a new approach for palaeoaltitude estimates based on pollen records example of the mercantour massif southeastern france at the earliest pliocene the altitude of the mercantour massif southern alps france during the earliest pliocene has been estimated using a new quantification method instead of classical methods using geomorphologic criteria our method uses biogeographic and climatologic criteria composition of the modern vegetation belts in the european and peri mediterranean mountains and pliocene annual temperature estimates obtained from fossil pollen data the climatic transfer function indicates for the coastal earliest pliocene of the studied area a mean annual temperature of 16 5oc such a temperature today occurs at 38 5on latitude in the mediterranean region the relation established by ozenda between the present day vertical and latitudinal vegetation assemblages evidences a shift of on average in western europe 110 m in altitude per degree in latitude as a consequence it is possible taking into account that the pliocene lapse rate was almost similar to the modern one to estimate the minimum altitude of the massif at the earliest pliocene the so obtained palaeoaltitude estimate is close to that obtained with the geomorphological method the mercantour massif was almost 2000 meters high at the earliest pliocene

geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

seismic hazard on the french riviera observations interpretations and simulations summary we present here a detailed analysis of a seismic data set recorded by a dense seismological network installed over 6 months in the southeast of france this experiment was set up at the boundary between the ligurian basin and the southern subalpine thrust belt the nice arc which is a complex tectonic region that undergoes low to moderate seismicity we recorded more than 500 microearthquakes among which 348 occurred exactly in the centre of the network during a very active seismic sequence that lasted mainly over 2 months we performed an absolute location of all of the events and calculated the magnitudes then we applied a cross correlation technique to gather similar events and to relocate relatively few of them this method revealed a very clear alignment of 19 events in a direction n120 oblique to the n20 general trend of seismicity focal mechanisms were determined for the four largest events and composite solutions for 32 smaller ones both the alignments of the earthquakes and the focal solutions revealed that two oblique segments of the fault were activated during the crisis the main segment 8 km long that was oriented nne with a left lateral strike slip movement is called the blausasc fault taking into account the tectonic evolution and the relationships between surface structures and the distribution of earthquakes and through a paleaoreconstruction of the tectonic evolution we propose that the blausasc fault is the hidden root of the peille laghet fault which has a mapped length of at least 15 km the smaller segment 0 6 km long that was activated during the crisis could be interpreted as an antithetic riedel fracture the active blausasc fault is located in a densely populated zone at only 10 km from the crowded cities of monaco and nice it is thus particularly interesting to analyse it for hazard assessment in the last section we present a simulation that is aimed at predicting what the ground motion in the city of nice would be like if an earthquake of magnitude 5 7 occurs on this fault for this we used the recordings of the largest event of the seismic sequence ml 3 2 and an empirical green s function summation scheme to simulate the ground motion at two stations situated in urban environments the values obtained show that especially on soft soil sites the effects of such an earthquake would be considerable in the city of nice

structure of a frontal cyclone a diagnostic study of a mid latitude cyclone has been carried out using routinely available numerical weather prediction model products and imagery the cyclone was intense but not exceptionally so and the results are believed to have some generality the detailed description of the cyclone structure just before it began to deepen rapidly integrates concepts from a number of researchers into a common framework a dominant feature of the cyclone close to its centre was the cloud head a region of cloud with a sharp convex outer edge which formed poleward of the main polar front cloud band the cloud head was caused by two flows that entered it from the east ascending and fanning out within it one flow the cold conveyor belt brought low wet bulb potential temperature w air back into the cloud head from low levels ahead of the warm front the other flow was due to high w air that peeled off from the base of the main warm sector airflow i e part of the warm conveyor belt and travelled in the boundary layer back towards the cyclone centre first undercutting dry air that had earlier descended from the upper troposphere called a dry intrusion and then ascending at the upper boundary of the cloud head above the cold conveyor belt the transverse circulation that gave the ascent within the cloud head also led to the cold front fracturing along its length into two separate sharp surface cold fronts with a more diffuse frontal region in between frontal fracture the two sharp surface cold fronts were associated with narrow cold frontal rainbands line convection one of the line convection segments forming the southern edge of the cloud head the overrunning of the dry intrusion in the region of the frontal fracture led to a structure known as a split front in which an upper level humidity front began to run ahead of the position of the surface cold front a feature of the cyclone at this intermediate stage in its evolution was that a large proportion of the precipitation was being generated by ascent of relatively cold air the cold conveyor belt in the cloud head as part of the thermally indirect circulation at the left exit of a developing secondary upper level jet

high resolution analysis of submarine lobes deposits seismic scale outcrops of the lauzanier area se alps france abstract the lauzanier area represents the northernmost extension of the annot sandstone series and contains deposits between 650 and 900 m thick this basin was active from upper bartonian or lower priabonian to early rupelian it is composed of two superposed units separated by a major unconformity the sediment supply is due to channelled flows coming from the south flow processes include mass flow to turbidity currents the size of the particles and the absence of fine grained sediment suggest a transport over a short distance the lower unit is made of coarse grained tabular beds interpreted as non channelled lobe deposits the upper unit is made of massive conglomerates interpreted as the channelled part of lobes these lobe deposits settle in a tectonically confined basin according to topographic compensation that occurs from bed scale to unit scale the abrupt progradation between the lower and the upper unit seems related to a major tectonic uplift in the area this uplift is also suggested by a change in the petrographic nature of the source and an abrupt coarsening of the transported clasts this field example allows providing high resolution analysis for depositional sedimentary sequences of terminal lobe deposits in a coarse grained turbidite system the outcrop analysis shows the lateral evolution of deposits and the system progradation allows a longitudinal analysis of facies evolution by superposing on the same outcrops the channelled lobe system and the non channelled lobe system these results of high resolution outcrop analysis can be extrapolated to results obtained on sedimentary lobes in recent deep sea turbidite system that are either restricted to cores or with a lesser resolution seismic

integration of 3d geological modeling and gravity surveys for geothermal prospection in an alpine region abstract thermal sources are common manifestations of geothermal energy resources in alpine regions the up flow of the fluid is well known to be often linked to cross cutting fault zones providing a significant volume of fractures since conventional exploration methods are challenging in such areas of high topography and complicated logistics 3d geological modeling based on structural investigation becomes a useful tool for assessing the overall geology of the investigated sites geological modeling alone is however less effective if not integrated with deep subsurface investigations that could provide a first order information on geological boundaries and an imaging of geological structures with this aim in the present paper the combined use of 3d geological modeling and gravity surveys for geothermal prospection of a hydrothermal area in the western alps was carried out on two sites located in the argentera massif nw italy the geothermal activity of the area is revealed by thermal anomalies with surface evidences such as hot springs at temperatures up to 70 c integration of gravity measurements and 3d modeling investigates the potential of this approach in the context of geothermal exploration in alpine regions where a very complex geological and structural setting is expected the approach used in the present work is based on the comparison between the observed gravity and the gravity effect of the 3d geological models in order to enhance local effects related to the geothermal system it is shown that a correct integration of 3d modeling and detailed geophysical survey could allow a better characterization of geological structures involved in geothermal fluids circulation particularly gravity inversions have successfully delineated the continuity in depth of low density structures such as faults and fractured bands observed at the surface and have been of great help in improving the overall geological model

mesoscale analysis of the activation of a cold front during cyclogenesis summary the archetypal mesoscale structure of an ana cold front comprises a narrow cold frontal rainband ncfr associated with line convection embedded within a wide cold frontal rainband wcfr due to the slantwise ascent associated with a strong transverse front mesoscale circulation whereas most mesoscale observational studies have concentrated on this mature stage the present paper explores by means of a detailed case study how such a mature frontal system develops from pre existing features the study is based upon the synthesis of data spanning many scales in the form of satellite imagery observations from conventional and multi parameter doppler radar and surface reports together with diagnostics from an operational mesoscale forecast model the cold frontal zone in this case is characterized by multiple cold fronts the dominant second cold front is studied in detail from the point of view of its evolution and its relationship to neighbouring fronts especially the leading front associated with the initial polar front cloud band the dominant cold front started as a shallow rope cloud in the cold sector and at a fairly early stage it produced a ncfr due to line convection then over a period of only a few hours a dry intrusion and an associated strong direct transverse front circulation led to the formation of a canopy of mid level cloud and a wcfr the wcfr was attributable not only to the rearward ascending outflow from the line convection but also to the re invigoration of ascent within the initial polar front cloud band that the line convection was undercutting although the transverse circulation was probably intensified by precipitation processes it is inferred that it was mainly a manifestation of the larger scale environmental flow that existed independently of the major precipitation features

morphodynamic evolution of the orb river languedoc france evidence of eustatic tectonic and climatic controls this study aims to reconstruct the cenozoic and pleistocene morphodynamic evolution of the orb a mediterranean river which crosses all the structural units of the south massif central border a geomorphological and sedimentological analysis of detrital deposits was carried out as a basis for correlating the different formations and reconstructing the palaeodrainage heavy minerals were used to reconstruct the main sedimentary palaeochannels since the messinian the successive orb longitudinal profiles show anomalies which can be caused by structure and by interactions between fluvial dynamics and tectonics evidence of volcanic heavy minerals on the faugeres mountains and in the upper pliocene deposits of the languedocian piedmont demonstrates that a north south flow took place during the upper pliocene nevertheless a palaeo orb existed at the place of the present course when the basaltic lava flows were spreading but headward erosion did not reach them until the upper pleistocene because the orb middle and high terraces do not contain volcanic minerals sourced from the escandorgue the successive orb longitudinal profiles show that headward erosion due to pleistocene low sea levels does not reach beyond beziers and that a tectonic hinge has functioned near the shoreline the non lithologic knickpoints are explained by the montagne noire and avant monts uplift up until the pleistocene a progressive continental uplift is necessary to explain the orb terraces staircase in the beziers district and the fluctuations of incision from upstream to downstream are due to laterally differential movements which are isostatic effects of thick regressive deposits on the gulf of lion shelf during the cold periods copyright 2008 john wiley sons ltd

sedimentary trace element constraints on the role of north atlantic igneous province volcanism in late paleocene early eocene environmental change abstract a growing body of geologic evidence suggests that emplacement of the north atlantic igneous province naip played a major role in global warming during the early paleogene as well as in the transient paleocene eocene thermal maximum petm event a 5 million year record of major and trace element abundances spanning 56 to 51 ma at deep sea drilling project sites 401 and 549 confirms that the majority of naip volcanism occurred as subaerial flows thus the trace element records provide constraints on the nature and scope of the environmental impact of the naip during the late paleocene early eocene interval subaerial volcanism would have injected mantle co2 directly into the atmosphere resulting in a more immediate increase in atmospheric greenhouse gas abundances than co2 input through submarine volcanism the lack of significant hydrothermalism contradicts recently proposed mechanisms for thermally destabilizing methane hydrate reservoirs during the petm any connection between naip volcanism and petm warming had to occur through the atmosphere

rare earth element concentrations and nd isotopes in the southeast pacific ocean 1 three vertical profiles of rare earth element concentrations and nd isotopic compositions have been measured in the remote southeast pacific ocean the three stations represent contrasting environments the oligotrophic center of the gyre station gyr the transition zone east of the south tropical front station egy and the peru chile upwelling marked by a pronounced oxygen minimum station upx rare earth concentrations display nutrient like vertical profiles except at upx where surface waters are enriched at this station nd isotopic compositions are clearly more radiogenic than in the open ocean suggesting that boundary exchange process is releasing lithogenic rare earth element from the volcanic andes unexpected radiogenic values end reaching 3 7 are also observed at 2000 m at station gyr in the upper circumpolar deep water that commonly have end values around 6 exchange processes related to hydrothermal activity are suspected to produce this increase in end in the vicinity of the east pacific rise these results provide some guidance for higher resolution studies planned in this region by the international geotraces program

hydrothermal manganese plumes in the mid atlantic ridge rift valley the concentration of dissolved manganese in sea water can be used as a chemical tracer of hydrothermal activity on the underlying sea floor here we present vertical profiles of seawater manganese concentrations above the rift valley of the mid atlantic ridge mar the values obtained indicate the presence of plumes that are presently active generated by hydrothermal vents in the rift valley these plumes are confined to the rift valley and do not spill over into the adjacent deep ocean basins differences between them suggest that there are at least five hydrothermal sources along this 1 700 km long section of mid ocean ridge

thermodynamic analytic fields from doppler radar data by means of the mandop analysis the paper is devoted to scale interaction studies it presents a new approach for retrieving mesoscale and convective scale thermodynamic fields from doppler radar data in order to diagnose processes involved in these interactions thermodynamic fields are retrieved analytically using the analytic form of the three dimensional wind field obtained by the mandop analysis in the non dissipative and stationary first order anelastic approximation of the equation of motion applications on simulated data and experimental data from the toga coare show the capability of this new method to retrieve the pressure and temperature fields at various scales of motion and in particular at mesoscale this new analysis will be used intensively on doppler radar data collected during the fronts and atlantic storm tracks experiment in order to diagnose the multiscale interaction processes associated with frontal wave and or secondary cyclogenesis

observations of mesoscale circulations within extratropical cyclones over the north atlantic ocean during erica abstract pseudo dual doppler analyses of two mesoscale circulations 20 40 km in horizontal dimensions that formed along a warm front within a rapidly deepening extratropical cyclone over the ocean are presented the circulations were analyzed using airborne doppler radar during erica experiment on rapidly intensifying cyclones over the atlantic iop intensive observing period 4 and are believed to be a type of frontal instability that has not been addressed in past theoretical studies of frontal waves and cyclones these features may be the shallow circulations that have been documented to play a role in cyclogenesis when they become coupled with an upper level baroclinic wave the present case is compared and contrasted with the only other well analyzed event during erica iop 5 a retrieval of the perturbation pressure and buoyancy fields using the kinematic wind fields is performed in order to facilitate the interpretation of the dynamic structure of these vortices in addition a set of equations

dynamical aspects of the october storm 1987 a study of a successful fine mesh simulation a diagnostic study of a successful numerical simulation of the october storm 1987 is described this good non operational forecast was obtained using the meteorological office s fine mesh model run from a revised analysis at 00 gmt on 15 october 1987 the meteorological office s mesoscale model was also run using initial conditions at 12 gmt 15 october obtained by interpolating the above fine mesh forecast fields to examine the benefits of very high horizontal resolution 15km grid length diagnostic maps and cross sections derived are used to address two scientific issues i the role of weak moist slantwise stability or alternatively positive slantwise convective potential energy ii the dynamical significance of the striking cloud structure the cloud head seen in the satellite imagery early in the storm s life it appears that the baroclinic zone in which the storm develops is highly receptive to forcing by an upper trough and the warm boundary layer air just ahead of the main surface front is characterized by substantial slantwise convective available energy the cloud head is identified with a region of intense slantwise ascent in the warm air just above the main frontal zone its great meridional extent is associated with the upper tropospheric outflow and horizontal spreading of air which has recently undergone rapid slantwise ascent the low level temperature field exhibits throughout the development period a remarkable shape preserving thermal ridge of considerable intensity the sensitivity of the forecast to the removal of surface energy fluxes and latent heat of condensation are investigated separately it is found that on the timescale of the simulation surface energy fluxes have negligible impact on the explosive development on the other hand the contribution of latent heat release to the development appears to dominate the dry baroclinic instability process

orogen parallel brittle extension as a major tectonic imprint in the neogene evolution of the south western alpine arc we present a new analysis of the late alpine brittle deformation in the southern branch of the western alpine arc focusing on the stack of internal metamorphic nappes east of the argentera external crystalline massif the regional scale fault network is dominated by a nw se striking right lateral fault system that follows the general curvature of the arc and controls the overall morphology of the area a second fault set strikes n s and is mainly represented by normal faults which accommodate orogen parallel extension structural analysis and paleostress tensors derived from inversion of fault slip data reveal a complex pattern of deformation involving extensional and strike slip deformation events the orogen parallel extension previously described in the internal zones at the east of the pelvoux massif is confirmed further south and we show that it is combined with right lateral strike slip deformation that increases in intensity towards the south west the stability of the minimum stress axis 3 direction suggests that extensional and transcurrent regimes are contemporaneous and highlights regional interferences between inner brittle extension parallel to the strike of the belt and the strike slip strain field driven by the counterclockwise rotation of the apulia adria plate the curved geometry of the belt constrains the direction of extension and the coupling relationship between the internal and external alpine zones we propose that the neogene tectonic history is a result of the unique curved tectonic architecture of the south western alps with respect to the rotation of the apulia adria indenting plate the southern tip of the western alpine arc represents a transitional zone between extension in the inner chain and strike slip compression in the outer parts

mesoscale dynamics of a deepening secondary cyclone in fastex iop16 three dimensional structure retrieved from dropsonde data the mesoscale dynamics of a secondary cyclone sampled during the field phase of the fronts and atlantic storm track experiment fastex intensive observation period iop 16 are documented using airborne dropsonde data the method proposed to recover the mesoscale analytical three dimensional 3 d dynamic fields from the dropsonde measurements is evaluated using simulated fields airborne in situ measurements and airborne doppler radar measurements these simulations and comparisons indicate that the method is able to resolve the mesoscale structures within the studied secondary cyclone both in the regions of clear air and precipitation it appears however that the most accurate description of the 3 d dynamic fields in both these regions would be obtained by combining doppler and dropsonde measurements the studied secondary cyclone is a fast moving frontal wave that developed on the trailing cold front of a parent low situated over greenland using the dropsonde derived 3 d fields the mesoscale flows involved in the organization of the secondary cyclone are described the potential vorticity and equivalent potential vorticity fields deduced from the basic analytical fields indicate that the atmosphere is roughly neutral to moist slantwise instability this configuration is known to significantly promote frontogenesis the vertical configuration of the jets and circulations within this secondary cyclone are compared with the coupling uncoupling scheme of shapiro a slight coupling is found between the thermally indirect circulation and the ageostrophic circulation the obtained coupling is however not as developed as in the ideal case described by shapiro which may explain the small upward velocities in our case airborne doppler radar and dropsonde measurements are combined so as to infer the multi scale processes involved in the mesoscale and convective scale organization of the atlantic secondary cyclones and to evaluate the new emerging theoretical interpretations of secondary cyclogenesis

drainage network geometry versus tectonics in the argentera massif french italian alps abstract the argentera massif french italian alps with its uniform lithology was selected to evaluate how known plio pleistocene tectonics have conditioned the drainage network geometry the drainage network was automatically derived and ordered from a 10 m resolution dem on hillshade images alignments of morphological features were identified the massif was subdivided into 22 domains of 50 km 2 within which the directions of every river channel segment and the direction of the aligned morphological features were compared and contrasted with the strike of tectonic structures measured in the field results suggest that the argentera drainage system is variously controlled by recent tectonics depending on the massif sector taken into account in the nw sector the vertical uplift is less because the strain has been accommodated in an oblique direction along a lateral thrust in the se sector strain in a predominantly vertical direction along a frontal thrust has resulted in a major vertical displacement accordingly the nw sector is characterized by i a strong geometric relationship between the main tectonic structures and the directions of river channels ii longitudinal main rivers bordering the massif and iii a general trellis pattern within the domains in the se sector the prolonged uplift has forced an original longitudinal drainage system to develop as a transverse system this change has occurred by means of fluvial captures that have been identified by the presence of windgaps fluvial elbows and knickpoints at the domain scale intense uplift of the se sector has prompted the drainage pattern to evolve as a dendritic type with no clear influence of structure in the channel orientations

the east pacific rise near 21 n 13 n and 20 s inferences for along strike variability of axial processes of the mid ocean ridge abstract data obtained along various segments of the mid ocean ridge mor are used to construct an idealized model for crustal accretion the model seeks to predict the topographic volcanic tectonic and hydrothermal characteristics of any given spreading segment of the mor as a function of distance away from the bounding transform faults this model is based on a series of detailed mapping efforts carried out on segments of the mor having a broad range of spreading rates between 2 and 16 cm yr this paper includes the results of the french searise program carried out during the summer of 1980 aboard the n o jean charcot and two american cruises conducted in 1981 aboard the r v melville

compositional variability in the ascending fluxes from a hydrothermal plume 1 sequentially sampling sediment traps set with 33 day sampling intervals were deployed with current meters on three moorings in the northeast pacific ocean between july 1994 and may 1995 one mooring was deployed near the main vent field on endeavour ridge on axis site 47 57 0 n 129 05 7 w a second 3 km west of the main vent site west site and the third 43 km northeast of the main vent site east or background site ascending and descending particles were collected near 1600 and 2000 m depth well above and within the top of laterally spreading hydrothermal plumes the elemental composition of particles was used to evaluate their origins biogenic fluxes were indicated by elevated ca or si hydrothermal fluxes by elevated fe mn and cu and lithogenic fluxes by elevated ti we link temporal variability in both the ascending and descending particle composition and flux to variations in lateral transport of hydrothermal constituents and to seasonal drawdown of hydrothermal plume particles by biogenic material from the upper ocean the relatively low hydrothermal fe content of ascending material late in the experiment is thought to be due to uptake by descending biogenic material these results suggest that seasonal productivity and particle export from the ocean surface can modulate the hydrothermal flux of elements to the waters above and to the sediments below

late stages of continent continent collision timing kinematic evolution and exhumation of the northern rim aar massif of the alps abstract the alpine front s external crystalline massifs represent exhumation of mid crustal basement during late stage continent continent collision we unravel the geodynamic evolution of the northalpine front aar massif by combining structural and low t thermochronometric data a crustal scale tectonic restoration neogene present and estimation of associated changes in exhumation rates become possible the european continental margin experienced multiple switches from horizontal to vertical and again to horizontal dominated tectonics early thrust related inversion of rift basins is followed by a switch to rapid vertical exhumation with deformation along steep reverse normal faults this vertical tectonics is related to a positive buoyancy force of the european crust induced by lower crustal delamination of the aar massif during an orogenic rollback process of the european lithosphere 22 20 ma differential rock uplift rates of up to 1 3 1 6 km myr resulted which decreased northwards to 0 1 km myr reducing buoyancy forces isostatic compensation led to a horizontal tectonic style again persisting compressional forces induced an orogen scale strain partitioning with dextral transpressive faults in the south and simultaneous crustal scale northwest directed thrusting in the north en bloc exhumation of the entire aar massif in the thrust s hanging wall occurred between 13 5 ma and 5 0 ma at rates of 0 5 0 9 km myr and 0 6 0 8 km myr respectively it is this late stage thrusting in combination with surface erosion which shaped today s prominent northalpine front switches between horizontal and vertical tectonics might generally be relevant for late continent continent collisional stages here buoyancy forces of non thinned continental crust entering the subduction zone cause a strong vertical tectonic deformation style instead of classical thrust tectonics

sr and nd isotopes as tracers of clastic sources in lake le bourget sediment nw alps france during the little ice age palaeohydrology implications geochemical methods major elements and sr nd isotopes have been used to 1 characterize lake le bourget sediments in the french alps 2 identify the current sources of the clastic sediments and estimate the source variability over the last 600 years major element results indicate that lake le bourget sediments consist of 45 clastic component and 55 endogenic calcite in addition several individual flood levels have been identified during the little ice age lia on the basis of their higher clastic content 70 potential sources of lake le bourget clastic sediments have been investigated from sr and nd isotope compositions the sediments from the sierroz river and leysse river which are mainly derived from the mesozoic calcareous massifs are characterised by lower 87sr 86sr ratios and slightly lower nd 0 ratios than the arve river sediments which are derived from the palaeozoic mont blanc external crystalline massifs the rhone river appears to have been the main source of clastic sediments into the lake for the last 600 years as evidenced by a similar sr and nd isotopic compositions analyzed in core b16 sediments 87sr 86sr 0 719 nd 0 10 and in the sediments of the rhone river 87sr 86sr 0 719 nd 0 9 6 the isotopic signatures of flood events and background samples from core b16 in lake le bourget are also similar this indicates that prior to 1800 the inputs into the lake have remained relatively homogeneous with the proportion of clastic component mainly being a function of the palaeohydrology of the rhone river early human modification deforestation and agriculture of the lake catchment before the 1800s appears to have had little influence on the source of clastic sediments

constraints from 40ar 39ar geochronology on the timing of alpine shear zones in the mont blanc aiguilles rouges region of the european alps the mont blanc and aiguilles rouges massifs which form part of the external crystalline massifs of the western european alps record a young and fast exhumation history as established by an extensive low temperature thermochronology and geochronology data set various kinematic and dynamic models for oligocene to neogene deformation and exhumation of the aiguilles rouges mont blanc system have been proposed however the timing of deformation along major shear zones in and around the massifs which is crucial to these models is still controversial our new 40ar 39ar data from key deformation zones in the mont blanc area show that nw directed thrusting lasted from oligocene to mid miocene times in the mont blanc massif before a nw ward jump of the deformation front to below the aiguilles rouges massif which led to updoming of the aiguilles rouges and mont blanc massifs this deactivated the main nw verging shear zones and caused back folding and back thrusting east of the mont blanc as well as upward extrusion of the aiguilles rouges massif subsequently there was a switch to more coaxial shortening between the aiguilles rouges and mont blanc massifs associated with strain partitioning and related dextral strike slip deformation on the eastern side of the mont blanc massif

interpretation of satellite imagery of a rapidly deepening cyclone model output and observational data are used to interpret in detail satellite images of a distinctive cloud system several hundred kilometres long which was observed before and during rapid cyclonic development that occurred over england conceptual models are forwarded which account for the structure of the major cloud areas and upper level moisture fields as observed by water vapour imagery immediately prior to and following the onset of vigorous cyclogenesis the cloud system corresponded to what r b weldon refers to as a baroclinic leaf cloud and was characterized by ana cold frontal ascent the baroclinic leaf lay within an area of enhanced ascent ahead of a major upper level trough a jet streak which originated upstream propagated rapidly around the base of the upper trough a tongue of dry air centred on the left flank of this jet streak lay immediately upstream of the leaf cloud and had a major influence on its subsequent development this intrusion of dry air was well represented by the meteorological office fine mesh model which showed it as a pronounced tongue of recently descended air with high potential vorticity which originated in the upper troposphere and lower stratosphere rapid cyclogenesis occurred as the dry intrusion overran low level air of high w within a warm conveyor belt at the southern tip of the leaf cloud interaction of the dry intrusion and baroclinic leaf cloud is shown to be particularly important in accounting for the detailed distribution of weather it also suggests a way of pinpointing the location and timing of vigorous cyclogenesis

the geochemistry of inorganic germanium in natural waters we present the initial results from a survey of the distribution of dissolved inorganic germanium in rivers in the oceans and in hydrothermal vents and plumes in the ocean germanium cycling mimics that of silica since siliceous organisms incorporate ge as a trace constituent in biogenic opal the vertical and horizontal distributions of ge concentrations in seawater are thus identical to those of silica ge si 0 7 10 6 and reflect uptake into and dissolution from the frustules of siliceous organisms germanium enters the ocean via dissolution of continental and seafloor silicates the naturally weathered flux from continents to oceans carries a dissolved ge si atom ratio in rivers of about 0 7 10 6 which reflects the ratio in average continental granites rivers draining industrial regions with significant coal combustion are contaminated with ge leached from fly ash particles resulting in ge si ratios up to tenfold above the naturally weathered background the flux to the oceans via high temperature alteration of seafloor basalts hot springs produces a ge anomaly in hydrothermal plumes over the east pacific rise crest 20 s combining the observed ge and 3he anomalies in plumes with 3he si observations in hot springs suggests that the ge si hydrothermal flux to the oceans is about 4 10 6 near the ratio for average oceanic basalts 2 6 10 6 vent effluents from the galapagos hot springs measured directly display ge si ratios of 16 10 6 suggesting that the ratio is variable between vent fields metalliferous sediments accumulating on the epr crest 17 s are enriched in germanium suggesting that a fraction of the hydrothermal germanium source on the rise crest is scavenged into these rapidly accumulating iron and manganese hydroxyoxide phases

increase in late neogene denudation of the european alps confirmed by analysis of a fission track thermochronology database abstract a sharp increase in deposited sediment volume since pliocene times has been observed worldwide and in particular around the european alps this phenomenon has been linked to a rise in denudation rates controlled by an increase of either climatic or tectonic forcing observation of in situ cooling histories for orogens is critical to assess the reality of the inferred increase in denudation rates and to determine whether this phenomenon is widespread or localized at active tectonic structures we exploit the unique density of fission track ages in the western european alps to reconstruct cooling isoage surfaces and to estimate exhumation rates on the orogen scale between 13 5 and 2 5 ma our novel technique is based on the association of isoage contours with age elevation relationships it uses map view interpolation enabling a spatio temporal analysis of exhumation rates over the entire western alps the resulting exhumation histories reconstructed for eight areas of the western alps display strong similarities in timing and rates with orogen wide average denudation rates inferred from sediment volumes this consistency validates the use of both techniques for the study of an orogen characterized by strong relief and high recent exhumation rates we conclude that exhumation rates in the western alps have increased more than twofold since late miocene times this increase may have been locally modulated by the distinct response of different tectonic units

three dimensional interface modelling with two dimensional seismic data the alpine crust mantle boundary summary we present a new approach to determine the 3 d topography and lateral continuity of seismic interfaces using 2 d derived controlled source seismic reflector data the aim of the approach is to give the simplest possible structure consistent with all reflector data and error estimates we define simplicity of seismic interfaces by the degree of interface continuity i e shortest length of ovsets and by the degree of interface roughness least surface roughness the method is applied to structural information of the crust mantle boundary moho obtained from over 250 controlled source seismic reflection and refraction profiles in the greater alpine region the reflected and refracted phases from the moho interface and their interpretation regarding crustal thickness are reviewed and their reliability weighted weights assigned to each reflector element are transformed to depth errors considering fresnel volumes the 2 d derived reflector elements are relocated in space 3 d migration and interpolation is performed between the observed reflector elements to obtain continuity of model parameters interface ovsets are introduced only where required according to the principle of simplicity the resulting 3 d model of the alpine crust mantle boundary shows two ovsets that divide the interface into a european an adriatic and a ligurian moho with the european moho subducting below the adriatic moho and with the adriatic moho underthrusting the ligurian moho each sub interface depicts the smoothest possible i e simplest surface fitting the reflector data within their assigned errors the results are consistent with previous studies for those regions with dense and reliable controlledsource seismic data the newly derived alpine moho interface however surpasses earlier studies by its lateral extent over an area of about 600 km by 600 km by quantifying reliability estimates along the interface and by obeying the principle of being consistently as simple as possible

co diagenesis of iron and phosphorus in hydrothermal sediments from the southern east pacific rise implications for the evaluation of paleoseawater phosphate concentrations abstract we present a detailed study of the co diagenesis of fe and p in hydrothermal plume fallout sediments from 19 s on the southern east pacific rise three distal sediment cores from 340 1130 km from the ridge crest collected during dsdp leg 92 were analysed for solid phase fe and p associations using sequential chemical extraction techniques the sediments at all sites are enriched in hydrothermal fe oxyhydr oxides but during diagenesis a large proportion of the primary ferrihydrite precipitates are transformed to the more stable mineral form of goethite and to a lesser extent to clay minerals resulting in the release to solution of scavenged p however a significant proportion of this p is retained within the sediment by incorporation into secondary goethite by precipitation as authigenic apatite and by readsorption to fe oxyhydr oxides molar p fe ratios for these sediments are significantly lower than those measured in plume particles from more northern localities along the southern east pacific rise and show a distinct downcore decrease to a depth of 12 m molar p fe ratios are then relatively constant to a depth of 35 m the fe and p speciation data indicate that diagenetic modification of the sediments is largely complete by a depth of 2 5 m and thus depth trends in molar p fe ratios can not solely be explained by losses of p from the sediment by diffusion to the overlying water column during early diagenesis instead these sediments are likely recording changes in dissolved p concentrations off the sepr possibly as a result of redistribution of nutrients in response to changes in oceanic circulation over the last 10 million years furthermore the relatively low molar p fe ratios observed throughout these sediments are not necessarily solely due to losses of scavenged p by diffusion to the overlying water column during diagenesis but may also reflect post depositional oxidation of pyrite originating from the volatile rich vents of the southern east pacific rise this study suggests that the molar p fe ratio of oxic fe rich sediments may serve as a proxy of relative changes in paleoseawater phosphate concentrations particularly if fe sulfide minerals are not an important component during transport and deposition

diachronous late stage exhumation across the western alpine arc constraints from apatite fission track thermochronology between the pelvoux and dora maira massifs we present new apatite fission track aft data from the central western alps that confirm the synchronicity and high cooling rates during latest miocene pliocene final exhumation of the external crystalline massifs but also provide evidence for diachronous neogene evolution along and across the internal arc to the se of the pelvoux massif across the front of the internal arc penninic frontal thrust the jump in aft ages c 22 ma and in final cooling rates is significantly larger than further north this difference results from reversal of movement along a major oligocene thrust in its hanging wall the western brianconnais zone provides a mean aft age of c 27 ma which is older than further north early cooling in the southern brianconnais zone would result from rapid erosion of the compressional fan structure built during the oligocene across the entire brianconnais and piemont nappe stack with the exception of the dora maira massif aft ages young eastward and span the entire miocene a period during which this structure underwent extension further north a reverse gradient with ages younging northwestward has been described prompting the question of the asymmetry of the internal western alpine arc during its late stage tectonic and morphological evolution

miocene lateral extrusion in the inner western alps revealed by dynamic fault analysis 1 from early miocene to the present day the core parts of the western european alps experienced brittle extensional deformations mostly in a strike parallel direction here we present new data constraining the brittle deformation of the vanoise area french alps and a synthesis of 312 paleostress tensors in the whole arc of the internal western alps the data show a continuous change in the direction of extension from n065 simplon area to n s vanoise area and to nnw sse briancon area the abundance of orogen perpendicular 3 axes increases from the north to the south in the brianconnais area an extensional reactivation of the basal penninic thrust seems to be the origin of the e w to ne sw oriented 3 in light of these new data and the regional paleostress synthesis we propose a predominant orogen parallel extension in the internal zone as a whole this orogen parallel extension is related to the indentation rotation of the apulian microplate and to the opening of the ligurian sea during the lower middle miocene the locally observed orogen perpendicular extension is interpreted as an effect of the exhumation of the internal crystalline massifs the uplift of the external crystalline massifs and or the present day geodynamics postorogenic gravitational collapse some transcurrent tectonics older than the extension in the valais area and younger than the extension farther south is observed in the entire inner western alps strike slip movements are correlated with the apulian rotation and local permutation of stress axes

plume dispersed hydrothermal particles a time series record of settling flux from the endeavour ridge using moored sensors abstract settling particles collected with moored sediment traps near an area of active hydrothermal venting in the northeast pacific ocean provide information about the deep sea distribution of hydrothermal material results of an 8 day near field single trap experiment and a 340 day multi instrument 5 trap deployment two kilometers from the endeavour ridge vent field show variability in the quantity and composition of the plume to sediment particle flux over time with depth and with distance from the vent field hydrothermal elemental fluxes vary by a factor of two among the four sampling intervals of the longer experiment a factor of three variation in fe s among these periods reflects temporal changes in phase composition changes in flux with depth for example a 200 fold increase in cu and zn between above and below plume traps are evidence of hydrothermal input comparison of fluxes determined in the near and far field experiments reveals the spatial influence of vent effluent near field particle flux exceeds that measured two kilometers away by a factor of 10 to 20 and is relatively enriched in fe cu and organic carbon but depleted in mn calculations of the residence time of the plume with respect to settling indicate that more than 90 percent of the particulate material is transported farther than two kilometers from the vent field interpretation of elemental mineralogical and grain size analyses suggest that chemical precipitation kinetics other physical and biological particle forming processes changes in vent output and lateral transport of hydrothermal material by abyssal currents are tenable explanations for our observations our findings suggest that these rate interdependent processes be included in realistic models of hydrothermal particle flux

extensional neotectonics around the bend of the western central alps an overview the western alps active tectonics is characterized by ongoing widespread extension in the highest parts of the belt and transpressive compressive tectonics along its borders we examine these contrasting tectonic regimes using a multidisciplinary approach including seismotectonics numerical modeling gps morphotectonics fieldwork and brittle deformation analysis extension appears to be the dominant process in the present day tectonic activity in the western alps affecting its internal areas all along the arc shortening in contrast is limited to small areas located along at the outer borders of the chain strike slip is observed throughout the alpine realm and in the foreland the stress orientation pattern is radial for 3 in the inner extensional zones and for 1 in the outer transcurrent tranpressional ones extensional areas can be correlated with the parts of the belt with the thickest crust quantification of seismic strain in tectonically homogeneous areas shows that only 10 20 of the geodesy documented deformation can be explained by the alpine seismicity we propose that alpine active tectonics are ruled by isostasy buoyancy forces rather than the ongoing shortening along the alpine europe adria collision zone this interpretation is corroborated by numerical modeling the neogene extensional structures in the alps formed under increasingly brittle conditions a synthesis of paleostress tensors for the internal parts of the west alpine arc documents major orogen parallel extension with a continuous change in 3 directions from ene wsw in the simplon area to n s in the vanoise area and to nnw sse in the briancon area minor orogen perpendicular extension increases from n to s this second signal correlates with the present day geodynamics as revealed by focal plane mechanisms analysis the orogen parallel extension could be related to the opening of the ligurian sea during the early middle miocene and to compression rotation of the adriatic indenter inducing lateral extrusion

mineralogy bulk and rare earth element geochemistry of massive sulphide associated hydrothermal sediments of the brunswick horizon bathurst mining camp new brunswick massive sulphides are spatially and temporally associated with iron formation if and other hydrothermal sedimentary rocks in the vicinity of the brunswick no 12 brunswick no 6 and austin brook deposits bathurst mining camp sulphide carbonate oxide and silicate predominant if is present carbonate predominant if is best developed in and around the brunswick no 12 deposit whereas hematite bearing if is absent here but prominent in the austin brook brunswick no 6 area the if is composed dominantly of si co2 fe mn and ca minor constituents include mg p ti al and s statistically significant interelement correlations between eu fe mn pb zn cd au ca sr ba p co2 and s indicate that these elements were precipitated from hydrothermal fluids vented onto the seafloor positive interelement correlations between si ti al mg k zr rare earth elements ree s except eu se v y yb co ni and cr reflect the presence of detrital clastic mafic and aluminosilicate minerals and

active deformation at the southwestern alps ligurian basin junction france italy boundary evidence for recent change from compression to extension in the argentera massif abstract several hundred earthquakes of small and moderate magnitude occur each year at the southwestern alps ligurian basin junction in addition the historical seismicity data attests for earthquakes of magnitude close to 6 5 despite the seismic hazard and the vulnerability of this region the present day driving mechanism of deformation and the major structures accommodating these deformations remain unclear this littoral area presents a strong topographic gradient from 3000 masl on the argentera alpine massif to 2500 m u s l in the ligurian basin and a strong structural inheritage resulting from 50 my geological evolution combining different processes such as continental collision and ocean basin opening we present new results about the kinematics of the corsica sardinia continental block with respect to the western alpine belt from 7 years of continuous gps measurements we show that a small part of the nubia eurasia convergence is certainly transferred northward of the maghrebides deformation belts to the corsica sardinia block in the southwesternmost alps from torino to the mediterranean coast the baselines reveal differential motions of lengthening between the po plain and the argentera and shortening between the argentera and the ligurian domain in a region where few focal solutions are available we determine seven new focal mechanisms located in the argentera massif these new data underline a quaternary change from compression to extension in that part of the western alpine belt the focal mechanisms calculated attest for extensional faulting at shallow level between 1 and 11 km depth we add 7 focal mechanisms from the literature to calculate the stress tensor a homogeneous solution indicates a direction of extension broadly perpendicular to the topographic axis culmination of the argentera in contrast the earthquakes recorded below 15 km at the northwestern margin of the po plain testify reverse faulting and a compressional state of stress in the deep crust thus we point out that the stress field is vertically heterogeneous in the crust of the argentera area the ligurian domain is mainly characterized by reverse and strike slip faulting the major earthquakes are located in the northern margin and at the ocean continent transition these earthquakes are assumed to result from the reactivation in a compressional state of stress of the structures formed during the oligo miocene opening of the ligurian basin finally we propose three hypotheses to explain the current deformation at the alps ligurian basin junction taking into account the far field kinematics between the nubia and the eurasia plates the topographic gradient between the argentera massif and the ligurian oceanic floor and the distribution of the deformations

pacific and atlantic bomb like deepenings in mature phase a comparative study the mesoscale dynamics of a secondary cyclone sampled during the field phase of the fronts and atlantic storm track experiment fastex are documented using airborne doppler radar data the high quality of the mesoscale airborne doppler dataset collected within this secondary cyclone is highlighted this study demonstrates however the need to combine in the near future airborne doppler radar and dropsonde measurements in order to access multiscale processes involved in the mature stage of this fastex cyclone both in clear air and in precipitating regions the studied secondary cyclone developed on the trailing cold front of a parent low situated over greenland and underwent the most explosive deepening roughly 54 mb in 24 hours sampled in the multiscale sampling area during fastex the main flows responsible for the mesoscale organization of the cyclone are a warm airflow emerging from the base of the synoptic warm conveyor belt that generates the most active part of the cloud head a dry intrusion approaching in the dry slot the cyclone centre a cold conveyor belt that contributes to the upward mass transport towards the upper part of the polar front cloud band and a cold northerly flow in the western part of the cloud head which tends to wrap around the low centre and is likely to release convective instability through air sea interactions this study also documents a slight shift in position between the high vertical vorticity core associated with the active part of the cloud head and the location of the pressure minimum the detailed three dimensional structure of this atlantic secondary cyclone is also compared with that gathered within another bomb like deepening defined as more than a 24 mb surface pressure drop in 24 hours observed over the pacific ocean during the coastal observation and simulation with topography coast experiment some similarities are found the main differences appear to be linked to the warm seclusion that is exclusive to the studied pacific cyclone more pronounced ascending motions are found within the cloud head of the pacific reference case and the deepening results from a more constructive effect of geostrophic and non geostrophic processes than for the atlantic reference case

the provenance of sediments in the barreme thrust top basin haute provence france abstract this paper records the results of an integrated analysis of heavy minerals sedimentary facies palaeocurrents and structural data the objective of the study was to evaluate the provenance of the sediments of the barreme thrust top basin this basin contains a late eocene to late oligocene succession of shallow marine alluvial and lacustrine sediments late eocene marine transgression resulted in starvation of clastic supply to the basin hence the calcaires nummulitiques received only a limited influx of heavy minerals derived from local sedimentary sources augmented by the first appearance of assemblages with andesitic affinities at c 42 41 ma clastic members associated with the overlying marnes bleues record a significant diversification of provenance and sediment transport paths clastic detritus supplied to the shallow marine gres de ville were derived from permo triassic sediments to the south conglomeratic submarine channels of the la poste member mark the introduction of alpine ophiolite blueschist derived minerals at c 37 35 ma eroded from the embrun ubaya thrust complex to the ne the deltaic st lions member is dominated by volcaniclastic assemblages completing the marine fill the shoreface gres de senez received detritus from the southerly maures esterel crystalline massif the succeeding oligocene continental sediments record an increasing supply of minerals from alpine lithologies the alluvial molasse rouge contains reworked sedimentary detritus including material cannibalized from the underlying marine tertiary and first cycle alpine minerals the succeeding lacustrine serie saumon serie grise show the increasing diversity of alpine suites the youngest sediments the fluvial gres verts signal a major influx of alpine derived assemblages related to reactivation of the embrun ubaye thrusts between c 28 27 and 25 24 ma

apatite fission track analysis in the argentera massif evidence of contrasting denudation rates in the external crystalline massifs of the western alps apatite fission track dating from a central transect in the argentera massif southernmost external crystalline massif ecm yielded ages between 8 05 0 6 and 2 4 0 2 myr with a positive age altitude correlation above 3 ma 1200 m recognising a thermal peak at c 250 c 33 ma based on stratigraphic metamorphic and 39ar 40ar data the present results suggest a slow cooling rate 8 5 c for the argentera massif during the oligocene early pliocene this rate compares with that from the pelvoux massif but contrasts with those observed in the northern ecm mont blanc and aar up to 14 c myr 1 for the same time interval this can be related to the different location of the ecm within the collided european margin at about 3 4 ma the denudation rate would have increased up to c 1 mm yr 1 in the argentera massif reaching the same value as in the belledonne and northern ecm likely a consequence of penninic thrust inversion

thermal history of the central gotthard and aar massifs european alps evidence for steady state long term exhumation 1 quantifying long term exhumation rates is a prerequisite for understanding the geodynamic evolution of orogens and their exogenic and endogenic driving forces here we reconstruct the exhumation history of the central aar and gotthard external crystalline massifs in the european alps using apatite and zircon fission track and apatite u th he data age elevation relationships and time temperature paths derived from thermal history modeling are interpreted to reflect nearly constant exhumation of 0 5 km ma since 14 ma a slightly accelerated rate 0 7 km ma occurred from 16 to 14 ma and again from 10 to 7 ma faster exhumation between 16 and 14 ma is most likely linked to indentation of the adriatic wedge and related thrusting along the alpine sole thrust which in turn caused uplift and exhumation in the external crystalline massifs the data suggest nearly steady moderate exhumation rates since 14 ma regardless of major exogenic and endogenic forces such as a change to wetter climate conditions around 5 ma or orogen perpendicular extension initiated in pliocene times recent uplift and denudation rates interpreted to be the result of climate fluctuations and associated increase in erosional efficiency are nearly twice this 0 5 km ma paleoexhumation rate

frontal wave stability during moist deformation frontogenesis part i linear wave dynamics abstract it has been shown that lower tropospheric potential vorticity zones formed during moist deformation frontogenesis will support growing waves if at some time the frontogenesis ceases in this paper the ways in which these waves are affected by the frontogenetic process are identified observations show that fronts in the eastern atlantic commonly feature saturated ascent regions characterized by zero moist potential vorticity furthermore in many cases the horizontal temperature gradient in the lowest one to two kilometers of the atmosphere is rather weak these features are incorporated in an analytical archetype the dynamical implications of saturated ascent in conditions of zero moist potential vorticity are represented in the model by assuming that adiabatic temperature changes are precisely balanced by diabatic tendencies the observed small temperature gradient at low levels is represented in the model by taking it to be zero in the lowest two kilometers consequently the forcing of the

litho structural control morphotectonics and deep seated gravitational deformations in the evolution of alpine relief a case study in the lower susa valley italian western alps abstract an integrated study of quaternary geology and geomorphology structural geology and morphotectonic lineament analysis has been performed for the lower susa valley in order to evaluate the relationships between neotectonics of the central internal side of the italian western alps and the morphodynamics of the mountain relief a regional nne ssw fault system the colle delle finestre fault zone cffz separates two sectors the middle and the lower susa valleys characterized by different fault patterns ene wsw regional faults represent the main brittle structures in the middle susa valley while e w faults prevail in the lower susa valley geomorphic anomalies plio quaternary deformed deposits and distribution of glacial deposits suggest differential uplift of fault bounded sectors distribution of deep seated gravitational slope deformations and landslides depends on lithological and structural controls suggesting a close relationship between post glacial morphodynamic evolution and quaternary fault activity this activity is also indicated by instrumental data and historical earthquakes ms ranging from 4 to 5 that struck the lower susa valley

quaternary erosion induced isostatic rebound in the western alps the high elevation and deep incision of the alps have traditionally been used as an argument for recent tectonic activity that has elevated the belt and increased erosion rates normal faulting and horizontal extension however dominate current tectonic activity and isostatic compensation of thinning crust should lead not to increased but to decreased mean elevations here we test the idea that enhanced quaternary erosion of the alps and isostatic compensation of the mass removed can account for the distribution of present day geodetically measured rates of vertical movement in the western alps using geophysical relief and kuhlemann s estimated average erosion rate for the alps we quantify the spatial distribution of erosion and the volume of eroded rock respectively from these we obtain a map of rock eroded within a given time span the calculated isostatic response of the alpine lithosphere to erosional unloading for a variety of values of the flexural rigidity of the alpine lithosphere reaches a maximum of 500 m since 1 ma in the inner swiss alps and vertical movement extends across the entire belt including peri alpine basins assuming a steady erosion rate since 1 ma this rebound accounts for half of the measured vertical motion of 1 1 mm yr in the southern valais thus a significant fraction 50 of the present day vertical movement results from the isostatic response to enhanced erosion during plio quaternary time

dynamics of a bomb like deepening secondary cyclone from airborne doppler radar during the second field phase of the coast coastal observations and simulations with topography experiment an extremely deep secondary cyclone was sampled over the open pacific ocean by an airborne doppler radar this secondary low led a few hours later to strong damage from central california to washington as it moved northward along the western us coast the present paper gives mesoscale dynamical insight into this deep secondary low it reveals a warm seclusion situation with the colder airflow that cyclonically encircles the low centre in quasi gradient wind balance state a conceptual representation of the mesoscale airflow circulation in the low centre area is given this study also validates new analysis methods developed to access three dimensional dynamical fields at mesoscale from airborne doppler radar measurements within secondary cyclones these methods will be used intensively to process airborne radar data gathered during the field phase of the fastex fronts and atlantic storm track experiment project so as to scrutinize multiscale processes involved in secondary cyclogenesis over the atlantic

late neogene erosion of the alps a climate driver as with many mountain belts globally the alps have seen a large increase in sediment yield in the late neogene the hypothesis that this increase results from climate change impacts on erosion rate over the past 5 ma is testable given the extensive work completed in the alps sediment budgets thermochronology based cooling rates and estimates of modern rock uplift and erosion in the western alps are reviewed to search for correlation in space and time that might fingerprint climatic events major increases in sediment yield are apparent starting in the late messinian 5 5 mya and accelerating toward the present day this suggests the occurrence of a series of climatic changes that increased erosion rates even as tectonic processes appear to have slowed or stopped at present tight correlations in time are difficult to establish and there remain open questions about the role of tectonics in the coupled system

dispersal patterns for hydrothermal plumes in the south pacific using manganese as a tracer abstract manganese profiles over the spreading axis of the east pacific rise epr between 22 15 s and 19 25 s disclose a series of plumes which are formed by buoyant emanations of hot hydrothermal vent fluids the plume ceilings or anomaly maxima can occur several hundred meters above the sea floor these plumes are dispersed laterally and are detectable as mid depth manganese anomalies 2000 km from the spreading axis along this section the plumes are dispersed mainly westward but at 30 s the plumes are advected eastward the asymmetrical dispersal pattern inferred from these data is coincident with the asymmetrical distribution of metalliferous sediments about the epr which suggests that plumes generated by high temperature venting play a dominant role in the formation of these sediments

neogene kinematics of the central and western alps evidence from fission track dating zircon and apatite fission track analysis has established the continuation of a zone of rapid change in mineral ages extending from the simplon fault zone in the simplon alps through the rhone valley and along the southeastern side of the mont blanc and belledonne massifs apatite fission track ages to the northwest of this zone generally range from 1 4 to 6 ma whereas those to the southeast range from 6 to 13 ma corresponding values for zircon are 11 13 and 16 26 ma respectively the zone corresponds to the position of the frontal pennine thrust in the mont blanc belledonne region this structure a prominent feature on recent deep seismic profiles may have been reactivated in the neogene with an important normal fault component this is suggested by apatite and zircon fission track ages in the footwall that are younger than those in the hanging wall and by the observed elimination of the lower pennine or simplon nappes along this fault zone in the rhone valley mont blanc belledonne region resulting in the juxtaposition of north penninic and helvetic ultra helvetic nappes at the current erosion level the distribution of fission track ages reflects this movement and the related neogene exhumation of the mont blanc and belledonne external massifs which has continued until less than 1 4 m y ago i e it is almost certainly still active and has tilted the overlying nappe sequence

the life cycle of an extratropical marine cyclone part ii mesoscale structure and diagnostics abstract this is the second of two articles describing the evolving structure and selected physical processes within an intense extratropical marine cyclone observed during the experiment on rapidly intensifying cyclones over the atlantic erica field program part i describes the 24 h frontal cyclone evolution through 6 h horizontal analyses of observations taken by specially deployed observing systems from air land and sea part ii presents frontal scale and precipitation structures and physical processes from analyses based primarily on research aircraft observations taken during three phases of the cyclone s life cycle horizontal analyses at 350 m above ground level describe the cyclone s mesoscale frontal baroclinic structure and associated flow patterns the vertical structure and evolution of the cyclone s cold front warm front and bent back front are illustrated in cross sectional analyses of potential temperature wind velocity potential vorticity pv front relative transverse flow vecto

the arc of the western alps in the light of geophysical data on deep crustal structure recently two international deep seismic campaigns in the western and central alps etude continentale et oceanique par reflexion et refraction sismique progetto strategico crosta profonda ecors crop roure et al 1996b and national research program 20 nrp 20 pfiffner et al 1997 have been completed here we present a synoptic interpretation of the wealth of geophysical data about deep crustal structure of the alps collected during the past 40 years including the two above mentioned geophysical projects the tectonic reinterpretation of the ecors crop high resolution seismic transect is based on an evaluation of the deep crustal structure by integrating new and literature data on surface geology combined with previously published interpretations regarding the central alps schmid et al 1996 this study reveals substantial differences in geometry and kinematics between transects across the western and central alps respectively at depth the transition between the central and western alps is marked by the western limits of an adriatic lower crustal wedge shaped structure and the northeastern limits of a similar structure made of european lower crustal material at the surface it coincides with a corridor of dextral strike slip along the tonale and simplon lines in addition the thickness of the seismogenic zone shows a remarkable variation from over 40 km beneath the penninic realm of the western alps to less than 20 km in the central alps the formation of the western alpine arc was initiated during convergence and collision before 35 myr ago when the adriatic micro plate moving northward with respect to the european foreland caused sinistral transpression in the western alps while the central and eastern alps underwent head on convergence and collision during the post collisional stage i e after 35 myr ago the arcuate shape of the western alps was accentuated by wnw directed movement and anticlockwise rotation of the adriatic microplate decoupled from the central and eastern alps along the tonale simplon dextral shear zone this led to wedging of lower crustal slices both in the western alps and in the central alps the new tectonic interpretation of the ecors crop transect allows a kinematic model to be established for crustal shortening in the western alps during the past 35 myr the ivrea mantle plays the role of a backstop in our tectonic model we distinguish three episodes of post collisional crustal shortening along the ecors crop transect from 35 to 30 ma the brianconnais basement was back thrusted over the gran paradiso units leading to 30 km of crustal shortening first episode in the early miocene movements concentrated mainly along the penninic frontal thrust and resulted in about 60 km shortening second episode post 12 ma shortening within the external massifs is associated with folding in the jura mountains when the crust was shortened by an additional 30 km third episode

hydrothermal methane and manganese variation in the plume over the superfast spreading southern east pacific rise abstract onboard analyses of dissolved ch4 and mn were conducted on the water column along the southern east pacific rise between 13 50 and 18 40 s during the 1993 ridge flux cruise many hydrothermal plumes were identified by chemical anomalies which overlie more than half of the surveyed ridge crest the ch 4 mn ratio in the plumes shows wide variability ranges from about 0 05 to 3 9 due to wide range of ch 4 concentration the ch 4 rich plumes were detected in the region of 16 00 18 40 s where vigorous magmatic budget was confirmed by previous studies moreover the ch 4 mn ratio of the plumes is highly correlated with other volatile metal parameters such as the s fe ratio in plume particulate these results strongly suggest that volatile input caused by magmatic perturbation to hydrothermal systems is responsible for the ch 4 mn variability in the southern epr plumes based on analogy of the case at the epr 9 50 n site the detection of several volatile rich plumes and the extensive hydrothermal flux of volatile species are attributed to frequent magmatic events in the superfast spreading southern epr

frontal instability generated by tropospheric potential vorticity anomalies the development of secondary disturbances on a two dimensional front is described using a linear stability analysis a two stage process is envisaged in which first strong frontogenesis produces condensation at the front this leads to the generation of a lower tropospheric zone of high potential vorticity pv lying along the front as frontogenesis weakens the second stage is entered in which an essentially steady front is susceptible to the growth of linear normal modes along the front owing to the existence of the pv anomaly or equivalently the frontal rainband thus for a typical band of width 160 km a frontal wave of some 800 km is produced with a growth rate of about 1 day 1 the dynamics of these modes is examined by considering both the realistic frontal flow as well as idealized strips of pv anomalies the idealized case is potentially applicable to a variety of meteorological situations such as upper jet streaks useful insight is gained from an analysis of the energetics of the modes this shows that for narrow frontal pv anomalies the waves main energy source is the basic kinetic energy and further they have a negative vertical heat flux recent observations suggest that frontal waves are indeed characterized by such a heat flux as most frontal zones involve significant condensation and therefore are likely to exhibit a lower tropospheric pv maximum it is stressed that studies of frontal waves need to include this aspect of the frontal structure

a case study of explosive cyclogenesis in the eastern pacific abstract an explosive cyclogenesis that occurred in the eastern pacific on 13 november 1981 is described and discussed on the basis of surface and upper air analyses and satellite imagery during one 12 h period the storm deepened by nearly 40 mb and subsequently attained a central pressure of 950 mb or less peak surface winds were in the 45 50 m s 1 range the limited area fine mesh lfm model 24 h forecast initialized at 0000 gmt on the thirteenth completely failed to predict the storm development the development took place within a strong baroclinic zone as a shallow frontal wave traveled from the relatively stable environment of a long wave ridge to the unstable environment of a long wave trough winds at jet stream level exceeded 90 m s 1 prior to the explosive deepening the lifted index in and ahead of the storm diminished and became negative prior to the rapid intensification measurements revealed that sensible and latent heat fluxes from the ocean contributed significantly to the reduced sta

the organization of convection in narrow cold frontal rainbands abstract narrow cold frontal rainbands are lines of intense precipitation that straddle surface cold fronts recent observational work has revealed that the rainfall within the band is organized into regularly spaced ellipsoidal cells called precipitation cores the rainband is coincident with a line of intense cyclonic shear associated with a low level jet that lies ahead of and parallel to the surface cold front numerous authors have suggested that the organization of cells in the rainband is the result of shear instability of the horizontal wind field to investigate this hypothesis a linear stability analysis was performed on an idealized frontal zone consisting of a line of convection coincident with a line of cyclonic shear to model the convective processes the air inside the rainband was assumed to be unstably stratified the presence of horizontal wind shear in an unstably stratified environment resulted in the existence of a mode with a short wave cutoff the coupling between the convective p

observations of the early evolution of an explosive oceanic cyclone during erica iop 5 part ii airborne doppler analysis of the mesoscale circulation and frontal structure abstract using airborne doppler radar data collected onboard the noaa p 3 aircraft during erica iop 5 the three dimensional wind field of the circulation center of an explosive extratropical cyclone is shown the cyclone was entering its rapid intensification stage at the time of the analysis the circulation formed along a frontal boundary and was characterized by mean vertical velocity vorticity and divergence values comparable to those derived for mature hurricanes in addition the circulation at this early stage of cyclone development was relatively shallow 2 5 km agl intense convection occurred within and surrounding the center of the circulation suggesting that diabatic effects played a role in its development it is believed that the mesoscale circulation is the preexisting shallow low that has been shown to form in association with explosive cyclogenesis the wind synthesis also revealed the structure of the bent back warm front which had undergone a scale contraction the intensity of t

iron and copper enrichment of suspended particles in dispersed hydrothermal plumes along the mid atlantic ridge particulate fe and cu concentrations are used in conjunction with dissolved mn values to identify hydrothermal venting at several sites along the mid atlantic ridge mar in dispersed hydrothermal plumes as defined by dissolved mn anomalies suspended matter fe and cu values were as high as 15 8 and 1100 g g respectively relative to al at 1 7 suspended matter fe and cu values correlate well with dissolved mn concentrations tracing the intensity of dispersed plumes in contrast with fe and cu particulate mn values in vent plumes were low at 700 1200 g g calculated al fe mn al ratios for mar particles increase with increasing dissolved mn concentrations this ratio is used to estimate the percent hydrothermal component of the suspended matter these sensitive tracers identify a 2 20 hydrothermal contribution to the 10 2 g of total suspended matter 1 found along the rift valley

a satellite derived classification scheme for rapid maritime cyclogenesis abstract guided by the conjecture that there exist characteristic synoptic scale flow patterns conducive to extratropical cyclogenesis a satellite based classification scheme is proposed to differentiate between various types of rapid maritime cyclogenesis in the western north atlantic region the scheme is derived from signatures in visible and infrared satellite imagery observed prior to and during rapid deepening consideration of the western north atlantic region is motivated by the presence of a relatively dense upstream observational network and by the absence of the direct influence of orography in a maritime environment the focus on rapid development is predicated upon the assumption that the cloud signatures will be more clearly defined than in cases of slower ordinary development examination of satellite imagery for an ensemble of 50 cyclogenesis events that occurred during the 1970s and 1980s 46 of which satisfied the experiment on rapidly intensifying cyclones over the atlantic criterio

exhumation controlled by transcurrent tectonics the argentera mercantour massif sw alps new apatite fission track aft and u th he ages from the argentera mercantour external crystalline massif of the sw alps document an exhumation history along transcurrent dextral faults significant aft age differences across the strikes of the main faults have been obtained from the ne 12 9 ma to the sw 5 2 ma and are linked to vertical uplifts along these right lateral transpressional structures such segmentation is not observed in ahe ages ahe ages have preserved younger ages 4 5 ma on the eastern hangingwall side of the high durance extensional system such an exhumation history is interpreted to result from a transition of transpressional to transtensional regimes at 8 5 ma during continuing adria europe convergence these data show that recent extensional deformation in the sw alps can be related to the development of a transtensional domain in the ubaye embrunais depression linked to ongoing strike slip deformation along the argentera mercantour

cenozoic denudation of corsica in response to ligurian and tyrrhenian extension results from apatite fission track thermochronology 1 the island of corsica france occupies a unique position in the western mediterranean since it has recorded both the cenozoic alpine orogenic history of the area as well as subsequent extensional collapse and oceanic basin formation we present 41 new apatite fission track aft ages and 23 measurements of track length distributions from corsica in order to elucidate its cenozoic thermal and morphological evolution aft ages vary from 10 5 0 8 ma to 53 8 4 1 ma and form a clear spatial pattern oldest ages are encountered in the southwest of the island with a broad band of ages between 20 and 30 ma running across the mountainous central area and ages 20 ma confined to the eastern half of the island samples along the western and northwestern coasts record kilometer scale erosional denudation linked to rifting in the ligurian provencal basin whereas samples from close to the extensionally inverted alpine deformation front record a later cooling phase related to tyrrhenian extension the eastward younging pattern of aft ages suggests the migration of a wave of erosional denudation from west to east across the island apparently controlled by the migrating locus of extension our aft data therefore support models of mediterranean extension controlled by slab roll back

structural analysis of the subbrianconnais and valais units in the area of moutiers savoy western alps paleogeographic and tectonic consequences valais and subbrianconnais units of the western alps of savoie underwent a common structural evolution postdating peak pressure conditions associated with high pressure metamorphism of internal parts of the valais units the first two phases due to roughly north south directed shortening are interpreted to be related to a nne ssw striking corridor of sinistral transpression between the internal western alps and the european foreland both phases led to nappe formation isoclinal folding and north south elongation only the third phase of deformation is related to wnw directed orogen perpendicular shortening thus far regarded as the predominant thrusting direction in the western alps late post 5 ma normal faulting evidenced by fission track dating reactivated the houiller front in the north and the penninic front in the south kinematics of movement observed along the present day houiller front and penninic front change from north to south in the north the houiller front indicates post d3 normal faulting while the penninic front preserved wnw directed thrusting d3 in the south the houiller front preserves syn d2 north directed thrusting whereas the penninic front is partly reactivated by post d3 normal faulting our observations clearly favor tectonic reasons for the disappearance of the valais units south of moutiers in present day map view

role of topography in isotherm perturbation apatite u th he and fission track results from the malta tunnel tauern window austria 1 apatite u th he and fission track age determinations of samples from a 20 km long near horizontal tunnel in the hochalm ankogel dome eastern tauern window austria are presented in order to determine the role of paleo topography in perturbing isotherms in the shallow crust apatite fission track ages 26 8 ma show no systematic correlation with distance along the tunnel or elevation two age components in the fission track data indicate cooling through 120 c at approximately 20 ma and 80 c at approximately 6 ma surface and tunnel u th he ages 17 9 ma and 13 5 ma respectively are consistently younger than the equivalent fission track ages u th he ages vary systematically along the tunnel with older ages at the northern and southern tunnel portals and younger ages in the central section geological factors faulting lithology appear to have had little effect on this age distribution the u th he age pattern is inconsistent with rock cooling underneath the present day hochalm ankogel dome topography the age minimum is interpreted to coincide with a paleotopographic maximum in the hochalm ankogel dome and suggests that the 40 60 c isotherms were warped sufficiently to affect apatite u th he ages the tunnel apatite u th he ages match synthetic he ages derived from a two dimensional numerical model of landscape evolution integrating the thermal model results with the data allows the relief development to be constrained and we calculate that the present day hochalm ankogel dome topography was formed at 7 to 10 ma

the effects of late alpine tectonics in the morphology of the argentera massif western alps italy france several swath profiles drainage morphometric parameters slope and drainage density maps were obtained by dtm analysis of the argentera massif western alps the spatial distribution of the analysed parameters indicates that the central southern sector is characterized by orographic and drainage characteristics very different from the rest of the massif two main systems of nw and wnw trending faults the orgials fault and valletta fault bound this area both faults belong to large scale fault zones the dextral strike slip bersezio fault and the south facing colle del sabbione thrust the orientations and kinematics of both faults indicate a late alpine pliocene to recent sw verging thrusting coupled with a dextral strike slip movement the central southern sector of the massif corresponds to the hanging wall of a sw verging late alpine thrust zone and underwent the highest post pliocene tectonic uplift in the argentera massif the uplift occurred in a transpressive setting with an n s shortening direction which is consistent with the post pliocene tectonics in the southern portion of the western alps r 2002 elsevier science ltd and inqua all rights reserved

interaction of an intense extratropical cyclone with coastal orography abstract observational analyses and numerical simulations are used to investigate the interaction of an intense extra tropical cyclone with the coastal orography of the pacific northwest known as the inauguration day cyclone the system made landfall upon the washington state coast on 20 january 1993 producing one of the most damaging wind storms in pacific northwest history the strongest winds accompanying the storm were associated with an intense low level pressure gradient that was concentrated along a bent back front mesoscale pressure perturbations produced by the time dependent interaction of the cyclone and bent back front with the coastal orography were isolated using numerical simulations the simulations showed that during the period of peak winds over puget sound there was only a minor enhancement of the local pressure gradient by troughing to the lee east of the olympic mountains gradual amplification of this olympic mountain lee trough over a period of 2 3 h extended the period of s

a major helium 3 source at 15 s on the east pacific rise an extensive plume of water enriched with helium 3 has been discovered in the deep pacific ocean at latitude 15 s on the east pacific rise in the core of the plume at a depth of 2500 meters over the ridge crest the helium 3 helium 4 ratio is 50 percent higher than the ratio in atmospheric helium indicating a strong injection of mantle or primordial helium at the spreading center axis through local hydrothermal systems the helium 3 plume is completely absent east of the rise but it can be traced over 2000 kilometers to the west above a newly observed physical feature a density discontinuity here caled the ridge crest front the injected plume provides a unique deep sea tracer with an asymmetric distribution which shows that the deep circulation across the rise is from east to west the striking intensity and lateral extent of this helium 3 anomaly compared to observations at known oceanic hydrohrmal sites suggest that the largest hydrothermal fields in the ocean are yet to be discovered and that they will be found near 15 s on the east pacific rise

deep structure of the alps what do we really know abstract in the last five decades the deep structure of the alps has been probed by every geophysical method applicable and the resulting amount of data is unmatched for any other orogen in this study an attempt is made to review the data and the proposed structural models with the aim of separating the certain from the probable and from the speculative information this can be achieved by first reviewing the theoretical resolving power and ambiguity of the applied interpretation methods and then analysing the proposed models the methods reviewed are inversion of surface wave data teleseismic and local earthquake seismic tomography near vertical reflection seismology wide angle reflection and refraction seismology and gravity modelling all information about the moho rated as certain is combined to give a moho map of the alpine area the information rated as certain and probable and additional qualitative arguments are used to discuss a crustal model of the western and central alps represented by two cross sections major structural elements in this crustal model are a thick overthrust penninic nappe system wedging at mid to lower crustal levels a discontinuous moho and strong variations along the strike of the orogen whereas the structures of the european upper crust and of the penninic nappe system are well constrained only few and isolated lower crustal structural elements are rated as certain finally the shape of the lower lithosphere in the alps is discussed by review and comparison of the results from surface wave teleseismic travel time residual and tomographic studies qualitative arguments suggest the existence of a lithospheric root or slab beneath the alps probable tomographic information suggests a south vergent european lithospheric slab beneath the southern alps and the po plain despite the considerable number of studies aimed at resolving the deepest part of alpine orogeny the available quantitative information on the sub moho structure cannot be rated as certain