the geochemistry and structural significance of a set of middle precambrian diabase dikes from the highland range southwestern montana the middle precambrian diabase dikes of the highland range in southwestern montana are moderate to high tio2 continental tholeiites and are related along a differentiation trend involving strong i

evidence of surface wave enhancement in the southwest indian ocean from satellite altimetry wave height data from geosat over the period november 1986 to february 1989 were used to survey the occurrence of wave amplification attenuation in the southwest indian ocean more than half of the wave profiles that were inspected revealed some enhancement in the agulhas current with 17 of the profiles showing fractional amplification of more than 40 relative to the background wave height other aspects that were considered included attenuation of wave height in the shelf region and the characterization of the agulhas return current by wave height variations

projected future climate changes in the context of geological and geomorphological hazards on palaeoclimate time scales enhanced levels of geological and geomorphological activity have been linked to climatic factors including examples of processes that are expected to be important in

the influence of unsteady depths and currents of tides on wind wave propagation in shelf seas abstract the influence of unsteady depths and currents on wind wave propagation on the scale of shelf seas such as the north sea is investigated the attention is focused on depth and current variations due to tides which are essentially stationary at the scale of a single wave but unsteady at the scale of wave propagation analytical solutions are derived for changes of monochromatic unidirectional linear waves due to a one dimensional tide in water with a constant bottom level it is shown that the change of absolute frequency due to variations of depth and current in time is of the same order of magnitude as the doppler shift and that it is not negligible as assumed in a quasi stationary approximation the common quasi stationary approximation leads to large errors in the predicted change of wave parameters in all situations considered here

large horizontal surface velocity shears in the ocean obtained from images of refracting swell and in situ moored current data aerial photographs showing strong refraction of swell near the northern california coastline were obtained on september 8 1982 the possibility that this refraction is due to a large horizontal current shear is discussed a maximum shear value of the order of 10 3 s 1 with the velocity directed along a linear slick like front is calculated from the wave data in the photo in situ current data obtained at 90 m depth at a nearby midshelf site on two surface moorings separated by 390 m also show occasional periods of large horizontal velocity shear on january 4 1982 a maximum horizontal shear of order 10 3 s 1 was observed for several hours these separate observations taken together indicate that large horizontal surface velocity shears of order 10 3 s 1 occur over the northern california continental shelf and that large surface current shear can be usefully detected and measured by high flying high resolution sensors

directional response of wind waves to a large wind shift abstract the directional response of a fully arisen sea to a 90 wind shift is studied using a combination of airborne radar and in situ directional wave observations the observations were made in february 1991 as a part of the surface wave dynamics experiment radar and buoy mean wave directions in several frequency bands are polynomial smoothed in fetch and duration coordinates and analyzed for the directional relaxation parameter b by using finite differences of the gridded smoothed data in a one dimensional advection equation for the mean wave direction the analysis is carried out using several different sets of buoy wind and wave data in an event window of 40 h in duration by 200 km in fetch 100 300 km offshore for the most well populated and reliable inverse wave age class in the study 1 2 u c 1 6 the authors find b 3 3 0 1 10 5 the data do not support any inference as to possible wave age dependence other than perhaps the null hypothesis b const u c frequencies near the

kinematic constraints on glacier contributions to 21st century sea level rise on the basis of climate modeling and analogies with past conditions the potential for multimeter increases in sea level by the end of the 21st century has been proposed we consider glaciological conditions required for large sea level rise to occur by 2100 and conclude that increases in excess of 2 meters are physically untenable we find that a total sea level rise of about 2 meters by 2100 could occur under physically possible glaciological conditions but only if all variables are quickly accelerated to extremely high limits more plausible but still accelerated conditions lead to total sea level rise by 2100 of about 0 8 meter these roughly constrained scenarios provide a most likely starting point for refinements in sea level forecasts that include ice flow dynamics

contribution of asian dust and volcanic material to the western philippine sea over the last 220 kyr as inferred from grain size and sr nd isotopes asian dust and volcanogenic materials are two major components in the northwestern pacific quantitatively distinguishing them and estimating their mass accumulation rates mars are very important for understanding regional and global climate change here we present the grain size composition of detrital sediments and the radiogenic strontium sr and neodymium nd isotopic compositions of different grain size fractions of detrital sediments that were recovered from the western philippine sea these new records show that the different grain size distributions can be associated with 1 asian dust from the western and central chinese deserts and chinese loess and 2 volcanogenic materials that were derived from the luzon islands the mars of this asian dust and volcanic materials are obtained by using weibull function fitting the mars of asian dust and volcanic materials are coupled with the glacial interglacial cycle these values are found to have been higher and more variable during the glacial period than during the interglacial period we argue that the strengthening aridity of the asian continent which is connected to solar insolation and ice volume variations from orbital eccentricity constitutes an important mechanism that drives the high mars of glacial dust in the western philippine sea the internal positive feedback of dust may be another important mechanism the significant increase in volcanic material during the glacial period was caused by sea level changes which were driven by the ice volume and solar insolation at high latitudes and by strengthened precipitation from the el nino southern oscillation enso which is driven by orbital eccentricity and precession cycles on the luzon islands

identifying the causes of sea level change global mean sea level change has increased from a few centimetres per century over recent millennia to a few tens of centimetres per century in recent decades a review of the latest work shows that global mean sea level rise is unlikely to exceed one metre over the twenty first century but regional departures from this global mean could reach several decimetres

spectral modeling of wave dissipation on negative current gradients abstract hindcast studies for the dutch wadden sea using the spectral wind wave model swan have shown the significant influence of currents on wave predictions in the tidal inlets in a number of cases with strong gradients in opposing partially blocking current wave heights are significantly overestimated ris and holthuijsen 1996 propose that such overestimations are due to insufficient steepness dissipation of waves on an opposing current gradient the present paper presents a new formulation for the enhanced breaking dissipation of waves on negative current gradients accelerating opposing current decelerating following current nonlinear effects are not included in detail for these partial blocking conditions but handled parametrically unlike the expression by ris and holthuijsen 1996 the proposed expression isolates the steepening effect of the current gradient on the waves so that inherently steep young wind sea is not overly dissipated this expression contains one additional unknown parameter which was calibrated using laboratory observations validation of this enhanced dissipation term for field cases of the amelander zeegat tidal inlet dutch wadden sea shows an improvement in the tidal channel for both opposing and following current situations with negative gradients in particular the results for the young wind sea on the tidal flats are not significantly affected as desired unlike with the expression of ris and holthuijsen 1996 however since the remaining dissipation terms in swan have been calibrated without this enhanced dissipation term the addition of the proposed formulation results in some deterioration of the overall statistics

tightening the siberian connection to western laurentia newly available geological and geophysical data tighten the proterozoic connection between the rifted margins of the northern siberian craton and western laurentia and permit a siberia laurentia australia troika with northern australia connected to the southern margin of the siberian craton the continental assembly is linked by a prominent 2 0 1 8 ga collisional belt and the ca 1 3 1 0 ga grenville orogen the reconstruction also aligns a 1 5 1 45 ga dike sill swarm that extends from the wyoming province through the belt purcell basin into the northern siberian craton separation of australia and siberia may have occurred by the early neoproterozoic but separation of siberia and laurentia may not have been completed until the early cambrian continental extension began along the zigzag siberia laurentia rift zone in the early mesoproterozoic rift related igneous and sedimentary assemblages dated at ca 1 5 1 38 and 1 2 to 1 0 ga correlate across the reconstructed siberia laurentia rift zone renewed rifting in the neoproterozoic and vendian culminated with seafloor spreading and thermal subsidence of the conjugate rift shoulders correlative archeocyathan reefs endemic olenellid trilobite fauna and exchange of detritus between the cratons imply that the rift may have remained relatively narrow until the atdabanian stage black sulfidic shales buried the archeocyathan reefs on the rapidly subsiding rift margins during the botomian sinsk event

1 08 ga diabase sills in the pahrump group california implications for development of the cordilleran miogeocline u pb baddeleyite ages of 1087 3 and 1069 3 ma for twodiabase sills that intrude the crystal spring formation of the pahrump group southeastern california provide a minimum estimate for the depositional age of the crystal spring formation the new ages high light the potential range in deposition ages for the pahrump group from 1087 ma to possibly as young as 600 ma for kingston peak glaciogenic sediments consequently there probably are significant disconformities within the pahrump group that separate unrelated tectonically distinct episodes of basin subsidence the crystal spring and beck spring formations are considered to be platform cover rocks preserved as a result of block faulting during deposition of the upper kingston peak formation the age of the pahrump sills is in excellent agreement with the age of sills that intrude the apache group central arizona and the unkar group grand canyon and supports earlier correlations of those units

observations of wind waves in the gulf stream frontal zone experimental results of a study of wind waves in the gulf stream frontal zone are presented measurements of two dimensional radar spectra of surface waves and surface current were performed during ship crossings of the gulf stream under different wind conditions waves reflected from the gulf stream were observed on the windward side for an along current wind these effects resulted in a widening of the spectrum angular distribution and a deviation of the mean wave direction from that of the wind trapped waves were observed under against current winds depending on wave age the trapped waves were either locally generated developing waves or entered into the jet downstream nearly fully developed waves trapped waves significantly increased the wave energy locally the experimental data are interpreted in terms of wave kinematics and the equation of spectrum evolution in the relaxation approximation

a numerical study of wave current interaction through surface and bottom stresses wind driven circulation in the south atlantic bight under uniform winds the influences of surface waves on ocean currents in the coastal waters of the south atlantic bight are investigated by using a coupled wave current modeling system the ocean circulation model employed is the three dimensional princeton ocean model pom and the wave model invoked is an improved third generation wave model wam the coupling procedure between the pom and the wam and the simulated coastal ocean circulation driven by uniform surface winds are presented the simulated results show that wind waves can significantly affect coastal ocean currents not only through an enhancement of wind stress but also through a modification of bottom stress wave induced wind stress increases the magnitude of currents both at the surface and near the seabed on the other hand wave induced bottom stress weakens the currents both at the sea surface and near the seabed therefore the net effect of surface wind waves on currents depends on the relative importance of current modulations by wave induced wind stress and bottom stress the results further indicate that at a fixed location the relative importance of wave induced surface and bottom shear stresses in coastal ocean circulation depends on the surface wind field for the constant wind cases considered in this study the effect of wave induced bottom stress is more significant in along shore wind conditions than in cross shore wind conditions

effects of the gulf stream on ocean waves in the present study a third generation numerical wave model is used to study effects of a straight gulf stream and a gulf stream ring on ocean waves in swell and storm conditions the model accounts for all relevant processes of propagation generation and dissipation of the waves including current effects without imposing a priori restraints on the spectral development of the waves the dominating mechanism affecting the waves appears to be current induced refraction even though the short crestedness of the incoming waves tends to mask its effects also in swell conditions depending on wind and wave conditions refraction may trap locally generated waves in the straight gulf stream or it may reflect wave energy back to the open ocean in the gulf stream ring refraction induces a considerable variation in significant wave height and short crestedness but it hardly affects the mean wave direction in storm conditions the processes of generation and dissipation are considerably enhanced in countercurrent situations and reduced following current situations

storm waves focusing and steepening in the agulhas current satellite observations and modeling strong ocean currents can modify the height and shape of ocean waves possibly causing extreme sea states in particular conditions the risk of extreme waves is a known hazard in the shipping routes crossing some of the main current systems modeling surface current interactions in standard wave numerical models is an active area of research that benefits from the increased availability and accuracy of satellite observations we report a typical case of a swell system propagating in the agulhas current using wind and sea state measurements from several satellites jointly with state of the art analytical and numerical modeling of wave current interactions in particular synthetic aperture radar and altimeter measurements are used to show the evolution of the swell train and resulting local extreme waves a ray tracing analysis shows that the significant wave height variability at scales 100 km is well associated with the current vorticity patterns predictions of the wavewatch iii numerical model in a version that accounts for wave current interactions are consistent with observations although their effects are still under predicted in the present configuration from altimeter measurements very large significant wave height gradients are shown to be well captured and also associated with the current vorticity patterns at global scale

palaeomagnetism of neoproterozoic glacial rocks of the huabei shield the north china block in gondwana abstract a palaeomagnetic study is reported of reddened facies fengtai formation of neoproterozoic glacial rocks which underlie early cambrian rocks with disconformity in the huabei north china sino korean block the diamictite preferred age 620 600 ma carries a dual polarity remanence residing in hematite of the red matrix the mean direction derived from 62 samples is d i 205 9 32 4 95 3 9 yielding a pole position at 233 e 62 n tests on the matrix deformed beneath dropstones suggest that remanence was fixed before full compaction although clasts near the base of the formation are largely overprinted overlying early cambrian sediments of the houjiashan and yutaishan formations have a similar remanence also of dual polarity d i 205 5 32 1 95 3 9 32 samples the magnetisation in the diamictite is therefore interpreted to have been acquired during loading by the ice sheet and or the overlying cambrian succession red shales from the liulaobei formation 890 840 ma near the base of the neoproterozoic succession in the huabei block yield a contrasting remanence of d i 59 4 75 3 95 7 1 19 samples equivalent to a pole position at 150 e 43 n pole positions from this study accord with lower middle cambrian poles from the australian and south china blocks with north china sited adjacent to northeastern australia in accordance with recent biogeographic and palaeogeographic models although the palaeolatitude derived from the fengtai diamictite 17 is cambrian in age and probably later than the glaciation the correlation with australia implies that glaciation in north china took place in low palaeolatitudes 20 and reinforces the view that late neoproterozoic glaciation at least at this perimeter of gondwana occurred at low latitudes neoproterozoic cambrian poles from north china south china and australia fail to conform to the popular rodinia reconstruction with the latter blocks adjacent to western north america and also fail to support the view that gondwana formed by the fusion of widely separated eastern and western segments during pan african orogeny instead they accord to poles from africa and south america in a precursor of gondwana protogondwana the subsequent palaeozoic derivation of this supercontinent was probably achieved by intracontinental strike slip motion during pan african deformation following extinction of the afro arabian arc

origins of mineral deposits belt purcell basin united states and canada an introduction the fill of the mesoproterozoic belt purcell basin which straddles the united states canada border within the rocky mountains of western north america fig 1 consists of marine and nonmarine clastic and carbonate strata 15 to 20 km thick three giant metal producing ore deposits or districts account for the bulk of the known metal endowment within the bounds of the belt purcell basin 1 the syndepositional sullivan pb zn ag deposit in southern british columbia total production pb 8 4 million tonnes mt zn 7 9 mt ag 0 0093 mt lydon 2000 2 the mesothermal pb zn ag veins of the coeur d alene district in northern idaho total production pb 7 5 mt zn 3 0 mt ag 0 052 mt long 1998 post 1997 data from usgs annual minerals yearbooks and 3 the cretaceous porphyry copper deposit and associated polymetallic veins in the butte district in montana total resource cu 35 mt zn 4 6 mt ag 0 044 mt long et al 1998 the sullivan mine closed in 2001 after more than 92 years of production mining of 26 major vein deposits in the coeur d alene district began in the 1880s and peaked about 1950 production in the coeur d alene district continues today from the galena and lucky friday mines the latter closed for 2012 to refurbish the mile deep vertical access shaft mining at butte began in 1875 with copper production peaking in 1917 mining continues today in the eastern upfaulted portion of the butte porphyry copper deposit at the continental mine fig 1 locations of major ore deposits within the belt purcell basin area along with other ore deposits and mineralized trends that are discussed in this issue deposit locations are plotted on a geologic map showing the distribution of five stratigraphic units within the belt purcell basin in the united states and canada lower belt formations include the prichard altyn appekunny chamberlain newland lahood

30 year satellite record reveals contrasting arctic and antarctic decadal sea ice variability a 30 year satellite record of sea ice extents derived mostly from satellite microwave radiometer observations reveals that the arctic sea ice extent decreased by 0 30 0 03 x 10 exp 6 square kilometers per 10 yr from 1972 through 2002 but by 0 36 plus or minus 0 05 x 10 exp 6 square kilometers per 10yr from 1979 through 2002 indicating an acceleration of 20 in the rate of decrease in contrast the antarctic sea ice extent decreased dramatically over the period 1973 1977 then gradually increased over the full 30 year period the antarctic ice extent decreased by 0 15 plus or minus 0 08 x 10 exp 6 square kilometers per 10 yr the trend reversal is attributed to a large positive anomaly in antarctic sea ice extent in the early 1970 s an anomaly that apparently began in the late 1960 s as observed in early visible and infrared satellite images

a case study of wave current interaction near an oceanic front high resolution directional wave spectrum data were obtained from two nasa airborne radars during the frontal air sea interaction experiment fasinex in february 1986 the observations show a significant change in the wave number spectrum across the front on the basis of surveys from a towed sensor and on satellite imagery the front location and current field are estimated a numerical model is developed for the wave current interaction and is used to model the wave refraction across the frontal current a parametric study is performed to demonstrate the effects of current meandering the main consequence of meandering is the formation of caustics and shadow zone regions in which the wave energy is significantly enhanced or reduced spectral simulation along the aircraft track reveals a reduction of more than 60 in wave energy in the shadow zone this is consistent with the observations

wave refraction in an ocean front side looking airborne radar near cape hatteras north carolina recorded images of ocean waves wind streaks and intermediate water bodies within the gulf stream front in the enclosed waters of pamlico sound the radar images showed good accuracy in defining directions and distinguished waves from wind streaks at overlapping frequencies in the spectrum in passing through the cyclonic shear in the gulf stream front waves from both sides turned to their left and so specified their directions of propagation differences between spectra obtained across the front are in accord with current refraction theory an inverse wave refraction calculation furnished current shear values from which horizontal profiles of water velocity were compiled the total calculated velocity change of 1 5 m s is similar to previous measurements a secondary front near shore contained a velocity difference of 0 25 m s velocity changes across the gulf stream front were correlated with temperature changes the radar there showed bands of high reflectivity at the edges of intermediate water bodies whose temperature differences implied very small velocity steps increased roughness at the intermediate water boundaries was attributed to current interaction with waves

quartz shielding of sub 10 μm zircons from radiation damage enhanced pb loss an example from a metamorphosed mafic dike northwestern wyoming craton abstract the coupling of two new approaches enabled acquisition of in situ u pb data from zircons as small as 5 m in a metamorphosed mafic dike from the northern madison range montana despite negligible zircon yield by mineral separation automated mineralogy rapidly identified 375 sub 20 m zircons in a single thin section subsequently zircon crystals were dated using modifications to the conventional sims technique to preferentially collect secondary ions emitted from a domain a few microns in size within the 20 m diameter analysis pit this approach allowed analysis of zircons too small to be dated by standard sims and tims methods u pb data define a discordia array with upper and lower intercepts of 1753 9 ma and 63 8 ma respectively 1 error mswd 1 5 we interpret the upper intercept to reflect zircon growth during high temperature and high pressure metamorphism 800 c 1 2 gpa based on textural relationships between the dated zircons and the peak metamorphic assemblage the lower intercept is attributable to the thermal pulse associated with emplacement of the nearby ca 75 ma tobacco root batholith percent discordance is linked with both textural setting and u concentration zircons located along grain boundaries or within fractured host grains display a positive correlation between u 1049 2817 ppm and percent discordance 12 82 that is consistent with radiation damage enhanced pb loss in contrast three zircons housed completely within unfractured quartz yield the most concordant analyses of the dataset 7 discordant despite u concentrations comparable to highly discordant matrix grains this relationship suggests that the included zircons were shielded from pb loss by the encapsulating quartz crystals the results imply that targeting zircons located completely within unfractured host phases may aid in isolating earlier portions of geologic histories the primary geological implication of this dataset is to increase the documented extent of paleoproterozoic high grade metamorphism in the northwestern wyoming craton

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

climate forcing of volcano lateral collapse evidence from mount etna sicily in this study we present evidence for early holocene climatic conditions providing circumstances favourable to major lateral collapse at mount etna sicily the volcano s most notable topographic feature is the valle del bove a 5 x 8 km cliff bounded amphitheatre excavated from the eastern flank of the volcano its origin due to prehistoric lateral collapse is corroborated by sturtzstrom deposits adjacent to the amphitheatre s downslope outlet but the age nature and cause of amphitheatre excavation remain matters for debate cosmogenic 3 he exposure ages determined for eroded surfaces within an abandoned watershed flanking the valle del bove support channel abandonment ca 7 5 ka bp as a consequence of its excavation in a catastrophic collapse event watershed development was largely dictated by pluvial conditions during the early holocene which are also implicated in slope failure a viable trigger is magma emplacement into rift zones in the eastern flank of a water saturated edifice leading to the development of excess pore pressures consequent reduction in sliding resistance detachment and collapse such a mechanism is presented as one potential driver of future lateral collapse in volcanic landscapes forecast to experience increased precipitation or melting of ice cover as a consequence of anthropogenic warming

swell transformation across the continental shelf part i attenuation and directional broadening abstract extensive wave measurements were collected on the north carolina virginia continental shelf in the autumn of 1999 comparisons of observations and spectral refraction computations reveal strong cross shelf decay of energetic remotely generated swell with for one particular event a maximum reduction in wave energy of 93 near the virginia coastline where the shelf is widest these dramatic energy losses were observed in light wind conditions when dissipation in the surface boundary layer caused by wave breaking whitecaps was weak and wave propagation directions were onshore with little directional spreading these observations suggest that strong dissipation of wave energy takes place in the bottom boundary layer the inferred dissipation is weaker for smaller amplitude swells for the three swell events described here observations are reproduced well by numerical model hindcasts using a parameterization of wave friction over a movable sandy bed directional spectra that are narrow off the s

volcanic winter and accelerated glaciation following the toba super eruption the eruption of toba in sumatra 73 500 years ago was the largest known explosive volcanic event in the late quaternary1 it could have lofted about 1015 g each of fine ash and sulphur gases to heights of 27 37 km creating dense stratospheric dust and aerosol clouds here we present model calculations that investigate the possible climatic effects of the volcanic cloud the increase in atmospheric opacity might have produced a volcanic winter 2 a brief pronounced regional and perhaps hemispheric cooling caused by the volcanic dust followed by a few years with maximum estimated annual hemispheric surface temperature decreases of 3 5 c the eruption occurred during the stage 5a 4 transition of the oxygen isotope record a time of rapid ice growth and falling sea level3 we suggest that the toba eruption may have greatly accelerated the shift to glacial conditions that was already underway by inducing perennial snow cover and increased sea ice extent at sensitive northern latitudes as the onset of climate change may have helped to trigger the eruption itself4 we propose that the toba event may exemplify a more general climate volcano feedback mechanism

large holocene landslides from pylon peak southwestern british columbia mount meager massif the northernmost volcano of the cascade volcanic belt has been the site of very large 10 7 m 3 landslides in the holocene epoch we document two complex landslides at pylon peak one of the peaks of the mount meager massif about 7900 14 c and 3900 14 c years ago about 8700 and 4400 calendar years ago together the two landslides displaced 6 1 0 8 m 3 of volcanic rock from the south flank of pylon peak into nearby meager creek valley each landslide consisted of at least two phases an early debris flow resulting from failure of hydrothermally altered pyroclastic rock at mid levels on the mountain and a later rock avalanche from a higher source both debris flows likely traveled down meager creek and preliminary evidence from drilling indicates the 4400 year old event traveled down lillooet river into areas that are now settled and where population density is increasing rapidly the mobility of the debris flows was due to the high content of fine weathered volcanic sediment and the availability of sufficient water the causes of the landslides are a wet climate and the presence of weak hydrothermally altered volcanic rock containing abundant phreatic water on glacially oversteepened slopes the landslides may have been triggered by earthquakes or by upwelling of magma to shallow depths within the volcano however they may also have occurred without specific triggers following extended periods of progressive weakening of the volcanic rocks

ice age as a trigger of active quaternary volcanism and tectonism abstract the stress accumulation within the crust caused by the surface mass redistribution associated with the glaciation deglaciation cycle during the quaternary was numerically evaluated in order to examine the relationship between active quaternary volcanism and tectonism in island arc areas and ice age the vertical gradient of horizontal stress difference in the lithosphere for a meltwater of 130 m in equivalent sea level reaches a maximum value of 0 8 mpa km which is corresponding to the equivalent buoyancy of about 100 kg m3 for magma filled cracks for an earth model with a lithospheric layer of 20 30 km thickness and with a viscosity greater than 1023 pa s the changes in stress difference during the stages of deglaciation of 10 000 years amount to 13 mpa for both the top and bottom of the thin lithosphere thus the additional stress difference within the crust may be effective for island arc areas with thin lithospheric thickness we therefore speculate that the stress accumulation associated with ice age may be an important trigger and or accelerator on the active quaternary volcanism and tectonism for the areas along the circum pacific

wave current interaction between hurricane matthew wave fields and the gulf stream abstracthurricanes interact with the gulf stream in the south atlantic bight sab through a wide variety of processes which are crucial to understand for prediction of open ocean and coastal haza

ocean wave directional spectra and wave current interaction in the agulhas from the shuttle imaging radar b synthetic aperture radar sir b synthetic aperture radar ocean wave spectra for a 200 km pass crossing the agulhas current off the coast of africa are analyzed a significant enhancement of one spectral peak along the northern edge of the current is attributed both to amplification of the waves by refraction dominated wave current interaction and to transient specular backscatter contributions spatially correlated to the waves

postglacial rebound and fault instability in fennoscandia summary the best available rebound model is used to investigate the role that postglacial rebound plays in triggering seismicity in fennoscandia the salient features of the model include tectonic stress due to spreading at the north atlantic ridge overburden pressure gravitationally self consistent ocean loading and the realistic deglaciation history and compressible earth model which best fits the sea level and ice data in fennoscandia the model predicts the spatio temporal evolution of the state of stress the magnitude of fault instability the timing of the onset of this instability and the mode of failure of lateglacial and postglacial seismicity the consistency of the predictions with the observations suggests that postglacial rebound is probably the cause of the large postglacial thrust faults observed in fennoscandia the model also predicts a uniform stress field and instability in central fennoscandia for the present with thrust faulting as the predicted mode of failure however the lack of spatial correlation of the present seismicity with the region of uplift and the existence of strike slip and normal modes of current seismicity are inconsistent with this model further unmodelled factors such as the presence of high angle faults in the central region of uplift along the baltic coast would be required in order to explain the pattern of seismicity today in terms of postglacial rebound stress the sensitivity of the model predictions to the evects of compressibility tectonic stress viscosity and ice model is also investigated for sites outside the ice margin it is found that the mode of failure is sensitive to the presence of tectonic stress and that the onset timing is also dependent on compressibility for sites within the ice margin the evect of earth rheology is shown to be small however ice load history is shown to have larger evects on the onset time of earthquakes and the magnitude of fault instability

wave current interaction near the gulf stream during the surface wave dynamics experiment this paper presents a case study on the wave current interaction near the local curvature of a gulf stream meander the wave data were obtained from in situ measurements by a pitch roll discus buoy during the surface wave dynamics experiment swade conducted off wallops island virginia from october 1990 to march 1991 owing to the advection of the gulf stream by the semidiurnal tide the discus buoy was alternately located outside and inside the gulf stream the directional wave measurements from the buoy show the changes in wave direction wave energy and directional spreading when waves encountered the current in the gulf stream meanders a wave refraction model using the ray tracing method with an estimated gulf stream velocity field and meandering condition was used to simulate wave refraction patterns and to estimate wave parameters at relative locations corresponding to buoy measurements the numerical simulation shows that a focusing zone of wave rays was formed near the boundary and behind the crest of a simulated gulf stream meander the focusing of wave rays causes changes in wave direction increases in wave energy and decreases in wave directional spreading which are in good agreement with the results from the buoy measurements

on the wave current interaction during the passage of a tropical cyclone in the bay of bengal abstract the impact of waves on currents and vice versa is an integral part of the complex coastal dynamics the wave current interaction is prominent in the coastal shelf slope regions particularly during the passage of a tropical cyclone in the present study we describe the importance of wave current interaction in the northern bay of bengal bob using a fully coupled three dimensional coupled ocean atmosphere wave sediment transport coawst modelling system the coawst model is applied to the case of a very severe cyclonic storm phailin that passed over the bob basin during 10 15 october 2013 to represent the interaction between waves and currents we utilized the newly implemented vortex force method in the coupled model numerical experiments with different coupling configuration within the coawst modelling framework were performed to separately identify the effects of wind tide and wave current interaction process a comparison of model results with the buoy observations of water elevations currents and wave measurements shows a good agreement between model and observed data various terms of the momentum balance were calculated from the model simulated and diagnosed parameters a comparison of the horizontal momentum balance term identifies the wave breaking induced acceleration as one of the leading terms along the storm affected the east coast of india further an increase in the apparent bed roughness caused by waves found to affect the values and distribution of the bottom shear stress the pressure gradient term showed significant changes to the pure tidal case the study highlights that the changes in the momentum balance caused by waves includes contributions from the variations in the water level and currents the most relevant effect on the coastal hydrodynamics was in the form of a wave induced setup near the location of landfall of the cyclone

distribution and chemical composition of tephra layers from eastern mediterranean abyssal sediments abstract most cores of late quaternary sediments from the eastern mediterranean sea contain many ash layers glass shards from discrete layers have been analysed chemically for major elements the layers from different cores have been correlated and unambiguously related to known volcanic events on the basis of the chemical data most of the layers are derived from explosive eruptions of the santorini volcanic complex other layers have their source in other volcanoes of the hellenic arc yali nisyros kos one layer originated from the campanian area italy

tyrrhenian sea tephrochronology of the oxygen isotope record for the past 60 000 years abstract a chronology of the marine oxygen isotope record of the past 60 ka is proposed by correlating eight marine ash layers with terrestrial volcanic deposits dated by the 14c and or k ar methods detailed oxygen isotope analyses were made on the planktonic foraminifera of three cores collected in the central tyrrhenian sea the origin of the ash layers was determined by major and trace elements analyses then the major pyroclastic terrestrial deposits were sampled and analysed in order to provide land sea correlations two ash layers occurred during the warm event that followed the first step of the deglaciation and which was dated at 12 6 0 5 ka b p another ash layer is present near the last glacial maximum that we have dated at 17 5 0 3 ka b p during isotopic stage 3 five ash layers were recognized and dated which allowed us to assign ages to the isotopically light oxygen peaks warmer interstadials at 31 1 5 ka and 33 4 1 6 ka denekamp at 37 5 2 ka hengelo and successively at 49 2 ka 52 4 2 2 ka 57 2 2 ka and 60 5 2 2 ka moershoofd complex

structural and u pb geochronological evidence for 1 47 ga rifting in the belt basin western montana structural mapping and u pb dates from mafic sills in the perma culmination of west central montana constrain the timing of a major rifting event in the early history of the belt basin magmatic zircon from the plains and paradise mafic sills within the prichard formation yielded u pb ages of 1469 2 5 and 1457 2 ma respectively the older sill invaded unconsolidated wet sediments at a depth of less than 1 6 km and its emplacement is coeval with widespread soft sediment folding mud diapirism and bathymetric collapse of the basin between members e and f of the prichard formation the youngest sill intruded near the base of the exposed section after significant accumulation of sediment had occurred in the basin correlation of these data with recent geochronologic results from the moyie sills in british columbia and purcell lava in montana suggests that the rifting and subsidence event was basin wide and that at least two thirds of the deposition of the belt supergroup occurred between 1470 and 14

slip rate variations on normal faults during glacial interglacial changes in surface loads geologic and palaeoseismological data document a marked increase in the slip rates of the wasatch fault and three adjacent normal faults in the basin and range province during the late pleistocene early holocene epochs the cause of this synchronous acceleration of fault slip and the subsequent clustering of earthquakes during the holocene has remained enigmatic although it has been suggested that the coincidence between the acceleration of slip and the shrinkage of lake bonneville after the last glacial maximum may indicate a causal relationship here we use finite element models of a discrete normal fault within a rheologically layered lithosphere to evaluate the relative importance of two competing processes that affect fault slip postglacial unloading the removal of mass which decreases the slip rate and lithospheric rebound which promotes faster slip we show that lithospheric rebound caused by regression of lake bonneville and deglaciation of adjacent mountain ranges provides a feasible mechanism for the high holocene rates of faulting in the wasatch region our analysis implies that climate controlled changes in loads applied to earth s surface may exert a fundamental control on the slip history of individual normal faults

observation of hurricane generated ocean swell refraction at the gulf stream north wall with the radarsat 1 synthetic aperture radar we analyze the refraction of long oceanic waves at the gulf stream s north wall off the florida coast as observed in imagery obtained from the radarsat 1 synthetic aperture radar sar during the passage of hurricane bonnie on august 25 1998 the wave spectra are derived from radarsat 1 sar images from both inside and outside the gulf stream from the image spectra we can determine both the long wave s dominant wavelength and its propagation direction with 180 spl deg ambiguity we find that the wavelength of hurricane generated ocean waves can exceed 200 m the calculated dominant wavelength from the sar image spectra agree very well with in situ measurements made by national oceanic and atmospheric administration national data buoy center buoys since the waves mainly propagate toward the continental shelf from the open ocean we can eliminate the wave propagation ambiguity we also discuss the velocity bunching mechanism we find that in this very long wave case the radarsat 1 sar wave spectra should not be appreciably affected by the azimuth falloff and we find that the ocean swell measurements can be considered reliable we observe that the oceanic long waves change their propagation directions as they leave the gulf stream current a wave current interaction model is used to simulate the wave refraction at the gulf stream boundary in addition the wave shoaling effect is discussed we find that wave refraction is the dominant mechanism at the gulf stream boundary for these very long ocean swells while wave reflection is not a dominant factor we extract 256 by 256 pixel full resolution subimages from the sar image on both sides of the gulf stream boundary and then derive the wave spectra the sar observed swell refraction angles at the gulf stream north wall agree reasonably well with those calculated by the wave current interaction model

rapid deglaciation as an initiator of volcanic activity an hypothesis volcanic activity on sub antarctic marion island is found to have occurred only during the interglacials the present volcano distribution is associated with a radial and peripheral fault system the location of which appears to be related to the former glacier distribution an hypothesis is presented suggesting that the faulting is a result of deglaciation and that the specific location of the faults is due to the differential stresses occurring between ice covered and ice free areas during isostatic uplift the faulting initiates volcanism due to the location of the island within a volcanic region

can deglaciation trigger earthquakes in n america a spherical self gravitating viscoelastic earth model is used to calculate the spatial and temporal evolution of the glacially induced lithospheric stress and fault stability in north america the predicted onset time of a pulse of earthquake activities the mode of failure and the magnitude of instability are investigated for three sites with different distance from the former ice margin it is found that glacial unloading is able to trigger paleo earthquakes within the ice margin near charlevoix 47 5 n 70 1 w and in wabash valley 38 5 n 87 w outside the ice margin however rebound stress decays away from the former ice margin thus glacial unloading is unlikely to have triggered the large m8 earthquakes in new madrid 36 6 n 89 5 w

tropical storms representation and diagnosis in climate models and the impacts of climate change tropical storms are located and tracked in an experiment in which a high resolution atmosphere only model is forced with observed sea surface temperatures ssts and sea ice the structure geographic distribution and seasonal variability of the model tropical storms show some similarities with observations the simulation of tropical storms is better in this high resolution experiment than in a parallel standard resolution experiment in an anomaly experiment sea ice ssts and greenhouse gas forcing are changed to mimic the changes that occur in a coupled model as greenhouse gases are increased there are more tropical storms in this experiment than in the control experiment in the northeast pacific and indian ocean basins and fewer in the north atlantic northwest pacific and southwest pacific region the changes in the north atlantic and northwest pacific can be linked to el nino like behaviour a comparison of the tracking results with two empirically derived tropical storm genesis parameters is carried out the tracking technique and a convective genesis parameter give similar results both in the global distribution and in the changes in the individual basins the convective genesis parameter is also applied to parallel coupled model experiments that have a lower horizontal resolution the changes in the global distribution of tropical storms in the coupled model experiments are consistent with the changes seen at higher resolution this indicates that the convective genesis parameter may still provide useful information about tropical storm changes in experiments carried out with models that cannot resolve tropical storms

volcanic aerosol records and tephrochronology of the summit greenland ice cores the recently collected greenland ice sheet project 2 gisp2 and greenland ice core project ice cores from summit greenland provide lengthy and highly resolved records of the deposition of both the aerosol h2so4 and silicate tephra components of past volcanism both types of data are very beneficial in developing the hemispheric to global chronology of explosive volcanism and evaluating the entire volcanism climate system the continuous time series of volcanic so42 for the last 110 000 years show a strong relationship between periods of increased volcanism and periods of climatic change the greatest number of volcanic so42 signals many of very high magnitude occur during and after the final stages of deglaciation 6000 17 000 years ago possibly reflecting the increased crustal stresses that occur with changing volumes of continental ice sheets and with the subsequent changes in the volume of water in ocean basins sea level change the increase in the number of volcanic so42 signals at 27 000 36 000 and 79 000 85 000 years ago may be related to initial ice sheet growth prior to the glacial maximum and prior to the beginning of the last period of glaciation respectively a comparison of the electrical conductivity of the gisp2 core with that of the volcanic so42 record for the holocene indicates that only about half of the larger volcanic signals are coincident in the two records other volcanic acids besides h2so4 and other so42 sources can complicate the comparisons although the threshold level picked to make such comparisons is especially critical tephra has been found in both cores with a composition similar to that originating from the vatnaoldur eruption that produced the settlement layer in iceland mid a d 870s from the icelandic eruption that produced the saksunarvatn ash 10 300 years ago and from the icelandic eruption s that produced the z2 ash zone in north atlantic marine cores 52 700 years ago the presence of these layers provides absolute time lines for correlation between the two cores and for correlation with proxy records from marine sediment cores and terrestrial deposits containing these same tephras the presence of both rhyolitic and basaltic shards in the z2 ash in thegisp2 core and the composition of the basaltic grains lend support to multiple icelandic sources torfajokull area and katla for the z2 layer deposition of the z2 layer occurs at the beginning of a stadial event further reflecting the possibility of a volcanic triggering by the effects of changing climatic conditions

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

wave current interaction study in the gulf of alaska for detection of eddies by synthetic aperture radar high resolution ers i synthetic aperture radar sar images are used to detect a mesoscale eddy such features limit dispersal of pollock larvae and therefore likely influence recruitment of fish in the gulf of alaska during high sea states and high winds the direct surface signature of the eddy was not clearly visible but the wave refraction in the eddy area was observed the rays of the wave field are traced out directly from the sar image the ray pattern gives information on the refraction pattern and on the relative variation of the wave energy along a ray through wave current interaction these observations are simulated by a ray tracing model which incorporates a surface current field associated with the eddy the numerical results of the model show that the waves are refracted and diverge in the eddy field with energy density decreasing the model data comparison for each ray shows the model predictions are in good agreement with the sar data

numerical simulations and observations of surface wave fields under an extreme tropical cyclone abstract the performance of the wave model wavewatch iii under a very strong category 5 tropical cyclone wind forcing is investigated with different drag coefficient parameterizations and ocean current inputs the model results are compared with field observations of the surface wave spectra from an airborne scanning radar altimeter national data buoy center ndbc time series and satellite altimeter measurements in hurricane ivan 2004 the results suggest that the model with the original drag coefficient parameterization tends to overestimate the significant wave height and the dominant wavelength and produces a wave spectrum with narrower directional spreading when an improved drag parameterization is introduced and the wave current interaction is included the model yields an improved forecast of significant wave height but underestimates the dominant wavelength when the hurricane moves over a preexisting mesoscale ocean feature such as the loop current in the gulf of mexico or a warm and co

miocene to holocene marine tephrostratigraphy offshore northern central america and southern mexico pulsed activity of known volcanic complexes we studied the tephra inventory of fourteen deep sea drill sites of three dsdp and odp legs drilled offshore guatemala and el salvador legs 67 84 138 and one leg offshore mexico leg 66 marine tephra layers reach back from the miocene to the holocene we identified 223 primary ash beds and correlated these between the drill sites with regions along the volcanic arcs and to specific eruptions known from land in total 24 correlations were established between marine tephra layers and to well known quaternary eruptions from el salvador and guatemala additional 25 tephra layers were correlated between marine sites another 108 single ash layers have been assigned to source areas on land resulting in a total of 157 single eruptive events tephra layer correlations to independently dated terrestrial deposits provide new time markers and help to improve or confirm age models of the respective drill sites applying the respective sedimentation rates derived from the age models we calculated ages for all marine ash beds hence we also obtained new age estimates for eight known but so far undated large terrestrial eruptions furthermore this enables us to study the temporal evolution of explosive eruptions along the arc and we discovered five pulses of increased activity 1 a pulse during the quaternary 2 a pliocene pulse between 6 and 3 ma 3 a late miocene pulse between 10 and 7 ma 4 a middle miocene pulse between 17 11 ma and 5 an early miocene pulse 21 ma

isotopic dating of meso and neoproterozoic mafic magmatism in the southern tobacco root mountains southwestern montana abstract new isotopic dating of mafic dikes in the southern tobacco root mountains of southwestern montana provides evidence for two distinct episodes of subparallel proterozoic mafic magmatism separated by about 700 m y previously published geochemical data from dikes in the southern tobacco root mountains had identified three geochemical groups termed groups a b and c with apparent rb sr ages of 1455 ma group a and 1100 1120 ma groups b and c sm nd dating of a geochemical group a dike yields an age of 1448 49 ma that is interpreted to represent the emplacement age of the dikes this age is similar to published u pb dates from mafic sills that intrude the nearby mesoproterozoic belt supergroup and laramide basement cored uplifts of the archean wyoming province paleomagnetic results from groups a and b dikes are similar suggesting that the were emplaced at about the same time we suggest that the mafic magmatism recorded by the southern tobacco root mountains group a c dikes at about 1450 ma probably corresponds to continental extension that accompanied development of the mesoproterozoic belt basin u pb dating of baddeleyite from the group b dikes provides evidence for a younger magmatic event with an age of 782 4 4 9 ma 95 confidence 7 1 ma incorporating uranium decay constant errors this date is similar to isotopic dates from neoproterozoic mafic dikes and sills exposed elsewhere in uplifts of the rocky mountain foreland and that intrude the mesoproterozoic strata of the belt supergroup geochronologic data from elsewhere in the northern cordillera and canadian shield indicate that the group b dikes in the southern tobacco root mountains are part of a regional 780 ma magmatic event that extended for more than 2400 km along the western margin of laurentia the origin of the magmatic event is not clear but may be related to a mantle plume and crustal extension accompanying initial breakup of the supercontinent rodinia and development of the proto pacific ocean no evidence of ca 1100 ma mafic magmatism in this part of the northern cordillera was found

measurements of sea state variations across oceanic fronts using laser profilometry abstract as part of the grand banks experiment in may 1979 airborne laser profilometer measurements of the ocean wave field were made across a large cold water extrusion situated over the newfoundland ridge the feature is actually an extension of the labrador current which is bordered on the west side by the gulf stream and on the east side by the north atlantic current star shaped flight patterns were flown over the fronts on each side of the cold water feature a graphic technique was applied to the apparent wavenumber spectra in order to determine the changes in wave energy wavelength and direction of propagation of the dominant wind wave and swell components as they move across the fronts at the western front the sea state increased abruptly and the results indicate that wave current interactions were the most important mechanism for wave modification although boundary layer effects were present and increased wave breaking was observed at the eastern front changes in the swell are compared to

mechanical models for correlation of ring fracture eruptions at pantelleria strait of sicily with glacial sea level drawdown recent k ar dating of eruptions at pantelleria a peralkaline volcanic island in the strait of sicily shows a correlation between eruption of pantellerite lavas from caldera ring fractures and low stands of sea level as determined from 18o stratigraphy post caldera pantellerite lavas associated with an 114 ky old caldera erupted along the ring fracture zone during a major low stand of sea level at about 67 ka the most recent episode of lava flow emplacement began about 20 ky ago during the last glacial maximum magma vented along the ring fault of a 45 ky old caldera from fractures radial to the caldera and along faults formed by intracaldera trapdoor uplift two mechanical models based on elasticity theory are presented to explain the correlation of post caldera ring fracture eruptions at pantelleria with lowering of sea level a simple analysis of a bending circular plate of thickness t r and radius r representing the magma chamber roof block shows that tensile stress is concentrated by a factor of 0 75r 2 t 2 at the lower perimeter of the plate when sea level drops stress changes may be even greater ift r is effectively less than the stratigraphic thickness due to layering of rocks in the roof block calculated stress changes due to a 100 m drawdown of sea level are similar in magnitude to stresses associated with dike propagation more realistic model geometries including different chamber shapes a conical volcanic edifice and sea level drawdown beyond the surface projection of the magma chamber were tested using the boundary element method lowering sea level generates a horizontal tensile stress above the chamber even when sea water is removed outboard of the magma chamber for some chamber geometries the magnitude of the tensile stress maximum is greater than the 1 mpa pressure of the 100 m of removed water and is of the right order of magnitude for dike propagation dikes initiated by the change of the stress field may originate and propagate along fractures inboard of the chamber margin the magnitudes of tensile maxima along the top of the chamber decrease as original sea level is moved outboard of the chamber margin and as the chamber thickness decreases when the depth to the top of the magma chamber reaches a critical value dependent on chamber geometry the propagation of dikes to the surface is inhibited

paleomagnetism of proterozoic mafic dikes from the tobacco root mountains southwest montana abstract paleomagnetic data from proterozoic mafic dikes in southwestern montana provides evidence for two distinct episodes of subparallel dike emplacement at ca 1450 and 780 ma published geochemical data from dikes in the southern tobacco root mountains has identified three distinct compositional groups termed groups a b and c geochronological data from the group a dikes yielded a sm nd age of 1448 49 ma emplacement of these dikes is thought to reflect mafic magmatism associated with extension accompanying development of the adjacent mesoproterozoic belt basin paleomagnetic results from these dikes and a group c dike yield antipodal magnetizations with a group mean direction of d 225 0 i 61 8 k 27 9 95 7 7 n 14 independent means 24 sites the average paleomagnetic pole 8 7 n 216 1 e a95 10 3 is considered to be primary on the basis of positive baked contact tests and similarity to poles of ca 1 45 1 4 ga from intrusions elsewhere in north america but is discordant with respect to poles from age equivalent sedimentary rocks of the meosoproterozoic belt supergroup 40ar 39ar dates from geochemical group b dikes are consistent with published u pb dates that demonstrate dike emplacement at 780 ma as part of the regional gunbarrel magmatic event hornblende concentrates from the group b dikes yield 40ar 39ar apparent ages of 778 772 ma whereas biotite from a baked contact zone yielded a plateau date of 788 ma paleomagnetic results from the group b dikes yield a mean direction of d 301 5 i 17 1 k 65 7 95 4 0 n 12 independent means 23 sites with a paleomagnetic pole at 14 6 n 127 0 e a95 3 2 the combination of geochronologic data results of a baked contact test and spatial agreement of the paleomagnetic poles with poles of similar age elsewhere in north america indicates that this is also a primary magnetization associated with dike emplacement paleomagnetic data from some of the tobacco root mountains dikes provide evidence that they were partially to completely remagnetized during latest cretaceous to early tertiary time perhaps due to thermal affects associated with emplacement of the late cretaceous tobacco root batholith the overall agreement of paleomagnetic poles from the proterozoic dikes with those of age equivalent rocks elsewhere in north america and agreement of the secondary magnetization with expected directions for the latest cretaceous early tertiary indicate that the rocks of the tobacco root mountains have not experienced significant tilting or vertical axis rotation since the mesoproterozoic the new paleomagnetic poles from this study thus provide key data for refining meso and neoproterozoic parts of the north american apw path

reconstructing the quaternary evolution of the world s most active silicic volcanic system insights from an 1 65 ma deep ocean tephra record sourced from taupo volcanic zone new zealand abstract the taupo volcanic zone tvz central north island new zealand is the most frequently active quaternary rhyolitic system in the world silicic tephras recovered from ocean drilling programme site 1123 41 47 16 s 171 29 94 w 3290 m water depth in the southwest pacific ocean provide a well dated record of explosive tvz volcanism since 1 65 ma we present major minor and trace element data for 70 quaternary tephra layers from site 1123 determined by electron probe microanalysis 1314 analyses and laser ablation inductively coupled plasma mass spectrometry 654 analyses trace element data allow for the discrimination of different tephras with similar major element chemistries and the establishment of isochronous tie lines between three sediment cores 1123a 1123b and 1123c recovered from site 1123 these tephra tie lines are used to evaluate the stratigraphy and orbitally tuned stable isotope age model of the site 1123 composite record trace element fingerprinting of tephras identifies 4 5 m and 7 9 m thick sections of repeated sediments in 1123a 49 0 53 5 mbsf metres below seafloor and 1123c 48 1 56 0 mbsf respectively these previously unrecognised repeated sections have resulted in significant errors in the site 1123 composite stratigraphy and age model for the interval 1 15 1 38 ma and can explain the poor correspondence between 18o profiles for site 1123 and site 849 equatorial pacific during this interval the revised composite stratigraphy for site 1123 shows that the 70 tephra layers when correlated between cores correspond to 37 38 individual eruptive events tephras 7 of which can be correlated to onshore tvz deposits the frequency of large volume tvz derived silicic eruptions as recorded by the deposition of tephras at site 1123 has not been uniform through time rather it has been typified by short periods 25 50 ka of intense activity bracketed by longer periods 100 130 ka of quiescence the most active period at least 1 event per 7 ka occurred between 1 53 and 1 66 ma corresponding to the first 130 ka of tvz rhyolitic magmatism since 1 2 ma 80 of tephras preserved at site 1123 and the more proximal site 1124 were erupted and deposited during glacial periods this feature may reflect either enhanced atmospheric transport of volcanic ash to these sites up to 1000 km from source during glacial conditions or more speculatively that these events are triggered by changes in crustal stress accumulation associated with large amplitude sea level changes only 8 of the 37 38 site 1123 tephra units 20 can be found in all three cores and 22 tephra units 60 are only present in one of the three cores whether a tephra is preserved in all three cores does not have any direct relationship to eruptive volume instead it is postulated that tephra preservation at site 1123 is patchy and influenced by the vigorous nature of their deposition to the deep ocean floor as vertical density currents at this site at least 5 cores would need to have been drilled within a proximity of 10 s to 100 s of metres of each other to yield a 99 chance of recovering all the silicic tephras deposited on the ocean surface above it in the past 1 65 ma

small scale open ocean currents have large effects on wind wave heights tidal currents and large scale oceanic currents are known to modify ocean wave properties causing extreme sea states that are a hazard to navigation recent advances in the understanding and modeling capability of open ocean currents have revealed the ubiquitous presence of eddies fronts and filaments at scales 10 100 km based on realistic numerical models we show that these structures can be the main source of variability in significant wave heights at scales less than 200 km including important variations down to 10 km model results are consistent with wave height variations along satellite altimeter tracks resolved at scales larger than 50 km the spectrum of significant wave heights is found to be of the order of 70 hs 2 g2 tm0 1 2 times the current spectrum where hs is the spatially averaged significant wave height tm0 1 is the energy averaged period and g is the gravity acceleration this variability induced by currents has been largely overlooked in spite of its relevance for extreme wave heights and remote sensing

large eruption triggered ocean island landslide at tenerife onshore record and long term effects on hazardous pyroclastic dispersal an extensive debris avalanche deposit has been discovered on canadas volcano tenerife canary islands the onshore component of the 733 3 ka abona landslide deposit exposes classic block facies and mixed facies across 90 km 2 three lines of evidence together show that the avalanche was triggered by an ignimbrite forming explosive eruption 1 the deposit is enclosed by phonolitic ignimbrites and is draped by a plinian fallout layer all within a single eruption unit 2 it contains prismatic jointed pumice blocks that were hot during landslide emplacement indicated by chilled rims and breadcrust surfaces 3 these blocks yield the same 40 ar 39 ar date as the associated ignimbrite and fall deposit landslide hummocks dammed surface water forming ephemeral lakes perched on the volcano flank phonolite dome growth destabilized the southeast sector of a mid pleistocene canadas caldera wall and created a major breach that affected the passage of destructive pyroclastic density currents on tenerife for 0 5 m y showing that landslides can have enduring consequences for pyroclastic dispersal and hazards

how temperature dependent elasticity alters host rock magmatic reservoir models a case study on the effects of ice cap unloading on shallow volcanic systems abstract in geodynamic numerical models of volcanic systems the volcanic basement hosting the magmatic reservoir is often assumed to exhibit constant elastic parameters with a sharp transition from the host rocks to the magmatic reservoir we assess this assumption by deriving an empirical relation between elastic parameters and temperature for icelandic basalts by conducting a set of triaxial compression experiments between 200 c and 1000 c results show a significant decrease of young s modulus from 38 gpa to less than 4 7 gpa at around 1000 c based on these laboratory data we develop a 2d axisymmetric finite element model including temperature dependent elastic properties of the volcanic basement as a case study we use the snaefellsjokull volcanic system western iceland to evaluate pressure differences in the volcanic edifice and basement due to glacial unloading of the volcano first we calculate the temperature field throughout the model and assign elastic properties accordingly then we assess unloading driven pressure differences in the magma chamber at various depths in models with and without temperature dependent elastic parameters with constant elastic parameters and a sharp transition between basement and magma chamber we obtain results comparable to other studies however pressure changes due to surface unloading become smaller when using more realistic temperature dependent elastic properties we ascribe this subdued effect to a transition zone around the magma chamber which is still solid rock but with relatively low young s modulus due to high temperatures we discuss our findings in the light of volcanic processes in proximity to the magma chamber such as roof collapse dyke injection or deep hydrothermal circulation our results aim at quantifying the effects of glacial unloading on magma chamber dynamics and volcanic activity

new isotopic data and a preliminary age for volcanics near the base of the windermere supergroup northeastern washington u s a new sm nd and rb sr data are presented from the volcanic member of the huckleberry formation a unit near the base of the upper proterozoic windermere supergroup in northeastern washington the isotopic data are compatible with a rift setting during deposition of windermere strata a best fit line through all the data yields an age of 795 ma with a large error of 115 ma 2 however a preliminary sm nd mineral whole rock age of 762 44 ma 2 obtained from a least altered basalt is within error of other age information from the canadian cordillera that broadly constrains the initiation of windermere deposition to 750 30 ma a synthesis of isotopic data of the results of tectonic subsidence analyses and of geologic relations within the windermere supergroup and the immediately overlying uppermost proterozoic lower cambrian strata leads to the conclusion that the windermere supergroup does not represent the rift deposits that led directly to the initiation of the early paleozoic miogeocline in

fluctuations of the campanian explosive volcanic activity south italy during the past 190 000 years as determined by marine tephrochronology abstract a statistical analysis of the time variations of the frequency of explosive events is derived from the detailed record of marine tephra in deep sea sediment cores of the central mediterranean sea the sequence of campanian events south italy shows several volcanic pulses during the past 190 000 years which were compared to the continental data these episodes which match the different phases of the geochemical evolution of magmas in this area occurred with a 23 kyr periodicity this may be related to the life time of the magma chambers involved in this area with such time cycles precessional forcing of the volcanic activity and or glacio eustatic pressure variations may be envisaged as causal phenomena

late cretaceous remagnetization of proterozoic mafic dikes southern highland mountains southwestern montana a paleomagnetic and 40ar 39ar study paleomagnetic results from early proterozoic metabasite sills and middle proterozoic diabase dikes from the southern highland mountains of southwestern montana give well defined dual polarity magnetizations that are statistically identical to those from a small late cretaceous pluton that cuts the dikes the concordance of paleomagnetic directions from rocks of three widely separated ages indicates that the proterozoic rocks were remagnetized probably during late cretaceous time paleomagnetic rock magnetic and petrographic observations from the metabasite and diabase samples indicate that remanence is carried primarily by low ti magnetite combining virtual geomagnetic poles from metabasite sills diabase dikes and the late cretaceous pluton we obtain a paleomagnetic pole at 85 5 n 310 7 e k 19 9 a 95 9 1 n 14 sites that is similar to a reference pole from the 74 ma adel mountain volcanics of western montana biotite and hornblende 40 ar 39 ar isotopic dates from host basement gneiss and a hornblende from a remagnetized metabasite sill yield ages of ca 1800 ma these dates probably record cooling of the southern highland mountains following high grade metamorphism at 1 9 1 8 ga the gneiss and metabasite age spectra show virtually no evidence of disturbance indicating that the basement rocks were never heated to temperatures sufficient to cause even partial resetting of their argon systems thus the overprint magnetization of the highland mountains rocks is not a thermoremanent magnetization acquired during conductive cooling of nearby late cretaceous plutons remagnetization of the metabasite sills and diabase dikes was probably caused by localized thermochemical and thermoviscous effects during circulation of late cretaceous hydrothermal fluids related to epithermal mineralization the absence of significant disturbance to the 40 ar 39 ar age spectrum from the remagnetized metabasite hornblende indicates that some secondary magnetizations may go unrecognized and undated even if 40 ar 39 ar dating is applied

tracking the arctic s shrinking ice cover another extreme september minimum in 2004 1 satellite passive microwave observations document an overall downward trend in arctic sea ice extent and area since 1978 while the record minimum observed in september 2002 strongly reinforced this downward trend extreme ice minima were again observed in 2003 and 2004 although having three extreme minimum years in a row is unprecedented in the satellite record attributing these recent trends and extremes to greenhouse gas loading must be tempered by recognition that the sea ice cover is variable from year to year in response to wind temperature and oceanic forcings

interactions between hurricane catarina 2004 and warm core rings in the south atlantic ocean 1 the unexpected evolution of the first recorded south atlantic hurricane catarina over waters with homogeneous sea surface temperatures sst of 24 c in march 2004 was a challenge to the weather forecast community this work concentrates on a thorough data driven comparative analysis to make reliable diagnostics of the role of the ocean in the genesis and evolution of catarina we used several high resolution multisatellite derived products including three microwave based sst data sets multisatellite collinear data of sea surface height ssh anomalies significant wave heights and wind speeds four quikscat ocean surface wind vector products including the 12 5 km resolution swath data daily fields of absolute objectively analyzed ssh and corresponding geostrophic currents and argo floats the synergic use of these data sets showed that catarina interacted strongly with four warm core rings wcrs forcing upwelling of isotherms and mixed layer waters these interactions minimized the known negative sst feedback as attested by the sst differences being less than 1 2 c although the sst in the region was around 24 c below the palmen threshold the surface air temperatures were 14 c which still furnished a large air sea temperature gradient capable of extracting large enthalpy fluxes from the wcrs influenced by ekman pumping it is shown here that catarina achieved category 1 over the ocean on 26 march with its maximum intensity of 34 m s seen in the 12 5 km swath winds

the arctic ice thickness anomaly of the 1990s a consistent view from observations and models 1 observations of sea ice draft from submarine cruises in much of the arctic ocean show that the ice cover was unusually thin in the mid 1990s here we limit our examination to digitally recorded draft data from eight cruises spanning the years 1987 to 1997 and find a decrease of about 1 m over the 11 year span comparisons of our modeled draft with observed draft show good agreement in the temporal change comparing average draft over entire cruises the rms discrepancy between modeled and observed draft is 0 3 m and the correlation is 0 98 agreement in the spatial patterns of draft is somewhat lower the rms discrepancy of 50 km averages of draft is 0 7 m and the correlation is 0 73 we review reports of interannual variations of ice thickness or volume from other model studies all models agree that thickness decreased by between 0 6 and 0 9 m from 1987 to 1996 our model shows a modest recovery in thickness from 1996 to 1999 for the 1950s 1960s and 1970s models tend to disagree on the size and to a lesser extent the timing or phase of interannual variations

a numerical study of wave refraction in shallow tidal waters wave observations taken at two shallow water sites off the coast of south west wales u k are examined the buoys are located in a region of strong semi diurnal tides and the observations show significant variation at semi diurnal frequencies in period amplitude and direction the interaction between tides and waves is studied using linear theory of wave refraction by slowly varying currents and depths it is shown that quasi steady analytical models fail to reproduce the tidally induced variations in wave parameters a linear ray tracing model including the effects of both spatial and temporal variations in the tidal currents and elevations improves the simulation of the observed modification of the waves short period waves respond to variations in current refraction over a tidal cycle long period waves are more influenced by variations in water depth over a tidal cycle

seasat synthetic aperture radar observations of wave current and wave topographic interactions this study investigated the capability of a spaceborne imaging radar system to detect subtle changes in the propagation characteristics of ocean wave systems specifically an evolving surface gravity wave system emanating from hurricane ella and propagating toward cape hatteras north carolina formed the basis of this investigation this wave system was successfully imaged by the seasat synthetic aperture radar sar during revolution 974 on september 3 1978 estimates of the dominant wavelength and direction of the ocean waves were derived from the sar data by using optical fourier transforms environmental data of the test area which included the surface velocity vector within the gulf stream the location of hurricane ella and local bathymetric information were used in conjunction with the sar data to form the basis of this comparative study favorable agreement was found between wave rays calculated by utilizing theoretical wave current and wave topographic interactions and sar observed dominant wavelength and direction changes across the gulf stream and continental shelf

correlation between rate of sea level change and frequency of explosive volcanism in the mediterranean volcanic activity has frequently been linked to quaternary environmental change either by driving climate modification1 2 or in response to environmental changes3 although a link has been established between large explosive eruptions and small 0 5 c brief 1 2 years falls in global temperatures4 both the evidence and mechanisms responsible for longer episodes of eruption induced planetary cooling remain questionable1 2 5 6 in contrast recent research based on ice core data suggests that rapid climate changes during the past 110 000 years increased explosive volcanic activity7 here we present a statistical analysis relating the frequency of explosive activity of mediterranean volcanoes based on dated8 9 10 11 tephra layers in deep sea sediment cores to the rate of late quaternary sea level change the nonlinear correlation between the two is tentatively explained in terms of dynamic responses of the volcanoes to stress related influences on various spatial scales the correlation supports a mechanism or mechanisms by which the climate driven growth and decay of large ice sheets can influence the eruptive chronologies of distant volcanic edifices via changes in global sea level