperite textures associated with differing host sediment properties peperites formed by mixing of magma and wet sediment are well exposed along punta china baja california mexico where two sills intrude a section of lava flows limestones and volcaniclastic rocks irregular lobes and dikes extend from the sills several meters into host sediments including highly comminuted flow top breccias lithic lapilli tuff breccias and shelly micrites whereas intrusive contacts with lava flows are sharp and planar where one sill intruded both coarse grained volcaniclastic rock and fine grained limestone textural differences between the hosts produced strikingly different styles of peperite blocky masses of the basaltic intrusions up to 1 m in size were dispersed for distances up to 3 m into host lithic lapilli tuff breccias the blocks consequently underwent in situ fragmentation as they were rapidly quenched the high degree of dispersion resulted from steam explosions as the magma enveloped pockets of water in the coarse grained permeable host elutriation of fine grained material from vertical pipes in tuff breccia above the lower sill provides evidence for meter scale fluidization of the host the contact zone between the basaltic magma and the shelly micrite host resembles a mixture of two viscous immiscible fluids fluidal peperite intrusion occurred behind a stable vapor film which entrained lime mud particles and carried them off grain by grain as magma advanced into the host thin section scale elutriation pipes formed microglobular peperite represents a frozen example of a fuel coolant interaction fci between basaltic magma and fluidized micrite host the intimate intermixing of magma and host at the submillimeter level is attributed to fluid instabilities developed along the magma vapor host interface such intimate intermixing of magma and water bearing fragmental debris is commonly a precursory step toward explosive hydrovolcanism

warming and freshening in the abyssal southeastern indian ocean abstract warming and freshening of abyssal waters in the eastern indian ocean between 1994 95 and 2007 are quantified using data from two closely sampled high quality occupations of a hydrographic section extending from antarctica northward to the equator these changes are limited to abyssal waters in the princess elizabeth trough and the australian antarctic basin with little abyssal change evident north of the southeast indian ridge as in previous studies significant cooling and freshening is observed in the bottom potential temperature salinity relations in these two southern basins in addition analysis on pressure surfaces shows abyssal warming of about 0 05 c and freshening of about 0 01 practical salinity scale 1978 pss 78 in the princess elizabeth trough and warming of 0 1 c with freshening of about 0 005 in the abyssal australian antarctic basin these 12 yr differences are statistically significant from zero at 95 confidence intervals over the bottom few to several hundred decibars of t

rapid freshening of antarctic bottom water formed in the indian and pacific oceans 1 repeat hydrographic sections occupied in 1995 and 2005 reveal a rapid decline in the salinity and density of antarctic bottom water throughout the australian antarctic basin the basin wide shift of the deep potential temperature salinity s relationship reflects freshening of both the indian and pacific sources of antarctic bottom water the s curves diverge for waters cooler than 0 1 c corresponding to a layer up to 1000 m thick over the antarctic continental slope and rise changes over the last decade are in the same direction but more rapid than those observed between the late 1960s and the 1990s when combined with recent observations of similar freshening of north atlantic deep water these results demonstrate that dense water formed in both hemispheres is freshening in response to changes in the high latitude freshwater balance and rapidly transmitting the signature of changes in surface climate into the deep ocean

melting of ice shelves and the mass balance of antarctica we calculate the present ice budget for antarctica from measurements of accumulation minus iceberg calving run off and in situ melting beneath the floating ice shelves the resulting negative mass balance of 469 gt year 1 differs substantially from other recent estimates but some components are subject to high temporal variability and budget uncertainties of 20 50 annual accumulation from an earlier review is adjusted to include the antarctic peninsula for a total of 2144 gt year 1 an iceberg production rate of 2016 gt year 1 is obtained from the volume of large icebergs calculated from satellite images since 1978 and from the results of an international iceberg census project ice shelf melting of 544 gt year 1 is derived from physical and geochemical observations of meltwater outflow glaciological field studies and modeling of the sub ice ocean circulation the highest melt rates occur near ice fronts and deep within sub ice cavities run off from the ice sheet surface and from beneath the grounded ice is taken to be 53 gt year 1 less than half of the negative mass balance need come from the grounded ice to account for the unattributed 0 45 mm year 1 in the ipcc best estimate of the recent global sea level rise

the diabatic deacon cell abstract southern ocean air sea fluxes from the coads dataset are examined for compatibility between buoyancy gain and northward ekman transport an analysis in density classes points to an upwelling of upper circumpolar deep water and subsequent buoyancy gain from air sea exchange as water flows northward in the ekman layer the upper circumpolar deep water layer is too shallow to admit southward geostrophic flow along topography and an eddy mass flux mechanism for southward transport in this layer to replenish the upwelling is advanced based on observed large scale potential vorticity gradients estimates of the strength and vertical structure of the meridional flow are given using repeated hydrographic sections and a new climatology

the distribution and formative processes of latent heat polynyas in east antarctica a study of polynya characteristics in east antarctica was undertaken using ice concentrations derived from special sensor microwave imager data for the period july 1987 august 1994 the areas of polynyas were defined as having an ice concentration 75 the analysis revealed a total of 28 coastal polynyas within the study region the spatial and temporal variability in areal extent was quantified the timing of mean maximum areal extent varied from june to october the bathymetry and wind regime at each polynya site was examined to gauge the relative importance of these parameters in polynya formation and maintenance in 20 locations shallow banks and shoals form grounding zones for icebergs and anchoring sites for fast ice which form barriers to the predominantly westward drift of the pack ice elsewhere north south coastal protrusions or alignments form similar barriers the subsequent removal of newly formed sea ice from the lee of such barriers by katabatic and synoptic winds maintains areas of reduced ice concentration and open water very few coastal polynyas are attributed solely to katabatic outflow the combined influence of bathymetry topography and winds is responsible for the characteristics of the majority of polynyas many were considered to be marginal characterised by occasional periods when the ice concentration falls below 75 an analysis of annual winter totals of areas with ice concentrations 75 shows no trends in total polynya areal extent over the period 1987 94 known locations of emperor penguin aptenodytes forsteri rookeries were also found to be associated with the locations of coastal polynyas

the contribution of alaskan siberian and canadian coastal polynyas to the cold halocline layer of the arctic ocean numerous arctic ocean circulation and geochemical studies suggest that ice growth in polynyas over the alaskan siberian and canadian continental shelves is a source of cold saline water which contributes to the maintenance of the arctic ocean halocline the purpose of this study is to estimate for the 1978 1987 winters the contributions of arctic coastal polynyas to the cold halocline layer of the arctic ocean the study uses a combination of satellite oceanographic and weather data to calculate the brine fluxes from the polynyas then an oceanic box model is used to calculate their contributions to the cold halocline layer of the arctic ocean this study complements and corrects a previous study of dense water production by coastal polynyas in the barents kara and laptev seas recurrent polynyas form on the canadian and alaskan coasts from banks island to the bering strait and on the siberian coast from the bering strait to the new siberian islands in the bering sea polynyas form in norton sound south and west of st lawrence island and in the gulf of anadyr two regions that account for almost 50 of the total dense water production are the siberian coastal polynyas in the adjacent regions of the gulf of anadyr and anadyr strait and the alaskan coastal polynyas which occur along the coast from cape lisburne to point barrow for all of the western arctic coastal regions examined the mean annual total brine flux is 0 5 0 2 sv combination of this flux with the contribution from the barents kara and laptev seas which is recalculated from data in the earlier study shows that over the entire arctic coastal polynyas generate about 0 7 1 2 sv of dense water this compares well with the theoretical estimates of 1 1 5 sv because an unknown fraction of the barents kara and laptev brine flux must go to the eurasian basin deep water the coastal polynyas alone cannot renew the halocline layer other potential brine generation mechanisms include overall freezing on the shelves and the response of the ice to infrequent violent storms for example during february 1982 an intense storm generated a large region of low ice concentration in the eastern chukchi sea over barrow canyon the refreezing of the region was followed by the flow of a dense plume down barrow canyon although the ocean dynamical response to this refreezing needs to be established the possible response of a barrow canyon flow to this refreezing event suggests that the overall refreezing in response to infrequent violent storms may be a potential source of the additional brine needed to maintain the arctic ocean halocline

peperite a review of magma sediment mingling the study of peperite is important for understanding magma water interaction and explosive hydrovolcanic hazards this paper reviews the processes and products of peperite genesis peperite is common in arc related and other volcano sedimentary sequences where it can be voluminous and dispersed widely from the parent intrusions it also occurs in phreatomagmatic vent filling deposits and along contacts between sediment and intrusions lavas and hot volcaniclastic deposits in many environments peperite can often be described on the basis of juvenile clast morphology as blocky or fluidal but other shapes occur and mixtures of different clast shapes are also found magma is dominantly fragmented by quenching hydromagmatic explosions magma sediment density contrasts and mechanical stress as a consequence of inflation or movement of magma or lava magma fragmentation by fluid fluid shearing and surface tension effects is probably also important in fluidal peperite fluidisation of host sediment hydromagmatic explosions forceful intrusion of magma and sediment liquefaction and shear liquification are probably the most important mechanisms by which juvenile clasts and host sediment are mingled and dispersed factors which could influence fragmentation and mingling processes include magma host sediment and peperite rheologies magma injection velocity volatile content of magma total volumes of magma and sediment involved total volume of pore water heated presence or absence of shock waves confining pressure and the nature of local and regional stress fields sediment rheology may be affected by dewatering compaction cementation vesiculation fracturing fragmentation fluidisation liquefaction shear liquification and melting during magma intrusion and peperite formation the presence of peperite intraclasts within peperite and single juvenile clasts with both sub planar and fluidal margins imply that peperite formation can be a multi stage process that varies both spatially and temporally mingling of juvenile clast populations formed under different thermal and mechanical conditions complicates the interpretation of magma fragmentation and mingling mechanisms

morphology of a crater filling lava lake margin the peninsula tuff cone tule lake national wildlife refuge california implications for formation of peperite textures abstract a crater filling lava lake basalt at the peninsula tuff cone in northeastern california has features on its base formed by interaction of the basalt with wet hydrovolcanic tuff a spectrum of features including elongated streamlined flute shaped lobes and irregular corrugations are exposed on the base of the lava lake flute shaped lobes range in amplitude from several centimeters to 0 5 m plunge downdip with respect to the subjacent layered tuff toward the center of the crater and are better defined at depths more than 3 m below the lava lake surface these may have been formed by growth of rayleigh taylor instability waves caused by the density contrast between the wet tuff and basalt combined with directed stress from flow of the lava lake radially outward from the crater formation of an insulating vapor film at the wet tuff basalt interface and downward pressure exerted by the lava lake allowed the edge of the lava lake to quench gradually and prevented formation of peperite at greater depths in the lake corrugations exposed on the upper 1 5 m of the lava lake margin increase in size from several millimeters to 10 cm in amplitude toward the top of the lava lake and approximately parallel the surface corrugations may be the remnant of fluidal peperite preserved on the edge of the lava lake where the peperite was eroded or may be deformation features formed within an insulating vapor film due to oscillation of the vapor film these were formed higher in the lava lake where the lava lake basalt was thinner wet tuff deposits confining the lava lake were thinner and temperature differences between the wet tuff and lava were greater if corrugations represent deformation of the lava edge within the vapor film rather than peperite formation they preserve an intermediate process that is involved in the formation of peperite this study offers a unique opportunity to evaluate some of the initial mechanisms involved in the formation of peperite based on features preserved in the lava where the host rock in this case hydrovolcanic tuff has been eroded but the properties of the host rock are known from adjacent exposures

sea ice production and export from coastal polynyas in the weddell and ross seas 1 for 1992 2008 we use data from the special sensor microwave imager ssm i and the advanced microwave scanning radiometer eos amsr e to examine differences in ice production and export in the weddell and ross seas we find that the ross production is three times that in the weddell the ross export twice that in the weddell in the ross the ice production has a statistically significant positive trend of about 21 km3 y 1 and approximately equals the export while in the weddell the production trend is statistically flat and provides only about 60 of the export for each sea comparison of the ice production with the total winter sea ice volume shows that the weddell polynyas produce 5 10 of the total the ross polynyas 20 50 the explanation for these differences is that in the ross the low pressure system is better situated for generation of large polynyas than in the weddell

reduced sea ice production due to upwelled oceanic heat flux in prydz bay east antarctica the coastal shelf region of east antarctica is hypothesized to be shielded from the offshore heat of circumpolar deep water cdw due to the dynamic barrier of the antarctic slope front yet modified cdw mcdw intrudes into the coastal environment in key locations with impacts on dense shelf water formation and ocean ice shelf interaction that remain largely unquantified using moored measurements and conductivity temperature depth instrumented seal hydrographic data collected in prydz bay east antarctica we find buoyancy driven upwelling of mcdw into the subsurface 50 m layer of the southeastern embayment wintertime convection extends as deep as 300 m entraining heat of the upwelled mcdw to the surface accumulated sensible heat supply to the surface through deep convection during june july reduces the potential sea ice production by 45 in the davis polynya demonstrating that stronger warmer mcdw intrusions onto the shelf will likely reduce the shelf water density and threaten antarctic bottom water formation

fluidization of wet sediments during the emplacement and cooling of various igneous bodies during the emplacement and cooling of igneous bodies fluidization of wet sediment by water vapour may occur by heating or by pressure relief during the opening of fractures momentary fluidization causes sediment reconstitution and local transport continuous fluidization can result in substantial sediment displacement theoretical considerations show that fluidization due to heating is not likely to occur at depths where pressure is much greater than 312 bars studies of the emplacement of sills of andesite ayrshire fluid rhyolite ramsey island and viscous rhyolite moelwyn hills recognize a wide range of phenomena attributable to wet sediment fluidization and in places modify existing interpretations the transgressive bases of the subaqueously welded ash flow tuffs of the capel curig volcanic formation are consistent with emplacement attended by fluidization of the subjacent sediment evidently fluidization is a means by which large volumes of wet sediment can be replaced by igneous material with minimal disturbance of the remaining host also fluidization can result in exceptionally complex contact relationships between sedimentary host and intrusive rocks and can cause fractures formed during cooling to be thoroughly pervaded by sediment fluidization is commonly associated with the formation of peperites

incremental dilation of magma filled fractures evidence from dykes on the isle of skye scotland abstract localised swarms of narrow 10 120 mm basaltic dykes occur at offsets and terminations of some larger basaltic dykes in skye scotland these narrow dykes cut and chill against each other and the larger dyke and its country rock the narrow dykes can only be traced a short distance into the larger dyke before terminating some of these terminations show the central parts of both dykes merging as the chilled margins vanish at other terminations the later dyke outcrop narrows progressively to a point these all show that after initial dilation and some crystallisation of material in the dyke fissure there were additional up to 11 increments of dilation increments were sufficiently spaced in time for preceding injections to have become solid time spans separating initial and later dilation may be sufficient for local crystallisation of dykes up to 3 2 m thick away from these terminations the dyke fissure remained an open void occupied by flowing magma during the successive increments of dilation this paper demonstrates that fluid filled dyke fissures can vary in width with time an observation consistent with the modern theoretical models of dyke emplacement that relate dyke width to magma input pressures and other magmatic parameters dyke offsets and terminations with late dilational increments are shown to provide a variety of other information on flow crystallisation and sealing of dyke fissures

mapping of sea ice production for antarctic coastal polynyas 1 active sea ice production in antarctic coastal polynyas causes dense water formation finally leading to antarctic bottom water aabw formation this study gives the first mapping of sea ice production in the antarctic ocean based on heat flux calculation with ice thickness data derived from satellite data the highest ice production occurs in the ross ice shelf polynya region the ice production there decreased by 30 from the 1990s to the 2000s which can be one candidate for causing the recent freshening of aabw the cape darnley polynya in east antarctica is found to be the second highest production area suggesting a possible aabw formation area according to our estimation around 10 of southern ocean sea ice is produced in the major antarctic coastal polynyas the mapping provides surface heat and salt flux conditions in the ice covered region which have not been well understood

pathways of basal meltwater from antarctic ice shelves a model study we investigate spreading pathways of basal meltwater released from all antarctic ice shelves using a circumpolar coupled ice shelf sea ice ocean model that reproduces major features of the southern ocean circulation including the antarctic circumpolar current acc several independent virtual tracers are used to identify detailed pathways of basal meltwaters the spreading pathways of the meltwater tracers depend on formation sites because the meltwaters are transported by local ambient ocean circulation meltwaters from ice shelves in the weddell and amundsen bellingshausen seas in surface subsurface layers are effectively advected to lower latitudes with the acc although a large portion of the basal meltwaters is present in surface and subsurface layers a part of the basal meltwaters penetrates into the bottom layer through active dense water formation along the antarctic coastal margins the signals at the seafloor extend along the topography showing a horizontal distribution similar to the observed spreading of antarctic bottom water meltwaters originating from ice shelves in the weddell and ross seas and in the indian sector significantly contribute to the bottom signals a series of numerical experiments in which thermodynamic interaction between the ice shelf and ocean is neglected regionally demonstrates that the basal meltwater of each ice shelf impacts sea ice and or ocean thermohaline circulation in the southern ocean

physiographic influences on dense shelf water cascading down the antarctic continental slope abstract predicting the source areas for antarctic bottom water aabw requires knowledge of how cold dense water masses form and move from the antarctic shelves to the continental slope here we use a review of nearly 50 years of direct hydrographic observations to infer the main broad scale influences on the distribution of dense shelf water dsw overflows that cascade down the continental slope around antarctica the dynamics and distribution of large ice shelves coastal polynyas and the physiography of the antarctic continental shelves are each considered the catalogue we present increases the number of dsw observations to 27 adds 20 additional stations where this process is likely to have occurred and identifies 41 areas where dsw appears to be absent our pan antarctic multi decadal review enhances the understanding of the formation and export of dsw and highlights the variability and complexity of ice ocean systems on high latitude continental margins the study also provides a context for understanding recent episodes of antarctic ice shelf instability and how the relationship between dsw and aabw may evolve with climatic and oceanographic changes

contrasting interactions of two magmas with the same water saturated hosts big bend national park texas abstract rhyolitic and mafic dikes cut lower tertiary sediments tuffs and mafic lavas of the eocene oligocene chisos formation in big bend national park texas two contrasting magmas injected into the same hosts under the same conditions provide a controlled experiment on magma host interaction peralkaline rhyolite dikes are extensive and stand in bold topographic relief on contact surfaces against mudstones close packed spheroids of chilled rhyolite indicate vigorous movement of magma within envelopes of fluid against sandstones the rhyolite dike contacts are more irregular and locally protrude as blunt fingers into the wall rock against mafic lava flows dike contacts are planar and the rhyolite is less altered mafic dikes cut the rhyolite dikes some contacts of these mafic dikes are peperitic indicating intrusion into soft wet sediment and tuff the same hosts of the older rhyolitic dikes must also have been water saturated and unconsolidated higher viscosity and lower temperature prevented rhyolite magma from forming detached bodies or engulfing its host to form peperites estimated pressures and contact temperatures approximate or exceed the critical point of water indicating that the fluid envelopes at rhyolite dike contacts were very unstable because even small temperature fluctuations would have produced wide variations in fluid density around the critical point the resulting volume instability triggered rapid pulsations in the fluid envelope deforming the contacts where permeability of the host was low hot fluid accumulated at contacts but where permeability was high fluid could escape before reaching high temperature

dynamic mingling of magma and liquefied sediments abstract hydrodynamic mingling of magma and liquefied sediments is generally accepted to represent the key process in the formation of some peperites experimental studies on simulant liquids and calculations based on recent empirical findings in the field of polymer research were undertaken to investigate the effectiveness of this process these studies show that for a wide range of shear rates a laminar flow behaviour of the system magma liquefied sediment can be expected i e turbulent mingling is not a realistic scenario formation of peperitic fabrics with grain sizes on a cm scale can hydrodynamically be explained under realistic intrusion velocities in addition to the hydrodynamics cooling processes must also be considered during peperite formation calculations of the cooling history of the juvenile magmatic component under realistic cooling conditions demonstrate a significant limitation of the hydrodynamic mingling time the consequence for peperite formation under normal intrusion conditions is that domains of magmatic melt and domains of liquefied sediment smaller than 10 cm are not probable however as smaller domain sizes peperitic grain sizes exist in nature we conclude that either those peperites represent the products of explosive events or that hydrodynamic mingling was accompanied by additional fragmentation processes

widespread freshening in the seasonal ice zone near 140 e off the adelie land coast antarctica from 1994 to 2012 long term water mass changes during 1994 2012 are examined from nine repeat hydrographic sections in the seasonal ice zone along 140 e off antarctica significant freshening trends are detected within most of the water masses from the bottom to surface bottom water freshened by 0 008 0 009 decade 1 below isopycnal surfaces and its layer thickness decreased by 120 160 dbar decade 1 throughout the study period in addition to general thinning the layer thickness was anomalously thin in 2012 suggesting a possible link with the sudden calving of the mertz glacier tongue and subsequent reduction in sea ice production winter water freshened by 0 03 decade 1 throughout the study period with significant interannual variability in the offshore region a long term increase in precipitation can explain a substantial portion of the freshening trend the lower circumpolar deep water on the continental slope underwent freshening at the same rate as the bottom water during the last two decades modified shelf water also shows robust freshening at a rate of 0 03 decade 1 combined with the freshening of near surface and bottom water masses in this region these data indicate freshening of the entire water column over the continental slope this widespread freshening is broadly consistent with the enhancement of the global hydrological cycle together with a possible acceleration of land ice melting key points antarctic bottom water freshened off adelie coast antarctica during 1994 2012 precipitation increase can cause a significant part of winter water freshening the freshening is consistent with the enhancement of global hydrological cycle 2013 american geophysical union all rights reserved

formation and export of dense shelf water from the adelie depression east antarctica 1 coastal polynyas in the adelie depression are an important source of antarctic bottom water to the australian antarctic basin we present time series april 1998 to may 1999 and august 1999 to february 2000 of data from temperature salinity sensors in both the adelie depression and the known outflow region of the adelie sill to describe the annual cycle of shelf water densities from april through september salinification beneath the polynya produces dense shelf waters during september october shelf water densities in the depression peak at 27 94 kg m 3 and the cooling and freshening signature of ice shelf water is observed north of buchanan bay in november december shelf water densities decrease as intrusions of warm and relatively fresh modified circumpolar deep water enter east of the adelie sill from january march the surface layer is conditioned by the cooling of the atmosphere which overturns the upper water column at the adelie sill observed daily mean currents were approximately 10 cm s 1 with intense instantaneous currents greater than 50 cm s 1 at the sill depth using an idealized outflow region with a rectangular cross sectional area 6 106 m2 we present the first estimates of shelf water export by potential density class assuming shelf water with a minimum density of 27 88 kg m 3 has sufficient negative buoyancy for downslope mixing and a fourfold volume increase 1 3 mixing ratio from entrainment the dense shelf water export of 0 1 0 5 sv results in an annual average production of bottom water in this region of between 0 4 and 2 0 sv the wide range in bottom water estimate results from data limitations and a narrowing of this range requires further mooring observations

antarctic bottom water production by intense sea ice formation in the cape darnley polynya antarctic bottom water fills much of the global abyssal ocean and is known to form in three main sites in the southern ocean data from instrumented elephant seals and moorings suggest an additional source of bottom water formation in the cape darnley polynya that is driven by sea ice production

experimental interaction of magma and dirty coolants the presence of water at volcanic vents can have dramatic effects on fragmentation and eruption dynamics but little is known about how the presence of particulate matter in external water will further alter eruptions volcanic edifices are inherently dirty places where particulate matter of multiple origins and grainsizes typically abounds we present the results of experiments designed to simulate non explosive interactions between molten basalt and various coolants ranging from homogeneous suspensions of 0 to 30 mass bentonite clay in pure water to heterogeneous and or stratified suspensions including bentonite sand synthetic glass beads and or naturally sorted pumice four types of data are used to characterise the interactions 1 visual video observations 2 grainsize and morphology of resulting particles 3 heat transfer data from a network of eight thermocouples and 4 acoustic data from three force sensors in homogeneous coolants with 20 sediment heat transfer is by forced convection and conduction and thermal granulation is less efficient resulting in fewer blocky particles larger grainsizes and weaker acoustic signals many particles are droplet shaped or and vesicular containing bubbles filled with coolant both of these particle types indicate significant hydrodynamic magma coolant mingling and many of them are rewelded into compound particles the addition of coarse material to heterogeneous suspensions further slows heat transfer thus reducing thermal granulation and variable interlocking of large particles prevents efficient hydrodynamic mingling this results primarily in rewelded melt piles and inefficient distribution of melt and heat throughout the coolant volume our results indicate that even modest concentrations of sediment in water will significantly limit heat transfer during non explosive magma water interactions at high concentrations the dramatic reduction in cooling efficiency and increase in mingling help to explain globular peperite and provide information relevant to analyses of premixing associated with highly explosive molten fuel coolant interactions in debris filled volcanic vents